Human type I pituitary adenylate cyclase activating polypeptide receptor (ADCYAP1R): localization to chromosome band 7p14 and integration into the cytogenetic, physical, and genetic map of chromosome 7

The gene encoding the human type I pituitary adenylate cyclase activating polypeptide receptor (ADCYAP1R1) was mapped to chromosome 7 by PCR analysis of genomic DNA from a human/rodent somatic cell hybrid mapping panel. This assignment was confirmed and the gene localized to chromosome band 7p14 by fluorescence in situ hybridization. A yeast artificial chromosome containing ADCYAP1R1 was identified in the CEPH "B" Mega-YAC library. This YAC includes two highly polymorphic dinucleotide repeat sequences that will facilitate genetic studies of the contribution of ADCYAP1R1 in disease states of the central nervous and neuroendocrine systems.

Localization of the gene encoding a neutral amino acid transporter-like protein to human chromosome band 19q13.3 and characterization of a simple sequence repeat DNA polymorphism

The gene encoding a human neutral amino acid transporter-like protein (SLC1A5) was mapped to chromosome band 19q13.3 by fluorescence in situ hybridization to metaphase chromosomes. A simple sequence repeat DNA polymorphism of the form (GT)n was identified in the 3'-untranslated region of SLC1A5 mRNA. Studies in the CEPH families showed significant evidence of linkage between this DNA polymorphism and markers localized to the distal long arm of chromosome 19.

Molecular mechanisms of agonist-induced desensitization of the cloned mouse kappa opioid receptor

Prolonged exposure of opioid receptors to agonists can cause desensitization, a cellular event linked to tolerance. Although evidence exists for mu and delta opioid receptor desensitization, much less information is available concerning the in vitro regulation of kappa opioid receptors because no cell lines exist that specifically express this class of opioid receptor. Recently we have cloned the mouse kappa opioid receptor. After expression in COS-7 cells, this protein exhibits the pharmacological specificity of a kappa 1 receptor and mediates agonist inhibition of cAMP formation. Continuous exposure of COS-7 cells expressing the kappa receptor to the agonist trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]- benzeneacetamide methanesulfonate salt (U50,488) reduces the specific binding of the kappa-selective agonist [3H]U69,593. Furthermore, the potency of U50,488 to inhibit the binding of the opiate antagonist [3H]naloxone to the kappa receptor is reduced. However, total specific binding of [3H]naloxone is not altered, indicating that short-term (2-4 hr) agonist treatment of the kappa receptor reduces the affinity of the receptor for agonists but does not reduce the density of kappa receptors. The reduction in affinity of the kappa receptor for agonists is dependent on the time of agonist exposure and is reversible. The reduced affinity of the receptor for agonists is associated with kappa receptor desensitization, because kappa receptor-mediated inhibition of cAMP formation is lost in cells pretreated with U50,488. The desensitization of the kappa receptor is dependent on the time and concentration of agonist treatment, is blocked by the kappa-selective antagonist nor-binaltorphimine and is reversible.(ABSTRACT TRUNCATED AT 250 WORDS)

Agonists and antagonists bind to different domains of the cloned kappa opioid receptor

Opium and its derivatives are potent analgesics that can also induce severe side effects, including respiratory depression and addiction. Opioids exert their diverse physiological effects through specific membrane-bound receptors. Three major types of opioid receptors have been described, termed delta, kappa, and mu. The recent molecular cloning of these receptor types opens up the possibility to identify the ligand-binding domains of these receptors. To identify the ligand-binding domains of the kappa and delta receptors, we have expressed in COS-7 cells the cloned mouse delta and kappa receptors and chimeric delta/kappa and kappa/delta receptors in which the NH2 termini have been exchanged. The opioid antagonist naloxone binds potently to wild-type kappa receptor but not to wild-type delta receptor. The kappa/delta chimera bound [3H]naloxone with high affinity. In contrast, the kappa-specific agonist [3H]U-69,593 did not bind to the kappa/delta chimera. These findings indicate that selective agonists and antagonists interact with different recognition sites in the kappa receptor and localize the antagonist-binding domain to the NH2 terminus. Consistent with the results of radioligand-binding studies, the kappa/delta chimera did not mediate kappa-agonist inhibition of cAMP formation. In contrast, the delta/kappa chimera did mediate kappa-agonist inhibition of cAMP formation, but this effect was not blocked by naloxone. Furthermore, a truncated kappa receptor lacking its NH2 terminus was able to mediate agonist inhibition of cAMP accumulation in a naloxone-insensitive manner. This result further indicates that the NH2 terminus of the kappa receptor contains the selective antagonist-binding domain. The ability to dissociate agonist- and antagonist-binding sites will facilitate the development of more specific kappa agonists, which could have analgesic properties devoid of side effects.

