Concerted remodelling of the postsynaptic spine and RNA granule by cLTP

Synaptic plasticity is the cellular foundation of learning and memory and, for these plastic changes to be stabilised into long-term memory, proteins must be synthesised at the synapse ^1,2 . RNA granules ensure that specific mRNAs are delivered and translated at the right time and place ^3,4 , but the signalling mechanisms linking synaptic activation to local translation are still largely unknown. Here, to investigate how postsynaptic signals modulate the RNA granule, we employed a spatially-restricted biotinylation approach to quantify protein accessibility and proximity in the postsynaptic and RNA granule subproteomes. Upon chemical long-term potentiation (cLTP), we observed a sharp increase in the accessibility of ribosomes, translation factors and RNA binding proteins belonging to the RNA granule. Similarly, strong alterations were observed in proteins of the postsynaptic density, but mostly in those involved in signalling. Specific proximity to DBN1 and IGF2BP1 as postsynaptic and RNA granule reporters unveiled a shift of the translation machinery towards the postsynaptic compartment, whereas specific translation initiation factors and RNA helicases displayed marked changes in their proximity to DBN1 and/or IGF2BP1. Finally, alteration of synapse development and signalling by DBN1 downregulation caused a highly significant decrease in the proximity of RNA granule proteins to IGF2BP1 after synaptic stimulation, establishing a causal link between postsynaptic events and RNA granule dynamics.