Archive for the ‘Somatic Stem Cells’ Category

Somatic cell nuclear transfer – Wikipedia

Somatic Stem Cells | Posted by admin
Nov 25 2016

In genetics and developmental biology, somatic cell nuclear transfer (SCNT) is a laboratory strategy for creating a viable embryo from a body cell and an egg cell. The technique consists of taking an enucleated oocyte (egg cell) and implanting a donor nucleus from a somatic (body) cell. It is used in both therapeutic and reproductive cloning. Dolly the Sheep became famous for being the first successful case of the reproductive cloning of a mammal.[1] "Therapeutic cloning" refers to the potential use of SCNT in regenerative medicine; this approach has been championed as an answer to the many issues concerning embryonic stem cells (ESC) and the destruction of viable embryos for medical use, though questions remain on how homologous the two cell types truly are.

The process of somatic cell nuclear transplant involves two different cells. The first being a female gamete, known as the ovum (egg/oocyte). In human SCNT experiments, these eggs are obtained through consenting donors, many times utilizing ovarian stimulation. The second being a somatic cell, referring to the cells of the human body. Skin cells, fat cells, and liver cells are only a few examples. The nucleus of the donor egg cell is removed and discarded, leaving it 'deprogrammed.' The nucleus of the somatic cell is also removed but is kept, the enucleated somatic cell is discarded. What is left is a lone somatic nucleus and an enucleated egg cell. These are then fused by inserting the somatic nucleus into the 'empty' ovum. After being inserted into the egg, the somatic cell nucleus is reprogrammed by its host egg cell. The ovum, now containing the somatic cell's nucleus, is stimulated with a shock and will begin to divide. The egg is now viable and capable of producing an adult organism containing all the necessary genetic information from just one parent. Development will ensue normally and after many mitotic divisions, this single cell forms a blastocyst (an early stage embryo with about 100 cells) with an identical genome to the original organism (i.e. a clone).[2] Stem cells can then be obtained by the destruction of this clone embryo for use in therapeutic cloning or in the case of reproductive cloning the clone embryo is implanted into a host mother for further development and brought to term.

Somatic cell nuclear transplantation has become a focus of study in stem cell research. The aim of carrying out this procedure is to obtain pluripotent cells from a cloned embryo. These cells genetically matched the donor organism from which they came.This gives them the ability to create patient specific pluripotent cells, which could then be used in therapies or disease research.[3]

Embryonic stem cells are undifferentiated cells of an embryo. These cells are deemed to have a pluripotent potential because they have the ability to give rise to all of the tissues found in an adult organism. This ability allows stem cells to create any cell type, which could then be transplanted to replace damaged or destroyed cells. Controversy surrounds human ESC work due to the destruction of viable human embryos. Leading scientists to seek an alternative method of obtaining stem cells, SCNT is one such method.

A potential use of stem cells genetically matched to a patient would be to create cell lines that have genes linked to a patient's particular disease. By doing so, an in vitro model could be created, would be useful for studying that particular disease, potentially discovering its pathophysiology, and discovering therapies.[4] For example, if a person with Parkinson's disease donated his or her somatic cells, the stem cells resulting from SCNT would have genes that contribute to Parkinson's disease. The disease specific stem cell lines could then be studied in order to better understand the condition.[5]

Another application of SCNT stem cell research is using the patient specific stem cell lines to generate tissues or even organs for transplant into the specific patient.[6] The resulting cells would be genetically identical to the somatic cell donor, thus avoiding any complications from immune system rejection.[5][7]

Only a handful of the labs in the world are currently using SCNT techniques in human stem cell research. In the United States, scientists at the Harvard Stem Cell Institute, the University of California San Francisco, the Oregon Health & Science University,[8]Stemagen (La Jolla, CA) and possibly Advanced Cell Technology are currently researching a technique to use somatic cell nuclear transfer to produce embryonic stem cells.[9] In the United Kingdom, the Human Fertilisation and Embryology Authority has granted permission to research groups at the Roslin Institute and the Newcastle Centre for Life.[10] SCNT may also be occurring in China.[11]

In 2005, a South Korean research team led by Professor Hwang Woo-suk, published claims to have derived stem cell lines via SCNT,[12] but supported those claims with fabricated data.[13] Recent evidence has proved that he in fact created a stem cell line from a parthenote.[14][15]

Though there has been numerous successes with cloning animals, questions remain concerning the mechanisms of reprogramming in the ovum. Despite many attempts, success in creating human nuclear transfer embryonic stem cells has been limited. There lies a problem in the human cell's ability to form a blastocyst; the cells fail to progress past the eight cell stage of development. This is thought to be a result from the somatic cell nucleus being unable to turn on embryonic genes crucial for proper development. These earlier experiments used procedures developed in non-primate animals with little success. A research group from the Oregon Health & Science University demonstrated SCNT procedures developed for primates successfully reprogrammed skin cells into stem cells. The key to their success was utilizing oocytes in metaphase II (MII) of the cell cycle. Egg cells in MII contain special factors in the cytoplasm that have a special ability in reprogramming implanted somatic cell nuclei into cells with pluripotent states. When the ovum's nucleus is removed, the cell loses its genetic information. This has been blamed for why enucleated eggs are hampered in their reprogramming ability. It is theorized the critical embryonic genes are physically linked to oocyte chromosomes, enucleation negatively affects these factors. Another possibility is removing the egg nucleus or inserting the somatic nucleus causes damage to the cytoplast, affecting reprogramming ability. Taking this into account the research group applied their new technique in an attempt to produce human SCNT stem cells. In May 2013, the Oregon group reported the successful derivation of human embryonic stem cell lines derived through SCNT, using fetal and infant donor cells. Using MII oocytes from volunteers and their improved SCNT procedure, human clone embryos were successfully produced. These embryos were of poor quality, lacking a substantial inner cell mass and poorly constructed trophectoderm. The imperfect embryos prevented the acquisition of human ESC. The addition of caffeine during the removal of the ovum's nucleus and injection of the somatic nucleus improved blastocyst formation and ESC isolation. The ESC obtain were found to be capable of producing teratomas, expressed pluripotent transcription factors, and expressed a normal 46XX karyotype, indicating these SCNT were in fact ESC-like.[8] This was the first instance of successfully using SCNT to reprogram human somatic cells. This study used fetal and infantile somatic cells to produce their ESC.

In April 2014, an international research team expanded on this break through. There remained the question of whether the same success could be accomplished using adult somatic cells. Epigenetic and age related changes were thought to possibly hinder an adult somatic cells ability to be reprogrammed. Implementing the procedure pioneered by the Oregon research group they indeed were able to grow stem cells generated by SCNT using adult cells from two donors, aged 35 and 75.Indicating age does not impede a cells ability to be reprogrammed[16][17]

Late April 2014, the New York Stem Cell Foundation was successful in creating SCNT stem cells derived from adult somatic cells. One of these lines of stem cells was derived from the donor cells of a type 1 diabetic. The group was then able to successfully culture these stem cells and induce differentiation. When injected into mice, cells of all three of the germ layers successfully formed. The most significant of these cells, were those who expressed insulin and were capable of secreting the hormone.[18] These insulin producing cells could be used for replacement therapy in diabetics, demonstrating real SCNT stem cell therapeutic potential.

