Molecular cloning, tissue distribution, and ontogeny of mRNA expression of growth hormone in orange-spotted grouper (Epinephelus coioides).

A full-length cDNA encoding for growth hormone (GH) was cloned from orange-spotted grouper (Epinephelus coioides) pituitary using reverse transcription and rapid amplification of cDNA ends (RACE). The GH precursor cDNA consists of 956 bp in size with a 85 bp 5'-untranslated region and 259 bp 3'-untranslated region. The 612 bp open reading frame encodes a 204 amino acid (aa) protein, which represents the precursor of grouper GH composed of a 17 aa signal peptide followed by a 187 aa mature GH polypeptide. The sequence of grouper GH shares 95% aa sequence homology with GH reported in gilthead sea bream (Sparus aurata), and it also exhibits structural features highly homologous to GH reported in other fish species in the domains representing conserved motifs of GH polypeptides. A single GH transcript of 0.93 kb in size has been detected with Northern blot in the pituitary. Using semi-quantitative PCR approach, dominant PCR products were observed in grouper pituitary, while less PCR products were detected in the brain, spleen, and ovary. The expression of GH mRNA could be detected in 1dph larvae, after that a significant increase in PCR products was found in 5-day-old fish larvae followed by a drop to very low levels in 15-day-old fish larvae. A second rise was then observed in 25-day-old grouper larvae. These findings suggest that in grouper GH mRNA expression can be detected in day 1 post-hatching larvae, and the GH present in eggs and larvae may play a key role in early development of grouper, especially during the process of metamorphosis of fish larva.