Understanding how DNA is selectively tagged with “do not use” marks

LA JOLLA—Not all of your genome needs to be active at any given time. Some regions are prone to hopping around the genome in problematic ways if left unchecked; others code for genes that need to be turned off in certain cells or at certain times. One way that cells keep these genetic elements under control is with the chemical equivalent of a “do not use” sign. This chemical signal, called DNA methylation, is known to vary in different cell types or at different stages of cellular development, but the details of how cells regulate exactly where to put DNA methylation marks have remained unclear. Read more »