Analysis of Chromatin Openness in Testicle Tissue of Yak and Cattle-Yak.

Cattle-yak, a crossbreed of yak and cattle, which can exhibit obvious heterosis and can adapt to the harsh environmental conditions of the Qinghai Tibet Plateau (QTP). However, F1 cattle-yak were found to be sterile because they were unable to produce sperm, which adversely restricted the fixation of heterosis. Many prior attempts have been made to decipher the mechanism underlying the spermatogenesis stagnation of cattle-yak. However, the open chromatin region (OCR) map of yak and cattle-yak testes has not been generated yet. Here, we have analyzed the OCRs landscape of testicular tissues of cattle-yak and yaks by performing ATAC-seq technology. The OCRs of cattle-yak and yak testes displayed similar genome distribution and showed priority in intergenic regions, introns and promoters. The pathway enrichment analysis indicated that the differential OCRs-related genes were involved in spermatogenesis, involving the cell cycle, as well as Hippo, mTOR, MAPK, Notch, and Wnt signaling pathways. The integration of ATAC-seq and mRNA-seq indicated that the majority of the gene expression levels were positively correlated with chromatin openness. At the same time, we have identified a number of transcription factors (TFs) related to spermatogenesis and the differential expression of these TFs may contribute to the spermatogenesis stagnation of the cattle-yak. Overall, the findings of this study provide valuable information for advancing the research related to yak crossbreeding improvement and sperm production stagnation of cattle-yak.