INDUCTION OF ECTOPIC EYES BY TARGETED EXPRESSION OF THE EYELESS GENE IN DROSOPHILA

The Drosophila gene eyeless (ey) encodes a transcription factor with b oth a paired domain and a homeodomain. It is homologous to the mouse S mall eye (Pax-6) gene and to the Aniridia gene in humans. These genes share extensive sequence identity, the position of three intron splice sites is conserved, and these genes are expressed similarly in the de veloping nervous system and in the eye during morphogenesis. Loss-of-f unction mutations in both the insect and in the mammalian genes have b een shown to lead to a reduction or absence of eye structures, which s uggests that ey functions in eye morphogenesis. By targeted expression of the ey com plementary DNA in various imaginal disc primordia of Dr osophila, ectopic eye structures were induced on the wings, the legs, and on the antennae. The ectopic eyes appeared morphologically normal and consisted of groups of fully differentiated ommatidia with a compl ete set of photoreceptor cells. These results support the proposition that ey is the master control gene for eye morphogenesis, Because homo logous genes are present in vertebrates, ascidians, insects, cephalopo ds, and nemerteans, ey may function as a master control gene throughou t the metazoa.