Fig. 4. Anillin and Peanut (septin) localization during cellularization. Indirect immunofluorescence of cold methanol fixed embryos using laser confocal imaging. (A,C) Wild-type; (B,D) anillin^PQ/RS-derived embryos. Scale bar: 5 µm. (A) Wild-type embryo in slow phase, sectioned perpendicular to embryo surface. The cellularization front is enriched in Anillin and Peanut. (a) Same embryo, sectioned parallel to the surface at the cellularization front, where Anillin and Peanut are almost colocalized. (B) anillin^PQ/RS-derived embryo in slow phase, sectioned perpendicular to embryo surface. Although Anillin is still present at the cellularization front, Peanut is largely absent, instead it localizes to foci at the apical surface and throughout the cell (arrowhead). (b) Same embryo, sectioned parallel to the surface at the cellularization front. Most of the Peanut is missing, and the remaining protein is present in foci that do not colocalize with Anillin. (C) Wild type embryo in late cellularization/early gastrulation, sectioned perpendicular to embryo surface. Anillin and Peanut colocalize at the cellularization front. The apical and lateral plasma membrane contains Peanut but not Anillin (arrowhead). (c) Same embryo, sectioned parallel to the surface at the cellularization front. Anillin and Peanut colocalize in the rings. (D) anillin^PQ/RS-derived embryo in late cellularization/early gastrulation, sectioned perpendicular to embryo surface. The cellularization front is disorganized, with most of the Anillin and Peanut missing. Within cells, Peanut is present in abnormal foci (white arrowhead) and nuclei are mis-positioned. (d) Same embryo, sectioned parallel to the surface at the cellularization front. Anillin and Peanut do not colocalize and contractile rings fail to form.