The impetus for SCNT-based stem cell research has been decreased by the development and improvement of alternative methods of generating stem cells. Methods to reprogram normal body cells into pluripotent stem cells were developed in humans in 2007. The following year, this method achieved a key goal of SCNT-based stem cell research: the derivation of pluripotent stem cell lines that have all genes linked to various diseases.[19] Some scientists working on SCNT-based stem cell research have recently moved to the new methods of induced pluripotent stem cells. Though recent studies have put in question how similar iPS cells are to embryonic stem cells. Epigenetic memory in iPS affects the cell lineage it can differentiate into. For instance, an iPS cell derived from a blood cell will be more efficient at differentiating into blood cells, while it will be less efficient at creating a neuron.[20] This raises the question of how well iPS cells can mimic the gold standard ESC in experiments, as stem cells are defined as having the ability to differentiate into any cell type. SCNT stem cells do not pose such a problem and continue to remain relevant in stem cell studies.

This technique is currently the basis for cloning animals (such as the famous Dolly the sheep),[21] and has been theoretically proposed as a possible way to clone humans. Using SCNT in reproductive cloning has proven difficult with limited success. High fetal and neonatal death make the process very inefficient. Resulting cloned offspring are also plagued with development and imprinting disorders in non-human species. For these reasons, along with moral and ethical objections, reproductive cloning in humans is proscribed.[22] Most researchers believe that in the foreseeable future it will not be possible to use the current cloning technique to produce a human clone that will develop to term. It remains a possibility, though critical adjustments will be required to overcome current limitations during early embryonic development in human SCNT.[23][24]

There is also the potential for treating diseases associated with mutations in mitochondrial DNA. Recent studies show SCNT of the nucleus of a body cell afflicted with one of these diseases into a healthy oocyte prevents the inheritance of the mitochondrial disease. This treatment does not involve cloning but would produce a child with three genetic parents. A father providing a sperm cell, one mother providing the egg nucleus and another mother providing the enucleated egg cell.[6]

Interspecies nuclear transfer (iSCNT) is a means of somatic cell nuclear transfer used to facilitate the rescue of endangered species, or even to restore species after their extinction. The technique is similar to SCNT cloning which typically is between domestic animals and rodents, or where there is a ready supply of oocytes and surrogate animals. However, the cloning of highly endangered or extinct species requires the use of an alternative method of cloning. Interspecies nuclear transfer utilizes a host and a donor of two different organisms that are closely related species and within the same genus. In 2000, Robert Lanza was able to produce a cloned fetus of a gaur, Bos gaurus, combining it successfully with a domestic cow, Bos taurus.[25]

Interspecies nuclear transfer provides evidence of the universality of the triggering mechanism of the cell nucleus reprogramming. For example, Gupta et al.,[26] explored the possibility of producing transgenic cloned embryos by interspecies somatic cell nuclear transfer (iSCNT) of cattle, mice, and chicken donor cells into enucleated pig oocytes. Moreover, NCSU23 medium, which was designed for in vitro culture of pig embryos, was able to support the in vitro development of cattle, mice, and chicken iSCNT embryos up to the blastocyst stage. Furthermore, ovine oocyte cytoplast may be used for remodeling and reprogramming of human somatic cells back to the embryonic stage.[27]

SCNT can be inefficient. Stresses placed on both the egg cell and the introduced nucleus in early research were enormous, resulting in a low percentage of successfully reprogrammed cells. For example, in 1996 Dolly the sheep was born after 277 eggs were used for SCNT, which created 29 viable embryos. Only three of these embryos survived until birth, and only one survived to adulthood.[21] As the procedure was not automated, but had to be performed manually under a microscope, SCNT was very resource intensive. The biochemistry involved in reprogramming the differentiated somatic cell nucleus and activating the recipient egg was also far from understood. However, by 2014, researchers were reporting success rates of 70-80% with cloning pigs[28] and in 2016 a Korean company, Sooam Biotech, was reported to be producing 500 cloned embryos a day.[29]

In SCNT, not all of the donor cell's genetic information is transferred, as the donor cell's mitochondria that contain their own mitochondrial DNA are left behind. The resulting hybrid cells retain those mitochondrial structures which originally belonged to the egg. As a consequence, clones such as Dolly that are born from SCNT are not perfect copies of the donor of the nucleus. This fact may also hamper the potential benefits of SCNT derived tissues/organs for therapy, as there may be an immunoresponse to the non-self mtDNA after transplant.

Proposals to use nucleus transfer techniques in human stem cell research raise a set of concerns beyond the moral status of any created embryo. These have led to some individuals and organizations who are not opposed to human embryonic stem cell research to be concerned about, or opposed to, SCNT research.[30][31][32]

One concern is that blastula creation in SCNT-based human stem cell research will lead to the reproductive cloning of humans. Both processes use the same first step: the creation of a nuclear transferred embryo, most likely via SCNT. Those who hold this concern often advocate for strong regulation of SCNT to preclude implantation of any derived products for the intention of human reproduction,[33] or its prohibition.[30]

A second important concern is the appropriate source of the eggs that are needed. SCNT requires human eggs, which can only be obtained from women. The most common source of these eggs today are eggs that are produced and in excess of the clinical need during IVF treatment. This is a minimally invasive procedure, but it does carry some health risks, such as ovarian hyperstimulation syndrome.

One vision for successful stem cell therapies is to create custom stem cell lines for patients. Each custom stem cell line would consist of a collection of identical stem cells each carrying the patient's own DNA, thus reducing or eliminating any problems with rejection when the stem cells were transplanted for treatment. For example, to treat a man with Parkinson's disease, a cell nucleus from one of his cells would be transplanted by SCNT into an egg cell from an egg donor, creating a unique lineage of stem cells almost identical to the patient's own cells. (There would be differences. For example, the mitochondrial DNA would be the same as that of the egg donor. In comparison, his own cells would carry the mitochondrial DNA of his mother.)

Potentially millions of patients could benefit from stem cell therapy, and each patient would require a large number of donated eggs in order to successfully create a single custom therapeutic stem cell line. Such large numbers of donated eggs would exceed the number of eggs currently left over and available from couples trying to have children through assisted reproductive technology. Therefore, healthy young women would need to be induced to sell eggs to be used in the creation of custom stem cell lines that could then be purchased by the medical industry and sold to patients. It is so far unclear where all these eggs would come from.

Stem cell experts consider it unlikely that such large numbers of human egg donations would occur in a developed country because of the unknown long-term public health effects of treating large numbers of healthy young women with heavy doses of hormones in order to induce hyperovulation (ovulating several eggs at once). Although such treatments have been performed for several decades now, the long-term effects have not been studied or declared safe to use on a large scale on otherwise healthy women. Longer-term treatments with much lower doses of hormones are known to increase the rate of cancer decades later. Whether hormone treatments to induce hyperovulation could have similar effects is unknown. There are also ethical questions surrounding paying for eggs. In general, marketing body parts is considered unethical and is banned in most countries. Human eggs have been a notable exception to this rule for some time.

To address the problem of creating a human egg market, some stem cell researchers are investigating the possibility of creating artificial eggs. If successful, human egg donations would not be needed to create custom stem cell lines. However, this technology may be a long way off.

SCNT involving human cells is currently legal for research purposes in the United Kingdom, having been incorporated into the Human Fertilisation and Embryology Act 1990 in 2001.[34] Permission must be obtained from the Human Fertilisation and Embryology Authority in order to perform or attempt SCNT.

