Polygenic expression of somatostatin in rainbow trout, Oncorhynchus mykiss: Evidence of a preprosomatostatin encoding somatostatin-14

Previously we reported the existence of two distinct cDNAs in rainbow trout that encode for separate preprosomatostatins (PPSS), each containing [Tyr( 7), Gly(10)]-somatostatin-14. In the present study, we used rainbow trout t o further characterize the polygenic origin of somatostatins (SSs), a pepti de hormone important in the regulation of growth, development, and metaboli sm of vertebrates. A two-phase rapid amplification of cDNA ends (RACE)-PCR was used for the isolation of selected cDNAs. We amplified and sequenced a ca. 350-bp 3' RACE-PCR fragment. Based upon this sequence we designed a sec ond gene-specific primer for 5' RACE-PCR which yielded a 452-bp fragment. S equence analysis revealed a 745-bp cDNA containing the complete 5'-untransl ated region, a single initiation site 118 bases from the most 5' end, and a single putative polyadenylation site 17 bases from the most. 3' end that w as terminated with a polyadenylated tail. The deduced protein is a 114-amin o acid PPSS molecule that contains a number of putative processing sites, p otentially yielding a 26-amino acid peptide that could be processed further to a 14-amino acid peptide identical in structure to mammalian SS-14. Nort hern analysis revealed that PPSS-I was expressed in the pancreas, stomach, intestine, and brain of rainbow trout. These results suggest a polygenic or igin of SS, possibly resulting from gene duplication events prior to the di vergence of teleosts. (C) 1999 Academic Press.