Rapid communication: diallelic single-stranded conformational polymorphism detected in the bovine prolactin gene

DNA polymorphism of 5' flanking region of prolactin gene and its association with litter size in sheep

A single nucleotide polymorphism of 5' flanking region of the prolactin gene was investigated in both high prolificacy breeds (Small Tail Han and Hu sheep) and low prolificacy breeds (Dorset and Suffolk sheep) using polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP). The results indicated that two genotypes (AA and AB) were detected in Small Tail Han sheep (n = 239), only one genotype (AA) was detected in Hu (n = 40), Dorset (n = 50) and Suffolk sheep (n = 39). The mutant homozygous genotype (BB) was not detected in four sheep breeds. In Small Tail Han sheep (n = 239), the frequency of genotypes AA and AB was 0.91 and 0.09, the frequency of the A and B alleles was 0.95 and 0.05, respectively. The fitness tests showed that the Small Tail Han sheep population was in Hardy-Weinberg equilibrium. Sequencing revealed a mutation (G-->T) at the position 63 bp of the 5' flanking region of prolactin gene in AB genotype compared with AA genotype in Small Tail Han sheep. The Small Tail Han ewes with AB genotype had 0.83 (p < 0.05) lambs more than those with AA genotype. These results preliminarily showed that the prolactin locus is either a major gene that influences the high prolificacy in Small Tail Han sheep or is in close linkage with such a gene.

Effect of new SNP within bovine prolactin gene enhancer region on expression in the pituitary gland

A new single nucleotide polymorphism was revealed using PCR-SSCP and sequencing methods within the bovine prolactin distal promoter region described as a functional enhancer. The A-->G transition at position -1043 abolishes the recognition site for Hsp92II restriction endonuclease, allowing for PCR-RFLP genotyping. The application of real-time PCR revealed that the prolactin gene expression level in the pituitary was higher in cattle with the AA genotype than in those with the GG genotype. EMSA analysis, however, showed increased nuclear protein binding to the sequence variant with G, suggesting a possible inhibition event, in which the transcription factors Pit1, Oct1, and YY1 could be involved.