ALS-linked FUS mutation impairs GEMIN5-dependent mRNA recruitment to neuronal late endosomes

Neurons depend on tightly regulated positioning of cellular components to maintain long-distance signaling, but the mechanisms guiding specific mRNAs to distant regions remain unclear. Here, we show that late endosomes function as selective RNA carriers in human motor neurons and uncover the molecular logic guiding their loading. Using APEX2-mediated proximity labeling, we identify the external transcriptome of RAB7A-positive endosomes and find a specific population of mRNAs enriched for endosomal, axonal, and synaptic functions. We find that mRNAs enriched in RAB7A endosomes contain evolutionarily conserved 5'UTRs that act as localization signals, and that the RNA-binding protein GEMIN5 interacts with these regions to promote endosomal RNA recruitment. Finally, we show that there is a conspicuous loss of endosome-associated transcripts in amyotrophic lateral sclerosis-associated conditions, accompanied by the mislocalization of GEMIN5 from endosomes. These findings uncover fundamental principles of RNA compartmentalization and highlight endosomal mRNA loading as a vulnerable axis in neuronal homeostasis.