Oviduct Epithelial Cells Constitute Distinct Lineages from the Ampulla to the Isthmus Related to High-Altitude Adaptation in Yak (Bos grunniens)

Abstract High-altitude adaptation is viewed as a biologically based process during which yaks respond to the harsh condition of coldness and low oxygen. Although high-altitude adaptation has been studied intensively, there is a lack of multi-omics analysis on its physiological mechanism. Therefore, in this study, 10X Genomics single-cell technology were adopted to identify cellular heterogeneity and trajectory differentiation in different parts of the yak oviduct, thus further exploring new cell markers and ligand-receptors. Besides, based on the comparison of oviduct epithelial cells from the ampulla and isthmus between the yak and bovine, genes and pathways related to altitude adaptation were discussed by bulk-seq. Single cell RNA sequencing (scRNA-seq) revealed 14 cell types defined by multiple specific molecular markers, the main cell types are epithelial cells, ciliated cells, secretory cells, basal cells, mesenchymal stem cells, T cells, B cells, monocytes, NK cells, macrophages, and fibroblasts, among which basal cells could be differentiated into secretory cells and ciliated cells. Apart from that, immune cells were the apex products of cell development, while ciliated cells had the characteristics of de-differentiation, and the new ligand-receptors CD74-COPa and CD74-APP were found. In addition, by bulk-seq, it was found that in the ampulla, there were 5149 differential genes (1875 up-regulated genes and 3274 down-regulated genes). YME1L1 was down-regulated significantly, whereas PPIB, PCBD, CYTB, RPL24, RPS5, and UBL5 were up-regulated to a great extent. In the isthmus, there were 6313 differential genes (2146 up-regulated genes and 4167 down-regulated genes). Among them, YME1L1, GSTA4, DNTTIP2, TMCO6, LRBA, and MYH14 were down-regulated obviously, while SNRPD3, CYTB, ADIPOQ, RNH1, PRDX5, DPF1, CRYAB, and PRXL2B were up-regulated dramatically. Through the comparison, it was observed that GSTA4 and YME1L1 were down-regulated, while CYTB was up-regulated in the ampulla and the isthmus. Beyond that, the oxidative phosphorylation pathway was explored. In conclusion, it was demonstrated that ciliated cells were featured with dedifferentiation, and new ligand receptors CD74-COPa and CD74-APP were discovered. Furthermore, GSTA4, YME1L1 and CYTB were main molecules of altitude adaptation, and the oxidative phosphorylation pathway was the key pathway of high-altitude adaptation. This study provides basic data on the heterogeneity and cell trajectory of yak oviduct from the single-cell sequence, and provides the key genes and pathways of yak high-altitude adaptation, as well as the theoretical basis and the data for revealing the low pregnancy rate and genetic breeding of yaks.