MTs are needed for myosin stability and sarcomere formation. Before nocodazole addition, young myotubes (A) displayed myosin structures colocalized with MTs. Images (B–D, F–H) are magnifications of the rectangle in (A). (B, F) are merged images of MTs (C, G) and myosin (D, H). At 105 s after drug addition (E), myosin remained only at the cell membrane (arrowhead in (F) and (H), movie 5_1). During myofibril formation (I, movie 5_2), Dsred-myosin incorporated into sarcomeres (arrowhead) and into nascent myofibrils (arrow). Nocodazole addition destabilized nascent myofibrils after 1 min (J, arrow; movie 5_3), but did not affect mature sarcomeres after 35 min of treatment (K, arrowhead). Bar=10 μm (A, I–K). Bar=1 μm (B–D).