Cloning Of PRL Gene Sequence And Its Polymorphism Association With Egg-laying Traits In Yangzhou Geese

Prolactin (PRL), also known as Luteotropin or Lactogen, is a protein hormone. It can inhibit pituitary gonadotropin secretion and stop avian follicular development, eventually leading to cessation of the egg laying, then it plays an importment role in the laying performance of poultry and is often seen as an important candidate gene which influencs avian broodiness and egg performance. Therefore, this experiment was conducted to clone PRL gene sequence. The single nucleotide polymorphism(SNP) sites of PRL gene sequence were detected by PCR-SSCP technique in Yangzhou geese and the correlation, between the polymorphism of PRL gene sequence and egg-laying traits, were analysed. The results are as follows:1. The sequence of 5'FR, exon1, intron1, exon2, intron2, exon3, intron3, exon4, intron4, exon5 and 3'FR of PRL gene were amplified from Yangzhou Geese genomic DNA by PCR. The PCR products were subcloned, whose length were respectively 671bp, 67bp, 1495bp, 182bp, 413bp, 108bp, 1389bp, 180bp, 1894bp, 418bp, 29bp. The total sequence length was 6846bp. The GenBank accession number of the nucleotide sequence of Yangzhou Geese PRL gene is GU984377.2. One TATA fragment and fourteen potential transcription factor binding sites were found in 5'FR. As the amplified 3'flanking region is short, so there is no AATAAA sequence found. Homology analysis reveals that the sequence of PRL gene CDS of Yangzhou Geese is contrasted with that of Magang geese, ducks, parrots, chickens and the homologies are respectively 99.7%, 98.6%, 92.2%, 93%. The homologies of the amino acid sequence of PRL compared with those of Magang geese, ducks, parrots, chickens are respectively 99.6%, 98.7%, 92.2%, 93.9%.3. In this experiment, nine pairs of primers were designed to screen the population of 197 Yangzhou Geese by PCR-SSCP, and the correlation, between the polymorphism of PRL gene sequence and laying performance, was analysed. The results indicated that: (1) There was a GA insertion/deletion in the intron 2 (I.e. in the transcriptional start site downstream 1776, 1777 sites) of PRL gene and the mutation led to 3 genotypes (AA, BB and AB). The chi-square test showed that the distribution of the three genotypes inconsistent with the Hardy-Weinberg equilibrium. Least square analysis on polymorphism of intron 2 and its relationship with the laying performance showed that egg production and the age at first egg of the three genotypes had no significant effect of genotype, but least square means of different genotypes corresponding relations were BB﹥AA﹥AB. (2) There was a mutation G→T in the start codon upstream 10 site of PRL gene, which resulted in 2 genotypes CC and DD. The chi-square test suggested that Yangzhou geese population were in the state of Hardy-Weinberg disequilibrium at the 5'flanking region in this Yangzhou geese population. Analysis on polymorphism of the 5'flanking region and its relationship with the laying performance showed that the average egg production of CC genotype geese was significantly higher than that of DD genotype geese( P=0.001) and the age at first egg of CC genotype geese was also significantly earlier than that of DD genotype geese(P=0.001)in an ovipository cycle.