Chromatin loops form a simple epigenetic switch that regulates Igf2 expression, according to the authors of a letter in Nature Genetics this week. The mechanism could model epigenetic regulation of long-distance interactions for other imprinted genes in the genome.

Wolf Reik's group in the Laboratory of Developmental Genetics and Imprinting at the Babraham Institute, Cambridge, UK, felt "under pressure" to test and prove their prediction of a year ago that the differentially methylated regions (DMRs) in Igf2 and H19 come into physical contact and interact to allow the intervening DNA to loop out, Reik told The Scientist.

The authors tested the prediction with two different strategies. In the first, Reik's team used yeast Gal4 insertion technology to show that in maternal chromosomes, Gal4 links up with the H19 DMR and the DMR1 of Igf2, while on the paternal chromosome it links up with the H19 DMR and the DMR2...

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