DIRECT DOWNSTREAM TARGETS OF PRONEURAL ACTIVATORS IN THE IMAGINAL DISC INCLUDE GENES INVOLVED IN LATERAL INHIBITORY SIGNALING

In Drosophila imaginal discs, the spatially restricted activities of t he achaete (ac) and scute (sc) proteins, which are transcriptional act ivators of the basic-helix-loop-helix class, define proneural clusters (PNCs) of potential sensory organ precursor (SOP) cells, Here, we rep ort the identification of several genes that are direct downstream tar gets of ac-sc activation, as judged by the following criteria. The gen es are expressed in the PNCs of the wing imaginal disc in an ac-sc-dep endent manner; the proximal promoter regions of all of these genes con tain one or two high-affinity ac-sc binding sites, which define the no vel consensus GCAGGTG(T/G)NNNYY; where tested, these binding sites are required in vivo for PNC expression of promoter-reporter fusion genes . Interestingly, these ac-sc target genes, including Bearded, Enhancer of split m7, Enhancer of split m8, and scabrous, are all known or bel ieved to function in the selection of a single SOP from each PNC, a pr ocess mediated by inhibitory cell-cell interactions. Thus, one of the earliest steps in adult peripheral neurogenesis is the direct activati on by proneural proteins of genes involved in restricting the expressi on of the SOP cell fate.