Exploring polymorphism of prolactin gene and its possible association with repeat breeding in buffaloes

Prolactin (PRL), a polypeptide hormone is important for a number of biological functions. In livestock, genetic polymorphism of PRL has been found to be associated with various production and reproduction traits. Here, we explored genetic variability in regulatory and signal peptide encoding regions of PRL gene and its possible association with fertility trait in water buffalo (Bubalus bubalis) - a major livestock species of South Asia. Showing low genetic variability overall across the buffalo populations, a total of three SNPs - two in promoter (-C754T and -A516G) and one in exon 2 (C3666T) were identified in 2.2 kb long region characterized from a pool of 12 buffalo populations. Importantly, the SNP at C3666T locus in exon 2 region caused a substitution of hydrophilic arginine (Arg, CGC) residue with hydrophobic cysteine (Cys, TGC) of signal peptide, leading to expansion of hydrophobic domain; and predictably found afflicting the cleavage site. Genotyping of two SNPs (-C754T and C3666T) was carried out by PCR-RFLP (BsrI) and tetra primer-ARMS PCR, respectively in 288 animals belonging to eight different riverine and swamp buffalo populations. The frequency of T allele, encoding hydrophobic cysteine in signal peptide at C3666T locus was found to be very high (0.882) in buffaloes, overall. Principle Coordinates Analysis revealed clustering of riverine buffalo populations (except Toda and Chilika), diverging from swamp type. A univariate logistic regression analysis conducted to explore association of buffalo PRL SNPs with fertility trait revealed that the genotypic frequencies for both loci (-C754T and C3666T) were found to have no significant difference between normal (n = 25) and repeat (n = 36) breeder Murrah buffaloes. Interestingly, a very high frequencies of T allele - responsible for Arg > Cys substitution - at C3666T locus were observed in both repeat (0.972) and normal (0.920) breeder groups. Since, maturation and secretion of the PRL hormone is strongly determined by signal peptide, our study provides an insight on the genetic variability in PRL promoter and signal peptide regions and its possible role in repeat breeding in buffaloes.