Muscle cells from L4 larvae express muscle-specific myosin and spontaneously contract in vitro.

(A) DIC and fluorescence micrographs of fixed muscle cells isolated from L4 stage myo3::GFP worms, which expresses GFP in both nucleus and mitochondria of muscle cells. Cells were immunostained for myosin heavy chain A (MHC-A), and stained for nuclei (DAPI). A wide band of myosin was observed near the cell center. (B) Time-lapse DIC series of spontaneous contraction in a muscle cell from myo3::GFP reporter strain. GFP indicates muscle identity. Dotted outlines show cell body shape as at 0 second, and are static throughout the sequence. Arrowheads show edges of cell body. Black arrowheads indicate initial boundary and are static throughout the sequence. White arrowheads indicate the newest cell edge positions. The overall cell shape changes from near rectangular (0 sec) to oval (5 sec) and back to near rectangular (10 sec). Time is in min∶sec. Scale bars are 5 µm.