Metazoan evolution and diversity of glutamate receptors and their auxiliary subunits.

Glutamate is the major excitatory neurotransmitter in vertebrate and invertebrate nervous systems. Proteins involved in glutamatergic neurotransmission, and chiefly glutamate receptors and their auxiliary subunits, play key roles in nervous system function. Thus, understanding their evolution and uncovering their diversity is essential to comprehend how nervous systems evolved, shaping cognitive function.

Supramolecular organization of NMDA receptors and the postsynaptic density.

The postsynaptic density (PSD) of all vertebrate species share a highly complex proteome with ∼1000 conserved proteins that function as sophisticated molecular computational devices. Here, we review recent studies showing that this complexity can be understood in terms of the supramolecular organization of proteins, which self-assemble within a hierarchy of different length scales, including complexes, supercomplexes and nanodomains. We highlight how genetic and biochemical approaches in mice are being used to uncover the native molecular architecture of the synapse, revealing hitherto unknown molecular structures, including highly selective mechanisms for specifying the assembly of NMDAR-MAGUK supercomplexes.

Evolution of complexity in the zebrafish synapse proteome.

The proteome of human brain synapses is highly complex and is mutated in over 130 diseases. This complexity arose from two whole-genome duplications early in the vertebrate lineage. Zebrafish are used in modelling human diseases; however, its synapse proteome is uncharacterized, and whether the teleost-specific genome duplication (TSGD) influenced complexity is unknown.

Calcium-permeable AMPA receptors and silent synapses in cocaine-conditioned place preference.

Exposure to cocaine generates silent synapses in the nucleus accumbens (NAc), whose eventual unsilencing/maturation by recruitment of calcium-permeable AMPA-type glutamate receptors (CP-AMPARs) after drug withdrawal results in profound remodeling of NAc neuro-circuits. Silent synapse-based NAc remodeling was shown to be critical for several drug-induced behaviors, but its role in acquisition and retention of the association between drug rewarding effects and drug-associated contexts has remained unclear. Here, we find that the postsynaptic proteins PSD-93, PSD-95, and SAP102 differentially regulate excitatory synapse properties in the NAc.

Haploinsufficiency of EHMT1 improves pattern separation and increases hippocampal cell proliferation.

Heterozygous mutations or deletions of the human Euchromatin Histone Methyltransferase 1 (EHMT1) gene are the main causes of Kleefstra syndrome, a neurodevelopmental disorder that is characterized by impaired memory, autistic features and mostly severe intellectual disability. Previously, Ehmt1 heterozygous knockout mice were found to exhibit cranial abnormalities and decreased sociability, phenotypes similar to those observed in Kleefstra syndrome patients. In addition, Ehmt1 knockout mice were impaired at fear extinction and novel- and spatial object recognition.

Altered thalamocortical development in the SAP102 knockout model of intellectual disability.

Genetic mutations known to cause intellectual disabilities (IDs) are concentrated in specific sets of genes including both those encoding synaptic proteins and those expressed during early development. We have characterized the effect of genetic deletion of Dlg3, an ID-related gene encoding the synaptic NMDA-receptor interacting protein synapse-associated protein 102 (SAP102), on development of the mouse somatosensory cortex. SAP102 is the main representative of the PSD-95 family of postsynaptic MAGUK proteins during early development and is proposed to play a role in stabilizing receptors at immature synapses.

NMDA receptors are selectively partitioned into complexes and supercomplexes during synapse maturation.

How neuronal proteomes self-organize is poorly understood because of their inherent molecular and cellular complexity. Here, focusing on mammalian synapses we use blue-native PAGE and 'gene-tagging' of GluN1 to report the first biochemical purification of endogenous NMDA receptors (NMDARs) directly from adult mouse brain. We show that NMDARs partition between two discrete populations of receptor complexes and ∼1.

PSD95 nanoclusters are postsynaptic building blocks in hippocampus circuits.

The molecular features of synapses in the hippocampus underpin current models of learning and cognition. Although synapse ultra-structural diversity has been described in the canonical hippocampal circuitry, our knowledge of sub-synaptic organisation of synaptic molecules remains largely unknown. To address this, mice were engineered to express Post Synaptic Density 95 protein (PSD95) fused to either eGFP or mEos2 and imaged with two orthogonal super-resolution methods: gated stimulated emission depletion (g-STED) microscopy and photoactivated localisation microscopy (PALM).

Identification of Vulnerable Cell Types in Major Brain Disorders Using Single Cell Transcriptomes and Expression Weighted Cell Type Enrichment.

The cell types that trigger the primary pathology in many brain diseases remain largely unknown. One route to understanding the primary pathological cell type for a particular disease is to identify the cells expressing susceptibility genes. Although this is straightforward for monogenic conditions where the causative mutation may alter expression of a cell type specific marker, methods are required for the common polygenic disorders.

The molecular evolution of the vertebrate behavioural repertoire.

How the sophisticated vertebrate behavioural repertoire evolved remains a major question in biology. The behavioural repertoire encompasses the set of individual behavioural components that an organism uses when adapting and responding to changes in its external world. Although unicellular organisms, invertebrates and vertebrates share simple reflex responses, the fundamental mechanisms that resulted in the complexity and sophistication that is characteristic of vertebrate behaviours have only recently been examined.

Canalization of genetic and pharmacological perturbations in developing primary neuronal activity patterns.

