Fig. 9. VP16En requires hth throughout the germ band to activate positive targets of En and only in anterior thoracic segments to activate negative targets. All panels show anterior segments (T1, T2, T3, A1, in register) of st11 embryos that express VP16En under the control of the paired-Gal4 driver. (A) In the absence of slp, VP16En (in ochre, seen with anti-HA) activates expression of hh (blue), especially in the midventral region. This point is already made in Fig. 6D for abdominal segments. The same effect is seen on en expression (not shown). (B) In the absence of hth (and also slp), VP16En no longer activates ectopic hh expression. This panel shows a slp hth double mutant with VP16En in brown and hh in blue. Almost all endogenous hh has disappeared and no ectopic expression is seen. (C) VP16En activates ectopic expression of wg in T2 and A1 (where paired-Gal4 is active) in an otherwise wild-type embryo. (D) In a hth mutant, ectopic wg expression is still activated in A1 but not in T2. (E,F) A similar effect is seen on the expression of slp, another negative targets of En.