A single-cell transcriptomic atlas characterizes cell types and their molecular features in yak ovarian cortex

The ovary as one of the most dynamic organs produces steroids to orchestrate female secondary sexual characteristics, harbors ovarian reserve for oocytes, releases mature oocytes for fertilization, and maintains pregnancy. Yak (Bos grunniens) is the only bovid animal that can adapt to the harsh climatic conditions on the Qinghai-Tibetan Plateau (altitudes of over 3000 m above sea level). However, the cellular atlas is composed of oocytes and other somatic cells, and their individual molecular characteristics remain to be elucidated in the yak ovary. Here, single-cell RNA sequencing (scRNA-seq) was performed to delineate the molecular signature of various cell types in the yak ovarian cortex. A cellular atlas of yak ovarian cortex was constructed successfully on the basis of the differentially expressed genes (DEGs) from the distinct cell types and their functional enrichment analysis, comprising endothelial cells, nature kill cells, stromal cells, smooth muscle cells, oocytes, macrophages, epithelial cells, and granulosa cells. Meanwhile, the signature genes were determined based on their expression specificity in each cell type. A cell-to-cell communication network was built in light of the differentially overexpressed ligand and receptor genes from each cell type. Further, the oocytes were subdivided into four subtypes based on their individual DEGs and the functional enrichment of the DEGs. FST and TOP2A were identified as maker genes for oocytes by immunostaining in the yak ovarian cortex. The cellular atlas reveals the biological characteristics of the ovarian cortex at the cellular molecular level and provides insights into female reproductive biology via cellular communications in the yak.