Interaction of RAFT1 with gephyrin required for rapamycin-sensitive signaling

RAFT1 (rapamycin and FKBP12 target 1; also called FRAP or mTOR) is a member of the ATM (ataxia telangiectasia mutated)-related family of proteins and functions as the in vivo mediator of the effects of the immunosuppressant rapamycin and as an important regulator of messenger RNA translation. In mammalian cells RAFT1 interacted with gephyrin, a widely expressed protein necessary for the clustering of glycine receptors at the cell membrane of neurons. RAFT1 mutants that could not associate with gephyrin failed to signal to downstream molecules, including the p70 ribosomal S6 kinase and the eIF-4E binding protein, 4E-BP1. The interaction with gephyrin ascribes a function to the large amino-terminal region of an ATM-related protein and reveals a role in signal transduction for the clustering protein gephyrin.

Poly(ADP-ribose) polymerase-deficient mice are protected from streptozotocin-induced diabetes

Streptozotocin (STZ) selectively destroys insulin-producing beta islet cells of the pancreas providing a model of type I diabetes. Poly(ADP-ribose) polymerase (PARP) is a nuclear enzyme whose overactivation by DNA strand breaks depletes its substrate NAD+ and then ATP, leading to cellular death from energy depletion. We demonstrate DNA damage and a major activation of PARP in pancreatic islets of STZ-treated mice. These mice display a 500% increase in blood glucose and major pancreatic islet damage. In mice with homozygous targeted deletion of PARP (PARP -/-), blood glucose and pancreatic islet structure are normal, indicating virtually total protection from STZ diabetes. Partial protection occurs in PARP +/- animals. Thus, PARP activation may participate in the pathophysiology of type I diabetes, for which PARP inhibitors might afford therapeutic benefit.

Nocturnal motor coordination deficits in neuronal nitric oxide synthase knock-out mice

Nitric oxide is formed in the brain primarily by neurons containing neuronal nitric oxide synthase (nNOS), though some neurons may express endothelial NOS (eNOS), and inducible NOS (iNOS) only occurs in neurons following toxic stimuli. Mice with targeted disruption of nNOS (nNOS-) display distended stomachs with hypertrophied pyloric sphincters reflecting loss of nNOS in myenteric plexus neurons. nNOS- animals resist brain damage following middle cerebral artery occlusions consistent with evidence that excess release of nitric oxide mediates neurotoxicity in ischemic stroke. Neuronal NOS- mice have no grossly evident defects in locomotor activity, breeding long-term depression in the cerebellum, long-term potentiation in the hippocampus, and overall sensorimotor function. However, nNOS- animals display excessive, inappropriate sexual behavior and dramatic increases in aggression. Because the cerebellum possesses the greatest levels of nNOS neurons in the brain, it was surprising that presumed cerebellar functions such as balance and coordination were grossly normal in nNOS- mice. These previous studies were all conducted during the day (between 1400 and 1600, lights on at 0700). We now report striking, discrete abnormalities in balance and motor coordination in nNOS-mice reflected selectively at night.

Cloning, characterisation and expression of the alpha-tubulin genes of the leech, Hirudo medicinalis

We have isolated two alpha-tubulin cDNAs from the leech, Hirudo medicinalis. Both encode putative proteins of 451 amino-acids which differ from each other at only two positions. Southern blotting suggests that there are only two alpha-tubulin genes in the leech. The genes contain two introns and, because of the extremely high homology of the nucleotide sequence from the second intron to the end of the genes, we have inferred that a gene conversion event about 9.5 million years ago has homogenised the Hirudo alpha-tubulin sequences. Using in situ hybridisation to tissue sections, we have shown that the two genes are probably expressed in all neurons of the leech ganglia and that their spatial distribution remains unchanged during neuronal regeneration. The deduced amino-acid sequences of the leech alpha-tubulins show that they have greatest similarity to those from a platyhelminth, echiuran and mollusc with rather less to arthropod alpha-tubulins. The protein sequences of the leech alpha-tubulins have been compared with representatives of those from across all phyla to determine if any specific feature labels certain isotypes of tubulin for neuronal expression.

