Characterization of the cDNA encoding a somatostatin variant in the chicken brain: Comparison of the distribution of the two somatostatin precursor mRNAs

Abstract

Although the existence of two somatostatin variants (SS1 and SS2) has now been demonstrated in the brain of mammals, amphibians, and fish, only one isoform of somatostatin (SS1) has been characterized to date in the brain of birds. Here we report cloning of the cDNA encoding a 101-amino-acid protein (PSS2) that encompasses the somatostatin variant [Pro(2)]somatostatin-14 (SS2) at its C-terminus. Sequence analysis indicated that chicken PSS2 is more closely related to fish PSS2 than to mammalian cortistatin precursors. Northern blot analysis showed that the chicken PSS1 gene is expressed in the central nervous system (CNS) and in the pancreas, whereas the PSS2 gene is expressed only in the CNS and not in peripheral organs. In situ hybridization histochemistry revealed that, in the chicken brain, PSS1 mRNA is more widely distributed than PSS2 mRNA. In particular, PSS1 mRNA expression was found in the hippocampus, the hyperstriatum, the preoptic area, the ventricular hypothalamic nuclei, the optic tectum, and several nuclei of the mesencephalon and rhombencephalon. In contrast, the distribution of PSS2 mRNA was restricted to a few regions of the brain, including the paraolfactory lobe, the paleostriatum, and some nuclei of the mesencephalon and rhombencephalon. The fact that the PSS1 and PSS2 genes are differently expressed in the brain and in peripheral organs indicates that, in chicken, the two somatostatin variants likely exert distinct functions. In particular, the observation that PSS1 mRNA, but not PSS2 mRNA, occurs in the preoptic area and in the ventral hypothalamic nuclei suggests that, of the two somatostatin isoforms, only SS1 acts as a hypophysiotropic factor.

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

“…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.…”

Chromosomal localization of three somatostatin genes in zebrafish. Evidence that the [Pro2]-somatostatin-14 isoform and cortistatin are encoded by orthologous genes

“…In addition to prepro-SS1 (PSS1), a second somatostatin precursor, encoded by a distinct gene, has been characterized in several representative species, including sturgeon (Trabucchi et al 2002), goldfish (also named PSSIII; Lin et al 1999), zebrafish (also named PSS3; Devos et al 2002), lungfish (Trabucchi et al 1999), frog (Tostivint et al 1996), chicken (Trabucchi et al 2003), mouse (de Lecea et al 1997a), rat (de Lecea et al 1996) and human (de Lecea et al 1997a, Fukusumi et al 1997. Peptides derived from this second precursor (named SS2 in non-mammalian species and cortistatin (CST) in mammals) exhibit a more variable structure than SS1 (Spier & de Lecea 2000, Tostivint et al 2004 (Fig.…”

“…In addition, their distributions in the brain are relatively different: while the SS2 gene is expressed in various subdivisions of the brain in all species studied so far (Tostivint et al 1996, Lin et al 1999, Trabucchi et al 1999, 2003, the CST gene is almost exclusively expressed in the telencephalon (de Lecea et al 1996(de Lecea et al , 1997a(de Lecea et al , 1997b. Although the parentage between the PSS2 gene and the PCST gene is supported by phylogenetic analysis (Trabucchi et al 1999, 2003, Devos et al 2002, the orthology of the two genes has not yet been demonstrated. The question of the evolutionary significance of the genes encoding the atypical SSII in catfish and zebrafish is also currently unanswered.…”

Comparative genomics provides evidence for close evolutionary relationships between the urotensin II and somatostatin gene families

“…The recent characterization of URP (6) and the existence of the somatostatin paralogs SS2͞CST (22)(23)(24)(25)(26)(27)(28)(29)(30)(31) provide the opportunity to revisit the possible relationships between the UII and somatostatin gene families. Using a comparative genomics approach, we show that the UII and somatostatin genes belong to the same gene superfamily.…”