Insulinoma-Associated Protein IA-2, a Vesicle Transmembrane Protein, Genetically Interacts with UNC-31/CAPS and Affects Neurosecretion in Caenorhabditis elegans

The exocytosis regulator complexin controls spontaneous synaptic vesicle release in a CAPS-dependent manner at C. elegans excitatory synapses

The balance between synaptic excitation and inhibition (E/I) is essential for coordinating motor behavior, yet the differential roles of exocytosis regulators in this balance are less understood. In this study, we investigated the roles of 2 conserved exocytosis regulators, complexin/CPX-1 and CAPS/UNC-31, in excitatory versus inhibitory synapses at Caenorhabditis elegans neuromuscular junctions. cpx-1 null mutants exhibited a marked increase in spontaneous release specifically at excitatory synapses, alongside an unequal reduction in excitatory and inhibitory evoked release. A clamping-specific knockin mutant, cpx-1(Δ12), which preserved evoked release, also showed a biased enhancement in excitatory spontaneous release. Conversely, the unc-31 null mutation, while maintaining normal spontaneous release, displayed a more pronounced reduction in evoked release at excitatory synapses. Notably, we found that CPX-1's clamping function is dependent on UNC-31 and is sensitive to external Ca2+. Pull-down experiments confirmed that CAPS/UNC-31 does not directly interact with complexin, implying an indirect regulatory mechanism. Moreover, complexin regulates activity-dependent synaptic plasticity, which is also UNC-31 dependent. The unexpected role of CAPS/UNC-31 in the absence of CPX-1 clamping function may underpin the synaptic E/I balance and coordinated behavioral outputs in different species.

The role of kinesin-1 in neuronal dense core vesicle transport, locomotion and lifespan regulation in C. elegans

Fast axonal transport is crucial for neuronal function and is driven by kinesins and cytoplasmic dynein. Here, we investigated the role of kinesin-1 in dense core vesicle (DCV) transport in C. elegans, using mutants in the kinesin light chains (klc-1 and klc-2) and the motor subunit (unc-116) expressing an ida-1::gfp transgene that labels DCVs. DCV transport in both directions was greatly impaired in an unc-116 mutant and had reduced velocity in a klc-2 mutant. In contrast, the speed of retrograde DCV transport was increased in a klc-1 mutant whereas anterograde transport was unaffected. We identified striking differences between the klc mutants in their effects on worm locomotion and responses to drugs affecting neuromuscular junction activity. We also determined lifespan, finding that unc-116 mutant was short-lived whereas the klc single mutant lifespan was wild type. The ida-1::gfp transgenic strain was also short-lived, but surprisingly, klc-1 and klc-2 extended the ida-1::gfp lifespan beyond that of wild type. Our findings suggest that kinesin-1 not only influences anterograde and retrograde DCV transport but is also involved in regulating lifespan and locomotion, with the two kinesin light chains playing distinct roles.

Disrupted hypothalamic transcriptomics and proteomics in a mouse model of type 2 diabetes exposed to recurrent hypoglycaemia

AIMS/HYPOTHESIS

Repeated exposures to insulin-induced hypoglycaemia in people with diabetes progressively impairs the counterregulatory response (CRR) that restores normoglycaemia. This defect is characterised by reduced secretion of glucagon and other counterregulatory hormones. Evidence indicates that glucose-responsive neurons located in the hypothalamus orchestrate the CRR. Here, we aimed to identify the changes in hypothalamic gene and protein expression that underlie impaired CRR in a mouse model of defective CRR.

METHODS

High-fat-diet fed and low-dose streptozocin-treated C57BL/6N mice were exposed to one (acute hypoglycaemia [AH]) or multiple (recurrent hypoglycaemia [RH]) insulin-induced hypoglycaemic episodes and plasma glucagon levels were measured. Single-nuclei RNA-seq (snRNA-seq) data were obtained from the hypothalamus and cortex of mice exposed to AH and RH. Proteomic data were obtained from hypothalamic synaptosomal fractions.

RESULTS

The final insulin injection resulted in similar plasma glucose levels in the RH group and AH groups, but glucagon secretion was significantly lower in the RH group (AH: 94.5±9.2 ng/l [n=33]; RH: 59.0±4.8 ng/l [n=37]; p<0.001). Analysis of snRNA-seq data revealed similar proportions of hypothalamic cell subpopulations in the AH- and RH-exposed mice. Changes in transcriptional profiles were found in all cell types analysed. In neurons from RH-exposed mice, we observed a significant decrease in expression of Avp, Pmch and Pcsk1n, and the most overexpressed gene was Kcnq1ot1, as compared with AH-exposed mice. Gene ontology analysis of differentially expressed genes (DEGs) indicated a coordinated decrease in many oxidative phosphorylation genes and reduced expression of vacuolar H+- and Na+/K+-ATPases; these observations were in large part confirmed in the proteomic analysis of synaptosomal fractions. Compared with AH-exposed mice, oligodendrocytes from RH-exposed mice had major changes in gene expression that suggested reduced myelin formation. In astrocytes from RH-exposed mice, DEGs indicated reduced capacity for neurotransmitters scavenging in tripartite synapses as compared with astrocytes from AH-exposed mice. In addition, in neurons and astrocytes, multiple changes in gene expression suggested increased amyloid beta (Aβ) production and stability. The snRNA-seq analysis of the cortex showed that the adaptation to RH involved different biological processes from those seen in the hypothalamus.

CONCLUSIONS/INTERPRETATION

The present study provides a model of defective counterregulation in a mouse model of type 2 diabetes. It shows that repeated hypoglycaemic episodes induce multiple defects affecting all hypothalamic cell types and their interactions, indicative of impaired neuronal network signalling and dysegulated hypoglycaemia sensing, and displaying features of neurodegenerative diseases. It also shows that repeated hypoglycaemia leads to specific molecular adaptation in the hypothalamus when compared with the cortex.

DATA AVAILABILITY

The transcriptomic dataset is available via the GEO ( http://www.ncbi.nlm.nih.gov/geo/ ), using the accession no. GSE226277. The proteomic dataset is available via the ProteomeXchange data repository ( http://www.proteomexchange.org ), using the accession no. PXD040183.

Inhibition of ribosome biogenesis in the epidermis is sufficient to trigger organism-wide growth quiescence independently of nutritional status in C. elegans

Interorgan communication is crucial for multicellular organismal growth, development, and homeostasis. Cell nonautonomous inhibitory cues, which limit tissue-specific growth alterations, are not well characterized due to cell ablation approach limitations. In this study, we employed the auxin-inducible degradation system in C. elegans to temporally and spatially modulate ribosome biogenesis, through depletion of essential factors (RPOA-2, GRWD-1, or TSR-2). Our findings reveal that embryo-wide inhibition of ribosome biogenesis induces a reversible early larval growth quiescence, distinguished by a unique gene expression signature that is different from starvation or dauer stages. When ribosome biogenesis is inhibited in volumetrically similar tissues, including body wall muscle, epidermis, pharynx, intestine, or germ line, it results in proportionally stunted growth across the organism to different degrees. We show that specifically inhibiting ribosome biogenesis in the epidermis is sufficient to trigger an organism-wide growth quiescence. Epidermis-specific ribosome depletion leads to larval growth quiescence at the L3 stage, reduces organism-wide protein synthesis, and induced cell nonautonomous gene expression alterations. Further molecular analysis reveals overexpression of secreted proteins, suggesting an organism-wide regulatory mechanism. We find that UNC-31, a dense-core vesicle (DCV) pathway component, plays a significant role in epidermal ribosome biogenesis-mediated growth quiescence. Our tissue-specific knockdown experiments reveal that the organism-wide growth quiescence induced by epidermal-specific ribosome biogenesis inhibition is suppressed by reducing unc-31 expression in the epidermis, but not in neurons or body wall muscles. Similarly, IDA-1, a membrane-associated protein of the DCV, is overexpressed, and its knockdown in epidermis suppresses the organism-wide growth quiescence in response to epidermal ribosome biogenesis inhibition. Finally, we observe an overall increase in DCV puncta labeled by IDA-1 when epidermal ribosome biogenesis is inhibited, and these puncta are present in or near epidermal cells. In conclusion, these findings suggest a novel mechanism of nutrition-independent multicellular growth coordination initiated from the epidermis tissue upon ribosome biogenesis inhibition.