Neurobehavioral deficits in mice lacking the erythrocyte membrane cytoskeletal protein 4.1

The erythrocyte membrane cytoskeletal protein 4.1 (4.1R) is a structural protein that confers stability and flexibility to erythrocytes via interactions with the cytoskeletal proteins spectrin and F-actin and with the band 3 and glycophorin C membrane proteins. Mutations in 4.1R can cause hereditary elliptocytosis, a disease characterized by a loss of the normal discoid morphology of erythrocytes, resulting in hemolytic anemia [1]. Different isoforms of the 4.1 protein have been identified in a wide variety of nonerythroid tissues by immunological methods [2-5]. The variation in molecular weight of these different 4.1 isoforms, which range from 30 to 210 kDa [6], has been attributed to complex alternative splicing of the 4.1R gene [7]. We recently identified two new 4.1 genes: one is generally expressed throughout the body (4. 1G) [8] and the other is expressed in central and peripheral neurons (4.1N) [9]. Here, we examined 4.1R expression by in situ hybridization analysis and found that 4.1R was selectively expressed in hematopoietic tissues and in specific neuronal populations. In the brain, high levels of 4.1R were discretely localized to granule cells in the cerebellum and dentate gyrus. We generated mice that lacked 4.1R expression; these mice had deficits in movement, coordination, balance and learning, in addition to the predicted hematological abnormalities. The neurobehavioral findings are consistent with the distribution of 4.1R in the brain, suggesting that 4.1R performs specific functions in the central nervous system.

Cain, a novel physiologic protein inhibitor of calcineurin

Calcineurin is a widely distributed protein phosphatase regulated by calcium and calmodulin. It mediates the immunosuppressive actions of drugs such as cyclosporin and FK506, and has been implicated in a number of calcium-sensitive pathways in the nervous system, including regulation of neurotransmitter release and modulation of long-term changes in synaptic plasticity. Calcineurin associates physiologically with other proteins, including calmodulin, FKBP12 (FK506-binding protein), the ryanodine receptor, and the inositol 1,4,5-trisphosphate receptor. We now report the identification, molecular cloning, and functional characterization of a novel protein, cain (calcineurin inhibitor), that interacts with and inhibits calcineurin. The full-length cain cDNA predicts a 240-kDa protein with no significant homology to any known protein. Cain associates with calcineurin both in vitro and in vivo, leading to a non-competitive inhibition of calcineurin activity. The putative calcineurin-binding domain of cain, a 38-amino acid region defined by mutational analysis, is highly basic. Like calcineurin, cain has a prominent neuronal expression and a wide tissue distribution. Cain's expression pattern in the brain closely resembles that of calcineurin, indicating a physiologic association between the two proteins.

Neurabin is a synaptic protein linking p70 S6 kinase and the neuronal cytoskeleton

p70 S6 kinase (p70(S6k)) is a mitogen-activated protein kinase that plays a central role in the control of mRNA translation. It physiologically phosphorylates the S6 protein of the 40s ribosomal subunit in response to mitogenic stimuli and is a downstream component of the rapamycin-sensitive pathway, which includes the 12-kDa FK506 binding protein and includes rapamycin and the 12-kDa FK506 binding protein target 1. Here, we report the identification of neurabin (neural tissue-specific F-actin binding protein), a neuronally enriched protein of 1,095 amino acids that contains a PDZ domain and binds p70(S6k). We demonstrate the neurabin-p70(S6k) interaction by yeast two-hybrid analysis and biochemical techniques. p70(S6k) and neurabin coimmunoprecipitate from transfected HEK293 cells. Site-directed mutagenesis of neurabin implicates its PDZ domain in the interaction with p70(S6k), and deletion of the carboxyl-terminal five amino acids of p70(S6k) abrogates the interaction. Cotransfection of neurabin in HEK293 cells activates p70(S6k) kinase activity. The mRNA of neurabin and p70(S6k) show striking colocalization in brain sections by in situ hybridization. Subcellular fractionation of rat brain demonstrates that neurabin and p70(S6k) both localize to the soluble fraction of synaptosomes. By way of its PDZ domain, the neuronal-specific neurabin may target p70(S6k) to nerve terminals.

