The g.-165 T>C Rather than Methylation Is Associated with Semen Motility in Chinese Holstein Bulls by Regulating the Transcriptional Activity of the HIBADH Gene

The 3-hydroxyisobutyrate dehydrogenase (HIBADH) is regarded as a human sperm-motility marker. However, the molecular mechanisms involved in the regulation of expression of the HIBADH gene in bulls remain largely unknown. HIBADH was detected in the testis, epididymis, and sperm via reverse transcription polymerase chain reaction and Western blot analysis. It is also expressed in the seminiferous epithelium, spermatids, and the entire epididymis, as detected by immunohistochemistry. Furthermore, HIBADH was expressed in the neck-piece and mid-piece of bull spermatids, as shown in the immunofluorescence assay. Using serially truncated bovine HIBADH promoters and luciferase constructs, we discovered an 878 bp (-703 bp to +175 bp) fragment that constitutes the core promoter region. One SNP g.-165 T>C of HIBADH was identified and genotyped in 307 Chinese Holstein bulls. Correlation analysis revealed that bulls with the TT genotype had higher initial sperm motility than those with the CC genotype (P < 0.05). Furthermore, the T- or C-containing loci (designated as pGL3-T and pGL3-C) were transiently transfected into MLTC-1 to test the effect of SNP on HIBADH expression. The luciferase reporter assay showed that the pGL3-T genotype exhibited 58% higher transcriptional activity than the pGL3-C genotype (P < 0.05). The bisulfite sequencing analysis revealed that the methylation pattern of the core promoter presented hypomethylation in the ejaculated semen in high-motility and low-motility bulls. The results demonstrated for the first time that the g.-165 T>C rather than methylation in the 5'-flanking region could affect the bovine sperm motility through the regulation of HIBADH gene transcriptional activity.