Cloning of the growth hormone receptor and its muscle-specific mRNA expression in black Muscovy duck (Cairina moschata).

The cDNA sequence of the growth hormone receptor (GHR) from the black Muscovy duck was obtained and compared to the mRNA expression of growth hormone (GH) in the breast and leg muscles during 2-13 weeks of age using quantitative RT-PCR. The cDNA sequence of the Muscovy duck GHR gene is 1903 bp in length, with an 1830 bp coding region that encodes 609 amino acids. It exhibits > 92.9% homology with the poultry GHR cDNA and amino acid sequences. Overall, GHR mRNA expression was the highest at 2 weeks and the lowest at 13 weeks of age, exhibiting different profiles in different muscles. In the breast muscles, the GHR mRNA level declined sharply at 2-4 weeks, maintained at a plateau at 4-10 weeks and decreased slightly at 10-13 weeks. In the leg muscles, a gradual and slow decrease was observed during the whole period of 2-13 weeks. Robust extra-pituitary GH mRNA expression was detected in the muscles and the expression profile was highly correlated with that of GHR mRNA, in contrast to the inverse correlation between the pituitary GH and tissue GHR levels shown previously. These data suggest that the locally synthesised GH in the muscles, rather than the pituitary GH, is more closely associated with GHR and may be more critical for the regulation of muscle growth and contribute to the tissue-specific effects of GH.