Two novel odorant receptor families expressed in spermatids undergo 5'-splicing

We report the identification of two novel families of odorant receptor (OdR)-like proteins, termed spermatid chemoreceptors (SCRs), in rat spermatids of the testis. The full-length genomic clones encode seven transmembrane domain receptors that share 35-40% identity with certain OdRs and are among the most divergent members of the OdR superfamily based on phylogenetic analysis. RNase protection assays and in situ hybridization studies confirmed the expression of SCRs in spermatids, the post-meiotic, differentiating cell population in the testis. SCR transcripts were undetectable in the prepubertal testis but were readily identified in spermatids of sexually maturing and mature testis. Rapid amplification of cDNA end-polymerase chain reaction and genomic clone sequencing led to the discovery that SCRs are spliced upstream of their presumptive starting methionines. 5'-Splicing of OdRs may regulate the expression of functional chemoreceptors.

The 13-kD FK506 binding protein, FKBP13, interacts with a novel homologue of the erythrocyte membrane cytoskeletal protein 4.1

We have identified a novel generally expressed homologue of the erythrocyte membrane cytoskeletal protein 4.1, named 4.1G, based on the interaction of its COOH-terminal domain (CTD) with the immunophilin FKBP13. The 129-amino acid peptide, designated 4.1G-CTD, is the first known physiologic binding target of FKBP13. FKBP13 is a 13-kD protein originally identified by its high affinity binding to the immunosuppressant drugs FK506 and rapamycin (Jin, Y., M.W. Albers, W.S. Lane, B.E. Bierer, and S.J. Burakoff. 1991. Proc. Natl. Acad. Sci. USA. 88:6677- 6681); it is a membrane-associated protein thought to function as an ER chaperone (Bush, K.T., B.A. Henrickson, and S.K. Nigam. 1994. Biochem. J. [Tokyo]. 303:705-708). We report the specific association of FKBP13 with 4.1G-CTD based on yeast two-hybrid, in vitro binding and coimmunoprecipitation experiments. The histidyl-proline moiety of 4.1G-CTD is required for FKBP13 binding, as indicated by yeast experiments with truncated and mutated 4.1G-CTD constructs. In situ hybridization studies reveal cellular colocalizations for FKBP13 and 4.1G-CTD throughout the body during development, supporting a physiologic role for the interaction. Interestingly, FKBP13 cofractionates with the red blood cell homologue of 4.1 (4.1R) in ghosts, inside-out vesicles, and Triton shell preparations. The identification of FKBP13 in erythrocytes, which lack ER, suggests that FKBP13 may additionally function as a component of membrane cytoskeletal scaffolds.

Molecularly cloned mammalian glucosamine-6-phosphate deaminase localizes to transporting epithelium and lacks oscillin activity

Glucosamine-6-phosphate deaminase (GNPDA) catalyzes the conversion of glucosamine-6-phosphate to fructose-6-phosphate, a reaction that under physiological conditions proceeds to the formation of fructose-6-phosphate. Though first identified in mammalian tissues in 1956, the enzyme has not previously been molecularly characterized in mammalian tissues, although a bacterial GNPDA has been cloned. Recently, a protein displaying similarity to bacterial GNPDA was purified and cloned from sperm extract. It was proposed that this protein was the factor, found in sperm extracts, that causes calcium oscillations in cells; thus, the protein was named 'oscillin.' We demonstrate that oscillin is the mammalian form of glucosamine 6-phosphate deaminase by showing that cloned oscillin has a robust GNPDA activity and can account for all such activity in mammalian tissues extracts. In situ hybridization and immunohistochemistry localize GNPDA selectively to tissues with high energy requirements such as the apical zone of transporting epithelia in the proximal convoluted tubules of the kidney and the small intestine; to neurons (but not glia) and especially to nerve terminals in the brain; and to motile sperm. Recombinant GNPDA and GNPDA purified to homogeneity from hamster sperm fail to elevate intracellular calcium when injected into mouse eggs over a wide range of concentrations under conditions in which sperm extracts elicit pronounced calcium oscillations. Thus, the calcium-releasing or oscillin activity of sperm extracts is due to a substance other than GNPDA. Since GNPDA is the sole enzyme linking hexosamine systems with glycolytic pathways, we propose that it provides a source of energy in the form of phosphosugar derived from the catabolism of hexosamines found in glycoproteins, glycolipids, and sialic acid-containing macromolecules. Evidence that GNPDA can regulate hexosamine stores comes from our observation that transfection of GNPDA into HEK-293 cells reduces cellular levels of sialic acid.

