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As we know, stem cells can convert to different cells of other organs, can male use their own stem cells to convert it into cells of female-only organs(and vice versa)?
I am assuming you are talking about embryological stem cells and embryological development of genitalia.
The answer is no.
Male stem cells have XY chromosomes. Y chromosome is the sex determining chromosome with SRY gene that determines testes development. Absence of the Y chromosome leads to female development by default. That is why XX forms women and there are people with only one X chromosome which are women. (Turner's syndrome)
It might be possible that SRY gene undergoes a mutation and the gene isn't expressed. There are Y chromosome linked diseases.
You should read up about Y chromosome and development of genitalia.
FDA Warns About Stem Cell Therapies
Some patients may be vulnerable to stem cell treatments that are illegal and potentially harmful.
Researchers hope stem cells will one day be effective in the treatment of many medical conditions and diseases. But unproven stem cell treatments can be unsafe—so get all of the facts if you’re considering any treatment.
Stem cells have been called everything from cure-alls to miracle treatments. But don’t believe the hype. Some unscrupulous providers offer stem cell products that are both unapproved and unproven. So beware of potentially dangerous procedures—and confirm what’s really being offered before you consider any treatment.
The facts: Stem cell therapies may offer the potential to treat diseases or conditions for which few treatments exist. Sometimes called the body’s “master cells,” stem cells are the cells that develop into blood, brain, bones, and all of the body’s organs. They have the potential to repair, restore, replace, and regenerate cells, and could possibly be used to treat many medical conditions and diseases.
But the U.S. Food and Drug Administration is concerned that some patients seeking cures and remedies are vulnerable to stem cell treatments that are illegal and potentially harmful. And the FDA is increasing its oversight and enforcement to protect people from dishonest and unscrupulous stem cell clinics, while continuing to encourage innovation so that the medical industry can properly harness the potential of stem cell products.
To do your part to stay safe, make sure that any stem cell treatment you are considering is either:
- FDA-approved, or
- Being studied under an Investigational New Drug Application (IND), which is a clinical investigation plan submitted and allowed to proceed by the FDA.
Best of H+: Total Gender Change within a Decade
[Editor’s note: recent medical developments such as growing a vagina in a laboratory, advances in gender prosthetics, creating sperm from skin cells, etc. suggest this article is worthy of re-read and a place in the very Best of H+.]
Recently I made a bet with a member of the Institute for Ethical and Emerging Technologies. That bet sounded to him like I was being wildly optimistic, and he jumped at it, thinking it was a sure bet that I would lose.
That bet was that by the end of this decade, medical technology would be able to change the gender of anyone to the opposite gender, with full reproductive abilities of the new gender.
That probably sounds wildly optimistic to most of you as well, but not to me. To be honest, I think the deck is stacked in my favor. Why? Because we are a lot closer to realizing this achievement than most of you probably realize.
To illustrate, take a look at this recent Wired article, which describes the current ability to use stem cells mixed with the fat from a patient’s own body to grow additional breast mass in women or to regrow breasts damaged by cancer. But that’s really very unimportant, because the real breakthrough is that this can be done for nearly every kind of tissue. It’s still at a primitive stage, but scientists already learned how to “program” the stem cells to become different types of tissue. They’ve made progress in making heart repairs , functional liver tissue, blood, teeth, bone, muscle, and they have even made progress on discovering how to manipulate stem cells to enable them to divide continuously. This is a small sampling of the various breakthroughs made in just the last few years in hundreds of labs all over the world. If you understand the implications of all those various articles, it is easy to see that we are learning how to program stem cells to do nearly anything that our body programs them to do. Each step of learning how to program stem cells leads to greater knowledge of how to control them more precisely.
But stem cells alone are not the only medical advances that are being made. Another major breakthrough going on in the medical field is in the improving abilities we are gaining in 3D printing. Not only have we discovered that stem cells can be programmed to repair already existing tissue, we are using modified inkjet printers to lay down layer after layer of them in a pattern, and to basically “print” biological tissue that will “grow” together into a complete organ.
Another technique being researched is the creation of “Biological Legos” in which stem cells are embedded in a block of “glue” which holds the cells together while they form natural intercellular bonds. Yet another technique is to use an already existing “scaffold” and fill the spaces with stem cells, growing a precisely shaped piece of tissue.
So not only are we learning to tell stem cells what to become, but we are learning how to dictate the shape of the tissues as well. The implications for plastic surgery should be obvious. Stem cells seem to offer us the promise that we will soon be able to restore the human body to the exact same state it was in prior to injury, enable us to regrow lost limbs, grow replacement organs on demand, and even reconstruct missing or lost tissue for reconstructive surgery. Soon, a mastectomy might routinely remove the cancer, and rebuild a healthy breast identical to the one removed. A heart attack might lead to a regenerated heart healthier after the attack than it was before, and even such routine needs like blood transfusions might be made by pulling your own stem cells to create a personalized supply.
But even this is pretty tame once you combine stem cells with the increasing complexity of automation, because a da Vinci surgeon robot is not going to remain under human control for very long. So think about those articles above, about how we are learning to guide stem cells to become nearly any tissue. Think about the day we can tell stem cells precisely what to become, and to grow in precise shapes. Then think about an autosurgeon connected to a sensor system allowing it to make a complete map of a human body in real time, as it is fed a body map for a desired shape. A decade from now, a plastic surgeon is likely to use body modeling software developed by MMOs and VR to enable you to decide precisely how you want to look, and then supervise the da Vinci autosurgeon as it uses your own body fat and skin cells to produce a stock of programmable stem cells, and then performs hundreds or even thousands of minimally invasive microsurgeries to place those programmed cells throughout your body, where they will become extra muscle mass, larger breasts, repair damaged internal organs, etc., allowing your future self the option of “resculpting” your personal appearance.
“But wait,” you say, “wasn’t this article about changing sex? So you’re saying that changing sex could be done this way too?”
Yes. However, just being able to control stem cells to the point that we can dictate what kind of cell they become, and what shape they will have at maturity isn’t all that’s involved. There are additional differences that have to be addressed in changing sex, such as hormones, biological function and reproductive function. But researchers have already discovered how to tell ovaries to become testes. While this is not as easy to reverse as you might think, because according to this study the ovaries apparently have to “fight” to stay ovaries, we are making great strides in understanding these various chemical and genetic “triggers”, including such seemingly unimportant ones as the triggers that promote the growth of blood vessels to various types of tissue. We’re also making progress at creating “artificial” ovaries, and stem cells have been successfully used to give rabbits larger penises.
This means that as we learn to control what a stem cell becomes, we will more than likely learn how to tell them to become male or female specific organ structures as well as more generic organs. With the abilities of cell printers to be able to make internal organs, an ability that I expect to replace organ transplants by mid to late decade, the ability to “print” sex organs seems assured. It’s rabbit penises now, but can you really believe that men won’t pay to get bigger sex organs even more than women pay to have bigger breasts? Especially when it becomes a matter of a single visit to a surgeon’s office that will heal faster than a vasectomy?
So, in a decade, I think it is quite likely that the patient seeking to alter their gender would start by seeing their surgeon, who would take a complete scan of the person. This scan would then be entered in to a program that would allow the patient and the surgeon to transform the patient’s body into the precise appearance desired. Once the body shape has been defined, the program would determine what changes would be needed, the amounts and types of stem cell stocks needed, the minimal surgery needed to reroute the urinary tract, nerves, etc. and then would proceed to extract the samples needed to create stem cell stocks. The creation of the proper organs would then begin, using a 3d printer to create the needed tissues. Once sufficient stocks were cultured the patient would be placed into the autodoc and, as the doctor supervised, be transformed.
It’s possible that even such steps as printing the organs might be unneeded as the autosurgeon might be able to construct the needed organs in situ.
This ability to control stem cells is why I think I’m stacking the deck. We already know quite a bit about how to do so, and the rate at which that we are making progress, as well as the potential uses for controllable stem cells, makes this a medical technology that will be developed much further over the next few years. Regenerative medicine not only promises to help cure such issues as heart disease and spinal cord injuries, but to grow replacement organs, replace missing and damaged tissue, and even to potentially allow such abilities as replacing missing limbs. It’s a vitally important area of research, and as Wired points out, with such “frivolous” uses as breast enhancement, and the eventual penile enhancement so close to market, it’s going to be the biggest medical money-maker of the next decade. It’s just one small part of the numerous advances that will be made in the next decade, but it’s one that is likely to make an enormous change to our social dynamics. Unlike silicone, there is no “unnaturalness” to a stem cell breast enhancement, and I’m certain that the ability to make any size breasts will likely emerge before mid-decade. Combine that with the ability to make bigger penises, which I also expect to come along mid-decade, and plastic surgery is likely to become as acceptable as getting a new hairstyle. As we continue to make progress, and gain further abilities to use stem cells to heal, regrow, or reshape the body, more people are likely to use them to make themselves look more attractive, enhance their bodies, or even to rejuvenate and repair the effects of aging. The potential uses for stem cells are enormous and, relatively speaking, changing someone’s sex is just one small possibility in thousands.
Inducing gametic cells from stem cells, and viceversa - PowerPoint PPT Presentation
Ally Hill March 2, 2009. Morgan Batson Biol 430. Robyn Sharma. Presentation Outline. Introduction. 1st Paper (Geijsen et al., 2004) germ cells from embryonic stem . &ndash PowerPoint PPT presentation
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Progenitor Hair Populations are Key to Understanding Male Pattern Baldness
It’s known that stem cells, the key players in regenerative processes in the body, play a key role in continually making new hair. This role created interest in studying hair follicle stem cells to better understand androgenetic alopecia (AGA), or male pattern baldness, the most frequent type of hair loss among men. Naturally, the hair follicle stem cells were the prime suspects for causing AGA. However, earlier this month a study by George Cotsarelis at the University of Pennsylvania School of Medicine and colleagues published in The Journal of Clinical Investigation (Garza et al., 2011) revealed that patients with AGA actually had had a normal amount of follicle stem cells in their scalps. Surprisingly, it was found that different progenitor cell populations, suspected to be derived from the hair follicle stem cells, were in fact the ones playing the key roles in causing AGA. (Progenitor cells are like stem cells in that they can differentiate into different cell types, but progenitors’ fates are more limited and they can replicate only a restricted number of times.) By better understanding the exact cell types involved, it may help researchers devise better therapies for treating AGA.
A Hair’s Life-Cycle: In order to understand AGA and the newly discovered key role of these progenitor cells in it, it’s helpful to first review the normal life of a hair. In the skin, every hair sits inside a hair follicle, a little cavity that goes down through the dermis layer and has connected sebaceous glands (which lubricate the hair by secreting an oily substance) an arrector pili (a small bundle of muscles that can make the hair stand on end) (see Hair Follicle figure). Each hair carries out its own life-cycle. The first lifecycle phase is called anagen, a growing period that about 85 percent of the hairs on a person’s head are in at any given time. During anagen, which can last two to six years for one hair, the hair grows at the rate of about five inches a year. After anagen, the hair enters catagen, a transitional one- to two week-long stage when the hair follicle and root both shrink. The hair then enters the last stage, telogen, which is a resting phase that lasts about five to six weeks, during which time the old hair does not grow. At the end of telogen the hair follicle re-enters anagen, the growth phase, and often a new hair will push the old one out, starting the growth cycle over again (Furdon & Clark, 2003 Garza et al., 2011).