The Conserved ASCL1/MASH-1 Ortholog HLH-3 Specifies Sex-Specific Ventral Cord Motor Neuron Fate in Caenorhabditis elegans

Neural specification is regulated by one or many transcription factors that control expression of effector genes that mediate function and determine neuronal type. Here we identify a novel role for one conserved proneural factor, the bHLH protein HLH-3, implicated in the specification of sex-specific ventral cord motor neurons in C. elegans. Proneural genes act in early stages of neurogenesis in early progenitors, but here, we demonstrate a later role for hlh-3. First, we document that differentiation of the ventral cord type C motor neuron class (VC) within their neuron class, is dynamic in time and space. Expression of VC class-specific and subclass-specific identity genes is distinct through development and is dependent on the VC position along the A-P axis and their proximity to the vulva. Our characterization of the expression of VC class and VC subclass-specific differentiation markers in the absence of hlh-3 function reveals that VC fate specification, differentiation, and morphology requires hlh-3 function. Finally, we conclude that hlh-3 cell-autonomously specifies VC cell fate.

Regulated Endocrine-Specific Protein-18, an Emerging Endocrine Protein in Physiology: A Literature Review

Regulated endocrine-specific protein-18 (RESP18), a novel 18-kDa protein, was first identified in neuroendocrine tissue. Subsequent studies showed that Resp18 is expressed in the adrenal medulla, brain, pancreas, pituitary, retina, stomach, superior cervical ganglion, testis, and thyroid and also circulates in the plasma. Resp18 has partial homology with the islet cell antigen 512, also known as protein tyrosine phosphatase, receptor type N (PTPRN), but does not have phosphatase activity. Resp18 might serve as an intracellular signal; however, its function is unclear. It is regulated by dopamine, glucocorticoids, and insulin. We recently reported that the targeted disruption of the Resp18 locus in Dahl salt-sensitive rats increased their blood pressure and caused renal injury. The aim of the present review was to provide a comprehensive summary of the reported data currently available, especially the expression and proposed organ-specific function of Resp18.

Oxytocin promotes heat stress tolerance via insulin signals in Caenorhabditis elegans

Oxytocin, has various physiological functions that have been well studied and many that remain unknown. Here, we aimed to determine new physiological functions of oxytocin using Caenorhabditis elegans. Oxytocin treatment promoted the restoration of movement after heat stress and enhanced the viability under heat stress. However, oxytocin had no effect on the life span and only little effect on the oxidative stress tolerance. In contrast, oxytocin treatment didn't promote the restoration of movement or enhance the viability of deficient mutants of ntr-1/2, which is the gene encoding the oxytocin receptor. In addition, for mutants of daf-16, daf-2, tax-4, and some insulin-like peptides, the heat stress tolerance effect by oxytocin was canceled. Furthermore, oxytocin increased the expression levels of the DAF-16 target genes. Our results suggest that oxytocin treatment promoted the heat stress tolerance of C. elegans via the insulin/IGF-1 signaling pathway.

Homeostatic Feedback Modulates the Development of Two-State Patterned Activity in a Model Serotonin Motor Circuit in Caenorhabditis elegans

Neuron activity accompanies synapse formation and maintenance, but how early circuit activity contributes to behavior development is not well understood. Here, we use the Caenorhabditis elegans egg-laying motor circuit as a model to understand how coordinated cell and circuit activity develops and drives a robust two-state behavior in adults. Using calcium imaging in behaving animals, we find the serotonergic hermaphrodite-specific neurons (HSNs) and vulval muscles show rhythmic calcium transients in L4 larvae before eggs are produced. HSN activity in L4 is tonic and lacks the alternating burst-firing/quiescent pattern seen in egg-laying adults. Vulval muscle activity in L4 is initially uncoordinated but becomes synchronous as the anterior and posterior muscle arms meet at HSN synaptic release sites. However, coordinated muscle activity does not require presynaptic HSN input. Using reversible silencing experiments, we show that neuronal and vulval muscle activity in L4 is not required for the onset of adult behavior. Instead, the accumulation of eggs in the adult uterus renders the muscles sensitive to HSN input. Sterilization or acute electrical silencing of the vulval muscles inhibits presynaptic HSN activity and reversal of muscle silencing triggers a homeostatic increase in HSN activity and egg release that maintains ∼12-15 eggs in the uterus. Feedback of egg accumulation depends upon the vulval muscle postsynaptic terminus, suggesting that a retrograde signal sustains HSN synaptic activity and egg release. Our results show that egg-laying behavior in C. elegans is driven by a homeostat that scales serotonin motor neuron activity in response to postsynaptic muscle feedback.SIGNIFICANCE STATEMENT The functional importance of early, spontaneous neuron activity in synapse and circuit development is not well understood. Here, we show in the nematode Caenorhabditis elegans that the serotonergic hermaphrodite-specific neurons (HSNs) and postsynaptic vulval muscles show activity during circuit development, well before the onset of adult behavior. Surprisingly, early activity is not required for circuit development or the onset of adult behavior and the circuit remains unable to drive egg laying until fertilized embryos are deposited into the uterus. Egg accumulation potentiates vulval muscle excitability, but ultimately acts to promote burst firing in the presynaptic HSNs which results in egg laying. Our results suggest that mechanosensory feedback acts at three distinct steps to initiate, sustain, and terminate C. elegans egg-laying circuit activity and behavior.

Insulin Signaling Deficiency Produces Immobility in Caenorhabditis elegans That Models Diminished Motivation States in Man and Responds to Antidepressants

Defects in insulin signaling have been reported in schizophrenia and major depressive disorder, which also share certain negative symptoms such as avolition, anhedonia, and apathy. These symptoms reflect diminished motivational states, which have been modeled in rodents as increased immobility in the forced swimming test. We have discovered that loss-of-function mutations in the insulin receptor (daf-2) and syntaxin (unc-64) genes in Caenorhabditis elegans, brief food deprivation, and exposure to DMSO produce immobility and avolition in non-dauer adults. The animals remain responsive to external stimuli; however, they fail to forage and will remain in place for >12 days or until they die. Their immobility can be prevented with drugs used to treat depression and schizophrenia and that reduce immobility in the forced swimming test. This includes amitriptyline, amoxapine, clozapine, and olanzapine, but not benzodiazepines and haloperidol. Recovery experiments confirm that immobility is induced and maintained by excessive signaling via serotonergic and muscarinic cholinergic pathways. The immobility response described here represents a potential protophenotype for avolition/anhedonia in man. This work may provide clues about why there is a significant increase in depression in patients with diabetes and suggest new therapeutic pathways for disorders featuring diminished motivation as a prominent symptom.

Excitatory and Inhibitory Neurons in the Hippocampus Exhibit Molecularly Distinct Large Dense Core Vesicles

Hippocampal interneurons comprise a diverse family of inhibitory neurons that are critical for detailed information processing. Along with gamma-aminobutyric acid (GABA), interneurons secrete a myriad of neuroactive substances via secretory vesicles but the molecular composition and regulatory mechanisms remain largely unknown. In this study, we have carried out an immunohistofluorescence analysis to describe the molecular content of vesicles in distinct populations of hippocampal neurons. Our results indicate that phogrin, an integral protein of secretory vesicles in neuroendocrine cells, is highly enriched in parvalbumin-positive interneurons. Consistently, immunoelectron microscopy revealed phogrin staining in axon terminals of symmetrical synapses establishing inhibitory contacts with cell bodies of CA1 pyramidal neurons. Furthermore, phogrin is highly expressed in CA3 and dentate gyrus (DG) interneurons which are both positive for PV and neuropeptide Y. Surprisingly, chromogranin B a canonical large dense core vesicle marker, is excluded from inhibitory cells in the hippocampus but highly expressed in excitatory CA3 pyramidal neurons and DG granule cells. Our results provide the first evidence of phogrin expression in hippocampal interneurons and suggest the existence of molecularly distinct populations of secretory vesicles in different types of inhibitory neurons.

