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Nuclear import of the DSCAM-cytoplasmic domain drives signaling capable of inhibiting synapse formation

ABSTRACT: DSCAM and DSCAML1 are immunoglobulin and cell adhesion-type receptors serving important neurodevelopmental functions including control of axon growth, branching, neurite self-avoidance and neuronal cell death. The signal transduction mechanisms or effectors of DSCAM receptors however, remain poorly characterized. We used a human ORFeome library to perform a high-throughput screen in mammalian cells and identified novel cytoplasmic signaling effector candidates including the Down syndrome kinase Dyrk1a, STAT3, USP21, and SH2D2A. Unexpectedly, we further found that the intracellular domains (ICDs) of DSCAM and DSCAML1 specifically and directly interact with IPO5, a nuclear import protein of the beta-importin family, via a conserved nuclear localization signal. The DSCAM ICD is released by gamma-secretase dependent cleavage and both the DSCAM and DSCAML1 ICDs efficiently translocate to the nucleus. Furthermore, RNA-sequencing confirms that expression of the DSCAM as well as the DSCAML1 ICDs alone can profoundly alter the expression of genes associated with neuronal differentiation and apoptosis, as well as synapse formation and function. Gain-of-function experiments using primary cortical neurons show that increasing the levels of either the DSCAM or the DSCAML1 ICD leads to an impairment of neurite growth. Strikingly, increased expression of either full-length DSCAM or the DSCAM ICD, but not the DSCAML1 ICD, significantly decreases synapse numbers in primary hippocampal neurons. Taken together, we identified a novel membrane-to-nucleus signaling mechanism by which DSCAM receptors can alter the expression of regulators of neuronal differentiation, synapse formation and function. Considering that chromosomal duplications lead to increased DSCAM expression in trisomy 21 our findings may help to uncover novel mechanisms contributing to intellectual disability in Down syndrome.

ORGANISM(S): Homo sapiens

PROVIDER: GSE122568 | GEO | 2019/02/08

REPOSITORIES: GEO

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Project description:Dysregulated neurite outgrowth and synapse formation underlie many psychiatric disorders. Wolfram syndrome (WS) mainly caused by WFS1 deficiency is a monogenic genetic disease manifested by severe psychiatric disorders. Due to athe lack of proper human disease models, the underlying mechanism is poorly understood. Particularly, whether and how WFS1 deficiency affects synapse formation remain elusive. By mirroring the complexity of human brain development with cerebral organoids derived from human embryonic stem cells (hESCs) harboring WFS1 loss of function (LOF), we found that WFS1-deficient cerebral organoids not only recapitulated the neuronal loss phenotype in WS patients, but also exhibited significantly impaired synapse formation associated with reduced astrocytes, suggesting a defective structural basis for psychiatric disorders elicited by WFS1 deficiency. To further unravel the complexity of interplay between neurons and astrocytes, each neural cell type was respectively differentiated from hESCs harboring WFS1 LOF. WFS1 deficiency in neurons autonomously delayed neuronal differentiation with altered expressions of genes associated with psychiatric disorders, and impaired neurite outgrowth and reduced synapse formation associated with elevated cytosolic calcium. Interestingly, WFS1 deficiency in astrocytes decreased the expression of glutamate transporter EAAT2 and compromised glutamate uptake, causing reduced neurite outgrowth with increased cytosolic calcium when co-cultured with wildtype (WT) neurons, highlighting pathogenic role of WFS1-deficient astrocytes. Importantly, restoring EAAT2 expression in astrocytes by riluzole treatment significantly alleviated reduced neurite outgrowth phenotype in WT neurons co-cultured with WFS1-deficient astrocytes. Altogether, our study provides novel insights into how WFS1 deficiency affects neurite outgrowth and synapse formation, potentially contributing to predisposition of psychiatric disorders, and offers a potential strategy of therapy.

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Nuclear import of the DSCAM-cytoplasmic domain drives signaling capable of inhibiting synapse formation

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