# Epigenetic regulation of X chromosomes during female mouse embryogenesis

> **NIH NIH R01** · UNIV OF MASSACHUSETTS MED SCH WORCESTER · 2020 · $376,875

## Abstract

Abstract
The development and reproduction of female mammals is dependent on dosage compensation
from sex chromosomes. Indeed, female mammals silence one of their two X chromosomes (X)
in a process called X inactivation (XCI), a paradigm for epigenetic gene silencing. In mice, XCI
occurs early during female embryogenesis in two waves. In embryos at the 2-4 cell stage, an
early imprinted form of XCI (iXCI) silences exclusively the paternal X (Xp). Around implantation,
however, female epiblast cells that give rise to somatic embryonic tissues undergo a major
epigenetic switch: These cells reactivate the silenced Xp (XCR) and undergo another, random
form of XCI (rXCI), silencing the paternal or maternal X with equal probability. Thus, tissues in
the adult female mouse generally display a random XCI pattern. Xist RNA is crucial for X-
silencing both during iXCI and rXCI and paints the inactive X from which it is expressed as a
cloud, triggering downstream repressive chromatin modifications and X-silencing. We
discovered that in mice the X-linked ubiquitin ligase RLIM is crucial for Xist functioning and
maintenance of Xist clouds during iXCI and that lack of Rlim disrupts embryo implantation due
to trophoblast failure. However, Rlim is dispensable for rXCI in epiblast cells of peri- and post-
implantation embryos. Thus, the reasons of how X dosage compensation defects inhibit
trophoblast functions as well as the pathways that regulate Xist during rXCI are unknown, and
regulatory pathways triggering the developmental switch from iXCI to rXCI in epiblasts remain
enigmatic.
 The research proposed in this grant is based on our published and preliminary work and
will use mouse genetics combined with a newly generated female ESC model that permits
investigations of XCI in the absence of Rlim. In particular, we will explore the effects of iXCI
failure on trophoblast stem cell fates (Aim 1), examine novel mechanisms of rXCI regulation in
female ESCs (Aim 2) and unravel in vivo mechanisms of XCR in female peri-implantation
embryos (Aim 3).
 The proposed research will identify novel mechanisms of trophoblast stem cell
maintenance, underlying regulation of Xist both during rXCI and iXCI and illuminate
mechanisms underlying XCR. The combined results will allow designing the first comprehensive
model of a iXCI/XCR/rXCI epigenetic switch that occurs in epiblast cells of developing female
mice. Expected results will have transformative impact in the fields of early mouse development,
stem cell biology, female reproduction and sex-specific epigenetic regulation.

## Key facts

- **NIH application ID:** 9932413
- **Project number:** 5R01GM128168-13
- **Recipient organization:** UNIV OF MASSACHUSETTS MED SCH WORCESTER
- **Principal Investigator:** INGOLF M BACH
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $376,875
- **Award type:** 5
- **Project period:** 2018-09-24 → 2022-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9932413

## Citation

> US National Institutes of Health, RePORTER application 9932413, Epigenetic regulation of X chromosomes during female mouse embryogenesis (5R01GM128168-13). Retrieved via AI Analytics 2026-06-11 from https://api.ai-analytics.org/grant/nih/9932413. Licensed CC0.

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