Investigating nuclear organization of the inactive X in female lymphocytes

Abstract

Abstract Autoimmune diseases are devastating, incurable disorders that affect over 20 million people in the US, and many of these disorders have a striking female bias. The genetic basis for this sex-bias arises from the X chromosome. Female mammals, with two X chromosomes, utilize the epigenetic process of X Chromosome Inactivation (XCI), which transcriptionally silences one X. Expression of the long noncoding RNA Xist from the inactive X (Xi) reorganizes the Xi into a compact, bipartite structure, and targets the Xi to the nuclear periphery in somatic cells. The paradigm of XCI maintenance in somatic cells is stable association of Xist RNA and heterochromatic marks on the Xi, which function to maintain the Xi structure. Recently, we found a dynamic mechanism of XCI maintenance in female lymphocytes. In naïve female B cells, Xist RNA is not localized to the Xi, but after stimulation Xist RNA and heterochromatin marks return to the Xi. How this dynamic XCI process impacts Xi structure in lymphocytes is unknown, including which factors regulate Xi nuclear organization in this system. Using a novel allele-specific imaging system, we will present new findings on the compaction and organization of the Xi in lymphocytes. Additionally, we are investigating the regulatory roles of chromatin organization and nuclear structure proteins for lymphocyte-specific XCI maintenance, and how these factors regulate X-linked gene expression. Together, these results underscore the importance of Xi structure for the fidelity of XCI in female lymphocytes.