The dorsal head epidermis is lost in response to reductions of Toy/ISWI levels. (A,D) SEM images of wild-type and Toy/ISWI double-knockdown flies. A deep fissure (arrow in D) is seen along the dorsal surface of the adult head between the two compound eyes when Toy/ISWI are reduced. This region normally consists of head epidermal tissue (B,C) Expression pattern of the DE-GAL4 driver. Toy/ISWI are reduced within the dorsal eye, head epidermis, and ocellar region at both 96 and 120 h AEL. (E,F) Although expression of the DE-GAL4 is maintained at 96 h AEL in Toy/ISWI knockdowns, it is lost at 120 h AEL (arrow in F). The loss of DE-GAL4 (which is an insertion in the mirror locus) suggests that the ocellar and head epidermis domains are losing their primary fate. Scale bar: 50 µm.