New functions of the Drosophila rhomboid gene during embryonic and adult development are revealed by a novel genetic method, enhancer piracy.

Localized expression of the Drosophila rhomboid (rho) gene has been proposed to hyperactivate EGF-Receptor signaling in specific cells during development of the embryo and adult. In this report we use a novel transposon based genetic method, enhancer piracy, to drive ectopic expression of a rho cDNA transgene by endogenous genomic enhancers. Many enhancer piracy transposon-rho insertions cause dominant phenotypes, over half of which cannot be duplicated by ubiquitous expression of rho. Genetic interactions between various dominant enhancer piracy alleles and mutations in the EGF-R/RAS signaling pathway indicate that many of these novel phenotypes result from ectopic activation of EGF-R signaling. Patterned mis-expression of the rho cDNA transgene correlates in several cases with localized dominant enhancer piracy phenotypes. Enhancer piracy lines reveal an unanticipated role for rho in imaginal disc formation and provide the first evidence that mis-expression of rho is sufficient for converting entire intervein sectors into veins. Enhancer piracy may prove to be a general strategy for obtaining dominant alleles of a gene of interest in diverse insects, worms, plants, and potentially in vertebrates such as mice and fish.