Actin comets are dynamic and cell cycle-dependent. (A) Comets vary in speed, length, width, and direction of movement. Six consecutive frames show the 3D-Max Projection of 8 sections (1 μm Z-step at 6 s intervals) through the top half of an embryo at pronuclear meeting. (B) Rh-phalloidin labels actin comets and colocalizes with GFP::MOE. Fixed 2- and 4-cell embryos from wild-type N2 and GFP::MOE transgenic animals (inset, magnified image of one comet tail). No DAPI staining is observed at the tips of comet tails. (C) The number of actin comets peaks just prior to prometaphase of the first cell cycle in WT and is influenced by RNAi of several actin-binding proteins. Actin comets were counted in the top half of the embryo during five consecutive time intervals of 3–4 minutes each, bounded by the following landmarks: 3 minutes before pseudocleavage (PC), pseudocleavage, prometaphase, metaphase, completion of cytokinesis, cytokinesis + 3 min. RNAi of Arp2/3 (ARX-1), CDC-42, and profilin (PFN-1), but not non-muscle myosin (NMY-2), significantly reduces the maximum number of comets. (D) Distribution and mean speed (0.22 ± 0.10 μm/s) of comet tails in the one-cell embryo. Measured speeds of individual comets (n = 21) were binned into 0.05 μm intervals. (E) A scatterplot of tail width and speed shows that tail width and speed are not correlated. Scale bars in A and B are 10 μm.