Molecular signatures associated with cognitive deficits in schizophrenia: a study of biopsied olfactory neural epithelium

Cognitive impairment is a key feature of schizophrenia (SZ) and determines functional outcome. Nonetheless, molecular signatures in neuronal tissues that associate with deficits are not well understood. We conducted nasal biopsy to obtain olfactory epithelium from patients with SZ and control subjects. The neural layers from the biopsied epithelium were enriched by laser-captured microdissection. We then performed an unbiased microarray expression study and implemented a systematic neuropsychological assessment on the same participants. The differentially regulated genes in SZ were further filtered based on correlation with neuropsychological traits. This strategy identified the SMAD 5 gene, and real-time quantitative PCR analysis also supports downregulation of the SMAD pathway in SZ. The SMAD pathway has been important in multiple tissues, including the role for neurodevelopment and bone formation. Here the involvement of the pathway in adult brain function is suggested. This exploratory study establishes a strategy to better identify neuronal molecular signatures that are potentially associated with mental illness and cognitive deficits. We propose that the SMAD pathway may be a novel target in addressing cognitive deficit of SZ in future studies.

Unique pharmacological actions of atypical neuroleptic quetiapine: possible role in cell cycle/fate control

Quetiapine is an atypical neuroleptic with a pharmacological profile distinct from classic neuroleptics that function primarily via blockade of dopamine D2 receptors. In the United States, quetiapine is currently approved for treating patients with schizophrenia, major depression and bipolar I disorder. Despite its widespread use, its cellular effects remain elusive. To address possible mechanisms, we chronically treated mice with quetiapine, haloperidol or vehicle and examined quetiapine-specific gene expression change in the frontal cortex. Through microarray analysis, we observed that several groups of genes were differentially expressed upon exposure to quetiapine compared with haloperidol or vehicle; among them, Cdkn1a, the gene encoding p21, exhibited the greatest fold change relative to haloperidol. The quetiapine-induced downregulation of p21/Cdkn1a was confirmed by real-time polymerase chain reaction and in situ hybridization. Consistent with single gene-level analyses, functional group analyses also indicated that gene sets associated with cell cycle/fate were differentially regulated in the quetiapine-treated group. In cortical cell cultures treated with quetiapine, p21/Cdkn1a was significantly downregulated in oligodendrocyte precursor cells and neurons, but not in astrocytes. We propose that cell cycle-associated intervention by quetiapine in the frontal cortex may underlie a unique efficacy of quetiapine compared with typical neuroleptics.

Naturally occurring free D-aspartate is a nuclear component of cells in the mammalian hypothalamo-neurohypophyseal system

It is generally believed that only L-amino acids have a physiological role in species other than bacteria. Recently, the existence of some D-amino acids, particularly D-aspartate, in various organs of several higher animals has been reported. Here we demonstrate that naturally occurring free D-aspartate is localized subcellularly to the heterochromatin in the nucleoli (but not in either the dendrites or axonal terminals) of magnocellular neurosecretory neurons in the rat hypothalamus, and also of microglia and pericytes in the posterior pituitary. Our results imply that naturally occurring free D-aspartate might have a physiological role in nuclear function in mammals. The findings provide new insight for the biological function of D-stereoisomers of amino acids as well as the organization of the nucleus of at least some eukaryotic cells.

The abnormal regulation of gene expression in autistic brain tissue

Autism is a pervasive developmental disorder of unknown etiology. It is likely caused by mutations in one or more genes. One approach to understanding the molecular changes that occur in autism is to measure gene expression in post-mortem brain samples from individuals diagnosed with autism. This may be accomplished with techniques such as cDNA microarrays or subtractive hybridization. In general, gene expression is regulated as a function of body region, developmental time, and physiological state. A premise of the approaches we describe is that gene expression is regulated in cells from autistic individuals as a consequence of the disease process. It may be useful to detect such changes in order to identify selective biological markers for autism. Additionally, the abnormal regulation of gene expression may reveal cellular pathways that have been disrupted, suggesting strategies for therapeutic intervention.

Neurobiology of Rett syndrome: a genetic disorder of synapse development

Rett syndrome is a developmental disorder that restricts brain growth beginning in the first year of life and evidence from neuropathology and neuroimaging indicates that axonodendritic connections are especially vulnerable. In a study of amino acid neurotransmitter receptors using receptor autoradiography in tissue slices of frontal cortex and the basal ganglia, we found a biphasic age-related pattern with relatively high receptor densities in young RS girls and lower densities at later time. Using microarray analysis of gene expression in frontal cortex, we found that some of the most prominent alterations occurred in gene products related to synapses, including the NMDA receptor NR1 subunit, the cytoskeletal protein MAP-2 and synaptic vesicle proteins. Using a new antibody that recognizes MeCP2, the transcription factor mutated in RS, we established that most neurons in the rodent brain express this transcription factor. We hypothesize that a major effect of mutations in the MeCP2 protein is to cause age-related disruption of synaptic proliferation and pruning in the first decade of life.

Postmortem brain abnormalities of the glutamate neurotransmitter system in autism

BACKGROUND

Studies examining the brains of individuals with autism have identified anatomic and pathologic changes in regions such as the cerebellum and hippocampus. Little, if anything, is known, however, about the molecules that are involved in the pathogenesis of this disorder.

OBJECTIVE

To identify genes with abnormal expression levels in the cerebella of subjects with autism.

