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************************************************************** * DISCLAIMER - The following is not medical advice, only the * * personal opinion of the writer. Any contemplated change in * * treatment or medication must be referred to your treating * * medical practitioner. Dr. J. F. Slattery PhD Soc * ************************************************************** I think it might be helpful when discussing stem cell research, if all concerned were aware of the meaning of the various terms used. For example, many on one side confuse the term "embryo" with the term "foetus". The following may help. Dr James F Slattery, PhD Soc Sci ************************************************************************** STEM CELL RESEARCH OVUM - a human female sex cell, an egg. SPERMATOZOON - a human male sex cell. ZYGOTE - cell formed by the fusion of a sperm and an ovum during fertilization,usually occurring in the ampulla of the fallopian tube, until the first division. When the zygote starts to divide and multiply, it is called an embryo. BLASTOCYST - an early stage embryo consisting of no more than 100 or so cells. FIBROBLAST - A fibroblast is a type of cell that synthesizes and maintains the extracellular matrix of many animal tissues. Fibroblasts provide a structural framework (stroma) for many tissues, and play a critical role in wound healing. They are the most common cells of connective tissue in animals. EMBRYO - in humans, the developing organism from about two weeks after fertilization to the end of the seventh or eighth week. POTENCY DEFINITIONS · Totipotent (a.k.a omnipotent) stem cells can differentiate into embryonic and extra-embryonic cell types. Such cells can construct a complete, viable, organism. These cells are produced from the fusion of an egg and sperm cell. Cells produced by the first few divisions of the fertilized egg are also totipotent. · Pluripotent stem cells are the descendants of totipotent cells and can differentiate into nearly all cells, i.e. cells derived from any of the three germ layers. · Multipotent stem cells can differentiate into a number of cells, but only those of a closely related family of cells. · Oligopotent stem cells can differentiate into only a few cells, such as lymphoid or myeloid stem cells. · Unipotent cells can produce only one cell type, their own, but have the property of self-renewal, which distinguishes them from non-stem cells (e.g. muscle stem cells). EMBRYONIC STEM CELLS Cells derived from the inner cell mass of an early stage embryo known as a blastocyst. Human embryos reach the blastocyst stage 4-5 days post fertilization, at which time they consist of 50-150 cells. In a developing embryo, stem cells can differentiate into all of the specialized embryonic tissues. Embryonic stem cells are pluripotent. This means they are able to differentiate into all derivatives of the three primary germ layers: ectoderm, endoderm, and mesoderm. These include each of the more than 220 cell types in the adult body. Pluripotency distinguishes embryonic stem cells from multipotent progenitor cells found in the adult; that only form a limited number of cell types. When given no stimuli for differentiation (i.e. when grown in vitro - in glass), embryonic stem cells maintain pluripotency through multiple cell divisions. ADULT STEM CELLS Undifferentiated cells, found throughout the body after embryonic development, which multiply by cell division to replenish dying cells and regenerate damaged tissues. Also known as somatic stem cells (meaning 'of the body'), they can be found in juvenile as well as adult animals and humans. The term refers to any cell that is found in a developed organism,which has two properties: the ability to divide and create another cell like itself and also divide and create a cell more differentiated than itself. Also known as somatic stem cells and germline (giving rise to gametes) stem cells, they can be found in children, as well as adults. The presence of pluripotent adult stem cells remains a subject of scientific debate; however, research has demonstrated that pluripotent stem cells can be directly generated from adult fibroblast cultures Because of their plasticity and potentially unlimited capacity for self-renewal, embryonic stem cells therapies have been proposed for regenerative medicine and tissue replacement after injury or disease. However, to date, no approved medical treatments have been derived from embryonic stem cells research. Adult stem cells and cord blood stems cells have thus far been the only stem cells used to successfully treat any diseases. Besides the ethical concerns of stem cell therapy, there is a technical problem of graft-versus-host disease associated with allogeneic (incompatible) stem cell transplantation. However, these problems may be solved using the recipient's own adult stem cells or via therapeutic cloning. CLONING To create a clone, a scientist removes the nucleus from a donor cell, then places it into an ovum (egg) from which the nucleus has been removed. The scientist then "tricks" the egg into thinking it's been fertilized. The egg develops into a blastocyst. The scientist can then remove the stem cells from this blastocyst or place it into a uterus where it has the potential to develop into a foetus. Here's where things get complicated. The original donated nucleus may have come from, say, a skin cell. For a viable foetus to develop, the egg needs to reprogram the genome of the skin cell, shutting off genes specific for skin tissue and turning on genes needed for embryonic development, genes that are normally dormant in tissue-specific cells. In other words, the egg needs to erase all tissue-specific memories from the skin cell and revert it into a genomic blank slate. But this entire process is almost never perfect, and nearly all cells in a cloned blastocyst retain some memory of their original source. As a result, the developing foetus inevitably has some degree of genetic abnormality. Most clones, in fact, die in utero or at birth. The few clones that make it into adulthood are often plagued by bizarre health complications. This is one reason why scientists generally believe that attempting to clone a human being is morally reprehensible. Scientific interest in adult stem cells has centred 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 adult stem cells in research and therapy is not considered to be controversial as they are derived from adult tissue samples rather than destroyed human embryos. They have mainly been studied in humans and model organisms such as mice and rats. Pluripotent adult stem cells are rare and generally small in number but can be found in a number of tissues including umbilical cord blood. A great deal of adult stem cell research has focused on clarifying their capacity to divide or self-renew indefinitely and their differentiation potential. In mice, pluripotent stem cells are directly generated from adult fibroblast cultures. Unfortunately, many mice don't live long with stem cell organs. Most adult stem cells are lineage-restricted (multipotent) and are generally referred to by their tissue origin (mesenchymal stem cell, adipose-derived stem cell, endothelial stem cell, etc.) Adult stem cell treatments have been successfully used for many years to treat leukaemia and related bone/blood cancers through bone marrow transplants. Adult stem cells are also used in veterinary medicine to treat tendon and ligament injuries in horses. The use of adult stem cells in research and therapy is not as controversial as embryonic stem cells, because the production of adult stem cells does not require the destruction of an embryo. Additionally, because in some instances adult stem cells can be obtained from the intended recipient, (an autograft) the risk of rejection is essentially non-existent in these situations. ---------------------------------------------------------------------- To sign-off Parkinsn send a message to: mailto:[log in to unmask] In the body of the message put: signoff parkinsn