Genetic Effects Of Nucleotide Variations In Chicken PRL, PRLR, And POU1F1 Genes On Reproductive Traits And POU1F1 On Growth Rate

Prolactin (PRL), secreted from anterior pituitary, plays extensive roles in reproduction, growth, and immunology in animals. In avian, PRL is especially crucial for reproduction traits such as broodiness and thus for egg production. It has been well established that PRL is closely related to the onset and maintenance of broody behavior. Based on the understanding of physiological pathway for broodiness, three genes related to broodiness including PRL, PRL receptor (PRLR), and pituitary-specific transcription factor (POU1F1)-encoding genes were selected as candidates to screen the genomic variation by means of PCR-SSCP protocol and analyze the association with chicken broodiness and other target traits.A 24-bp insertion/deletion (+/—) mutation, 5'-ACAAGAAGAGACAAGACAAGGAAG-3', was identified in the promotor (-377³54bp, GenBank accession no. AB011438) of PRL gene. The genotypic distribution profile of PRLpro2 varied among breeds or lines with White Leghorn only +/+ and Beijing-you or Silkies —/—, while +/+, +/—, and —/— existed in other Chinese breeds, brown layers, and broilers. Studies on the Blue-shell chickens under floor condition showed that the PRLpro2 deletion (—) allele was significantly (p<0.05) associated with broody traits including nesting days, broody days, repeats of broody cycles, duration of broodiness, and broody frequency (%). Further investigation in dwarf layers and Blue-shell chickens under cage system indicated that PRLpro2 did not influence egg production traits including age at first egg, body weight at first egg, weight of first egg, egg weight at 40 wks, and egg number at 40 wks or 300 d (p>0.05).Nucleotide variations were identified in exon 3 and 6 of PRLR gene respectively. A single nucleotide polymorphism (SNP), A9026G (GenBank accession no. AY237377), in exon 3 of PRLR was also detected, which led to a nucleotide transition in the 5'-untranslated region (5'-UTR) of PRLR cDNA. Two SNP, T14771C and G14820A (GenBank accession no. AY237376), were detected in exon 6 of the PRLR. The T14771C transition led to an amino acid variation, Leu340Ser, in PRLR, whereas the G14820A transition was a synonymous mutation. For Blue-shell and Silkies under cage system, PRLR3 and PRLR6 were not significantly associated with broody traits (P>0.05). For Silkies without broody occurrence in the first half egg laying cycle, PRLR3 and PRLR6 did not influence egg production traits including age at first egg, weight of first egg, egg weight at 40 wks, and egg number at 40 wks (P>0.05).A nucleotide transversion in exon 6 of POU1F1 gene from adenine (A) to thymidine (T) at position 980 of the open reading frame of the POU1F1 cDNA (GenBank accession no. AF029892) was identified. This nucleotide transversion results in an alteration of codon 299 from AAC to ATC, which leads to a change from asparagine (Asn) to isoleucine (Ile) in the POU domain of POU1F1. POU1F1₆ did not significantly influence broody and egg production traits, as well as plasma PRL level at 20, 30, and 40 wks of age (P>0.05), which suggested that the POU1F1₆ polymorphism may not affect the expression of PRL gene. Studies on cross combinations and Beijing-you chicken (male) revealed apositive relationship between genotype AA and early body weight (p<0.05). For further confirmation of the association, a cross between heterozygous genotypes, AT (?) × AT (?), was carried out in Shou-guang chicken to generate a Mendelian segregating population. Results showed that body weight at each stage did not exhibit difference (P>0.05) among genotypes in female chickens. For female chickens, however, the body weight at 14 wks of age for AA was greater (p<0.05) than that for TT. Therefore, P0U1F1₆ is an effective molecular marker that can be used in MAS program for early growth rate in chicken, especially for male chickens.The better understanding of the mechanism of broodiness stands great significance not only for avian genetics, behavior, and endocrinology, but also for the acceleration of poultry breeding progress against broodiness to enhance egg producti...