Comparative Transcriptome Analysis Of Spermatogenesis Arrest In Cattle-yak

The male infertility of cattle-yak, which is the hybrid offspring of cattle and yak,is a difficult problem for cross-breeding and improvement of yak. In this study, weused high-throughput sequencing technology to obtain the transcriptomes of thetesticular tissues of both cattle-yak and yak, and investigated the expression profilesof the genes regulating hormones, spermatogenesis and apoptosis. The results showedthat：①There were17,784and18,529genes expressed in cattle-yak and yak testiculartissues respectively, and statistical analysis revealed5,000genes with increasedmRNA levels and4,089with reduced levels in cattle-yak testicular tissue as comparedwith those in yak.②The genes involved in testosterone synthesis and Inhibin alpha chain have ahigh level of expression in cattle-yak testicular tissue, and the former with increasedexpression maybe induce the secretion of intratesticular testosterone which can beup-regulated the expression of latter, that possible restrain the secretion of follicle-stimulating hormone of the pituitary gland, but not of luteinizing hormone. It maybecause imbalance or deficiency of hormones in cattle-yak which lead to male infertility.③By compared the expression of the testicular marker genes between the twospecies, we showed that expressions of the genes regulating SSC, sertoli cell, Leydigcell and myoid cell(fibrosis of testis) are increased, whereas those controllingdifferentiation of SSCs(especially those expressed at late stage of spermatid formation)are reduced. The abnormal of self-renewal and differentiation of SSCs, which may betightly associated with the disorder of retinoic acid signaling pathway, might lead tospermatogenesis dysfunction in cattle-yak. Syce3, Fkbp6and Dmrt7are down-regulated significantly in cattle-yak testicular tissue, which maybe inhibit theformation of synaptonemal complex between homologous chromosomes, especiallybetween sex chromosomes. Spo11and Dmc1are involved in double strand break andhomologous repair process respectively, and are down-regulated in cattle-yak resultingin reduced numbers of synaptonemal complex and impaired homologous repair respectively. Tnp2, Hmgb4, H1fnt that are regulated by Crem,GRTH/DDX25with suppressed expression and involved in formation of concentratednucleus are hardly transcriptionally active, confirmed the research findings thatdifferentiation of germocyte occurs only at round-spermatid stage.④Proapoptosis genes, such as p53, TNF-α, Trail, Bmp8b, Bax, Caspase-3,Caspase-6and Caspase-7are up-regulated, and apoptosis genes, such as survivin,Bcl-2are down-regulated, suggesting increased cell death in cattle-yak testicular tissue.Together, our analysis of transcriptomes of the testicular tissues of cattle-yak and yakmoves a step toward revealing the mechanism of cattle-yak male infertility andprovides the theoretical basis for cross-breeding and improvement of yak.