Cyst contributes to the initial formation of an AJ belt. (A) Localization of Baz in the apico-lateral domain of the lateral ectoderm at the onset of germband extension. Reduction of cyst expression through the combination of maternal shRNA (using MTD-GAL4) and maternal heterozygosity for Df(cyst) resulted in Baz planar hyperpolarization into foci. Additional incorporation of maternal heterozygosity for a null apkc allele enhanced the hyperpolarization of Baz. A control shRNA, or the combined heterozygosity of Df(cyst) and apkc, had no apparent effects. Scale bar, 5 µm. (B) Quantification of the data shown in A. n values represent embryo numbers. (C) Side views (top) and apical domain surface projections (bottom) showing indistinguishable apical polarization and apical levels of aPKC with Cyst depletion versus controls at the onset of germband extension. Dlg labels the lateral domain. Scale bar, 5 µm. (D) Quantification of the data shown in C. Each point is a quantification of one embryo. (E) Cytochalasin D produces Baz hyperpolarization at the onset of germband extension, in contrast to carrier DMSO control. Scale bar, 5 µm. (F) Cytochalasin D has no apparent effect on apical aPKC levels at the onset of germband extension. Each point is a quantification of one embryo. For B, D, and F, pairwise comparisons were done using Student’s t test in Microsoft Excel. Data presented as mean + SEM.