Every hair sits inside a hair follicle, which goes down through the epidermis and dermis of the skin. Connected to the follicle are sebaceous glands, which release oils onto the hair, and arrector pili muscles, which can cause hairs to stand on end. The bulge is where the majority of the hair follicle stem cells reside, and these can give rise to multipotent progenitor cells.
Androgenetic Alopecia: Normally, the new hair will grow similar to how the last one did. However, with AGA this isn’t the case. In AGA, hair follicles get smaller over time, and consequently make smaller and smaller, eventually microscopic, hairs. How is this caused? It’s not that well understood it’s known that testosterone is necessary for this miniaturization (as inhibiting testosterone conversion to its active form can delay AGA progression), but not much else is known about what causes AGA (Garza et al., 2011).
But even if it’s not known what happens to cause AGA, researchers have done a lot of work to figure out what stem cells are normally active in the hair follicle. Within a hair follicle, there are stem cells that reside in an area called the hair follicle “bulge,” which is a small compartment located where the outer root sheath meets the arrector pili muscle (see Hair Follicle figure). The stem cells in the bulge are multipotent epithelial stem cells, and can become, or differentiate into, all the epithelial cell types in the follicle (including hair follicles, epidermis, and sebaceous glands) (Oshima et al., 2001). They’re intimately involved in the hair follicle lifecycle. Given this, it shouldn’t come as a surprise that if these stem cells are destroyed, so is the hair follicle (Ohyama et al., 2006 Ohyama 2007).
ISC Biology Question Paper 2014 Solved for Class 12
** Answer is not given due to change in the present syllabus.
(Attempt all questions)
(a) Mention one significant difference between each of the following :
(i) Parenchyma and sclerenchyma.
(ii) Epistasis and dominance.
(iii) Hormones of ovulatory phase and hormones of luteal phase.
(iv) Symplastic movement and apoplastic movement.
(v) Phenotype and Genotype.
(b) Give reasons for the following :
(i) Testes descend into the scrotum before birth.
(ii) Secondary growth does not occur in monocot stems.
(iii) Nitrogenous fertilizers are not applied in fields where leguminous crops grow.
(iv) Genetic code is ‘universal’.
(v) At higher temperatures, green plants start evolving CO2 instead of 02.
(c) Each of the following questions/statements has four suggested answers. Rewrite the correct answer in each case. 
(i) Typhoid is classified as a :
(A) Viral disease
(B) Genetic disorder
(C) Bacterial disease
(D) Protozoan disease
(ii) Bt cotton is resistant to :
(iii) Roots and shoots lengthen through the activity of:
(A) Apical meristem
(B) Vascular cambium
(C) Lateral meristem
(D) Cork cambium
(iv) An antiviral protein released from infected and dying cells is :
(v) Opening and closing of stomata is due to
(A) Ca 2+
(B) Na +
(C) K +
(d) State the best-known contribution of: 
(i) Alec Jeffery
(ii) P.K. Sethi
(iii) Hugo de Vries
(e) Expand the following:
|(i) Fundamental soft plant tissue made-up of thin walled cells that forms the major part of leaves, roots, stem pith and fruit pulp.||Mechanical strengthening or supportive plant tissue made-up of thick walled long cells or fibres and short cells sclereids.|
|(ii) In this two pairs of non-allelic genes are involved a gene pair inhibits the expression of another non-allelic gene.||Out of a pair of alleomorphic genes, the one which appears in Fj generation, is called dominant and the phenomenon is called dominance.|
|Hormones of Ovulatory phase||Hormones of Luteal phase|
|(iii) Estrogen and Luteinizing hormone bring about ovulation and causes a empty graafian follicle to develop into a corpus luteum which produces progesterone.||Progesterone hormore stimulates the uterine lining development before implantation of a fertilized egg.|
|Symplastic movement||Apoplastic movement|
|(iv) Water moves from cell to cell in the cytoplasm via the plasma membranes and plasmodesmata.||Water moves from cell to cell via spaces in the outer cellulose cell walls.|
|(v) It is the externally observable characters, controlled by genes||It is the genetic constitution of an organism with regard to a character.|
(b) (i) Sperm formation requires a temperature which is few degree less than the normal body temperature. Scrotum has almost no fat insulation so it keeps the testes at a cooler temperature. Also contraction or relaxation of muscles of scrotum moves the testes close to or far from heat of the body according to the environmental temperatures.
(ii) Secondary growth does not occur in monocot stem because it does not contain the meristematic tissue-cambium, which is responsible for secondary growth in plants. Vascular bundles are closed.
(iii) Nitrogenous fertilizers are not -needed in fields where leguminous crops grow because these plants have root nodules containing nitrogen fixing bacteria. They convert the nitrogen of soil air to nitrates which is used by these plants. The nitrates mix with the soil when these plants are ploughed under.
(iv) Genetic code is universal, triplet because it consist of three out of four nitrogenous bases-adenine, guanine, thymine and cytosine. These four bases in different triplet com-binations from all the various types of proteins, formed by genetic coding.
(v) At higher temperatures and high oxygen concentration, CO2 may be released by some plants instead of O2 because the main enzyme of photosynthesis -RuBP-carboxylase or Rubisco functions as RuBP-oxygenase. It splits RuBP into PGA and phosphoglycolic acid. The later is changed to glycolic acid and then to glycine. In the mitochondria, glycine forms serine and CO2, which is released. This process is called photorespiration. It undergoes photosynthesis.
(c) (i) Bacterial disease.
(iii) Apical meristems.
(v) K +
(d) (i) DNA fingerprinting.
(iii) Gave the term mutation.
(ii) Developed “Jaipur foot.
(e) (i) Severe Combined Immune Deficiency.
(ii) Zygote Intrafallopian Transfer.
Part-II (50 Marks)
(Answer any two questions)
(a) Describe the Miller and Urey experiment on the origin of life. 
(b) Define the following : 
(i) Frame shift mutations.
(ii) Genetic drift.
(a) Oparin-Haldane’s concept of biochemical basis of origin of life was put to a test by Stanley Miller and Harold C. Urey (1953) in laboratory by creating the probable conditions of primitive earth. They designed their apparatus of glass tubes and flasks as shown in the figure and created an atmosphere containing hydrogen, ammonia, methane and water vapour in one chamber of the apparatus and allowed condensed liquids to accumulate in another chamber. Energy was supplied by heating the liquid containing chamber as well as by electric sparks from electrodes in the gaseous chamber. The experiment was run continuously for a week and then they analysed the chemical composition of the liquid inside the apparatus. They found that the liquid contained a large number of complex organic compounds including some amino acids such as glycine, adenine and asparatic acid.
However, from the result of this experiment, they suggested that the electrical discharge, produced during lightening in the primitive atmosphere of earth containing hydrogen, ammonia, nitrogen and water vapour might have resulted in the formation of amino acids and other essential organic building blocks (sugars, nucleotides, etc.) of living organisms and possibly these could thus have formed life on the primitive earth. Thus, the experiment of Miller and Urey provides support for the biochemical concept of origin of life of Oparin and Haldane.
(b) (i) A frameshift mutation is a genetic mutation caused by a deletion or insertion of a single base in a DNA sequence (code) that shifts the way the sequence is read.
(ii) Genetic drift refers to the change in a type and ffequencey of genes in a population due to a random occurrence.
(a) Name and define the three types of natural selection. 
(b) State the following: 
(i) Hardy-Weinberg’s principle
(ii) Theory of recapitulation.
(a) Three types of natural selection are f
(1) Stabilizing or Balancing Selection : It leads to the elimination of organisms having overspecialized characters and maintains homogenous population which is genetically constant. It favours the average or normal phenotypes while eliminates the individual with extreme expression, e.g., sickle cell anaemia in human beings.
(2) Direction or Progressive Selection : In this selection, the population changes towards one particular direction alongwith change in environment. As environment is undergoing, continuous change, the organism having acquired new characters survive, and others are eliminated e.g., Industrial melanism.
(3) Disruptive or Diversifying Selection : It is a type of natural selection which favours extreme expression of certain traits to increase variance in a population. It breaks a homogeneous population into many adapted forms and results in balanced polymorphism, e.g., Three types of snails in sea.
(b) (i) The Hardy-Weinberg principles states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.
(ii) It states that ontogeny recapitulates phytogeny. It means that embryos, in their development repeat the evolutionary history of their ancestors in a short, abbreviated form.
(a) Mention the important features of the Neanderthal man. 
(b) What are homologous organs? How do they help in providing evidence for organic evolution? 
(a) A typical Neanderthal man had
- Height less than 150 cm.
- Heavily built with strong and outwardly curved thigh bones.
- Cranial capacity of 1450 cm3.
- Brow ridges prominent.
- Skull thick-boned, depressed and protuded behind.
- Forehead was low and sloping.
- Devised and used flint tools.
- Lived in caves and used animal skin to cover themselves.
- Buried their dead with ceremonies.
(b) Organs having different functions but have similar embryogenic origin and development and having similar relationship with adjacent organs are called homologous organs.
They indicate close relationship between their possessors, e.g., the forelimbs Of human, wing of bird, leg of horse and flipper of a seal are all apparently different from one another in structure and function, yet they are all built on the same pentadactyl plan, having the same number of bones, muscles, blood vessels and nerves arranged in the same pattern and developed similarly. Therefore, the most reasonable explanation is that the forelimb of all of these animals were inherited long ago from a common ancestor.
(Answer any two questions)
(a) Describe the different types of vascular bundles. 
(b) Give three anatomical differences between a monocot root and a dicot root. 
(c) Explain the effect of light and temperature on photosynthesis. 
(a) There are mainly three types of vascular bundles :
(i) Radial: These are the vascular bundles in which the xylem and the phloem lie radially side-by-side (e.g., in roots of seed plants). This is found in roots.
(ii) Conjoint : Those in which the two types of vascular tissues lie on same radius. Here xylem and phloem together form a bundle. They are of two sub-types :
(a) Collateral, and
(a) Collateral: The xylem and phloem lie together on the same radius in the position that xylem lies inwards and the phloem outwards. In dicotyledonous stem, the cambium is found to be present in between xylem and phloem, such bundles are called open (e.g., in Helianthus), and in monocotyledonous stems, the cambium is absent, it is called closed
(b) Bicollateral: In such vascular bundles, the phloem is found to be present on both sides of xylem. Simultaneously two cambium strips also occur. Various elements in a bundle are arranged in the following order – outer phloem, outer cambium, xylem, inner cambium and inner phloem. Such bundles are commonly found in the members of family Cucurbitaceae. Such bundles are always open.
