ALS-associated FUS mutation alters motoneuron RNA expression and circuits.

Amyotrophic Lateral Sclerosis (ALS) is a neurological disease characterized by degeneration of upper and lower motoneurons (MNs), leading to progressive muscle atrophy and death.1 Several mutations have been associated with familiar ALS, a fraction of which targets RNA binding proteins with multiple functions in RNA metabolism, like as FUS/TLS.2,3 The pleiotropic role played by FUS on RNA drives the speculation that aberrant RNA pathways might underlie crucial mechanisms of neurodegeneration in ALS, and raises the fascinating hypoth- esis of ALS as an RNA disorder. To get novel insights into the molecular implications of FUS-dependent neurotoxicity in the cell type specifically targeted in ALS, we in vitro differentiated HB9::GFP mouse Embryonic Stem Cells (mESCs)4 into wild type or mutant MNs reproducing the aggressive human FUS mutation P525L (FUSP517L in mice). GFP(+) MNs were then purified and RNA was sequenced for global analysis of long and short transcripts. By combining the potential of stem cell-based cellular biology with high-throughput screenings and integrative molecular analyses, we are investigating from innovative per- spectives the gene pathways orchestrated by FUS in healthy or affected MNs. Changes in mRNA and microRNA expression profiles suggest how specific deregulated genes impinge on ALS pathogenesis, whereas following mechanistic characterizations identify novel FUS-dependent RNA circuits in MNs. Revealing altered expression of long non-coding and circular RNAs,5 both emerging as essential players in nervous system physiopatholo- gy, is propaedeutic to on-going functional studies aimed to shed light on yet unexplored noncoding sides of neurodegeneration.