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

Impact of gene/genome duplications on the evolution of the urotensin II and somatostatin families

The present review describes the molecular evolution of two phylogenetically related families of neuropeptides, the urotensin II (UII) and somatatostatin (SS) families. The UII family consists of four paralogous genes called UII, URP, URP1 and URP2 and the SS family is composed of six paralogous genes named SS1, SS2, SS3, SS4, SS5 and SS6. All these paralogs are present in teleosts, while only four of them, UII, URP, SS1 and SS2 are detected in tetrapods. Comparative genomics showed that most of these genes, namely UII, URP, URP1 and URP2 on the one hand and SS1, SS2 and SS5 on the other hand arose through the 2R. In contrast, the teleost-specific 3R had a much more moderate impact since it only concerned the UII and SS1 genes, which once duplicated, generated a second UII copy and SS4, respectively. The two remaining genes, SS3 and SS6, arose through tandem duplications of the SS1 and SS2 genes respectively, probably in the stem lineage of actinopterygians, before the emergence of teleosts. The history of the UII and SS families has also been marked by massive gene lost, both in tetrapods and in teleosts, but only after the 3R in this latter lineage. Finally, ancestral UII and SS genes are thought to have arisen through tandem duplication of a single ancestral gene, largely before the 1R. An important challenge for the future will be to understand the physiological significance of the molecular diversity of these two families.

Molecular cloning of the cDNAs encoding three somatostatin variants in the dogfish (Scylorhinus canicula)

It has been recently shown that the somatostatin gene family was likely composed of at least three paralogous genes in the common ancestor of all extant jawed vertebrates. These three genes, namely SS1, SS2 and SS5, are thought to have been generated through the two rounds of whole-genome duplications (2R) that took place early during the vertebrate evolution. In the present study, we report the cloning of three distinct somatostatin cDNAs from the dogfish Scylorhinus canicula, a member of the group of cartilaginous fish. We decided to call these cDNAs, at least provisionally, SSa, SSb and SSc, respectively. Two of them, SSa and SSb, encode proteins that both contain the same tetradecapeptide sequence at their C-terminal extremity (AGCKNFFWKTFTSC). This putative peptide is identical to that generated by the SS1 gene in other vertebrate species. The last cDNA, SSc, encodes a protein that contains at its C-terminal extremity the same peptide sequence as that generated by the SS2 gene in teleosts (APCKNFFWKTFTSC). Phylogenetic analysis showed that the SSa and SSc genes likely correspond to the dogfish counterparts of the SS1 and SS2 genes, respectively. In contrast, the phylogenetic status of the SSb gene is less clear. Several lines of evidence suggest that it could correspond to the SS5 gene, but this view will need to be confirmed, for example by synteny analysis. Finally, RT-PCR analysis revealed that SSa, SSb and SSc genes are differentially expressed in dogfish tissues, suggesting that the corresponding peptides may exert distinct functions.

Glucose and lipid metabolism in the pancreas of rainbow trout is regulated at the molecular level by nutritional status and carbohydrate intake

Glucose and lipid metabolism in pancreatic islet organs is poorly characterized. In the present study, using as a model the carnivorous rainbow trout, a glucose-intolerant fish, we assessed mRNA expression levels of several genes involved in glucose and lipid metabolism (including ATP-citrate lyase; carnitine palmitoyltransferase-1 isoforms, CPT; the mitochondrial isoform of the phosphoenolpyrutave carboxykinase, mPEPCK and pyruvate kinase, PK) and glucosensing (glucose transporter type 2, Glut2; glucokinase, GK and the potassium channel, K(ATP)) in Brockmann bodies. We evaluated the response of these parameters to changes in feeding status (food deprived vs. fed fish) as well as to changes in the amount of carbohydrate (dextrin) in the diet. A general inhibition of the glycolytic (including the glucosensing marker GK) and β-oxidation pathways was found when comparing fed versus food-deprived fish. When comparing fish feeding on either low- or high-carbohydrate diets, we found that some genes related to lipid metabolism were more controlled by the feeding status than by the carbohydrate content (fatty acid synthase, CPTs). Findings are discussed in the context of pancreatic regulation of glucose and lipid metabolism in fish, and show that while trout pancreatic metabolism can partially adapt to a high-carbohydrate diet, some of the molecular actors studied seem to be poorly regulated (K(ATP)) and may contribute to the glucose intolerance observed in this species when fed high-carbohydrate diets.

