Characterization of the cDNA encoding a somatostatin variant in the chicken brain: comparison of the distribution of the two somatostatin precursor mRNAs.
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.
European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and Molecular Neuroendocrinology, INSERM U413, UA CNRS, University of Rouen, 76821 Mont-Saint-Aignan, France.
Michele
M
Trabucchi
Hervé
H
Tostivint
Isabelle
I
Lihrmann
Sabine
S
Blähser
Mauro
M
Vallarino
Hubert
H
Vaudry
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000378:metabolism*; D002645:Chickens / Q000235:genetics*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000302:isolation & purification*; D005260:Female; D015870:Gene Expression; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000235:genetics / Q000302:isolation & purification; D012322:RNA Precursors / Q000378:metabolism*; D017385:Sequence Homology; D013004:Somatostatin / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification; D014018:Tissue Distribution
D018076:DNA, Complementary; D011498:Protein Precursors; D012322:RNA Precursors; D013004:Somatostatin