Integrative analysis of transcriptome and metabolome reveals the heterogeneity of ovarian follicles between high-altitude Yak (Bos grunniens) and Low-altitude cattle (Bos taurus)

Differences including reproductive efficiency have been proved existence between high-altitude yak (Bos grunniens) and low-altitude cattle (Bos taurus), however, the discrepancies of ovarian follicles across them are still elusive. In the present study, RNA-seq results exhibited an obvious separation of yak and cattle granulosa cells (GCs), and 2329 differently expressed genes (DEGs) was obtained, with 1297 upregulated and 1032 downregulated DEGs in yaks. Advanced analysis revealed that DEGs were mainly enriched in cellular structure, DNA packaging and remodeling (GO and GSEA), hypoxia adaptability, energy metabolism (KEGG and GSEA), and epigenetic modification of histones (Reactome and GSEA). Metabolite profiles of yak and cattle follicular fluid (FF) were depicted by LC-MS/MS non-target metabolomics, and 350 different metabolites (DMs) were acquired, with 242 upregulated and 108 downregulated DMs in yaks. The KEGG pathway enrichment results demonstrated that DMs were primarily enriched in metabolism including lipid, carbohydrate and nucleic acid metabolism. Finally, twenty-nine pathways were significant enriched via integrative analysis, most of which were associated with metabolism including carbohydrate metabolism (e.g. Glycolysis / Gluconeogenesis) and lipid metabolism (e.g. Sphingolipid metabolism). Of note, the key hypoxia adaptation pathway, HIF-1 signaling pathway, was predominant enriched. Overall, we ascertained that the heterogeneity in ovarian follicles of yaks and cattle was existence, which were mainly reflected on hypoxia adaptation and energy metabolism. These results implied that the above processes were evolved specifically for the normal development of yak follicles under plateau atmosphere.