N‐WASP is required for Amphiphysin‐2/BIN1‐dependent nuclear positioning and triad organization in skeletal muscle and is involved in the pathophysiology of centronuclear myopathy

Abstract

Mutations in amphiphysin-2/BIN1, dynamin 2, and myotubularin are associated with centronuclear myopathy (CNM), a muscle disorder characterized by myofibers with atypical central nuclear positioning and abnormal triads. Mis-splicing of amphiphysin-2/BIN1 is also associated with myotonic dystrophy that shares histopathological hallmarks with CNM. How amphiphysin-2 orchestrates nuclear positioning and triad organization and how CNM-associated mutations lead to muscle dysfunction remains elusive. We find that N-WASP interacts with amphiphysin-2 in myofibers and that this interaction and N-WASP distribution are disrupted by amphiphysin-2 CNM mutations. We establish that N-WASP functions downstream of amphiphysin-2 to drive peripheral nuclear positioning and triad organization during myofiber formation. Peripheral nuclear positioning requires microtubule/Map7/Kif5b-dependent distribution of nuclei along the myofiber and is driven by actin and nesprins. In adult myofibers, N-WASP and amphiphysin-2 are only involved in the maintenance of triad organization but not in the maintenance of peripheral nuclear positioning. Importantly, we confirmed that N-WASP distribution is disrupted in CNM and myotonic dystrophy patients. Our results support a role for N-WASP in amphiphysin-2-dependent nuclear positioning and triad organization and in CNM and myotonic dystrophy pathophysiology.

Nesprins anchor kinesin-1 motors to the nucleus to drive nuclear distribution in muscle cells

“…Previous work, based on overexpression of the KASH domain to displace endogenous nesprins, suggested that nesprins are not necessary for distributing nuclei in myotubes (Falcone et al, 2014;Metzger et al, 2012). In our system, siRNA-mediated depletion of nesprins reported here had a more substantial impact on nuclear distribution (Fig.…”

Nuclear migration events throughout development

“…The fourth nuclear migration event in developing myotubes is towards the periphery of the syncytium, similar to how nuclei move in myofibers that recover from injury (Falcone et al, 2014;Romero, 2010) (Fig. 2D).…”

“…2D). This nuclear movement is dependent on the correct spreading of the nuclei in the previous step, as well as a complex formed between the F-BAR protein amphiphysin-2 and the actinnucleator neuronal Wiskott-Aldrich Syndrome protein (N-WASP) (Falcone et al, 2014). Furthermore, amphiphysin-2 is recruited to the surface of nuclei through an interaction with nesprin-2 (D' Alessandro et al, 2015).…”

Prix Master 2016 de la SFM

“…Les réseaux de cytosquelette d'actine et de microtubules sont totalement remodelés durant la maturation des fibres musculaires avec une forte accumulation péri-nucléaire observée en comparaison à leur organisation dans des cellules mononuclées. Récemment, ces réseaux cytosquelettiques ont été mis en évidence comme un potentiel support à la « périphé-risation » des noyaux [5]. Les conséquences fonctionnelles d'une mauvaise localisation des noyaux sur les fibres ont longtemps suscité des interrogations.…”

“…stratégie d'identification protéomique différentielle entre des fibres musculaires immatures et matures grâce à une méthode originale de culture in vitro de cellules primaires de souris ( Figure 1A) [5]. Cette analyse nous a permis d'identifier et de sélectionner un premier groupe de protéines (249) (Figure 1B).…”