The NMDA receptor subunit GluN3A regulates a program of synaptic activity-induced and MEF2C-dependent transcription

N-methyl-D-aspartate type glutamate receptors (NMDARs) are key mediators of synaptic activity-regulated gene transcription in neurons, both during development and in the adult brain. Developmental differences in the GluN2 subunit composition of NMDARs determines whether NMDARs activate the transcription factor CREB. However, whether the developmentally-regulated GluN3A subunit also modulates NMDAR-induced transcription was unknown. Here we show that knocking down GluN3A in rat hippocampal neurons promotes the inducible transcription of a subset of NMDAR-sensitive genes. This enhancement is mediated by the accumulation of phosphorylated p38 MAP kinase in the nucleus, which drives the activation of the transcription factor MEF2C and promotes the transcription of a subset of synaptic activity-induced genes including Bdnf and Arc. Our evidence that GluN3A negatively regulates MEF2C-dependent transcription reveals a novel mechanism by which NMDAR subunit composition confers specificity on the program of synaptic activity-regulated gene transcription in developing neurons. Overall design: Biological triplicate RNA-seq samples from cultured embryonic (E18.5) rat hippocampal neurons at 7 days in in vitro with Grin3a being knocked down by lentiviral shRNA or Ctrl lentiviral infection for comparison. There are 3 biological replicates per knockdown (kd) and 3 matched controls infected with the lentiviral vector (Ctrl) for each of two treatments (12 samples total). For each genetic condition (Ctrl or KD) there are two treatment conditions, either 1µm TTX for 48 hours (TTX) or 1µM TTX for 48 hours followed by 6 hours of TTX withdrawal (TTXwd).