Embryonic stem cells are taken from a young embryo. They are generally taken from the inner cell mass of a blastocyst. They may also be derived from early blastomeres taken from a "morula", which is an embryo of 4 to 32 cells. An embryo reaches the blastocyst stage about 4–5 days after fertilization. At that point they contain about 50-150 cells. However, implantation (attaching to the uterine wall) does not occur until at least 9 days after fertilization. Neurulation (primordial development of the central nervous system) occurs about a week later.[1] Embryonic stem cells are harmful to the recipient because they tend to grow tumors, and safer alternatives that do not use embryos are available, but many abortion supporters still insist on using embryonic stem cells in order to justify the concept of abortion.
Embryonic stem cells can differentiate into the three "germ layers": ectoderm, endoderm and mesoderm. The 220 types of cells in humans are all based on these germ layers. Some scientists have shown effectively that embryonic stem cells have greater differentiation potential, and divide into greater numbers, than adult stem cells can.
Background
Embryonic stem cells are pluripotent and thus can turn into any of the 3 germ layer types.[2]
Even though embryonic stem cells can differentiate into more cell types than can adult stem cells, like with in vitro fertilization, they require the destruction of the embryo, i.e. abortion. After harvesting embryonic stem cells, they can be cultured for an extended period of time and induced to proliferate without the need to destroy more embryos, though stem cell lines tend to drift genetically and become unusable after years of continuous culturing. New human embryonic stem cell lines are generated from the discarded embryos of in vitro fertilization clinics rather than the fertilization of human eggs for the express purpose of producing stem cell lines. There is some research that shows that embryonic stem cells might be obtainable without destruction of the embryo, though this research is not definite yet.[3]
Largely driven by federal bans on using NIH funds to produce new human embryonic cell lines, much attention has been shifted away from embryonic stem cells to induced pluripotent stem cells (iPS cells). This type of cell is generated from adult (differentiated) cells though genetic manipulation and possess many of the properties of embryonic stem cells. iPS cells are a major leap forward in stem cell research and provide the distinct advantage of generating pluripotent stem cells from any adult individual. Thus, replacement cells and tissues generated from iPS cells can be immunologically compatible with the recipient if the iPS cells were initially germinated from cells donated by the recipient; this significantly reduces the risk of tissue rejection. This advancement in the stem cell field would not have likely come to pass this soon if not for the push to ban human embryonic stem cell research in the US.
History
In 2001 President Bush allowed federal funding for research performed only on the 60 human embryonic stem cell lines that were in existence at the time.[4] Cell lines drift genetically and morphologically over time, and due largely to the ban on producing more embryonic stem cell lines with NIH funds, researchers focused on producing embryonic-like stem cells from adult (differentiated) cells; these cells are known and induced pluripotent stem cells (iPS cells). These cells have similar properties to embryonic stem cells but do no require the destruction of or any use of human embryos - humans donate their own cells (e.g. skin cells) and though slight genetic manipulation these cells, they can be reverted into essentially an undifferentiated state and gain the ability to become nearly any cell in the body (i.e. pluripotency). This major advance in the stem cell and medical fields came much sooner than most researchers expected; this can be credited largely to the Bush ban regarding human embryonic stem cells.
Despite the strong genetic similarities, the production of chimpanzee stem cell lines have been problematic, though stem cells have been produced for other non-human primates.
Controversy
Pro-life conservatives consider taking stem cells from human embryos tantamount to abortion, as a human life is ended.
- Those who value human life from the point of conception, oppose embryonic stem cell research because the extraction of stem cells from this type of an embryo requires its destruction. In other words, it requires that a human life be killed.[5]
Many liberals, on the other hand, claim that all the embryos used for stem cell research are already condemned to death because most of them are the byproduct of in vitro fertilization, a procedure that requires the production of a number of embryos far in excess of the number that are successfully implanted. Few parents choose to cryogenically store these excess embryos, and with no further use for these embryos, they are often destroyed. Thus, liberals claim that embryonic stem cell research does not result in the destruction of any additional embryos.[6] Conservatives argue that unused embryos can be adopted within a 10-year window of viability [7] and thus saved from destruction; however, embryo adoption is very rare and far too few prospective adoptive parents exist for all unused embryos to be adopted.
References
- ↑ http://9e.devbio.com/
- ↑ http://learn.genetics.utah.edu/content/tech/stemcells/sctypes/
- ↑ http://www.cmda.org/AM/Template.cfm?Section=Stem_Cell_Research&TEMPLATE=/CM/ContentDisplay.cfm&CONTENTID=12577
- ↑ https://www.whitehouse.gov/news/releases/2001/08/20010809-2.html
- ↑ Pros And Cons Of Stem Cell Research
- ↑ http://humrep.oxfordjournals.org/cgi/content/full/18/4/672
- ↑ http://www.embryoadoption.org/