In the United States, the practice remains legal, as it has not been addressed by federal law.[35] However, in 2002, a moratorium on United States federal funding for SCNT prohibits funding the practice for the purposes of research. Thus, though legal, SCNT cannot be federally funded.[36] American scholars have recently argued that because the product of SCNT is a clone embryo, rather than a human embryo, these policies are morally wrong and should be revised.[37]

In 2003, the United Nations adopted a proposal submitted by Costa Rica, calling on member states to "prohibit all forms of human cloning in as much as they are incompatible with human dignity and the protection of human life."[38] This phrase may include SCNT, depending on interpretation.

The Council of Europe's Convention on Human Rights and Biomedicine and its Additional Protocol to the Convention for the Protection of Human Rights and Dignity of the Human Being with regard to the Application of Biology and Medicine, on the Prohibition of Cloning Human Being appear to ban SCNT of human beings. Of the Council's 45 member states, the Convention has been signed by 31 and ratified by 18. The Additional Protocol has been signed by 29 member nations and ratified by 14.[39]

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Somatic cell nuclear transfer - Wikipedia

Somatic cell – Wikipedia

Somatic Stem Cells | Posted by admin
Nov 02 2016

A somatic (Greek: /soma = body) or vegetal cell is any biological cell forming the body of an organism; that is, in a multicellular organism, any cell other than a gamete, germ cell, gametocyte or undifferentiated stem cell.[1]

In contrast, gametes are cells that fuse during sexual reproduction, germ cells are cells that give rise to gametes, and stem cells are cells that can divide through mitosis and differentiate into diverse specialized cell types. For example, in mammals, somatic cells make up all the internal organs, skin, bones, blood and connective tissue, while mammalian germ cells give rise to spermatozoa and ova which fuse during fertilization to produce a cell called a zygote, which divides and differentiates into the cells of an embryo. There are approximately 220 types of somatic cells in the human body.[1]

Theoretically, these cells are not germ cells (the source of gametes), they never transmit to their descendants the mutations they have undergone. However, in sponges, non-differentiated somatic cells form the germ line and, in Cnidaria, differentiated somatic cells are the source of the germline.

The word "somatic" is derived from the Greek word sma, meaning "body".

As multicellularity evolved many times, sterile somatic cells did too. The evolution of an immortal germline producing specialized somatic cells involved the emergence of mortality, and can be viewed in its simplest version in volvocine algae.[2] Those species with a separation between sterile somatic cells and a germ line are called Weismannists. However, Weismannist development is relatively rare (e.g., vertebrates, arthropods, Volvox), as great part of species have the capacity for somatic embryogenesis (e.g., land plants, most algae, many invertebrates).[3][4]

Like all cells, somatic cells contain DNA arranged in chromosomes. If a somatic cell contains chromosomes arranged in pairs, it is called diploid and the organism is called a diploid organism. (The gametes of diploid organisms contain only single unpaired chromosomes and are called haploid.) Each pair of chromosomes comprises one chromosome inherited from the father and one inherited from the mother. For example, in humans, somatic cells contain 46 chromosomes organized into 23 pairs. By contrast, gametes of diploid organisms contain only half as many chromosomes. In humans, this is 23 unpaired chromosomes. When two gametes (i.e. a spermatozoon and an ovum) meet during conception, they fuse together, creating a zygote. Due to the fusion of the two gametes, a human zygote contains 46 chromosomes (i.e. 23 pairs).

However, a large number of species have the chromosomes in their somatic cells arranged in fours ("tetraploid") or even sixes ("hexaploid"). Thus, they can have diploid or even triploid germline cells. An example of this is the modern cultivated species of wheat, Triticum aestivum L., a hexaploid species whose somatic cells contain six copies of every chromatid.

In recent years, the technique of cloning whole organisms has been developed in mammals, allowing almost identical genetic clones of an animal to be produced. One method of doing this is called "somatic cell nuclear transfer" and involves removing the nucleus from a somatic cell, usually a skin cell. This nucleus contains all of the genetic information needed to produce the organism it was removed from. This nucleus is then injected into an ovum of the same species which has had its own genetic material removed. The ovum now no longer needs to be fertilized, because it contains the correct amount of genetic material (a diploid number of chromosomes). In theory, the ovum can be implanted into the uterus of a same-species animal and allowed to develop. The resulting animal will be a nearly genetically identical clone to the animal from which the nucleus was taken. The only difference is caused by any mitochondrial DNA that is retained in the ovum, which is different from the cell that donated the nucleus. In practice, this technique has so far been problematic, although there have been a few high-profile successes, such as Dolly the Sheep and, more recently, Snuppy, the first cloned dog. Somatic cells have also been collected in the practice of cryoconservation of animal genetic resources as a means of conserving animal genetic material, including to clone livestock.

Development of biotechnology has allowed for the genetic manipulation of somatic cells. This biotechnology deals with some ethical controversy in human genetic engineering.

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Somatic cell - Wikipedia

Embryonic and Somatic Stem Cells, Whats the Difference?

Somatic Stem Cells | Posted by admin
Nov 02 2016

Stem cells are undifferentiated cells found in body having capability to develop into different types of cells in the body. Whenever there is a cell division of stem cells, each stem cell has the ability to remain a stem cell or become another type of cell having more specialized functions. In body, stem cells can differentiate into other kind of body cells by having the following capabilities;

1) Proliferation; The stem cells are capable to renew even after long periods of inactivity and capable of self-renewal during cell division. 2) Unspecialized; They are unspecialized which later give arise to specialized cells. 3) Differentiation; They are able to differentiate them under special conditions and functions.

There are two kinds of stem cell:

1) Embryonic stem cells. Those stem cells are derived from developing embryo. These cells are mostly use for in-vitro fertilization. 2) Somatic stem cells. Commonly known as adult stem cell. They are defined according to their location within the body.

Embryonic stem cells Somatic Pluripotent. Non pluripotent. Can easily grow in culture Not that easy. A large number of cells are required for stem cell replacement therapies.

The somatic stem cells can be further classified into mesenchymal stem cells and hematopoietic stem cells. The somatic stem cells are found in specific region of organ known as stem cell niche. The organs from where stem cell niche are found are in brain, skeletal muscle, gut, liver, pancreas, bone marrow, ovarian epithelium teeth, and testis.

The Somatic stem cells have been demonstrated as; Hematopoietic stem cells; Give rise to all kinds of blood cells. Mesenchymal stem cells; Give rise to all kinds of bone cells. Neural stem cells; Give rise to all kinds of neuronal and non neuronal cells in brain. Epithelial stem cells; Give rise to different kinds of cells of digestive tract. Skin stem cells; give rise to all the epidermis and ketatinocytes of skin.

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Embryonic and Somatic Stem Cells, Whats the Difference?

Adult stem cell – Wikipedia

Somatic Stem Cells | Posted by admin
Oct 21 2016

Adult stem cells are undifferentiated cells, found throughout the body after development, that multiply by cell division to replenish dying cells and regenerate damaged tissues. More accurately known as somatic stem cells (from Greek , meaning of the body), because they are usually more plentiful in juvenile (child) than in adult animal and human bodies.

Scientific interest in adult stem cells is centered on their ability to divide or self-renew indefinitely, and generate all the cell types of the organ from which they originate, potentially regenerating the entire organ from a few cells. Unlike embryonic stem cells, the use of human adult stem cells in research and therapy is not considered to be controversial, as they are derived from adult tissue samples rather than human embryos designated for scientific research. They have mainly been studied in humans and model organisms such as mice and rats.