Parapinopsin, a novel catfish opsin localized to the parapineal organ, defines a new gene family

Multiple sites of extraretinal photoreception are present in vertebrates, but the molecular basis of extraretinal phototransduction is poorly understood. This study reports the cloning of the first opsin specifically expressed in the directly photosensitive pineal and parapineal of cold-blooded vertebrates. This opsin, identified in channel catfish and termed parapinopsin, defines a new gene family of vertebrate photopigments and is expressed in a majority of parapinealocytes and a subset of pineal photoreceptor cells. Parapinopsin shows a caudal-rostral gradient of expression within the pineal organ. This study also reports the cloning of partial cDNAs encoding the channel catfish orthologues of rhodopsin and the red cone pigment-the full complement of retinal opsins in the species. In situ hybridization studies using probes derived from these retinal opsins, together with parapinopsin, reveal no expression of retinal opsins in pineal and parapineal organ and no expression of any opsin tested in the "deep brain," iris, or dermal melanophores. These data imply that phototransduction in these sites of extraretinal photoreception must be mediated by novel opsins.

Developmental expression pattern of phototransduction components in mammalian pineal implies a light-sensing function

Whereas the pineal organs of lower vertebrates have been shown to be photosensitive, photic regulation of pineal function in adult mammals is thought be mediated entirely by retinal photoreceptors. Extraretinal regulation of pineal function has been reported in neonatal rodents, although both the site and molecular basis of extraretinal photoreception have remained obscure. In this study we examine the developmental expression pattern of all of the principal components of retinal phototransduction in rat pineal via cRNA in situ hybridization. All of the components needed to reconstitute a functional phototransduction pathway are expressed in the majority of neonatal pinealocytes, although the expression levels of many of these genes decline dramatically during development. These findings strongly support the theory that the neonatal rat pineal itself is photosensitive. In addition, we observe in neonatal pinealocytes the expression of both rod-specific and cone-specific phototransduction components, implying the existence of functionally different subtypes of pinealocytes that express varying combinations of phototransduction enzymes.

The development of excitatory synapses in cultured spinal neurons

Immunohistochemical studies of synapses in the CNS have demonstrated that glutamate receptors (GluRs) are concentrated at postsynaptic sites in vivo and in vitro (Baude et al., 1995). The mechanisms leading to receptor clustering at excitatory synapses are far less understood than those governing acetylcholine receptor accumulation at the neuromuscular junction () or glycine receptor aggregation at central inhibitory synapses (). Using cultured rat spinal cord neurons, we demonstrate that clustering of the AMPA receptor subunit GluR1 is among the earliest events in excitatory synapse formation in vitro, coincident with the onset of miniature EPSCs and in many cases preceding presynaptic vesicle accumulation. Postsynaptic receptor clustering is induced in a highly specific and reiterative pattern, independent of receptor activation, by contact with a subset of axons capable of inducing receptor clusters. The subunit composition of AMPA receptor clusters varied significantly between neurons but was invariant within a given neuron. The presence of either GluR2 or GluR3 was common to all receptor clusters. Neither high-affinity glutamate transporters nor NMDA receptors appeared to be concentrated with AMPA receptor subunits at these excitatory synapses.