METHOD

Brain samples from a total of 10 individuals with autism and 23 matched controls were collected, mainly from the cerebellum. Two cDNA microarray technologies were used to identify genes that were significantly up- or downregulated in autism. The abnormal mRNA or protein levels of several genes identified by microarray analysis were investigated using PCR with reverse transcription and Western blotting. alpha-Amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA)- and NMDA-type glutamate receptor densities were examined with receptor autoradiography in the cerebellum, caudate-putamen, and prefrontal cortex.

RESULTS

The mRNA levels of several genes were significantly increased in autism, including excitatory amino acid transporter 1 and glutamate receptor AMPA 1, two members of the glutamate system. Abnormalities in the protein or mRNA levels of several additional molecules in the glutamate system were identified on further analysis, including glutamate receptor binding proteins. AMPA-type glutamate receptor density was decreased in the cerebellum of individuals with autism (p < 0.05).

CONCLUSIONS

Subjects with autism may have specific abnormalities in the AMPA-type glutamate receptors and glutamate transporters in the cerebellum. These abnormalities may be directly involved in the pathogenesis of the disorder.

Microarray analysis of differential gene expression in lead-exposed astrocytes

The toxic metal lead is a widespread environmental health hazard that can adversely affect human health. In an effort to better understand the cellular and molecular consequences of lead exposure, we have employed cDNA microarrays to analyze the effects of acute lead exposure on large-scale gene expression patterns in immortalized rat astrocytes. Our studies identified many genes previously reported to be differentially regulated by lead exposure. Additionally, we have identified novel putative targets of lead-mediated toxicity, including members of the family of calcium/phospholipid binding annexins, the angiogenesis-inducing thrombospondins, collagens, and tRNA synthetases. We demonstrate the ability to distinguish lead-exposed samples from control or sodium samples solely on the basis of large-scale gene expression patterns using two complementary clustering methods. We have confirmed the altered expression of candidate genes and their encoded proteins by RT-PCR and Western blotting, respectively. Finally, we show that the calcium-dependent phospholipid binding protein annexin A5, initially identified as a differentially regulated gene by our microarray analysis, is directly bound and activated by nanomolar concentrations of lead. We conclude that microarray technology is an effective tool for the identification of lead-induced patterns of gene expression and molecular targets of lead.

Gene expression profiling in postmortem Rett Syndrome brain: differential gene expression and patient classification

The identification of mutations in the transcriptional repressor methyl-CpG-binding protein 2 (MECP2) gene in Rett Syndrome (RTT) suggests that an inappropriate release of transcriptional silencing may give rise to RTT neuropathology. Despite this progress, the molecular basis of RTT neuropathogenesis remains unclear. Using multiple cDNA microarray technologies, subtractive hybridization, and conventional biochemistry, we generated comprehensive gene expression profiles of postmortem brain tissue from RTT patients and matched controls. Many glial transcripts involved in known neuropathological mechanisms were found to have increased expression in RTT brain, while decreases were observed in the expression of multiple neuron-specific mRNAs. Dramatic and consistent decreases in transcripts encoding presynaptic markers indicated a specific deficit in presynaptic development. Employing multiple clustering algorithms, it was possible to accurately segregate RTT from control brain tissue samples based solely on gene expression profile. Although previously achieved in cancers, our results constitute the first report of human disease classification using gene expression profiling in a complex tissue source such as brain.

Assessment of neural cell adhesion molecule (NCAM) in autistic serum and postmortem brain

Studies have identified structural abnormalities in areas of the autistic brain, with a pattern suggesting that a neurodevelopmental anomaly took place. Neural cell adhesion molecule (NCAM), which is involved in development of the central nervous system, was previously shown to be decreased in the serum of autistic individuals. In the present study, we measured NCAM protein in the sera from controls, patients with autism, siblings of autistic patients, and individuals with other neurologic disorders, but found no significant differences. We also measured NCAM protein in autistic postmortem brain samples and found the longest isoform, NCAM-180, to be significantly decreased. In addition, we investigated the mRNA expression of NCAM in these brain samples using cDNA microarrays and RT-PCR. Results show that NCAM mRNA levels are not altered in autism.

Emerging technologies for large-scale screening of human tissues and fluids in the study of severe psychiatric disease

Neuropsychiatric diseases such as schizophrenia and bipolar disorder are major causes of morbidity throughout the world. Despite extensive searches, no single gene, RNA transcript, or protein has been found which can, on its own, account for these disorders. Recently, the availability of genomic tools such as cDNA microarrays, serial analysis of gene expression (SAGE) and large-scale sequencing of cDNA libraries has allowed researchers to assay biological samples for a large number of RNA transcripts. Similarly, proteomic tools allow for the quantitation of a large number of peptides and proteins. These methods include two-dimensional electrophoresis and surface-enhanced laser desorption/ionization (SELDI). We have initiated experiments which apply these techniques to the comparison of RNAs and proteins expressed in clinical samples obtained from individuals with psychiatric diseases and controls. These methods have the potential to identify pathways that are involved in the pathogenesis of complex psychiatric disorders. The characterization of these pathways may allow for the development of new methods for the diagnosis and treatment of schizophrenia, bipolar disorder, and other human psychiatric diseases.

