Fig. 1. Effect of blebbistatin treatment on the early cellular cleavage cycles in zebrafish embryos. (A,C,E,G,I) Selected images from a time course study of a live control embryo showing the following stages: furrow initiation (A), maximal furrow ingression (C), second cleavage cycle (E), third cleavage cycle (G) and 32-cell stage (I). (B,D,F,H,J) Selected images from a live blebbistatin-treated embryo at the same time points. Ingression of the first (arrowhead) and second (arrow) cleavage furrows are not affected by blebbistatin treatment, and furrows for the third cleavage cycle can initiate apparently normally (left asterisk in H) or exhibit a reduction in furrow initiation (right asterisk in H). However, blebbistatin-treated embryos do not form an adhesive septum after furrow completion (arrowheads in F and H indicate the location where the first furrow membrane has regressed), and the embryos develop as a syncytium (J). Images are side views. In panels A-H, arrowheads, arrows and asterisks indicate the location of first, second and third cleavage furrows, respectively.