Evolutionary history of the somatostatin and somatostatin receptors

Somatostatin and its receptors have a critical role in mammalian growth through their control pattern of secretion of growth hormone, but the evolutionary history of somatostatin and somatostatin receptors are ill defined. We used comparative whole genome analysis of Danio rerio, Carassius auratus, Xenopus tropicalis, Gallus gallus, Monodelphis domestica, Homo sapiens, Sus scrofa, Bos taurus, Mus musculus, Rattus norvegicus, Canis lupus familiaris, Ovis aries, Equus caballus, Pan troglodytes and Macaca mulatto to identify somatostatin and somatostatin receptors in each species. To date, we have identified a minimum of two genes of somatostatin and five somatostatin receptor genes in mammalian species with variable forms. We established a clear evolutionary history of the somatostatin system and traced the origin of the somatostatin system to 395 million years ago (MYA), identifying critical steps in their evolution.

New insight into the molecular evolution of the somatostatin family

The present review describes the molecular evolution of the somatostatin family and its relationships with that of the urotensin II family. Most of the somatostatin sequences collected from different vertebrate species can be grouped as the products of at least four loci. The somatostatin 1 (SS1) gene is present in all vertebrate classes from agnathans to mammals. The SS1 gene has given rise to the somatostatin 2 (SS2) gene by a segment/chromosome duplication that is probably the result of a tetraploidization event according to the 2R hypothesis. The somatostatin-related peptide cortistatin, first identified in rodents and human, is the counterpart of SS2 in placental mammals. In fish, the existence of two additional somatostatin genes has been reported. The first gene, which encodes a peptide usually named somatostatin II (SSII), exists in almost all teleost species investigated so far and is thought to have arisen through local duplication of the SS1 gene. The second gene, which has been characterized in only a few teleost species, encodes a peptide also named SSII that exhibits a totally atypical structure. The origin of this gene is currently unknown. Nevertheless, because the two latter genes are clearly paralogous genes, we propose to rename them SS3 and SS4, respectively, in order to clarify the current confusing nomenclature. The urotensin II family consists of two genes, namely the urotensin II (UII) gene and the UII-related peptide (URP) gene. Both UII and URP exhibit limited structural identity to somatostatin so that UII was originally described as a "somatostatin-like peptide". Recent comparative genomics studies have revealed that the SS1 and URP genes, on the one hand, and the SS2 and UII genes, on the other hand, are closely linked on the same chromosomes, thus confirming that the SS1/SS2 and the UII/URP genes belong to the same superfamily. According to these data, it appears that an ancestral somatostatin/urotensin II gene gave rise by local duplication to a somatostatin ancestor and a urotensin II ancestor, whereupon this pair was duplicated (presumably by a segment/chromosome duplication) to give rise to the SS1-UII pair and the SS2-URP pair.

Polygenic expression of somatostatin in orange-spotted grouper (Epinephelus coioides): molecular cloning and distribution of the mRNAs encoding three somatostatin precursors

In the present study, three preprosomatostatin (PSS) cDNAs were characterized from hypothalamus of orange-spotted grouper Epinephelus coioides. The first cDNA encodes a 123-amino acid protein (PSSI) that contains the SS14 sequence at its C-terminal extremity and that is identical to that of PSSI of human and other vertebrates. The second cDNA encodes a 127-amino acid protein (PSSII) that contains the SS28 sequence with [Tyr7, Gly10]-SS14 at its C-terminus. The third cDNA encodes a 110-amino acid protein (PSSIII) that contains the somatostatin variant [Pro2]-SS14 at its C-terminal extremity. All these three PSS mRNAs were expressed in brain and pituitary with different mRNA levels. In peripheral tissues, PSSII was more widely distributed than PSSI and PSSIII. High mRNA levels of PSS were found in stomach, intestine and ovary. PSS mRNAs were detected throughout embryogeny and early larval development. Its levels increased with the embryonic development and maintained a higher level during larva developing. The mRNA distribution suggests that the three grouper PSS products play important physiological functions in adult fish as well as in cell growth and organ differentiation in embryo and larva development.

