Polymorphism Of Progesterone Receptor Gene And Steroid 21-Hydroxylase Gene And Their Relationship With Litter Size Of Sheep

The progesterone receptor(PGR)gene and steroid 21-hydroxylase (CYP21) gene were studied as candidate genes for the prolificacy in sheep in the present study by techniques of PCR single-strand conformational polymorphism (PCR-SSCP),restriction endonuclease and gene cloning. Samples used in this research represented for high prolificacy breeds (Small Tail Han Sheep—205 in total), medium prolificacy breeds (Hu Sheep—49 in total) and low prolificacy breeds (Dorset sheep and Texel Sheep—80 in total) were obtained from Shandong Jiaxiang Farm, Zhejiang Yuhang Hu Sheep Farm and Beijing Gaote Farm respectively.(1)As for PGR gene, fifteen pairs of primers were designed to detect single nucleotide polymorphisms of exon 1 to exon 9 of PGR gene in high prolificacy breeds (Small Tail Han Sheep) ,medium prolificacy breeds(Hu Sheep) and low prolificacy breeds (Dorset sheep and Texel Sheep) by PCR-SSCP according to the sequence of bovine PGR gene. Only the products amplified by primer P9 displayed polymorphism. For primer P9, three genotypes (AA, AG and GG) were detected in Small Tail Han, Hu and Dorset sheep, and two genotypes (AA and AG) in Texel sheep. Sequencing revealed one mutation (217A→G) of PGR gene in the genotype GG in comparison to the genotype AA, and this mutation did not cause any amino acid changes. The ewes with genotype GG or AG had 0.97 (P<0.05) and 0.64 (P<0.05) lambs more than those with genotype AA, and the difference of the litter size between GG and AG genotypes was non-significant (P>0.05) in Small Tail Han sheep.(2)As for the steroid 21-hydroxylase (CYP21) gene, ten pairs of primers were designed to detect single nucleotide polymorphisms of exons 1～10 of CYP21 gene in high prolificacy breed (Small Tail Han sheep), medium prolificacy breed (Hu sheep) and low prolificacy breeds (Dorset and Texel sheep) by PCR-SSCP and digestion with restriction endonucleases according to the sequence of bovine CYP21 gene. Only the products amplified by primer P8 displayed polymorphisms. For primer P8, two genotypes (AA and AB) were detected in Small Tail Han, Hu and Dorset sheep by digesting the PCR products with HinPⅠ1, and only one genotype (AA) was found in Texel sheep; meanwhile, two genotypes (CC and CD) were detected in all the four sheep breeds by digesting the PCR products with BcnⅠ. Sequencing revealed one mutation (2340A→G) of CYP21 gene in the genotype AB in comparison to the genotype AA; another mutation (2376G→A) of CYP21 gene in the genotype CD in comparison to the genotype CC, and these mutations did not cause any amino acid changes. The Small Tail Han sheep with genotype AB had 0.96 (P<0.05) lambs more than those with genotype AA; and the difference of the litter size between genotypes CC and CD was not significant (P>0.05). These results preliminarily indicated that the CYP21 gene and PGR gene are potential DNA markers for improving litter size in sheep.