Regulation of Brain-Derived Neurotrophic Factor Exocytosis and Gamma-Aminobutyric Acidergic Interneuron Synapse by the Schizophrenia Susceptibility Gene Dysbindin-1

AbstractBackgroundGenetic variations in dystrobrevin binding protein 1 (DTNBP1 or dysbindin-1) have been implicated as risk factors in the pathogenesis of schizophrenia. The encoded protein dysbindin-1 functions in the regulation of synaptic activity and synapse development. Intriguingly, a loss of function mutation in Dtnbp1 in mice disrupted both glutamatergic and gamma-aminobutyric acidergic transmission in the cerebral cortex; pyramidal neurons displayed enhanced excitability due to reductions in inhibitory synaptic inputs. However, the mechanism by which reduced dysbindin-1 activity causes inhibitory synaptic deficits remains unknown.MethodsWe investigated the role of dysbindin-1 in the exocytosis of brain-derived neurotrophic factor (BDNF) from cortical excitatory neurons, organotypic brain slices, and acute slices from dysbindin-1 mutant mice and determined how this change in BDNF exocytosis transsynaptically affected the number of inhibitory synapses formed on excitatory neurons via whole-cell recordings, immunohistochemistry, and live-cell imaging using total internal reflection fluorescence microscopy.ResultsA decrease in dysbindin-1 reduces the exocytosis of BDNF from cortical excitatory neurons, and this reduction in BDNF exocytosis transsynaptically resulted in reduced inhibitory synapse numbers formed on excitatory neurons. Furthermore, application of exogenous BDNF rescued the inhibitory synaptic deficits caused by the reduced dysbindin-1 level in both cultured cortical neurons and slice cultures.ConclusionsTaken together, our results demonstrate that these two genes linked to risk for schizophrenia (BDNF and dysbindin-1) function together to regulate interneuron development and cortical network activity. This evidence supports the investigation of the association between dysbindin-1 and BDNF in humans with schizophrenia

Pathophysiological Mechanism of Neurodevelopmental Disorders—Overview

Technological advancements in next-generation DNA sequencing have enabled elucidation of many genetic causes of neurodevelopmental disorders (NDDs) over the last two decades [...

Functions of CNKSR2 and Its Association with Neurodevelopmental Disorders

The Connector Enhancer of Kinase Suppressor of Ras-2 (CNKSR2), also known as CNK2 or MAGUIN, is a scaffolding molecule that contains functional protein binding domains: Sterile Alpha Motif (SAM) domain, Conserved Region in CNK (CRIC) domain, PSD-95/Dlg-A/ZO-1 (PDZ) domain, Pleckstrin Homology (PH) domain, and C-terminal PDZ binding motif. CNKSR2 interacts with different molecules, including RAF1, ARHGAP39, and CYTH2, and regulates the Mitogen-Activated Protein Kinase (MAPK) cascade and small GTPase signaling. CNKSR2 has been reported to control the development of dendrite and dendritic spines in primary neurons. CNKSR2 is encoded by the CNKSR2 gene located in the X chromosome. CNKSR2 is now considered as a causative gene of the Houge type of X-linked syndromic mental retardation (MRXHG), an X-linked Intellectual Disability (XLID) that exhibits delayed development, intellectual disability, early-onset seizures, language delay, attention deficit, and hyperactivity. In this review, we summarized molecular features, neuronal function, and neurodevelopmental disorder-related variations of CNKSR2

Functions of Rhotekin, an Effector of Rho GTPase, and Its Binding Partners in Mammals

Rhotekin is an effector protein for small GTPase Rho. This protein consists of a Rho binding domain (RBD), a pleckstrin homology (PH) domain, two proline-rich regions and a C-terminal PDZ (PSD-95, Discs-large, and ZO-1)-binding motif. We, and other groups, have identified various binding partners for Rhotekin and carried out biochemical and cell biological characterization. However, the physiological functions of Rhotekin, per se, are as of yet largely unknown. In this review, we summarize known features of Rhotekin and its binding partners in neuronal tissues and cancer cells

