Fig. 6.

Toy and ISWI are required during the second larval instar to suppress formation of the second antenna. (A-H) Lim1 expression reaches its final pattern at 72 h AEL and remains just within the A1 segment for the rest of larval development. (I) In Toy/ISWI mutants a single Lim1 ring is seen as late as 96 h AEL. (J-L) The second antenna begins to develop at 100 h AEL and is complete by 108 h AEL. (M-O) Sustained reductions of Toy/ISWI that begin during embryogenesis or the first two larval instars all lead to the formation of a second ectopic antenna. (P) However, if the targeting of Toy/ISWI begins at the L2/L3 transition (or later), then a second antennal field does not form. (M) Embryogenesis (24 h at 18°C). (N) First/second larval transition (72 h at 18°C). (O) Mid/late second instar (84 h at 18°C). (P) Second/third larval transition (108 h at 18°C). (Q,R) If Toy/ISWI activity is restored during embryogenesis or the first larval instar then a second antenna is not produced. (S,T) However, if Toy/ISWI are restored only after the L1/L2 transition, then an ectopic antenna emerges. (Q) Embryonic/first instar transition (24 h at 30°C). (R) Mid first instar (30 h at 30°C). (S) First/second instar transition (42 h at 30°C). (T) Mid second instar (48 h at 30°C). Scale bar: 50 µm.