TLR4 Gene Polymorphism and its Association with Mastitis Resistance in Indigenous and Crossbred Cattle of Tamil Nadu, India

Abstract

TLR4 gene is one of the candidate genes for mastitis resistance in cattle. This gene has three exons and PCR with nine sets of primers produced nine amplicons. The amplicons were sequenced from both ends, assembled and screened for SNPs. Totally, 221 dairy cows (Jersey crossbreds, Holstein Friesian crossbreds and indigenous breeds) were genotyped either by PCR-RFLP or tetra-primer ARMS-PCR. Genotyping results showed that one SNP was in 5’UTR region, two SNPs in intron 1, one in exon 2 and seven in exon 3. Out of 11 SNPs, allele frequencies were found to differ between healthy and mastitic cows in six SNPs viz. SNPs 245, 5053, 5134, 9422, 9787 and 9794. At SNP position 5134, the G allele frequency got reduced from 0.71 in healthy cows to 0.50 in mastitic cows but the A allele frequency increased from 0.29 in healthy cows to 0.50 in mastitic cows. The SNP 5053T>G resulted from transversion while the SNPs 5087G>A and 5134G>A resulted from transitions. In SNP 5134G>A, the frequency of both the alleles were in equal proportions in mastitic animals. The SNP 9787C>T in exon 3 had shown no appreciable change in the allele frequencies in both normal and mastitis animals. Homology modeling of TLR4 gene revealed no change in the length of the amino acids of TLR4 protein. The amino acid tyrosine present in the position 674 in the protein chain of Bos tauruswas replaced lysine in crossbreds. No association was found between TRL4 genotypes and somatic cell scores in the breeds studied.