ANALYSIS OF CUBITUS INTERRUPTUS REGULATION IN DROSOPHILA EMBRYOS AND IMAGINAL DISKS

The cubitus interruptus (ci) gene of Drosophila is expressed in all an terior compartment cells in both embryos and imaginal disks where it e ncodes a putative zinc-finger protein related to the vertebrate Gli an d C. elegans Tra-1 proteins. Using ci/lacZ fusions, we located regulat ory sequences responsible for the normal pattern of ci expression, and obtained evidence that separate elements regulate its expression in e mbryos and imaginal disks. Mutants that delete a portion of this regul atory region express ci ectopically in the posterior compartments of t heir wing imaginal disks and have wings with malformed posterior compa rtments. Similar deletions of ci/lacZ fusion constructs also result in ectopic posterior compartment expression. Evidence that the engrailed protein normally represses ci in posterior compartments includes the expansion of ci expression into posterior compartment cells that lack engrailed function, diminution of ci expression upon overexpression of engrailed protein in anterior compartment cells, and the ability of e ngrailed protein to bind to the ci regulatory region in vivo and in vi tro. We suggest that engrailed protein directly represses ci expressio n in posterior compartment cells.