The IA-2 gene family: homologs in Caenorhabditis elegans, Drosophila and zebrafish

Regenerative neurogenic response from glia requires insulin-driven neuron-glia communication

Understanding how injury to the central nervous system induces de novo neurogenesis in animals would help promote regeneration in humans. Regenerative neurogenesis could originate from glia and glial neuron-glia antigen-2 (NG2) may sense injury-induced neuronal signals, but these are unknown. Here, we used Drosophila to search for genes functionally related to the NG2 homologue kon-tiki (kon), and identified Islet Antigen-2 (Ia-2), required in neurons for insulin secretion. Both loss and over-expression of ia-2 induced neural stem cell gene expression, injury increased ia-2 expression and induced ectopic neural stem cells. Using genetic analysis and lineage tracing, we demonstrate that Ia-2 and Kon regulate Drosophila insulin-like peptide 6 (Dilp-6) to induce glial proliferation and neural stem cells from glia. Ectopic neural stem cells can divide, and limited de novo neurogenesis could be traced back to glial cells. Altogether, Ia-2 and Dilp-6 drive a neuron-glia relay that restores glia and reprogrammes glia into neural stem cells for regeneration.

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.

The Genetic Basis of Natural Variation in Drosophila melanogaster Immune Defense against Enterococcus faecalis

Dissecting the genetic basis of natural variation in disease response in hosts provides insights into the coevolutionary dynamics of host-pathogen interactions. Here, a genome-wide association study of Drosophila melanogaster survival after infection with the Gram-positive entomopathogenic bacterium Enterococcus faecalis is reported. There was considerable variation in defense against E. faecalis infection among inbred lines of the Drosophila Genetics Reference Panel. We identified single nucleotide polymorphisms associated with six genes with a significant (p < 10^-08, corresponding to a false discovery rate of 2.4%) association with survival, none of which were canonical immune genes. To validate the role of these genes in immune defense, their expression was knocked-down using RNAi and survival of infected hosts was followed, which confirmed a role for the genes krishah and S6k in immune defense. We further identified a putative role for the Bomanin gene BomBc1 (also known as IM23), in E. faecalis infection response. This study adds to the growing set of association studies for infection in Drosophila melanogaster and suggests that the genetic causes of variation in immune defense differ for different pathogens.

Transcription elongation rate has a tissue-specific impact on alternative cleavage and polyadenylation in Drosophila melanogaster

Alternative polyadenylation (APA) is a mechanism that generates multiple mRNA isoforms with different 3'UTRs and/or coding sequences from a single gene. Here, using 3' region extraction and deep sequencing (3'READS), we have systematically mapped cleavage and polyadenylation sites (PASs) in Drosophila melanogaster, expanding the total repertoire of PASs previously identified for the species, especially those located in A-rich genomic sequences. Cis-element analysis revealed distinct sequence motifs around fly PASs when compared to mammalian ones, including the greater enrichment of upstream UAUA elements and the less prominent presence of downstream UGUG elements. We found that over 75% of mRNA genes in Drosophila melanogaster undergo APA. The head tissue tends to use distal PASs when compared to the body, leading to preferential expression of APA isoforms with long 3'UTRs as well as with distal terminal exons. The distance between the APA sites and intron location of PAS are important parameters for APA difference between body and head, suggesting distinct PAS selection contexts. APA analysis of the RpII215^C4 mutant strain, which harbors a mutant RNA polymerase II (RNAPII) with a slower elongation rate, revealed that a 50% decrease in transcriptional elongation rate leads to a mild trend of more usage of proximal, weaker PASs, both in 3'UTRs and in introns, consistent with the "first come, first served" model of APA regulation. However, this trend was not observed in the head, suggesting a different regulatory context in neuronal cells. Together, our data expand the PAS collection for Drosophila melanogaster and reveal a tissue-specific effect of APA regulation by RNAPII elongation rate.

