DISTAL-LESS IS A DOWNSTREAM GENE OF DEFORMED REQUIRED FOR VENTRAL MAXILLARY IDENTITY

The homeotic selector (HOM) proteins are required for the diversificat ion of the anterior-posterior axis of the Drosophila body plan, assign ing unique identities to regional domains of cells comprising one or a few parasegments or segments. The HOM proteins apparently accomplish this task by the transcriptional regulation of numerous downstream gen es. At present few downstream genes are known, so models of how downst ream genes mediate HOM functions are based more on intuition than info rmation. Our results indicate that Distal-less is a downstream gene of the HOM gene Deformed, and Distal-less function is required for the e laboration of a subset of the maxillary epidermal identities specified by Deformed. The regulatory effect of Deformed on Distal-less is medi ated by a ventral maxillary-specific enhancer located 3' of the Distal -less transcription unit. We propose that Deformed and Distal-less, bo th of which encode homeodomain transcription factors that are persiste ntly expressed in ventral maxillary cells, combinatorially specify a s ubsegmental code required for a group of cells to differentiate maxill ary cirri.