Fig. 5. Cysts are apical compartments within the cell boundary in unicellular and intracellular branches in exp mutants.

(A-B”’) Stage 15 w¹¹¹⁸ and exp¹³⁵ embryos were immunostained with the apical membrane marker Crb, basolateral membrane marker Cor, and tracheal nuclei marker Trh, to visualize apical-basal polarity in wild type and exp¹³⁵ mutant embryos. Unicellular branch GBs were shown. Both Crb (green) and Cor (red) appear as single lines without overlapping in wild type embryos (A-A”’). Similarly, cysts outlined by Crb do not overlap with Cor in exp¹³⁵ mutant embryos (B-B”’), indicating that cysts are apical compartments. (G-H”’) Stage 15 w¹¹¹⁸ and exp¹³⁵ embryos containing btl-Gal4 mCD8-GFP that outlines the cell boundary were immunostained for Crb and the AJ marker Shg. Shg (blue) labels a line of autocellular junctions along the apical membrane (red) in wild type GB (G-G”’). Similarly, Shg (blue) labels a line of autocellular junctions despite cyst (red) formation in exp¹³⁵ embryos, suggesting that cysts are part of the extracellular lumen in unicellular branches (HH”’). (C-F”) Stage 15 w¹¹¹⁸ and exp¹³⁵ embryos containing btl-Gal4 mCD8-GFP were immunostained for Crb and the cell membrane marker GFP. In wild type embryos, Crb (red) appears as a line within the cell boundary marked by mCD8-GFP (green) in unicellular branch GB (C-C”) and intracellular branch LG (E-E”). Similarly in exp¹³⁵ mutant embryos, cysts (white arrowheads) in GB (D-D”) and LG (F-F”) are also within the mCD8-GFP labeled cell boundary. Nuclei were labeled by asterisks.