Impairments in contractility and cytoskeletal organisation cause nuclear defects in nemaline myopathy

Nemaline myopathy (NM) is a genetically heterogeneous skeletal muscle disorder caused by mutations predominately affecting contractile filaments, in particular thin filament structure and/or regulation. The underlying cellular pathophysiology of this disease remains largely unclear. Here, we report novel pathological defects in skeletal muscle fibres of mice and patients with NM, including disrupted nuclear envelope, altered chromatin arrangement, and disorganisation of the cortical cytoskeleton. We demonstrate that such nuclear defects are caused by impairment of muscle fibre contractility, and that cytoskeletal organisation determines nuclear morphology. Our results overlap with findings in diseases caused by mutations in nuclear envelope or cytoskeletal proteins. Given the important role of nuclear shape and envelope in regulating gene expression, and the cytoskeleton in maintaining muscle fibre integrity, our findings are likely to underlie some of the hallmarks of NM, which include broad transcriptional alterations, arrested muscle fibre growth, contractile filament disarray and altered mechanical properties.