(iii) Concentric : In this type, one type of vascular tissue surrounds the other. The concentric bundles may be of two subtypes, amphivasal and amphicribal. In amphivasal bundle, the xylem surrounds the phloem found in Dracaena, Yucca and other monocots and some dicots. If the phloem surrounds the xylem then it is called amphicribal as found in many ferns. Such concentric bundles are always closed.
- Cortex is comparatively narrow.
- Phloem parenchyma present.
- Endodermis is less thickened and casparian strips are more prominent.
- Number of vascular bundles is 2 to 3, 6 or rarely 8.
- Xylem elements are polygonal.
- Pith is mostly absent.
- Cortex is wide.
- Phloem parenchyma absent.
- Endodermis invisible only in young root.
- Vascular bundles are numerous.
- Xylem elements are oval or round.
- Pith is always present.
(c) (i) Light : The intensity of light affects the rate of photosynthesis and thus controls the rate of production of ATP and NADPH2 . An increase in light intensity will increase the rate pf photosynthesis (if no other factor is limiting). Beyond the light saturation inten-sity, the increased intensity of light does not increase the rate of photosynthesis. That intensity of light at which the CO2 used in photosynthesis is equal to that of liberated during respiration is called the light compensation point. The rate of photosynthesis does not depends upon the duration of light but the amount of carbohydrate produced, depends upon the duration of light. The quality of light also affects the process as it occurs only in the visible part of spectrum i.e., 380 nm – 760 nm wavelengths. It usually does not take place in ultraviolet and infrared rays as these rays are injurious to proto-plasm. The highest rate of photosynthesis is in red light followed by blue light while green light is least effective in photosynthesis as most of it is reflected back.
(ii) Temperature : Temperature along with other environmental conditions affects photo-synthesis in a number of ways. At low temperature, the rate of photosynthesis is low because the enzymes are affected adversly. At high temperature also, the enzymes get denatured and the rate of photosynthesis declines. The optimum range of temperature for photosynthesis is 20°C – 35°C. Upto 35°C, the process shows a progressive increase with rise in temperature and this increase follow vant Hoff’s Law, according to which the rate of chemical reaction doubles for every 10°C rise of temperature of other factors are not limiting.
(a) Explain the transpiration pull theory for ascent of sap. 
(b) Explain the process of spermatogenesis in humans. 
(c) Define the following : 
(a) Cohesion and Transpiration Pull Theory : This theory was first proposed by Dixon and Jolly (1894) and is based on the following features :
(i) Cohesion and Adhesion : Mutual attraction between water molecules is called cohesion. The walls of tracheids and vessels of xylem are made-up of lignin and cellulose and have stomg affinity for water (adhesion).
(ii) Tension : Transpiration pull develops a negative pressure or tension in xylem sap which is transmitted down to the root.
The moist walls of mesophyll cells in leaf lose water vapour to the intercellular spaces. Sufficient quantity of water is transpired through intercellular spaces of the mesophyll cells through stomata. This is because, dry air outside the leaf has lower water potential than moist air of leaf, as a result water diffuses out of stomata and diffusion pressure deficit (DPD) increases. As a result, more water is sucked from adjoining inner mesophyll . cells and ultimately from xylem tissue. This tension is transmitted down to the roots.
The water column does not break because of cohesive and adhesive forces.
(b) The process of spermatogenesis occurs in the male gonads-testes. Testes are made-up of many seminiferous tubules lined by germinal epithelium. Cells of germinal layer divide to form spermatozoa in the following four steps :
(1) Spermatocytogenesis : The germinal epithelial cells which enter the process of spermatogenesis are called primary germ cells. Each primary cell by repeated mitotic divisions gives rise to a number of (unspecialized) cells called spermatogonia. They also keep dividing and enter the next phase.
Growth Phase : The spermatogonia increase in size and grows. Each spermatogonium divides mitotically to form two primary spermatocytes which are diploid and joined by their cytoplasm. The primary spermatocytes undergo meiosis.
(2) Meiosis I : The primary spermatocytes undergo the 1st meiotic or maturation division, each form two haploid (x) secondary spermatocytes.
(3) Meiosis II : The secondary spermatocytes undergo Ilnd meiotic division and produces two spermatids. A spermatid is a round cell with a spherical nucleus.
(4) Spermiogenesis : It is the process of transformation of circular spermatid to a spermatozoan. In this process, the nucleus of the spermatid becomes the head of the sperm, the golgi apparatus, containing proteolytic enzymes, becomes the acrosome cap, mitochondria form middle part and centrosome form the tail.
(c) (i) Placentation : It is the arrangement of ovules inside the ovary.
(ii) Parthenocarpy : The formation of fruits without fertilization is called parthenocarpy e.g., Banana.
(iii) Diffusion : It is the movement of molecules or ions of solid, liquid or gas from their higher concentration to their lower concentration area.
(a) Why are xylem and phloem classified as complex tissues? Describe the structure of phloem. 
(b) Describe the ultra-structure of chloroplast. 
(c) State three functions of the placenta. 
(a) Xylem and phloem are called as complex tissues because they are formed of more than one type of cells. Xylem is composed of tracheids, tracheae, xylem parenchyma and xylem fibres. Tracheids and tracheae (vessels) are called as conducting elements.
Phloem is made-up of four types of cells :
(i) Sieve elements : In lower vascular plants, single celled structures called sieve cells are present while the Angiosperms have the multicellular sieve tube members. They are long tubular channels. They are formed of elongated living cells without nucleus and arranged end to end in vertical rows. The end walls of the individual sieve tubes are perforated by number of pores. The end walls of sieve cells are known as sieve plates. These plates connect the adjacent sieve cells to form a continuous long distance channel for the transport of food materials.
(ii) Companion cells : Sieve tube members of the Angiosperms are accompanied by highly specialised parenchyma cells called as companion cells. They are in contact with cytoplasm of the sieve tube members by plasmodesmata in their thin walls.
Companion cells have nucleus, richly granular cytoplasm and vacuoles. They control the activities of sieve tube members.
(iii) Phloem parenchyma : The phloem parenchyma cells are living, thin walled and the most simple ones. They contain starch, tannins and crystals. These cells perform the function of storage and lateral translocation of food substances.
(iv) Phloem fibres : The phloem fibres or sclerenchyma cells are the components of phloem. The fibres may be septate or non-septate and may be dead or non-living at maturity. They provide mechanical support to the plant body.
(b) Chloroplast is a oval structure surrounded by two unit membrane separated from one another by a space called periplastidial space. Internally the chloroplast is disc like structures the grana embedded in a colourless matrix called stroma.
Each granum is made-up of a stack of closed compartment called thylakoids. Each thylakoid consists of two parallel membranes joined at their margins. The membranes of thylakoids contain layer of paricles called quantasomes (photosynthesis units). Each quantasome has 230 molecules of chlorophyll. In stroma, there are many membranes running parallel to each other throughout the length of chloroplast which are called lamellae.
Different grana are connected with each other through tubular connection called stroma lamellae. Each chloroplast contains nearly 40-60 grana embedded in the stroma.
Grana are the sites for the light reaction and stroma is the site for dark reaction of photosynthesis.
(c) In mammals, placenta performs the following functions :
- It helps in the nutrition of embryo as the nutrients like amino acids, monosugars, vitamins, etc., diffuse from maternal blood into foetal blood through placenta.
- It helps in respiration of the embryo as 02 of the maternal blood and C02 of foetal blood diffuse through placenta.
- It also helps in excretion of the embryo as nitrogenous wastes of foetal blood like urea diffuse into maternal blood through placenta.
- It also acts as an endocrine gland as it secretes certain hormones like estrogen, relaxin, progesterone and Human Chorionic Gonadotropin (HCG).
(Answer any two questions>
(a) Describe the experiment performed by Griffith. What conclusions did he infer from his observations? 
(b) What is artificial insemination? Mention two ways in which it is useful in breeding of dairy animals. 
(c) What is single cell protein? Give its source and significance. 
(a) The bacterium Diplococcus pneumoniae causes pneumonia in humans. Frederick Griffith observed two strains of this bacteria. One strain has polysaccharide forming a large capsule around the cell called the smooth types (S). The colony of such cells has a smooth appearance. The other strain bacterial cells do not have the polysaccharide capsule and the colony formed by these cells has an irregular appearance and is called the rough type (R). The S-strain is virulent while the R-strain is non-virulent.
In his experiments, Griffith injected mice with live R-type of bacteria. They did not develop the disease. When he injected ‘S’-type of bacteria, the mice developed the disease and died. However, when heat killed S-type of bacteria were injected into the mice, they did not develop ‘ pneumonia. However, when he injected the mice with a mixture of living R-type (non-virulent)
with heat-killed S-type (virulent) bacteria, the mice developed the disease and died. Griffith observed that in the blood of dead mice, both R and S type of bacteria were present. He thus concluded that heat killed smooth type bacteria caused a transformation of the living rough type into live S-type bacteria. Later experiments by other scientists suggested that DNA and not proteins is the genetic material.
(b) Artificial insemination is performed to get improved and better variety of animals. In this method, semen from the desired type of animal (e.g., bull) is collected and preserved by chemical methods or freezing. This preserved semen is then injected into the genital tract of the chosen cow during its maximum fertility period. Normal reproductive process then occurs and the progeny thus obtained is a hybrid of desired characters.
Artificial insemination is useful in breeding animals because :
- It is economical as semen from a desired animal e.g., bull can be transported to far away places while transporting the animal is not easy.
- High quality semen is available all the time but a high-quality bull may not be available all the time and at all places.
(c) Single cell protein (SCP) refers to dried microbial cells or total protein extracted from pure microbial cell culture. SCP is not pure protein. It refers to the whole cells of bacteria, yeast, filamentous fungi or algae. It also contains carbohydrates, lipids, nucleic acids, mineral salts and vitamins. The composition depends upon the organism and the substrate on which it grows, sources – Chlorella (algae), Rhodopseudomonas capsulate (bacteria), Trichoroderma (fungi). Significance SCP can be used as food supplement to humans food or animals as feed. It has application in animal nutrition as fattening calves, poultry and fish breeding. In food, it is used as aroma carriers, vitamin carriers, emulsifying aids and to improve nutrition value of baked products, soups, in ready to serve meals and in the technical field in paper processing, leather processing and as foam stabilisers.
(a) How did Hershey and Chase prove that DNA is the genetic material? 
(b) Give one main application of each of the following : 
(c) Explain the role of stem cells in medical treatment. 
(a) Alfred Hershey and Martha Chase conducted experiments on virus T2 bacteriophage that attacks the common bacterium Escherichia coli. The bacteriophage has two chemical components i.e., protein and DNA. Protein forms the external structures like head, sheath and tail fibres and a DNA molecule is in the head. The phage attacks E. coli by attaching with its tail fibres to the bacterial wall and injecting its genetic material into the bacterial cell to produce new phages.
Hershey and Chase labelled the DNA and protein components of the phage separately with specific radioactive tracers and then followed these components through the life cycle of the phage. They developed two strains of the virus, one with labelled protein and other with labelled DNA. Almost all proteins contain sulphur which is not found in DNA while all DNA molecules contain phosphorus which is not found in proteins. The T2 phages grown in the presence of radioactive sulphur (35S) has labelled proteins and T2 phages grown in presence of radioactive phosphorus (32P) had labelled DNA.
