Two Protein N-Acetylgalactosaminyl Transferases Regulate Synaptic Plasticity by Activity-Dependent Regulation of Integrin Signaling

Using a Drosophila whole-genome transgenic RNAi screen for glycogenes regulating synapse function, we have identified two protein alpha-N-acetylgalactosaminyltransferases (pgant3 and pgant35A) that regulate synaptic O-linked glycosylation (GalNAc alpha 1-O-S/T). Loss of either pgant alone elevates presynaptic/postsynaptic molecular assembly and evoked neurotransmission strength, but synapses appear restored to normal in double mutants. Likewise, activity-dependent facilitation, augmentation, and posttetanic potentiation are all suppressively impaired in pgant mutants. In non-neuronal contexts, pgant function regulates integrin signaling, and we show here that the synaptic Position Specific 2 (alpha PS2) integrin receptor and transmembrane tenascin ligand are both suppressively downregulated in pgant mutants. Channelrhodopsin-driven activity rapidly (<1 min) drives integrin signaling in wild-type synapses but is suppressively abolished in pgant mutants. Optogenetic stimulation in pgant mutants alters presynaptic vesicle trafficking and postsynaptic pocket size during the perturbed integrin signaling underlying synaptic plasticity defects. Critically, acute blockade of integrin signaling acts synergistically with pgant mutants to eliminate all activity-dependent synaptic plasticity.