Localization of inositol trisphosphate receptor subtype 3 to insulin and somatostatin secretory granules and regulation of expression in islets and insulinoma cells

Calcium ions play a central role in stimulus-secretion coupling in pancreatic beta cells, and an elevation of cytosolic Ca2+ levels is necessary for insulin secretion. Inositol 1,4,5-trisphosphate mobilizes intracellular Ca2+ stores in the beta cell by binding to specific receptors that are ligand-activated Ca2+ channels. The inositol trisphosphate receptors comprise a family of structurally related proteins with distinct but overlapping tissue distributions. Previous studies indicated that the predominant inositol trisphosphate receptor subtype expressed in rat pancreatic islets was the protein designated IP3R-3. We have confirmed the expression of IP3R-3 in pancreatic islets by immunohistocytochemistry and localized this protein to the secretory granules of insulin-secreting beta cells and somatostatin-secreting delta cells by immunogold electron microscopy. Secretory granules contain high levels of Ca2+, and the presence of IP3R-3 in the granule provides a mechanism for mobilizing granule Ca2+ stores in response to glucose and/or hormones. The release of Ca2+ from granule stores would increase the Ca2+ concentration in the surrounding cytoplasm and promote rapid exocytosis of granules, especially those granules in close proximity to the plasma membrane. The levels of IP3R-3 were increased in pancreatic islets of diabetic rats and rats that had been refed after a period of fasting. They were also increased in rat insulinoma RINm5F cells cultured in 25 mM glucose compared with cells cultured in 5 mM glucose. The localization of IP3R-3 to secretory granules of insulin-secreting beta cells and somatostatin-secreting delta cells suggests that granule Ca2+ stores actively participate in the secretory process and that their release is regulated by inositol 1,4,5-trisphosphate. The regulation of IP3R-3 levels by glucose, diabetes, and refeeding may allow the beta cell to adjust the insulin secretory response to changing physiological conditions.

Immunological detection of isoforms of the somatostatin receptor subtype, SSTR2

Somatostatin (SRIF) induces its diverse physiological actions through interactions with different receptor subtypes. Multiple SRIF receptor subtypes have recently been cloned. To analyze the physical properties of receptor subtype SSTR2, two different peptide-directed antibodies were generated against SSTR2. Antibody "2e3," directed against the peptide SSCTINWPGESGAWYT (residues 191-206), corresponding to a region in the predicted third extracellular domain of mouse SSTR2, and antibody "2i4," directed against the peptide SGTEDGERSDS (residues 333-343) from the predicted cytoplasmic tail of mouse SSTR2, were developed. In Chinese hamster ovary (CHO) cells stably expressing the mouse SSTR2 gene (CHOB), the antibody 2e3 recognized specifically a protein of 93-kDa protein by immunoblotting. No specific immunoreactivity was detected by 2e3 in nontransfected CHO cells or CHO cells stably expressing vector alone or human SSTR1 or mouse SSTR3 genes. The antibody 2i4 specifically immunoprecipitated SSTR2 solubilized from CHOB cells that could be labeled with the SSTR2-specific ligand 125I-MK-678. Furthermore, both 2e3 and 2i4 specifically immunoprecipitated 93-kDa [35S]methionine-labeled proteins from CHOB cells, indicating that they recognize the same proteins. In contrast to studies in CHOB cells, immunoblotting studies showed that 2e3 detected specifically a single 148-kDa protein from different regions of the rat brain that have previously been shown to express high levels of SSTR2 mRNA and SRIF receptors with high affinity for 125I-MK-678. In contrast, no immunoreactivity was detected in rat kidney, liver, or lung, which do not express SSTR2. No 93-kDa protein was detected specifically in the rat brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of expression of the human fructose transporter (GLUT5) by cyclic AMP

