Axonal ER tubules control local translation via P180/RRBP1-mediated ribosome interactions

Local mRNA translation in axons is critical for the spatial and temporal regulation of the axonal proteome. A wide variety of mRNAs are localized and translated in axons, however how protein synthesis is regulated at specific subcellular sites in axons remains unclear. Here, we establish that the axonal endoplasmic reticulum (ER) supports axonal translation in developing neurons. Axonal ER tubule disruption impairs local translation and ribosome distribution. Using nanoscale resolution imaging, we find that ribosomes make frequent contacts with axonal ER tubules in a translation-dependent manner and are influenced by specific extrinsic cues. We identify P180/RRBP1 as an axonally distributed ribosome receptor that regulates local translation and binds to mRNAs enriched for axonal membrane proteins. Importantly, the impairment of axonal ER – ribosome interactions causes defects in axon morphology. Our results establish an important role for the axonal ER in dynamically localizing mRNA translation which is important for proper neuron development. To identify mRNAs interacting with P180/RRBP1 in neurons we performed RNA-sequencing after pulldown of P180-GFPbio using GFPbio as a control condition in primary cortical neurons/. Two biological replicates were obtained and sequenced.