Four cell stage zebrafish embryo, stained with 100 micromolar Bodipy 505/515. In the upper portion of the image, the yolk cell contains large spherical yolk platelets. The blastomeres undergoing meroblastic cleavage in the lower portion of the image are joined by cytoplasmic bridges to the yolk cell. Cell nuclei are not stained by Bodipy 505/515, and thus appear as dark circles. Bodipy 505/515 partitions into yolk platelets which appear as white spheres and particles distributed through the cytoplasm of the blastomeres. Yolk platelets within the cytoplasm of the yolk cell are also intensely stained. During every prophase there is a major onset of motility of the yolk platelets. The platelets are pulled into tubular forms, sometimes fragmenting. During telophase and interphase, the platelets re-coalesce into spherical bodies. Larger yolk platelets tend to be localized in the peripheral cytoplasm of cleaving blastomeres. Also notice the periodic fragmentation of the yolk mass within the yolk cell. The sequence continues through 16-cell stage. This video made available by Mark Cooper thru Zebrafish - The Living Laboratory. The videos in this group can also be found in the Developmental Landmarks page of the Fishscope web site.