DREF is required for EGFR signalling during Drosophila wing vein development

The DNA replication‐related element binding factor (DREF) has been suggested as being involved in regulation of DNA replication‐ and proliferation‐related genes in Drosophila. Recently, by searching the Drosophila genome database, we also found DRE‐like sequences in the 5′‐flanking regions of many genes with other functions. In addition, immunostaining of polytene chromosomes with an anti‐DREF monoclonal antibody revealed that DREF can bind to a hundred regions of polytene chromosomes, suggesting regulation of multiple genes and multiple roles in vivo. When we over‐expressed DREF protein or inverted repeat RNA of the DREF gene in wing imaginal discs using the GAL4‐UAS targeted expression system in Drosophila, the results were veins of increased width and a loss of veins, respectively. With DREF over‐expression, Rolled, a Drosophila MAPK homologue, was ectopically activated. Furthermore, half reduction of the D‐raf gene dose suppressed this DREF‐induced vein of increased width phenotype. In addition, when DREF transcripts were reduced by introducing double‐stranded RNA of the DREF gene into S2 cells, the D‐raf gene promoter activity was diminished to 4%. These data indicate that DREF is involved in regulation of vein formation through the activation of EGFR signalling in the Drosophila wing imaginal discs.