After developing these strains, Hershey and Chase allowed each strain to infect the bacteria. Soon after infection, the bacterial cells were gently agitated in a blender to separate the adhering phage particles. It was observed that only radioactive 32P was found in the bacterial cells and 32S was present only in viral coats in the surrounding medium and not inside the bacterial cells. When they studied the viral progeny for radioactivity, it was found that it had only 32P and no 35S .
The results clearly show that only DNA is the genetic material and not protein coat.
(b) (i) MRI-Mapping of brain tissues and study tissue metabolism.
(ii) Ultrasound – Used in diagnosis of various diseases of the heart, gall bladder, liver, pancreas, uterus and ovary.
(iii) ECG – Diagnosis of various heart diseases like coronary thrombosis, myocardial ischaemia, etc.
(c) Stem cells are found in all multicellular organisms and are capable of dividing to form new cells which can the differentiated into various types of specialized cells.
Role of Stem cells in Medical treatment:
- The stem cells have been used for treatment of various cancers like leukemia and lymphoma.
- It may also be used for treatment of severe autoimmune diseases like multiple sclerosis.
- Study of human embryonic stem cells will yield information about the complex events that occur during human development.
- Embryonic stem cells may be directed to differentiate into specific cell types, offer the possibility of renewable source of replacement cells and tissues to treat diseases like Alzheimer’s disease, spinal cord injury, stroke, bums, diabetes, arthritis and heart diseases.
(a) Write short notes on : 
(i) Multiple Alleles
(ii) Artificial measures to control population.
(b) What complications will arise if the blood of an Rh positive person is transfused to an Rh negative person and vice versa? 
(c) State any three goals of the human genome project. 
(a) (i) Multiple Alleles : Most genes occur in two alternative forms, both controlling the same character and occupy the same locus in homologous chromosomes. These different form of the same gene are called alleles. However, some genes may occur in more than two allelic forms and they are called multiple alleles. A set of such multiple alleles may contain 3 to 20 or even more members which occupy the same locus in homologous chromosomes. In such a set of multiple alleles one member is always dominant and one recessive to all others. An individual carry only two such alleles e.g., ABO blood groups.
(ii) Artificial method to control population : The unreliable the natural methods of con-traception and are replaced by artificial methods :
(a) Contraceptive pills : Birth control pills which contain hormones, prevent a woman from getting pregnant if used regularly. Contraceptive pills also help women to have regular menstrual cycles and reduce the chances of anemia.
(b) Barrier contraception : Most popular barriers are the condom and the diaphragm that keep the sperm coming in contact with eggs in female reproductive system.
(c) Intra uterine device (IUD) : It is small device placed in the uterus to prevent pregnancy. Once the medicated IUD is in place, it can provide birth control for 5 to 10 years.
(d) Injection for birth control: Vaccination is another method of birth control. This vaccine is effective for three months and has to be applied four times a year.
(b) The Rh-factor or Rh-antigen was first reported in Rhesus monkeys RBCs by Landsteiner. Later it was found in most of human population. 85-99% of population, depending upon the race, have the Rh-factor, hence are Rh + ve. There is no antibody against Rh-antigen in human body. The Rh-antigen is produced due to a dominant gene, hence Rh + ve individuals are presented as RR or Rr with Rh-ve as rr.
Rh-ve blood can be given safely to a Rh + ve individual. But when Rh + ve blood is transfused into Rh -ve person, then during first transfusion, there is no complexity arising because of absence of Rh-antibody in the recipients blood but this transfusion induces the synthesis of antibodies in recipients blood. In case of second transfusion of Rh (+ ve) blood to Rh (- ve) person, the RBCs of donors blood starts clumping due to presence of previously formed antibodies in recipients blood, thus causing death of the recipient. Hence Rh-factor should be determined before any blood transfusion.
(c) Human Genome Project (HGP) is an international research program to analyse the complete genetic material of human being and also selected experimental animals. HGP’s goal is to decode the complete DNA material or genome of human beings by 2003 and make them accessible for further biological study.
We thank Ansgar Klebes, Ed Laufer, Jean Maines, Jessica Treisman, Ting Xie, the Bloomington Drosophila Stock Center, Tsinghua Fly Center, Vienna Drosophila RNAi Center (VDRC), and Developmental Studies Hybridoma Bank (DSHB) for fly stocks or antibodies, Ansgar Klebes for communicating unpublished data, and Kyra Yang for proofreading the manuscript.
Xuewen Li, F.Y., B.D. and R.X. conceived and designed the experiments and analyzed the data Xuewen Li, F .Y., H.C., B.D. and Xinghua Li performed the experiments R.X. wrote the manuscript.
This work was supported by the Ministry of Science and Technology of the People's Republic of China National Basic Science 973 grants [2011CB812700 and 2014CB850002].
A better brew
Advances in cell culture media mean that scientists increasingly know what has gone into the mix, and cells are enjoying a more natural environment — even in the lab.
Cells that thrive in the lab make for happy researchers. And vice versa: biology experiments can grind to a halt if investigators fail to get their cell cultures growing in the right nutrient medium.
That is why the market for such culture media is a lively one, with scores of commercial and home-brewed mixes available to help biologists to deal with all the different cell types that their experiments might require. But although the field of cell culturing can draw on generations of experience, making the right choice of medium is still more of an art than a science.
Even slight differences in media can have a large impact on cells — often for no clear reason. Many scientists mix their own culture media, but that can hamper the reproducibility of scientific findings. John Masters, an experimental pathologist at University College London and editor of numerous books on animal and human cell culture, says that the recipe for such 'home-brews' can be difficult to follow owing to the sheer number of ingredients, as well as variations in purity and content between suppliers, variations between batches from a single supplier, and the difficulties of making relatively small quantities of a labile mixture of chemicals consistently.
However, as scientists come to terms with the importance of knowing exactly what their cells are thriving on, the field is becoming more rigorous. Some researchers, for example, are trying to eliminate culture-media components that originate from animals, because of fears that they could contaminate or infect potential human therapeutics down the line. Other investigators are trying to make growth media reproduce a natural environment more realistically — for example by creating three-dimensional (3D) tissue structures.
Some cells are hard to please
A prime example of the importance of good culture media is in the burgeoning field of induced pluripotent stem cells (iPSCs) — adult cells that have had their molecular clocks turned back to regain the any-fate-is-possible state of their infancy 1 . These cells can be redirected to become many cell types, offering prospects for regenerative medicine 2 using lab-grown tissues to replace or renew aged, injured or diseased tissue in patients.
At the RIKEN Center for Developmental Biology in Kobe, Japan, for example, opthalmologist Masayo Takahashi is hoping to gain approval soon for the first clinical trial of an iPSC-based treatment, for age-related macular degeneration, in which portions of the retina begin to die. Takahashi's goal is to replace the diseased parts of the retina with reprogrammed skin cells.
Meanwhile, basic researchers are exploring 'transdifferentiation': a genetic approach that converts one type of cell into a completely different one, skipping reversion to the stem-cell phase entirely. An example is the work of Rudolf Jaenisch and Yosef Buganim at the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts. Using a process based on cell culture, the researchers have shown that connective-tissue cells can be transformed into cells that express markers specific to Sertoli cells, which are normally found in the testis 3 . The results may help researchers to solve the puzzle of male infertility, and may pave the way for techniques for growing cell types that are currently difficult or even impossible to culture.
Buganim says the “specific culture medium used is crucial for the particular fate the cells assume”. Transdifferentiated cells, iPSCs or cultured neurons each need their own culture media tailored to the needs of the cells and cell type. The media might have or lack certain growth factors, for example, or create high or low oxygen levels, all of which allow cells to retain their normal characteristics and properties, says Buganim.
More generally, stem-cell researchers in academic or industry labs need media and substrates to maintain and grow their cells, and to coax them down a series of developmental pathways, says Bradley Garcia, who directs technology and business development at Primorigen Biosciences in Madison, Wisconsin, which develops and sells such products. Media tuned to cells' requirements can also keep differentiated stem cells, whether liver or heart cells or neurons, in culture for days, months or even more than a year.
Cells can be unpredictable, growing more readily in one medium than another for no apparent reason. And stem cells, according to Scott Monsma, senior director of research and development at Primorigen, are “balanced on a razor-edge”, and will differentiate in response, for example, to rough handling, overcrowding and stress. These factors make stem-cell-media development challenging, but at the same time, the medical potential of stem cells raises demand for such media, companies say.
Some scientists use feeder-based systems to get their stem cells growing. In these systems, a layer of supporting cells, such as mouse embryonic fibroblasts, supply the medium with growth factors. But these systems can be prone to error, warns Erik Hadley, senior scientist in research and development at Stemcell Technologies, a spin-off from the British Columbia Cancer Agency that is based in Vancouver, Canada, and sells stem-cell media. Not only is each batch of feeder cells different, but it is also hard to control the amount and timing of excreted growth factors, making it difficult for researchers to know which ingredients make cells respond in what way.
To combat these issues, Stemcell Technologies sells a feeder-free stem-cell maintenance medium called mTeSR1. A follow-on product, TeSR2, is completely free of animal proteins, and another, TeSR-E8, which was released in January, contains a set of eight components with a formulation based on work by James Thomson, a stem-cell researcher at the University of Wisconsin–Madison. The media are sold by Stemcell Technologies under patent licences from the university. Life Technologies in Carlsbad, California, also sells a version, called Essential 8 Medium.
Defining exactly what has gone into a culture medium takes the field beyond alchemy and helps scientists to reproduce findings from colleagues, as well as to approach clinical applications, says Mikhail Kolonin, a stem-cell researcher at the University of Texas Health Science Center in Houston.
No more animal pharma
In addition to problems with feeder systems, another stumbling block to reproducibility is that the growth factors, proteins and other nutrients in stem-cell media typically come from fetal bovine serum, which can comprise up to one-fifth of a medium's volume, says Monsma. Each batch of serum — which is part of the blood — comes from a different animal and contains different amounts of components. “The point is, we don't know what's inside,” says Kolonin. That is one reason why stem-cell scientists eyeing clinical applications are becoming wary of using products that contain serum.
Another reason is that cells grown in animal products for use in tissue transplantation can “potentially cause an immune response in patients”, says Kolonin. Contamination can have even more serious consequences, as the experience with mad cow disease showed, says Nathan Allen, a product marketing manager in the cell-culture and bioprocessing business at Thermo Fisher Scientific, headquartered in Waltham, Massachusetts. In the mad-cow episode, a UK outbreak of variant Creutzfeldt–Jakob disease was caused by contamination of food with the infectious agent of bovine spongiform encephalopath.
The US Food and Drug Administration has asked manufacturers to avoid animal-derived components in therapeutics. This preference affects preclinical research, because ideally, technology choices in the early stages of development should set the pattern for manufacturing further down the road, says Roberta Morris, business director at Thermo Fisher Scientific.
