Antipsychotic drug treatment alters expression of mRNAs encoding lipid metabolism-related proteins.

Using an automated PCR-based genomics approach, TOtal Gene expression Analysis (TOGA), we have examined gene expression profiles of mouse striatum and frontal cortex in response to clozapine and haloperidol drug treatment. Of 17 315 mRNAs observed, TOGA identified several groups of related molecules that were regulated by drug treatment. The expression of some genes encoding proteins involved in neurotransmission, signal transduction, oxidative stress, cell adhesion, apoptosis and proteolysis were altered in the brains of both clozapine- and haloperidol-treated mice as recognized by TOGA. Most notable was the differential expression of those genes whose products are associated with lipid metabolism. These include apolipoprotein D (apoD), the mouse homolog of oxysterol-binding protein-like protein 8 (OSBPL8), a diacylglycerol receptor (n-chimerin), and lysophosphatidic acid (LPA) acyltransferase. Real-time PCR analysis confirmed increases in the RNA expression of apoD (1.6-2.2-fold) and OSBPL8 (1.7-2.6-fold), and decreases in the RNA expression of n-chimerin (1.5-2.2-fold) and LPA acyltransferase (1.5-fold) in response to haloperidol and/or clozapine treatment. Additional molecules related to calcium homeostasis and signal transduction, as well as four sequences of previously unidentified mRNAs, were also confirmed by real-time PCR to be regulated by drug treatment. While antipsychotic drugs may affect several metabolic pathways, lipid metabolism/signaling pathways may be of particular importance in the mechanisms of antipsychotic drug action and in the pathophysiology of psychiatric disorders.

No hypothermic response to serotonin in 5-HT7 receptor knockout mice.

With data from recently available selective antagonists for the 5-HT(7) receptor, it has been hypothesized that 5-hydroxytryptamine (5-HT)-induced hypothermia is mediated by the 5-HT(7) receptor, an effect previously attributed to other receptor subtypes. It has been established that the biologically active lipid oleamide allosterically interacts with the 5-HT(7) receptor to regulate its transmission. The most well characterized effects of oleamide administration are induction of sleep and hypothermia. Here, we demonstrate, by using mice lacking the 5-HT(7) receptor, that 5-HT-induced hypothermia is mediated by the 5-HT(7) receptor. Both 5-HT and 5-carboxamidotryptamine, a 5-HT(1) and 5-HT(7) receptor agonist, in physiological doses fail to induce hypothermia in 5-HT(7) knockout mice. In contrast, oleamide was equally effective in inducing hypothermia in mice lacking the 5-HT(7) receptors as in wild-type mice. When administered together, 5-HT and oleamide showed additive or greater than additive effects in reducing body temperature. Taken together, the results show that 5-HT-induced hypothermia is mediated by the 5-HT(7) receptor, and that oleamide may act through an independent mechanism as well as at an allosteric 5-HT(7) receptor site to regulate body temperature.

Clozapine increases apolipoprotein D expression in rodent brain: towards a mechanism for neuroleptic pharmacotherapy.

In contrast to typical neuroleptic drugs, which have high affinities for dopamine D2 receptors, clozapine binds to multiple neurotransmitter receptors. The mechanisms responsible for its superior clinical efficacy over typical neuroleptics remain unknown. Using an automated genomics approach, total gene expression analysis (TOGA), we found an approximately threefold increase in the accumulation of the mRNA encoding apolipoprotein D (apoD) in mouse striatum in response to chronic treatment with clozapine. While in control animals, apoD is expressed predominantly in astrocytes, in situ hybridization and immunohistochemical studies indicated a substantial increase in apoD expression in neurons of the striatum, globus pallidus and thalamus after 2 weeks of clozapine treatment. Clozapine-induced increases in apoD expression were also observed in some white matter regions. These results suggest that apoD is a mediator in the mechanisms of clozapine and thus that deficiencies in aspects of lipid metabolism may be responsible for psychoses.

Developmental regulation of two isoforms of Ca(2+)/calmodulin-dependent protein kinase I beta in rat brain.

