Molecular mechanisms governing X chromosome inactivation; a model for understanding epigenetic regulation of the genome in differentiation and development. (360G-Wellcome-081385_Z_06_Z)

The key goal of this proposal is to understand the mechanism of X chromosome inactivation. In this unusual form of genetic regulation the genes on a single X chromosome in female cells are co-ordinately silenced early in development, conferring dosage equivalence between XX females and XY males. The X inactivation process is regulated by a cis-acting non-coding RNA, the X inactive specific transcript (Xist). Xist RNA 'coats' the X chromosome from which it is transcribed, triggering formation of a repressive chromatin configuration along the entire length of the chromosome. Chromosome silencing is then faithfully maintained through subsequent cell divisions. X inactivation provides an excellent model system for studying epigenetic mechanisms and their role in regulating the genome through differentiation and development. It remains unclear both how Xist is regulated in early development and how Xist RNA induces chromosome wide silencing. Four interrelated projects are proposed. These build on our current understanding of factors involved in this process, aiming to elucidate detailed molecular interactions, and additionally set out to identify novel factors using genetic and biochemical screens, RNAi in tissue culture cells and biochemical purification of complexes from ES cells respectively.