Uterine epithelial ESR1 is required for postnatal uterine epithelial lineage specification in mice

Abstract

Understanding how epithelial cells in the female reproductive tract (FRT) differentiate is crucial for reproductive health. At birth, FRT epithelia exhibit developmental plasticity, marking a critical window to understand lineage specification in both normal development and disease. Multipotent epithelial cells can differentiate into a luminal-columnar type in the uterus or a stratified-squamous type with basal cells in the cervix. Classical tissue recombination studies established that mesenchymal signals direct these fate choices, yet the epithelial-intrinsic mechanisms remain poorly defined. Despite the significance of these processes, early epithelial fate decisions are largely uncharacterized, representing a major gap in our understanding of epithelial biology within the FRT. Clinical data and mouse models indicate that exposure of the unspecified uterus to diethylstilbestrol, a synthetic estrogen, induced epithelial stratification, implicating estrogen receptor alpha (ESR1) in uterine epithelial fate specification. To address this gap, we combined in vivo mouse models with in vitro Endometrial Epithelial Organoid (EEO) cultures to interrogate the epithelial-intrinsic role for ESR1 in uterine epithelial fate specification. Here, we identify retinoic acid signaling and branched actin nucleation as processes disrupted by the developmental ablation of uterine epithelial Esr1, and provide evidence that regulation of the branched actin cytoskeleton is essential to faithful uterine epithelial lineage commitment. We also provide data suggesting a general mechanism by which non-canonical retinoic acid signaling regulates branched actin assembly, in turn regulating cell cycle progression of undifferentiated neonatal uterine epithelia.