MBL2 Gene Polymorphisms And Its Association With Semen Quality And Progeny Performance In Bull

In this study, the polymorphisms of bovine Mannan-Binding Lectin-C (MBL2) gene were detected in 218 Chinese Holstein bulls via PCR-SSCP and nucleotide sequencing. The SNPs identified were analyzed with bioinformatic analysis tools and their correlation with semen quality, milk performance and mastitis resistance of the progeny were analyzed, as well as MBL2 expression in different organizations, in order to provide molecular marker information for breeding. The results were as followed:1. Three novel SNPs were detected in the promoter (g.895A/T, g.905 A/G and g.956 T/C), four SNPs in exon 1 (g.1164 G/A, g.1197 C/A, g.1198 G/A and g.1207 T/C) and a novel SNP in exon 2 (g.1676 C/T). The g.1164 G/A and g.1197 C/A were identified as non-synonymous mutations, which changed the amino acid at coden 31 (Arg-Gln) and coden 42 (Pro-Gln), respectively. Only the g.1164 G/A and g.1676 C/T met with the Hardy-Weinberg disequilibrium (p>0.05). Gene sequencing results revealed that the g.905 A/G and g.956 T/C, g.1198 G/A and g.1207 T/C were closely linked which were regarded as g.905 W/M and g.1198 W/M (W for wild type allele and M for the mutant) respectively, in the correlation analysis.2. Bioinformatic analysis revealed that there were no CpG island in the 5’flanking region, but a TATA box, several enhancers and general transcription factors (TFⅡD) were found. In addition, a large number of transcription factor binding sites were also found including NF-1, AP-2, GR, SP1, c-Myb et al. The SNPs g.895A/T, g.905 A/G and g.956 T/C were located in GR, c-Myb and NF-E, respectively. The mutation of the three SNPs lead to the change of binding sites of the transcription factors which may further affect the expression of MBL2 gene. The mutation of g.1164 G/A and g.1197 C/A result in the absence of a C-type lectin domain compared with the wild type polypeptide chain which may alter MBL-C protein secondary structure. Protein disulfide bridge analysis shows that the mutations lead to the alternation of disulfide bridges both in numbers, bond strength and location which may further affect protein assembly.3. Correlation analysis indicated that the polymorphism of MBL2 gene had significant correlation on semen quality, progeny performance and mastitis resistance. The wild type in g.905 W/M, g.1164 G/A, g.1197 C/A loci and the heterozygous in g.895A/T, g.1198 W/M loci have an advantage on semen quality and progeny performance to be the beneficial genotypes. The wild type in g.895A/T, g.905 W/M, g.1198 W/M loci and the heterozygous in g.1197C/A locus have an advantage on mastitis resistance to be the beneficial genotypes.4. Expression analysis of mRNA in variant tissues of dairy cattle showed that MBL2 mRNA was expressed in all detected tissues, including liver, heart, mammary, lung, kidney and muscle. The expression of MBL2 mRNA in the liver is significantly higher than other tissues. The liver and mammary of cattles with mastitis had higher MBL2 expression than the ones are healthy (p<0.05). It was low expression of MBL2 in lung, kidney and muscle in both diseased and healthy individuals.In summary, bovine MBL2 gene 5’ UTR and exons were rich of polymorphisms, which may ultimately affect semen quality, progeny performance and mastitis resistance by regulating gene expression and MBL-C protein secondary structure.