3′ UTR variants of ALS ‐linked RNAs modify subcellular and cellular phenotypes

While most human genes express mRNA 3′untranslated region (3′UTR) variants of different lengths, their impact on cell physiology and disease remains largely unknown. Here, we studied 3′UTR length heterogeneity in amyotrophic lateral sclerosis (ALS) and determined that three ALS‐linked transcripts exhibit lengthening of their 3′UTRs in patient samples. We investigated phenotypical effects in a neuronal cell line expressing these 3′UTRs and observed that expression of these unique 3′UTRs induces morphological changes at different levels. Among the most expressed 3′UTR variants in ALS, NEFH 3′UTR‐Long induces the formation of nuclear RNA clusters, and Superoxide Dismutase 1 3′UTR‐Long diminishes filopodia in the plasma membrane. Sequestosome 1 3′UTR‐Long did not show major changes in nuclear RNA clusters or filopodia. Our findings provide the first evidence that 3′UTRs can modulate cellular phenotype independent of the coding region, further expanding the impact of alterations in mRNA biogenesis in ALS.