Functional analysis of an eye enhancer of the Drosophila eyes absent gene:Differential regulation by eye specification genes

Genes involved in eye development are highly conserved between vertebrates and Drosophila. Given the complex genetic network controlling early eye dev elopment, identification of regulatory sequences controlling gene expressio n will provide valuable insights toward understanding central events of ear ly eye specification. We have focused on defining regulatory elements criti cal for Drosophila eyes absent (eya) expression. Although eya has a complex expression pattern during development, analysis of eye-specific mutations in the gene revealed a region selectively deleted in the eye-specific allel es. Here we have performed detailed analysis of the region deleted in the e ye-specific eya(2) allele. This analysis shows that this region can direct early eya gene expression in a pattern consistent with that of normal eya i n eye progenitor cells. Functional studies indicate that this element will restore appropriate eya transcript expression to rescue the eye-specific al lele. We have examined regulation of this element during eye specification, both in normal eye development and in ectopic eye formation. These studies demonstrate that the element was activated upon ectopic expression of the eye specification genes eyeless and dachshund, but does not respond to ecto pic expression of eya or sine oculis. The differential regulation of this e lement by genes involved during early retinal formation reveals new aspects of the genetic hierarchy of eye development. (C) 2000 Academic Press.