Synaptotagmin I is a molecular target for lead

Lead poisoning can cause a wide range of symptoms with particularly severe clinical effects on the CNS. Lead can increase spontaneous neurotransmitter release but decrease evoked neurotransmitter release. These effects may be caused by an interaction of lead with specific molecular targets involved in neurotransmitter release. We demonstrate here that the normally calcium-dependent binding characteristics of the synaptic vesicle protein synaptotagmin I are altered by lead. Nanomolar concentrations of lead induce the interaction of synaptotagmin I with phospholipid liposomes. The C2A domain of synaptotagmin I is required for lead-mediated phospholipid binding. Lead protects both recombinant and endogenous rat brain synaptotagmin I from proteolytic cleavage in a manner similar to calcium. However, lead is unable to promote the interaction of either recombinant or endogenous synaptotagmin I and syntaxin. Finally, nanomolar concentrations of lead are able to directly compete with and inhibit the ability of micromolar concentrations of calcium to induce the interaction of synaptotagmin I and syntaxin. Based on these findings, we conclude that synaptotagmin I may be an important, physiologically relevant target of lead.

Control of fusion pore dynamics during exocytosis by Munc18

Intracellular membrane fusion is mediated by the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins. All vesicle transport steps also have an essential requirement for a member of the Sec1 protein family, including the neuronal Munc18-1 (also known as nSec1) in regulated exocytosis. Here, in adrenal chromaffin cells, we expressed a Munc18 mutant with reduced affinity for syntaxin, which specifically modified the kinetics of single-granule exocytotic release events, consistent with an acceleration of fusion pore expansion. Thus, Munc18 functions in a late stage in the fusion process, where its dissociation from syntaxin determines the kinetics of postfusion events.

Effects of lead on gene expression

Lead poisoning is a worldwide, environmental health-hazard that affects children and adults. In this review we discuss the effects of lead on gene expression due to both general and specific mechanisms. In particular we focus on the ability of lead to substitute for biologically essential metals such as calcium and zinc in metal-binding domains of cytoplasmic enzymes, nuclear transcription factors and other proteins. The binding of lead to these proteins causes an alteration of their activity resulting in aberrant expression of their own genes and in some cases their target genes. Finally, we discuss the impact of microarray technology on the study of the genome-wide effects of lead and other toxicants on gene expression.

DRAGON: Database Referencing of Array Genes Online

"Database Referencing of Array Genes ONline" or "DRAGON" is a web-accessible database that aids in the analysis of differential gene expression data as a biological annotation tool. Users of DRAGON can submit data sets containing large lists of genes and then choose particular characteristics that DRAGON supplies for all genes on the list rapidly and simultaneously.

AVAILABILITY

The DRAGON database is available for queries on the DRAGON web site www.kennedykrieger.org/pevsnerlab/dragon.htm.

CONTACT

pevsner@kennedykrieger.org or cbouton@jhmi.edu

Regulation of rat magnocellular neurosecretory system by D-aspartate: evidence for biological role(s) of a naturally occurring free D-amino acid in mammals

Little evidence is available for the physiological function of D-amino acids in species other than bacteria. Here we demonstrate that naturally occurring freed -aspartate (D-Asp) is present in all magnocellular neurons of rat hypothalamus. The levels of this naturally occurring D-amino acid were elevated during lactation and returned to normal thereafter in the magnocellular neurosecretory system, which produces oxytocin, a hormone responsible for milk ejection during lactation. Intraperitoneal injections of D-Asp reproducibly increased oxytocin gene expression and decreased the concentration of circulating oxytocin in vivo. Similar changes were observed in the vasopressin system. These results provide evidence for the role(s) of naturally occurring free D-Asp in mammalian physiology. The findings argue against the conventional concept that only L-stereoisomers of amino acids are functional in higher species.

Induction of vascular endothelial growth factor in human astrocytes by lead. Involvement of a protein kinase C/activator protein-1 complex-dependent and hypoxia-inducible factor 1-independent signaling pathway

The mechanism(s) underlying lead neurotoxicity are not fully elucidated. cDNA expression microarray analysis identified lead-sensitive genes in immortalized human fetal astrocytes (SV-FHA). Of the represented genes expressed, vascular endothelial growth factor (VEGF) was one of the most sensitive. Lead induced VEGF mRNA 3-fold and VEGF protein approximately 2-fold with maximum mRNA induction following incubation with 10 micrometer lead acetate for 24 h. Phorbol 12-myristate 13-acetate (PMA), a potent protein kinase C (PKC) activator, increased VEGF mRNA 2-fold and PKC inhibition by GF-109203 completely blocked VEGF induction by lead. Expression of dominant-negative PKC-epsilon, but not PKC-alpha, completely inhibited VEGF mRNA induction by lead. Lead activated the transcription factor AP-1 and increased AP-1-dependent luciferase expression >2-fold. Transfection of cells with a c-jun dominant-negative effectively inhibited both AP-1 activation and VEGF mRNA induction by lead. Hypoxia-inducible factor 1 (HIF-1) activity in SV-FHAs was moderately increased by lead (86%) and PMA (96%). Pretreatment with GF-109203 completely inhibited these effects of lead and PMA. However, lead did not alter HIF-1-dependent luciferase expression and a HIF-1alpha dominant-negative had no effects on the induction of VEGF mRNA by lead. These findings indicate that lead induces VEGF expression in SV-FHAs via a PKC/AP-1-dependent and HIF-1-independent signaling pathway.

