(A) Left: A wild-type adult antenna. The first (A1), second (A2), and third (A3) antennal segments and the arista (Ar) are indicated. Right: A mature antennal disc stained for Hth (blue), Dll (red), and the ss reporter B6.9/lacZ (Emmons et al. 2007) (green). Hth is expressed in the primordia of A1, A2, and A3; Dll is expressed in A2, A3, and the arista; and ss is expressed in A3 and the arista. (B) Five conserved domains within ss522 and their deletion derivatives are indicated. The antennal expression each drives in vivo is shown to the right. (C) Conservation of the sequence of domain 4 in 12 Drosophila species; dashes indicate identity, red hatch marks indicate 3 bp insertions relative to the D. melanogaster sequence.