Fig. 1. Expression and phenotypes of Dll in the Drosophila antenna and leg. (A) Wild-type adult Drosophila antenna. The arista (ar) vibrates in response to sound, putting torque on the third antennal segment (a3), which then rotates. A large chordotonal organ, the Johnston’s organ, inside the second antennal segment (a2) processes and transmits auditory information via the antennal nerve through the first antennal segment (a1) to the brain. The antenna also serves as a major olfactory organ. a3 is covered with olfactory sensilla. (B) Dll expression, visualized via use of a ß-galactosidase-encoding enhancer trap, in a late pupal antenna. Dll is expressed from distal a2 through the arista. (C) A weak combination of hypomorphic Dll alleles results in antenna toward leg transformations. Distal a3 and the proximal part of the arista are transformed to medial leg structures. (D) Wild-type adult Drosophila leg. The proximal-most coxa (cx) and distal-most claws (cl) are indicated. tr, trochanter; fe, femur; ti, tibia; t1-t5, first to fifth tarsal segments. (E) Dll expression, visualized via use of a ß-galactosidase-encoding enhancer trap, in a late pupal leg. Dll is expressed in the distal trochanter, weakly in the tibia, and in the tarsal segments. (F) A weak combination of hypomorphic Dll alleles results in truncation of distal leg structures.

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