A stem cell possesses two properties:

To ensure self-renewal, stem cells undergo two types of cell division (see Stem cell division and differentiation diagram). Symmetric division gives rise to two identical daughter cells, both endowed with stem cell properties, whereas asymmetric division produces only one stem cell and a progenitor cell with limited self-renewal potential. Progenitors can go through several rounds of cell division before finally differentiating into a mature cell. It is believed that the molecular distinction between symmetric and asymmetric divisions lies in differential segregation of cell membrane proteins (such as receptors) between the daughter cells.

Adult stem cells express transporters of the ATP-binding cassette family that actively pump a diversity of organic molecules out of the cell.[2] Many pharmaceuticals are exported by these transporters conferring multidrug resistance onto the cell. This complicates the design of drugs, for instance neural stem cell targeted therapies for the treatment of clinical depression.

Adult stem cell research has been focused on uncovering the general molecular mechanisms that control their self-renewal and differentiation.

Discoveries in recent years have suggested that adult stem cells might have the ability to differentiate into cell types from different germ layers. For instance, neural stem cells from the brain, which are derived from ectoderm, can differentiate into ectoderm, mesoderm, and endoderm.[6] Stem cells from the bone marrow, which is derived from mesoderm, can differentiate into liver, lung, GI tract and skin, which are derived from endoderm and mesoderm.[7] This phenomenon is referred to as stem cell transdifferentiation or plasticity. It can be induced by modifying the growth medium when stem cells are cultured in vitro or transplanting them to an organ of the body different from the one they were originally isolated from. There is yet no consensus among biologists on the prevalence and physiological and therapeutic relevance of stem cell plasticity. More recent findings suggest that pluripotent stem cells may reside in blood and adult tissues in a dormant state.[8] These cells are referred to as "Blastomere Like Stem Cells" (Am Surg. 2007 Nov;73:1106-10) and "very small embryonic like" - "VSEL" stem cells, and display pluripotency in vitro.[8] As BLSC's and VSEL cells are present in virtually all adult tissues, including lung, brain, kidneys, muscles, and pancreas[9] Co-purification of BLSC's and VSEL cells with other populations of adult stem cells may explain the apparent pluripotency of adult stem cell populations. However, recent studies have shown that both human and murine VSEL cells lack stem cell characteristics and are not pluripotent.[10][11][12][13]

Stem cell function becomes impaired with age, and this contributes to progressive deterioration of tissue maintenance and repair.[14] A likely important cause of increasing stem cell dysfunction is age-dependent accumulation of DNA damage in both stem cells and the cells that comprise the stem cell environment.[14] (See also DNA damage theory of aging.)

Hematopoietic stem cells are found in the bone marrow and umbilical cord blood and give rise to all the blood cell types.[15]

Mammary stem cells provide the source of cells for growth of the mammary gland during puberty and gestation and play an important role in carcinogenesis of the breast.[16] Mammary stem cells have been isolated from human and mouse tissue as well as from cell lines derived from the mammary gland. Single such cells can give rise to both the luminal and myoepithelial cell types of the gland, and have been shown to have the ability to regenerate the entire organ in mice.[16]

Intestinal stem cells divide continuously throughout life and use a complex genetic program to produce the cells lining the surface of the small and large intestines.[17] Intestinal stem cells reside near the base of the stem cell niche, called the crypts of Lieberkuhn. Intestinal stem cells are probably the source of most cancers of the small intestine and colon.[18]

Mesenchymal stem cells (MSCs) are of stromal origin and may differentiate into a variety of tissues. MSCs have been isolated from placenta, adipose tissue, lung, bone marrow and blood, Wharton's jelly from the umbilical cord,[19] and teeth (perivascular niche of dental pulp and periodontal ligament).[20] MSCs are attractive for clinical therapy due to their ability to differentiate, provide trophic support, and modulate innate immune response.[19] These cells have the ability to differentiate into various cell types such as osteoblasts, chondroblasts, adypocytes, neuroectodermal cells, and hepatocytes.[21] Bioactive mediators that favor local cell growth are also secreted by MSCs. Anti-inflammatory effects on the local microenvironment, which promote tissue healing, are also observed. The inflammatory response can be modulated by adipose-derived regenerative cells (ADRC) including mesenchymal stem cells and regulatory T-lymphocytes. The mesenchymal stem cells thus alter the outcome of the immune response by changing the cytokine secretion of dendritic and T-cell subsets. This results in a shift from a pro-inflammatory environment to an anti-inflammatory or tolerant cell environment.[22][23]

Endothelial stem cells are one of the three types of multipotent stem cells found in the bone marrow. They are a rare and controversial group with the ability to differentiate into endothelial cells, the cells that line blood vessels.

The existence of stem cells in the adult brain has been postulated following the discovery that the process of neurogenesis, the birth of new neurons, continues into adulthood in rats.[24] The presence of stem cells in the mature primate brain was first reported in 1967.[25] It has since been shown that new neurons are generated in adult mice, songbirds and primates, including humans. Normally, adult neurogenesis is restricted to two areas of the brain the subventricular zone, which lines the lateral ventricles, and the dentate gyrus of the hippocampal formation.[26] Although the generation of new neurons in the hippocampus is well established, the presence of true self-renewing stem cells there has been debated.[27] Under certain circumstances, such as following tissue damage in ischemia, neurogenesis can be induced in other brain regions, including the neocortex.

Neural stem cells are commonly cultured in vitro as so called neurospheres floating heterogeneous aggregates of cells, containing a large proportion of stem cells.[28] They can be propagated for extended periods of time and differentiated into both neuronal and glia cells, and therefore behave as stem cells. However, some recent studies suggest that this behaviour is induced by the culture conditions in progenitor cells, the progeny of stem cell division that normally undergo a strictly limited number of replication cycles in vivo.[29] Furthermore, neurosphere-derived cells do not behave as stem cells when transplanted back into the brain.[30]

Neural stem cells share many properties with haematopoietic stem cells (HSCs). Remarkably, when injected into the blood, neurosphere-derived cells differentiate into various cell types of the immune system.[31]

Olfactory adult stem cells have been successfully harvested from the human olfactory mucosa cells, which are found in the lining of the nose and are involved in the sense of smell.[32] If they are given the right chemical environment these cells have the same ability as embryonic stem cells to develop into many different cell types. Olfactory stem cells hold the potential for therapeutic applications and, in contrast to neural stem cells, can be harvested with ease without harm to the patient. This means they can be easily obtained from all individuals, including older patients who might be most in need of stem cell therapies.

