Reproductive Cloning - Identifying the Research Obstacles to Success

Reproductive cloning in humans will not happen anytime soon. The birth of Dolly the sheep proved adult cells can be reprogrammed all the way back to an original totipotent state. Dr. Ian Wilmut's team reprogrammed a cell from the udder of an adult sheep, placed the nucleus of that now-totipotent cell into an enucleated sheep egg, and provided an electric shock which caused the egg cytoplasm to respond as if it had been fertilized. Months later, Dolly was born and created a worldwide sensation.

Performing the same feat in humans will require years of additional research and experimentation. At present, the rate of successful fertilizations in animal experiments is very low. Vast numbers of human eggs would be required to move reproductive cloning forward. However, significantly improving the rate of successful fertilization is merely the first hurdle. The overarching meta-question relates to whether the early embryo produced in a cloning procedure is developmentally equivalent to an early embryo produced in a woman's womb.

For example, following physiological fertilization unknown factors in the egg cytoplasm reset all the epigenetic marks on the sperm DNA. Are these mechanisms intact in the cloned zygote? Is epigenetic reprogramming done in exactly the same manner as is done physiologically? Are there errors and what are the consequences for normal development?

Relative telomere length may also be a factor in potentially abnormal development of the clone. A telomere is a region of repetitive nucleotide sequences at the end of a strand of chromosomal DNA. A telomere-shortening mechanism creates a limit to the number of divisions a cell may undergo - effectively limiting the life of the cell. In physiological fertilization an enzymatic telomere elongation program restores optimal telomere length to every cell's set of chromosomes.1 It is hypothesized that this genetic program acts to ensure sufficient telomere reserves to ensure integrity of the species. Is such telomere restoration intact in a cloned human early embryo? The answer is completely unknown.

The potential for genetic abnormalities and increased susceptibility to various diseases in cloned humans is also a matter for conjecture. Dolly the sheep was healthy throughout her lifetime. Of course we have many more concerns regarding human health and many more regulations regarding experimentation on humans. How can research on reproductive cloning proceed if experimentation itself is the only way to identify potential harms and mechanisms for avoiding them? This is a very difficult question. At present it seems that the best way to increase knowledge is to encourage extensive work in animal cloning.

1Schaetzlein S, et al: Telomere length is reset during early mammalian embryogenesis. Proc Natl Acad Sci USA 101(21):8034-8038, 2004

David Lemberg, M.S. in Bioethics, Albany Medical College, May 2010
Consultant, Author, Speaker. Research interests - health care and health care policy, reproductive technologies, genetics and genomics, K-12 science education Executive Producer, SCIENCE AND SOCIETY, http://scienceandsociety.net Twitter - http://twitter.com/david_lemberg Visit SCIENCE AND SOCIETY for cutting-edge interviews with Nobel Laureates, trendsetting industry executives, and best-selling authors in the fields of cancer research, genetics, health care policy, nanotechnology, and space exploration.

Article Source: http://EzineArticles.com/?expert=David_Lemberg
http://EzineArticles.com/?Reproductive-Cloning---Identifying-the-Research-Obstacles-to-Success&id=3577629