DNA from more than 900 horses was analysed, several of them from the white Lipizzaner horses from the Spanish Riding School in Vienna. In all white horses, but not in any black, brown or chestnut coloured horse, the exact same DNA change was found, a large segment of DNA duplication. This mutation does not change any protein coding gene, but regulate how active two other genes will be. The Grey horse is also very interesting from a medical point of view since the mutation also predisposes for development of melanoma. About 75% of Grey horses older than 15 years of age have a benign form of melanoma that in some cases develops into a malignant melanoma. Thus, the study reported today has also given new insight in a molecular pathway that may lead to tumour development. “We propose that the Grey mutation stimulates growth of melanocytes and that this leads to a premature loss of the melanocyte stem cells needed for hair pigmentation whereas the mutation promotes an expansion of some of the melanocytes causing skin pigmentation,” says Leif Andersson. Domestic animals constitute extraordinary models for evolution of biological diversity as already recognized by Charles Darwin. The white horse is a beautiful illustration of the importance of regulatory mutations as a major underlying mechanism for phenotypic diversity within and between species. The Grey mutation does not change any protein structure but it affects the genetic regulation of two genes. The researchers found that the white horses carry an extra copy of a DNA segment located in one of these genes. “It is very likely that regulatory mutations like the one we found in these white horses constitute the dominating class of mutations explaining differences between breeds of domestic animals as well as between species like humans and chimpanzee,” concludes Leif Andersson. Referens: A cis-acting regulatory mutation causes premature hair greying and susceptibility to melanoma in the horse Gerli Rosengren Pielberg, Anna Golovko, Elisabeth Sundström, Ino Curik, Johan Lennartsson, Monika H Seltenhammer, Thomas Druml, Matthew Binns, Carolyn Fitzsimmons, Gabriella Lindgren, Kaj Sandberg, Roswitha Baumung, Monika Vetterlein, Sara Strömberg, Manfred Grabherr, Claire Wade, Kerstin Lindblad-Toh, Fredrik Pontén, Carl-Henrik Heldin, Johann Sölkner & Leif Andersson Nature Genetics Published online: 20 July 2008, doi:10.1038/ng.185 ......... ZenMaster
For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/ and http://www.geocities.com/giantfideli/index.html
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