Fig. 3. slam^waldo M^–Z^– mutants have a cellularization defect. (A-D) Wild type, (E-H) slam^waldo M^–Z^– mutants, embryos are stained with -myosin in green to mark the advancing basal-most part of the cell membrane, and in red with DAPI to mark the nuclei. Arrows mark cellularization front. I-K are stained with -Vasa to mark germ cells. (A,E) Pre-cellularization embryos, the nuclei are lined up under the plasma membrane, which has not begun to invaginate. slam^waldo M^–Z^– is indistinguishable from wild type at this stage. (B,F) Mid-cellularization, nuclei are elongating in both wild type and slam^waldo M^–Z^–. The membrane has begun to invaginate in wild type, but not in slam^waldo M^–Z^–. (C,G) Mid-late cellularization, in wild type, the nuclei have continued to elongate as the membrane has advanced almost to the end of the nuclei. The membrane in slam^waldo M^–Z^– still has not begun to invaginate. (D,H) End of cellularization, in wild type, the membrane has now reached its final basal position, past the nuclei, and has pinched off individual cells. In slam^waldo M^–Z^–, the membrane has begun to invaginate, but it does not advance beyond the nuclei once it begins to pinch off. The nuclei are trapped in the pinching membrane. The appearance of two lines of basal Myosin staining is due to the section being slightly tangential, revealing apposing membranes. (I) slam^waldo M^–/–Z^–/– mutant. (J) M^–/–Z^–/+ slam cellularizes properly. (K) Germ cell migration is normal in M^–/–Z^–/+ slam, stage 14.