MDGAs are fast-diffusing molecules that delay excitatory synapse development by altering neuroligin behavior

MDGAs are molecules that can bind neuroligins in cis and interfere with trans-synaptic neurexin-neuroligin interactions, thereby impairing synapse development. However, the sub-cellular localization and dynamics of MDGAs, as well as their specific mode of action in neurons are still unclear. Here, using both surface immunostaining of endogenous MDGAs and single molecule tracking of recombinant MDGAs in dissociated hippocampal neurons, we show that MDGA1 and MDGA2 molecules are homogeneously distributed and exhibit fast membrane diffusion, with a small reduction in mobility across neuronal maturation in culture Using shRNAs and CRISPR/Cas9 strategies to knock-down/out MDGA1 or MDGA2, we demonstrate an increase in the density of excitatory synapses accompanied by enhanced membrane immobilization and an increase in the phosphotyrosine level of neuroligins associated with excitatory post-synaptic differentiation. Finally, we show that decreasing MDGA expression level reduces the mobility of AMPA receptors and increases the frequency of AMPA receptor mediated mEPSCs. Overall, our results support a mechanism by which interactions between MDGAs and neuroligin-1 delays the assembly of functional excitatory synapses containing AMPA receptors.