Regulation of somatostatins and their receptors in fish

The multifunctional nature of the somatostatin (SS) family of peptides results from a multifaceted signaling system consisting of many forms of SS peptides that bind to a variety of receptor (SSTR) subtypes. Research in fish has contributed important information about the components, function, evolution, and regulation of this system. Somatostatins or mRNAs encoding SSs have been isolated from over 20 species of fish. Peptides and deduced peptides differ in their amino acid chain length and/or composition, and most species of fish possess more than one form of SS. The structural heterogeneity of SSs results from differential processing of the hormone precursor, preprosomatostatin (PPSS), and from the existence of multiple genes that give rise to multiple PPSSs. The PPSS genes appear to have arisen through a series of gene duplication events over the course of vertebrate evolution. The numerous PPSSs of fish are differentially expressed, both in terms of the distribution among tissues and in terms of the relative abundance within a tissue. Accumulated evidence suggests that nutritional state, season/stage of sexual maturation, and many hormones [insulin (INS), glucagon, growth hormone (GH), insulin-like growth factor-I (IGF-I), and 17beta-estradiol (E2)] regulate the synthesis and release of particular SSs. Fish and mammals possess multiple SSTRs; four different SSTRs have been described in fish and several of these occur as isoforms. SSTRs are also wide spread and are differentially expressed, both in terms of distribution of tissues as well as in terms of relative abundance within tissues. The pattern of distribution of SSTRs may underlie tissue-specific responses of SSs. The synthesis of SSTR mRNA and SS-binding capacity are regulated by nutritional state and numerous hormones (INS, GH, IGF-I, and E2). Accumulated evidence suggests the possibility of both tissue- and subtype-specific mechanisms of regulation. In many instances, there appears to be coordinate regulation of PPSS and of SSTR; such regulation may prove important for many processes, including nutrient homeostasis and growth control.

Regulation of pancreatic somatostatin gene expression by insulin and glucagon

Rainbow trout were used as a model system to study the effects of insulin and glucagon on the expression of preprosomatostatins (PPSS). We previously showed that the endocrine pancreas of trout contains three mRNAs that encode for distinct somatostatin-containing peptides: PPSS I, which contains somatostain-14 (SS-14) at its C-terminus, and two separate PPSS IIs, PPSS II' and PPSS II'', each containing [Tyr7, Gly10]-SS-14 at their C-terminus. Rainbow trout injected (100 ng/g body weight) with insulin displayed elevated expression of PPSS II' and PPSS II'' mRNAs. Glucagon-injected (100 ng/g body weight) animals displayed elevated pancreatic expression of all PPSS mRNAs compared to saline-injected control animals. Insulin directly stimulated the expression of pancreatic PPSS II' and PPSS II'' mRNAs in vitro in a dose-dependent manner in the presence of 4mM glucose. Glucagon, in the presence of 10mM glucose, directly stimulated the expression of all PPSS mRNAs in a dose-dependent manner in vitro. These results indicate that the pancreatic expression of PPSS mRNAs is differentially regulated by insulin and glucagon and that the regulatory pattern is dependent on glucose concentration.

Brain mapping of three somatostatin encoding genes in the goldfish

In the present study the brain distribution of three somatostatin (SRIF)-encoding genes, PSS-I, PSS-II, and PSS-III, was analyzed by in situ hybridization (ISH) in the goldfish. The PSS-I mRNA showed the widest distribution throughout the brain, whereas PSS-II transcripts were restricted to some hypothalamic nuclei. On the other hand, PSS-III presents an intermediate distribution pattern. All SRIF encoding genes are expressed in hypophysiotropic nuclei supporting the idea that, in addition to SRIF-14, [Pro(2)] SRIF-14, and gSRIF-28 have pituitary-controlling functions. Moreover, each of the genes is expressed in nuclei directly associated with feeding behavior, suggesting a role for SRIF peptides in the central control of food intake and energy balance. Alternatively, they might have a role in processing sensory information related with feeding behavior, since PSS genes are expressed in the main gustatory, olfactory, and visual centers, which project to the hypothalamic feeding center in teleost fish.

Growth hormone and insulin-like growth factor-1 differentially stimulate the expression of preprosomatostatin mRNAs in the Brockmann bodies of rainbow trout, Oncorhynchus mykiss

