Single Nucleotide Polymorphisms In Chicken ESRα Gene And Association With Early Egg Production

The estrogen receptor (ESR) is a member of the nuclear receptor superfamily, including two subunits, estrogen receptor alpha (ESRα) and beta (ESRβ). ESR is a ligand-activated transcription factor containing several biding site in animals. ESR influences the expression and regulation of estrogen gene in the tissues, and therefore, affects the development of follicle in the reproduction cycle of female vertebrate.ESRαgene was selected as a candidate to screen the genomic variation by means of PCR-SSCP, and the association of ESRαgene polymorphisms with early egg production traits was analyzed. According to the sequence published (chicken FSHβgene :GenBank accession No. NC₀06090), fourteen primers were designed and used to amplify the 5'flanking regulation region and all exons of ESRα. The WenChang chicken (WCh, n=150), a Chinese local breed, was studied in the study, with the Babcock (n=99) , an egg-type chicken, as a reference population.The SSCP detection showed that no polymorphism was found in all translated regions of ESRαgene in the two populations. The genotype in exon 5 of WCh chicken was different from Babcock. Sequencing of this fragment revealed an A→G transition in Babcock which did not led to amino acid variation in exon 5, and a T→C transition in WC chicken which resulted in the replacement of Leu by Ser, compared with the sequences in GenBank.Two genotypes were detected in 5'flanking regulation region of WC chickens. Four SNPs, A-34G, T-76C, T-79C, C-102T, were identified. The frequency of allele C and D were 0.897, 0.103, respectively.χ² test suggested that the population were in the state of Hardy-Weinberg equilibrium at the two sites. Association analysis of early egg production traits showed that there were no differences between genotypes CC and CD in egg production traits of WCh chicken, including age at first egg, weight of first egg, egg weight at 40 weeks, and egg number at 40 weeks (P>0.05).The intron 1 fragment of ESRαgene was polymorphismic. Sequencing revealed two nucleotide variations, T122C and C169T, in Babcock. The frequency of genotypes MM, MN, and NN were 0.151, 0.586, and 0.263, respectively.χ² test suggested that the population were in the state of Hardy-Weinberg equilibrium at the two sites. Three SNPs, T122C, A155G, C169T were identified in WCh chicken. Furthermore, A155G created 6 extra enzyme cutting sites, XbaI, BfaI, Bgâ…¢, BstYI, Sau3AI, and DpnI, at 150～160bp position, identical to the enzyme cutting sites at 130～140bp position in intron1. The frequencies of genotype EE, EF, FF were 0.187, 0.580, and 0.233, respectively.χ² test suggested that the WCh chickens were in the state of Hardy-Weinberg equilibrium at the two sites. The egg numbers at 40 weeks of genotype EF and FF were higher than that of EE(P<0.01); moreover, there was significant difference between EF and FF (P<0.05). The results suggested that the allele F was the favorable and could be a novel molecular marker for early egg production traits.