Polymorphisms Of Chicken Prolactin Receptor Gene And Its Association With Broodiness And Egg Production Traits

It's generally accepted that broodiness is a major component of loss of egg production in birds, but other researchers just have the opposite viewpoint. A native breed, Ningdu Sanhuang chicken (DNH), was observed phenotypic broody traits including broodiness frequency (BQ) and duration of broodiness (BD) at 300-days, and egg production traits including age at first egg (AF), total egg number at 300-days (TE) and total abnormal egg number at 300-days (TAE). In order to make clear whether broody behavior have effect on egg production, association and correlation analysis between the two traits were conducted. Prolactin (PRL) is generally accepted to be crucial to the onset and maintenance of broodiness in birds. Binding of PRL to its receptor causes a series of physiologial and biochemical reactions during birds' broodiness. Considering the importance of chicken prolactin receptor (cPRL-R), association analysis between SNPs and broody and egg production traits were conducted.Correlation analysis results showed a great significant correlation between broody traits and egg production traits (P < 0.01). Chickens with an elder AF were inclined to express broody behavior. Nonbroody chickens laid more eggs at 300-days, with the number of 38.49 more than that of broody ones. Broody chickens laid less abnormal eggs at 300-days, with the number of 1.67 less than that of nonbroody ones. BD was not related to AF and TAE (P > 0.05), but it had a great significant negative correlation with TE (r = -0.789, P < 0.01). The results, which indicated that BD was a major component affecting TAE, had been supporting the viewpoint that broodiness affects the egg laying performance in birds.Ten pairs of primers were used to amplify the nucleotide sequences of part of exons and introns of cPRL-R. Sequencing results revealed four nucletide mutations in cPRL-R, SNP1 ( A10862G in exon 3 which is a 5'-UTR mutation), SNP2(A25670G in exon 6 which is a synonymous mutation), SNP3 (G30716A in intron 8) and SNP4 (A31900G in exon 10 which lead to an amino acid variantion, Asn628Ser in cPRL-R protein ). Bioinformatics analysis showed that A31900G mutation give rise to a lost of transcription factor binding site of Sox5 (92 points) and GATA-1 (91 points). Protein structure prediction analysis showed that the Asn628Ser mutation in PRL-R may have no effect on its senior structure, indicating that the mutation site may play a role in transcriptional but not protein level. We screened four SNPs of the cPRL-R gene in five Chinese native breeds including Gushi, Jiuyuan Black, New Yangzhou, Sichuan Mountain Black-bone and Ningdu Sanhuang chickens. The genotypic frequencies were the same as genetic frequencies because the cPRL-R gene located on Z-choromose. x~2 test results showed great significant differences in the distribution of the genotypic and genic frequencies among the five groups. The polymorphism information content (PIC) of the four loci in different breeds showed moderate polymorphism. With the highest egg production and lowest broodiness frequency among five groups, New Yangzhou chickens' dominant genotype in SNP1, SNP2 and SNP3 is D-, F- and H-, respectively, but the rest 4 groups is just the opposite, with C-, E-and G-, except for SNP4 of Ningdu Sanhuang chickens, which H- is the domimant genotype.x~2 test results showed that SNP4 was great significantly associated with BQ (P < 0.01). The average BF of genotype H- (58.49%) was 11.54% higher than that of G- (46.95%). Association analysis results showed that SNP4 was significantly associated with BD (P < 0.05). The average BD of genotype G- (8.33) was 2.4 days more than that of H- (5.93). SNP2 was significantly associated with TE (P < 0.05). The average TE of genotype D-(116) was 2.4 higher than that with C- (113.62). SNP3 was significantly associated with AF (P < 0.05). The average AF of genotype E- (136.26) was 3 days later than that of F-(33.83). SNP4 was significantly associated with TE (P < 0.05). The average TE of genotype H- (117.31) was 5 eggs more than that of G-(112.24). These results were consistent with the distribution of dominant genotype of New Yangzhou chickens. The haplotype analysis indicated that the main haplotype combinations had great significant effect on AF (P < 0.01). The haplotype Z4 had the earliest AF and Z1 had the latest one. Multiple comparison results showed that the AF of haplotype Z4 differ great significantly with Z1, Z2, Z8 and Z10 (P < 0.01), and differ significantly with Z5 (P < 0.05). No significant difference were observed among the rest haplotype. Haplotype Z8, with the D-F-H genotype, had an earlier AF, laid more eggs and expressed less BD than that of haplotype Z1, which including C-E-G genotype. The result was also consistant with the distribution of dominant genotype of New Yangzhou chickens and genetic effects of single SNP on broodiness and egg production traits, indicating that SNP2, SNP3 and SNP4 may have great genetic effect on chickens' broodiness and egg production traits and could be a good molecular marker.It was concluded that chickens with a latter AF were inclined to express broody behavior and BD had a very significant negative correlation with egg production. Association analysis results showed that the polymorphisms of cPRL-R gene was significantly or great significantly associated with broodiness and egg production traits. We inferred that cPRL-R gene could be an important candidate gene affecting broodiness and egg production traits.