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Archive - Jul 22, 2011

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Scientists Complete First Genome-Wide Mapping of 5hmC in Human Embryonic Stem Cells

Stem cell researchers at UCLA have generated the first genome-wide mapping of a DNA modification called 5-hydroxymethylcytosine (5hmC) in embryonic stem cells, and discovered that it is predominantly found in genes that are turned on, or active. The finding by researchers with the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA may prove to be important in controlling diseases like cancer, where the regulation of certain genes plays a role in disease development. "Any way you can control genes will be hugely important for human disease and cancer," said Dr. Steven E. Jacobsen, a professor of molecular, cell and developmental biology in the Life Sciences and a Howard Hughes Medical Institute investigator. "Cancer is generally a problem of genes being inappropriately turned off or mutated, like tumor suppressors genes, or genes that should be off getting switched on." The study appears in the July issue of the journal Genome Biology. 5hmC is formed from the DNA base cytosine by adding a methyl group and then a hydroxy group. The molecule is important in epigenetics - the study of changes in gene expression caused by mechanisms other than changes in the DNA sequence - because the newly formed hydroxymethyl group on the cytosine can potentially switch a gene on and off, Dr. Jacobsen said. The molecule 5hmC was only recently discovered, and its function has not been clearly understood, Dr. Jacobsen said. Until now, researchers didn't know where 5hmC was located within the genome. "That is important to know because it helps you to understand how it is functioning and what it's being used for," said Dr. Jacobsen, who also is a researcher with UCLA's Jonsson Comprehensive Cancer Center.

Genes of Endangered River Turtle Reveal Ancient Influence of Maya Indians

A genetic study focusing on the Central American river turtle (Dermatemys mawii) recently turned up surprising results for a team of Smithsonian scientists involved in the conservation of this critically endangered species. Small tissue samples collected from 238 wild turtles at 15 different locations across their range in Southern Mexico, Belize, and Guatemala revealed a "surprising lack" of genetic structure, the scientists write in a paper published online on May 17, 2011, in the journal Conservation Genetics. The turtles, which are entirely aquatic, represent populations from three different river basins that are geographically isolated by significant distance and high mountain chains. "We were expecting to find a different genetic lineage in each drainage basin," explains the paper's main author Dr. Gracia González-Porter of the Center for Conservation and Evolutionary Genetics at the Smithsonian Conservation Biology Institute. "Instead, we found the mixing of lineages. It was all over the place." Despite appearing isolated, the genetic data showed the different turtle populations had been in close contact for years. "But how?" the researchers wondered. The best possible explanation, Dr. González-Porter and her colleagues say, is that for centuries humans have been bringing the turtles together. The turtles have been used as food, in trade, and in rituals for millennia, widely transported and customarily kept in holding ponds until they were needed. “For centuries, this species has been part of the diet of the Mayans and other indigenous people who lived in its historic distribution range," the scientists point out in their paper. "D.