Pathophysiologic changes in IA-2/IA-2β null mice are secondary to alterations in the secretion of hormones and neurotransmitters

IA-2 and IA-2β are transmembrane proteins of dense-core vesicles (DCV). The deletion of these proteins results in a reduction in the number of DCV and the secretion of hormones and neurotransmitters. As a result, this leads to a variety of pathophysiologic changes. The purpose of this review is to describe these changes, which are characterized by glucose intolerance, female infertility, behavior and learning abnormalities and alterations in the diurnal circadian rhythms of blood pressure, heart rate, spontaneous physical activity and body temperature. These findings show that the deletion of IA-2 and IA-2β results in multiple pathophysiologic changes and represents a unique in vivo model for studying the effect of hormone and neurotransmitter reduction on known and still unrecognized targets.

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.

Deletion of Ia-2 and/or Ia-2β in mice decreases insulin secretion by reducing the number of dense core vesicles

AIMS/HYPOTHESIS

Islet antigen 2 (IA-2) and IA-2β are dense core vesicle (DCV) transmembrane proteins and major autoantigens in type 1 diabetes. The present experiments were initiated to test the hypothesis that the knockout of the genes encoding these proteins impairs the secretion of insulin by reducing the number of DCV.

METHODS

Insulin secretion, content and DCV number were evaluated in islets from single knockout (Ia-2 [also known as Ptprn] KO, Ia-2β [also known as Ptprn2] KO) and double knockout (DKO) mice by a variety of techniques including electron and two-photon microscopy, membrane capacitance, Ca(2+) currents, DCV half-life, lysosome number and size and autophagy.

RESULTS

Islets from single and DKO mice all showed a significant decrease in insulin content, insulin secretion and the number and half-life of DCV (p < 0.05 to 0.001). Exocytosis as evaluated by two-photon microscopy, membrane capacitance and Ca(2+) currents supports these findings. Electron microscopy of islets from KO mice revealed a marked increase (p < 0.05 to 0.001) in the number and size of lysosomes and enzymatic studies showed an increase in cathepsin D activity (p < 0.01). LC3 protein, an indicator of autophagy, also was increased in islets of KO compared with wild-type mice (p < 0.05 to 0.01) suggesting that autophagy might be involved in the deletion of DCV.

CONCLUSIONS/INTERPRETATION

We conclude that the decrease in insulin content and secretion, resulting from the deletion of Ia-2 and/or Ia-2β, is due to a decrease in the number of DCV.

Aspartyl aminopeptidase, encoded by an evolutionarily conserved syntenic gene, is colocalized with its cluster in secretory granules of pancreatic islet cells

Aspartyl aminopeptidase (DAP), encoded by the DNPEP gene, is believed to be a cytosolic protein with high enzymatic activity in the neuroendocrine tissues. Bioinformatic analysis revealed that the genomic segment spanning the DNPEP gene is evolutionarily conserved from Caenorhabditis elegans to humans. In the present study, we sought to determine whether the expression of DAP is associated with its clustered genes when expressed in pancreatic islet cells. Using anti-DAP specific antibody in immunofluorescent stainings, we found that DAP was specifically expressed in islet alpha cells but not in exocrine acinar cells. Moreover, using electron microscopy, we found that DAP was associated with a lysosomal-like structure and secretory granules, suggesting that it plays an important role in post-translational processing and the secretion of hormones in islet cells. The identification and characterization of DNPEP syntenic genes confirm that conserved clustered genes can preferentially be expressed in the same signaling pathway.

