Abstract
The porcine endometrium undergoes dynamic cellular remodeling across the estrous cycle, yet epithelial heterogeneity and differentiation trajectories remain incompletely characterized. In this study, a single-cell transcriptomic atlas of the endometrial epithelium during the follicular and luteal phases in Meishan pigs was generated using high-resolution single-cell RNA sequencing. Canonical epithelial cell types were identified, including glandular epithelium (GE), secretory glandular epithelium (secretory GE), luminal epithelium (LE), ciliated epithelium, as well as an epithelial stem cell subpopulation marked by ALDH1A3 and LGR5 and a progenitor subpopulation marked by ALDH1A1. During the follicular phase, the epithelium was primarily composed of ALDH1A3+LGR5+ stem cells and ALDH1A1+ progenitor cells, whereas GE, secretory GE, and LE predominated during the luteal phase. Integrated trajectory inference and RNA velocity analyses suggested a continuous differentiation trajectory from ALDH1A3+LGR5+ stem cells through ALDH1A1+ progenitors toward GE. Gene expression patterns indicated that glandular epithelial formation was associated with activation of transcriptional regulatory programs and increased mitochondrial respiratory activity. In contrast, differentiation toward the secretory glandular epithelial lineage was characterized by early activation of stress-response pathways, secretion-related genes, and specific metabolic programs. Several transcription factors, including ZFP36L1, TRPS1, and KLF6, were associated with glandular differentiation, whereas MBD4, CREB3L4, ZNF524, SPDEF, USF1, XBP1, and MLX were predicted to contribute to glandular secretory function. These genes showed significant associations with sow reproductive traits in a phenome-wide association study. Overall, this study provides a single-cell framework for understanding epithelial dynamics in the porcine endometrium across the estrous cycle.