Hair follicles contain two types of stem cells, one of which appears to represent a remnant of the stem cells of the embryonic neural crest. Similar cells have been found in the gastrointestinal tract, sciatic nerve, cardiac outflow tract and spinal and sympathetic ganglia. These cells can generate neurons, Schwann cells, myofibroblast, chondrocytes and melanocytes.[33][34]

Multipotent stem cells with a claimed equivalency to embryonic stem cells have been derived from spermatogonial progenitor cells found in the testicles of laboratory mice by scientists in Germany[35][36][37] and the United States,[38][39][40][41] and, a year later, researchers from Germany and the United Kingdom confirmed the same capability using cells from the testicles of humans.[42] The extracted stem cells are known as human adult germline stem cells (GSCs)[43]

Multipotent stem cells have also been derived from germ cells found in human testicles.[44]

The therapeutic potential of adult stem cells is the focus of much scientific research, due to their ability to be harvested from the patient.[45][46][47] In common with embryonic stem cells, adult stem cells have the ability to differentiate into more than one cell type, but unlike the former they are often restricted to certain types or "lineages". The ability of a differentiated stem cell of one lineage to produce cells of a different lineage is called transdifferentiation. Some types of adult stem cells are more capable of transdifferentiation than others, but for many there is no evidence that such a transformation is possible. Consequently, adult stem therapies require a stem cell source of the specific lineage needed, and harvesting and/or culturing them up to the numbers required is a challenge.[48][49] Additionally, cues from the immediate environment (including how stiff or porous the surrounding structure/extracellular matrix is) can alter or enhance the fate and differentiation of the stem cells.[50]

Pluripotent stem cells, i.e. cells that can give rise to any fetal or adult cell type, can be found in a number of tissues, including umbilical cord blood.[51] Using genetic reprogramming, pluripotent stem cells equivalent to embryonic stem cells have been derived from human adult skin tissue.[52][53][54][55][56] Other adult stem cells are multipotent, meaning they are restricted in the types of cell they can become, and are generally referred to by their tissue origin (such as mesenchymal stem cell, adipose-derived stem cell, endothelial stem cell, etc.).[57][58] A great deal of adult stem cell research has focused on investigating their capacity to divide or self-renew indefinitely, and their potential for differentiation.[59] In mice, pluripotent stem cells can be directly generated from adult fibroblast cultures.[60]

Adult stem cell treatments have been used for many years to successfully treat leukemia and related bone/blood cancers utilizing bone marrow transplants.[61] The use of adult stem cells in research and therapy is not considered as controversial as the use of embryonic stem cells, because the production of adult stem cells does not require the destruction of an embryo.

Early regenerative applications of adult stem cells has focused on intravenous delivery of blood progenitors known as Hematopetic Stem Cells (HSC's). CD34+ hematopoietic Stem Cells have been clinically applied to treat various diseases including spinal cord injury,[62] liver cirrhosis [63] and Peripheral Vascular disease.[64] Research has shown that CD34+ hematopoietic Stem Cells are relatively more numerous in men than in women of reproductive age group among spinal cord Injury victims.[65] Other early commercial applications have focused on Mesenchymal Stem Cells (MSCs). For both cell lines, direct injection or placement of cells into a site in need of repair may be the preferred method of treatment, as vascular delivery suffers from a "pulmonary first pass effect" where intravenous injected cells are sequestered in the lungs.[66] Clinical case reports in orthopedic applications have been published. Wakitani has published a small case series of nine defects in five knees involving surgical transplantation of mesenchymal stem cells with coverage of the treated chondral defects.[67] Centeno et al. have reported high field MRI evidence of increased cartilage and meniscus volume in individual human clinical subjects as well as a large n=227 safety study.[68][69][70][71] Many other stem cell based treatments are operating outside the US, with much controversy being reported regarding these treatments as some feel more regulation is needed as clinics tend to exaggerate claims of success and minimize or omit risks.[72]

In recent years, acceptance of the concept of adult stem cells has increased. There is now a hypothesis that stem cells reside in many adult tissues and that these unique reservoirs of cells not only are responsible for the normal reparative and regenerative processes but are also considered to be a prime target for genetic and epigenetic changes, culminating in many abnormal conditions including cancer.[73][74] (See cancer stem cell for more details.)

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Adult stem cell - Wikipedia

Somatic stem cells in the human endometrium.

Somatic Stem Cells | Posted by admin
Oct 07 2016

The existence of human endometrial somatic stem cells was proposed in the mid-20th century for the first time. This hypothesis became stronger and was revised by two authors between 1978 and 1989. Nevertheless, it was not until 2004 that scientific evidence was first published. As we describe here, the great regenerative capability of the human endometrium has been finally questioned in the last 8 years, and this period can be considered the most productive in endometrial stem cell biology given the new scientific information recapitulated to date. We provide a detailed summary based on the actual scientific knowledge obtained about (1) the existence of somatic stem cells in murine (detected with label-retaining cell methods) and human (cells isolated by different methods) endometria, (2) the involvement of bone marrow as a putative extrauterine source of endometrial somatic stem cells, (3) the implication and biological pathways of these cells in several pathologies like endometriosis and endometrial cancer, and (4) the future of endometrial somatic stem cells in regenerative medicine to provide new strategies in autologous transplant and bioengineering.

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Somatic stem cells in the human endometrium.

Glossary | stemcells.nih.gov

Somatic Stem Cells | Posted by admin
Sep 17 2016

Adult stem cellSee somatic stem cell.

AstrocyteA type of supporting (glial) cell found in the nervous system.

BlastocoelThe fluid-filled cavity inside the blastocyst, an early, preimplantation stage of the developing embryo.

BlastocystApreimplantationembryo consisting of a sphere made up of an outer layer of cells (thetrophoblast), a fluid-filled cavity (theblastocoel), and a cluster of cells on the interior (theinner cell mass).

Bone marrow stromal cellsA population of cells found in bone marrow that are different from blood cells.

Bone marrow stromal stem cells (skeletal stem cells)A multipotent subset of bone marrow stromal cells able to form bone, cartilage, stromal cells that support blood formation, fat, and fibrous tissue.

Cell-based therapiesTreatment in which stem cells are induced to differentiate into the specific cell type required to repair damaged or destroyed cells or tissues.

Cell cultureGrowth of cells in vitro in an artificial medium for research.

Cell divisionMethod by which a single cell divides to create two cells. There are two main types of cell division depending on what happens to the chromosomes: mitosis and meiosis.

ChromosomeA structure consisting of DNA and regulatory proteins found in the nucleus of the cell. The DNA in the nucleus is usually divided up among several chromosomes.The number of chromosomes in the nucleus varies depending on the species of the organism. Humans have 46 chromosomes.

Clone (v) To generate identical copies of a region of a DNA molecule or to generate genetically identical copies of a cell, or organism; (n) The identical molecule, cell, or organism that results from the cloning process.

CloningSee Clone.

Cord blood stem cellsSee Umbilical cord blood stem cells.

Culture mediumThe liquid that covers cells in a culture dish and contains nutrients to nourish and support the cells. Culture medium may also include growth factors added to produce desired changes in the cells.

DifferentiationThe process whereby an unspecialized embryonic cell acquires the features of a specialized cell such as a heart, liver, or muscle cell. Differentiation is controlled by the interaction of a cell's genes with the physical and chemical conditions outside the cell, usually through signaling pathways involving proteins embedded in the cell surface.

Directed differentiationThe manipulation of stem cell culture conditions to induce differentiation into a particular cell type.

DNADeoxyribonucleic acid, a chemical found primarily in the nucleus of cells. DNA carries the instructions or blueprint for making all the structures and materials the body needs to function. DNA consists of both genes and non-gene DNA in between the genes.

EctodermThe outermost germ layer of cells derived from the inner cell mass of the blastocyst; gives rise to the nervous system, sensory organs, skin, and related structures.

EmbryoIn humans, the developing organism from the time of fertilization until the end of the eighth week of gestation, when it is called a fetus.

Embryoid bodiesRounded collections of cells that arise when embryonic stem cells are cultured in suspension. Embryoid bodies contain cell types derived from all threegerm layers.

Embryonic germ cellsPluripotent stem cells that are derived from early germ cells (those that would become sperm and eggs). Embryonic germ cells are thought to have properties similar to embryonic stem cells.

Embryonic stem cellsPrimitive (undifferentiated) cells that are derived from preimplantation-stageembryos, are capable of dividing without differentiating for a prolonged period in culture, and are known to develop into cells and tissues of the three primary germ layers.