Identification and expression of the family of classical protein-tyrosine phosphatases in zebrafish

Protein-tyrosine phosphatases (PTPs) have an important role in cell survival, differentiation, proliferation, migration and other cellular processes in conjunction with protein-tyrosine kinases. Still relatively little is known about the function of PTPs in vivo. We set out to systematically identify all classical PTPs in the zebrafish genome and characterize their expression patterns during zebrafish development. We identified 48 PTP genes in the zebrafish genome by BLASTing of human PTP sequences. We verified all in silico hits by sequencing and established the spatio-temporal expression patterns of all PTPs by in situ hybridization of zebrafish embryos at six distinct developmental stages. The zebrafish genome encodes 48 PTP genes. 14 human orthologs are duplicated in the zebrafish genome and 3 human orthologs were not identified. Based on sequence conservation, most zebrafish orthologues of human PTP genes were readily assigned. Interestingly, the duplicated form of ptpn23, a catalytically inactive PTP, has lost its PTP domain, indicating that PTP activity is not required for its function, or that ptpn23b has lost its PTP domain in the course of evolution. All 48 PTPs are expressed in zebrafish embryos. Most PTPs are maternally provided and are broadly expressed early on. PTP expression becomes progressively restricted during development. Interestingly, some duplicated genes retained their expression pattern, whereas expression of other duplicated genes was distinct or even mutually exclusive, suggesting that the function of the latter PTPs has diverged. In conclusion, we have identified all members of the family of classical PTPs in the zebrafish genome and established their expression patterns. This is the first time the expression patterns of all members of the large family of PTP genes have been established in a vertebrate. Our results provide the first step towards elucidation of the function of the family of classical PTPs.

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.

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.

Sex, diabetes and the kidney

The incidence and the rate of progression of nondiabetic renal disease is generally greater in men compared with age-matched women, suggesting that the female sex is protective and/or that the male sex is a risk factor for the development and progression of nondiabetic renal disease. In diabetes, even though the male sex still appears to be a risk factor, this relationship is not as strong as it is in nondiabetic renal disease. Experimental evidence suggests that both estrogens and androgens play an important role in the pathophysiology of renal disease. Thus one of the potential mechanisms for the absence of a clear sex difference in the setting of diabetes may be alterations in sex hormone levels. Indeed, studies suggest that diabetes is a state of an imbalance in sex hormone levels; however, whether these changes correlate with the decline in renal function associated with diabetes is unclear. Furthermore, diabetic renal disease rarely develops before puberty, and the onset of puberty accelerates microalbuminuria, supporting the idea of the involvement of sex hormones in the development and progression of the disease. However, other than a handful of experimental studies indicating that treatment with or removal of sex hormones alters the course of diabetic renal disease, very few studies have actually directly examined the correlation between sex hormones and the disease development and progression. Further studies are necessary to determine the precise contribution of sex hormones in the pathophysiology of diabetic renal disease to develop novel and potentially sex-specific therapeutic treatments.

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.

Drosophila ia2 modulates secretion of insulin-like peptide

Islet antigen-2 (IA-2) is a major autoantigen in type I diabetes. To throw light on the function of IA-2 we examined the role of ia2, a Drosophila homologue, during Drosophila development. In situ hybridization showed that ia2 was expressed in the central nervous system and midgut region. The neuronal expression pattern of ia2 was very similar to that of IA-2 in mammals. Disruption of gut-specific ia2 expression by double stranded RNA interference (dsRNAi) resulted in defects in gut development, and this phenotype was rescued by overexpression of hexokinase. Until now the roles of IA-2 and hexokinase in insulin signaling have been described separately but we found that ia2 modulated the expression of both insulin and hexokinase. Moreover this modulation seems to be important for gut development during metamorphosis. As the pancreas develops from the gut during vertebrate development, our results suggest a possible role of IA-2 in insulin and hexokinase regulation.

