Polymorphism in genes of growth hormone receptor (GHR) and insulin-like growth factor-1 (IGF1) and its association with both the IGF1 expression in liver and its level in blood in Polish Holstein-Friesian cattle.

BACKGROUND: Polymorphisms in the bovine ghr and igf1 genes. Ghr and igf1 genes have been associated with milk and meat production of cattle. However, the molecular and physiological mechanisms underlying such associations are unknown. The objective of this study was to examine the effects of polymorphisms in 5'-regions of the bovine ghr and igf1 genes on the igf1 gene expression in the liver and on the level of IGF1 in blood of Polish Holstein-Friesian cattle.

METHODS: Individual and combined effects of single nucleotide polymorphisms (SNPs) in the 5'noncoding regions of the bovine igf1 and ghr genes on the IGF1 level in blood and igf1 gene expression in liver were examined. One SNP in the igf1 gene and four SNPs in the ghr gene were analyzed. IGF1 level in blood was measured by radioimmunoassay (RIA) in 211 heifers and bulls of Polish Holstein-Friesian cattle (of Black-and-White type). The igf1 gene expression was measured in livers of bulls carrying different igf1 and ghr genotypes (from three to nine animals per genotype) using real-time reverse transcription-PCR methods with the gapdh gene as a reference.

RESULTS: We showed that C/T transition in the promoter region of the igf1 gene influences the gene expression; relative igf1 expression was higher for animals with the CC genotype than for those with the TT and CT genotypes. TESS analysis showed that C/T transition in the igf1 gene co-localizes with the NF1 transcription factor binding site. Also, the ghr genotype appeared to significantly influence the igf1 gene expression in the liver, and we found the highest expression for the genotypes: RFLP-AluI (AT), RFLP-Fnu4HI(CC), and RFLP-NsiI(GA), and for the combined ghr genotype: AluI(AT)/ Fnu4HI(CC)/NsiI(GA). We discovered a significant association between the igf1 genotype and the IGF1 blood level. The highest IGF1 content in blood serum was found in CC genotype animals (1024 ng/ml) vs 698 ng/m and 859 ng/min in the TT and CT igf1 genotypes, respectively. Moreover, we noticed significant differences between ghr genotypes. The highest blood levels of IGF1 were for the animals carrying the ghr genotypes: RFLP-AluI(AA), RFLP-Fnu4HI(CC), and RFLP-NsiI(AG). Ghr haplotypes also significantly affected the IGF1 blood level. Animals of the combined ghr genotypes AluI(AA)/AccI(CC)/Fnu4HI(CC)/NsiI(AG) and AluI(AA)/AccI(CT)/Fnu4HI (CC)/ NsiI(AG) had a higher IGF1 concentration in blood than other genotype carriers.

CONCLUSIONS: The present results indicate that the effects of polymorphism in the igf1 and ghr genes on cattle milk or meat production traits could be at least partially mediated through their effects on the igf1 gene expression in the liver and the IGF1 level in blood.

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