Molecular characterization and expression of Spata22 in testes of the sterile male cattle-yak

The male hybrid of cattle and yak is sterile, while the female is fertile. This is caused by aberrations with the process of spermatogenesis. SPATA22 plays a critical role in the pairing of homologous chromosomes, synapsis, DNA repair, and meiotic recombination; dysregulation of which can disrupt these processes, resulting in meiotic arrest and male sterility in mammals. The expression and molecular characterization of Spata22 have not been studied in the sterile hybrid cattle-yak. This study isolated, sequenced and characterised the coding sequence of the Spata22 gene of the cattle-yak, and compared the relative mRNA and protein expression. There was a remarkable reduction in Spata22 mRNA and protein expression in the cattle-yak compared to the yak and cattle. The SPATA22 protein was located in the adluminal compartment of the tubules. Thirteen mutation sites consisting of ten amino changes and 3 insertions were found in the cattle-yak sequence. The cattle-yak protein sequence contains motifs which are potential binding sites for genes that play a crucial role in meiotic recombination and DNA repair. Histological evaluation revealed no advanced-stage germ cells, except a few spermatogonia, spermatocytes and Sertoli cells. These findings give an insight into the role of Spata22 in the hybrid sterility of cattle-yak and pave the way for more future research into genetic engineering involving the construction of a functional Spata22 gene copy into the genome of sterile male cattle-yak to restore normal spermatogenesis in the sterile hybrid. This will help improve desirable traits in the yak through hybridization.