Histological evaluation and Prdm9 expression level in the testis of sterile male cattle-yaks

The main objective of the present study was to reveal whether the histological structure of testis and the Prdm9 (PR domain containing 9) mRNA level in testis of hybrid sterile yak (i.e. cattle-yaks) differed from that of normal adult yak (Bos grunniens). A partial conserved sequences of yak Prdm9 gene from yak testis was cloned using RT-PCR for the first time, and a 1084 bp fragment was obtained, which showed high nucleotide and amino acid similarities with those of cattle. Based on this sequence, a quantitative real-time PCR method was developed to compare Prdm9 mRNA levels in the testes of adult yaks (n=8), yak calves (n=4), and hybrid sterile yaks (n=4). Results showed that the mRNA levels of Prdm9 decreased dramatically in the testes of sexually immature yak calves and sterile male cattle-yaks compared with that of normal adult yaks. In addition, compared with normal adult yaks, most seminiferous tubules of cattle-yaks had only Sertoli cells and a few spermatogonia but no spermatocytes, while a few other seminiferous tubules of cattle-yaks contained pachytene arrested spermatocytes. Cell apoptosis analysis showed that more spermatogonial cells and/or spermatocytes in cattle-yaks were subject to apoptosis than adult yaks. Our results suggest that Prdm9 gene might be associated with the male infertility of cattle-yaks.