Decoding the X-chromosome Dynamics in the Adult Female Brain - Project Summary/Abstract Ovarian hormone fluctuations critically shape the brain and behavior and represent a major contributor to female specific risks for neuropsychiatric disorders including depression and anxiety disorders. Another female-specific factor is a double dose of the X chromosome, one of which is typically “inactivated” during development and stays in a repressed form in somatic female cells including neurons. A subset of genes called “X escapees” are able to escape this inactivation and contribute to sex-specific gene expression across tissues including the brain. While some cell-, tissue-, and species-specific escapees have been described, “dynamic X escapees” are unknown. However, in our recent study, we described putative “estrous cycle-dependent X escapees” associated with substantial dynamism in 3D genome structure of the X chromosome across the mouse estrous cycle. Intriguingly, we have a strong indication that the volume of the inactive X chromosome (Xi) changes in response to fluctuating ovarian hormones. We hypothesize that Xi undergoes conformational changes in neurons across the ovarian cycle, which can alter both X-linked and autosomal gene expression and contribute to behavioral adaptation in response to reproductive hormone changes. In this project, we will perform two independent aims to test our hypothesis, by studying the estrous cycle effects in two mouse genetic models. In Aim 1, we will use the ΔXist mutant mice that will allow us to perform allele-specific genomics analyses and distinguish between active (Xa) and inactive (Xi) X chromosomes and confirm hormone-induced Xi plasticity. In Aim 2, we will use the 39,XO female mice that lack the inactive X chromosome and will allow us to assess the functional role of Xi and its dynamics in gene regulation and behavior. In both aims, we will use cutting-edge, neuron-specific genomics assays to characterize gene expression (RNA-seq) and 3D genome organization (Hi-C) in ventral hippocampal neurons across the estrous cycle. We will also test anxiety-related behavior in XO mice and compare it to XX and XY counterparts, to determine whether the inactive X chromosome interacts with the estrous cycle to regulate behavior. Our findings can provide radically novel insights into sex-specific brain regulation, opening new avenues for sex-and gender-informed treatments of brain disorders, with critical implications for women’s mental health.