The effect of cyclic AMP on the expression of the fructose transporter, GLUT5, was studied in Caco-2 cells, a human colon cancer cell line that differentiates spontaneously in culture into cells with the properties of small intestine enterocytes. Treatment of differentiated Caco-2 cells with 50 microM forskolin, which stimulates adenylate cyclase and raises intracellular cyclic AMP levels, increased fructose uptake 2-fold and raised GLUT5 protein and mRNA levels 5- and 7-fold respectively. The increased GLUT5 mRNA levels in forskolin-treated cells are a result of stabilization of GLUT5 mRNA in these cells and increased transcription. The effect of cyclic AMP on GLUT5 transcription was assessed by measuring the activity of human GLUT5 promoter-reporter gene constructs in forskolin-treated differentiated Caco-2 cells. The results showed that forskolin stimulated the activity of the GLUT5-reporter gene constructs and this stimulatory effect was mediated by cis-acting regulatory sequences.

Molecular model of human beta-cell glucokinase built by analogy to the crystal structure of yeast hexokinase B

Recent studies have shown that mutations in human beta-cell glucokinase that impair the activity of this key regulatory enzyme of glycolysis can cause early-onset non-insulin-dependent diabetes mellitus (NIDDM). The amino acid sequence of human glucokinase has 31% identity with yeast hexokinase, a related enzyme for which the crystal structure has been determined. This homology has allowed us to model the three-dimensional structure of human glucokinase by analogy to the crystal structure of yeast hexokinase B. This model of human glucokinase provides a basis for understanding the effects of mutations on its enzymatic activity. Residues in the active site and on the surface of the binding cleft for glucose are highly conserved in both enzymes. Regions far from the active site are predicted to differ in conformation, and 10 insertions or deletions that range in size from 1 to 7 residues are located on the protein surface between elements of secondary structure. The model structure suggests that human glucokinase binds glucose in a similar manner to yeast hexokinase. The glucose-binding site contains a conserved aspartic acid, two conserved glutamic acids, and two conserved asparagines that form hydrogen bond interactions with the hydroxyls of the glucose similar to those observed in other sugar-binding proteins. Mutation of residues in the predicted glucose-binding site has been found to greatly reduce enzymatic activity. This model will be useful for future structure/function studies of glucokinase.

Compensation in pancreatic beta-cell function in subjects with glucokinase mutations

The relationship between the in vivo insulin secretory responsiveness of the pancreatic beta-cell to glucose and the flux of glucose through the enzyme glucokinase was investigated in six subjects with heterozygous glucokinase mutations and in six matched control subjects. This was done by combining data published previously on the in vivo dose-response relationships between glucose and insulin secretion and on the in vitro enzymatic properties of wild-type and mutant forms of glucokinase. The flux of glucose through glucokinase (GK flux) in these subjects was estimated using a model based on the approximate Michaelis-Menten kinetics of wild-type and mutant forms of the enzyme. In two subjects with glucokinase mutations, which resulted in only a small reduction in enzymatic activity, the decrease in insulin secretion was directly proportional to the decrease in GK flux predicted using a Michaelis-Menten model for both mutant and wild-type glucokinase. However, in four subjects with glucokinase mutations, which resulted in severe reductions in enzymatic activity, insulin secretion was reduced compared with control subjects but less than predicted. This latter result implies the existence of a compensatory change in the beta-cells of such subjects, which results in a relative increase in insulin secretory response. We propose modifications to the simple model relating glucose concentration and GK flux, including glucose-induced overexpression of the normal allele and a role of glucokinase regulatory protein. The modifications take into account the possibility that the degree of compensation may be directly related to the severity of the mutation.

