Human Cloning According to Rudolf Jaenisch
According to Rudolf Jaenisch, somatic-cell nuclear transfer for reproductive cloning has received some support based on the idea that it holds a key for studying and treating various diseases. However, explains that cloned embryos, unlike embryos from in vitro fertilization have very little to no chance of developing in to normal human beings. This is largely due to the fact that the cloned embryos do not get an opportunity to go through gametogenesis and fertilization which is necessary for the normal development of the embryo into a normal organism - a challenge that is not likely to be overcome in the near future.
Dolly the sheep
While both the in vitro and cloned embryo have some similarities, Jaenisch notes that a majority of the cloned mammals that have been derived from nuclear transfer tend to die off during gestation while those that survive end up with abnormalities. Results of gene-expression analyses have shown that between 4 and 5 percent of the overall genome and between 30 and 50 percent of imprinted genes are not correctly expressed in tissues of the newborn mice, which is sufficient evidence that the practice should note supported because of the serious gene-expression abnormalities. As with the case with Dolly the sheep, the cloned organisms have been showed to develop severe pathological alterations in various organs and major metabolic disturbances, which show that even if these conditions are not noticed early on, they are likely to develop with age causing suffering for the organism.
The issues identified in mice and other organisms during research are also highly likely to affect human beings in the event that the practice is expanded to humans. While it has been suggested that some of these issues can be solved with scientific progress in the near future, Jaenisch notes that some of the problems are not likely to be solved. Here, Jaenisch explains that for cloning to be safe, then it is essential that to parental genomes of the somatic donor cell be physically separated and individual treated in oocyte-appropriate and sperm-appropriate ways. However, given that this is not yet possible, there are significant barriers to successful cloning, which in turn mean that nuclear transfer practice is unsafe. While reprogramming has been shown to present problems in reproductive cloning, this is not the case when it comes to its therapeutic applications. According to Jaenisch, 20 years of studies in generating mouse chimeras with embryonic stem cells has not shown any important defects or tumor forming potential of the cells. This is because the blastocyct tend to retain epigenetic memory of the donor nucleus which contributes to the normal development of the fetus and postnatal and the fact that the therapeutic use of nuclear transfer heavily relies on direct differentiation of functional cells in culture rather than the formation of the fetus.
Need for a discussion
Given that the embryonic stem cells obtained from a fertilized embryo can participate in the generalization of all normal embryonic tissues, Jaenisch notes that embryonic stem cells that are generated through nuclear transfer also have the same potential. Regardless, using embryos that are either generated through in vitro fertilization or nuclear cloning for generating embryonic stem cells is still a controversial topic. However, Jaenisch holds that understanding the difference between the in vitro created embryo and cloned embryo can help bring more light and thus a more rational discussion with regards to nuclear-transfer technology.