Comments by Rudolf Jaenisch, Whitehead Institute for Biomedical Research, Cambridge, Mass.
"The fact that DNA methylation--a modification in which methyl groups are added to cytosine residues--was involved in gene expression had been suggested for a long time," says Rudolf Jaenisch, a professor of biology at the Whitehead Institute for Biomedical Research in Cambridge, Mass., and the Massachusetts Institute of Technology.
One reason he cites is that "it was known the hypermethylated genes were not expressed and that removing the methyl groups during their development leads to their activation."
MYSTERY: While it is apparent that methylation maintains genomic imprints, Rudolf Jaenisch says that scientists still do not know how it works.
"It had been postulated that methylation may be the marker that allowed for the differential expression, but we were not sure." To test this possibility, he says, the researchers gauged the effects of methylation on three different imprinted genes: H19; ...
