Single-Cell Analysis of the Endometrial Characteristics of Meishan Pigs Across the Estrous Cycle

Abstract Background: The Meishan pig, native to China, is renowned for its superior reproductive capabilities, including a high ovulation rate, substantial uterine capacity, and an impressively high rate of embryo implantation. The endometrium plays a pivotal role in facilitating embryo implantation and sustaining pregnancy. It is regulated by ovarian hormones and uterine prostaglandins and undergoes a complex series of coordinated processes across the estrous cycle, including proliferation, differentiation, shedding, and regeneration. A detailed examination of the intricate sow endometrial gene expression patterns during this cycle can yield valuable insights into creating ideal conditions for successful embryo implantation and early embryonic development. To gain a comprehensive understanding of the Meishan pig endometrial biological functions across the estrous cycle, we specifically used uterine tissues in the proliferative and secretory phases for single-cell transcriptomic sequencing. Results: The comprehensive transcriptional profile of uterine cells was elucidated throughout the estrous cycle in Meishan pigs. We identified 7 distinct cell types within the primary cell categories, with 4 subpopulations specifically discerned among the endometrial epithelial cells. Considerable variability was observed in the types and quantities of epithelial cell subpopulations spanning the proliferative and secretory phases of the estrous cycle. Significantly, SOX9-expressing epithelial cells were characterised as potential endometrial epithelial stem cells in Meishan pigs. NURP1 and HES1were identified as potential marker genes for these stem cells. Pseudotime analysis indicated that these SOX9-expressing epithelial cells can differentiate into glandular epithelial (GE) or luminal epithelial (LE) cells. We also observed that SOX9-expressing epithelial cells may differentiate into ciliated epithelial (CE) cells. There was a marked increase in the number of GE and CE cells during the secretory phase compared to the proliferative phase. GE cells are vital for processes such as glycolysis, amino acid biosynthesis, and N-glycan biosynthesis, all of which are crucial for supplying essential nutrients required for embryo implantation and early stages of embryonic development. Conclusions: We reveal the integrated transcriptional profile of uterine cells in sexually mature Meishan pigs and delineate the gene expression patterns within the uterine horns throughout the estrous cycle. These findings provide potential new diagnostic indicators for determining the estrous cycle in sows.