Neuronal late endosomes serve as selective RNA hubs disrupted by ALS-linked FUS mutation

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 found a specific population of mRNAs enriched for endosomal, axonal and synaptic functions.

We find that mRNAs enriched in Rab-7 endosomes contain evolutionarily conserved 5′UTRs which act as localization signals, and that the RNA-binding protein GEMIN5 interacts with these regions to promote endosomal RNA recruitment. Finally, we show that in ALS-associated conditions there is a conspicuous loss of endosome-associated transcripts and 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.