The EARP Complex and Its Interactor EIPR-1 Are Required for Cargo Sorting to Dense-Core Vesicles

The dense-core vesicle is a secretory organelle that mediates the regulated release of peptide hormones, growth factors, and biogenic amines. Dense-core vesicles originate from the trans-Golgi of neurons and neuroendocrine cells, but it is unclear how this specialized organelle is formed and acquires its specific cargos. To identify proteins that act in dense-core vesicle biogenesis, we performed a forward genetic screen in Caenorhabditis elegans for mutants defective in dense-core vesicle function. We previously reported the identification of two conserved proteins that interact with the small GTPase RAB-2 to control normal dense-core vesicle cargo-sorting. Here we identify several additional conserved factors important for dense-core vesicle cargo sorting: the WD40 domain protein EIPR-1 and the endosome-associated recycling protein (EARP) complex. By assaying behavior and the trafficking of dense-core vesicle cargos, we show that mutants that lack EIPR-1 or EARP have defects in dense-core vesicle cargo-sorting similar to those of mutants in the RAB-2 pathway. Genetic epistasis data indicate that RAB-2, EIPR-1 and EARP function in a common pathway. In addition, using a proteomic approach in rat insulinoma cells, we show that EIPR-1 physically interacts with the EARP complex. Our data suggest that EIPR-1 is a new interactor of the EARP complex and that dense-core vesicle cargo sorting depends on the EARP-dependent trafficking of cargo through an endosomal sorting compartment.

Animal cells package and store many important signaling molecules in specialized compartments called dense-core vesicles. Molecules stored in dense-core vesicles include peptide hormones like insulin and small molecule neurotransmitters like dopamine. Defects in the release of these compounds can lead to a wide range of metabolic and mental disorders in humans, including diabetes, depression, and drug addiction. However, it is not well understood how dense-core vesicles are formed in cells and package the appropriate molecules. Here we use a genetic screen in the microscopic worm C. elegans to identify proteins that are important for early steps in the generation of dense-core vesicles, such as packaging the correct molecular cargos in the vesicles. We identify several factors that are conserved between worms and humans and point to a new role for a protein complex that had previously been shown to be important for controlling trafficking in other cellular compartments. The identification of this complex suggests new cellular trafficking events that may be important for the generation of dense-core vesicles.

Pioneer Axon Navigation Is Controlled by AEX-3, a Guanine Nucleotide Exchange Factor for RAB-3 in Caenorhabditis elegans

Precise and accurate axon tract formation is an essential aspect of brain development. This is achieved by the migration of early outgrowing axons (pioneers) allowing later outgrowing axons (followers) to extend toward their targets in the embryo. In Caenorhabditis elegans the AVG neuron pioneers the right axon tract of the ventral nerve cord, the major longitudinal axon tract. AVG is essential for the guidance of follower axons and hence organization of the ventral nerve cord. In an enhancer screen for AVG axon guidance defects in a nid-1/Nidogen mutant background, we isolated an allele of aex-3 aex-3 mutant animals show highly penetrant AVG axon navigation defects. These defects are dependent on a mutation in nid-1/Nidogen, a basement membrane component. Our data suggest that AEX-3 activates RAB-3 in the context of AVG axon navigation. aex-3 genetically acts together with known players of vesicular exocytosis: unc-64/Syntaxin, unc-31/CAPS, and ida-1/IA-2. Furthermore our genetic interaction data suggest that AEX-3 and the UNC-6/Netrin receptor UNC-5 act in the same pathway, suggesting AEX-3 might regulate the trafficking and/or insertion of UNC-5 at the growth cone to mediate the proper guidance of the AVG axon.

A Conserved GEF for Rho-Family GTPases Acts in an EGF Signaling Pathway to Promote Sleep-like Quiescence in Caenorhabditis elegans

Sleep is evolutionarily conserved and required for organism homeostasis and survival. Despite this importance, the molecular and cellular mechanisms underlying sleep are not well understood. Caenorhabditis elegans exhibits sleep-like behavioral quiescence and thus provides a valuable, simple model system for the study of cellular and molecular regulators of this process. In C. elegans, epidermal growth factor receptor (EGFR) signaling is required in the neurosecretory neuron ALA to promote sleep-like behavioral quiescence after cellular stress. We describe a novel role for VAV-1, a conserved guanine nucleotide exchange factor (GEF) for Rho-family GTPases, in regulation of sleep-like behavioral quiescence. VAV-1, in a GEF-dependent manner, acts in ALA to suppress locomotion and feeding during sleep-like behavioral quiescence in response to cellular stress. Additionally, VAV-1 activity is required for EGF-induced sleep-like quiescence and normal levels of EGFR and secretory dense core vesicles in ALA. Importantly, the role of VAV-1 in promoting cellular stress-induced behavioral quiescence is vital for organism health because VAV-1 is required for normal survival after cellular stress.

FRPR-4 Is a G-Protein Coupled Neuropeptide Receptor That Regulates Behavioral Quiescence and Posture in Caenorhabditis elegans

Neuropeptides signal through G-protein coupled receptors (GPCRs) to regulate a broad array of animal behaviors and physiological processes. The Caenorhabditis elegans genome encodes approximately 100 predicted neuropeptide receptor GPCRs, but in vivo roles for only a few have been identified. We describe here a role for the GPCR FRPR-4 in the regulation of behavioral quiescence and locomotive posture. FRPR-4 is activated in cell culture by several neuropeptides with an amidated isoleucine-arginine-phenylalanine (IRF) motif or an amidated valine-arginine-phenylalanine (VRF) motif at their carboxy termini, including those encoded by the gene flp-13. Loss of frpr-4 function results in a minor feeding quiescence defect after heat-induced cellular stress. Overexpression of frpr-4 induces quiescence of locomotion and feeding as well as an exaggerated body bend posture. The exaggerated body bend posture requires the gene flp-13. While frpr-4 is expressed broadly, selective overexpression of frpr-4 in the proprioceptive DVA neurons results in exaggerated body bends that require flp-13 in the ALA neuron. Our results suggest that FLP-13 and other neuropeptides signal through FRPR-4 and other receptors to regulate locomotion posture and behavioral quiescence.

Ida-1, the Caenorhabditis elegans orthologue of mammalian diabetes autoantigen IA-2, potentially acts as a common modulator between Parkinson's disease and Diabetes: role of Daf-2/Daf-16 insulin like signalling pathway

The lack of cure to age associated Parkinson's disease (PD) has been challenging the efforts of researchers as well as health care providers. Recent evidences suggest that diabetic patients tend to show a higher future risk for PD advocating a strong correlation between PD and Diabetes, thus making it intriguing to decipher common genetic cues behind these ailments. We carried out studies on ida-1, the C. elegans orthologue of mammalian type-1 diabetes auto-antigen IA-2 towards achieving its functional workup vis-à-vis various associated endpoints of PD and Diabetes. Employing transgenic C. elegans strain expressing "human" alpha synuclein (NL5901) under normal and increased glucose concentrations, we studied aggregation of alpha synuclein, content of dopamine, expression of dopamine transporter, content of reactive oxygen species, locomotor activity, nuclear translocation of FOXO transcription factor Daf-16, and quantification of Daf2/Daf-16 mRNA. Our findings indicate that ida-1 affords protection in the studied disease conditions as absence of ida-1 resulted in higher alpha-synuclein aggregation under conditions that mimic the blood glucose levels of diabetic patients. We also observed reduced dopamine content, decreased motility, defective Daf-16 translocation and reduced expression of Daf-2 and Daf-16. Our studies establish important function of ida-1 as a modulator in Daf-2/Daf-16 insulin like signalling pathway thus possibly being a common link between PD and Diabetes.

