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Fig. 5. Hh signaling restricts terminal branching to the P compartment. Broken lines indicate the dorsal midline, and white arrowheads indicate the terminal branch. (A,E,H,K) Stage 16 embryos labeled with anti-EN (purple), with the trachea shown in green (GFP-moe). Anterior is leftwards. (B) Double-labeling of en-lacZ (purple) and the trachea (green; GFP-moe). The terminal branch runs along the anterior border of the en-lacZ stripe. (C,F,I) Images taken from Movies 1 (C), 3 (F) and 4 (I) showing migration patterns of the terminal branch. The length (in µm) of one terminal branch (colored purple) is indicated in C. (D,G,J) Expression of SRF (purple). (A-D) Wild-type embryos. Terminal branches are aligned along the AP compartment borders. In C, terminal cells are pseudo-colored with purple to highlight the shape of terminal branches. (E-G) When Hh signaling is hyperactivated by Ci^Act in the trachea, terminal branches are not confined within the P compartment and cell extensions pointing in the AP direction are observed (arrowhead). (H-J) Downregulation of Hh signaling in the trachea by Ci^R expression results in the formation of secondary terminal branches that extend outside the P compartment (red arrowheads). Compare this with terminal branches that formed first (white arrowheads). An example of a single terminal cell extending two terminal branch (colored green) is labeled with asterisk in J. (K,K') Hh expressed in a broad longitudinal band in the DE (using the ush-gal4 driver) caused terminal branch misguidance. Tracheal cells were visualized with btl-gfp-moe. (L) Expression pattern of ush;gfpNLS. (M-O) Expression of ptc-lacZ. Expression in terminal cells (yellow circle) was low in control embryos (M) but was elevated when Ci^Act was ectopically expressed in the trachea using btl-Gal4 (N) and was reduced by Ci^R (O). The yellow arrowhead indicates an epidermal cell expressing a high level of ptc-lacZ. Broken green line in M indicates the outline of the DB detected by GFP (for clarity, the GFP signal is not shown).

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