Fig 2. Crb and Baz are neither detectably expressed nor required for apical–basal polarity in adult midgut ECs.

(A) Adult midgut epithelium from a female carrying a GFP protein trap insertion in the endogenous Crb locus stained with anti-GFP (green). Crb-GFP is not detectable in the adult midgut epithelium. Cora (red) and aPKC (white) are also shown. (B) ECs homozygous for crb^8F105 (marked by GFP, green). The apical domain forms normally as revealed by the apical localization of Myo7a (red). (C) Conditional mis-expression of UAS-Crb in adult midgut ECs using MyoIA-GAL4; tubP-GAL80^ts. Crb (green) localises to the BL but does not perturb SJ formation as revealed by Tsp2a (red). (D) Adult midgut epithelium expressing Baz-GFP under endogenous control (protein trap line), stained with anti-GFP (green) and anti-Baz (white). Baz/Baz-GFP is not detectable in ECs but is expressed in ISCs, in which it localises apically (white arrowhead). Cora (red) labels the SJ. (E) ECs homozygous mutant for baz⁴ (marked by GFP, green). The apical brush border forms normally as revealed by staining for F-actin with phalloidin (red). (F) Ectopic expression of UAS-Baz-GFP in adult midgut ECs using MyoIA-GAL4; tubP-GAL80^ts has no effect on the formation of the apical SJ marked by Dlg (red). Baz-GFP localises to the apical domain and AJs (green). Scale bars, 10 μm. AJ, adherens junction; aPKC, atypical protein kinase C; Baz, Bazooka; BL, basal labyrinth; Cora, Coracle; Crb, Crumbs; Dlg, Discs large; EC, enterocyte; GFP, green fluorescent protein; MyoIA, Myosin IA; Myo7a, Myosin 7a; SJ, septate junction; Tsp2a, Tetraspanin 2a; tubP, tubulin promoter; UAS, Upstream Activation Sequence.