Fig. 2. Time-lapse fluorescent microscopy reveals the accumulation and dynamics of GFP-myosin in post-mitotic C2C12 myocytes. Fluorescent images of two different cells (A,B) from the same field are shown at various times after starting observation. Cells were infected 24 hours before the start of the time-lapse sequence. (A) The GFP-myosin is first detected near the periphery of the cell in globular intermediates (the position of the nucleus, N, is indicated). The fluorescence intensity and number of globules increases with time and the globules move about the cytoplasm as this mono-nucleate myocyte elongates. In this example, the globular intermediate is pulled along with the elongating cell, and stretches into a 25-30 µm long fiber that is labeled with arrowheads in the 16 hour 30 minutes frame. (B) Another cell elongates (arrowhead marks the end of the cell) and with the elongation there is a redistribution of the globular intermediates to the very tip of the cytoplasmic extension. Cells were maintained at 34°C with a heated microscope stage and perfused with heated media. A time-lapse movie of this experiment can be found in Supplemental Data (http://jcs.biologists.org/supplemental).