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A large portion of the human genome (approximately 98 percent) does not encode genes. Long thought to be "junk DNA," these portions, researchers continue to learn, can play a role in genetic activity and, subsequently, in health and sickness. According to researchers at the German Institute of Human Nutrition, one such junk fragment might actually prevent symptoms of type 2 diabetes in obese mammals.
Type 2 diabetes is the most common form of diabetes, accounting for about 90 to 95 percent of all cases in the U.S., according to the National Institute of Health, and primarily affects overweight people. These recent findings, published in PLoS Genetics, identify a likely contributor to obesity-linked type 2 diabetes. In particular, the researchers found that obese mice lacking a particular fragment of noncoding DNA called a retrotransposon had type 2 diabetes-like symptoms.
Transposons are a form of "jumping DNA" that can move about, embedding themselves randomly into the genome and possibly disrupting genetic activity. Retrotransposons insert into the genome, and then can replicate, making new copies that can insert elsewhere in the genome.
Computational analysis suggests that the retrotransposon identified in this study has embedded itself in at least eight different places in the mouse genome. One known site is in the Zfp69 gene. Consequently the gene can no longer be fully transcribed--converted—into RNA.
In mice that did not have the retrotransposon, the Zfp69 gene was made into RNA, and these mice had higher blood glucose and more fat in their livers (both indicators of diabetes) than obese mice carrying the retrotransposon. The group found similar results in human tissue.
These findings are unexpected in that usually interfering with RNA production triggers or promote diseases. The results also provide evidence that transposons, once regarded as useless, might have important beneficial functions in the cell.
Image of the mice used in the study provided by the German Institute of Health. The white mouse on the left is the Swiss Jim Lambert mouse, and the mouse on the right is the New Zealand Obese mouse.