# Zoologisches Institut, Universität Zürich, Winterthurstr. 190, CH-8057 Zürich, Switzerland, Theodor-Boveri-Institut, Universität Würzburg, Lehrstuhl für Genetik, Am Hubland, D-97074 Würzburg, Deutschland,
The secreted Hedgehog (Hh) protein is essential for pattern formation in imaginal discs. In the eye disc, Hh is produced by differentiating photoreceptor cells and induces expression of dpp and the proneural gene atonal in adjacent anterior cells located in the morphogenetic furrow. Consequently regularly spaced clusters of cells within the morphogenetic furrow initiate neural development. By becoming Hh secreting cells they propagate the morphogenetic furrow. We have investigate the role of the Zn-finger transcription factor Cubitus interruptus (Ci) in this patterning process. We find that Ci performs a dual function in eye patterning. Ci acts as a repressor of hh expression in anterior cells and mediates Hh signalling by controlling dpp and atonal expression in the cell within the morphogenetic furrow.
Within each growing ommatidial clusters, the R7 photoreceptor is recruited by the activation of the Sevenless receptor tyrosine kinase. In a screen of new components acting as dominant suppressors of the rough eye phenotype caused by the constitutive activation of Sevenless we identified a new gene, daughter of sevenless, (dos). Genetic epistasis experiments suggest that dos acts downstream of sevenless but upstream or in parallel with Ras1. It encodes a multi-adaptor protein with a PH domain and multiple putative SH2-binding sites. Dos is required for signalling from various receptor tyrosine kinase including the Drosophila EGF receptor homolog and Torso.