Embryonic stem cell lineEmbryonic stem cells, which have been cultured under in vitro conditions that allow proliferation without differentiation for months to years.

EndodermThe innermost layer of the cells derived from the inner cell mass of the blastocyst; it gives rise to lungs, other respiratory structures, and digestive organs, or generally "the gut."

EnucleatedHaving had its nucleus removed.

EpigeneticThe process by which regulatory proteins can turn genes on or off in a way that can be passed on during cell division.

Feeder layerCells used in co-culture to maintain pluripotent stem cells. For human embryonic stem cell culture, typical feeder layers include mouse embryonic fibroblasts (MEFs) or human embryonic fibroblasts that have been treated to prevent them from dividing.

FertilizationThe joining of the male gamete (sperm) and the female gamete (egg).

FetusIn humans, the developing human from approximately eight weeks after conception until the time of its birth.

GameteAn egg (in the female) or sperm (in the male) cell. See also Somatic cell.

GastrulationThe process in which cells proliferate and migrate within the embryo to transform the inner cell mass of the blastocyst stage into an embryo containing all three primary germ layers.

GeneA functional unit of heredity that is a segment of DNA found on chromosomes in the nucleus of a cell. Genes direct the formation of an enzyme or other protein.

Germ layersAfter the blastocyst stage of embryonic development, the inner cell mass of the blastocyst goes through gastrulation, a period when the inner cell mass becomes organized into three distinct cell layers, called germ layers. The three layers are the ectoderm, the mesoderm, and the endoderm.

Hematopoietic stem cellA stem cell that gives rise to all red and white blood cells and platelets.

Human embryonic stem cell (hESC)A type of pluripotent stem cell derived from early stage human embryos, up to and including the blastocyststage. hESCs are capable of dividing without differentiating for a prolonged period in culture and are known to develop into cells and tissues of the three primary germ layers.

Induced pluripotent stem cell (iPSC)A type of pluripotent stem cell, similar to an embryonic stem cell, formed by the introduction of certain embryonic genes into a somatic cell.

In vitroLatin for "in glass;" in a laboratory dish or test tube; an artificial environment.

In vitro fertilizationA technique that unites the egg and sperm in a laboratory instead of inside the female body.

Inner cell mass (ICM)The cluster of cells inside the blastocyst. These cells give rise to the embryo and ultimately the fetus. The ICM may be used to generate embryonic stem cells.

Long-term self-renewalThe ability of stem cells to replicate themselves by dividing into the same non-specialized cell type over long periods (many months to years) depending on the specific type of stem cell.

MeiosisThe type of cell division a diploid germ cell undergoes to produce gametes (sperm or eggs) that will carry half the normal chromosome number. This is to ensure that when fertilization occurs, the fertilized egg will carry the normal number of chromosomes rather than causing aneuploidy (an abnormal number of chromosomes).

Mesenchymal stem cellsA term that is currently used to define non-blood adult stem cells from a variety of tissues, although it is not clear that mesenchymal stem cells from different tissues are the same.

MesodermMiddle layer of a group of cells derived from the inner cell mass of the blastocyst; it gives rise to bone, muscle, connective tissue, kidneys, and related structures.

MicroenvironmentThe molecules and compounds such as nutrients and growth factors in the fluid surrounding a cell in an organism or in the laboratory, which play an important role in determining the characteristics of the cell.

MitosisThe type of cell division that allows a population of cells to increase its numbers or to maintain its numbers. The number of chromosomes in each daughter cell remains the same in this type of cell division.

MultipotentHaving the ability to develop into more than one cell type of the body. See also pluripotent and totipotent.

Neural stem cellA stem cell found in adult neural tissue that can give rise to neurons and glial (supporting) cells. Examples of glial cells include astrocytes and oligodendrocytes.

NeuronsNerve cells, the principal functional units of the nervous system. A neuron consists of a cell body and its processesan axon and one or more dendrites. Neurons transmit information to other neurons or cells by releasing neurotransmitters at synapses.

OligodendrocyteA supporting cell that provides insulation to nerve cells by forming a myelin sheath (a fatty layer) around axons.

ParthenogenesisThe artificial activation of an egg in the absence of a sperm; the egg begins to divide as if it has been fertilized.

PassageIn cell culture, the process in which cells are disassociated, washed, and seeded into new culture vessels after a round of cell growth and proliferation. The number of passages a line of cultured cells has gone through is an indication of its age and expected stability.

PluripotentThe state of a single cell that is capable of differentiating into all tissues of an organism, but not alone capable of sustaining full organismal development.

Scientists demonstrate pluripotency by providing evidence of stable developmental potential, even after prolonged culture, to form derivatives of all three embryonic germ layers from the progeny of a single cell and to generate a teratoma after injection into an immunosuppressed mouse.

Polar bodyA polar body is a structure produced when an early egg cell, or oogonium, undergoes meiosis. In the first meiosis, the oogonium divides its chromosomes evenly between the two cells but divides its cytoplasm unequally. One cell retains most of the cytoplasm, while the other gets almost none, leaving it very small. This smaller cell is called the first polar body. The first polar body usually degenerates. The ovum, or larger cell, then divides again, producing a second polar body with half the amount of chromosomes but almost no cytoplasm. The second polar body splits off and remains adjacent to the large cell, or oocyte, until it (the second polar body) degenerates. Only one large functional oocyte, or egg, is produced at the end of meiosis.

PreimplantationWith regard to an embryo, preimplantation means that the embryo has not yet implanted in the wall of the uterus. Human embryonic stem cells are derived from preimplantation-stage embryos fertilized outside a woman's body (in vitro).

ProliferationExpansion of the number of cells by the continuous division of single cells into two identical daughter cells.

Regenerative medicineA field of medicine devoted to treatments in which stem cells are induced to differentiate into the specific cell type required to repair damaged or destroyed cell populations or tissues. (See also cell-based therapies).

Reproductive cloningThe process of using somatic cell nuclear transfer (SCNT) to produce a normal, full grown organism (e.g., animal) genetically identical to the organism (animal) that donated the somatic cell nucleus. In mammals, this would require implanting the resulting embryo in a uterus where it would undergo normal development to become a live independent being. The firstmammal to be created by reproductive cloning was Dolly the sheep, born at the Roslin Institute in Scotland in 1996. See also Somatic cell nuclear transfer (SCNT).

SignalsInternal and external factors that control changes in cell structure and function. They can be chemical or physical in nature.

Somatic cellAny body cell other than gametes (egg or sperm); sometimes referred to as "adult" cells. See also Gamete.

Somatic cell nuclear transfer (SCNT)A technique that combines an enucleated egg and the nucleus of a somatic cell to make an embryo. SCNT can be used for therapeutic or reproductive purposes, but the initial stage that combines an enucleated egg and a somatic cell nucleus is the same. See also therapeutic cloning and reproductive cloning.

Somatic (adult) stem cellA relatively rare undifferentiated cell found in many organs and differentiated tissues with a limited capacity for both self renewal (in the laboratory) and differentiation. Such cells vary in their differentiation capacity, but it is usually limited to cell types in the organ of origin. This is an active area of investigation.

Stem cellsCells with the ability to divide for indefinite periods in culture and to give rise to specialized cells.

Stromal cellsConnective tissue cells found in virtually every organ. In bone marrow, stromal cells support blood formation.