Subtractive hybridization analysis of region-specific gene expression in brain has demonstrated a mRNA species enriched in rat hypothalamus [K.M. Gautvik, L. de Lecea, V.T. Gautvik, P.E. Danielson, P. Tranque, A. Dopazo, F.E. Bloom, J.G. Sutcliffe, Proc. Natl. Acad. Sci. USA 93 (1996) 8733-8738.]. We here show that this mRNA encodes a Ca(2+)/calmodulin-dependent (CaM) kinase belonging in the CaM kinase I beta subgroup. cDNA analysis showed that this enzyme was differentially spliced into two isoforms (designated beta1 and beta2) with distinct C-termini. The C-terminal of the translated CaM kinase I beta2 protein (38.5 kDa molecular size), contained 25 amino acid residues not present in the beta1 isoform. The two isoforms were differentially developmentally regulated, with the beta1 isoform being present in rat embryos from day 18 and the beta2 isoform being present from day 5 postnatally. In situ hybridization analysis of adult rat CNS showed CaM kinase I beta2 mRNA being enriched in the hypothalamus and the hippocampal formation. Expression was also observed in a number of ventral limbic structures and in the thalamus. Northern blot analysis showed additional expression of multiple beta2 isoforms in heart and skeletal muscle. The human mRNA showed a similar distribution. Our data suggest that the two isoforms of CaM kinase I beta, created by a splicing process occurring within a week around birth, may have distinct pre- and postnatal functions in a distinct set of CNS neurons and excitable tissues.

Rhes: A striatal-specific Ras homolog related to Dexras1.

We have characterized an apparently full-length cDNA corresponding to a rat mRNA, SE6C, previously identified by subtractive hybridization as being expressed predominantly in the striatal region of the brain. The SE6C mRNA encodes a 266 amino acid protein with significant similarity to members of the Ras-like GTP-binding protein family; thus, we have chosen the name Rhes, for Ras homolog enriched in striatum. The human homolog was found in a genomic sequence from human chromosome 22q13.1 and shares 95% identity with rat Rhes. Among the family of small G-proteins, Rhes shares 62% identity with Dexras1, a mouse dexamethasone-inducible Ras-like protein. Both Rhes and Dexras1 have substantially longer C-termini than other members of the Ras-like small G-protein family. Divergence between the C-terminal sequences of Rhes and Dexras1 suggests that, although their functions are probably similar, they have unique properties. Bacterially expressed Rhes binds GTP, suggesting that the protein indeed has GTPase functionality. Although Rhes was not induced by dexamethasone, its full expression is dependent upon thyroid hormone availability. Its accumulation is postnatal, consistent with the dependence upon thyroid hormone. It is noteworthy that most striatum-"specific" mRNAs characterized to date encode components of signal transduction cascades.

RGS9: a regulator of G-protein signalling with specific expression in rat and mouse striatum.

A clone of the regulator of G-protein signalling, RGS9, was isolated from a rat striatum-minus-cerebellum-minus-hippocampus subtracted library generated by directional tag polymerase chain reaction subtraction. The full-length cDNA clone encodes a 444 amino acid protein containing an 118 amino acid RGS domain, which corresponds to an evolutionarily conserved domain that is present in all members of the RGS family of proteins. Outside of the homology domain, RGS9 shows more extended similarity to human RGS6 and RGS7, rat RGS12, and the C. elegans protein EGL-10. During embryonic and early postnatal stages of development, two RGS9 transcripts of approximately 1.4 Kb and 1.8 Kb were detected in whole brain. After postnatal day 10, accumulation of the larger transcript increased progressively until adulthood at the expense of the smaller transcript, which was undetectable in the adult. In adult rat brain, the 1.8-Kb RGS9 transcript was detected in the striatum but not in other brain regions or peripheral tissues. In situ hybridization in rat and mouse demonstrates that RGS9 mRNA is expressed predominantly in medium-sized, spiny neurons of the neostriatum and in neurons of the nucleus accumbens and olfactory tubercle. Relatively strong signals were also detected in some hypothalamic nuclei. Its selective expression suggests that RGS9 may play an important role in modulation of the complex signalling pathways of the basal ganglia.

