imprinting control region

Imprinted genes often come in clusters, and rather than each gene being labeled separately, a single master switch nearby controls the whole neighborhood. An imprinting control region is that master switch: a stretch of DNA that directs which parent's copies in the cluster are expressed.

Such a region carries a parent-specific epigenetic mark, usually DNA methylation established in the egg or sperm. Because the region is methylated on the copy from one parent but not the other, it sets up a difference that the cell reads out, switching genes in the cluster on for one parental allele and off for the other.

These regions act over a distance, often by controlling whether insulator proteins bind or whether non-coding RNAs are made, which in turn governs nearby promoters. Deleting or mismarking an imprinting control region can disrupt the expression of several genes at once.

Because they coordinate whole imprinted clusters, faults in these control regions underlie several imprinting disorders, and they are central to understanding how parent of origin shapes gene expression.