Fig. 5. Myosin activity is required for the distal aggregation of the zebrafish germ plasm. Control (A,B) and blebbistatin-treated (C,D) embryos labeled for the vasa RNA, a component of the zebrafish germ plasm, using in situ hybridization and for DNA using DAPI. B and D show the same embryo as in A and C, respectively, under the DAPI fluorescence channel, revealing that the embryos are at a similar stage in the cell cycle, immediately before the third cell division. At this stage, the germ plasm has already undergone a distal aggregation during furrow formation, and appears as compact aggregates at the distal ends of furrows of the first two cellular cycles (A). Inhibition of myosin function does not interfere with the recruitment of the germ plasm to the furrow (C), but the recruited germ plasm aggregate maintains its original rod-like structure and does not undergo further aggregation to the distal end of the furrow. Brackets in C delineate the extent of the germ plasm aggregate at the cleavage furrows. Images are animal views. Arrowheads and arrows indicate the first and second cleavage furrows, respectively, which are recognizable by the pattern of nuclear division.