The hypocretins: hypothalamus-specific peptides with neuroexcitatory activity.

We describe a hypothalamus-specific mRNA that encodes preprohypocretin, the putative precursor of a pair of peptides that share substantial amino acid identities with the gut hormone secretin. The hypocretin (Hcrt) protein products are restricted to neuronal cell bodies of the dorsal and lateral hypothalamic areas. The fibers of these neurons are widespread throughout the posterior hypothalamus and project to multiple targets in other areas, including brainstem and thalamus. Hcrt immunoreactivity is associated with large granular vesicles at synapses. One of the Hcrt peptides was excitatory when applied to cultured, synaptically coupled hypothalamic neurons, but not hippocampal neurons. These observations suggest that the hypocretins function within the CNS as neurotransmitters.

Cortistatin is expressed in a distinct subset of cortical interneurons.

Cortistatin is a presumptive neuropeptide that shares 11 of its 14 amino acids with somatostatin. In contrast to somatostatin, administration of cortistatin into the rat brain ventricles specifically enhances slow wave sleep, apparently by antagonizing the effects of acetylcholine on cortical excitability. Here we show that preprocortistatin mRNA is expressed in a subset of GABAergic cells in the cortex and hippocampus that partially overlap with those containing somatostatin. A significant percentage of cortistatin-positive neurons is also positive for parvalbumin. In contrast, no colocalization was found between cortistatin and calretinin, cholecystokinin, or vasoactive intestinal peptide. During development there is a transient increase in cortistatin-expressing cells in the second postnatal week in all cortical areas and in the dentate gyrus. A transient expression of preprocortistatin mRNA in the hilar region at P16 is paralleled by electrophysiological changes in dentate granule cells. Together, these observations suggest mechanisms by which cortistatin may regulate cortical activity.

Cloning, mRNA expression, and chromosomal mapping of mouse and human preprocortistatin.

Cortistatin is a 14-residue putative neuropeptide with strong structural similarity to somatostatin and is expressed predominantly in cortical GABAergic interneurons of rats. Administration of cortistatin into the brain ventricles specifically enhances slow-wave sleep, presumably by antagonizing the effects of acetylcholine on cortical excitability. Here we report the identification of cDNAs corresponding to mouse and human preprocortistatin and the mRNA distribution and gene mapping of mouse cortistatin. Analysis of the nucleotide and predicted amino acid sequences from rat and mouse reveals that the 14 C-terminal residues of preprocortistatin, which make up the sequence that is most similar to somatostatin, are conserved between species. Lack of conservation of other dibasic amino acid residues whose cleavage by prohormone convertases would give rise to additional peptides suggests that cortistatin-14 is the only active peptide derived from the precursor. As in the rat, mouse preprocortistatin mRNA is present in GABAergic interneurons in the cerebral cortex and hippocampus. The preprocortistatin gene maps to mouse chromosome 4, in a region showing conserved synteny with human 1p36. The human putative cortistatin peptide has an arginine for lysine substitution, compared to the rat and mouse products, and is N-terminally extended by 3 amino acids.

Fatty acid amide hydrolase, the degradative enzyme for anandamide and oleamide, has selective distribution in neurons within the rat central nervous system.

Fatty acid amide hydrolase (FAAH) is a membrane-bound enzyme activity that degrades neuromodulatory fatty acid amides, including oleamide and anandamide. A single 2.5-kb FAAH mRNA is distributed throughout the rat CNS and accumulates progressively between embryonic day 14 and postnatal day 10, remains high until postnatal day 30, then decreases into adulthood. FAAH enzymatic activity, as measured in dissected brain regions, was well correlated with the distribution of its messenger RNA. In situ hybridization revealed profound distribution of FAAH mRNA in neuronal cells throughout the CNS. The most prominent signals were detected in the neocortex, hippocampal formation, amygdala, and cerebellum. The FAAH distribution in the CNS suggests that degradation of neuromodulatory fatty acid amides at their sites of action influences their effects on sleep, euphoria, and analgesia.