We previously characterized three cDNAs obtained from the endocrine pancreas (Brockmann body) of rainbow trout that encode for distinct preprosomatostatin (PPSS) molecules: PPSS I containing somatostain-14 (SS-14) at its C-terminus and two separate PPSS IIs, PPSS II' and PPSS II'', containing [Tyr7,Gly10]-SS-14 at their C-termini. In this study, we examined the control of PPSS I, PPSS II', and PPSS II'' mRNA expression by growth hormone (GH) and insulin-like growth factor-1 (IGF-1). Rainbow trout implanted with GH for 21 days displayed elevated pancreatic expression of all PPSS mRNAs compared to control animals. Growth hormone directly stimulated the expression of all pancreatic PPSS mRNAs in vitro in a dose-dependent manner; however, GH was a more potent stimulator of PPSS II' expression than of PPSS I or PPSS II'' expression. Insulin-like growth factor-1 also directly stimulated the expression of PPSS mRNAs in a dose-dependent manner in Brockmann bodies incubated in vitro; IGF-1 was a more potent stimulator of PPSS I and PPSS II' expression than of PPSS II'' expression. These results indicate that the expression of PPSS mRNAs in the Brockmann body of trout is differentially regulated by GH and IGF-1 and suggest that SS mediate the feedback regulation of GH and IGF-1.

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.

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

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.

Localization of somatostatin mRNAs in the brain and pancreas of rainbow trout (Oncorhynchus mykiss)

Rainbow trout possess three distinct mRNAs, each encoding a separate precursor: PPSS I, which contains a 14-amino acid sequence at its C-terminus (somatostatin-14) that is highly conserved among vertebrates, as well as two others, PPSS II' and PPSS II", both containing [Tyr(7), Gly(10)]-somatostatin-14 at their C-terminus. In this study, we used RNA template-specific PCR and in situ hybridization to determine the distribution and cellular localization of PPSS mRNAs in the brain and Brockmann body of rainbow trout. PPSS I, PPSS II' and PPSS II" were expressed in the Brockmann body and pituitary; the expression of PPSS mRNAs in the brain was region specific. PPSS I mRNA was expressed in the Brockmann body predominantly by cells other than those that expressed PPSS IIs; however, there were several instances where PPSS I and PPSS IIs were co-expressed within the same cell. Of the PPSS II-expressing cells, many were observed to express both PPSS II' and PPSS II" mRNA; however, some cells expressed only PPSS II' mRNA, while other cells expressed only PPSS II" mRNA. In the brain, PPSS I mRNA was expressed in the optic tectum (OT) and in many hypothalamic nuclei, including the nucleus rotundus (NR), nucleus anterioris hypothalami (NAH), nucleus anterior tuberis (NAT), nucleus lateral tuberis (NLT), as well as in the pituitary (adenohypophysis). PPSS II" mRNA was present in the same regions as PPSS I mRNA; however, PPSS II' mRNA was present primarily in OT, NAT, NLT and adenohypohysis. These results indicate that PPSS mRNAs are expressed differently by different cells, suggesting that cell-specific mechanisms are involved with the control of PPSS expression and that particular biological responses may be associated with a specific SS isoform.

Somatostatin family of peptides and its receptors in fish

Somatostatin (SRIF or SS) is a phylogenetically ancient, multigene family of peptides. SRIF-14 is conserved with identical primary structure in species of all classes of vertebrates. The presence of multiple SRIF genes has been demonstrated in a number of fish species and could extend to tetrapods. Three distinct SRIF genes have been identified in goldfish. One of these genes, which encodes [Pro2]SRIF-14, is also present in sturgeon and African lungfish, and is closely associated with amphibian [Pro2,Met13]SRIF-14 gene and mammalian cortistatin gene. The post-translational processing of SRIF precursors could result in multiple forms of mature SRIF peptides, with differential abundance and tissue- or cell type-specific patterns. The main neuroendocrine role of SRIF-14 peptide that has been determined in fish is the inhibition of pituitary growth hormone secretion. The functions of SRIF-14 variant or larger forms of SRIF peptide and the regulation of SRIF gene expression remain to be explored. Type 1 and type 2 SRIF receptors have been identified from goldfish and a type 3 SRIF receptor has been identified from an electric fish. Fish SRIF receptors display considerable homology with mammalian counterparts in terms of primary structure and negative coupling to adenylate cyclase. Although additional types of receptors remain to be determined, identification of the multiple gene family of SRIF peptides and multiple types of SRIF receptors opens a new avenue for the study of physiological roles of SRIF, and the molecular and cellular mechanisms of SRIF action in fish.Key words: somatostatin, somatostatin receptor, growth hormone, fish.