Human G-protein-coupled inwardly rectifying potassium channel (GIRK1) gene (KCNJ3): localization to chromosome 2 and identification of a simple tandem repeat polymorphism

The gene encoding the human G-protein-coupled inwardly rectifying potassium channel designated GIRK1 (gene symbol, KCNJ3) was mapped to chromosome 2 by analyzing its segregation in a panel of human-hamster somatic cell hybrids. This assignment was confirmed by fluorescence in situ hybridization to metaphase chromosomes, and the gene was further localized to band 2q24.1. A highly informative simple tandem repeat DNA polymorphism of the form (CA)n was identified and used to localize KCNJ3 within the genetic map of the long arm of chromosome 2.

Alternative splicing of human inwardly rectifying K+ channel ROMK1 mRNA

Recent studies have identified a new family of inwardly rectifying K+ channels, members of which are known by the acronyms ROMK1, IRK1, and GIRK1. We have isolated cDNAs encoding the human homologue of ROMK1 from an adult kidney cDNA library. The sequences of the human kidney ROMK1 cDNA clones indicated that they were derived from at least two types of mRNAs, human ROMK1A and human ROMK1B, differing in sequence at their 5' ends. The isolation of the human ROMK1 gene, localized to chromosome band 11q24 by fluorescence in situ hybridization, indicated that the different ROMK1 transcripts were generated by alternative splicing. Human ROMK1A mRNA was predicted to encode a protein of 389 amino acids, having 93% identity with the 391-residue rat ROMK1 protein, and expression studies in Xenopus oocytes indicated that it encoded a Ba(2+)-sensitive inwardly rectifying K+ channel with properties similar to those reported for cloned rat ROMK1. Human ROMK1B mRNA was predicted to encode a protein of 372 amino acids whose sequence was truncated at the amino terminus but otherwise identical to that of the human ROMK1A protein. Translation of human ROMK1B mRNA was predicted to initiate at a codon corresponding to Met-18 of human ROMK1A mRNA. Reverse transcriptase-polymerase chain reaction amplification of human kidney mRNA revealed human ROMK1A and -B transcripts as well as a third type of transcript, human ROMK1C mRNA, which was predicted to encode a protein identical to human ROMK1B. Human ROMK1A, -B, and -C transcripts were identified in kidney, whereas only human ROMK1A mRNA could be detected in pancreatic islets and other tissues in which human ROMK1 was expressed at low levels. Thus, tissue-specific alternative splicing of human ROMK1 mRNA may result in the expression of a family of ROMK1 proteins.

Gi alpha 1 selectively couples somatostatin receptor subtype 3 to adenylyl cyclase: identification of the functional domains of this alpha subunit necessary for mediating the inhibition by somatostatin of cAMP formation

