The Low Expression Of Dmrt7is Associated With Spermatogenic Arrest In Cattle-yak

Cattle-yak, the first hybrid generation of cattle and yak, shows obvious heterosis. However, F1male cattle-yak cannot produce sperm, which prevents the heterosis from being inherited. The inability of cattle-yak to produce sperm has become a major problem in the crossbreeding of yak, and the molecular mechanism for male cattle-yak sterility is not clear. Dmrt7, a member of the Dmrt (doublesex and mab-3related transcriptional factor) family of genes, plays an important role in male sex chromosome synapsis. In our study, the coding region sequence of yak and cattle-yak Dmrt7was cloned by molecular cloning techniques, and the sequence, conserved domains, functional sites, and secondary and tertiary structures of the Dmrt7-encoded protein were predicted and analyzed°using bioinformatics methods. The coding region sequences of the Dmrt7gene, encoding370amino acids, were consistent in yak and cattle-yak. The protein encoded by yak and cattle-yak Dmrt7contains a DM domain. We detected Dmrt7mRNA expression in the testis, but not in any other tissue tested. Dmrt7mRNA and protein expression was significantly higher in testis of cattle and yak than that in cattle-yak (P<0.01). Histological analysis indicated that seminiferous tubules in male cattle-yak were highly vacuolated and contained primarily Sertoli cells and spermatogonia, while those of cattle and yak contained abundant primary spermatocytes. The male cattle-yak testis contained a significantly larger number of apoptotic cells than those of cattle and yak, as assessed by TUNEL analysis. The accumulation of SCP3-positive spermatocytes indicated the arrest of spermatogenesis at the pachytene stage in the cattle-yak. These results suggest that low levels of Dmrt7expression lead to male sterility in cattle-yak.