The function of the nervous system depends on the integrity of synapses and the patterning of electrical activity in brain circuits. The rapid advances in genome sequencing reveal a large number of mutations disrupting synaptic proteins, which potentially result in diseases known as synaptopathies. However, it is also evident that every normal individual carries hundreds of potentially damaging mutations.

Neurobeachin Regulates Glutamate- and GABA-Receptor Targeting to Synapses via Distinct Pathways.

Neurotransmission and synaptic strength depend on expression of post-synaptic receptors on the cell surface. Post-translational modification of receptors, trafficking to the synapse through the secretory pathway, and subsequent insertion into the synapse involves interaction of the receptor with A-kinase anchor proteins (AKAPs) and scaffolding proteins. Neurobeachin (Nbea), a brain specific AKAP, is required for synaptic surface expression of both glutamate and GABA receptors.

NMDA receptor subunits and associated signaling molecules mediating antidepressant-related effects of NMDA-GluN2B antagonism.

Drugs targeting the glutamate N-methyl-d-aspartate receptor (NMDAR) may be efficacious for treating mood disorders, as exemplified by the rapid antidepressant effects produced by single administration of the NMDAR antagonist ketamine. Though the precise mechanisms underlying the antidepressant-related effects of NMDAR antagonism remain unclear, recent studies implicate specific NMDAR subunits, including GluN2A and GluN2B, as well as the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR) subunit glutamate receptor interacting molecule, PSD-95. Here, integrating mutant and pharmacological in mice, we investigated the contribution of these subunits and molecules to antidepressant-related behaviors and the antidepressant-related effects of the GluN2B blocker, Ro 25-6981.

Quantitative differences in developmental profiles of spontaneous activity in cortical and hippocampal cultures.

Background: Neural circuits can spontaneously generate complex spatiotemporal firing patterns during development. This spontaneous activity is thought to help guide development of the nervous system. In this study, we had two aims.

Human post-mortem synapse proteome integrity screening for proteomic studies of postsynaptic complexes.

Background: Synapses are fundamental components of brain circuits and are disrupted in over 100 neurological and psychiatric diseases. The synapse proteome is physically organized into multiprotein complexes and polygenic mutations converge on postsynaptic complexes in schizophrenia, autism and intellectual disability. Directly characterising human synapses and their multiprotein complexes from post-mortem tissue is essential to understanding disease mechanisms.

Flattop regulates basal body docking and positioning in mono- and multiciliated cells.

Planar cell polarity (PCP) regulates basal body (BB) docking and positioning during cilia formation, but the underlying mechanisms remain elusive. In this study, we investigate the uncharacterized gene Flattop (Fltp) that is transcriptionally activated during PCP acquisition in ciliated tissues. Fltp knock-out mice show BB docking and ciliogenesis defects in multiciliated lung cells.

Motor impairments, striatal degeneration, and altered dopamine-glutamate interplay in mice lacking PSD-95.

Excessive activation of the N-methyl-d-aspartate (NMDA) receptor and the neurotransmitter dopamine (DA) mediate neurotoxicity and neurodegeneration under many neurological conditions, including Huntington's disease (HD), an autosomal dominant neurodegenerative disease characterized by the preferential loss of medium spiny projection neurons (MSNs) in the striatum. PSD-95 is a major scaffolding protein in the postsynaptic density (PSD) of dendritic spines, where a classical role for PSD-95 is to stabilize glutamate receptors at sites of synaptic transmission. Our recent studies indicate that PSD-95 also interacts with the D1 DA receptor localized in spines and negatively regulates spine D1 signaling.

A polygenic burden of rare disruptive mutations in schizophrenia.

Schizophrenia is a common disease with a complex aetiology, probably involving multiple and heterogeneous genetic factors. Here, by analysing the exome sequences of 2,536 schizophrenia cases and 2,543 controls, we demonstrate a polygenic burden primarily arising from rare (less than 1 in 10,000), disruptive mutations distributed across many genes. Particularly enriched gene sets include the voltage-gated calcium ion channel and the signalling complex formed by the activity-regulated cytoskeleton-associated scaffold protein (ARC) of the postsynaptic density, sets previously implicated by genome-wide association and copy-number variation studies.

De novo mutations in schizophrenia implicate synaptic networks.

Inherited alleles account for most of the genetic risk for schizophrenia. However, new (de novo) mutations, in the form of large chromosomal copy number changes, occur in a small fraction of cases and disproportionally disrupt genes encoding postsynaptic proteins. Here we show that small de novo mutations, affecting one or a few nucleotides, are overrepresented among glutamatergic postsynaptic proteins comprising activity-regulated cytoskeleton-associated protein (ARC) and N-methyl-d-aspartate receptor (NMDAR) complexes.

Tolerance to ethanol intoxication after chronic ethanol: role of GluN2A and PSD-95.

The neural and genetic factors underlying chronic tolerance to alcohol are currently unclear. The GluN2A N-methyl-D-aspartate receptors (NMDAR) subunit and the NMDAR-anchoring protein PSD-95 mediate acute alcohol intoxication and represent putative mechanisms mediating tolerance. We found that chronic intermittent ethanol exposure (CIE) did not produce tolerance [loss of righting reflex (LORR)] or withdrawal-anxiety in C57BL/6J, GluN2A or PSD-95 knockout mice assayed 2-3 days later.