THE DROSOPHILA SINE OCULIS LOCUS ENCODES A HOMEODOMAIN-CONTAINING PROTEIN REQUIRED FOR THE DEVELOPMENT OF THE ENTIRE VISUAL-SYSTEM

The transformation of an unpatterned epithelium into a patterned one i sa fundamental issue in morphogenesis. This transformation occurs in a dramatic fashion in the developing eye imaginal disc, the primordium of the Drosophila compound eye. Molecular and developmental analyses r eveals that the sine oculis (so) locus encodes a homeodomain-containin g protein that is expressed and required in the unpatterned epithelium prior to morphogenesis. In mutants, cells undergo apoptosis. These fi ndings argue that so plays an essential role in controlling the initia l events of pattern formation in the eye disc. So is also expressed an d required for the development of the rest of the fly visual system, i ncluding the optic lobes (i.e., those regions of the brain that proces s visual information). So is expressed in the optic lobe primordium pr ior to its invagination from the embryonic ectoderm; in so mutants, th e optic robe primordium fails to invaginate.