Overexpression of the autoantigen IA-2 puts beta cells into a pre-apoptotic state: autoantigen-induced, but non-autoimmune-mediated, tissue destruction

IA-2 is a major autoantigen in type 1 diabetes and autoantibodies to it have become important diagnostic and predictive markers. IA-2 also is an intrinsic transmembrane component of dense core secretory vesicles and knock-out studies showed that IA-2 is a regulator of insulin secretion. Here we show that overexpression of IA-2 puts mouse insulinoma MIN-6 beta cells into a pre-apoptotic state and that exposure to high glucose results in G2/M arrest and apoptosis. Molecular study revealed a decrease in phosphoinositide-dependent kinase (PDK)-1 and Akt/protein kinase B (PKB) phosphorylation. Treatment of IA-2-transfected cells with IA-2 siRNA prevented both G2/M arrest and apoptosis and increased Akt/PKB phosphorylation. A search for IA-2 interacting proteins revealed that IA-2 interacts with sorting nexin (SNX)19 and that SNX19, but not IA-2, inhibits the conversion of PtdIns(4,5)P2 to PtdIns(3,4,5)P3 and thereby suppresses the phosphorylation of proteins in the Akt signalling pathway resulting in apoptosis. We conclude that IA-2 acts through SNX19 to initiate the pre-apoptotic state. Our findings point to the possibility that in autoimmune diseases, tissue destruction may be autoantigen-induced, but not necessarily immunologically mediated.

The Jerusalem Perinatal Study cohort, 1964-2005: methods and a review of the main results

The Jerusalem Perinatal Study recorded information on population-based cohorts of 92 408 live- and stillbirths in 1964-76, and their parents, with active surveillance of infant deaths and birth defects. Data on maternal conditions, obstetric complications and interventions during labour and delivery were recorded for 92% of the births. Subsets were surveyed with antenatal interviews in 1965-68 (n = 11 467), paediatric admissions to hospital (n = 17 782) and postpartum interviews in 1975-76 (n = 16 912). Data from some offspring were linked to records of a health examination at age 17. The offspring, mothers and fathers have been traced recently, their vital status assessed, and the data linked to Israel's Cancer Registry and Psychiatric Registry. This paper describes the different types of data available, their sources, and some potential biases. Characteristics of this unique population are shown. Findings from the study are reviewed and a list of references is provided. The cohorts provide a unique source of data for a wide variety of studies.

IA-2beta, but not IA-2, is induced by ghrelin and inhibits glucose-stimulated insulin secretion

Ghrelin is a newly discovered peptide and an endogenous ligand for growth hormone (GH) secretagogue (GHS) receptor. It has been shown to possess various central and peripheral effects, including GH secretion, food intake, and gastric and cardiac effects. Ghrelin and the GHS receptor are expressed also in pancreatic islets. We have identified several ghrelin-induced genes by PCR-select subtraction methods, among which is a beta-cell autoantigen for type 1 diabetes, IA-2beta. Administration of ghrelin increased IA-2beta mRNA in mouse brain, pancreas, and insulinoma cell lines (MIN6 and betaTC3). However, the expression of IA-2, another structurally related beta-cell autoantigen, was not induced by ghrelin. Administration of ghrelin or overexpression of IA-2beta, but not overexpression of IA-2, inhibited glucose-stimulated insulin secretion in MIN6 insulinoma cells and, moreover, inhibition of IA-2beta expression by the RNA interference technique ameliorated ghrelin's inhibitory effects on glucose-stimulated insulin secretion. These findings strongly suggest that inhibitory effects of ghrelin on glucose-stimulated insulin secretion are at least partly due to increased expression of IA-2beta induced by ghrelin. Our data demonstrate the link among ghrelin, IA-2beta, and glucose-stimulated insulin secretion.

Cytoplasmic Transport Signal is Involved in Phogrin Targeting and Localization to Secretory Granules

Phogrin is an integral glycoprotein primarily expressed in neuroendocrine cells. The predominant localization of phogrin is on dense-core secretory granules, and the lumenal domain has been shown to be involved in its efficient sorting to the regulated secretory pathway. Here, we present data showing that a leucine-based sorting signal [EExxxIL] within the cytoplasmic tail contributes its steady-state localization to secretory granules. Deletion mutants in the tail region failed to represent granular distribution in pancreatic beta-cell line, MIN6, and anterior pituitary cell line, AtT-20. A sorting signal mutant with two glutamic acids substituted into alanines (EE/AA) is primarily accumulated in the Golgi area instead of secretory granules, and another mutant (IL/AA) is trapped at the plasma membrane due to a defect in endocytosis. We further demonstrate that the leucine-based sorting signal of phogrin specifically interacts with both adaptor protein (AP)-1 and AP-2 clathrin adaptor complexes in vitro. These observations, along with previous studies, suggest that distinct domains of phogrin mediate proper localization of this transmembrane protein on secretory granules.