SubculturingTransferring cultured cells, with or without dilution, from one culture vessel to another.

Surface markersProteins on the outside surface of a cell that are unique to certain cell types and that can be visualized using antibodies or other detection methods.

TeratomaA multi-layered benign tumor that grows from pluripotent cells injected into mice with a dysfunctional immune system. Scientists test whether they have established a human embryonic stem cell (hESC) line by injecting putative stem cells into such mice and verifying that the resulting teratomas contain cells derived from all three embryonic germ layers.

Therapeutic cloningThe process of using somatic cell nuclear transfer (SCNT) to produce cells that exactly match a patient. By combining a patient's somatic cell nucleus and an enucleated egg, a scientist may harvest embryonic stem cells from the resulting embryo that can be used to generate tissues that match a patient's body. This means the tissues created are unlikely to be rejected by the patient's immune system. See also Somatic cell nuclear transfer (SCNT).

TotipotentThe state of a cell that is capable of giving rise to all types of differentiated cells found in an organism, as well as the supporting extra-embryonic structures of the placenta. A single totipotent cell could, by division in utero, reproduce the whole organism. (See also Pluripotent and Multipotent).

TransdifferentiationThe process by which stem cells from one tissue differentiate into cells of another tissue.

TrophoblastThe outer cell layer of the blastocyst. It is responsible for implantation and develops into the extraembryonic tissues, including the placenta, and controls the exchange of oxygen and metabolites between mother and embryo.

Umbilical cord blood stem cellsStem cells collected from the umbilical cord at birth that can produce all of the blood cells in the body. Cord blood is currently used to treat patients who have undergone chemotherapy to destroy their bone marrow due to cancer or other blood-related disorders.

UndifferentiatedA cell that has not yet developed into a specialized cell type.

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Glossary | stemcells.nih.gov

Stem Cell Basics IV. | stemcells.nih.gov

Somatic Stem Cells | Posted by admin
Sep 17 2016

An adult stem cell is thought to be an undifferentiated cell, found among differentiated cells in a tissue or organ. The adult stem cell can renew itself and can differentiate to yield some or all of the major specialized cell types of the tissue or organ. The primary roles of adult stem cells in a living organism are to maintain and repair the tissue in which they are found. Scientists also use the term somatic stem cell instead of adult stem cell, where somatic refers to cells of the body (not the germ cells, sperm or eggs). Unlike embryonic stem cells, which are defined by their origin (cells from the preimplantation-stage embryo), the origin of adult stem cells in some mature tissues is still under investigation.

Research on adult stem cells has generated a great deal of excitement. Scientists have found adult stem cells in many more tissues than they once thought possible. This finding has led researchers and clinicians to ask whether adult stem cells could be used for transplants. In fact, adult hematopoietic, or blood-forming, stem cells from bone marrow have been used in transplants for more than 40 years. Scientists now have evidence that stem cells exist in the brain and the heart, two locations where adult stem cells were not at firstexpected to reside. If the differentiation of adult stem cells can be controlled in the laboratory, these cells may become the basis of transplantation-based therapies.

The history of research on adult stem cells began more than 60 years ago. In the 1950s, researchers discovered that the bone marrow contains at least two kinds of stem cells. One population, called hematopoietic stem cells, forms all the types of blood cells in the body. A second population, called bone marrow stromal stem cells (also called mesenchymal stem cells, or skeletal stem cells by some), were discovered a few years later. These non-hematopoietic stem cells make up a small proportion of the stromal cell population in the bone marrow and can generate bone, cartilage, and fat cells that support the formation of blood and fibrous connective tissue.

In the 1960s, scientists who were studying rats discovered two regions of the brain that contained dividing cells that ultimately become nerve cells. Despite these reports, most scientists believed that the adult brain could not generate new nerve cells. It was not until the 1990s that scientists agreed that the adult brain does contain stem cells that are able to generate the brain's three major cell typesastrocytes and oligodendrocytes, which are non-neuronal cells, and neurons, or nerve cells.

Adult stem cells have been identified in many organs and tissues, including brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin, teeth, heart, gut, liver, ovarian epithelium, and testis. They are thought to reside in a specific area of each tissue (called a "stem cell niche"). In many tissues, current evidence suggests that some types of stem cells are pericytes, cells that compose the outermost layer of small blood vessels. Stem cells may remain quiescent (non-dividing) for long periods of time until they are activated by a normal need for more cells to maintain tissues, or by disease or tissue injury.

Typically, there is a very small number of stem cells in each tissue and, once removed from the body, their capacity to divide is limited, making generation of large quantities of stem cells difficult. Scientists in many laboratories are trying to find better ways to grow large quantities of adult stem cells in cell culture and to manipulate them to generate specific cell types so they can be used to treat injury or disease. Some examples of potential treatments include regenerating bone using cells derived from bone marrow stroma, developing insulin-producing cells for type1 diabetes, and repairing damaged heart muscle following a heart attack with cardiac muscle cells.

Scientists often use one or more of the following methods to identify adult stem cells: (1) label the cells in a living tissue with molecular markers and then determine the specialized cell types they generate; (2) remove the cells from a living animal, label them in cell culture, and transplant them back into another animal to determine whether the cells replace (or "repopulate") their tissue of origin.

Importantly, scientists must demonstrate that a single adult stem cell can generate a line of genetically identical cells that then gives rise to all the appropriate differentiated cell types of the tissue. To confirm experimentally that a putative adult stem cell is indeed a stem cell, scientists tend to show either that the cell can give rise to these genetically identical cells in culture, and/or that a purified population of these candidate stem cells can repopulate or reform the tissue after transplant into an animal.

As indicated above, scientists have reported that adult stem cells occur in many tissues and that they enter normal differentiation pathways to form the specialized cell types of the tissue in which they reside.

Normal differentiation pathways of adult stem cells. In a living animal, adult stem cells are available to divide for a long period, when needed, and can give rise to mature cell types that have characteristic shapes and specialized structures and functions of a particular tissue. The following are examples of differentiation pathways of adult stem cells (Figure 2) that have been demonstrated in vitro or in vivo.

Figure 2. Hematopoietic and stromal stem cell differentiation. Click here for larger image. ( 2008 Terese Winslow)

Transdifferentiation. A number of experiments have reported that certain adult stem cell types can differentiate into cell types seen in organs or tissues other than those expected from the cells' predicted lineage (i.e., brain stem cells that differentiate into blood cells or blood-forming cells that differentiate into cardiac muscle cells, and so forth). This reported phenomenon is called transdifferentiation.

Although isolated instances of transdifferentiation have been observed in some vertebrate species, whether this phenomenon actually occurs in humans is under debate by the scientific community. Instead of transdifferentiation, the observed instances may involve fusion of a donor cell with a recipient cell. Another possibility is that transplanted stem cells are secreting factors that encourage the recipient's own stem cells to begin the repair process. Even when transdifferentiation has been detected, only a very small percentage of cells undergo the process.

In a variation of transdifferentiation experiments, scientists have recently demonstrated that certain adult cell types can be "reprogrammed" into other cell types in vivo using a well-controlled process of genetic modification (see Section VI for a discussion of the principles of reprogramming). This strategy may offer a way to reprogram available cells into other cell types that have been lost or damaged due to disease. For example, one recent experiment shows how pancreatic beta cells, the insulin-producing cells that are lost or damaged in diabetes, could possibly be created by reprogramming other pancreatic cells. By "re-starting" expression of three critical beta cell genes in differentiated adult pancreatic exocrine cells, researchers were able to create beta cell-like cells that can secrete insulin. The reprogrammed cells were similar to beta cells in appearance, size, and shape; expressed genes characteristic of beta cells; and were able to partially restore blood sugar regulation in mice whose own beta cells had been chemically destroyed. While not transdifferentiation by definition, this method for reprogramming adult cells may be used as a model for directly reprogramming other adult cell types.

