Differential mRNA expression and promoter methylation status of SYCP3 gene in testes of yaks and cattle-yaks.

Synaptonemal complex protein 3 (SYCP3) is a DNA-binding protein located on the lateral elements of the synaptonemal complex. This protein plays an important role in homologous chromosome pairing and is necessary for male meiosis of spermatogenesis. To further understand the SYCP3 gene function and its relationship to cattle-yak male sterility, we investigated the characteristics of the bovine SYCP3 (bSYCP3) gene as well as its transcription level and epigenetic modification status. The bSYCP3 gene encodes a 225-amino acid protein with the Cor1 motif and two coiled-coil-forming regions, homologous with other mammals (59-77% identity overall). Real-time PCR analysis indicated that the expression level of bSYCP3 mRNA in yak testes was significantly higher than that in cattle-yak (p < 0.05). The methylation level of the bSYCP3 promoter (mainly 7th, 13th and 17th CpG sites) in cattle-yaks (40%) was significantly higher than that in yaks (0%) (p < 0.05). This suggests that bSYCP3 plays an important role in meiosis of bovine spermatogenesis; further, interspecific hybridization between yak and cattle might influence bSYCP3 gene expression in cattle-yak testes, which might be influenced by bSYCP3 gene promoter methylation.