FMRFamide-like FLP-13 neuropeptides promote quiescence following heat stress in Caenorhabditis elegans

Among the most important decisions an animal makes is whether to engage in active movement and feeding behavior or to become quiescent. The molecular signaling mechanisms underlying this decision remain largely unknown. The nematode Caenorhabditis elegans displays sleep-like quiescence following exposures that result in cellular stress. The neurosecretory ALA neuron is required for this stress-induced recovery quiescence, but the mechanisms by which ALA induces quiescence have been unknown. We report here that quiescence induced by heat stress requires ALA depolarization and release of FMRFamide-like neuropeptides encoded by the flp-13 gene. Optogenetic activation of ALA reduces feeding and locomotion in a FLP-13-dependent manner. Overexpression of flp-13 is sufficient to induce quiescent behavior during normally active periods. We have here identified a major biological role for FMRFamide-like neuropeptides in nematodes, and we suggest that they may function in a similar capacity in other organisms.

Two Rab2 interactors regulate dense-core vesicle maturation

Peptide neuromodulators are released from a unique organelle: the dense-core vesicle. Dense-core vesicles are generated at the trans-Golgi and then sort cargo during maturation before being secreted. To identify proteins that act in this pathway, we performed a genetic screen in Caenorhabditis elegans for mutants defective in dense-core vesicle function. We identified two conserved Rab2-binding proteins: RUND-1, a RUN domain protein, and CCCP-1, a coiled-coil protein. RUND-1 and CCCP-1 colocalize with RAB-2 at the Golgi, and rab-2, rund-1, and cccp-1 mutants have similar defects in sorting soluble and transmembrane dense-core vesicle cargos. RUND-1 also interacts with the Rab2 GAP protein TBC-8 and the BAR domain protein RIC-19, a RAB-2 effector. In summary, a pathway of conserved proteins controls the maturation of dense-core vesicles at the trans-Golgi network.

Advances in the cellular immunological pathogenesis of type 1 diabetes

Type 1 diabetes is an autoimmune disease caused by the immune-mediated destruction of insulin-producing pancreatic β cells. In recent years, the incidence of type 1 diabetes continues to increase. It is supposed that genetic, environmental and immune factors participate in the damage of pancreatic β cells. Both the immune regulation and the immune response are involved in the pathogenesis of type 1 diabetes, in which cellular immunity plays a significant role. For the infiltration of CD4(+) and CD8(+) T lymphocyte, B lymphocytes, natural killer cells, dendritic cells and other immune cells take part in the damage of pancreatic β cells, which ultimately lead to type 1 diabetes. This review outlines the cellular immunological mechanism of type 1 diabetes, with a particular emphasis to T lymphocyte and natural killer cells, and provides the effective immune therapy in T1D, which is approached at three stages. However, future studies will be directed at searching for an effective, safe and long-lasting strategy to enhance the regulation of a diabetogenic immune system with limited toxicity and without global immunosuppression.

A novel CaM kinase II pathway controls the location of neuropeptide release from Caenorhabditis elegans motor neurons

Neurons release neuropeptides via the regulated exocytosis of dense core vesicles (DCVs) to evoke or modulate behaviors. We found that Caenorhabditis elegans motor neurons send most of their DCVs to axons, leaving very few in the cell somas. How neurons maintain this skewed distribution and the extent to which it can be altered to control DCV numbers in axons or to drive release from somas for different behavioral impacts is unknown. Using a forward genetic screen, we identified loss-of-function mutations in UNC-43 (CaM kinase II) that reduce axonal DCV levels by ∼90% and cell soma/dendrite DCV levels by ∼80%, leaving small synaptic vesicles largely unaffected. Blocking regulated secretion in unc-43 mutants restored near wild-type axonal levels of DCVs. Time-lapse video microscopy showed no role for CaM kinase II in the transport of DCVs from cell somas to axons. In vivo secretion assays revealed that much of the missing neuropeptide in unc-43 mutants is secreted via a regulated secretory pathway requiring UNC-31 (CAPS) and UNC-18 (nSec1). DCV cargo levels in unc-43 mutants are similarly low in cell somas and the axon initial segment, indicating that the secretion occurs prior to axonal transport. Genetic pathway analysis suggests that abnormal neuropeptide function contributes to the sluggish basal locomotion rate of unc-43 mutants. These results reveal a novel pathway controlling the location of DCV exocytosis and describe a major new function for CaM kinase II.

par-1, atypical pkc, and PP2A/B55 sur-6 are implicated in the regulation of exocyst-mediated membrane trafficking in Caenorhabditis elegans

The exocyst is a conserved protein complex that is involved in tethering secretory vesicles to the plasma membrane and regulating cell polarity. Despite a large body of work, little is known how exocyst function is controlled. To identify regulators for exocyst function, we performed a targeted RNA interference (RNAi) screen in Caenorhabditis elegans to uncover kinases and phosphatases that genetically interact with the exocyst. We identified seven kinase and seven phosphatase genes that display enhanced phenotypes when combined with hypomorphic alleles of exoc-7 (exo70), exoc-8 (exo84), or an exoc-7;exoc-8 double mutant. We show that in line with its reported role in exocytotic membrane trafficking, a defective exoc-8 caused accumulation of exocytotic soluble NSF attachment protein receptor (SNARE) proteins in both intestinal and neuronal cells in C. elegans. Down-regulation of the phosphatase protein phosphatase 2A (PP2A) phosphatase regulatory subunit sur-6/B55 gene resulted in accumulation of exocytic SNARE proteins SNB-1 and SNAP-29 in wild-type and in exoc-8 mutant animals. In contrast, RNAi of the kinase par-1 caused reduced intracellular green fluorescent protein signal for the same proteins. Double RNAi experiments for par-1, pkc-3, and sur-6/B55 in C. elegans suggest a possible cooperation and involvement in postembryo lethality, developmental timing, as well as SNARE protein trafficking. Functional analysis of the homologous kinases and phosphatases in Drosophila median neurosecretory cells showed that atypical protein kinase C kinase and phosphatase PP2A regulate exocyst-dependent, insulin-like peptide secretion. Collectively, these results characterize kinases and phosphatases implicated in the regulation of exocyst function, and suggest the possibility for interplay between the par-1 and pkc-3 kinases and the PP2A phosphatase regulatory subunit sur-6 in this process.

The Caenorhabditis elegans interneuron ALA is (also) a high-threshold mechanosensor

BACKGROUND

To survive dynamic environments, it is essential for all animals to appropriately modulate their behavior in response to various stimulus intensities. For instance, the nematode Caenorhabditis elegans suppresses the rate of egg-laying in response to intense mechanical stimuli, in a manner dependent on the mechanosensory neurons FLP and PVD. We have found that the unilaterally placed single interneuron ALA acted as a high-threshold mechanosensor, and that it was required for this protective behavioral response.

RESULTS

ALA was required for the inhibition of egg-laying in response to a strong (picking-like) mechanical stimulus, characteristic of routine handling of the animals. Moreover, ALA did not respond physiologically to less intense touch stimuli, but exhibited distinct physiological responses to anterior and posterior picking-like touch, suggesting that it could distinguish between spatially separated stimuli. These responses required neither neurotransmitter nor neuropeptide release from potential upstream neurons. In contrast, the long, bilaterally symmetric processes of ALA itself were required for producing its physiological responses; when they were severed, responses to stimuli administered between the cut and the cell body were unaffected, while responses to stimuli administered posterior to the cut were abolished.