A major cellular action of the neuropeptide somatostatin (SRIF) is the inhibition of adenylyl cyclase activity. SRIF induces this effect after its interaction with membrane-bound receptors. Five SRIF receptors (SSTRs), which differ in their functional coupling to adenylyl cyclase, have recently been cloned. The third SSTR cloned, SSTR3, effectively mediates the inhibition of adenylyl cyclase by SRIF. The molecular mechanism by which SRIF modulates intracellular cAMP synthesis via SSTR3 was investigated by initially identifying which G alpha subunits are involved in coupling SSTR3 to adenylyl cyclase. SRIF did not inhibit cAMP formation in Chinese hamster ovary cells stably expressing SSTR3 and Gi alpha 2 or Gi alpha 3 but lacking Gi alpha 1. However, SRIF did inhibit forskolin-stimulated cAMP formation in Chinese hamster ovary cells stably expressing SSTR3 and Gi alpha 1, indicating that Gi alpha 1 selectively couples SSTR3 to adenylyl cyclase. To investigate the functional domains of Gi alpha 1 necessary for interaction with SSTR3, a chimeric alpha subunit (Gi alpha 2/Gi alpha 1) was constructed, consisting of the amino-terminal two thirds of Gi alpha 2 ligated to the carboxyl-terminal third of Gi alpha 1. SRIF inhibited cAMP formation in cells expressing SSTR3 and the Gi alpha 2/Gi alpha 1 chimera. These findings indicate that the carboxy-terminal third of Gi alpha 1 interacts with SSTR3 and is important in transmitting the signal of SSTR3 activation to adenylyl cyclase. In contrast, a similar Gi alpha 2/Gi alpha 3 chimera did not couple SSTR3 to adenylyl cyclase, further indicating that Gi alpha 3 does not contribute to SRIF inhibition of adenylyl cyclase activity. These findings demonstrate that Gi alpha 1 selectively couples SSTR3 to adenylyl cyclase, and they indicate that the carboxyl-terminal region of this alpha subunit is involved in mediating SRIF inhibition of adenylyl cyclase activity.

Stimulation of tyrosine phosphatase and inhibition of cell proliferation by somatostatin analogues: mediation by human somatostatin receptor subtypes SSTR1 and SSTR2

The effects of somatostatin analogues RC-160 and SMS-201-995 on tyrosine phosphatase and cell proliferation were investigated in COS-7 and NIH 3T3 cells expressing human somatostatin receptor subtype 1 or 2 (SSTR1 or SSTR2). Binding experiments were performed on membranes from COS-7 cells expressing human SSTR1 or SSTR2 using 125I-labeled [Tyr11]S-14 or [Tyr3]SMS-201-995, respectively. The somatostatin analogues RC-160 and SMS-201-995 exhibited low affinity for SSTR1 (IC50 of 0.43 and 1.5 microM, respectively) and high affinity for SSTR2 (IC50 of 0.27 and 0.19 nM). Addition of these analogues to cells expressing either SSTR1 or SSTR2 did not result in an inhibition of adenylate cyclase activity. In SSTR2-expressing cells, both analogues induced a rapid stimulation of a tyrosine phosphatase activity (EC50: RC-160, 2 pM; SMS-201-995, 6 pM) and an inhibition of serum-stimulated proliferation (EC50: RC-160, 6.3 pM; SMS-201-995, 12 pM). In SSTR1-expressing cells, only RC-160 induced stimulation of a tyrosine phosphatase activity. Both analogues caused an inhibition of cell proliferation at a concentration higher than 10 nM in accordance with their affinities for the SSTR1 receptor subtype. A good correlation between the affinities of RC-160 and SMS-201-995 for each receptor subtype and their potencies to inhibit cell proliferation suggests the involvement of these receptors in cell growth regulation. Tyrosine phosphatase was stimulated by both these analogues in SSTR2 and by RC-160 in SSTR1 at affinities similar to their ability to inhibit growth and bind to receptors, implicating tyrosine phosphatase as a transducer of the growth inhibition signal. We also found that mRNAs of receptor subtypes were variably expressed in different pancreatic and colon cancer cell lines, indicating the necessity of a precise analysis of receptor subtypes in target tissues before therapy with analogues.

Localization of the glucagon receptor gene to human chromosome band 17q25

The gene encoding the human glucagon receptor (GCGR) was mapped to chromosome band 17q25 by fluorescence in situ hybridization to metaphase chromosomes. An Alu variable poly(A) DNA polymorphism was identified in this gene. Studies in the CEPH families showed significant evidence of linkage between DNA polymorphism and markers localized to the distal long arm of chromosome 17.

