Comparative analyses of sequence structure, evolution, and expression of four somatostatin receptors in orange-spotted grouper (Epinephelus coioides)

Somatostatins (SSs) and somatostatin receptors (SSTRs) play important roles in the growth, development and metabolism of vertebrates. In the present study, four SSTRs were isolated from orange-spotted grouper (Epinephelus coioides), a coral fish of high commercial value cultivated in Southeast Asia. Phylogenetic tree analysis grouped the four SSTRs as two distinct groups of SSTR1 and SSTR2/3/5. Four SSTRs exhibited high homology across the vertebrates. The expression of four grouper SSTR mRNAs was studied in 11 tissues. The highest level of SSTR1 mRNA was found in forebrain. The mRNAs of SSTR2 and SSTR3 were highly expressed in pituitary, forebrain and liver. The levels of SSTR5 mRNA were low in most tissues except for pituitary and intestine. The expression of four grouper SSTR mRNAs was investigated in seven embryonic stages and five early larval development stages. The highest levels of SSTR1 and 2 mRNAs appeared during hatching, while the highest levels of SSTR3 and 5 mRNAs were found in brain vesicle stage. Intraperitoneal injection of SS14 significantly increased the levels of all four SSTR mRNAs in pituitary and SSTR1, 3 mRNAs in liver in a dose-dependent manner, but no effect on SSTR2 and 5 in liver. These observations contribute to the understanding of the evolution of SSTR family and offer information on structure, distribution and function of fish SSTRs.