Neuronal nitric oxide synthase alternatively spliced forms: prominent functional localizations in the brain

Neuronal nitric-oxide synthase (nNOS) is subject to alternative splicing. In mice with targeted deletions of exon 2 (nNOS(delta/delta)), two alternatively spliced forms, nNOS beta and gamma, which lack exon 2, have been described. We have compared localizations of native nNOS alpha and nNOS beta and gamma by in situ hybridization and immunohistochemistry in wild-type and nNOS(delta/delta) mice. To assess nNOS catalytic activity in intact animals we localized citrulline, which is formed stoichiometrically with NO, by immunohistochemistry. nNOS beta is prominent in several brain regions of wild-type animals and shows 2-to 3-fold up-regulation in the cortex and striatum of nNOS(delta/delta) animals. The persistence of much nNOS mRNA and protein, and distinct citrulline immunoreactivity (cit-IR) in the ventral cochlear nuclei and some cit-IR in the striatum and lateral tegmental nuclei, indicate that nNOS beta is a major functional form of the enzyme in these regions. Thus, nNOS beta, and possibly other uncharacterized splice forms, appear to be important physiological sources of NO in discrete brain regions and may account for the relatively modest level of impairment in nNOS(delta/delta) animals.

Neurite outgrowth through lesions of neonatal opossum spinal cord in culture

The aim of these experiments was to analyze neurite outgrowth during regeneration of opossum spinal cord isolated from Monodelfis domestica and maintained in culture for 3-5 days. Lesions were made by crushing with forceps. In isolated spinal cords of animals aged 3 days, neurites entered the crush and grew along the basal lamina of the pia mater. Growth cones with pleiomorphic appearance containing vesicles, mitochondria and microtubules were abundant in the marginal zone, as were synaptoid contacts with active zones facing basal lamina. In preparations from animals aged 11-12 days, the lesion site was disrupted and contained only degenerating axons, debris and vesicles. Axons and growth cones entered the edge of the lesion but did not extend into it. Lesions in young animals extended over distances of more than 1 mm and contained no radial glia. The damaged area in older preparations was restricted to the crush site with normal astrocytes, oligodendrocytes and neurons immediately adjacent to the lesion. Thus, similar crushes produced more extensive damage in younger spinal cords that were capable of regeneration than in older cords that were not. Dorsal root ganglion fibers labeled with carbocyanine dye (DiI) were observed by video imaging as they grew through lesions. Individual growth cones examined subsequently by electron microscopy had grown again along pial basal lamina. After 5 days in culture dorsal root stimulation gave rise to discharges in ventral roots beyond the lesion indicating that synaptic connections were formed by growing fibers.

Expression and localization of amiloride-sensitive sodium channel indicate a role for non-taste cells in taste perception

Salty taste is blocked by the diuretic amiloride, which inhibits specific sodium channels. We have isolated an amiloride-sensitive sodium channel (ASSC) from taste tissues by polymerase chain reaction and screening of a cDNA library prepared from rat circumvallate papillae. Northern analysis reveals ASSC in taste and non-taste tissues with the highest level of expression of ASSC in the lung. In situ hybridization establishes ASSC localizations in the epithelia of lung and colon as well as tongue epithelial layers containing and lacking taste buds. These results support a model in which ASSC in non-taste cells regulates responses of taste cells to salt as well as other tastants.

cDNA libraries from a few neural cells

One of the most powerful approaches to the molecular analysis of differential gene expression is to construct cDNA libraries corresponding to different tissues or developmental stages, and then to enrich for genes expressed in a particular tissue or at a particular time by subtractive hybridisation. Our aim is to reduce the complexity of neuronal cDNA libraries by generating libraries from the mRNA of a single cell. The system chosen is the Retzius cell of the leech, a large neurone which can be unambiguously dissected out. A cDNA library was generated from one leech ganglion (containing about 400 neurons) by anchor 1-oligo dT priming, the addition of dG tails, second strand synthesis primed by an anchor 2-oligo dC primer, followed by PCR from the two anchor regions. XBaI and EcoRI sites were included in the respective anchor primers, between the dT or dC run and the PCR primer sequence, allowing high-efficiency directional cloning. Eight clones picked and sequenced at random gave five with some homology to a known protein and three novel genes. The average insert size in the library was 600 bp, 0.2% of the clones hybridised to repetitive DNA, and 20/30,000 clones gave signals with the Drosophila actin gene. This approach has now been extended to a few pooled Retzius cells.