Differential expression of messenger RNAs for somatostatin receptor subtypes SSTR1, SSTR2 and SSTR3 in adult rat brain: analysis by RNA blotting and in situ hybridization histochemistry

The messenger RNAs encoding three somatostatin receptor subtypes, SSTR1, SSTR2 and SSTR3, were detected in rat by RNA blotting and in situ hybridization histochemistry to identify the sites of synthesis and expression of these somatostatin receptor subtypes. RNA blotting revealed that SSTR1 messenger RNA of 3.8 kilobases was highly expressed in cerebral cortex, hippocampus, midbrain and hypothalamus. In situ hybridization histochemistry revealed that SSTR1 messenger RNA was localized to discrete layers of the cerebral cortex, the piriform cortex and the dentate gyrus of the hippocampus. SSTR1 messenger RNA was expressed at low levels in the cerebellum and pituitary and was not detectable in striatum or other peripheral organs. At least two SSTR2 messenger RNAs were detected by RNA blotting of 2.4 and 2.8 kilobases which correspond to the size of the spliced and unspliced forms of this receptor messenger RNA. SSTR2 messenger RNA detected by in situ hybridization is diffusely expressed in cerebral cortex and amygdala but is discretely localized to dentate gyrus in the hippocampus, medial habenula and ventromedial and dorsomedial nuclei and arcuate nucleus of the hypothalamus. The levels of SSTR2 messenger RNA are very low in the cerebellum and were not observed in the striatum or peripheral tissues other than the pituitary or adrenal gland. A single SSTR3 messenger RNA of 4.0 kilobases was seen in hippocampus, cerebral cortex, midbrain, hypothalamus and pituitary. However, the tissue with the highest levels of SSTR3 messenger RNA is the cerebellum with messenger RNA localized to the granule cell layer. The expression of the three different somatostatin receptor messenger RNAs are distinct but overlapping. Such distinct expression may contribute to the selective biological roles of the receptor subtypes.

Insulin secretory abnormalities in subjects with hyperglycemia due to glucokinase mutations

Pancreatic beta-cell function was studied in six subjects with mutations in the enzyme glucokinase (GCK) who were found to have elevated fasting and postprandial glucose levels in comparison to six normoglycemic controls. Insulin secretion rates (ISRs) were estimated by deconvolution of peripheral C-peptide values using a two-compartment model and individual C-peptide kinetics obtained after bolus intravenous injections of biosynthetic human C-peptide. First-phase insulin secretory responses to intravenous glucose and insulin secretion rates over a 24-h period on a weight maintenance diet were not different in subjects with GCK mutations and controls. However, the dose-response curve relating glucose and ISR obtained during graded intravenous glucose infusions was shifted to the right in the subjects with GCK mutations and average ISRs over a glucose range between 5 and 9 mM were 61% lower than those in controls. In the controls, the beta cell was most sensitive to an increase in glucose at concentrations between 5.5 and 6.0 mM, whereas in the patients with GCK mutations the point of maximal responsiveness was increased to between 6.5 and 7.5 mM. Even mutations that resulted in mild impairment of in vitro enzyme activity were associated with a > 50% reduction in ISR. The responsiveness of the beta cell to glucose was increased by 45% in the subjects with mutations after a 42-h intravenous glucose infusion at a rate of 4-6 mg/kg per min. During oscillatory glucose infusion with a period of 144 min, profiles from the subjects with mutations revealed reduced spectral power at 144 min for glucose and ISR compared with controls, indicating decreased ability to entrain the beta cell with exogenous glucose. In conclusion, subjects with mutations in GCK demonstrate decreased responsiveness of the beta cell to glucose manifest by a shift in the glucose ISR dose-response curve to the right and reduced ability to entrain the ultradian oscillations of insulin secretion with exogenous glucose. These results support a key role for the enzyme GCK in determining the in vivo glucose/ISR dose-response relationships and define the alterations in beta-cell responsiveness that occur in subjects with GCK mutations.