For that reason, new commercial media are increasingly serum-free, says Allen. His company offers a number of serum-free media and defined media free of all components originating from animals. But banishing animal products is not easy, if only because converting media containing serum or with undefined supplements into a more chemically defined version means massively reworking a proprietary recipe, which affects manufacturing.
All of this can make media expensive. Last autumn, Sigma-Aldrich in St Louis, Missouri, launched a stem-cell maintenance medium as part of its Stemline series. The medium is not completely free of animal products, but is composed of defined components and does not contain the types of crude protein preparation found in many formulations, such as serum or pituitary extracts, says Dan Allison, principal research scientist at Sigma-Aldrich. It was designed to cater for labs that are working towards industrial applications for stem cells and that will need high volumes of media, says the company.
Monsma says that creating media without animal components, using only chemical compounds and supplements of non-animal origin — such as human serum albumin or recombinant growth factors — means that the proteins must be expressed in human cells or bacteria, then purified and tested. His company and others are setting up capabilities to manufacture such media. For example, Primorigen is collaborating with several university labs to convert a differentiation medium into one that is animal-component-free.
For stem-cell researchers, shifting away from animal products means abandoning some lab staples, such as mouse feeder cells. Furthermore, some substances traditionally used to coat cell culture dishes are not animal-free. Matrigel — a product that was previously made by Becton, Dickinson of Franklin Lakes, New Jersey, but was sold to Corning Inc. in Corning, New York, last autumn — is a gel used to coat dishes, and is derived from a type of mouse tumour. Researchers at the University of Michigan in Ann Arbor have noted that, although Matrigel has helped scientists to define what iPSCs need, its animal origins and variability are problematic if cells are being cultured as eventual patient therapeutics 4 .
Engineering in the mix
Some scientists will be satisfied only by mixing their own cell culture media. They “tend to know what they are doing and be highly experienced”, says Masters.
But most, he adds, “are generally not interested in the basics of how to do it properly, just the end product”. They want to be able to buy media off the shelf. Companies have begun catering for scientists who want more defined media. Firms interviewed by Nature say that their products are superior to home-brew because they can exert more quality control over the way they source, store, mix and evaluate ingredients, and can manufacture media under controlled conditions.
Engineered media can make a difference. For example, stem cells are deep frozen until their use in the lab, with scientists using a variety of cryopreservation media, including home-brews. But an ongoing challenge in the field is that most cells do not survive the thaw, says Hadley.
“Most researchers are generally not interested in the basics of how to do it properly, just the end product.”
Towards the end of last year, Thermo Fisher Scientific began to sell a serum-free, animal-origin-free cryopreservation medium called HyCryo for standard cell lines, and a separate one, HyCryo-STEM, for stem cells. HyCryo-STEM is engineered to improve the recovery rate of stem cells after thawing. Scientists working with neural stem cells can usually recover only 10–20% of cells, and increasing that proportion is not easy with the typical home-brewed freezing media used in labs, says Cindy Neeley, a cell-culture specialist at Thermo Fisher. In tests, the company's new medium is as good as home-brew, and for neural stem cells the recovery increased to 50–60%, she says.
Improving cell-culture environments also means improving containers. Taking an engineering approach, Po Ki Yuen, a bioengineer at Corning, has built a 96-well plate that nurtures growing cells while removing waste — which is toxic — and replenishing media, without an external pump 5 . Not only does the plate require less than the usual amount of daily media exchange, says Yuen — thus minimizing the need for human intervention and lowering the risk of contamination — but it also has fluid movement that is a bit more like that of the body than that of a classic lab vessel.
The idea for the plate, which emerged during a product-development session with two colleagues, he says, is to take advantage of pressure differences between wells that contain different amounts of fluid. Narrow strips of filter paper or a cellulose membrane connect the wells, so that fluid is forced to flow in a controllable way into the adjacent connected well until the liquid heights reach the same level in both. “The flow rate in our perfusion plate can be controlled by liquid height difference between connected wells, and the dimensions and pore size of the strip of cellulose membrane or filter paper,” says Yuen.
The 96-well version is not yet on the market but a 6-well version is, says Brian Douglass, a business-development manager at Corning. Cells in the 6-well version can last for at least 72 hours without media exchange, says Yuen. And, says Douglass, less-frequent media exchange means that “researchers get their weekends back”.
Scientists and companies are also exploring 3D environments in which to foster tissue-like growth of cell clusters, keeping cells close and in constant communication. In this kind of architecture, stem cells can grow into rounded aggregates called embryoid bodies, which is part of the differentiation process.
This means that cells must not attach to the surface of their container, because if they do, they will grow in a spread-out single layer, says Neeley. Thermo Fisher Scientific has developed a series of dishes and multiple-well plates with a polystyrene surface that offers low-adhesion properties. Scaffolds can be used to shape cell clusters as they grow, but the three-dimensionality collapses once the scaffold is removed, like a tent without its supporting poles. They can also block a researcher's view through a microscope.
To cater for researchers seeking viable 3D cell-culture options, Thermo Fisher Scientific has developed a culture plate called Nunclon Sphera. “The cells, instead of sticking to the surface, aggregate with themselves and form a three-dimensional sphere in the culture environment,” says Neeley. When cultured in this plate, cells grow into spheres that the scientists can transfer from one vessel to another using a pipette, without disrupting the form, she says. Customers are currently beta-testing the product.
Other plate-focused efforts rely on more radical architectural changes. Three-dimensional cell culture dates back more than 100 years, says Ross Harrison, a biologist at Johns Hopkins University in Baltimore, Maryland. He cultured neural tissue in a hanging drop of frog lymph and was able to observe live nerve cells sprouting axons, the long extensions through which neurons send messages to other neurons.
Now, a Swiss company, InSphero in Schlieren, is using the hanging-drop technique as the basis for a multiple-well plate made of the conventional polystyrene but with redesigned wells. After building a prototype, the Swiss Federal Institute of Technology (ETH) in Zurich set up the fledgling firm in the institute's technology park, says Jens Kelm, a biotechnologist formerly at the University of Zurich who founded InSphero four years ago along with University of Zurich colleague Wolfgang Moritz and ETH engineer Jan Lichtenberg. The firm is just moving into its own facilities.
Unlike typical round-bottomed wells, InSphero's wells have a V-shaped lower part, similar in appearance to a champagne flute. At its very bottom, the well is flat. In a hanging drop of medium, cells settle and grow as spheroids in a way that enables microscopy, says Kelm.
Getting the cells into the well also meant changing the well openings, which are shaped like a very narrow flower vase so that they fit tightly around a pipette tip. The researchers found that air-tight contact between the well opening and the pipette tip allowed them to deposit near-identical amounts into each well, which is important for making sure that the results are comparable between wells. To arrive at the design, says Kelm, “we started experimenting with pipette tips, cut them off and put in drops from the top and looked at how they came out at the bottom”.
In 2011, InSphero began a partnership with PerkinElmer in Waltham, Massachusetts, allowing the plates to be incorporated into PerkinElmer's automated screening instruments, which are used by drug companies. What began as a marketing deal has morphed into the companies collaborating on assay development for example, they create plates that hold spheroids of liver microtissue ready for drug toxicity tests.
Kelm sees a broad international market for his technology. European laws that prohibit the use of animals in cosmetics testing have left the industry clamouring for in vitro models, such as his microtissues. Drug developers and chemical companies also want cell-based assays to test toxicity. And hanging-drop technology can be used to culture stem cells, an area that could expand as these cells move towards medical applications.
Nadia Benkirane-Jessel, a biologist at the French National Institute of Health and Medical Research (INSERM) in Strasbourg, uses InSphero's technology to investigate ways to shorten recovery times for people undergoing bone-repair procedures and, potentially, bone regeneration. To position bone cells correctly for growth, Benkirane-Jessel seeds cells that have grown into spherical microtissues onto 3D nanofibres developed in her lab for use in mice. She also plans to use InSphero's technology for a product developed by her spin-off company, Artios Nanomed in Strasbourg, in the field of bone and cartilage regeneration.
Another academic spin-off that is developing 3D cell culture is n3D Biosciences in Houston. As chief scientific officer and company co-founder Glauco Souza explains, the technology seeds tissue by levitating cells and bringing them together 6 . The first step is to decorate cells with NanoShuttle, the company's magnetic nanoparticle assembly of gold and iron oxide crosslinked with polylysine, he says. Next, the cell culture dish is exposed to a magnetic field. “When the magnetic field is applied, it brings the cells together while levitating them,” he says.
What keeps cells growing, Souza explains, is the cell–cell interaction that the levitation process promotes, which is more like the body's environment than conventional cell culture. The technology also makes media exchange easier, because a magnet can hold the tissue in place, he says.
Souza, a physical chemist formerly at the MD Anderson Cancer Center in Houston, says that research with this technology at the company and in collaborating academic labs shows that the resultant microtissues have in vivo-like morphology and protein production, enabling them to be used in in vitro drug-testing models. n3D Biosciences has customers in university labs and pharmaceutical companies, and is focusing on high-throughput toxicity testing and drug development.
Kolonin uses the technology to study fat tissue, and also considers it a possible environment for growing stem cells into organs. Recreating an organ in a dish requires all the organ's cell types to be present and to make connections. In a flat dish, however, one cell type usually takes over because it happens to respond best to the media or to the plastic, and other cells are quickly lost, he says. That situation is different with the n3D technology. “You plate cells out, throw particles at them . overnight, and put them into the magnetic field, and the next day you already have the spheroids,” he says. The spheroids include all the cell types. “It literally takes one day.”
Magnetic levitation has been a good way to model adipose tissue, Kolonin adds, and to culture stem cells while retaining their ability to differentiate 7 .
The magnetic particles may cause adverse consequences for the cells that contain them, but, these are a minority of the cells in culture. The microtissues stay together and the cells tend to spit out the particles, which then remain in the matrix outside the cells.
“There has been a boom of late in 3D formats, and I think the field is rapidly adopting and critically evaluating these technologies.”
“There has been a boom of late in 3D formats, and I think the field is rapidly adopting and critically evaluating these technologies,” says Jeffrey Morgan, a bioengineer at Brown University in Providence, Rhode Island. He thinks that when cells contact, interact with and communicate with other cells rather than with artificial scaffolds, the cell culture more closely replicates the in vivo environment, especially that in solid organs such as the heart and liver, where cell density is high.
Morgan invented what he calls the 3D Petri dish, and in 2009 he founded a company: Microtissues, based in Providence. In a deal that went through last year, Sigma-Aldrich is distributing the dish. Morgan's customers are academic biomedical researchers, pharmaceutical firms doing toxicity testing and cell-therapy companies exploring how to prepare cell clusters for possible transplantation.
The 3D Petri dish came about when, to guide the growth of tissue-like multicellular spheroids, Morgan and his graduate student Anthony Napolitano began making moulds in the lab. They wanted a material that was non-adhesive for cells, which is the “direct opposite” of the classic plastic Petri dish, says Morgan. At the same time, the researchers needed a material that would not interfere with the small cell–cell adhesive forces that drive cell clustering. The material they chose was agarose, which forms a commonly used hydrogel and is made of 98% water, which is why Morgan says that his approach is “like sculpting water”.
