Generating imaginal disc clones in Drosophila

INTRODUCTIONImaginal disc primordia appear in Drosophila embryos as clusters of cells that invaginate from the embryonic epithelium. During metamorphosis, the imaginal discs form much of the outer covering of the developing adult. Generation of genetic mosaics is useful for removing or adding gene function to imaginal cells. Mitotic recombinants can be generated in a small percentage of disc cells at any stage; each cell then divides normally, forming a clone of genetically altered tissue. Mitotic recombination is induced between homologous chromosomes to generate homozygotic cells in heterozygotic flies. This is done either by irradiating heterozygotic larvae, or by using heat-shock-induced expression of flippase recombinase (FLPase) to induce recombination between FLPase recombination targets (FRTs) inserted into selected chromosome arms. In the FLPout technique, heat-shock-induced expression of FLPase joins a ubiquitous promoter to a selected coding sequence by removing blocking DNA flanked by FRTs. This technique can be used with an upstream activation sequence (UAS)-GAL4. A GAL4 FLPout clone expresses GAL4, which in turn drives the expression of any gene coupled to the UAS promoter. This protocol describes methods for generating such mosaics, by which genetic changes can be limited to small groups of imaginal cells.