Roles of Rho small GTPases in the tangentially migrating neurons

Rho small GTPases are members of the Ras superfamily of monomeric 20~30 kDa GTP-binding proteins. These proteins function as molecular switches that regulate various cellular processes such as migration, adhesion and proliferation. Cycling between GDP-bound inactive and GTP-bound active forms is regulated by guanine nucleotide exchange factors (GEFs), GTPase activating proteins (GAPs) and GDPdissociation inhibitors (GDIs). Among 20 different mammalian Rho GTPases identified to date, RhoA, Rac1 and Cdc42 have been most extensively investigated; regulation of migration, adhesion and proliferation by these proteins have been well documented in a variety of cell types, including neurons. In neurons, RhoA, Rac1 and Cdc42 are crucial for axon guidance, dendrite formation and spine morphogenesis, where molecular machineries required for cell migration and adhesion play essential roles. Recently, accumulating experimental data indicate the participation of Rho GTPases in neuronal cell migration. To establish the cortical lamination and synapse network formation, highly specialized modes of neuron migration are essential, which include 1) radial migration of excitatory pyramidal neurons along radial glial fibers, 2) tangential migration of GABAergic cortical (inhibitory) interneurons along emerging axon tracts and 3) chain migration of interneurons ensheathed in a glial network, which is observed only in olfactory bulb-directed adult neurogenesis. While roles of Rho GTPases in the radial migration have been well reviewed, knowledge of their functions in tangential migration and chain migration are fragmentary to date. In this review, we focus on the roles of Rho small GTPases and their related molecules in tangential migration, together with the possible application of the electroporation method to analyses for this mode of migration in embryonic and postnatal mouse brain

MUNC18–1 gene abnormalities are involved in neurodevelopmental disorders through defective cortical architecture during brain development

Abstract While Munc18–1 interacts with Syntaxin1 and controls the formation of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNARE) complex to regulate presynaptic vesicle fusion in developed neurons, this molecule is likely to be involved in brain development since its gene abnormalities cause early infantile epileptic encephalopathy with suppression-burst (Ohtahara syndrome), neonatal epileptic encephalopathy and other neurodevelopmental disorders. We thus analyzed physiological significance of Munc18–1 during cortical development. Munc18–1-knockdown impaired cortical neuron positioning during mouse corticogenesis. Time-lapse imaging revealed that the mispositioning was attributable to defects in radial migration in the intermediate zone and cortical plate. Notably, Syntaxin1A was critical for radial migration downstream of Munc18–1. As for the underlying mechanism, Munc18–1-knockdown in cortical neurons hampered post-Golgi vesicle trafficking and subsequent vesicle fusion at the plasma membrane in vivo and in vitro, respectively. Notably, Syntaxin1A-silencing did not affect the post-Golgi vesicle trafficking. Taken together, Munc18–1 was suggested to regulate radial migration by modulating not only vesicle fusion at the plasma membrane to distribute various proteins on the cell surface for interaction with radial fibers, but also preceding vesicle transport from Golgi to the plasma membrane. Although knockdown experiments suggested that Syntaxin1A does not participate in the vesicle trafficking, it was supposed to regulate subsequent vesicle fusion under the control of Munc18–1. These observations may shed light on the mechanism governing radial migration of cortical neurons. Disruption of Munc18–1 function may result in the abnormal corticogenesis, leading to neurodevelopmental disorders with MUNC18–1 gene abnormalities

Expression of Drebrin, an actin binding protein, in basal cell carcinoma, trichoblastoma and trichoepithelioma

Drebrin, an F-actin binding protein, is known to play important roles in cell migration, synaptogenesis and neural plasticity. Although drebrin was long thought to be specific for neuronal cells, its expression has recently been reported in non-neuronal cells. As for skin-derived cells, drebrin was shown to be enriched at adhering junctions (AJs) in cultured primary keratinocytes and also be highly expressed in basal cell carcinoma (BCC) cells. Since BCC and two types of benign neoplasm, trichoblastoma and trichoepithelioma, are considered to derive from the same origin, follicular germinative cells, it is sometimes difficult to morphologically distinguish BCC from trichoblastoma and trichoepithelioma. In this study, we performed immunohistochemical staining of drebrin in BCC, trichoblastoma and trichoepithelioma, to examine whether drebrin could serve as a biomarker for BCC diagnosis. In western blotting, drebrin was detected highly and moderately in the lysates from a squamous cell carcinoma cell line, DJM-1, and normal human epidermis, respectively. In immunofluorescence analyses, drebrin was colocalized with markers of AJs and tight junctions in DJM-1 cells and detected at cellcell junction areas of human normal epidermis tissue. We then examined the distribution patterns of drebrin in BCC, trichoblastoma and trichoepithelioma. In BCC tissues, intense and homogeneous drebrin expression was observed mainly at tumor cell-cell boundaries. In contrast, drebrin was stained only weakly and nonhomogeneously in trichoblastoma and trichoepthelioma tissue samples. For differential diagnosis of BCC, drebrin may be a novel and useful marker