Fig. 2. The mbt phenotype in third instar eye imaginal discs. Shown are apical-to-basal projection views of wild-type (A,C,E) and mbt^P1 (B,D,F) eye imaginal discs stained with anti-Mbt (A,B) or anti-Arm (C,D). A merge of both stains is seen in E,F. Below each projection view, an apical-to-basal cross-section is shown (the bracket indicates the apical-basal extension of the eye disc). Photoreceptor cell differentiation starts in the morphogenetic furrow and involves the step-wise recruitment of eight photoreceptor cells in a single ommatidium. In the wild type, Mbt and Arm colocalise at the AJs of all photoreceptor cells as soon as they become integrated into the ommatidial clusters (E). Despite the absence of detectable levels of Mbt protein in mbt^P1 mutant eye discs (B), AJs between photoreceptor cells do form in the mutant, although some irregularities are already evident (arrow in D). (G,H) Anti-Elav staining of wild-type (G) and mbt^P1 mutant eye discs (H). Occasionally, mbt^P1 ommatidia contain fewer differentiating photoreceptor cells (arrow). The morphogenetic furrow is on the left-hand side in all figures. Scale bar: 10 µm.