The Drosophila Distal-less (Dll) gene was identified in the early 1980s by means of dominant and recessive mutations that caused both striking antenna-to-leg transformations and leg truncations. The gene initially was named "Bristle on arista" or "Brista" because one aspect of the phenotype is the formation of leg bristles on the antenna (Sato  Drosophila Information Service 60:180-182; Sunkel and Whittle  Wilhelm Roux's. Arch. Dev. Biol. 196:124-132). Subsequent studies have revealed that Dll encodes a homeodomain transcription factor (Cohen et al.  Nature 338:432-434) that is expressed throughout limb development from embryogenesis on (Cohen  Nature 343:173-177; Weigmann and Cohen  Development 126:3823-3830). Dll is required for the elaboration of distal pattern elements in the antenna, the legs, the limb-derived gnathal structures (Cohen and Jurgens  Nature 482-485), and the anal plate (Gorfinkiel et al.  Mech. Dev. 868:113-123) and can initiate proximodistal axis formation when expressed ectopically (Gorfinkiel et al.  Genes Dev. 11:2259-2271). Dll homologs are expressed in developing appendages in at least six coelomate phyla, including chordates (Akimenko et al.  J. Neurosci. 14:3475-3486; Beauchemin and Savard  Dev. Biol. 154:55-65; Bulfone et al.  Mech. Dev. 40:129-140; Dolle et al.  Differentiation 49:93-99; Ferrari et al.  Mech. Dev. 52:257-264; Panganiban et al.  Proc. Natl. Acad. Sci. USA 94:5162-5166; Simeone et al.  Proc. Natl. Acad. Sci. USA 91:2250-2254), consistent with requirements for Dlx function in normal limb development across the animal kingdom. Distal-less also has been implicated in various aspects of vertebrate neurogenesis (see reviews by Kraus and Lufkin  J. Cell. Biochem. 32-33:133-140 and the accompanying review by Beanan and Sargent  Dev. Dyn. 218:000-000). Here, I outline what is known about Dll function and regulation in Drosophila.
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