Scientists have discovered a pattern in the DNA sequence of the mouse genome that may play a fundamental part in the way DNA molecules regulate gene expression. The research, led by Emory University scientists along with colleagues at Jacobs University, Bremen, Germany, will be published in the Aug. 22 Advance Online publication of the journal Nature.
Ever since scientists cracked the basic code of chemical bases that comprise the genome of humans and animals, scientists have been uncovering layers of other chemical modifications of gene functioning that can be inherited along with the DNA sequence. This field of discovery, called epigenetics, turns out to be just as important as the genetic sequence itself in controlling whether genes are turned on or off, which determines whether or not they manufacture proteins.
For the past several decades, scientists have known that DNA methylation, a biochemical reaction that adds a methyl group to DNA, is one of these epigenetic processes that marks genes for silencing, which means they do not manufacture proteins. Another kind of modification, called histone methylation, also marks histone proteins that are part of the complex packaging of DNA within the nucleus of cells.
How and where this critical selection process is accomplished--for either silencing or expression-- has been a mystery, however. DNA methylation occurs across the animal genomes, almost always at the C base position of a CG dinucleotide (sequence of two base pairs) in the genetic sequence.
Most expressed genes are based on the simultaneous expression of two copies of a geneone from the mother and one from the father. A small subset of genes, however, are allele-expression specific, meaning only one copy of the gene is expressed, from either the mother or the father, with the gene from the other parent being methylated, or silenced. This kind of differential gene expression is called "imprinting." In the mouse ge
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