Skeletal muscles are composed of hundreds of multinucleated muscle fibers (myofibers) whose myonuclei are regularly positioned all along the myofiber's periphery except the few ones clustered underneath the neuromuscular junction (NMJ) at the synaptic zone. This precise myonuclei organization is altered in different types of muscle disease, including centronuclear myopathies (CNMs). However, the molecular machinery regulating myonuclei position and organization in mature myofibers remains largely unknown. Conversely, it is also unclear how peripheral myonuclei positioning is lost in the related muscle diseases. Here, we describe the microtubule-associated protein, MACF1, as an essential and evolutionary conserved regulator of myonuclei positioning and maintenance, in cultured mammalian myotubes, in Drosophila muscle, and in adult mammalian muscle using a conditional muscle-specific knockout mouse model. In vitro, we show that MACF1 controls microtubules dynamics and contributes to microtubule stabilization during myofiber's maturation. In addition, we demonstrate that MACF1 regulates the microtubules density specifically around myonuclei, and, as a consequence, governs myonuclei motion. Our in vivo studies show that MACF1 deficiency is associated with alteration of extra-synaptic myonuclei positioning and microtubules network organization, both preceding NMJ fragmentation. Accordingly, MACF1 deficiency results in reduced muscle excitability and disorganized triads, leaving voltage-activated sarcoplasmic reticulum Ca2+ release and maximal muscle force unchanged. Finally, adult MACF1-KO mice present an improved resistance to fatigue correlated with a strong increase in mitochondria biogenesis.
All data generated or analysed during this study are included in the manuscript and supporting files. Source data files have been provided for all Figures
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Animal experimentation: All of the experiments and procedures were conducted in accordance with the guidelines of the local animal ethics committee of the University Claude Bernard - Lyon 1 and in accordance with French and European legislation on animal experimentation and approved by the ethics committee CECCAPP (ref APAFIS#17455-2018091216033835v5) and the French ministry of research.
- Mohammed Akaaboune, University of Michigan, United States
- Received: May 18, 2021
- Accepted: August 10, 2021
- Accepted Manuscript published: August 27, 2021 (version 1)
© 2021, Ghasemizadeh et al.
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