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Fig. 6. DPP signaling inhibits terminal branch extension. (A) When a high level of
Dpp signaling was maintained by expressing dpp, elongating terminal
branches were misoriented and were stalled (white arrowheads). Compare this
with the control terminal branch shown in
Fig. 5C. Overexpression of Dpp
promoted excess recruitment of tracheal cells into DB
(Vincent et al., 1997), but
the number of terminal cells expressing SRF remained one per DB (data not
shown). (B-F) Premature reduction of Dpp signaling by overexpression of Dad
causes misdirection of the terminal branch. (B) Time-lapse images of a
terminal branch that crossed the dorsal midline (arrowhead). (C-F) Phenotypes
of Dad expression in terminal branches were classified as either class 1 (C,
normal), class 2 (D, drifting along the AP axis) or class 3 (E, midline
crossing). Class 2 and 3 phenotypes included another subcategory, the class 4
phenotype (F, bipolar elongation). The asterisk indicates that this phenotype
is a subset included within the class 2 and 3 phenotypes. A total of 103
terminal branches that reached dorsal midline (broken line) were scored.
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