CONCLUSION

C. elegans neurons are typically classified into three major groups: sensory neurons with specialized sensory dendrites, interneurons, and motoneurons with neuromuscular junctions. Our findings suggest that ALA can autonomously sense intense touch and is thus a dual-function neuron, i.e., an interneuron as well as a novel high-threshold mechanosensor.

CAPS and Munc13: CATCHRs that SNARE Vesicles

CAPS (Calcium-dependent Activator Protein for Secretion, aka CADPS) and Munc13 (Mammalian Unc-13) proteins function to prime vesicles for Ca(2+)-triggered exocytosis in neurons and neuroendocrine cells. CAPS and Munc13 proteins contain conserved C-terminal domains that promote the assembly of SNARE complexes for vesicle priming. Similarities of the C-terminal domains of CAPS/Munc13 proteins with Complex Associated with Tethering Containing Helical Rods domains in multi-subunit tethering complexes (MTCs) have been reported. MTCs coordinate multiple interactions for SNARE complex assembly at constitutive membrane fusion steps. We review aspects of these diverse tethering and priming factors to identify common operating principles.

Pseudophosphatases: methods of analysis and physiological functions

Protein tyrosine phosphatases (PTPs) are key enzymes in the regulation of cellular homeostasis and signaling pathways. Strikingly, not all PTPs bear enzymatic activity. A considerable fraction of PTPs are enzymatically inactive and are known as pseudophosphatases. Despite the lack of activity they execute pivotal roles in development, cell biology and human disease. The present review is focused on the methods used to identify pseudophosphatases, their targets, and physiological roles. We present a strategy for detailed enzymatic analysis of inactive PTPs, regulation of inactive PTP domains and identification of binding partners. Furthermore, we provide a detailed overview of human pseudophosphatases and discuss their regulation of cellular processes and functions in human pathologies.

Cyclin-dependent kinase 5 regulates the polarized trafficking of neuropeptide-containing dense-core vesicles in Caenorhabditis elegans motor neurons

The polarized trafficking of axonal and dendritic proteins is essential for the structure and function of neurons. Cyclin-dependent kinase 5 (CDK-5) and its activator CDKA-1/p35 regulate diverse aspects of nervous system development and function. Here, we show that CDK-5 and CDKA-1/p35 are required for the polarized distribution of neuropeptide-containing dense-core vesicles (DCVs) in Caenorhabditis elegans cholinergic motor neurons. In cdk-5 or cdka-1/p35 mutants, the predominantly axonal localization of DCVs containing INS-22 neuropeptides was disrupted and DCVs accumulated in dendrites. Time-lapse microscopy in DB class motor neurons revealed decreased trafficking of DCVs in axons and increased trafficking and accumulation of DCVs in cdk-5 mutant dendrites. The polarized distribution of several axonal and dendritic markers, including synaptic vesicles, was unaltered in cdk-5 mutant DB neurons. We found that microtubule polarity is plus-end out in axons and predominantly minus-end out in dendrites of DB neurons. Surprisingly, cdk-5 mutants had increased amounts of plus-end-out microtubules in dendrites, suggesting that CDK-5 regulates microtubule orientation. However, these changes in microtubule polarity are not responsible for the increased trafficking of DCVs into dendrites. Genetic analysis of cdk-5 and the plus-end-directed axonal DCV motor unc-104/KIF1A suggest that increased trafficking of UNC-104 into dendrites cannot explain the dendritic DCV accumulation. Instead, we found that mutations in the minus-end-directed motor cytoplasmic dynein, completely block the increased DCVs observed in cdk-5 mutant dendrites without affecting microtubule polarity. We propose a model in which CDK-5 regulates DCV polarity by both promoting DCV trafficking in axons and preventing dynein-dependent DCV trafficking into dendrites.

Characterization of Genetic Differences within the Centrally Projecting Edinger-Westphal Nucleus of C57BL/6J and DBA/2J Mice by Expression Profiling

Detailed examination of the midbrain Edinger–Westphal (EW) nucleus revealed the existence of two distinct nuclei. One population of EW preganglionic (EWpg) neurons was found to control oculomotor functions, and a separate population of EW centrally projecting (EWcp) neurons was found to contain stress- and feeding-related neuropeptides. Although it has been shown that EWcp neurons are highly responsive to drugs of abuse and behavioral stress, a genetic characterization of the EWcp was needed. To identify genetic differences in the EWcp of inbred mouse strains that differ in behaviors relevant to EWcp function, we used publicly available tools from the Allen Brain Atlas to identify 68 transcripts that were selectively expressed in the EWcp, and examined their expression within tissue punch microdissection samples containing the EWcp of adult male C57BL/6J (B6) and DBA/2J (D2) mice. Using 96-well quantitative real-time PCR (qPCR) arrays that included the EWcp-specific genes, several other genes of interest, and five housekeeping genes, we identified strain differences in expression of 11 EWcp-specific genes (BC023892, Btg3, Bves, Cart, Cck, Ghsr, Neto1, Postn, Ptprn, Rcn1, and Ucn), two immediate early genes (Egr1 and Fos), and one dopamine-related gene (Drd5). All significant expression differences were greater in B6 vs. D2 mice, and several of these were verified either at the protein level using immunohistochemistry (IHC) or in silico using microarray data sets from whole brain and other brain areas. These results demonstrate a significant advance in our understanding of the EWcp on three levels. First, we generated a list of EWcp-specific genes (most of which had not yet been reported within the EWcp in the literature) that will be informative for future studies of EWcp function. Second, due to similarity in results from qPCR and IHC, we revealed that strain differences in basal EWcp neuropeptide content are accounted for by differential transcription and number of peptidergic neurons, rather than by differential rates of peptide release. And third, our identification of differentially expressed EWcp-specific genes between B6 and D2 mice may hold powerful insight into the neurogenetic contributions of the EWcp to stress- and addiction-related behaviors.

Transcriptional changes in Teladorsagia circumcincta upon encountering host tissue of differing immune status

The aim of this study was to elucidate transcriptional changes in the parasitic nematode Teladorsagia circumcincta upon encountering either naïve or immune ovine hosts. Pools of 100 000 exsheathed 3rd- stage T. circumcincta larvae were exposed in vitro to either an immune or naïve ovine abomasal environment, RNA was extracted from the larvae and sequenced using the Roche 454 platform. Each sample produced approximately 82 000 reads that assembled to give approximately 5500 Isotigs (contigs). The two sequence datasets were clustered together to give a total of 6969 clusters of which 18 were differentially expressed (P<0·001) between the two groups. Clusters with a predominance of reads in larvae exposed to the immune abomasal environment encoded homologues of peptidyl-glycine alpha-amidating monooxygenase, heat shock-protein 16-2 and IDA-1, a tyrosine phosphatase-like receptor protein. Clusters with a predominance of reads in the naïve environment encoded homologues of cytochrome b, EGg Laying defective family member 21 and NADH dehydrogenase subunit 5. Gene ontology analyses indicated that larvae exposed to the immune environment showed an increase in expression of genes involved in 'carbon utilization', 'response to stimulus' and 'developmental process'. These data suggest that T. circumcincta modulates gene expression in response to the immune status of the host.

HID-1 is a novel player in the regulation of neuropeptide sorting

Peptide hormones and neuropeptides are packaged and stored in a specialized intracellular organelle called the dense core vesicle. It remains elusive how peptide cargoes are correctly sorted. In the present study, we show that a highly conserved Golgi-localized protein named HID-1 acts to prevent mis-sorting of peptide cargoes to lysosomes for degradation via a PtdIns3P-dependent trafficking pathway. Epistasis analysis suggests that rab-2 is epistatic to hid-1.

