Association of prolactin and prolactin receptor gene polymorphisms with economic traits in breeder hens of indigenous chickens of Mazandaran province

Polymorphisms in 5’-flanking region of prolactin (PRL), exon 2 and exon 5 of prolactin receptor (PRLR) genes and its association with growth and egg traits were examined in breeder hens of Mazandaran native fowls breeding station. A single nucleotide polymorphism at site C-2402T and a 24 bp nucleotide sequence insertion at situation -382 in 5’-flanking regions of PRL gene were identified. PCR amplification together with Restriction Fragment Length Polymorphism (RFLP) and direct agarose gel electrophoresis were used to identify different genotypes at C-2402T and a 24 bp indel (insertion-deletion) at the site of -358 of PRL gene, respectively. Nucleotide substitution of C to T and a 24 nucleotides insertion (I) or deletion (D) in promoter region of PRL gene resulted in three genotypes with the frequency of CC (0.10), CT (0.84), TT (0.06) and II (0.39), ID (0.40), DD (0.21), respectively. There were no heterozygous females and only two genotypes A/A (0.54), B/B (0.46) and AA (0.72), BB (0.28) were identified in exon 2 and exon 5 of PRLR gene using PCR-Single Strand Conformation Polymorphism (PCR-SSCP) and PCR-RFLP analyses, respectively. A novel mutation consists of a BamHI restriction site found in the exon 5 of PRLR gene. The results showed significant association between SNP in exon 2 with body weight at hatch, age at sexual maturity, and between SNP in exon 5 and egg number. Individuals with AA genotype produced higher eggs than BB genotype (P<0.05). These results showed that the PRLR locus can be considered as a major gene that may influence the production traits in chicken.