N-Methyl-d-aspartate receptors (NMDARs) control synaptic plasticity and brain development in a manner determined by receptor subunit composition. Pathogenic variants in GRIN2A gene, encoding the NMDAR GluN2A subunit, can cause gain or loss of function of receptors containing the affected subunit and are associated with intellectual disability and epilepsy in patients. While in vitro studies of recombinant receptors have yielded some insights, animal experimental models are essential to better understand the relationship between the molecular pathology of the variants and the disease. Here we introduce a zebrafish model of GluN2A loss of function to study system-level effects of zebrafish grin2Aa and grin2Ab gene deletion. Our electrophysiological analysis revealed functional differences between receptors containing zebrafish GluN2Aa/b and GluN2Bb paralogs comparable with mammalian receptors containing GluN2A versus GluN2B subunits. Both grin2Aa-/- and grin2Ab-/- as well as double-knock-out grin2A-/- zebrafish larvae showed increased locomotor activity in a novel environment. Proteomic analysis suggested that the relative proportion of GluN2B-containing NMDARs may be increased in grin2A mutant fish. Our results highlight fundamental similarities between zebrafish and mammalian NMDAR signaling and validate the use of zebrafish as a model organism to study the neurodevelopmental role of NMDARs. The newly created transgenic zebrafish strains complement the rodent models of GluN2A loss of function and can be used for high-throughput testing of pharmacological or genetic treatment strategies for patients with GRIN2A gene variants.

• Keywords
• CRISPR-Cas9, Grin genes, channelopathy, glutamate receptors, zebrafish,
• MeSH
• Zebrafish MeSH
• Epilepsy * genetics   physiopathology   MeSH
• Animals, Genetically Modified MeSH
• Disease Models, Animal MeSH
• Swimming * physiology   MeSH
• Zebrafish Proteins * genetics   MeSH
• Receptors, N-Methyl-D-Aspartate * genetics   deficiency   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• N-methyl D-aspartate receptor subtype 2A MeSH Browser
• NR2B NMDA receptor MeSH Browser
• Zebrafish Proteins * MeSH
• Receptors, N-Methyl-D-Aspartate * MeSH

N-methyl-D-aspartate receptors (NMDARs) are a subtype of ionotropic glutamate receptors critical for synaptic transmission and plasticity, and for the development of neural circuits. Rare or de-novo variants in GRIN genes encoding NMDAR subunits have been associated with neurodevelopmental disorders characterized by intellectual disability, developmental delay, autism, schizophrenia, or epilepsy. In recent years, some disease-associated variants in GRIN genes have been characterized using recombinant receptors expressed in non-neuronal cells, and a few variants have also been studied in neuronal preparations or animal models. Here we review the current literature on the functional evaluation of human disease-associated variants in GRIN1, GRIN2A and GRIN2B genes at all levels of analysis. Focusing on the impact of different patient variants at the level of receptor function, we discuss effects on receptor agonist and co-agonist affinity, channel open probability, and receptor cell surface expression. We consider how such receptor-level functional information may be used to classify variants as gain-of-function or loss-of-function, and discuss the limitations of this classification at the synaptic, cellular, or system level. Together this work by many laboratories worldwide yields valuable insights into NMDAR structure and function, and represents significant progress in the effort to understand and treat GRIN disorders. Keywords: NMDA receptor , GRIN genes, Genetic variants, Electrophysiology, Synapse, Animal models.

• MeSH
• Genetic Predisposition to Disease MeSH
• Genetic Variation MeSH
• Humans MeSH
• Neurodevelopmental Disorders genetics   MeSH
• Nerve Tissue Proteins genetics   metabolism   MeSH
• Receptors, N-Methyl-D-Aspartate * genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• GRIN1 protein, human MeSH Browser
• N-methyl D-aspartate receptor subtype 2A MeSH Browser
• NR2B NMDA receptor MeSH Browser
• Nerve Tissue Proteins MeSH
• Receptors, N-Methyl-D-Aspartate * MeSH