Neuropeptide gene families in Caenorhabditis elegans

Neuropeptides are short sequences ofamino acids that function in all multicellular organisms to communicate information between cells. The first sequence ofa neuropeptide was reported in 1970' and the number of identified neuropeptides remained relatively small until the 1990s when the DNA sequence of multiple genomes revealed treasure troves ofinformation. Byblasting away at the genome, gene families, the sizes ofwhich were previously unknown, could now be determined. This information has led to an exponential increase in the number of putative neuropeptides and their respective gene families. The molecular biology age greatly benefited the neuropeptide field in the nematode Caenorhabditis elegans. Its genome was among the first to be sequenced and this allowed us the opportunity to screen the genome for neuropeptide genes. Initially, the screeningwas slow, as the Genefinder and BLAST programs had difficulty identifying small genes and peptides. However, as the bioinformatics programs improved, the extent of the neuropeptide gene families in C. elegans gradually emerged.

HID-1, a new component of the peptidergic signaling pathway

hid-1 was originally identified as a Caenorhabditis elegans gene encoding a novel conserved protein that regulates the decision to enter into the enduring dauer larval stage. We isolated a novel allele of hid-1 in a forward genetic screen for mutants mislocalizing RBF-1 rabphilin, a RAB-27 effector. Here we demonstrate that HID-1 functions in the nervous system to regulate neuromuscular signaling and in the intestine to regulate the defecation motor program. We further show that a conserved N-terminal myristoylated motif of both invertebrate and vertebrate HID-1 is essential for its association with intracellular membranes in nematodes and PC12 cells. C. elegans neuronal HID-1 resides on intracellular membranes in neuronal cell somas; however, the kinesin UNC-104 also transports HID-1 to synaptic regions. HID-1 accumulates in the axons of unc-13 and unc-31 mutants, suggesting it is associated with neurosecretory vesicles. Consistent with this, genetic studies place HID-1 in a peptidergic signaling pathway. Finally, a hid-1 null mutation reduces the levels of endogenous neuropeptides and alters the secretion of fluorescent-tagged cargos derived from neuronal and intestinal dense core vesicles (DCVs). Taken together, our findings indicate that HID-1 is a novel component of a DCV-based neurosecretory pathway and that it regulates one or more aspects of the biogenesis, maturation, or trafficking of DCVs.

Paired and LIM class homeodomain proteins coordinate differentiation of the C. elegans ALA neuron

The ancient origin of sleep is evidenced by deeply conserved signaling pathways regulating sleep-like behavior, such as signaling through the Epidermal growth factor receptor (EGFR). In Caenorhabditis elegans, a sleep-like state can be induced at any time during development or adulthood through conditional expression of LIN-3/EGF. The behavioral response to EGF is mediated by EGFR activity within a single cell, the ALA neuron, and mutations that impair ALA differentiation are expected to confer EGF-resistance. Here we describe three such EGF-resistant mutants. One of these corresponds to the LIM class homeodomain (HD) protein CEH-14/Lhx3, and the other two correspond to Paired-like HD proteins CEH-10/Chx10 and CEH-17/Phox2. Whereas CEH-14 is required for ALA-specific gene expression throughout development, the Prd-like proteins display complementary temporal contributions to gene expression, with the requirement for CEH-10 decreasing as that of CEH-17 increases. We present evidence that CEH-17 participates in a positive autoregulatory loop with CEH-14 in ALA, and that CEH-10, in addition to its role in ALA differentiation, functions in the generation of the ALA neuron. Similarly to CEH-17, CEH-10 is required for the posterior migration of the ALA axons, but CEH-14 appears to regulate an aspect of ALA axon outgrowth that is distinct from that of the Prd-like proteins. Our findings reveal partial modularity among the features of a neuronal differentiation program and their coordination by Prd and LIM class HD proteins.

UNC-31/CAPS docks and primes dense core vesicles in C. elegans neurons

UNC-31 or its mammalian homologue, Ca(2+)-dependent activator protein for secretion (CAPS), is indispensable for exocytosis of dense core vesicle (DCV) and synaptic vesicle (SV). From N- to the C-terminus, UNC-31 contains putative functional domains, including dynactin 1 binding domain (DBD), C2, PH, (M)UNC-13 homology domain (MHD) and DCV binding domain (DCVBD), the last four we examined in this study. We employed UNC-31 null mutant C. elegans worms to examine whether UNC-31 functions could be rescued by ectopic expression of full length UNC-31 vs each of these four domain-deleted mutants. Full length UNC-31 cDNA rescued the phenotypes of C. elegans null mutants in response to Ca(2+)-elevation in ALA neurons. Surprisingly, MHD deletion also rescued UNC-31 exocytotic function in part because the relatively high Ca(2+) level (pre-flash Ca(2+) was 450 nM) used in the capacitance study could bypass the MHD defect. Nonetheless, the three other domain-truncation cDNAs had almost no rescue on Ca(2+) evoked secretion. Importantly, this genetic null mutant rescue strategy enabled physiological studies at levels of whole organism to single cells, such as locomotion assay, pharmacological study of neurotransmission at neuromuscular junction, in vivo neuropeptide release measurement and analysis of vesicular docking. Our results suggest that each of these UNC-31 domains support distinct sequential molecular actions of UNC-31 in vesicular exocytosis, including steps in vesicle tethering and docking that bridge vesicle with plasma membrane, and subsequently priming vesicle by initiating the formation of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) core complex.

Impaired dense core vesicle maturation in Caenorhabditis elegans mutants lacking Rab2

Uncoordinated movement in Rab2 mutants is caused by impaired retention of cargo on dense core vesicles, not by defective synaptic vesicle release. (Also see the companion article by Sumakovic et al. in this issue.)

Despite a key role for dense core vesicles (DCVs) in neuronal function, there are major gaps in our understanding of DCV biogenesis. A genetic screen for Caenorhabditis elegans mutants with behavioral defects consistent with impaired DCV function yielded five mutations in UNC-108 (Rab2). A genetic analysis showed that unc-108 mutations impair a DCV function unrelated to neuropeptide release that, together with neuropeptide release, fully accounts for the role of DCVs in locomotion. An electron microscopy analysis of DCVs in unc-108 mutants, coupled with quantitative imaging of DCV cargo proteins, revealed that Rab2 acts in cell somas during DCV maturation to prevent the loss of soluble and membrane cargo. In Rab2 null mutants, two thirds of these cargoes move to early endosomes via a PI(3)P-dependent trafficking pathway, whereas aggregated neuropeptides are unaffected. These results reveal how neurons solve a challenging trafficking problem using the most highly conserved animal Rab.

Loss of the transcriptional repressor PAG-3/Gfi-1 results in enhanced neurosecretion that is dependent on the dense-core vesicle membrane protein IDA-1/IA-2

It is generally accepted that neuroendocrine cells regulate dense core vesicle (DCV) biogenesis and cargo packaging in response to secretory demands, although the molecular mechanisms of this process are poorly understood. One factor that has previously been implicated in DCV regulation is IA-2, a catalytically inactive protein phosphatase present in DCV membranes. Our ability to directly visualize a functional, GFP-tagged version of an IA-2 homolog in live Caenorhabditis elegans animals has allowed us to capitalize on the genetics of the system to screen for mutations that disrupt DCV regulation. We found that loss of activity in the transcription factor PAG-3/Gfi-1, which functions as a repressor in many systems, results in a dramatic up-regulation of IDA-1/IA-2 and other DCV proteins. The up-regulation of DCV components was accompanied by an increase in presynaptic DCV numbers and resulted in phenotypes consistent with increased neuroendocrine secretion. Double mutant combinations revealed that these PAG-3 mutant phenotypes were dependent on wild type IDA-1 function. Our results support a model in which IDA-1/IA-2 is a critical element in DCV regulation and reveal a novel genetic link to PAG-3-mediated transcriptional regulation. To our knowledge, this is the first mutation identified that results in increased neurosecretion, a phenotype that has clinical implications for DCV-mediated secretory disorders.