A user casts molten agarose in the micro-moulds, allows it to gel, then removes the micro-moulded agarose and places it in a standard multiple-well dish. Cell media and cells are pipetted into the dish, and cells then settle by gravity into each of the micro-wells and self-assemble into a multicellular spheroid at the bottom of each moulded well. The micro-moulds can be autoclaved and reused to cast more gels.
The mould makes spheroids that are uniform in shape, says Morgan. Their size can be varied with the number of cells that are seeded. The cells are easier to harvest than in scaffold-based methods. They spill out when the gel is inverted, allowing further tests.
Although stem-cell research and advances in cell culture are quickly advancing, viable cell therapies are years away from the market, says Chuck Oehler, chief executive of Primorigen. But companies such as his regularly get calls from people seeking stem-cell-based cures. Neither are stem-cell scientists immune to hope.
A researcher who did not wish to be identified is diabetic, and has been dependent on insulin for more than 30 years. A few years ago, he had a transplant of insulin-producing islet cells from cadavers, which allowed him to go for nearly one year without insulin injections and also lessened some of his symptoms, such as numbness in his fingers and toes.
“So the potential seems to be there, if the work we and others are doing to ensure production of cells with adequate, lasting function can be produced,” says the researcher. As a practitioner, he knows the scientific reality. “But given the impact that regenerative medicine can have on my quality of life and on my loved ones, it is easy to understand how those less familiar with the science and industry can be frustrated or impatient with the rate of progress.”
Fuchs E, Horsley V . Ferreting out stem cells from their niches. Nature Cell Biol 2011 13:513–518.
Medema JP, Vermulen L . Microenvironmental regulation of stem cells in intestinal homeostasis and cancer. Nature 2011 474:318–326.
Simons BD, Clevers H . Strategies for homeostatic stem cell self-renewal in adult tissues. Cell 2011 145:851–862.
Li L, Clevers H . Coexistence of quiescent and active adult stem cells in mammals. Science 2010 327:542–545.
Cotsarelis G, Cheng SZ, Dong G, Sun TT, Lavker RM . Existence of slow-cycling limbal epithelial basal cells that can be preferentially stimulated to proliferate: Implications on epithelial stem cells. Cell 1989 57:201–209.
Cotsarelis G, Sun TT, Lavker RM . Label-retaining cells reside in the bulge area of pilosebaceous unit: implications for follicular stem cells, hair cycle, and skin carcinogenesis. Cell 1990 61:1329–1337.
Golebiewska A, Brons NH, Bjerkvig R, Niclou SP . Critical appraisal of the side population assay in stem cell and cancer stem cell research. Cell Stem Cell 2011 8:136–147.
Storms RW, Trujillo AP, Springer JB, et al. Isolation of primitive human hematopoietic progenitors on the basis of aldehyde dehydrogenase activity. Proc Natl Acad Sci USA 1999 96:9118–9123.
Passegué E, Jamieson CH, Ailles LE, Weissman IL . Normal and leukemic hematopoiesis: are leukemias a stem cell disorder or a reacquisition of stem cell characteristics? Proc Natl Acad Sci USA 2003 100(Suppl 1):11842–11849.
Notta F, Doulatov S, Laurenti E, Poeppl A, Jurisica I, Dick JE . Isolation of single human hematopoietic stem cells capable of long-term multilineage engraftment. Science 2011 333:218–221.
Majeti R, Park CY, Weissman IL . Identification of a hierarchy of multipotent hematopoietic progenitors in human cord blood. Cell Stem Cell 2007 1:635–645.
Osawa M, Hanada K, Hamada H, Nakauchi H . Long-term lymphohematopoietic reconstitution by a single CD34-low/negative hematopoietic stem cell. Science 1996 273:242–245.
Kiel MJ, Yilmaz OH, Iwashita T, Yilmaz OH, Terhorst C, Morrison SJ . SLAM family receptors distinguish hematopoietic stem and progenitor cells and reveal endothelial niches for stem cells. Cell 2005 121:1109–1121.
Xin L, Lawson DA, Witte ON . The Sca-1 cell surface marker enriches for a prostate-regenerating cell subpopulation that can initiate prostate tumorigenesis. Proc Natl Acad Sci USA 2005 102:6942–6947.
Burger PE, Xiong X . Coetzee S, et al. Sca-1 expression identifies stem cells in the proximal region of prostatic ducts with high capacity to reconstitute prostatic tissue. Proc Natl Acad Sci USA 2005 102:7180–7185.
Lawson DA, Xin L, Lukacs RU, Cheng D, Witte ON . Isolation and functional characterization of murine prostate stem cells. Proc Natl Acad Sci USA 2007 104:181–186.
Leong KG, Wang BE, Johnson L, Gao WQ . Generation of a prostate from a single adult stem cell. Nature 2008 456:804–808.
Hong SH, Rampalli S, Lee JB, et al. Cell fate potential of human pluripotent stem cells is encoded by histone modifications. Cell Stem Cell 2011 9:24–36.
Bergmann O, Bhardwaj RD, Bernard S, et al. Evidence for cardiomyocyte renewal in humans. Science 2009 324:98–102.
Spalding KL, Arner E, Westermark PO, et al. Dynamics of fat cell turnover in humans. Nature 2008 453:783–787.
Arner P, Bernard S, Salehpour M, et al. Dynamics of human adipose lipid turnover in health and metabolic disease. Nature 2011 478:110–113.
Katoh M, Shaw C, Xu Q, et al. An orderly retreat: Dedifferentiation is a regulated process. Proc Natl Acad Sci USA 2004 101:7005–7010.
Brawley C, Matunis E . Regeneration of male germline stem cells by spermatogonial dedifferentiation in vivo. Science 2004 304:1331–1334.
Dor Y, Brown J, Martinez OI, Melton DA . Adult pancreatic beta-cells are formed by self-duplication rather than stem-cell differentiation. Nature 2004 429:41–46.
Cobaleda C, Jochum W, Busslinger M . Conversion of mature B cells into T cells by dedifferentiation to uncommitted progenitors. Nature 2007 449:473–477.
Heyworth C, Pearson S, May G, Enver T . Transcription factor-mediated lineage switching reveals plasticity in primary committed progenitor cells. EMBO J 2002 21:3770–3781.
Zhou Q, Brown J, Kanarek A, Rajagopal J . Melton DA . In vivo reprogramming of adult pancreatic exocrine cells to beta-cells. Nature 2008 455:627–632.
Zhou Q, Melton DA . Extreme makeover: converting one cell into another. Cell Stem Cell 2008 3:382–388.
Chambers SM, Studer L . Cell fate plug and play: Direct reprogramming and induced pluripotency. Cell 2011 145:827–830.
Pang ZP, Yang N, Vierbuchen T, et al. Induction of human neuronal cells by defined transcription factors. Nature 2011 476:220–223.
Caiazzo M, Dell'Anno MT, Dvorestskova E, et al. Direct generation of functional dopaminergic neurons from mouse and human fibroblasts. Nature 2011 476:224–227.
Yoo AS, Sun AX, Li L, et al. MicroRNA-mediated conversion of human fibroblasts to neurons. Nature 2011 476:228–231.
Huang P, He, Z, Ji S, et al. Induction of functional hepatocyte-like cells from mouse fibroblasts by defined factors. Nature 2011 475:386–389.
Sekiya S, Suzuki A . Direct conversion of mouse fibroblasts to hepatocyte-like cells by defined factors. Nature 2011 475:390–393.
Collombat P, Xu X, Ravassard P, et al. The ectopic expression of Pax4 in the mouse pancreas converts progenitor cells into α and subsequently β cells. Cell 2009 138:449–462.
Kondo T, Raff M . Oligodendrocyte precursor cells reprogrammed to become multipotential CNS stem cells. Science 2000 289:1754–1757.
Yamanaka S . Elite and stochastic models for induced pluripotent stem cell generation. Nature 2009 460:49–52.
Shackleton M, Quintana E, Fearon ER, Morrison SJ . Heterogeneity in cancer: cancer stem cells versus clonal evolution. Cell 2009 138:822–829.
Anderson K, Lutz C, van Delft FW, et al. Genetic variegation of clonal architecture and propagating cells in leukaemia. Nature 2011 469:356–361.
Notta F, Mullighan CG, Wang JC, et al. Evolution of human BCR-ABL1 lymphoblastic leukaemia-initiating cells. Nature 2011 469:362–367.
Visvader JE . Cells of origin in cancer. Nature 2011 469:314–322.
Lim E, Vaillant F, Wu D, et al. Aberrant luminal progenitors as the candidate target population for basal tumor development in BRCA1 mutation carriers. Nat Med 2009 15:907–913.
Molyneux G, Geyer FC, Magnay FA, et al. BRCA1 basal-like breast cancers originate from luminal epithelial progenitors and not from basal stem cells. Cell Stem Cell 2010 7:403–417.
Proia TA, Keller PJ, Gupta PB, et al. Genetic predisposition directs breast cancer phenotype by dictating progenitor cell fate. Cell Stem Cell 2011 8:149–163.
Liu C, Sage JC, Miller MR, et al. Mosaic analysis with double markers reveals tumor cell of origin in glioma. Cell 2011 146:209–221.
Quintana E, Shackleton M, Sabel MS, Fullen DR, Johnson TM, Morrison SJ . Efficient tumour formation by single human melanoma cells. Nature 2008 456:593–598.
Ishizawa K, Rasheed ZA, Karisch R, et al. Tumor-initiating cells are rare in many human tumors. Cell Stem Cell 2010 7:279–282.
Alison MR, Guppy NJ, Lim SML, Nicholson LJ . Finding cancer stem cells: Are aldehyde dehydrogenases fit for purpose? J Pathol 2010 222:335–344.
Pastrana E, Silva-Vargas V, Doetsch F . Eyes wide open: a critical review of sphere-formation as an assay for stem cells. Cell Stem Cell 2011 8:486–498.
Al-Hajj M, Wicha MS, Benito-Hernandez A, Morrison SJ, Clarke MF . Prospective identification of tumorigenic breast cancer cells. Proc Natl Acad Sci USA 2003 100:3983–3938.
Hirschmann-Jax C, Foster AE, Wulf GG, et al. A distinct "side population" of cells with high drug efflux capacity in human tumor cells. Proc Natl Acad Sci USA 2004 101:14228–14233.
Engelmann K, Shen H, Finn OJ . MCF7 side population cells with characteristics of cancer stem/progenitor cells express the tumor antigen MUC1. Cancer Res 2008 68:2419–2426.
Ginestier C, Hur MH, Charafe-Jauffret E, et al. ALDH1 is a marker of normal and malignant human mammary stem cells and a predictor of poor clinical outcome. Cell Stem Cell 2007 1:555–567.
