Disruption of grin2A , an epilepsy-associated gene, produces altered spontaneous swim behavior in zebrafish

ABSTRACT 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 to mammalian receptors containing GluN2A vs. GluN2B subunits. Both grin2Aa−/− and grin2Ab−/−, as well as double-knockout 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. Competing Interest Statement The authors have declared no competing interest. Abbreviations - ABD - agonist-binding domain - ANOVA - analysis of varinace - ATD - amino-terminal domain - CAN - copy abundance number - CTD - C-terminal domain - dpf - days post fertilization - ECS - extracellular solution - FDR - false discovery rate - GFP - green fluorescent protein - HEK293T - human embryonic kidney 293T - hGluN - human variant of GluN subunit - ISH - in-situ hybridization - LSD - least significant difference - M1 – M4 - membrane helices 1 -4 - MBD - mean bout distance - MBF - mean bout frequency - MTD - mean travelled distance - NMDAR - N-methyl-D-aspartate receptor - RT-qPCR - reverse transcription PCR - SEM - standard error of the mean - TMD - transmembrane domain - τw - weighted tau of double-exponential fit - zGluN - zebrafish variant of GluN subunit