Fig. 7. Parallel activities of ElB and Dpp pathway. (A,B) In wild-type embryos, at stage 14 Sal expression (red) is restricted to the dorsal trunk, and kni-lacZ (green), a Dpp-target gene, is expressed in several tracheal branches including the dorsal branches shown here. (C,D) In elB mutant embryos, expression of kni was retained. Note, however, that the number of kni-expressing cells in the dorsal branches was reduced. The remaining kni cells were located within the dorsal trunk (arrows in D). In addition, in contrast to wild-type embryos, some of the dorsal branch cells continued to express Sal (arrows in C). Thus, while ElB is not necessary for kni expression, it is required in conjunction with Kni for repression of Sal expression in the dorsal branches, and for the capacity of all putative dorsal branch cells to detach from the dorsal trunk. (E) Additional experiments demonstrated that ElB and Dpp function in parallel. Expression of elB RNA is not elevated when activated Tkv is induced in all tracheal cells by btl-Gal4. (F) The same driver can induce uniform tracheal expression of elB when crossed to the EP2039 element upstream to elB. (G) In btl-Gal4/EP2039 embryos, defects in visceral branch were observed (arrowhead) while the LTa appeared normal. (H) In btl-Gal4/UAS-tkv* embryos, an excess of dorsal branch cells was detected (arrowhead) while again the LTa was normal. (I) In embryos misexpressing both constructs in the trachea, an excess of LTa cells was observed (arrow).

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