Abstract:In this article we report the molecular cloning and characterization of a nonmammalian myostatin (growth and differentiation factor-8, MSTN) homolog from the orange spotted grouper (Epinephelus coioides) by polymerase chain reaction (PCR) cloning. The grouper MSTN gene consists of two introns [Intron I (363 bp) and Intron II (811 bp)] flanked by three exons [Exon I (379 bp), Exon II (371 bp) and Exon III (381 bp)]. A full-length cDNA clone (2608 bp) of the MSTN gene (GenBank DQ493889, nucleotide sequence in the coding region identical to GeneBank AY856860) was also isolated. This cDNA encodes a polypeptide of 376 amino acid residues that showed 25% to 96% homology with MSTNs of molluscan, teleostean, avian, and mammalian species. Phylogenetic analysis of the grouper MSTN polypeptide confirmed the evolutionary relationships of this MSTN with other known MSTNs. Results of reverse transcription (RT)-PCR analysis of the total RNA extracted from different tissues revealed that MSTN gene is expressed not only in the skeletal muscle, but also in other tissues. MSTN mRNA was also detected in different embryonic developmental and larval stages. Because the tissue-specific expression of MSTN gene in grouper is different from that in mammals, it might suggest that MSTN gene may possess additional functions other than regulating muscle growth in fish.