High-Altitude Stress Orchestrates mRNA Expression and Alternative Splicing of Ovarian Follicle Development Genes in Tibetan Sheep

SIMPLE SUMMARY: To achieve optimal growth performance and improved fertility in animals living on high plateaus, it is important to understand how high-altitude stress reduces fertility in females. This study analyzed the transcriptome dynamics of Tibetan sheep ovaries under high-altitude stress. High-altitude stress suppressed the expression of follicular development marker genes and impaired the luteinizing hormone/follicle-stimulating hormone signaling pathway. High-altitude stress also increased abnormally spliced isoforms of transcription factors and RNA processing factors. Therefore, high-altitude stress may reduce the fertility of Tibetan sheep by disrupting the normal expression/hormone signaling of follicular development genes. Further work is needed to decipher whether this phenomenon is a unique feature of Tibetan sheep or a general mechanism in animals under high-altitude stress. ABSTRACT: High-altitude stress threatens the survival rate of Tibetan sheep and reduces their fertility. However, the molecular basis of this phenomenon remains elusive. Here, we used RNA-seq to elucidate the transcriptome dynamics of high-altitude stress in Tibetan sheep ovaries. In total, 104 genes were characterized as high-altitude stress-related differentially expressed genes (DEGs). In addition, 36 DEGs contributed to ovarian follicle development, and 28 of them were downregulated under high-altitude stress. In particular, high-altitude stress significantly suppressed the expression of two ovarian lymphatic system marker genes: LYVE1 and ADAMTS-1. Network analysis revealed that luteinizing hormone (LH)/follicle-stimulating hormone (FSH) signaling-related genes, such as EGR1, FKBP5, DUSP1, and FOS, were central regulators in the DEG network, and these genes were also suppressed under high-altitude stress. As a post-transcriptional regulation mechanism, alternative splicing (AS) is ubiquitous in Tibetan sheep. High-altitude stress induced 917 differentially alternative splicing (DAS) events. High-altitude stress modulated DAS in an AS-type-specific manner: suppressing skipped exon events but increasing retained intron events. C(2)H(2)-type zinc finger transcription factors and RNA processing factors were mainly enriched in DAS. These findings revealed high-altitude stress repressed ovarian development by suppressing the gene expression of LH/FSH hormone signaling genes and inducing intron retention of C(2)H(2)-type zinc finger transcription factors.