Neuronal function relies on careful regulation of the local proteome in the two distinct neuronal domains, the somatodendritic and axonal domains. It is unclear how organelle organization, inter-organelle communication and protein trafficking are linked and how this contributes to local organelle/protein availability in neurons.

Axonal endolysosomes play key roles in axon development and maintenance. Our lab has found that somatic ER tubules are required for proper lysosome transport into the axon. Somatic ER tubule disruption causes accumulation of enlarged and less motile lysosomes at the soma. We identified a somatic ER tubule array, enriched at a pre-axonal region, which ensures co-stabilization of ER tubule – MT – lysosome contacts to promote kinesin-1-driven lysosome fission and their translocation into the axon. In addition, we have recently investigated how biosynthetic lysosomal proteins are delivered to lysosomes in these highly polarized cells to ensure proper lysosomal function. We developed Protein Origin, Trafficking And Targeting to Organelle Mapping (POTATOMap), by combining trafficking synchronization and proximity-labelling based proteomics, to unravel the trafficking routes and interactome of the biosynthetic lysosomal membrane protein LAMP1 at specified time points. This approach, combined with advanced microscopy, enabled us to identify the neuronal domain-specific trafficking machineries of biosynthetic LAMP1. We revealed a role in replenishing axonal lysosomes, in delivery of newly synthesized axonal synaptic proteins, and interactions with RNA granules to facilitate hitchhiking in the axon.

Thus, organelle organization and inter-organelle communication through organelle contacts and protein trafficking play key roles in maintaining the axonal proteome.