Effect of a single nucleotide polymorphism in the growth hormone secretagogue receptor (GHSR) gene on growth rate in pigs.

The growth hormone secretagogue receptor (GHSR) gene controls growth hormone (GH) release by inducing a strong stimulatory effect on the endogenous ligand, ghrelin. In this study, we examined the possible role of GHSR in the growth traits of four pig breeds, namely Tibetan pigs (n=45), Diannan small-eared pigs (n=40), Yorkshire pigs (n=45), and New Huai pigs (n=122). Single nucleotide polymorphisms (SNPs) in these pigs were identified by polymerase chain reaction (PCR) sequencing and genotyping was performed using PCR-restriction fragment length polymorphisms (PCR-RFLPs). A SNP (C/A) named C-1595A (the "C" allele), which is located 1595bp upstream of the initiation codon of the GHSR gene, was found at a higher frequency in the fast-growing Yorkshire pigs than in the slow-growing Tibetan and Diannan small-eared pigs. In preliminary assays, the C-1595A genotype was found to be associated with growth traits in New Huai pigs. Quantitative real-time PCR and western blotting assays were used to measure the levels of GHSR1a, a functionally active form of the GHSR protein, in the tissues of the growth axis. The estimated levels of mRNA and protein in pituitary and liver tissues were significantly higher in Yorkshire pigs than in Diannan small-eared or Tibetan pigs (P<0.05). The results indicated that GHSR had a positive influence on the growth rate of pigs and suggested that the C-1595A SNP could be of value as a molecular marker for improving the production performance of pig breeds.