The 5HT5A serotonin receptor is expressed predominantly by astrocytes in which it inhibits cAMP accumulation: a mechanism for neuronal suppression of reactive astrocytes.

The mRNA for the 5-hydroxytryptamine receptor 5-HT5A was detected at embryonic day 18 in the rat central nervous system and peaked by postnatal day 20. At all time points examined, 5-HT5A immunoreactivity observed on astrocyte cell bodies and in the stellate processes not only colocalized with the astrocyte-specific marker glial fibrillary acidic protein (GFAP) but was coordinately regulated with GFAP, increasing during development and during gliosis. Transfection of 5-HT5A into glioma cells prevented the 5-HT-induced increase in cAMP observed in untransfected cells and decreased the relative forskolin response by approximately 20%, suggesting that the 5-HT5A receptor couples negatively to adenylyl cyclase in astrocytes. Together, these results indicate a neuron-to-astrocyte serotonergic signaling pathway mediating cAMP concentrations, which could provide a neuronally driven mechanism for regulating astrocyte physiology with relevance to gliosis.

Overview of the most prevalent hypothalamus-specific mRNAs, as identified by directional tag PCR subtraction.

We applied the directional tag PCR subtractive hybridization method to construct a rat hypothalamic cDNA library from which cerebellar and hippocampal sequences had been depleted, enriching 20-30-fold for sequences expressed selectively in the hypothalamus. We studied a sample of 94 clones selected for enrichment in the subtracted library. These clones corresponded to 43 distinct mRNA species, about half of which were novel. Thirty-eight of these 43 mRNAs (corresponding to 85 of the clones in the sample) exhibited enrichment in the hypothalamus; 23 were highly enriched. In situ hybridization studies revealed that one novel species was restricted to cells in a small bilaterally symmetric area of the paraventricular hypothalamus. Other novel mRNAs showed substantial enrichment in basal diencephalic structures, particularly the hypothalamus, without restriction to single hypothalamic nuclei. The data suggest that the hypothalamus utilizes at least two distinct strategies for employing its selectively expressed proteins. Secretory neuropeptides utilized for intercellular communication are produced by functionally discrete nuclei, while several other proteins are shared by structures that are unrelated in their physiological roles but may share biochemical systems.

A cortical neuropeptide with neuronal depressant and sleep-modulating properties.

Acetylcholine (ACh) plays a key role in the transitions between the different phases of sleep: Slow-wave sleep requires low ACh concentrations in the brain, whereas rapid-eye-movement (REM) sleep is associated with high levels of ACh. Also, these phases of sleep are differentially sensitive to a number of endogenous neuropeptides and cytokines, including somatostatin, which has been shown to increase REM sleep without significantly affecting other phases. Here we report the cloning and initial characterization of cortistatin, a neuropeptide that exhibits strong structural similarity to somatostatin, although it is the product of a different gene. Administration of cortistatin depresses neuronal electrical activity but, unlike somatostatin, induces low-frequency waves in the cerebral cortex and antagonizes the effects of acetylcholine on hippocampal and cortical measures of excitability. This suggests a mechanism for cortical synchronization related to sleep.

G-protein gamma 7 subunit is selectively expressed in medium-sized neurons and dendrites of the rat neostriatum.

We used subtractive hybridization to isolate clones of gamma 7, a 68 residue G-protein gamma subunit. Northern blotting and in situ hybridization reveal that the gamma 7 subunit mRNA is expressed primarily in medium-sized neurons of the neostriatum and nucleus accumbens and neurons of the olfactory tubercle, and at low levels in the dentate gyrus of the hippocampal formation and laminae II-III, and V of the neocortex. The gamma 7 mRNA is translocated into dendrites of neurons in the neostriatum and the dentate gyrus of the hippocampus. gamma 7 is expressed at relatively very low concentrations in peripheral tissues. The selective pattern of gamma 7 expression within the brain is highly reminiscent of those of the striatum-enriched adenylyl cyclase ACST, dopamine receptors, and the alpha subunit of G(olf), suggesting that, in striatum, gamma 7 may be a subunit of a G(olf) alpha-containing G protein that couples dopamine receptors selectively to ACST.

