Fig. 5. Time-lapse DIC analysis of cellularization front ingression. Embryo genotype as indicated. The top of each panel is the embryo surface. (A) In wild-type embryos, a distinct cellularization front (between arrows) can be seen passing through the nuclei. The entire cellularization process takes 70 minutes at 22°C and the membrane ingresses 35 µm from the embryo surface. (B) In mutant embryos, the cellularization front (between arrows) is less distinct. (C) Kymograph analysis of a wild-type embryo. A strip perpendicular to the embryo surface, the width of a nucleus, was cut out of time-lapse images as in A. Strips from each frame were pasted together to give a distance versus time plot (scale bars in F). The most obvious line in the kymograph, indicated by the white arrows, is the cellularization front. Its rate of movement is given by its angle: horizontal indicates static; vertical indicates fast moving. Ingression of the front occurs at three distinct rates, with breaks between them indicated by the white arrows. The black arrow indicates the base of the nucleus, that moves downwards as the nuclei elongate. (D) Second example of a kymograph of a wild-type embryo. (E) Kymograph of an anillin^HP/RS-derived embryo (strong maternal alleles). No initiation phase is evident. As soon as the front can be tracked, it ingresses at a roughly constant and slow rate. A distinct transition to a faster rate can be observed (white arrow), but both slow and fast rates of ingression are slower that their wild-type counterparts. The black arrow indicates the base of the nucleus, which moves downwards as the nuclei elongate. (F) Kymograph of an anillin^RV/RV-derived embryo (weak maternal allele). Ingression kinetics are similar to those in E.