Drosophila terminalia as an appendage-like structure

In Drosophila, the homeotic gene Distal-less (Dll) has a fundamental role i n the establishment of the identity of ventral appendages such as the leg a nd antenna. This study reports the expression pattern of Dll in the genital disc, the requirement of Dll activity for the development of the terminali a and the activation of Dll by the combined action of the morphogenetic sig nals Wingless (Wg) and Decapentaplegic (Dpp). During the development of the two components of the anal primordium - the hindgut and the analia - only the latter is dependent on Dll and hedgehog (hh) functions. The hindgut is defined by the expression of the homeobox gene even-skipped. The lack of Dl l function in the anal primordia transforms the anal tissue into hindgut by the extension of the eve domain. Meanwhile targeted ectopic Dll represses eve expression and hindgut formation. The Dll requirement for the developme nt of both anal plates in males and only for the dorsal anal plate in femal es, provides further evidence for the previously held idea that the analia arise from two primordia. In addition, evaluation was made of the requireme nt for the optomotor-blind (omb) gene which, as in the leg and antenna, is located downstream to Dpp. These results suggest that the terminalia show s imilar behaviour to the lex disc or the antennal part of the eye-antennal d isc consistent with both the proposed ventral origin of the genital disc an d the evolutive consideration of the terminalia as an ancestral appendage. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.