Syntaxin 7 and VAMP-7 are soluble N-ethylmaleimide-sensitive factor attachment protein receptors required for late endosome-lysosome and homotypic lysosome fusion in alveolar macrophages

Endocytosis in alveolar macrophages can be reversibly inhibited, permitting the isolation of endocytic vesicles at defined stages of maturation. Using an in vitro fusion assay, we determined that each isolated endosome population was capable of homotypic fusion. All vesicle populations were also capable of heterotypic fusion in a temporally specific manner; early endosomes, isolated 4 min after internalization, could fuse with endosomes isolated 8 min after internalization but not with 12-min endosomes or lysosomes. Lysosomes fuse with 12-min endosomes but not with earlier endosomes. Using homogenous populations of endosomes, we have identified Syntaxin 7 as a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) required for late endosome-lysosome and homotypic lysosome fusion in vitro. A bacterially expressed human Syntaxin 7 lacking the transmembrane domain inhibited homotypic late endosome and lysosome fusion as well as heterotypic late endosome-lysosome fusion. Affinity-purified antibodies directed against Syntaxin 7 also inhibited lysosome fusion in vitro but had no affect on homotypic early endosome fusion. Previous work suggested that human VAMP-7 (vesicle-associated membrane protein-7) was a SNARE required for late endosome-lysosome fusion. A bacterially expressed human VAMP-7 lacking the transmembrane domain inhibited both late endosome-lysosome fusion and homotypic lysosome fusion in vitro. These studies indicate that: 1) fusion along the endocytic pathway is a highly regulated process, and 2) two SNARE molecules, Syntaxin 7 and human VAMP-7, are involved in fusion of vesicles in the late endocytic pathway in alveolar macrophages.

High throughput analysis of gene expression in the human brain

The human brain is thought to have the greatest complexity of gene expression of any region of the body, reflecting the diverse functions of neurons and glia. Studies of gene expression in the human brain may yield fundamental information about the phenotype of brain cells in different stages of development, in different brain regions, and in different physiological and pathological states. As the human genome project nears completion, several technological advances allow the analysis of thousands of expressed genes in a small brain sample. This review describes available sources of human brain material, and several high throughput techniques used to measure the expression of thousands of genes. These techniques include expressed sequence tag (EST) sequencing of cDNA libraries; differential display; subtractive hybridization; serial analysis of gene expression (SAGE); and the emerging technology of high density DNA microarrays. Measurement of gene expression with microarrays and other technologies has potential applications in the study of human brain diseases, including cognitive disorders for which animal models are typically not available. Gene expression measurements may be used to identify genes that are abnormally regulated as a secondary consequence of a disease state, or to identify the response of brain cells to pharmacological treatments.

Detection of endogenous biotin in various tissues: novel functions in the hippocampus and implications for its use in avidin-biotin technology

Significant amounts of endogenous biotin were detected by avidin-peroxidase in fixed rat kidney, liver, and brain. The staining was indistinguishable from the true signals of immunoreactivity and could not be consistently blocked by pretreatment with avidin. The finding that certain neurons in the hippocampus contain more biotin than neurons in other areas of the brain suggests that biotin might have novel functions in the brain other than its well-known role as cofactor of carboxylases. Critical examination of published immunohistochemical localization studies on rat kidney strongly suggests that many false-positive results have been considered as true signals. Interference of endogenous biotin in any study using avidin-biotin technology must be considered if biological tissues are involved. The published data obtained by this method should therefore be reevaluated. Furthermore, appropriate controls, blockers and caution in interpreting results must be exercised, not only in immunohistochemistry but also in any applications of avidin-biotin technology.

Human very long-chain acyl-CoA synthetase and two human homologs: initial characterization and relationship to fatty acid transport protein

Several human genes with a high degree of homology to rat very long-chain acyl-CoA synthetase (rVLCS) and mouse fatty acid transport protein (mFATP) were identified. Full-length cDNA clones were obtained for three genes, and predicted amino acid sequences were generated. Initial characterization indicated that one gene was most likely hVLCS, the human ortholog of rVLCS. The other two (hVLCS-H1 and hVLCS-H2) were more closely related to rVLCS than to mFATP. Phylogenetic analysis of amino acid sequences confirmed that hVLCS-H1 and hVLCS-H2 were evolutionarily closer to VLCSs than FATPs. Alignment of predicted amino acid sequences of human, rat and mouse VLCSs and FATPs revealed the existence of two highly conserved motifs. While one motif is also present in long-chain acyl-CoA synthetases, the other serves to distinguish the VLCS/FATP family from the long-chain synthetase family. Elucidation of the biochemical functions of all VLCS/FATP family members should provide new insights into cellular fatty acid metabolism.

X-linked adrenoleukodystrophy: genes, mutations, and phenotypes

X-linked adrenoleukodystrophy (X-ALD) is a complex and perplexing neurodegenerative disorder. The metabolic abnormality, elevated levels of very long-chain fatty acids in tissues and plasma, and the biochemical defect, reduced peroxisomal very long-chain acyl-CoA synthetase (VLCS) activity, are ubiquitous features of the disease. However, clinical manifestations are highly variable with regard to time of onset, site of initial pathology and rate of progression. In addition, the abnormal gene in X-ALD is not the gene for VLCS. Rather, it encodes a peroxisomal membrane protein with homology to the ATP-binding cassette (ABC) transmembrane transporter superfamily of proteins. The X-ALD protein (ALDP) is closely related to three other peroxisomal membrane ABC proteins. In this report we summarize all known X-ALD mutations and establish the lack of an X-ALD genotype/phenotype correlation. We compare the evolutionary relationships among peroxisomal ABC proteins, demonstrate that ALDP forms homodimers with itself and heterodimers with other peroxisomal ABC proteins and present cDNA complementation studies suggesting that the peroxisomal ABC proteins have overlapping functions. We also establish that there are at least two peroxisomal VLCS activities, one that is ALDP dependent and one that is ALDP independent. Finally, we discuss variable expression of the peroxisomal ABC proteins and ALDP independent VLCS in relation to the variable clinical presentations of X-ALD.

