Polymorphism Of Prolactin Gene And Its Relationship With Prolificacy Of Small Tail Han Sheep

The prolactin (PRL) gene was studied as a candidate gene for the prolificacy of five different sheep breeds, namely small tail Han sheep (142), Hu sheep (40), Texel sheep (36), Dorset sheep (36) and Corriedale sheep (28). Single nucleotide polymorphisms of PRL coding sequence were detected among these five sheep breeds. Furthermore, the genetic relationship between the polymorphism of Prolactin and the prolificacy of Small Tail Han Sheep was explained.The results from the SSCP method showed:(1) In the PCR products of the 2nd pair of primers, single nucleotide polymorphism (SNP) was detected in five different sheep breeds.(2) Among the other PCR products (the 1St, 3rd, 4th, 5th pair of primers), SNP was detected only in Hu Sheep.(3) In the PCR products of the 2nd pair of primers, three genotypes were detected, that is, CC, CD and DD. However, The DD genotype wasn't found in Dorset.(4) By the means of cloning and sequencing, the entire PRL coding sequence were obtained, whose length is 926bp. Compared with the relavant sequence in cattle (Locus: AF426315), their homology of DNA is reach to 98.25%; Moreover, compared with the PRL gene mRNA of sheep (Locus: NM₀01009306), its homology are 98%(Wild genotype) and 97%(Mutational genotype). The homology of DNA between the wild genotype and the mutational genotype is 98.7%(914/926). The entire PRL coding sequence codes 240 amino acids and their homology of amino acid is 98.75%(237/240).(5) There are twelve nucleotide mutations, which were detected by SSCP among the entire PRL coding sequence. Corresponding with these mutations, three mutations of amino acide were found. Namely, Leu→Pro (27th), Ala→Val (149th), Tyr→His (206th).According to the Equilibirum analysis of Hardy-Weinberg for PRL gene in five sheep breeds, the result ofχ² value of primer 2 respectively are 0.6494(Small tail hart sheep), 0.0230 (Hu sheep),4.5325 (Texel sheep),0.2213 (Dorset sheep),0.8245(Corriedale sheep). The results indicated that Texel sheep was significantly biased from Hardy-Weinberg equilibrium (P＜0.05), but Small tail Hart sheep, Hu sheep, Dorset sheep and Corriedale sheep were kept in Hardy-Weinberg equilibrium (P＞0.05).Among Small tail hart sheep with litter size, least squares analysis showed that the litter size of CC genotype had 0.39 (P＜0.05) or 0.98(P＜0.05) lambs more than those with genotype CD or DD; the litter size of CD genotype had 0.59 (P＞0.05) lambs more than those with genotype DD.Data obtained in this expriment indicated that the polymorphism of the wild genotype of PRL gene is probably associated with lower expression of PRL, which will promote the reproductivity of sheep, in Small tail han sheep.