Four structurally distinct neuron-specific olfactomedin-related glycoproteins produced by differential promoter utilization and alternative mRNA splicing from a single gene.

Four structurally related neuron-specific 1B426b mRNAs, designated AMY, BMY, AMZ, and BMZ, have been isolated from rat brain cDNA libraries. The four mRNAs are related to one another by their shared M region and by two pairs of alternative 5' (A, B) or 3' (Y, Z) regions. All four possible combinations were detected. The four transcripts are derived by differential promoter utilization (to generate A or B 5' ends) and alternative splicing (to generate Y or Z 3' ends) of the primary transcripts of the single D2Sutle gene. All four mRNAs were detected in most brain regions, but were enriched within the cortex and hippocampus. In the pituitary only the two A-type and in the adrenal glands only the two B-type mRNAs were detected. In situ hybridization shows a highly heterogeneous distribution across brain regions, paralleling the Northern blot results and additionally identifying the reactive cells as neurons. The cDNAs encode related glycoproteins of 125, 153, 457, and 485 amino acids, which have been detected immunochemically. The AMZ and BMZ proteins show significant sequence similarity with olfactomedin, an extracellular matrix protein of bullfrog olfactory epithelium, suggesting the possibility of a matrix-related function for these rat glycoproteins in neurons and neurosecretory cells.

Chromosomal mapping of mouse genes expressed selectively within the central nervous system.

We have used RFLP analysis on DNA from a panel of interspecific (C57BL/6J x Mus spretus) F1 x M. spretus backcross offspring to assign the genes encoding 10 neuron-specific mRNAs and 2 loci corresponding to cyclophilin 2-related sequences to the mouse chromosomal map. The Pss1 locus encoding the forebrain-enriched protein kinase C substrate RC3, a component of dendritic spines, mapped to proximal Chr 9. The Camkl locus encoding the calmodulin-binding protein kinase-like vesicle protein 1G5 mapped to distal Chr 9. The Gng7 locus encoding the gamma 7 G-protein subunit, highly enriched in the striatum and presumptively coupled to dopamine receptors, mapped to mid-Chr 10. The Htr1f, Htr5a, Htr5b, and Htr7loci, encoding four serotonin receptors, mapped to Chr 16, 5, 1, and 19, respectively. The Peplb locus, encoding a CD26 ectopeptidase-like neuronal membrane protein activated by kainate and long-term potentiation, mapped to Chr 5. The D2Sut1e and Cpu3 loci, encoding neural proteins of unknown functions, mapped to Chrs 2 and 9, respectively. Two cyclophilin 2-related loci, Cphn2-r1 and Cphn2-r2, mapped to different regions of Chr 9. Comparison of these 12 newly mapped loci with the existing mouse map and known regions of syntenic homology with the human map, along with the known features and expression profiles of the products of these genes, suggests a few candidates for mouse mutations and human neurological and immunological deficits, including the Tourette syndrome and Bloom syndrome genes.

1G5: a calmodulin-binding, vesicle-associated, protein kinase-like protein enriched in forebrain neurites.

We have characterized cDNA clones of 1G5, an mRNA highly enriched in the mammalian forebrain that encodes a 504-residue protein found in association with perikaryal membranes and neurites. The protein, which accumulates predominantly postnatally, is associated with vesicles in both axons and dendrites. The sequence of the 1G5 protein highly resembles those of protein kinases with serine/threonine specificity; however, although most residues universally conserved among protein kinases are present, a few signature residues are absent from the 1G5 protein. Furthermore, although recombinant 1G5 protein binds calmodulin in the presence of calcium, it lacks kinase activity with a sample substrate.

