Apoptosis of crs blood cells. (A-E) Live wild-type (A) and mutant (B-E) embryos incubated with acridine orange at 36 to 38 hpf. The area bracketed in ventral tail (B) is shown at higher magnification (C) with far right arrow indicating the same labeled blood cell in panels B and C. Areas over the yolk sac (B) and in the ventral tail (C) are shown at higher magnification in panels D and E, respectively. Arrowheads indicate the same labeled blood cells in panels C and E. Fluorescent images overlay bright-field images (D-E) and labeled cells are surrounded by unlabeled blood cells over the yolk sac (D) and in the tail vessels; CA indicates caudal artery and CV caudal vein (E). (F) Whole-mount immunofluorescence on 36 hpf mutant embryos with an antibody against activated caspase-3 overlies a bright-field image in the ventral tail. The yolk extension (yolk ext) and anus are marked for orientation. (G-H) Whole-mount in situ hybridization for c-myb⁺ stem cells at 42 hpf in wild-type (G) and mutant (H) embryos. Brackets delineate the positive progenitor population. Arrows in panel H mark positive cells in the mutant.