Effect of 17beta-estradiol on the expression of somatostatin genes in rainbow trout (Oncorhynchus mykiss)

In the present study, the effects of 17beta-estradiol (E(2)) treatment on the expression of preprosomatostatin (PPSS) I, PPSS II', and PPSS II" mRNA in the hypothalamus and endocrine pancreas (Brockmann body), as well as the effects of E(2) treatment on plasma somatostatin (SS)-14 and -25 concentrations in sexually immature rainbow trout (Oncorhynchus mykiss), were investigated. E(2) treatment significantly (P < 0.001) depressed both plasma SS-14 and SS-25. In the hypothalamus, E(2) treatment significantly (P < 0.001) decreased the levels of PPSS I and PPSS II" mRNA. However, there was no effect of E(2) treatment on PPSS II' mRNA levels. In the pancreas, E(2) treatment had no significant effect on the levels of either PPSS II' mRNA or PPSS II" mRNA. However, E(2) treatment significantly (P < 0.005) decreased levels of PPSS I mRNA. These data suggest that E(2) acts, in part, to increase plasma growth hormone levels in rainbow trout by decreasing the endogenous inhibitory somatostatinergic tone by inhibiting plasma levels of both SS-14 and SS-25 and hypothalamic levels of mRNA encoding these proteins.

Glucose regulates pancreatic preprosomatostatin I expression

Rainbow trout were used as a model system to evaluate the role of glucose in regulating the expression of preprosomatostatin I. Glucose increased pancreatic levels of preprosomatostatin I mRNA in vivo, in concert with elevated plasma somatostatin levels, and in vitro. Glucose-stimulated expression of preprosomatostatin I mRNA required the uptake, phosphorylation, and subsequent metabolism of the sugar in pancreatic islets. These results suggest that glucose modulates both the production and release of somatostatin.

Ultrastructure and immunocytochemistry of the islet organ of osteoglossomorpha (Teleostei)

Both routine electron microscopy and immunocytochemistry with protein A-gold were used to identify the cell types within the islet organs of four species of teleosts (Osteoglossum bicirrhosum, Pantodon buchholzi, Notopterus chitala, and Gnathonemus petersii) within Osteoglossomorpha, a subdivision with an ancient lineage. Four primary endocrine cell types, A, B, D, and F, were identified within the islets of the four species examined. The B- and D-cells were located mainly in the central core of the islet in the four species. In general, the A-cells were located at the islet periphery in all of the four species but in P. buchholzi and N. chitala they were also differently distributed toward the islet core. F-cells were present only at the islet periphery. Granules of B-cells in three species had a relatively homogeneous shape of the matrix core, but in O. bicirrhosum, the shape varied greatly. Variation in matrix shape of B-cell granules may indicate a different conformation of insulin molecules among at least some species of osteoglossomorphs, and this observation may have some taxonomic significance. Two somatostatin-containing (SST) D-cell types (D1 and DX) with granules of different shape were observed in all four species of osteoglossomorphs. The granules of the two D-cells immunostained either with anti-SST-25 and anti-SST-14 (D1-cells) or with anti-SST-34 (DX-cells). Immunocytochemistry confirmed that A-cells, containing glucagon-family peptides, and F-cells, containing peptides of the pancreatic polypeptide family, had granules of different shape. The cells of the islet organs of these osteoglossomorphs are more similar to those in more derived teleosts than they are to those of nonteleost actinopterygians.

Rainbow trout (Oncorhynchus mykiss) possess two somatostatin mRNAs that are differentially expressed

Previously, we isolated a 624-bp cDNA encoding for a 115-amino acid preprosomatostatin containing [Tyr7,Gly10]-somatostatin (SS)-14 (now designated PPSS-II') obtained from the endocrine pancreas (Brockmann bodies) of rainbow trout. In this study we have characterized a second cDNA obtained from trout pancreas that is 600-bp in length and encodes for a 111-amino acid precursor containing [Tyr7,Gly10]-SS-14 (PPSS-II''). The nucleotide and amino acid identity between the two cDNAs is 82.3 and 80.5%, respectively. Both PPSS-II' and PPSS-II'' mRNA were present in esophagus, pyloric ceca, stomach, upper and lower intestine, and pancreas, whereas only SS-II" mRNA was present in brain. PPSS-II'' mRNA was more abundant than PPSS-II' mRNA in pancreas, whereas PPSS-II' mRNA was more abundant than PPSS-II" mRNA in stomach. Fasting increased pancreatic PPSS-II'' mRNA levels but had no effect on the levels of PPSS-II' mRNA. These results indicate the existence of two nonallelic pancreatic SS-II genes that are differentially expressed, both in terms of distribution among tissues and in terms of relative abundance within the tissues.