Adult-like but regressive increase of intima-media thickness and roughness in a child with type 1 diabetes

A 12-yr-old Kosovo-Albanian boy with insufficiently controlled type 1 diabetes since his second year of life developed severely increased intima-media thickness (IMT) and roughness (IMR) of the common carotid artery (CCA): max/mean IMT=0.81/0.68 mm and IMR=0.048 mm. Intima-media thickening, comparable with that in a 50- to 60-yr-old healthy adult, decreased within 41 months (max/mean carotid IMT=0.72/0.56 mm and IMR=0.036 mm) by intensive treatment of diabetes. Moyamoya disease (MMD), complicated by cerebral infarction, occurred coincidentally but regressed within 6 months. This case report points out that (i) chronic hyperglycemia in childhood may lead to adult-like increase of carotid IMT/IMR as early signs of subclinical atherosclerosis, (ii) increased carotid IMT/IMR may be regressive by intensive diabetes control, and (iii) a screening examination for carotid IMT/IMR should be considered in patients at high risk of atherosclerosis.

The dense core transmembrane vesicle protein IA-2 is a regulator of vesicle number and insulin secretion

IA-2 is an enzymatically inactive member of the transmembrane protein tyrosine phosphate family located in dense core secretory vesicles and a major autoantigen in type 1 diabetes. Recent studies showed that targeted disruption of the IA-2 gene in mice resulted in impairment of insulin secretion and glucose intolerance. Insulin homeostasis, however, is a complex process involving a cascade of regulatory factors, and IA-2 is widely expressed in neuroendocrine cells throughout the body. Consequently, it is uncertain whether the impairment of insulin secretion in IA-2 knockout mice is a direct result of the knockout of IA-2 in beta cells or to counter regulatory alterations resulting from IA-2 knockout in other neuroendocrine cells. To define the function of IA-2, we studied the secretion of insulin in a single cell type, MIN-6, by overexpressing and knocking down IA-2. Our experiments showed that overexpression of IA-2 resulted in a 6-fold increase in glucose- or K+-induced insulin secretion and a approximately 3-fold increase in the number of secretory vesicles and the insulin content of cells. In contrast, knockdown of endogenous IA-2 by short interfering RNA resulted in nearly a complete loss of glucose-induced insulin secretion and a 50% decrease in basal insulin release. The half-life of insulin in cells overexpressing IA-2 was nearly twice as great as that in mock-transfected cells, suggesting that IA-2 was stabilizing the insulin-containing vesicles. From these results we conclude that in beta cells, IA-2 is an important regulator of dense core vesicle number and glucose-induced and basal insulin secretion.

Dense core vesicle dynamics in Caenorhabditis elegans neurons and the role of kinesin UNC-104

We have developed a model system in Caenorhabditis elegans to perform genetic and molecular analysis of peptidergic neurotransmission using green fluorescent protein (GFP)-tagged IDA-1. IDA-1 represents the nematode ortholog of the transmembrane proteins ICA512 and phogrin that are localized to dense core secretory vesicles (DCVs) of mammalian neuroendocrine tissues. IDA-1::GFP was expressed in a small subset of neurons and present in both axonal and dendritic extensions, where it was localized to small mobile vesicular elements that at the ultrastructural level corresponded to 50 nm electron-dense objects in the neuronal processes. The post-translational processing of IDA-1::GFP in transgenic worms was dependent on the neuropeptide proprotein convertase EGL-3, indicating that the protein was efficiently targeted to the peptidergic secretory pathway. Time-lapse epifluorescence microscopy of IDA-1::GFP revealed that DCVs moved in a saltatory and bidirectional manner. DCV velocity profiles exhibited multiple distinct peaks, suggesting the participation of multiple molecular motors with distinct properties. Differences between velocity profiles for axonal and dendritic processes furthermore suggested a polarized distribution of the molecular transport machinery. Study of a number of candidate mutants identified the kinesin UNC-104 (KIF1A) as the microtubule motor that is specifically responsible for anterograde axonal transport of DCVs at velocities of 1.6 microm/s-2.7 microm/s.

