How is transcription factor function impeded during X chromosome silencing? (360G-Wellcome-203817_Z_16_A)

In the nucleus of every cell DNA is present as pairs of parentally-inherited chromosomes, from which genes are expressed to perform biological functions. In most mammals, including humans and mice, females tend to have two X chromosomes whereas males have one X and a Y chromosome, which lacks most of the genes present on the X. Thus in order to ensure that the dosage of gene expression from essential X-linked genes is similar between both sexes, almost all genes on one female X chromosome are silenced during development. X inactivation is mediated by a long non-coding RNA, Xist, which spreads to coat the chromosome and coordinates silencing through the recruitment of relatively few factors implicated in specific chromatin remodelling pathways. Beyond its intrinsic biological significance in mammalian development, it is a tractable model system for investigating general molecular mechanisms by which chromosomes are silenced. My reseach will focus on the question of how transcription factors that normally bind enhancers and promoters to activate genes are prevented from performing their functions as the X chromosome is silenced. I will investigate this question in cellular and in vivo models of X inactivation, including in mutant cell lines defective for chromosome silencing.