Depletion of Mettl3 in cholinergic neurons causes adult-onset neuromuscular degeneration.

Motor neuron (MN) demise is a hallmark of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Post-transcriptional gene regulation can control RNA's fate, and defects in RNA processing are critical determinants of MN degeneration. N-methyladenosine (mA) is a post-transcriptional RNA modification that controls diverse aspects of RNA metabolism. To assess the mA requirement in MNs, we depleted the mA methyltransferase-like 3 (METTL3) in cells and mice. METTL3 depletion in embryonic stem cell-derived MNs has profound and selective effects on survival and neurite outgrowth. Mice with cholinergic neuron-specific METTL3 depletion display a progressive decline in motor behavior, accompanied by MN loss and muscle denervation, culminating in paralysis and death. Reader proteins convey mA effects, and their silencing phenocopies METTL3 depletion. Among the mA targets, we identified transactive response DNA-binding protein 43 (TDP-43) and discovered that its expression is under epitranscriptomic control. Thus, impaired mA signaling disrupts MN homeostasis and triggers neurodegeneration conceivably through TDP-43 deregulation.