Targeted disruption of the IA-2beta gene causes glucose intolerance and impairs insulin secretion but does not prevent the development of diabetes in NOD mice

Insulinoma-associated protein (IA)-2beta, also known as phogrin, is an enzymatically inactive member of the transmembrane protein tyrosine phosphatase family and is located in dense-core secretory vesicles. In patients with type 1 diabetes, autoantibodies to IA-2beta appear years before the development of clinical disease. The genomic structure and function of IA-2beta, however, is not known. In the present study, we determined the genomic structure of IA-2beta and found that both human and mouse IA-2beta consist of 23 exons and span approximately 1,000 and 800 kb, respectively. With this information, we prepared a targeting construct and inactivated the mouse IA-2beta gene as demonstrated by lack of IA-2beta mRNA and protein expression. The IA-2beta(-/-) mice, in contrast to wild-type controls, showed mild glucose intolerance and impaired glucose-stimulated insulin secretion. Knockout of the IA-2beta gene in NOD mice, the most widely studied animal model for human type 1 diabetes, failed to prevent the development of cyclophosphamide-induced diabetes. We conclude that IA-2beta is involved in insulin secretion, but despite its importance as a major autoantigen in human type 1 diabetes, it is not required for the development of diabetes in NOD mice.

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

IA-2 (insulinoma-associated protein 2), a major autoantigen in type 1 diabetes, is a receptor-tyrosine phosphatase-like protein associated with the membrane of secretory granules of neural and endocrine-specific cells. Loss of IA-2 activity in the mouse results in reduced insulin release and additional phenotypes, consistent with a general effect on neurosecretion and hormone release. To gain further insight into the cellular mechanisms of IA-2 function, we have studied the Caenorhabditis elegans homolog, CeIA-2 encoded by the ida-1 gene. Using two independent putative null alleles of ida-1, we demonstrate that animals lacking CeIA-2 activity are viable and exhibit subtle defects. Genetic studies of mutants in ida-1 and several genes involved in neurosecretory vesicle cargo release and signaling highlight two roles for CeIA-2. First, CeIA-2 has a specific and novel genetic interaction with UNC-31/CAPS, a protein that has been shown in other systems to regulate dense-core vesicle cargo release. Second, loss of CeIA-2 activity enhances weak alleles in the insulin-like signaling pathway. These results suggest that CeIA-2 may be an important factor in dense-core vesicle cargo release with parallels to insulin signaling in mammals.

Multimerization of the protein-tyrosine phosphatase (PTP)-like insulin-dependent diabetes mellitus autoantigens IA-2 and IA-2beta with receptor PTPs (RPTPs). Inhibition of RPTPalpha enzymatic activity