Charafe-Jauffret E, Ginestier C, Iovino F, et al. Breast cancer cell lines contain functional cancer stem cells with metastatic capacity and a distinct molecular signature. Cancer Res 2009 69:1302–1313.
Pece S, Tosoni D, Confalonieri S, et al. Biological and molecular heterogeneity of breast cancers correlates with their cancer stem cell content. Cell 2010 140:62–73.
Hwang-Verslues WW, Kuo WH, Chang PH, et al. Multiple lineages of human breast cancer stem/progenitor cells identified by profiling with stem cell markers. PLoS One 2009 4:e8377.
Park SY, Lee HE, Li H, Shipitsin M, Gelman R, Polyak K . Heterogeneity for stem cell-related markers according to tumor subtype and histologic stage in breast cancer. Clin Cancer Res 2010 16:876–887.
Deng S, Yang X, Lassus H, et al. Distinct expression levels and patterns of stem cell marker, aldehyde dehydrogenase isoform 1 (ALDH1), in human epithelial cancers. PLoS One 2010 5:e 10277.
Meyer MJ, Fleming JM, Lin AF, Hussnain SA, Ginsburg E, Vonderhaar BK . CD44 pos CD49f hi CD133/2 hi defines xenograft-initiating cells in estrogen receptor-negative breast cancer. Cancer Res 2010 70:4624–4633.
Cicalese A, Bonizzi G, Pasi CE, et al. The tumor suppressor p53 regulates polarity of self-renewing divisions in mammary stem cells. Cell 2009 138:1083–1095.
Singh SK, Hawkins C, Clarke ID, et al. Identification of human brain tumour initiating cells. Nature 2004 432:396–401.
Beier D, Hau P, Proescholdt M, et al. CD133(+) and CD133(-) glioblastoma-derived cancer stem cells show differential growth characteristics and molecular profiles. Cancer Res 2007 67:4010–4015.
Bleau AM, Hambardzumyan D, Ozawa T, et al. PTEN/PI3K/Akt pathway regulates the side population phenotype and ABCG2 activity in glioma tumor stem-like cells. Cell Stem Cell 2009 4:226–235.
Son MJ, Woolard K, Nam DH, Lee J, Fine HA . SSEA-1 is an enrichment marker for tumor-initiating cells in human glioblastoma. Cell Stem Cell 2009 4:440–452.
Piccirillo SG, Combi R, Cajola L, et al. Distinct pools of cancer stem-like cells coexist within human glioblastomas and display different tumorigenicity and independent genomic evolution. Oncogene 2009 28:1807–1811.
Chen R, Nishimura MC, Bumbaca SM, et al. A hierarchy of self-renewing tumor-initiating cell types in glioblastoma. Cancer Cell 2010 17:362–375.
Mazzoleni S, Politi LS, Pala M, et al. Epidermal growth factor receptor expression identifies functionally and molecularly distinct tumor-initiating cells in human glioblastoma multiforme and is required for gliomagenesis. Cancer Res 2010 70:7500–7513.
Inda MM, Bonavia R, Mukasa A, et al. Tumor heterogeneity is an active process maintained by a mutant EGFR-induced cytokine circuit in glioblastoma. Genes Dev 2010 24:1731–1745.
Anido J, Sáez-Borderías A, Gonzàlez-Juncà A, et al. TGF-β receptor inhibitors target the CD44(high)/Id1(high) glioma-initiating cell population in human glioblastoma. Cancer Cell 2010 18:655–668.
Lottaz C, Beier D, Meyer K, et al. Transcriptional profiles of CD133 + and CD133 − glioblastoma-derived cancer stem cell lines suggest different cells of origin. Cancer Res 2010 70:2030–2040.
Yan X, Ma L, Yi D, et al. A CD133 − related gene expression signature identifies an aggressive glioblastoma subtype with excessive mutations. Proc Natl Acad Sci USA 2011 108:1591–1596.
Eyler CE, Wu Q, Yan K, et al. Glioma stem cell proliferation and tumor growth are promoted by nitric oxide synthase-2. Cell 2011 146:53–66.
Broadley KW, Hunn MK, Farrand KJ, et al. Side population is not necessary or sufficient for a cancer stem cell phenotype in glioblastoma multiforme. Stem Cells 2011 29:452–461.
Bonavia R, Inda MM, Cavenee WK, Furnari FB . Heterogeneity maintenance in glioblastoma: a social network. Cancer Res 2011 71:4055–4060.
O'Brien CA, Pollett A, Gallinger S, Dick JE . A human colon cancer cell capable of initiating tumour growth in immunodeficient mice. Nature 2007 445:106–110.
Ricci-Vitiani L, Lombardi DG, Pilozzi E, et al. Identification and expansion of human colon-cancer-initiating cells. Nature 2007 445:111–115.
Todaro M, Alea MP, Di Stefano AB, et al. Colon cancer stem cells dictate tumor growth and resist cell death by production of interleukin-4. Cell Stem Cell 2007 1:389–402.
Dalerba P, Dylla SJ, Park IK, et al. Phenotypic characterization of human colorectal cancer stem cells. Proc Natl Acad Sci USA 2007 104:10158–10163.
Du L, Wang H, He L, et al. CD44 is of functional importance for colorectal cancer stem cells. Clin Cancer Res 2008 14:6751–6760.
Odoux C, Fohrer H, Hoppo T, et al. A stochastic model for cancer stem cell origin in metastatic colon cancer. Cancer Res 2008 68:6932–6941.
Shmelkov SV, Butler JM, Hooper AT, et al. CD133 expression is not restricted to stem cells, and both CD133 + and CD133 − metastatic colon cancer cells initiate tumors. J Clin Invest 2008 118:2111–2120.
Vermeulen L, Todaro M, de Sousa Mello F, et al. Aldehyde dehydrogenase 1 is a marker for normal and malignant human colonic stem cells (SC) and tracks SC overpopulation during colon tumorigenesis. Cancer Res 2009 69:3382–3389.
Kemper K, Sprick MR, de Bree M, et al. The AC133 epitope, but not the CD133 protein, is lost upon cancer stem cell differentiation. Cancer Res 2010 70:719–729.
Inoda S, Hirohashi Y, Torigoe T, et al. Cytotoxic T lymphocytes efficiently recognize human colon cancer stem-like cells. Am J Pathol 2011 178:1805–1813.
Wilson BJ, Schatton T, Zhan Q, et al. ABCB5 identifies a therapy-refractory tumor cell population in colorectal cancer patients. Cancer Res 2011 71:5307–5316.
Medema JP, Vermeulen L . Microenvironmental regulation of stem cells in intestinal homeostasis and cancer. Nature 2011 474:318–326.
Patrawala L, Calhoun T, Schneider-Broussard R . Zhou J-J, Claypool K, Tang DG . Side population (SP) is enriched in tumorigenic, stem-like cancer cells whereas ABCG2 + and ABCG2 − cancer cells are similarly tumorigenic. Cancer Res 2005 65:6207–6219.
Huss WJ, Gray DR, Greenberg NM, Mohler JL, Smith GJ . Breast cancer resistance protein-mediated efflux of androgen in putative benign and malignant prostate stem cells. Cancer Res 2005 65:6640–6650.
Collins AT, Berry PA, Hyde C, Stower MJ, Maitland NJ . Prospective identification of tumorigenic prostate cancer stem cells. Cancer Res 2005 65:10946–10951.
Patrawala L, Calhoun T, Schneider-Broussard R, et al. Highly purified CD44 + prostate cancer cells from xenograft human tumors are enriched in tumorigenic and metastatic progenitor cells. Oncogene 2006 25:1696–1708.
Patrawala L, Calhoun-Davis T, Schneider-Broussard R, Tang DG . Hierarchical organization of prostate cancer cells in xenograft tumors: The CD44 + α2β1 + cell population is enriched in tumor-initiating cells. Cancer Res 2007 67:6796–6805.
Miki J, Furusato B, Li H, et al. Identification of putative stem cell markers, CD133 and CXCR4, in hTERT-immortalized primary nonmalignant and malignant tumor-derived human prostate epithelial cell lines and in prostate cancer specimens. Cancer Res 2007 67:3153–3161.
Gu G, Yuan J, Wills M, Kasper S . Prostate cancer cells with stem cell characteristics reconstitute the original human tumor in vivo. Cancer Res 2007 67:4807–4815.
Li HW, Chen X, Calhoun-Davis T, Claypool K, Tang DG . PC3 Human prostate carcinoma cell holoclones contain self-renewing tumor-initiating cells. Cancer Res 2008 68:1820–1825.
Jeter C, Badeaux M, Choy G, et al. Functional evidence that the self-renewal gene NANOG regulates human tumor development. Stem Cells 2009 27:993–1005.
Dubrovska A, Kim S, Salamone RJ, et al. The role of PTEN/Akt/PI3K signaling in the maintenance and viability of prostate cancer stem-like cell populations. Proc Natl Acad Sci USA 2009 106:268–273.
Li T, Su Y, Mei Y, et al. ALDH1A1 is a marker for malignant prostate stem cells and predictor of prostate cancer patients' outcome. Lab Invest 2010 90:234–244.
van den Hoogen C, van der Horst G, Cheung H, et al. High aldehyde dehydrogenase activity identifies tumor-initiating and metastasis-initiating cells in human prostate cancer. Cancer Res 2010 70:5163–5173.
Rajasekhar VK, Studer L, Gerald W, Socci ND, Scher HI . Tumour-initiating stem-like cells in human prostate cancer exhibit increased NF-κB signalling. Nat Commun 2011 2:162.
Liu C, Kelnar K, Liu B, et al. The microRNA miR-34a inhibits prostate cancer stem cells and metastasis by directly repressing CD44. Nature Med 2011 17:211–215.
Ho MM, Ng AV, Lam S, Hung JY . Side population in human lung cancer cell lines and tumors is enriched with stem-like cancer cells. Cancer Res 2007 67:4827–4833.
Eramo A, Lotti F, Sette G, Pilozzi E, Biffoni M . Identification and expansion of the tumorigenic lung cancer stem cell population. Cell Death Differ 2008 15:504–414.
Jiang T, Collins BJ, Jin N, Watkins DN, Brock MV . Achaete-scute complex homologue 1 regulates tumor-initiating capacity in human small cell lung cancer. Cancer Res 2009 69:845–854.
Bertolini G, Roz L, Perego P, Tortoreto M, Fontanella E . Highly tumorigenic lung cancer CD133 + cells display stem-like features and are spared by cisplatin treatment. Proc Natl Acad Sci USA 2009 106:16281–16286.
Levina V, Marrangoni A, Wang T, et al. Elimination of human lung cancer stem cells through targeting of the stem cell factor-c-kit autocrine signaling loop. Cancer Res 2010 70:338–346.
Eramo A, Haas TL, De Maria R . Lung cancer stem cells: tools and targets to fight lung cancer. Oncogene 2010 29:4625–4635.
Sullivan JP, Spinola M, Dodge M, et al. Aldehyde dehydrogenase activity selects for lung adenocarcinoma stem cells dependent on notch signaling. Cancer Res 2010 70:9937–9948.
