Fig. 5.

Crb is required to maintain polarity during late tubule development as they undergo cell rearrangements. (A,A′) In early stage 13 crb mutant embryos, Baz localises normally to the apical membrane of the tubules and the tubule lumen is clearly visible (arrows). (B,B′) In late stage 13 crb mutant embryos there are regions of tubule cells in which Baz has become delocalised and the lumen of the tubule is disrupted (arrow). (C,C′) By stage 14, polarity is disrupted throughout the tubules and there is no apparent lumen (arrow). (D-E″) When Crb is overexpressed in the tubules, there is no effect on polarity at the beginning of stage 13; Baz remains tightly localised to the apical domain (D′). In late stage 13, Crb spreads down the basolateral membranes of the cells and Baz is no longer restricted to the apical domain (E). (F,G) In wild-type tubules Fas II (green) localises along the lateral membranes of tubule cells (arrow) and does not overlap with apical Baz (red) (F). Stellate cells (Tsh, green) integrate into the epithelium during tubule elongation (G). (H-J) In ct mutant embryos the tubules do not elongate but remain as blisters at the junction between the hindgut and midgut (H,I arrows). (I) Tsh-expressing stellate cells are absent from the tubules of ct mutant embryos. (J) Fas II (green) and Baz (red) localisation is not affected in ct mutant tubule cells. (K-L′) ct;crb double mutants have a tubule phenotype similar to single ct mutants; the cells form epithelial blisters of columnar cells, with Baz (red) and Fas II (green) localised to distinct domains.