Most receptor-type protein-tyrosine phosphatases (RPTPs) contain two tandem PTP domains. For some RPTPs the enzymatically inactive membrane-distal phosphatase domains (D2) were found to bind enzymatically active membrane proximal PTP (D1) domains, and oligomerization has been proposed as a general regulatory mechanism. The RPTP-like proteins IA-2 and IA-2beta, major autoantigens in insulin-dependent diabetes mellitus, contain just a single enzymatically inactive PTP-like domain. Their physiological role is as yet enigmatic. To investigate whether the catalytically inactive cytoplasmic domains of IA-2 and IA-2beta are involved in oligomerization, we exploited interaction trap assay in yeast and glutathione S-transferase pull-down and co-immunoprecipitation strategies on lysates of transfected COS-1 cells. The results show that IA-2 and IA-2beta are capable of homo- and heterodimerization to which both the juxtamembrane region and the phosphatase-like segment can contribute. Furthermore, they can form heterodimers with some other RPTP members, most notably RPTPalpha and RPTPepsilon, and down-regulate RPTPalpha enzymatic activity. Thus, in addition to homo-dimerization, the enzymatic activity of receptor-type PTPs can be regulated through heterodimerization with other RPTPs, including the catalytically inactive IA-2 and IA-2beta.

Different regulated expression of the tyrosine phosphatase-like proteins IA-2 and phogrin by glucose and insulin in pancreatic islets: relationship to development of insulin secretory responses in early life

IA-2 and phogrin are tyrosine phosphatase-like proteins that may mediate interactions between secretory granules and cytoskeleton in islets and neuroendocrine tissues. We investigated factors that regulate IA-2 and phogrin expression and their relationship to maturation of insulin secretory responses that occur after birth. Islet content of IA-2, but not phogrin, increased during the first 10 days of life in rats, when insulin secretion in response to glucose increased to adult levels. In cultured 5-day-old rat islets, IA-2 protein and mRNA was increased by glucose and agents that potentiate insulin secretion by the cAMP pathway. Addition of insulin increased IA-2 protein levels and insulin biosynthesis without affecting IA-2 mRNA. Blocking insulin secretion with diazoxide or insulin action with insulin receptor antibodies inhibited glucose-induced increases in IA-2 protein, but not those of mRNA. Phogrin expression was unchanged by all agents. Thus, IA-2 is regulated at the mRNA level by glucose and elevated cAMP, whereas locally secreted insulin modulates IA-2 protein levels by stimulating biosynthesis. In contrast, phogrin expression is insensitive to factors that modify beta-cell function. These results demonstrate differential regulation of two closely related secretory granule components and identify IA-2 as a granule membrane protein subject to autocrine regulation by insulin.

The zinc-finger transcription factor INSM1 is expressed during embryo development and interacts with the Cbl-associated protein

Here we describe the isolation and characterization of the mouse homolog of the human zinc-finger transcription factor INSM1 (IA-1) and identify an interacting protein. A 2.9-kb cDNA with an open reading frame of 1563 nucleotides, corresponding to a translated protein of 521 amino acids, was isolated from a mouse beta TC-1 cDNA library. Mouse INSM1 was found to be 86% identical to human INSM1 and both proteins contain proline-rich regions and multiple zinc-finger DNA-binding motifs. Sequencing of mouse Insm1 genomic DNA revealed that it is an intronless gene. Chromosomal mapping localized Insm1 to chromosome 2. Northern blot analysis showed that mouse Insm1 expression begins at 10.5 days in the embryo, decreases after 13.5 days, and is barely detected at 18.5 days. In mouse brain, Insm1 is strongly expressed for 2 weeks after birth but shows little or no expression thereafter. Transfection of cells with GFP-tagged INSM1 revealed that INSM1 is expressed exclusively in the nucleus. We identified proteins that interacted with INSM1 by the yeast two-hybrid system and the binding of one of them, Cbl-associated protein (CAP), to INSM1 was confirmed by in vitro pull-down experiments, nuclear colocalization, and co-immunoprecipitation assays. Further studies showed that both INSM1 and CAP proteins were present in the nucleus of insulinoma cells and that endogenous INSM1 protein was co-precipitated with antibody to CAP. These findings raise the possibility that during embryo development CAP may enter the nucleus through its own nuclear localization signal or by binding to INSM1.