Chiou SH, Wang ML, Chou YT, et al. Coexpression of Oct4 and Nanog enhances malignancy in lung adenocarcinoma by inducing cancer stem cell-like properties and epithelial-mesenchymal transdifferentiation. Cancer Res 2010 70:10433–10444.
Leung EL, Fiscus RR, Tung JW, et al. Non-small cell lung cancer cells expressing CD44 are enriched for stem cell-like properties. PLoS One 2010 5:e 14062.
Curtis SJ, Sinkevicius KW, Li D, et al. Primary tumor genotype is an important determinant in identification of lung cancer propagating cells. Cell Stem Cell 2010 7:127–133.
Damelin M, Geles KG, Follettie MT, et al. Delineation of a cellular hierarchy in lung cancer reveals an oncofetal antigen expressed on tumor-initiating cells. Cancer Res 2011 71:4236–4246.
Lapidot T, Sirard C, Vormoor J, et al. A cell initiating human acute myeloid leukaemia after transplantation into SCID mice. Nature 1994 367:645–648.
Bonnet D, Dick JE . Human acute myeloid leukemia is organized as a hierarchy that originates from a primitive hematopoietic cell. Nat Med 1997 3:730–737.
Hope KJ, Jin L, Dick JE . Acute myeloid leukemia originates from a hierarchy of leukemic stem cell classes that differ in self-renewal capacity. Nat Immunol 2004 5:738–743.
Sarry JE, Murphy K, Perry R, et al. Human acute myelogenous leukemia stem cells are rare and heterogeneous when assayed in NOD/SCID/IL2Rγc-deficient mice. J Clin Invest 2011 121:384–395.
Shipitsin M, Campbell LL, Argani P, et al. Molecular definition of breast tumor heterogeneity. Cancer Cell 2007 11: 259–273.
Park SY, Gönen M, Kim HJ, Michor F, Polyak K . Cellular and genetic diversity in the progression of in situ human breast carcinomas to an invasive phenotype. J Clin Invest 2010 120:636–644.
Lotem J, Sachs L . Epigenetics and the plasticity of differentiation in normal and cancer stem cells. Oncogene 2006 25:7663–7672.
Hendrix MJ, Seftor EA, Hess AR, Seftor RE . Molecular plasticity of human melanoma cells. Oncogene 2003 22:3070–3075.
Casal C, Torres-Collado AX, Plaza-Calonge Mdel C, et al. ADAMTS1 contributes to the acquisition of an endothelial-like phenotype in plastic tumor cells. Cancer Res 2010 70:4676–4686.
Wang R, Chadalavada K, Wilshire J, et al. Glioblastoma stem-like cells give rise to tumour endothelium. Nature 2010 468:829–833.
Ricci-Vitiani L, Pallini R, Biffoni M, et al. Tumour vascularization via endothelial differentiation of glioblastoma stem-like cells. Nature 2010 468:824–828.
Sharma SV, Lee DY, Li B, et al. A chromatin-mediated reversible drug-tolerant state in cancer cell subpopulations. Cell 2010 141:69–80.
Yan H, Chen X, Zhang Q, et al. Drug-tolerant cancer cells show reduced tumor-initiating capacity: Depletion of CD44 + cells and evidence for epigenetic mechanisms. PLoS One 2011 6:e 24397.
Chaffer CL, Brueckmann I, Scheel C, et al. Normal and neoplastic nonstem cells can spontaneously convert to a stem-like state. Proc Natl Acad Sci USA 2011 108:7950–7955.
Gupta PB, Fillmore CM, Jiang G, et al. Stochastic state transitions give rise to phenotypic equilibrium in populations of cancer cells. Cell 2011 146:633–644.
Das B, Tsuchida R, Malkin D, et al. Hypoxia enhances tumor stemness by increasing the invasive and tumorigenic side population fraction. Stem Cells 2008 26:1818–1830.
Mathieu J, Zhang Z, Zhou W, et al. HIF induces human embryonic stem cell markers in cancer cells. Cancer Res 2011 71:4640–4652.
Koh MY . Lemos R Jr, Liu X, Powis G . The hypoxia-associated factor switches cells from HIF-1α- to HIF-2α-dependent signaling promoting stem cell characteristics, aggressive tumor growth and invasion. Cancer Res 2011 71:4015–4027.
Mani SA, Guo W, Liao MJ, et al. The epithelial-mesenchymal transition generates cells with properties of stem cells. Cell 2008 133:704–715.
Santisteban M, Reiman JM, Asiedu MK, et al. Immune-induced epithelial to mesenchymal transition in vivo generates breast cancer stem cells. Cancer Res 2009 69:2887–2895.
Iliopoulos D, Hirsch HA, Struhl K . An epigenetic switch involving NF-kappaB, Lin28, Let-7 MicroRNA, and IL6 links inflammation to cell transformation. Cell 2009 139:693–706.
Iliopoulos D, Lindahl-Allen M, Polytarchou C, Hirsch HA, Tsichlis PN, Struhl K . Loss of miR-200 inhibition of Suz12 leads to polycomb-mediated repression required for the formation and maintenance of cancer stem cells. Mol Cell 2010 39:761–772.
Asiedu MK, Ingle JN, Behrens MD, Radisky DC, Knutson KL . TGFβ/TNFα-mediated epithelial-mesenchymal transition generates breast cancer stem cells with a claudin-low phenotype. Cancer Res 2011 71:4707–4719.
Iliopoulos D, Hirsch HA, Wang G, Struhl K . Inducible formation of breast cancer stem cells and their dynamic equilibrium with non-stem cancer cells via IL6 secretion. Proc Natl Acad Sci USA 2011 108:1397–1402.
Jeter CR, Liu B, Liu X, et al. NANOG promotes cancer stem cell characteristics and prostate cancer resistance to androgen deprivation. Oncogene 2011 30:3833–3845.
Arzumanyan A, Friedman T, Ng IO, Clayton MM, Lian Z, Feitelson MA . Does the hepatitis B antigen HBx promote the appearance of liver cancer stem cells? Cancer Res 2011 71:3701–3708.
Su YJ, Lai HM, Chang YW, Chen GY, Lee JL . Direct reprogramming of stem cell properties in colon cancer cells by CD44. EMBO J 2011 30:3186–3199.
Scaffidi P . Misteli T . In vitro generation of human cells with cancer stem cell properties. Nat Cell Biol 2011 13:1051–1061.
Hwang WL, Yang MH, Tsai ML, et al. SNAIL regulates interleukin-8 expression, stem cell-like activity, and tumorigenicity of human colorectal carcinoma cells. Gastroenterology 2011 141:279–291.
Paranjape AN, Mandal T, Mukherjee G, Kumar MV, Sengupta K, Rangarajan A . Introduction of SV40ER and hTERT into mammospheres generates breast cancer cells with stem cell properties. Oncogene 2011 Aug 29. doi: 10.1038/onc.2011.378.
Bissell MJ, Labarge MA . Context, tissue plasticity, and cancer: are tumor stem cells also regulated by the microenvironment? Cancer Cell 2005 7:17–23.
Liu S, Ginestier C, Ou SJ, et al. Breast cancer stem cells are regulated by mesenchymal stem cells through cytokine networks. Cancer Res 2011 71:614–624.
Li X, Lewis MT, Huang J, et al. Intrinsic resistance of tumorigenic breast cancer cells to chemotherapy. J Natl Cancer Inst 2008 100:672–679.
Reim F, Dombrowski Y, Ritter C, et al. Immunoselection of breast and ovarian cancer cells with trastuzumab and natural killer cells: selective escape of CD44 high /CD24 low /HER2 low breast cancer stem cells. Cancer Res 2009 69:8058–8066.
Liu H, Patel MR, Prescher JA, et al. Cancer stem cells from human breast tumors are involved in spontaneous metastases in orthotopic mouse models. Proc Natl Acad Sci USA 2010 107:18115–18120.
Yu F, Yao H, Zhu P, et al. let-7 regulates self renewal and tumorigenicity of breast cancer cells. Cell 2007 131:1109–1123.
Emmink BL, Van Houdt WJ, Vries RG, et al. Differentiated human colorectal cancer cells protect tumor-initiating cells from irinotecan. Gastroenterology 2011 141:269–278.
Dubrovska A, Elliott J, Salamone RJ, et al. Combination therapy targeting both tumor-initiating and differentiated cell populations in prostate carcinoma. Clin Cancer Res 2010 16:5692–5702.
Hirsch HA, Iliopoulos D, Tsichlis PN, Struhl K . Metformin selectively targets cancer stem cells, and acts together with chemotherapy to block tumor growth and prolong remission. Cancer Res 2009 69:7507–7511.
Shats I, Gatza ML, Chang JT, et al. Using a stem cell-based signature to guide therapeutic selection in cancer. Cancer Res 2011 71:1772–1780.
Eppert K, Takenaka K, Lechman ER, et al. Stem cell gene expression programs influence clinical outcome in human leukemia. Nat Med 2011 17:1086–1093.
In recent decades, attention to adipose tissue has increased in parallel with a rising epidemic of obesity and its negative effects on whole body metabolism and increased incidence of various illnesses and conditions. Only recently have research efforts shifted to understanding the developmental biology of this tissue (Han et al., 2011 Rodeheffer et al., 2008 Tang et al., 2011 Tang et al., 2008). The complexity of the various adipose lineages (white, brown, induced brown, subcutaneous, visceral, etc.), the difficulty in working with such a fragile cell type, and the non-contiguous nature of this tissue has made it difficult to understand its developmental origin, and multiple origins might exist. However, with the generation of developmental tools, such as lineage tracing, researchers are now poised to understand the developmental cues and origin of adipose tissue and to answer a slew of interesting and undefined questions. For instance, what are the cell types of origin of the adipose lineage? What is the timing of adipose lineage determination and specification? Do adipose stem cells arise in situ on the blood vessel or do they migrate and arrive from elsewhere? What are the signals derived from the blood vessel niche that stimulate these stem cells to proliferate and differentiate or that hold them in the quiescent state? What is the importance of adipose stem cells to the homeostasis and maintenance of the fat pad under both normal energy intake and excess nutrient load? Do other anti-diabetes drugs alter adipose stem cell biology, similar to TZD treatment? Do growth factors and development signaling pathways alter stem cell behavior and adipocyte formation? In the midst of the obesity epidemic, the recent discoveries and the answers to these open-ended questions would provide hope that there is light at the end of the tunnel.
We thank members of our laboratory for their support, especially Kentaro Kato and Ken-ichi Tominaga for their fruitful discussions. This work was supported in part by a grant from the Ministry of Education, Culture, Sports, Science and Technology to Kiyokazu Agata and Satoru Kobayashi a Research Project for Future Program from the Japan Society for the Promotion of Science to Satoru Kobayashi Core Research for Evolutional Science and Technology (CREST) project of Japan Science and Technology Agency to Satoru Kobayashi and a grant from the National Institute of Agrobiological Sciences (Bio Design Program) to Hidefumi Orii and Satoru Kobayashi.