Tramtrack co-operates to prevent ectopic sensilla development in the adult PNS. P. Badenhorst 1, A. Travers 2. 1) Lab Molecular Cell Biol, NCI, Bethesda, MD 20892-4255; 2) MRC Laboratory of Molecular Biology, Hills Rd, Cambridge CB2 2QH, England.
The correct development of the Drosophila PNS requires tight control of the appearance of sensilla mother cells (SMCs). Single SMCs arise from territories - proneural clusters - defined by expression of the achaete-scute complex genes. The production of ectopic SMCs outside of these regions is prevented by transcriptional repression of proneural genes. We demonstrate that the BTB/POZ domain transcriptional repressor tramtrack (ttk) co-operates in this repression. Ttk is expressed ubiquitously, except in proneural clusters and sensory mother cells. Over-expression of Ttk represses proneural genes and inhibits sensilla formation. Loss of Ttk enhances bristle promoting mutants. Functional dissection shows that only for the BTB domain and the zinc finger DNA-binding motif are required absolutely for neural repression. We show that the BTB motif is a protein-protein interaction motif and can tetramerise. Analysis of a series of Ttk target promoters is consistent with formation of a repressive DNA architecture on target promoters.