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What is Parthenogenesis? Applications of Parthenogenetic Stem CellsBY: Padma Kumar | Category: Stem-Cells | Submitted: 2011-01-17 20:25:33
Article Summary: "This article explains whether Parthenogenetic stem cells could be a viable alternative to embryonic stem cells. Parthnogenesis is a biological phenomenon entailing the process of initiating development of the embryo..."
The question whether it is ethically correct to use human embryos to produce embryonic stem cells remains a bone of contention. There are strong arguments in support and against the use of human embryos----for what is reckoned ultimately as a research endeavor. That being the case, scientists have been looking at other methods to obtain stem cells.
Currently there are three methods to get pluripotent stem cells in primates excluding Homo sapiens. a) From embryos obtained via in vitro fertilization; b) from adult tissues including bone marrow cells c) through parthenogenesis
This article will focus on parthenogenesis.
What is parthenogenesis
Parthnogenesis is a biological phenomenon entailing the process of initiating development of the embryo, without any contribution by the male of the species. In other words, the embryo is made primarily from the female oocyte without any contribution from the male. In parthenogenesis the egg starts developing as if it has already been fertilized keeping the two sets of chromosomes.
In lower organisms parthenogenesis is a fairly common method of reproduction --- examples being snakes, ants, fish, and birds. As regards these creatures, a single egg can develop without male contribution---and this process is parthenogenesis. Placental mammals do not have this type of reproduction.
Parthenogenesis in human context
In the human context the idea is to make an embryo with the full compliment of 46 chromosomes. This could be done by: a) by stimulating eggs which are diploid causing them to divide b) by causing an egg late in its maturation cycle with twenty three chromosomes to replicate genetic material. In that case a full complement of genes is obtained.
Perhaps the first instance of parthenogenetic cells in humans has resulted from the research efforts of Stemron Corporation led by David Wininger who succeeded in making parthenogenetic human embryos to the blastocyst stage from which stem cells could be sourced.
How is parthenogenesis different from cloning
In cloning, an enucleated egg cell is kept ready. Into this is put the nucleus of a diploid cell from a donor. The resulting cell is stimulated so that it undergoes continued mitosis. This results in an offspring that is genetically identical to the donor.
Parthenogenesis is totally different. It is based on the genetic material contained within the egg cell itself. The eggs that are subject to parthenogenesis could be either haploid or diploid depending on whether the eggs were produced by meiosis or mitosis oogenesis. So the outcomes could be different.
Examples of parthenogenesis
In nature there are several examples of parthenogenesis. Some types of sharks have produced offspring without male participation. Examples are the blacktip shark and the hammerhead shark. Another example is the Bdelloid rotifiers which have this asexual reproduction method.
Parthenogenesis as a means of reproduction can also be found in the following creatures:
* Plant-lice (Aphides)
Applications of parthenogenesis
In parthogenesis also embryos are destroyed to make stem cells. But these embryos in any case could never have progressed to the birth stage. Therefore use of these embryos is not perceived to have ethical concerns unlike embryonic stem cell research.
That apart, theoretically if a defective gene has to be replaced then human parthenogenetic stem cells can be created and can be matched to the egg donor from the immunity aspect. In this regard, human parthenogenetic stem cell lines have been created by International Stem Cell Corporation (ISCO) from unfertilized human eggs. This is a patented technology and it does not have bad effects on the human embryo.
Parthenogenetic stem cells could be used to treat diseases such as:
• Huntington's disease
• Beta Thalessemia
• Tuberous sclerosis
• International Stem Cell Corporation has a range of skin care products using its proprietary Parthenogenic Stem Cells technology in combination with nanotechnology. The underlying basis of these formulations is that human parthenogenetic stem cells are reckoned to have beneficial effects on human skin cells especially anti-aging benefits and skin rejuvenation effects.
• Human Parthenogenic Stem Cells have been differentiated to cells for treatment of diabetes.
• Human Parthenogenic Stem Cells have also been used to make retinal cells to treat age related macular degeneration.
• Ultimately it will be possible to have parthogenic stem cell banks to meet individual needs.
Mostly donor tissue is used in regenerative medicine. When that is not available embryonic stem cells are used as source for pluripotent cells. But for getting the embryonic stem cells embryos get destroyed. Destruction of embryos has ethical, political and legal limitations. But parthenogenesis (as egg can be turned into embryo without sperm) can be used for sourcing embryonic stem cells thus avoiding the ethical compulsions.
To make stem cells for an individual would be costly business but not so if parthenogenic stem cells banks were to be created.
In parthenogenesis the two sets of chromosomes are identical. This is unlike the normal practice when one set of chromosome comes from the father and the other from the mother. The cells produced this way will not cause unwanted immune reactions as the surface protein on the cells has less of variation.
Parthenogenetic stem cells can only be made from eggs. Therefore it is not possible to make suitable stem cells in the case of women post menopause. On the contrary matching stem cells can be made for any person through therapeutic cloning.
Are there any ethical concerns in using this technique akin to obtaining embryonic stem cells
Human embryos have a moral locus standii in that it is reckoned as something that is coming to a life form. Even from the religious point of view, the moment from conception to birth is reckoned as a period of development of the human body and hence has a moral value attached to it.
But in the case of parthenogenic embryos it cannot be reckoned as a typical human embryo. The reason is, it cannot complete the birth process to be born as a human being unless combined with the outer cells of the early embryo (trophoblast cells) which could lead to placenta formation. In other words, the father's gene imprint is necessary for placenta formation. At the same time the parthenogenic embryos have the full complement of human DNA. Now the question is to decide if these embryos are rudiments of life just like normal human embryo. Are they of lesser human origin because they can't come to life by itself?
Even parthenogenic embryos have an ethical issue about it. Isn't this creating embryos designed for early death and hence by itself an ethically debatable event.
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