Chromatin Structure and Nuclear Organization Dynamics during X-Chromosome Inactivation

Early development of female mammals is accompanied by transcriptional inactivation of one of their two X chromosomes. This leads to monoallelic expression of most of the X chromosome and ensures dosage compensation with respect to males (XY). One of the most surprising aspects of this phenomenon is that the two X homologs are treated differently even though they are present within the same nucleus. In eutherian mammals, such as humans and mice, either the maternal or the paternal X is inactivated during early embryogenesis. Once set up, the silent state is epigenetically transmitted as cells divide, so that adult females are mosaics of clonal cell populations, which express either of their two X chromosomes. The past years have been marked by the discovery of several molecular events that accompany chromosome-wide silencing.