Cellular and molecular approaches to neural repair in the medicinal leech

Investigation of repair processes and the effects of damage in the leech has the advantage that it is possible to work with single neurons, and that leech neurons can regenerate. The effects of surface topology on neuronal outgrowth in culture were investigated using patterned substrates produced by photolithography. On grooved substrates with a depth, width and separation of 2 microns, the processes of cultured neurons showed significant alignment. In studies on regeneration, different mechanosensory neurons were shown to respond differently to lesions of their axons. High threshold units (N cells) respond by sprouting of additional processes from the axon hillock region within the CNS, whereas low threshold cells respond with a sprouting only at the lesion site in the nerve root and not within the CNS. Sprouted processes are retained for over a year. When a neuron of a particular modality is killed, cells of the same modality (but not the other) expand their receptive fields to cover the denervated skin. Single channel patch clamp recording experiments have been initiated on damaged neurons. Experiments are in progress to clone genes whose expression is regulated after peripheral nerve injury.

Longitudinal effect of amitriptyline and fluoxetine treatment on plasma phenylacetic acid concentrations in depression

Unconjugated (U-PAA), conjugated (C-PAA), and total phenylacetic acid (T-PAA) concentrations in blood plasma and monoamine oxidase (MAO) activity in platelets towards phenylethylamine (PE) were determined in 40 drug-free, depressed patients (23 melancholic, 17 nonmelancholic) from five psychiatric treatment centers, and in 34 normal healthy volunteers. No significant differences were found between controls and all depressed patients or between melancholic and nonmelancholic depressed patients. Treatment of the depressed patients with amitriptyline or fluoxetine over a 6-week period resulted in clinical improvement and in a significant increase in plasma PAA concentrations. A decline in the Beck and Hamilton rating scores during treatment correlated significantly with increases in the concentrations of unconjugated, conjugated, and total phenylacetic acid but not with MAO activity, which did not change during treatment. At each of the three assessment times, however, plasma PAA concentrations and psychiatric rating scores were not significantly correlated. Except for higher end-of-study T-PAA concentrations in the amitriptyline-treated subjects, no significant differences were found between the effects of the two drugs with regard to plasma phenylacetic acid levels, MAO activity, or rating scores.

Deuterium-labelled p-tyramine challenge test and phenolsulfotransferase activity in depressed patients--failure to replicate decreased p-tyramine conjugation in depression

1. Depressed and normal subjects were challenged with deuterium-labelled p-tyramine and urine was collected for 3 h. 2. Urinary excretion of conjugated p-tyramine was not significantly different between normal, melancholic and non-melancholic depressed subjects. 3. Platelet phenolsulfotransferase activity to p-tyramine (p less than 0.05) and to phenol (p less than 0.005) were significantly lower in the depressed patients.

A comparison of fluoxetine and amitriptyline in the treatment of major depression

Fluoxetine, a new serotonin uptake blocking antidepressant, was compared with amitriptyline in a double-blind study. Patients were diagnosed as having major depression, according to DSM-III criteria, when interviewed with the Diagnostic Interview Schedule. There was significant improvement in patient and observer ratings of depression in both groups, with no difference between groups. Recent memory improved significantly in the fluoxetine group but not in the amitriptyline group. Numbers of patients reporting side-effects were similar but the profiles of side-effects were different, with more patients on amitriptyline reporting anticholinergic and intolerable side-effects.

A case of atypical psychosis associated with alexithymia and a left fronto-temporal lesion: possible correlations

The case history is presented of a man with an atypical psychosis and classical clinical features of alexithymia. On his last admission, the patient presented with starvation and hypernatremic coma. A CT scan, which was done because of the coma, revealed a large left fronto-temporal arachnoid cyst. The significance of this finding is reviewed in the light of previously suggested organic bases for alexithymia and related syndromes. Although the symptom of alexithymia is present, the patient's other symptoms do not fit readily into existing diagnostic categories and the resulting diagnostic dilemma is discussed.