In addition to reprogramming cells to become a specific cell type, it is now possible to reprogram adult somatic cells to become like embryonic stem cells (induced pluripotent stem cells, iPSCs) through the introduction of embryonic genes. Thus, a source of cells can be generated that are specific to the donor, thereby increasing the chance of compatibility if such cells were to be used for tissue regeneration. However, like embryonic stem cells, determination of the methods by which iPSCs can be completely and reproducibly committed to appropriate cell lineages is still under investigation.

Many important questions about adult stem cells remain to be answered. They include:

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Human embryonic stem cells derived by somatic cell nuclear …

Somatic Stem Cells | Posted by admin
Aug 03 2015

(A) Nuclear DNA genotyping from four human NT-ESC lines (hESO-NT1, hESO-NT2, hESO-NT3, and hESO-NT4) determined by microsatellite parentage analysis. A total of 24 microsatellite markers were used for each analysis. The representative markers for D2S1333 and D4S413 loci demonstrate that the nuclear DNA in these cell lines was exclusively derived from the somatic HDF-f cell line. No contribution of oocyte nuclear DNA was detected. (B) mtDNA genotyping by Sanger sequencing demonstrated that all NT-ESC lines contain oocyte mtDNA. (C) Cytogenetic G-banding analysis confirmed that all NT-ESCs exhibited a normal 46XX karyotype (hESO-NT1 result is representative). (D) Human NT-ESCs expressed standard pluripotency markers detected by immunocytochemistry for antibodies against OCT4, NANOG, SOX2, SSEA-4, TRA-160, and TRA-181. Original magnification, 200; Ph, phase contrast. Note that the upper-left image for hESO-NT1 is the same shown in Figure 2F. The upper-right image for hESO-7 is the same shown in Figure S5 (upper-right). (E) Histological analysis of teratoma tumors produced after injection of human NT-ESCs into SCID mice. An arrow and arrowhead in the top panel indicate intestinal-type epithelium with goblet cells (endoderm) and cartilage (mesodermal), respectively. An arrow and arrowhead in the lower panel depict neuroecto-dermal (ectoderm) and muscle (mesoderm) tissues, respectively. Original magnification, 200. See also Figures S4 and S5 and Tables S4 and S5.

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Human embryonic stem cells derived by somatic cell nuclear ...

Comparative proteomic analysis of human somatic cells …

Somatic Stem Cells | Posted by admin
Jul 20 2015

Induced pluripotent stem cells (iPSCs) are somatic cells that have been reprogrammed to a pluripotent state via introduction of defined transcription factors. iPSCs are a valuable resource for regenerative medicine, but whether iPSCs are identical to embryonic stem cells (ESCs) remains unclear. In this study, we performed comparative proteomic analyses of human somatic cells [human newborn foreskin fibroblasts (hFFs)], human iPSCs (hiPSCs) derived from hFFs, and H9 human ESCs (hESCs). We reprogrammed hFFs to a pluripotent state using 4 core transcription factors: Oct4 (O), Sox2 (S), Klf4 (K), and c-Myc (M). The proteome of hiPSCs induced by 4 core transcription factors was relatively similar to that of hESCs. However, several proteins, including dUTPase, GAPDH, and FUSE binding protein 3, were differentially expressed between hESCs and hiPSCs, implying that hiPSCs are not identical to hESCs at the proteomic level. The proteomes of iPSCs induced by introducing 3, 5, or 6 transcription factors were also analyzed. Our proteomic profiles provide valuable insight into the factors that contribute to the similarities and differences between hESCs and hiPSCs and the mechanisms of reprogramming.

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Somatic cell – Wikipedia, the free encyclopedia

Somatic Stem Cells | Posted by admin
Jul 15 2015

A somatic (Greek: /soma = body) or vegetative cell is any biological cell forming the body of an organism; that is, in a multicellular organism, any cell other than a gamete, germ cell, gametocyte or undifferentiated stem cell.[1]

In contrast, gametes are cells that fuse during sexual reproduction, germ cells are cells that give rise to gametes, and stem cells are cells that can divide through mitosis and differentiate into diverse specialized cell types. For example, in mammals, somatic cells make up all the internal organs, skin, bones, blood and connective tissue, while mammalian germ cells give rise to spermatozoa and ova which fuse during fertilization to produce a cell called a zygote, which divides and differentiates into the cells of an embryo. There are approximately 220 types of somatic cells in the human body.[1]

The word "somatic" is derived from the Greek word sma, meaning "body".

As multicellularity evolved many times, sterile somatic cells did too. The evolution of an immortal germline producing specialized somatic cells involved the emergence of mortality, and can be viewed in its simplest version in volvocine algae.[2] Those species with a separation between sterile somatic cells and a germ line are called Weismannists. However, Weismannist development is relatively rare (e.g., vertebrates, arthropods, Volvox), as great part of species have the capacity for somatic embryogenesis (e.g., land plants, most algae, many invertebrates).[3][4]

Like all cells, somatic cells contain DNA arranged in chromosomes. If a somatic cell contains chromosomes arranged in pairs, it is called diploid and the organism is called a diploid organism. (The gametes of diploid organisms contain only single unpaired chromosomes and are called haploid.) Each pair of chromosomes comprises one chromosome inherited from the father and one inherited from the mother. For example, in humans, somatic cells contain 46 chromosomes organized into 23 pairs. By contrast, gametes of diploid organisms contain only half as many chromosomes. In humans, this is 23 unpaired chromosomes. When two gametes (i.e. a spermatozoon and an ovum) meet during conception, they fuse together, creating a zygote. Due to the fusion of the two gametes, a human zygote contains 46 chromosomes (i.e. 23 pairs).

However, a large number of species have the chromosomes in their somatic cells arranged in fours ("tetraploid") or even sixes ("hexaploid"). Thus, they can have diploid or even triploid germline cells. An example of this is the modern cultivated species of wheat, Triticum aestivum L., a hexaploid species whose somatic cells contain six copies of every chromatid.

In recent years, the technique of cloning whole organisms has been developed in mammals, allowing almost identical genetic clones of an animal to be produced. One method of doing this is called "somatic cell nuclear transfer" and involves removing the nucleus from a somatic cell, usually a skin cell. This nucleus contains all of the genetic information needed to produce the organism it was removed from. This nucleus is then injected into an ovum of the same species which has had its own genetic material removed. The ovum now no longer needs to be fertilized, because it contains the correct amount of genetic material (a diploid number of chromosomes). In theory, the ovum can be implanted into the uterus of a same-species animal and allowed to develop. The resulting animal will be a nearly genetically identical clone to the animal from which the nucleus was taken. The only difference is caused by any mitochondrial DNA that is retained in the ovum, which is different from the cell that donated the nucleus. In practice, this technique has so far been problematic, although there have been a few high profile successes, such as Dolly the Sheep and, more recently, Snuppy, the first cloned dog.

Development of Biotechnology has allowed for the genetic manipulation of somatic cells.This biotechnology deals with some ethical controversy in Human genetic engineering.

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Somatic cell - Wikipedia, the free encyclopedia