Modulation of oncogenic potential by alternative gene use in human prostate cancer

Only a small percentage of primary prostate cancers have genetic changes. In contrast, nearly 90% of clinically significant human prostate cancers seems to express high levels of the nuclear phosphoprotein pp32 by in situ hybridization. Because pp32 inhibits oncogene-mediated transformation, we investigated its paradoxical expression in cancer by comparing the sequence and function of pp32 species from paired benign prostate tissue and adjacent prostatic carcinoma from three patients. Here we demonstrate that pp32 is expressed in benign prostatic tissue, but pp32r1 and pp32r2, closely-related genes located on different chromosomes, are expressed in prostate cancer. Although pp32 is a tumor suppressor, pp32r1 and pp32r2 are tumorigenic. Alternative use of the pp32, pp32r1 and pp32r2 genes may modulate the oncogenic potential of human prostate cancer.

The expanding beta 4-galactosyltransferase gene family: messages from the databanks

From a systematic search of the UniGene and dbEST databanks, using human beta 4-galactosyltransferase (beta 4GalT-I), which is recognized to function in lactose biosynthesis, as the query sequence, we have identified five additional gene family members denoted as beta 4GalT-II, -III, -IV, -V, and -VI. Complementary DNA clones containing the complete coding regions for each of the five human homologs were obtained or generated by a PCR-based strategy (RACE) and sequenced. Relative to beta 4GalT-I, the percent sequence identity at the amino acid level between the individual family members, ranges from 33% (beta 4GalT-VI) to 55% (beta 4GalT-II). The highest sequence identity between any of the homologs is between beta 4GalT-V and beta 4GalT-VI (68%). beta 4GalT-II is the ortholog of the chicken beta 4GalT-II gene, which has been demonstrated to encode an alpha-lactalbumin responsive beta 4-galactosyltransferase (Shaper et al., J. Biol. Chem., 272, 31389-31399, 1997). As established by Northern analysis, beta 4GalT-II and -IV show the most restricted pattern of tissue expression. High steady state levels of beta 4GalT-II mRNA are seen only in fetal brain and adult heart, muscle, and pancreas; relatively high levels of beta 4GalT-VI mRNA are seen only in adult brain. When the corresponding mouse EST clone for each of the beta 4GalT family members was used as the hybridization probe for Northern analysis of murine mammary tissue, transcription of only the beta 4GalT-I gene could be detected in the lactating mammary gland. These observations support the conclusion that among the six known beta 4GalT family members in the mammalian genome, that have been generated through multiple gene duplication events of an ancestral gene(s), only the beta 4GalT-I ancestral lineage was recruited for lactose biosynthesis during the evolution of mammals.

Regulation of Munc-18/syntaxin 1A interaction by cyclin-dependent kinase 5 in nerve endings

The Munc-18-syntaxin 1A complex has been postulated to act as a negative control on the regulated exocytotic process because its formation blocks the interaction of syntaxin with vesicle SNARE proteins. However, the formation of this complex is simultaneously essential for the final stages of secretion as evidenced by the necessity of Munc-18's homologues in Saccharomyces cerevisiae (Sec1p), Drosophila (ROP), and Caenorhabditis elegans (Unc-18) for proper secretion in these organisms. As such, any event that regulates the interaction of these two proteins is important for the control of secretion. One candidate for such regulation is cyclin-dependent kinase 5 (Cdk5), a member of the Cdc2 family of cell division cycle kinases that has recently been copurified with Munc-18 from rat brain. The present study shows that Cdk5 bound to its neural specific activator p35 not only binds to Munc-18 but utilizes it as a substrate for phosphorylation. Furthermore, it is demonstrated that Munc-18 that has been phosphorylated by Cdk5 has a significantly reduced affinity for syntaxin 1A. Finally, it is shown that Cdk5 can also bind to syntaxin 1A and that a complex of Cdk5, p35, Munc-18, and syntaxin 1A can be fashioned in the absence of ATP and promptly disassembled upon the addition of ATP. These results suggest a model in which p35-activated Cdk5 becomes localized to the Munc-18-syntaxin 1A complex by its affinity for both proteins so that it may phosphorylate Munc-18 and thus permit the positive interaction of syntaxin 1A with upstream protein effectors of the secretory mechanism.

Regulation of CFTR chloride channels by syntaxin and Munc18 isoforms

The cystic fibrosis gene encodes a cyclic AMP-gated chloride channel (CFTR) that mediates electrolyte transport across the luminal surfaces of a variety of epithelial cells. The molecular mechanisms that modulate CFTR activity in epithelial tissues are poorly understood. Here we show that CFTR is regulated by an epithelially expressed syntaxin (syntaxin 1A), a membrane protein that also modulates neurosecretion and calcium-channel gating in brain. Syntaxin 1A physically interacts with CFTR chloride channels and regulates CFTR-mediated currents both in Xenopus oocytes and in epithelial cells that normally express these proteins. The physical and functional interactions between syntaxin 1A and CFTR are blocked by a syntaxin-binding protein of the Munc18 protein family (also called n-Secl). Our results indicate that CFTR function in epithelial cells is regulated by an interplay between syntaxin and Munc18 isoforms.

