Functional analysis of an eye specific enhancer of the eyeless gene in Drosophila

The development of the Drosophila compound eye requires the function of a s et of evolutionarily conserved genes. Among these, the Drosophila Pax-6 gen e eyeless (ey) plays a major role. ey has been considered a master control gene of eye development in the animal kingdom because targeted expression o f ey and vertebrate as well as invertebrate homologs lead to the formation of ectopic eyes in Drosophila. We demonstrate that an intron of the ey gene contains an enhancer that regulates the eye specific expression of the gen e in the eye disc primordia of embryos and in the eye imaginal discs of thi rd instar larvae. Moreover, a 212-bp enhancer element is necessary and suff icient for the enhancer function. It is partially conserved in Drosophila h ydei and contains putative Pax-6 Paired domain binding sites. We show that several binding sites are required for the eye specific expression, and, th erefore, me propose a Pax-6-like molecule to be a positive transactivator f or the eye specific ey expression, This transactivator recently has been id entified as twin of eyeless, the second Pax-6 gene in Drosophila.