DSP1, a Drosophila HMG protein, is involved in spatiotemporal expression of the homoeotic gene Sex combs reduced

Background information. The Pc-G (Polycomb group) and trx-G (trithorax group) genes play a key role in the regulation of the homoeotic genes. The homoeotic gene Scr (Sex combs reduced) contained in the Antennapedia complex specifies segmental identity of the labial and prothoracic segments in Drosophila. Regulation of Scr requires the action of different enhancer elements spread over several kilobases. We previously identified an HMGB (high mobility group)-like protein DSP1 (dorsal switch protein 1), which works like a trx-G protein for the normal Scr expression. Results. In the present study, we attempted to characterize the regulatory sequences involved in the maintenance of the Scr activation by DSP1. We report here, using a transgenic line for the Scr10.0Xbal-regulatory element, that lack of DSP1 affects the function of a reporter gene in legs' imaginal discs but not in embryos. We show by immunolocalization that DSP1 is recruited on polytene chromosomes to the insertion site of the transgene. Moreover, using chromatin immunoprecipitation experiments, we identify two regions of 1 kb in Scr10.0Xbal as the main DSP1 targets. Conclusion. These results provide strong evidence that the Scr gene expression is influenced by direct interaction between DSP1 and two Scr regulation elements. In addition, our results show that this interaction undergoes dynamic changes during development.