Within secretory cells, hormones are packaged into vesicles (called DCVs) that are released upon stimulation. The number of DCVs is regulated to meet the secretory demands of the cell by a mechanism that is poorly understood, although a protein in the membrane of DCVs, called IA-2, is thought to play a role. A genetic screen in the nematode C. elegans is used, here, to find mutations that mis-regulate the corresponding worm protein called IDA-1. Capitalizing on the simple neuroanatomy of the nematode and its transparency, we visualize IDA-1 protein levels directly in the animal using a fluorescent tag. We find that mutations in the transcription factor PAG-3/Gfi-1 result in elevated levels of IDA-1 protein, increased numbers of presynaptic DCVs, and behaviors consistent with increased neurosecretion. Our results demonstrate that IDA-1/IA-2 protein levels correlate with the biogenesis, utilization, or stability of DCVs. We propose that PAG-3 normally down regulates the production of IDA-1, thus serving as part of the mechanism underlying DCV regulation. This is the first reported mutation that increases DCV numbers and secretion, offering insight into DCV homeostasis and a potential therapeutic target for diseases that would benefit from a boost in neuroendocrine secretion.

Gene silencing of phogrin unveils its essential role in glucose-responsive pancreatic beta-cell growth

OBJECTIVE

Phogrin and IA-2, autoantigens in insulin-dependent diabetes, have been shown to be involved in insulin secretion in pancreatic beta-cells; however, implications at a molecular level are confusing from experiment to experiment. We analyzed biological functions of phogrin in beta-cells by an RNA interference technique.

RESEARCH DESIGN AND METHODS

Adenovirus-mediated expression of short hairpin RNA specific for phogrin (shPhogrin) was conducted using cultured beta-cell lines and mouse islets. Both glucose-stimulated insulin secretion and cell proliferation rate were determined in the phogrin-knockdown cells. Furthermore, protein expression was profiled in these cells. To see the binding partner of phogrin in beta-cells, coimmunoprecipitation analysis was carried out.

RESULTS

Adenoviral expression of shPhogrin efficiently decreased its endogenous expression in pancreatic beta-cells. Silencing of phogrin in beta-cells abrogated the glucose-mediated mitogenic effect, which was accompanied by a reduction in the level of insulin receptor substrate 2 (IRS2) protein, without any changes in insulin secretion. Phogrin formed a complex with insulin receptor at the plasma membrane, and their interaction was promoted by high-glucose stimulation that in turn led to stabilization of IRS2 protein. Corroboratively, phogrin knockdown had no additional effect on the proliferation of beta-cell line derived from the insulin receptor-knockout mouse.

CONCLUSIONS

Phogrin is involved in beta-cell growth via regulating stability of IRS2 protein by the molecular interaction with insulin receptor. We propose that phogrin and IA-2 function as an essential regulator of autocrine insulin action in pancreatic beta-cells.

Developmentally regulated Ca2+-dependent activator protein for secretion 2 (CAPS2) is involved in BDNF secretion and is associated with autism susceptibility

The postnatal development of the cerebellum is accomplished via a series of cytogenetic and morphogenetic events encoded in the genome. To decipher the underlying genetic basis of these events we have systematized the spatio-temporal gene expression profiles during mouse cerebellar development in the Cerebellar Development Transcriptome Database (CDT-DB). Using the CDT-DB, Ca(2+)-dependent activator protein for secretion 2 (CAPS2 or CADPS2) was identified as a developmentally regulated gene that is predominantly expressed in cerebellar granule cells (GCs) with an expression peak around the first or second postnatal week. CAPS2 protein is concentrated in parallel fiber (PF) terminals and is associated with secretory vesicles containing brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3). CAPS2 enhances release of BDNF and NT-3, both of which are essential for normal cerebellar development. CAPS2-deficient (CAPS2(-/-)) mice show reduced secretion of BDNF and NT-3; consequently, the cerebella of these mice exhibit developmental deficits, such as delayed development and increased cell death in GCs, fewer branched dendrites on Purkinje cells (PCs), and loss of the intercrural fissure. The PF-PC synapses have aberrant cytoarchitectures and electrophysiological properties. These abnormal cellular and morphological phenotypes are more severe around the cerebellar vermis, in which hypoplasia has been reported in autism patients. Moreover, CAPS2(-/-) mice had fewer cortical and hippocampal parvalbumin-positive interneurons and some autistic-like behavioral phenotypes. In the CAPS2 genes of some autistic patients an aberrant splicing variant and non-synonymous SNPs have been identified. These recent studies implicate CAPS2 in autism susceptibility. Therefore, CAPS2(-/-) mice will be a useful model animal in which to study aspects of the neuropathology and behaviors characteristic of developmental disorders.

Localization of insulinoma associated protein 2, IA-2 in mouse neuroendocrine tissues using two novel monoclonal antibodies

AIMS

Insulinoma-associated protein 2 (IA-2) is a member of the protein tyrosine phosphatase family that is localized on the insulin granule membrane. IA-2 is also well known as one of the major autoantigens in Type 1 diabetes mellitus. IA-2 gene deficient mice were recently established and showed abnormalities in insulin secretion. Thus, detailed localization of IA-2 was studied using wild-type and IA-2 gene deficient mice.

MAIN METHODS

To localize IA-2 expression in mouse neuroendocrine tissues, monoclonal antibodies were generated against IA-2 and western blot and immunohistochemical analyses were carried out in IA-2(+/+) mice. IA-2(-/-) mice served as a negative control.

KEY FINDINGS

Western blot analysis revealed that the 65 kDa form of IA-2 was observed in the cerebrum, cerebellum, medulla oblongata, pancreas, adrenal gland, pituitary gland, muscular layers of the stomach, small intestine, and colon. By immunohistochemical analysis, IA-2 was produced in endocrine cells in pancreatic islets, adrenal medullary cells, thyroid C-cells, Kulchitsky cells, and anterior, intermediate, and posterior pituitary cells. In addition, IA-2 was found in somatostatin-producing D-cells and other small populations of cells were scattered in the gastric corpus. IA-2 expression in neurites was confirmed by the immunostaining of IA-2 using primary cultured neurons from the small intestine and nerve growth factor (NGF)-differentiated PC12 cells.

SIGNIFICANCE

The IA-2 distribution in peripheral neurons appeared more intensely in neurites rather than in the cell bodies.

Expression and function of IA-2 family proteins, unique neuroendocrine-specific protein-tyrosine phosphatases

IA-2 (also known as islet cell antigen ICA-512) and IA-2 beta (also known as phogrin, phosphatase homologue in granules of insulinoma) are major autoantigens in insulin-dependent diabetes mellitus (IDDM). Autoantibodies against both proteins are expressed years before clinical onset, and they become predictive markers for high-risk subjects. However, the role of these genes in the IDDM pathogenesis has been reported fairly negative by recent studies. IA-2 and IA-2 beta are type I transmembrane proteins that possess one inactive protein-tyrosine phosphatase (PTP) domain in the cytoplasmic region, and act as one of the constituents of regulated secretory pathways in various neuroendocrine cell types including pancreatic beta-cells. Existence of IA-2 homologues in different species suggests a fundamental role in neuroendocrine function. Studies of knockout animals have shown their involvement in maintaining hormone content, however, their specific steps in the secretory pathway IA-2 functions as well as their molecular mechanisms in the hormone content regulation are still unknown. More recent studies have suggested a novel function showing that they contribute to pancreatic beta-cell growth. This review attempts to show the possible biological functions of IA-2 family, focusing on their expression and localization in the neuroendocrine cells.

Neuroendocrine signals modulate the innate immunity of Caenorhabditis elegans through insulin signaling

Communication between the immune and nervous systems, each of which is able to react rapidly to environmental stimuli, may confer a survival advantage. However, precisely how the nervous system influences the immune response and whether neural modulation of immune function is biologically important are not well understood. Here we report that neuronal exocytosis of neuropeptides from dense core vesicles suppressed the survival of Caenorhabditis elegans and their clearance of infection with the human bacterial pathogen Pseudomonas aeruginosa. This immunomodulatory function was mediated by INS-7, an insulin-like neuropeptide whose induction was associated with Pseudomonas virulence. INS-7 secreted from the nervous system functioned in a non-cell autonomous way to activate the insulin pathway and alter basal and inducible expression of immunity-related genes in intestinal cells.

