Telomere epigenetics: a higher-order control of telomere length in mammalian cells

Telomeres are capping structures at the ends of eukaryotic chromosomes composed of TTAGGG repeats bound to an array of specialized proteins. Telomeres, together with centromeres, have been classically considered heterochromatic regions. Constitutive heterochromatin domains typically consist of repetitive DNA and have a very low gene content. In addition, constitutive heterochromatin is characterized by a number of hallmark histone modifications, as well as DNA modifications. In the case of pericentric heterochromatin, several activities responsible for these epigenetic modifications have been recently identified and characterized. In contrast, very little is still known on the architecture of telomeric chromatin, as well as on the activities that may regulate its structure and function. Here, we will discuss recent findings suggesting that telomeric chromatin shares many features with pericentric chromatin, and that disruption of telomeric heterochromatin results in changes in telomere length.