MTM1 depletion impairs BIN1 tubule positioning in differentiated muscle fibres. (A) Knockdown of Mtm1 did not alter BIN1 membrane tubulation in cultured myotubes. Immunofluorescence using anti-BIN1 antibodies was performed on C2C12 myotubes, wild type or knocked down for MTM1. Images represent confocal z-stack projections. (B) Orientation of BIN1-positive structures is altered in Mtm1 KO isolated muscle fibres compared with WT fibres. Immunofluorescence using anti-BIN1 antibodies was performed on muscle fibres isolated from 5-week-old wild type and Mtm1 KO mice. Mtm1 KO fibres are atrophic. Confocal planes in the middle of fibres. Scale bars, 10 μm. BIN1, amphiphysin 2; KO, knockout; MTM1, myotubularin; WT, wild type.