unpaired, wingless, and decapentaplegic have independent expression domains. unpaired (upd) (green), wingless (Wg) (red) and decapentaplegic (dpp) (blue) do not overlap in a Drosophila third instar antennal disc. In this issue, Ayala-Camargo et al. show that these factors mutually repress each other's expression and that this repression is critical for the formation of a single proximo-distal axis per leg or antenna. upd-Gal4, UAS-gfp enhancer trap (green); Wg protein (red) and dpp-lacZ (anti Beta-galactosidase) (blue). Anterior is to the left and dorsal is up. See Ayala-Camargo et al., Developmental Dynamics 236:2721-2730. © 2007 Wiley-Liss, Inc.