Research On Hybrid Sterility Gene Prdm9of Yak

The main objective of the present study was to reveal molecular mechanism of yakhybrid male sterility. Methods such as3’-RACE, RT-PCR were used to clone cDNAsequence of Prdm9gene from the total RNA of yak and cattle testes. The sequenceobtained were2580bp and2421bp in length for yak and cattle, respectively. The openreading frame of yak and cattle Prdm9gene contain10synonymous,10nonsynonymous,and11amino acid differences.The zinc finger sequences of Prdm9gene in Maiwa yaks (n=11), Jiulong yaks(n=10), Changtai yaks (n=12) and cattle (n=6) were amplified using specific PCRprimers designed according to the conserved sequences flanking the zinc finger region ofPrdm9gene. The results showed that all Prdm9sequences amplified from the three yakbreeds or populations coded identical amino acid motifs composed of five tandem C2H2zinc finger domains，while those from cattle coded3different amino acid motifs，whichcomprised5,7or8tandem C2H2zinc finger domains respectively，with amino aciddifferences are located at the important positive selection sites. In addition, ten of the19amino acid differences between cattle and yak zinc finger domains were at the importantpositive selection sites.Real-time quantitative PCR method was performed to analyze Prdm9mRNA levelsin the testes of adult yaks (n=20), cattle-yaks (n=8), yak calves (n=4) and cattle (n=4).The results revealed that the mRNA levels of Prdm9dramatically decreased in the testesof sexually immature yak calves and sterile male cattle-yak compared with normal adultyaks and cattle.Our study suggests that the different numbers of zinc finger and amino aciddifferences at the positive selection sites of Prdm9gene between yak and cattle, and thechanged expression of Prdm9gene in the testes, may be associated with yak interspecifichybrid male sterility.