Evolution of transcriptional control of the Drosophila gap gene hunchback. S.J. Lemke ^{1, 2}, A.H. Prell ¹, U. Schmidt-Ott ². 1) Molekulare Entwicklungsbiologie, Max-Planck-Institut fuer biophysikalische Chemie, Goettingen, Niedersachsen, Germany; 2) Department of Organismal Biology and Anatomy, The University of Chicago, 1027 East 57 th Street, Chicago, IL 60637, USA.

   Gene circuitry in early development of Drosophila provides a detailed model of a developmental gene-network. Recently, we proposed that Bicoid, one of its key transcriptional activators, is an evolutionary novelty in higher (Cyclorrhaphan) flies (Stauber et al. PNAS 99: 274-279). Based on this model we expect that cis-regulatory control of hunchback, a principal target of Bicoid, had been redesigned during the evolution of flies (Diptera). In previous studies reporter constructs in transgenic Drosophila embryos were found to be directly regulated either by Bicoid or by Caudal and an unidentified anterior factor (possibly Orthodenticle), depending on whether they were supplemented with hunchback-regulatory DNA from Drosophila or Musca, or from Tribolium, respectively (Bonneton et al. MOD 66, 143-156; Wolff et al. Development 125, 3645-3654). These and additional experiments suggest that anterior expression of hunchback switched from Caudal- (and Orthodenticle?) to Bicoid-dependent regulation. This switch might have taken place during the radiation of Cyclorrhaphan flies when Bicoid most likely evolved. Accordingly, one would expect that hunchback regulatory DNA from lower Diptera and from Tribolium drive similar reporter gene expression in transgenic Drosophila in a similar pattern. To test this hypothesis we started to analyze the expression of multiple reporter constructs with putative upstream regulatory DNA of Dipteran hunchback homologues in transgenic Drosophila embryos.