Review on Study of Toll like Receptor 2 Gene and its Polymorphic Relationship with Mastitis in Cattle A Review on Study of Toll Like and its

Mastitis is defined as an inflammatory reaction of the parenchyma of the mammary glands to bacterial, chemical, thermal or mechanical injury. SCC is used as an indicator to detect mastitis in individual cow. TLR2 is a membrane protein, a receptor, which is expressed on the surface of certain cells and recognizes foreign substances and passes on appropriate signals to the cells of the immune system. Bovine TLR2 was assigned to Bos taurus (BTA) chromosome 17 using radiation hybrid mapping. Detection of molecular markers associated with mastitis resistance would be useful towards marker assisted selection (MAS) at an early age of dairy animals to reduce the economic losses. Hence purpose of this study is to review identification of SNPs in the bovine TLR2 gene and to evaluate their association with incidences of subclinical mastitis in dairy cattle. Nucleotide sequences of bovine TLR2, TLR4 and TLR6 genes were screened by (Mariotti et al., 2009) to identify novel SNPs in 16 different bovine European cattle breeds. In total eight SNPs were identified of which three SNPs were found in TLR2 and were deposited in NCBI dbSNP. TLR2_738 was fixed in seven breeds (Highlands, Jersey, Limousine, Marchigiana, Maremmana, Simmenthal and South Devon). Significant deviations from Hardy-Weinberg equilibrium in the overall populations studied (p-value < 0.01) were observed in three SNPs at two loci: TLR2_591, TLR2_738 and TLR4_2043. These three SNPs (TLR2_591, TLR2_738 and TLR2_767) identified in TLR2 were suggested to be associated with disease resistance in cattle. The polymorphisms of the TLR2 gene using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 297 Chinese Holstein-Friesian cattle were studied by (Zhang et al., 2009). The relationship between gene polymorphism and somatic cell score (SCS) was also analysed. A polymorphic site was identified, where there was a mutation C->A at position 106 bp, which resulted in Asp being replaced by Glu. Genotypes AA, AB and BB were detected by digesting the fragment with restriction endonuclease EcoRV in the population. B allele was predominant and allele frequency A and B were estimated as 0.7845 and 0.2155, respectively. The χ 2 test indicated that the polymorphic locus displayed no deviation from the Hardy-Weinberg equilibrium (P<0.05). In Chinese Holstein-Friesian cattle the SCS of BB and AB genotypes were significantly higher than AA genotypes. mastitis Effect of TLR2 gene on subclinical mastitis in and Brown cattle were studied. Animals with highest and lowest SCS were chosen to sequence TLR2 gene and then the SNP sites were detected with PCR-RFLP. The results revealed presence of 3 SNP sites viz . E+189, E+631 and E+2260. Among these sites E++189 was found to be associated with resistance to mastitis for BB genotype. When E+2260 site was mutated and translated into termination codon, the SCC increased in animals with AB genotypes. It indicated that the mutation was harmful to mastitis resistance of cattle. The SCS in Xinjiang brown cattle was lower than that in Holstein. Finally in this study E+189 and E+631 SNP sites were reported to affect mastitis resistance of cattle and the possible reason of the stronger resistance in Xinjiang brown cattle was attributed to the differences in distribution between two breeds (HF and Xinjiang Brown cattle) for E+189 and E+631 sites (Bai et al., 2011). To evaluate the role of TLR2 during intramammary infections the association of SNPs and somatic cell scores in 151 Xinjiang Brown cattle and 138 Holsteins were analysed (Bai et al., 2012). The associations of genotypes or haplotypes with SCS were analyzed. These results revealed: 15 SNPs viz . , E+653, E+945, E+978, E+1010, E+1250, E+1688, E+1707, E+1779, E+1782, E+1891, E+1995, E+2025, E+2055, E+2214 and E+2295 which were detected from 289 cows. It was observed that distribution of the 14 SNPs were significantly different from Xinjiang brown cattle and Holstein ( P < 0.001) except for the E+945 ( P > 0.05).