Two members of a distinct subfamily of 5-hydroxytryptamine receptors differentially expressed in rat brain.

We report two serotonin (5-hydroxytryptamine, 5-HT) receptors, MR22 and REC17, that belong to the G-protein-associated receptor superfamily. MR22 and REC17 are 371 and 357 amino acids long, respectively, as deduced from nucleotide sequence and share 68% mutual amino acid identity and 30-35% identity with known catecholamine and 5-HT receptors. Saturable binding of 125I-labeled (+)-lysergic acid diethylamide to transiently expressed MR22 in COS-M6 cells was inhibited by ergotamine > methiothepin > 5-carboxamidotryptamine > 5-HT. For REC17, the rank of potency was ergotamine > 5-carboxamidotryptamine > methiothepin > methysergide > 5-HT. Both were insensitive to 5-HT1A, 5-HT1D or 5-HT2 serotonergic ligands [8-hydroxy-2-(di-n-propylamino)tetralin, sumatriptan, and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane]. The mRNAs encoding MR22 were detected in the CA1 region of hippocampus, the medial habenula, and raphe nuclei. In contrast, mRNAs encoding REC17 were found throughout the rat central nervous system. We propose that REC17 and MR22, designated as 5-HT5 alpha and 5-HT5 beta, represent a distinct subfamily of 5-HT receptors.

Molecular cloning and functional expression of 5-HT1E-like rat and human 5-hydroxytryptamine receptor genes.

Sequential polymerase chain reaction experiments were performed to amplify a unique sequence representing a guanine nucleotide-binding protein (G-protein)-coupled receptor from rat hypothalamic cDNA. Degenerate oligonucleotides corresponding to conserved amino acids from transmembrane domains III, V, and VI of known receptors [5-HT1A, 5-HT1C, and 5-HT2; 5-HT is serotonin (5-hydroxytryptamine)] were used as primers for the sequential reactions. The resulting product was subcloned and used to screen a rat genomic library to identify a full-length clone (MR77) containing an intronless open reading frame encoding a 366-amino acid seven-transmembrane domain protein. The human homolog was isolated, and its encoded protein had 93% overall amino acid identity with the rat sequence. Within the conserved transmembrane domains, the sequences exhibit approximately 52%, 59%, 65%, and 68% amino acid identity with the known rat 5-HT1A, rat 5-HT1B, rat 5-HT1D, and human 5-HT1E receptors, respectively. MR77 was subcloned into a eukaryotic expression vector system and expressed in CosM6 cells. Studies on broken cell preparations indicate that the expressed receptor exhibits 125I-labeled d-lysergic acid diethylamide (LSD) binding that can be displaced by serotonin but not by other biogenic amines. The specific binding is displaced by the selective 5-HT1D agonist sumatriptan but not by the mixed 5-HT1A/1D agonist 5-carboxyamidotryptamine. 125I-labeled LSD binding was competitively antagonized by the ergot alkaloids methysergide and ergotamine. HeLa cells transfected with the MR77 gene exhibited inhibition of adenylate cyclase in response to serotonin. MR77 is expressed at low levels throughout the brain, with the greatest expression in the cortex, hippocampus, and striatum. MR77 thus represents a 5-HT receptor of the 5-HT1 class, and we propose that, based on the pharmacological characterization, MR77 represents an additional 5-HT1E-like receptor.

Primary structure of mouse secretogranin III and its absence from deficient mice.

The rat brain- and pituitary-specific 1B1075 mRNA encodes a chromogranin/secretogranin-like protein, called secretogranin III (SgIII), that is a component of intracellular dense core vesicles. In order to study the function of this gene product in a mouse model system, we have isolated the murine homolog of the rat 1B1075 mRNA. This mRNA contains 2163 bp encoding a putative protein of 421 amino acids. Cleavage of the strong putative signal sequence would yield a mature protein of 51 kDa. The sequence of the encoded murine protein preserves the structural features that suggest SgIII is a member of the granin family, and allowed us to recognize and correct errors in our published rat sequence.