Regulation of insulin granule turnover in pancreatic beta-cells by cleaved ICA512

Insulin maintains homeostasis of glucose by promoting its uptake into cells from the blood. Hyperglycemia triggers secretion of insulin from pancreatic beta-cells. This process is mediated by secretory granule exocytosis. However, how beta-cells keep granule stores relatively constant is still unknown. ICA512 is an intrinsic granule membrane protein, whose cytosolic domain binds beta2-syntrophin, an F-actin-associated protein, and is cleaved upon granule exocytosis. The resulting cleaved cytosolic fragment, ICA512-CCF, reaches the nucleus and up-regulates the transcription of granule genes, including insulin and ICA512. Here, we show that ICA512-CCF also dimerizes with intact ICA512 on granules, thereby displacing it from beta2-syntrophin. This leads to increased granule mobility and insulin release. Based on these findings, we propose a model whereby the generation of ICA512-CCF first amplifies insulin secretion. The ensuing reduction of granule stores would then increase the probability of newly generated ICA512-CCF to reach the nucleus and enhance granule biogenesis, thus allowing beta-cells to constantly adjust production of granules to their storage size and consumption. Pharmacological modulation of these feedback loops may alleviate deficient insulin release in diabetes.

Neuropeptides

The role of neuropeptides in modulating behavior is slowly being elucidated. With the sequencing of the C. elegans genome, the extent of the neuropeptide genes in C. elegans can be determined. To date, 113 neuropeptide genes encoding over 250 distinct neuropeptides have been identified. Of these, 40 genes encode insulin-like peptides, 31 genes encode FMRFamide-related peptides, and 42 genes encode non-insulin, non-FMRFamide-related neuropeptides. As in other systems, C. elegans neuropeptides are derived from precursor molecules that must be post-translationally processed to yield the active peptides. These precursor molecules contain a single peptide, multiple copies of a single peptide, multiple distinct peptides, or any combination thereof. The neuropeptide genes are expressed extensively throughout the nervous system, including in sensory, motor, and interneurons. In addition, some of the genes are also expressed in non-neuronal tissues, such as the somatic gonad, intestine, and vulval hypodermis. To address the effects of neuropeptides on C. elegans behavior, animals in which the different neuropeptide genes are inactivated or overexpressed are being isolated. In a complementary approach the receptors to which the neuropeptides bind are also being identified and examined. Among the knockout animals analyzed thus far, defects in locomotion, dauer formation, egg laying, ethanol response, and social behavior have been reported. These data suggest that neuropeptides have a modulatory role in many, if not all, behaviors in C. elegans.

CAPS1 and CAPS2 regulate stability and recruitment of insulin granules in mouse pancreatic beta cells

CAPS1 and CAPS2 regulate dense-core vesicle release of transmitters and hormones in neuroendocrine cells, but their precise roles in the secretory process remain enigmatic. Here we show that CAPS2(-/-) and CAPS1(+/-);CAPS2(-/-) mice, despite having increased insulin sensitivity, are glucose intolerant and that this effect is attributable to a marked reduction of glucose-induced insulin secretion. This correlates with diminished Ca(2+)-dependent exocytosis, a reduction in the size of the morphologically docked pool, a decrease in the readily releasable pool of secretory vesicles, slowed granule priming, and suppression of second-phase (but not first-phase) insulin secretion. In beta cells of CAPS1(+/-);CAPS2(-/-) mice, the lowered insulin content and granule numbers were associated with an increase in lysosome numbers and lysosomal enzyme activity. We conclude that although CAPS proteins are not required for Ca(2+)-dependent exocytosis to proceed, they exert a modulatory effect on insulin granule priming, exocytosis, and stability.

Analysis of synaptic transmission in Caenorhabditis elegans using an aldicarb-sensitivity assay

Caenorhabditis elegans has emerged as a powerful model system for studying the biology of the synapse. Here we describe a widely used assay for synaptic transmission at the C. elegans neuromuscular junction. This protocol monitors the sensitivity of C. elegans to the paralyzing affects of an acetylcholinesterase inhibitor, aldicarb. Briefly, adult worms are incubated in the presence of aldicarb and scored for the time-course of aldicarb-induced paralysis. Animals harboring mutations in genes that affect synaptic transmission generally exhibit a change in their sensitivity to aldicarb (either increased sensitivity for enhancements in synaptic transmission or decreased sensitivity for blockage in synaptic transmission). This technique provides a simple assay for the accurate comparative analysis of synaptic transmission in multiple C. elegans strains. The protocol described can be performed relatively quickly and is a practical alternative to other techniques used to study synaptic transmission. This protocol can also be modified to follow the paralytic effects with other pharmacological reagents. The assay can be performed in about 3-6 hours depending on the severity of synaptic transmission defects.

Caenorhabditis elegans SDF-9 enhances insulin/insulin-like signaling through interaction with DAF-2

SDF-9 is a modulator of Caenorhabditis elegans insulin/IGF-1 signaling that may interact directly with the DAF-2 receptor. SDF-9 is a tyrosine phosphatase-like protein that, when mutated, enhances many partial loss-of-function mutants in the dauer pathway except for the temperature-sensitive mutant daf-2(m41). We propose that SDF-9 stabilizes the active phosphorylated state of DAF-2 or acts as an adaptor protein to enhance insulin-like signaling.

Crystal structure of the major diabetes autoantigen insulinoma-associated protein 2 reveals distinctive immune epitopes

Insulinoma-associated protein-2 (IA-2) is a major autoantigen in type 1 diabetes that occurs through autoimmune-mediated beta-cell destruction. We present here the crystal structure of the protein tyrosine phosphatase (PTP)-like domain of human IA-2. The structure reveals a canonical PTP domain with the closed WPD loop over the active site pocket, explaining the lack of enzyme activity in the native protein. The structural interpretation of previous mutagenesis studies indicates that the B-cell epitopes are concentrated on two distinctive regions on peripheral loops of the central beta-sheet surrounding T-cell epitopes within the sheet. The detailed structural information on immune epitopes provides a framework for the future development of immune intervention strategies against diabetes.

Characterization of kynurenine aminotransferase III, a novel member of a phylogenetically conserved KAT family

Kynurenine aminotransferase (KAT) is an enzyme responsible for synthesis of kynurenic acid (KYNA), a well established neuroprotective and anticonvulsant agent, involved in synaptic transmission and implicated in the pathophysiology of schizophrenia, Huntington's disease and other neurological disorders. We have shown previously that kat2-/- mice had lower hippocampal KYNA levels and were more hyperactive than wild-type mice. However, these abnormalities occur early and are transitory coinciding with restoration of KYNA levels, suggesting that compensatory changes or ontogenetic expression of another unknown homolog may account for the normalization of KYNA levels in the adult kat2-/- mice brain. Here, we report the isolation of a novel KAT molecule, kat3, from mouse and human brain cDNA libraries. The encoded 454 amino acids of human KAT III share 64.8% similarity to that of KAT I and 30.1% to KAT II. Northern blot analysis demonstrated that kat3 mRNA is widely expressed but with higher expression levels in liver, kidney, heart, and neuroendocrine tissues. RT-PCR and Northern analysis showed that kat3 expression starts as early as postnatal day (PND) 7 and peaks in adult. The mRNA level of kat3 and kat1 when measured together is significantly higher at PND 60 in kat2-/- mice than those of wild-type mice indicating possible co-regulation of expression levels. RNA-interference (RNAi) directed towards transcripts for either R03A10.4 or F28H6.3 in Caenorhabditis elegans which are kat1 and kat3 orthologs, respectively, did not result in any gross abnormalities. Our results show that upregulation of kat3 and kat1 may be responsible for the phenotypic rescue on kat2-/- mice.