Fig. 1. Cytokinesis in grasshopper spermatocytes. (A) A polarization microscope sequence (Movie 1, http://jcs.biologists.org/supplemental/) showing behavior of mitochondria during cell cleavage in Melanoplus femurrubrum spermatocytes. Time is given in minutes. In metaphase (0 minutes), mitochondria (m) are scattered around the spindle apparatus (microtubules appear as black fibers). During early to mid anaphase (10-14 minutes), mitochondria accumulate around the spindle midzone (arrowheads, 32 minutes), and later bundle with and move poleward along peripheral microtubules of the central spindle (32-54 minutes). The cleavage furrow initiates (arrows, 54 minutes) and ingresses (72-93 minutes) at the midzone, which is symmetric to the bipolar spindle. (B) Localization of microtubules (green), actin filaments (red), and chromosomes (blue) in cells fixed at various stages during cell cleavage. Actin filaments, distributed randomly through the cell in early anaphase (e, red), relocate to the microtubule overlapping zone where mitochondria accumulate (b,f, arrows) in late anaphase, corresponding to the 32-minute stage shown in A. During furrow initiation, actin filaments (g, red) further accumulate at the light-stained midzone (c, arrows) of the newly assembled central spindle (c,g, green). During furrow ingression, actin filaments (h, red) become extremely condensed on both sides of the narrowed midzone (d, arrows). Scale bars: 10 µm.