Growth hormone receptor gene expression in the skeletal muscle of normal and double-muscled bovines during foetal development.

The expression of the growth hormone receptor (GHR) gene was investigated in semitendinosus muscle during bovine foetal development in both normal and double-muscled Charolais foetuses which differ with respect to muscle development. Northern-blot analysis of foetal muscle RNA preparations with a GHR cDNA probe identified the 4.5 kb GHR mRNA as early as 130 days post-conception. In double-muscled animals, the expression of GHR mRNA increased from 130 to 210 days of gestation while it stayed stable in normal ones. It was significantly higher (P < 0.05) in double-muscled foetuses compared to normal ones from the second third of gestation. Northern-blot analysis of foetal muscle RNA preparations from both genotypes with a beta-actin cDNA probe, revealed lower beta-actin gene expression in double-muscled foetuses than in normal ones, suggesting a delay in the differentiation of muscle cells. In situ hybridisation revealed the localisation of specific GHR mRNA in muscle cells at all gestation stages analysed (130, 170, 210 days post-conception) but not in connective tissue surrounding the muscle cells. At the adult stage, the hybridisation signal was also very high and observed in muscle cells only. These results show the ontogeny of GHR mRNA in bovine muscle and demonstrate a difference between normal and double-muscled animals.