Uncovering the mechanisms of X-chromosome inactivation and cell fate specification in early human development.

Mammalian dosage compensation between XX female and XY male is mediated by X-chromosome inactivation (XCI). Failure to undergo XCI in mice is lethal in XX individuals. XCI has served as an important paradigm to study epigenetic regulation. Studies in mouse pluripotent stem cells (PSCs) have revealed insights into the transcriptional and chromatin dynamics of XCI and its mechanisms. However, recent work suggests important differences in XCI in mouse and human embryos. The timing and dynamics of XCI and the role of long non-coding RNAs appear to differ between mouse and human. Here, I will make use of human naïve pluripotent stem cells to model XCI in humans. I will induce human naïve pluripotent stem cells to differentiate into specific lineages, and use molecular analyses to document XCI. I will examine the kinetics of gene expression using single-cell resolution approaches including RNA sequencing and RNA in situ hybridization. I will document the expression of long non-coding RNAs and chromatin regulators. I will also investigate mechanisms by using pluripotent stem cell line mutated for candidate regulators of XCI, as well as gain of function studies. This work will help to better understand the regulation of epigenetic mechanisms and early human embryo development.