Targeted disruption of the protein tyrosine phosphatase-like molecule IA-2 results in alterations in glucose tolerance tests and insulin secretion

IA-2 is a major autoantigen in type 1 diabetes. Autoantibodies to IA-2 appear years before the development of clinical disease and are being widely used as predictive markers to identify individuals at risk for developing type 1 diabetes. IA-2 is an enzymatically inactive member of the transmembrane protein tyrosine phosphatase family and is an integral component of secretory granules in neuroendocrine cells. To study its function, we generated IA-2-deficient mice. Northern and Western blot analysis showed that neither IA-2 mRNA nor protein was expressed. Physical examination of the IA-2(- /-) animals and histological examination of tissues failed to reveal any abnormalities. Nonfasting blood glucose levels, measured over 6 months, were slightly elevated in male IA-2(-/-) as compared to IA-2(+ /+) littermates, but remained within the nondiabetic range. Glucose tolerance tests, however, revealed statistically significant elevation of glucose in both male and female IA-2(-/-) mice and depressed insulin release. In vitro glucose stimulation of isolated islets showed that male and female mice carrying the disrupted gene released 48% (P < 0.001) and 42% (P < 0.01) less insulin, respectively, than mice carrying the wild-type gene. We concluded that IA-2 is involved in glucose-stimulated insulin secretion.

Patterns of gene expression in the developing adult sea urchin central nervous system reveal multiple domains and deep-seated neural pentamery

The adult sea urchin central nervous system (CNS) is composed of five radial nerve cords connected to a circular nerve ring. Although much is known about the molecular mechanisms underlying the development and function of the nervous systems of many invertebrate and vertebrate species, virtually nothing is known about these processes in echinoderms. We have isolated a set of clones from a size-selected cDNA library prepared from the nervous system of the sea urchin Heliocidaris erythrogramma for use as probes. A total of 117 expressed sequence clones were used to search the GenBank database. Identified messages include genes that encode signaling proteins, cytoskeletal elements, cell surface proteins and receptors, cell proliferation and differentiation factors, transport and channel proteins, and a RNA DEAD box helicase. Expression was analyzed by RNA gel blot hybridization to document expression through development. Many of the genes have apparently neural limited expression and function, but some have been co-opted into new roles, notably associated with exocytotic events at fertilization. Localization of gene expression by whole-mount in situ hybridization shows that the morphologically simple sea urchin radial CNS exhibits complex organization into localized transcriptional domains. The transcription patterns reflect the morphological pentamery of the echinoderm CNS and provide no indication of an underlying functional bilateral symmetry in the CNS.

Regulation of CNS and motor axon guidance in Drosophila by the receptor tyrosine phosphatase DPTP52F

Receptor-linked protein tyrosine phosphatases (RPTPs) regulate axon guidance and synaptogenesis in Drosophila embryos and larvae. We describe DPTP52F, the sixth RPTP to be discovered in Drosophila. Our genomic analysis indicates that there are likely to be no additional RPTPs encoded in the fly genome. Five of the six Drosophila RPTPs have C. elegans counterparts, and three of the six are also orthologous to human RPTP subfamilies. DPTP52F, however, has no clear orthologs in other organisms. The DPTP52F extracellular domain contains five fibronectin type III repeats and it has a single phosphatase domain. DPTP52F is selectively expressed in the CNS of late embryos, as are DPTP10D, DLAR, DPTP69D and DPTP99A. To define developmental roles of DPTP52F, we used RNA interference (RNAi)-induced phenotypes as a guide to identify Ptp52F alleles among a collection of EMS-induced lethal mutations. Ptp52F single mutant embryos have axon guidance phenotypes that affect CNS longitudinal tracts. This phenotype is suppressed in Dlar Ptp52F double mutants, indicating that DPTP52F and DLAR interact competitively in regulating CNS axon guidance decisions. Ptp52F single mutations also cause motor axon phenotypes that selectively affect the SNa nerve. DPTP52F, DPTP10D and DPTP69D have partially redundant roles in regulation of guidance decisions made by axons within the ISN and ISNb motor nerves.