Most imprinted loci have key regulatory elements that are methylated on onl
y one of the parental chromosomes. For several of these 'differentially met
hylated regions', recent studies establish that the unmethylated chromosome
has a specialized chromatin organization that is characterized by nuclease
hypersensitivity. The novel data raise the question of whether specific pr
oteins and associated chromatin features regulate the allele-specificity of
DNA methylation at these imprinting control elements.