Fig. 7. Wg signaling contributes to the activation of the positive targets of En. (A) Expression of Wg with paired-Gal4 in the absence of en and slp leads to weak, but significant expression of hh in oddnumbered segments (where hh decays in slp^-). Panels (B) and (C) are repeated from Fig. 6A,C to allow comparison with the effect of Wg. As seen, Wg and En have a similarly weak positive impact on hh expression. Together, Wg signaling (here induced with activated Armadillo, A^*) and En cause strong activation of hh expression (panel D). (E) hh transcription in a wg^CX4 embryo overexpressing En under the control of paired-Gal4. The histochemical reaction was allowed to proceed for a long time to reveal the weak signal. Expression is weak. Therefore, En can partially activate hh transcription in the absence of Wg signaling but Wg signaling is required for full activation. Indeed, as shown in (F), co-expression of En and activated Armadillo leads to strong hh expression. Remember that VP16En is a stronger activator than En in slp mutants. This is probably because VP16En activates Wg expression (Fig. 3D). Therefore, in the absence of slp, expression of VP16En leads to expression of both wg and en, thus causing maximal activation of hh expression.

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