Polygenic expression of somatostatin in the sturgeon Acipenser transmontanus: Molecular cloning and distribution of the mRNAs encoding two somatostatin precursors

Abstract

The sequence of somatostatin-14 (SS1) has been strongly preserved throughout the evolution of vertebrates from agnathans to mammals. In Acipenseridae (sturgeons), two isoforms of somatostatin have been characterized to date: somatostatin-14 has been identified from the gastrointestinal tract of the pallid sturgeon Scaphirhynchus albus and [Pro(2)]somatostatin-14 has been identified from the pituitary of the Russian sturgeon Acipenser gueldenstaedti. In the present study, we report the cloning of two distinct somatostatin cDNAs from the brain of the sturgeon Acipenser transmontanus. One of the cDNAs encodes a 116-amino acid protein (PSS1) that contains the SS1 sequence at its C-terminal extremity and, thus, is clearly orthologous to other vertebrate PSS1. The other cDNA encodes a 111-amino acid protein that contains the somatostatin variant [Pro(2)]somatostatin-14 at its C-terminal extremity. This second precursor exhibits more than 67% identity with the recently characterized lungfish PSS2 and goldfish PSS2. Reverse transcriptase-polymerase chain reaction analysis revealed that PSS1 is expressed in the central nervous system, the pancreas and the gut, whereas PSS2 is found in the central nervous system but not in the digestive system. In situ hybridization histochemistry showed that the PSS1 and PSS2 genes are differently expressed in numerous regions of the sturgeon brain. Interestingly, PSS1 and PSS2 mRNAs are present in the hypothalamus suggesting that, in sturgeon, both SS1 and SS2 may play hypophysiotropic functions. The PSS2 mRNA but not the PSS1 mRNA was found in the intermediate lobe of the pituitary. The present data demonstrate that two somatostatin genes are expressed in the sturgeon brain: one precursor generates somatostatin-14 and the other one gives rise to a [Pro(2)]somatostatin-14 variant, which is orthologous to goldfish, lungfish, and frog SS2.

Molecular and expression characterization of two somatostatin genes in the Chinese sturgeon, Acipenser sinensis

“…SS genes displayed different expression levels in the brain of lungfish (Trabucchi et al, 1999), white sturgeon (Trabucchi et al, 2002), goldfish (Yunker et al, 2003), grouper (Ye et al, 2005) and Siberian sturgeon (Adrio et al, 2008). In this study, the two AsSS genes expressed in all subdivisions of brain and pituitary with different expression levels (Fig.…”

“…The strong conservation of SS2-derived SS 24 suggests that it may represent a functionally active peptide. The [Pro 2 ]-SS 14 product of AsSS2 was identical with that of SS2 from white sturgeon and lungfish, and only differs in the Thr 13 residue compared with [Pro 2 , Met 13 ]-SS 14 of frog (Lin et al, 1999;Trabucchi et al, 2002). About ten aa in the CST peptide are homologous to those of fish [Pro 2 ]-SS 14 , especially with the same Gly 2 →Pro 2 substitution.…”

“…SS1 and SS3s were expressed in the pituitary of rainbow trout (Alexander et al, 2001). In white sturgeon, SS2 but not SS1 mRNA was found in the pars intermedia of the pituitary (Trabucchi et al, 2002). Goldfish SS1 and SS3, but not SS2 were detected in cultured pituitary cells (Yunker et al, 2003).…”

“…The monobasic cleavage site at Arg 64 which can be used to generate SS-28 has been also fully preserved in all Osteichthyii (Tostivint et al, 2004). Although it is thought that this monobasic cleavage site is generally not used in teleosts (Conlon et al, 1997), the primary structure of the N-terminal segment of AsSS-28 is conserved to that of the white sturgeon (Trabucchi et al, 2002) and with only one substitution (Gly 4 →Ser 4 ) between Chinese sturgeon and human SS-28 ( Fig. 2A).…”

“…The somatostatin 1 (SS1) gene has been cloned from all vertebrate classes from agnathans to mammals (Conlon et al, 1997;Lin et al, 1998;Tostivint et al, 2004). Somatostatin 2 (SS2), the duplicated gene of SS1 by a segment/chromosome duplication, has been characterized in numerous vertebrates, including frog (Vaudry et al, 1992;Tostivint et al, 1996), rat (de Lecea et al, 1996), human (de Lecea et al, 1997;Fukusumi et al, 1997), mouse (de Lecea et al, 1997), chicken (Trabucchi et al, 2003), lungfish (Trabucchi et al, 1999), goldfish (Lin et al, 1999), white sturgeon (Trabucchi et al, 2002), grouper (Ye et al,20 05), zebrafish (GenBank accession No. BG307388), opossum ((DS)ENSMODG00000002663), and pufferfish (GenBank accession No.…”