Mutations in the glucokinase gene are not a major cause of late-onset type 2 (non-insulin-dependent) diabetes mellitus in Japanese subjects

The role of the glucokinase gene in the development of diabetes in a group of 349 Japanese subjects with late-onset Type 2 diabetes was examined. These diabetic subjects and 197 non-diabetic controls were typed at two simple tandem repeat DNA polymorphisms in the glucokinase gene termed GCK2 and GCK3. Six and five alleles were evident in Japanese subjects at GCK2 and GCK3, respectively. There were no significant differences in allele, genotype or haplotype frequencies between diabetic and normal groups. In addition, the glucokinase gene of 340 diabetic and 170 non-diabetic Japanese subjects was screened for mutations using single strand conformation polymorphism analysis. Four nucleotide substitutions were identified: a silent substitution in exon 4 in the codon for proline 145 (CCC-->CCG), and A-->T, C-->G, and C-->A substitutions in introns 1b, 3, and 5, respectively. There were no significant differences in the frequencies of these nucleotide substitutions between diabetic and non-diabetic groups. These results suggest that glucokinase gene defects are not a major cause of late-onset Type 2 diabetes in Japanese subjects.

Pharmacological characterization of the cloned kappa-, delta-, and mu-opioid receptors

Opioid drugs, such as morphine, and the endogenous opioid peptides, namely the enkephalins, endorphins, and dynorphins, exert a wide spectrum of physiological and behavioral effects, including effects on pain perception, mood, motor control, and autonomic functions. These effects are mediated via membrane-bound receptors, of which the best characterized are the kappa, delta, and mu receptors. The existence of these distinct types of opioid receptors has recently been confirmed by molecular cloning. In the present study, we have examined the pharmacological profiles of the cloned kappa, delta, and mu receptors using a battery of widely employed opioid agents. Our results suggest that the cloned kappa and mu receptors have pharmacological characteristics similar to those of the endogenously expressed kappa 1 and mu receptors, respectively. The cloned delta receptor displays a pharmacological profile consistent with that of a delta 2 receptor. Opioid agents with abuse potential possess high affinities for the mu receptor. The availability of the cloned receptors will facilitate the identification and development of more specific and selective compounds with greater therapeutic potential and fewer undesirable side effects.

Localization of somatostatin (SRIF) SSTR-1, SSTR-2 and SSTR-3 receptor mRNA in rat brain by in situ hybridization

In situ hybridization histochemistry was performed to analyse the distribution of the messenger RNA (mRNA) of three putative somatostatin (SRIF) receptors in rat brain, using oligonucleotide probes derived from the cDNA coding for SSTR-1, SSTR-2, and SSTR-3 receptors. SSTR-1 signals were found in layers V-VI of the cerebral cortex, in primary olfactory cortex, taenia tecta, subiculum, entorhinal cortex, granular layer of the dentate gyrus, amygdala and cerebellar nuclei. Signals for SSTR-2 were found in the frontal cerebral cortex (layers IV, V and VI), taenia tecta, claustrum, endopiriform nucleus, locus coeruleus, medial habenula, subiculum, granular cell layer of the dentate gyrus and amygdala. High levels of SSTR-3 hybridization were found in the olfactory bulb, primary olfactory cortex, islands of Calleja, medial habenula, amygdala, granular layer of the dentate gyrus, various thalamic and pontine nuclei and in the granular and Purkinje cell layers of the cerebellum. The distribution of the hybridization signals of the oligoprobes is consistent with the labelling of specific SRIF binding sites in rat brain. Especially, SSTR-2 and SSTR-1 oligos seem to label regions in which SS-1 and SS-2 receptors, respectively, have been previously characterized in autoradiographical studies. The situation is less clear with SSTR-3 mRNA, since SRIF binding in adult rats is usually low or absent in cerebellum, although some cerebellar nuclei appear to be labelled in the adult. The localization of SSTR-1, SSTR-2 and SSTR-3 mRNAs suggests that SRIF receptor subtypes in rat brain show profound differences in their distribution and are involved in a variety of central, in addition to neuroendocrine, functions.