Human syntaxin 7: a Pep12p/Vps6p homologue implicated in vesicle trafficking to lysosomes

The movement of hydrolases and other proteins to lysosomes is accomplished by vesicle trafficking. Specific vesicles are targeted from the trans-Golgi network via a prelysosomal compartment to lysosomes. The specificity of vesicle transport is thought to occur through the interaction of vesicle proteins with receptors on a particular target membrane. The syntaxins are a family of transmembrane proteins that have been implicated as vesicle receptors involved in vesicle docking and fusion. Syntaxins 1-4 are localized to the plasma membrane, and in particular, syntaxin 1a mediates synaptic vesicle docking in the nerve terminal. Syntaxins 5 and 6 have been localized to cis-Golgi and trans-Golgi network compartments, respectively. We now report the identification of syntaxin 7 from a human brain cDNA library. The syntaxin 7 gene is localized to human chromosome 6. By Northern analysis, the syntaxin RNA was found to be broadly distributed. Based on its homology to yeast and plant vacuolar syntaxins, we propose that syntaxin 7 has a role in vesicle trafficking between the Golgi complex and lysosomes. In vitro binding studies reveal that syntaxin 7 binds alphaSNAP, a key regulator of transport vesicle fusion at multiple stages of the secretory pathway.

Mammalian homologues of yeast vacuolar protein sorting (vps) genes implicated in Golgi-to-lysosome trafficking

Sec1p, Vps33p, Vps45p and Sly1p constitute a family of proteins implicated in vesicle trafficking at distinct stages of the yeast secretory pathway. Several mammalian homologues of Sec1p have been described, including n-sec1 which has been implicated in the regulation of synaptic vesicle docking at the nerve terminal. We have characterized cDNA clones encoding three additional mammalian homologues belonging to this family: r-vps33a and r-vps33b from rat, which are 30 and 26% identical to yeast Vps33p, respectively, and h-vps45 from human which is 38% identical to yeast Vps45p at the amino acid (aa) level. Phylogenetic analysis of 16 Sec1p-related proteins from several species is consistent with the hypothesis that the evolution of this gene family parallels the specialization of vesicle trafficking to distinct intracellular compartments. By Northern analysis, each of these genes is expressed in all tissues examined (brain, spleen, lung, liver, skeletal muscle, kidney, testis). While n-sec1 binds syntaxin 1a, 2, and 3, r-vps33a, r-vps33b and h-vps45 do not bind any of the known syntaxins. We propose that the three proteins bind as yet unidentified syntaxin homologues involved in vesicle trafficking between the Golgi apparatus, prelysosomal compartment(s), and the lysosome.

The three-dimensional structure of bovine odorant binding protein and its mechanism of odor recognition

Odorant binding protein (OBP) is the major odorant binding component of mammalian nasal mucosa. The two structures of bovine OBP reported in this paper (one crystallized as purified and one soaked in the presence of a selenium-containing odorant) show that: (i) the OBP dimer is composed of two compact domains related by an approximate two-fold axis of symmetry; (ii) between residues 122 and 123 the polypeptide chains cross from one domain to the other such that each domain is formed by residues from both monomers; (iii) purified OBP already contains two bound odorant molecules (one per monomer)-odorant binding occurs by replacement of these molecules with the added odorant; and (iv) the structure of the odorant binding site can explain OBP's extraordinarily broad odorant specificity.

The role of Sec1p-related proteins in vesicle trafficking in the nerve terminal

Vesicle trafficking at multiple stages of the secretory pathway depends on a family of soluble proteins related to yeast Sec1p. In yeast, this family consists of four members: the late-acting Sec1p that is required for vesicular transport between the Golgi apparatus and the cell surface; Vps33p and Vps45p which are required for trafficking between the Golgi complex and the lysosome-like vacuole; and Sly1p that is essential for trafficking between the endoplasmic reticulum and the Golgi apparatus. In mammalian systems, homologues of these proteins have been identified. In particular, a neural-specific Sec1p homologue (n-sec1/Munc-18) binds the plasma membrane protein syntaxin and may regulate synaptic vesicle docking. The Sec1p family of proteins is essential for vesicle trafficking in both regulated and constitutive trafficking pathways, and n-sec1 is critical in the regulated release of neurotransmitter from the nerve terminal.

Two rat homologs of clathrin-associated adaptor proteins

A cDNA clone predicted to encode a 46,757-Da protein was isolated from a library derived from the electric lobe of the ray Discopyge ommata. Two rat homologs, p47A and p47B, were subsequently isolated. These three proteins share approx. 80% amino acid (aa) identity to each other and have 27-30% aa identity to rat AP50 and mouse AP47, the medium-chain subunits of adaptor complexes associated with clathrin-coated vesicles. These complexes are involved in receptor-mediated pathways of intracellular transport. Rat p47A mRNA is expressed in all tissues examined, including brain, heart, kidney, liver, lung, muscle and spinal cord. Rat p47B mRNA is detected exclusively in brain and spinal cord, and may participate in nervous system-specific functions such as biogenesis or recycling of synaptic vesicles.

