Yanagimachi Cloning Research To Be Featured In Scientific JournalsUniversity of Hawaiʻi
Several attempts at cloning have produced animals with somatic defects that haven‘t been directly related to genetic mutations. The most prevalent of these is Large Offspring Syndrome (LOS) in which cloned animals have higher than normal placental and birth weights.
Professor Ryuzo Yanagimachi, a professor of anatomy and reproductive biology at the University of Hawaiʻi at Manoa‘s John A. Burns School of Medicine, is addressing this problem and a probable cause for it, in two new papers regarding his team‘s work with cloning mice at UH Manoa.
The first paper, entitled "DNA Methylation Variation in Cloned Mice," was recently published in Volume 30, Issue 2 of Genesis, and the second paper, entitled "Epigentic Instability in ES Cells and Cloned Mice," will be published in the July 5 issue of Science.
The first joint research collaboration by the University of Hawaii (led by Professor Ryuzo Yanagimachi) and the University of Tokyo (led by Professor Kunio Shiota) revealed that cloned mice are not perfect copies of the original mouse.
The researchers believed that the abnormalities in some of the cloning experiments might have something to do with DNA methylation, which is a non-genetic modification of one of the four basic DNA characters: G, C, A and T. In order for cells in complex animals such as humans and large vertebrates to do their myriad of specific tasks it is necessary to have modifications in the DNA, and these modifications are known as DNA methylations or genomic imprinting.
The common theory right now is that body cells such as liver, neuronal or muscle cells have tissue-specific DNA methylations, which regulate protein and enzyme production and the balance of chemicals within the cell.
To examine how DNA in cloned mice is methylated, the team studied the methylation status of the placental and skin DNA of cloned mouse fetuses immediately before birth. The analysis of randomly selected 1490 CpG islands located around genes, rich in the dinucleotide CpG, revealed that several of them were faultily methylated. To their surprise, each cloned animal had different abnormalities in DNA methylation.
Once DNA goes through reproduction (germ line), the methylation pattern of the DNA resets itself. Therefore offspring of the clone do not seem to experience the clone‘s problems.
The second paper, featured in Science, was done in collaboration with the Whitehead Institute of the Massachusetts Institute of Technology (lead by Dr. Rudolf Jeanisch). The research revealed that the genomic imprinting status of embryonic stem (ES) cells is much more unstable than hitherto imagined. These ES cells have the ability to develop into any type of body cell. The use of cloning technology makes it possible to produce ES cells from peripheral organs such as skin and fat cells. The produced ES cells could then be coaxed to develop into somatic cells lost from the body permanently. This powerful technology would open a new field of medicine. The collaborations findings demonstrate that the epigenetic status of ES cell DNA is vulnerable to culture conditions during incubation resulting in abnormal expression of imprinted genes. This observation implies that cells and tissues produced from ES cells under non-optimal conditions may not be normal in a physiological or functional sense. The team‘s findings is a warning to scientists that they must be very cautious in handling ES cells which may be subsequently used for therapeutic purposes.
It is very possible that the vast majority (>97%) of cloned embryos die of extensive errors in DNA methylation. Faulty DNA methylation is known to cause developmental abnormalities and various diseases, including some forms of cancer. It is of primary importance to find a way to eliminate or minimize faulty DNA methylation in cloned offspring regardless of whether cloning is used for reproductive or therapeutic purposes, including cell, tissue and organ replacement therapies.
With this uncertain behavior of DNA methylation during cloning, human cloning should not be conducted. A human clone may survive, but no one would know what genes were faultily methylated or what would be the outcome in terms of physical or mental abnormalities. In fact Professor Yanagimachi believes that "it is outrageous and irresponsible to try human cloning at this time".
Professor Yanagamachi‘s group has an extensive background in normal reproduction, assisted reproduction, cloning and genetic technology at the University of Hawaiʻi at Manoa. The National Academy of Sciences recently inducted Yanagimachi into the academy as a member, in recognition of his lifetime achievements in his field.