Maturity-onset diabetes of the young

Maturity-onset diabetes of the young (MODY) is a subtype of noninsulin dependent diabetes mellitus (NIDDM). It is characterized by an early age of onset and autosomal dominant mode of inheritance. These features and the availability of large multigenerational pedigrees make MODY useful for genetic studies of diabetes. In the large, 5-generational RW pedigree, MODY is tightly linked to genetic markers on chromosome 20q. Affected subjects in this family show abnormalities of carbohydrate metabolism varying from impaired glucose tolerance (IGT) to severe diabetes. Approximately 30% of diabetic subjects become insulin requiring and vascular complications occur. MODY is also linked to the glucokinase gene on chromosome 7p and many different mutations associated with MODY have been identified in this gene. MODY due to mutations in the glucokinase gene is a relatively mild form of diabetes with mild fasting hyperglycemia and IGT in the majority. IT is rarely insulin requiring and rarely has vascular complications. Clinical studies indicate that the genetic or primary defect in MODY is characterized by deranged and deficient insulin secretion and not by insulin resistance and that there are quantitative and qualitative differences in insulin secretory defects which differentiate subjects with MODY due to glucokinase mutations from those with mutations in the gene on chromosome 20q. These differences correlate with the severity of diabetes between these two genetic forms of MODY.

Abnormal insulin secretion, not insulin resistance, is the genetic or primary defect of MODY in the RW pedigree

Maturity-onset diabetes of the young (MODY) is a form of non-insulin-dependent diabetes mellitus (NIDDM) associated with autosomal-dominant inheritance. In the RW pedigree, MODY is associated with polymorphic DNA markers on chromosome 20q. To determine the early abnormalities of insulin action and insulin secretion in MODY, we studied nondiabetic members of the RW pedigree with and without the gene marker. Six nondiabetic marker-negative and 5 nondiabetic marker-positive members of the RW pedigree were studied, as were 4 diabetic marker-positive family members. Unrelated, young, healthy subjects served as comparison groups. Insulin action and insulin secretion were assessed with a frequently sampled intravenous glucose tolerance test. Insulin secretion was further assessed during constant glucose infusion by deconvolution of plasma C-peptide and by pulse analysis. The nondiabetic marker-positive group had normal sensitivity to insulin and unimpaired acute insulin response to intravenous glucose (AIRglu). However, the nondiabetic marker-positive group had decreased mean plasma C-peptide concentration and reduced absolute amplitude of insulin secretory oscillations during prolonged glucose infusion. These responses to prolonged glucose infusion were similar to those observed in the diabetic group. No alterations of insulin secretion were observed in the nondiabetic marker-negative family members. Deranged and deficient insulin secretion, and not insulin resistance, appears to be the genetic or primary abnormality that characterizes nondiabetic individuals who are predisposed to MODY in the RW pedigree.(ABSTRACT TRUNCATED AT 250 WORDS)

Human hexokinase II: localization of the polymorphic gene to chromosome 2

Type 2 (non-insulin-dependent) diabetes mellitus is characterized by decreased levels of glucose 6-phosphate in skeletal muscle. It has been suggested that the lower concentrations of glucose 6-phosphate contribute to the defect in glucose metabolism noted in muscle tissue of subjects with Type 2 diabetes or subjects at increased risk of developing Type 2 diabetes. Lower levels of glucose 6-phosphate could be due to a defect in glucose uptake, or phosphorylation, or both. Hexokinase II is the isozyme of hexokinase that is expressed in skeletal muscle and is responsible for catalysing the phosphorylation of glucose in this tissue. The recent demonstration that mutations in another member of this family of glucose phosphorylating enzymes, glucokinase, can lead to the development of Type 2 diabetes prompted us to begin to examine the possible role of hexokinase II in the development of this genetically heterogeneous disorder. As a first step, we have cloned the human hexokinase II gene (HK2) and mapped it to human chromosome 2, band p13.1, by fluorescence in situ hybridization to metaphase chromosomes. In addition, we have identified and characterized a simple tandem repeat DNA polymorphism in HK2 and used this DNA polymorphism to localize this gene within the genetic linkage map of chromosome 2.