THE DROSOPHILA SERUM RESPONSE FACTOR GENE IS REQUIRED FOR THE FORMATION OF INTERVEIN TISSUE OF THE WING AND IS ALLELIC TO BLISTERED

The adult Drosophila wing is formed by an epithelial sheet, which diff erentiates into two non-neural tissues, vein or intervein. A large num ber of genes, many of them encoding components of an EGF-receptor sign aling pathway, have previously been shown to be required for different iation of vein tissue, Much less is known about the molecular control of intervein differentiation. Here we report that the Drosophila homol og of the mammalian Serum Response Factor gene (DSRF), which encodes a MADS-box containing transcriptional regulator, is expressed in the fu ture intervein tissue of wing imaginal discs, In adult flies carrying only one functional copy of the DSRF gene, additional vein tissue deve lops in the wing, indicating that DSRF is required to spatially restri ct the formation of veins, In mitotic clones lacking DSRF, intervein t issue fails to differentiate and becomes vein-like in appearance, Gene tic and molecular evidence demonstrates that DSRF is encoded by the bl istered locus, which produces ectopic veins and blistered wings when m utant, Our results show that DSRF plays a dual role during wing differ entiation. It acts in a dosage-dependant manner to suppress the format ion of wing veins and is required cell-autonomously to promote the dev elopment of intervein cells, We propose that DSRF acts at a key step b etween regulatory genes that define the early positional values in the developing wing disc and the subsequent localized expression of inter vein-specific structural genes.