Comparative RNA-Seq Analysis of Differentially Expressed Genes in the Epididymides of Yak and Cattleyak.

Background: Cattleyak are the Fl hybrids between (♀) yak (Bos grunniens) and (♂) cattle (Bos taurus). Cattleyak exhibit higher capability in adaptability to a harsh environment and display much higher performances in production than the yak and cattle. The cattleyak, however, are females fertile but males sterile. All previous studies greatly focused on testes tissues to study the mechanism of male infer-tility in cattleyak. However, so far, no transcriptomic study has been conducted on the epididymides of yak and cattleyak.

Objective: Our objective was to perform comparative transcriptome analysis between the epididymides of yak and cattleyak and predict the etiology of male infertility in cattleyak.Methods: We performed comparative transcriptome profiles analysis by mRNA sequencing in the epidi-dymides of yak and cattleyak.

Results: In total 3008 differentially expressed genes (DEGs) were identified in cattleyak, out of which 1645 DEGs were up-regulated and 1363 DEGs were down-regulated. Thirteen DEGs were validated by quantitative real-time PCR. DEGs included certain genes that were associated with spermatozoal matura-tion, motility, male fertility, water and ion channels, and beta-defensins. LCN9, SPINT4, CES5A, CD52, CST11, SERPINA1, CTSK, FABP4, CCR5, GRIA2, ENTPD3, LOC523530 and DEFB129, DEFB128, DEFB127, DEFB126, DEFB124, DEFB122A, DEFB122, DEFB119 were all downregu-lated, whereas NRIP1 and TMEM212 among top 30 DEGs were upregulated. Furthermore, protein processing in endoplasmic reticulum pathway was ranked at top-listed three significantly enriched KEGG pathways that as a consequence of abnormal expression of ER-associated genes in the entire ER protein processing pathway might have been disrupted in male cattleyak which resulted in the down-regulation of several important genes. All the DEGs enriched in this pathway were downregulated ex-cept NEF.

Conclusion: Taken together, our findings revealed that there were marked differences in the epididymal transcriptomic profiles of yak and cattleyak. The DEGs were involved in spermatozoal maturation, mo-tility, male fertility, water and ion channels, and beta-defensins. Abnormal expression of ER-associated genes in the entire ER protein processing pathway may have disrupted protein processing pathway in male cattleyak resulting in the downregulation of several important genes involved in sperm maturation, motility and defense.