HEDGEHOG IS AN INDIRECT REGULATOR OF MORPHOGENETIC FURROW PROGRESSIONIN THE DROSOPHILA EYE DISC

Pattern formation in the eye imaginal disc of Drosophila occurs in a w ave that moves from posterior to anterior. The anterior edge of this w ave is marked by a contracted band of cells known as the morphogenetic furrow behind which photoreceptors differentiate. The movement of the furrow is dependent upon the secretion of the signalling protein Hedg ehog (Hh) by more posterior cells, and it has been suggested that Hh a cts as an inductive signal to induce cells to enter a furrow fate and begin differentiation. To further define the role of Hh in this proces s, we have analysed clones of cells lacking the function of the smooth ened (smo) gene, which is required for transduction of the Hh signal a nd allows the investigation of the autonomous requirement for hh signa lling. These experiments demonstrate that the function of hh in furrow progression is indirect. Cells that cannot receive/transduce the Hh s ignal are still capable of entering a furrow fate and differentiating normally. However, hh is required to promote furrow progression and re gulate its rate of movement across the disc, since the furrow is signi ficantly delayed in smo clones.