c-MAF transduces motor neuron firing to sustain fast-glycolytic myofibers and neuromuscular junctions
Jauliac, E.; Backer, S.; Sadaki, S.; GONDIN, J.; Fessard, A.; Escoffier, H.; Roullat, M.; Di Gallo, M.; Levesque, A.; Pereira, D.; Dos Santos, M.; Vuong, V.; Ham, A.; Letourneur, F.; Pierre, R.; Ruegg, M. A.; Birchmeier, C.; Fujita, R.; Sotiropoulos, A.; Maire, P.
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This study examined how motoneuron activity influences transcription factor binding in mouse fast glycolytic Myh4+ muscle fibers. Single nucleus multiomics of innervated versus denervated tibialis anterior muscles revealed altered chromatin accessibility: SIX and c-MAF binding sites decreased while JUN, FOS, and RUNX1 sites increased in denervated Myh4+ myonuclei. c-MAF showed strong nuclear enrichment after 100 Hz stimulation and periods of increased motoneuron activity but was absent following denervation, establishing it as a primary readout of fast motoneuron firing. Genome-wide analysis demonstrated that c-MAF binding site spacing encodes functionally distinct muscle gene programs. Analysis of constitutive and inducible skeletal muscle-specific c-Maf mutants revealed that c-MAF loss caused region-specific MYH4+ fiber atrophy, MYH1/MYH2 fiber type shifts resembling ALS G93A mouse phenotypes, and progressive neuromuscular junction fragmentation with increased motoneuron terminal sprouting and ectopic reinnervation. These findings establish c-MAF as a critical mediator linking motoneuron activity to muscle gene regulation, fiber integrity, and neuromuscular junction maintenance in fast glycolytic fibers.
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