Specificity and regulation of a synaptic vesicle docking complex

Synaptic vesicles are proposed to dock at the presynaptic plasma membrane through the interaction of two integral membrane proteins of synaptic vesicles, VAMP and synaptotagmin, and two plasma membrane proteins, syntaxin and SNAP-25. We have characterized the binding properties of these proteins and observed SNAP-25 potentiation of VAMP 2 binding to syntaxins 1a and 4 but not syntaxins 2 or 3. n-sec1, a neuron-specific syntaxin-binding protein, bound syntaxin with nanomolar affinity, forming a complex that is distinct from the previously identified 7S and 20S syntaxin-containing complexes. This suggests that syntaxin exists in at least three states: bound to n-sec1, in a 7S particle, and in a 20S particle. Recombinant n-sec1 inhibited VAMP or SNAP-25 binding to syntaxin. We propose that the specific associations of VAMP, SNAP-25, and syntaxin mediate vesicle docking and that a syntaxin/n-sec1 complex precedes and/or regulates formation of these complexes.

Mechanisms of vesicle docking and fusion: insights from the nervous system

Upon stimulation of nerve cells, synaptic vesicles fuse with the presynaptic plasma membrane to release neurotransmitter. The biochemical pathway responsible for synaptic-vesicle docking and fusion is now being elucidated. Many of the proteins implicated in this process have homologs elsewhere in the cell. The docking and fusion mechanism discussed in this review may account for the specificity of vesicular trafficking throughout both regulated and constitutive secretory pathways.

n-Sec1: a neural-specific syntaxin-binding protein

We have identified n-Sec1, a rat brain homolog of the yeast Sec1p protein that participates in the constitutive secretory pathway between the Golgi apparatus and the plasma membrane. The rat brain cDNA is predicted to encode a 68-kDa protein with 65% amino acid identity to Drosophila rop, 59% identity to Caenorhabditis elegans unc-18, and 27% identity to Saccharomyces cerevisiae Sec1p. By RNA blot analysis, n-Sec1 mRNA expression is neural-specific. An anti-peptide antiserum directed against the n-Sec1 carboxyl terminus detects a 68-kDa protein in rat brain cytosol and membranes, but not in peripheral tissues. In the presence of syntaxin 1a, a plasma membrane protein implicated in synaptic vesicle docking, n-Sec1 becomes membrane-associated. n-Sec1 binds to syntaxin 1a, 2, and 3 fusion proteins coupled to agarose beads, but not to syntaxin 4 fusion protein or beads coupled to a variety of other proteins. These findings indicate that n-Sec1 is a neural-specific, syntaxin-binding protein that may participate in the regulation of synaptic vesicle docking and fusion.

Association of three small GTP-binding proteins with cholinergic synaptic vesicles

Several small (low molecular weight) GTP-binding proteins are associated with cholinergic synaptic vesicles derived from the electric organ of electric ray. Using GTP overlay techniques and direct micro sequencing we analyzed the association of small GTP-binding proteins with synaptic vesicles. Both experimental procedures revealed the specific occurrence of multiple small GTP-binding proteins with this organelle. Moreover, direct amino acid sequence analysis assigned at least three different small GTP-binding proteins, ora3, o-ral and o-rab3, to the vesicular compartment. Furthermore, the data reflect the relative abundance of these three proteins on the vesicle membrane, thereby demonstrating the predominant occurrence of o-rab3, the only exclusively synaptic vesicle specific small GTP-binding protein.

5'-nucleotidase from the electric ray electric lobe. Primary structure and relation to mammalian and procaryotic enzymes

A cDNA encoding a 5'-nucleotidase was identified by screening a lambda gt10 cDNA library from the electric lobe of Discopyge ommata using a cDNA probe containing the complete open reading frame coding for the rat liver enzyme. Nucleotide sequence analysis defines an open reading frame of 577 amino acids, corresponding to a calculated molecular mass of 63,833 Da. The N-terminus of the mature protein, as determined by direct protein sequencing, is preceded by 29 amino acid residues comprising a signal peptide. The C-terminus contains a stretch of hydrophobic amino acids, considered to be cleaved on post-translational modification and exchanged for glycosylphosphatidylinositol as a membrane anchor. The predicted protein contains four potential N-linked glycosylation sites. Electric ray 5'-nucleotidase shares 61% amino acid identity with the enzymes from rat liver and human placenta, and about 23% with bacterial proteins possessing 5'-nucleotidase activity and also additional enzyme activities like UDP-glucose hydrolase. Polyclonal antibodies raised against 5'-nucleotidase from mammalian sources or the electric ray electric organ reveal mutual cross-reactivity. Interestingly, there are 5-7 domains highly conserved in procaryotes and vertebrates in enzymes exhibiting 5'-nucleotidase, 3'-nucleotidase or phosphodiesterase activity. 5'-nucleotidase isolated from Torpedo electric organ hydrolyzes UDP-glucose at 8% of the rate of AMP hydrolysis. The possible phylogenetic origin of vertebrate 5'-nucleotidase from multifunctional nucleotide hydrolases is discussed.

A synaptic vesicle specific GTP-binding protein from ray electric organ

A cDNA encoding a synaptic vesicle associated GTP-binding protein was identified by screening a lambda gt11 expression library derived from the electric lobe of Discopyge ommata with polyclonal antibodies recognizing vesicle-specific proteins of Mr 25,000. Nucleotide sequence analysis defines an open reading frame of 218 amino acids. The protein belongs to the ras superfamily and shares about 75% amino acid identity with smg-25A, B and C identified in bovine brain and rab3A characterized in rat brain. Northern blot analysis revealed a 4.5 kb transcript present only in neural tissues, the highest level of expression being observed in electric lobe. Western blot analysis of total tissue homogenates derived from D. ommata detected the protein in electric organ, forebrain and to a lesser extent in electric lobe and spinal cord. No immunoreactivity was detected in non-neuronal tissues. Blotting of subcellular fractions derived from electric ray electric organ revealed that the GTP-binding protein co-purifies with synaptic vesicles. The neural specific expression and the localization to synaptic vesicles suggest a role of this protein in synaptic vesicle trafficking and targeting.

Odorant-binding protein. Characterization of ligand binding

We have characterized the odorant binding properties of purified bovine odorant-binding protein (OBP) using as a ligand [3H]3,7-dimethyloctan-1-ol ([3H]DMO). A broad variety of odorants, including terpenes, aldehydes, esters, and musks, bind to OBP with affinities of 0.2 to 100 microM. Odorant affinities for OBP correlate most closely with their stimulation of an odorant-sensitive adenylyl cyclase as well as hydrophobicity. We also measured the kinetics of binding for the ligands, [3H]DMO and 2-isobutyl-3-[3H]methoxypyrazine. Dissociation of both is markedly accelerated in the presence of excess unlabeled ligand. Competition curves of displacers for [3H]DMO binding are shallow, and saturation binding isotherms for 3H-odorants are curvilinear. These kinetic and equilibrium binding properties suggest that OBP interactions with odorant ligands are negatively cooperative.

Abnormal renal mobility--an indication for surgical intervention

Movable kidney is a debated entity and therefore not diagnosed in many cases. According to our experience the diagnosis should be made much more frequent in patients who suffer from loin and/or abdominal pain which is relieved by recumbent position. Twenty-nine cases of patients who suffered from loin and/or abdominal pain and were diagnosed as suffering from abnormal renal mobility by medical history, intravenous pyelogram, angiography and dynamic scanning were operated upon with a reported high rate of relief of pain (87%; 25/29). The technique employed was the modified Deming operation.

Molecular mechanisms of olfaction

Recent studies provide initial insights into molecular mechanisms of olfaction. The identification of an odorant-sensitive adenylate cyclase which responds to most odorants, affords a second messenger system following odorant interactions with receptors. Cyclic nucleotide- and odorant-gated ion channels have been demonstrated in olfactory cilia, providing signalling systems in place of or in addition to protein phosphorylation. A unique odorant-binding protein localized to nasal mucosa binds odorants in proportion to their odoriferous potencies. Molecular cloning of the isolated protein reveals it to be a member of a family of proteins that serve as carriers for small lipophilic molecules such as retinol and cholesterol. The odorant-binding protein is localized to lateral nasal glands whose secretions are atomized into the tip of the nose where the binding protein presumably interacts with odorants in the inspired air.

Molecular cloning of odorant-binding protein: member of a ligand carrier family

Odorant-binding protein (OBP) is found in nasal epithelium, and it selectively binds odorants. Three complementary DNAs encoding rat odorant-binding protein have now been cloned and sequenced. One clone contains an open reading frame predicted to encode an 18,091-dalton protein. RNA blot analysis confirms the localization of OBP messenger RNA in the nasal epithelium. This OBP has 33 percent amino acid identity to alpha 2-microglobulin, a secreted plasma protein. Other members of an alpha 2-microglobulin superfamily bind and transport hydrophobic ligands. Thus, OBP probably binds and carries odorants within the nasal epithelium to putative olfactory receptors.

Odorant-binding protein and its mRNA are localized to lateral nasal gland implying a carrier function

Odorant-binding protein selectively binds various odorants and is discretely concentrated in nasal mucosa and secretions. We have localized rat odorant-binding protein mRNA to the lateral nasal gland by in situ hybridization histochemistry and have also localized the protein to this gland by immunohistochemistry and by tritiated-odorant autoradiography. The lateral nasal gland extends a long duct toward the external nares. Odorant-binding protein, released from this duct, may transport odorants to olfactory receptor neurons.

Odorant-binding protein: localization to nasal glands and secretions

An odorant-binding protein (OBP) was isolated from bovine olfactory and respiratory mucosa. We have produced polyclonal antisera to this protein and report its immunohistochemical localization to mucus-secreting glands of the olfactory and respiratory mucosa. Although OBP was originally isolated as a pyrazine binding protein, both rat and bovine OBP also bind the odorants [3H]methyldihydrojasmonate and 3,7-dimethyl-octan-1-ol as well as 2-isobutyl-3-[3H]methoxypyrazine. We detect substantial odorant-binding activity attributable to OBP in secreted rat nasal mucus and tears but not in saliva, suggesting a role for OBP in transporting or concentrating odorants.

Fetal methylazoxymethanol acetate-induced lesions cause reductions in dopamine receptor-mediated catalepsy and stereotypy

Telencephalic hypoplasia induced by methylazoxymethanol acetate (MAM) resulted in increased activity of tyrosine hydroxylase in the striatum, indicative of a relative increase in the density of dopaminergic terminals in the remaining tissue. Administration of the dopamine receptor stimulant, apomorphine, or the receptor blocker, haloperidol, produced less stereotypy and catalepsy, respectively, in rats lesioned with methylazoxymethanol, compared to controls. These behavioral changes probably resulted from the loss of striatal perikarya and consequent decrease in nigrostriatal dopaminergic target sites caused by methylazoxymethanol.

Parametric influences on catalepsy

Normal haloperidol-injected rats were tested on a standard catalepsy bar test, using varying bar heights, diameters, and descent latency measurement criteria. The results demonstrated that all these small procedural differences can markedly influence the duration of catalepsy exhibited by rats and should be standardized in catalepsy experiments.