ECTOPIC EXPRESSION IN DROSOPHILA

There are now several different methods for ectopic expression in Drosophila, each with its merits and its limitations. The first technique is to drive expression of a gene using the transcriptional regulatory sequences from a defined promoter. Tissue-specific promoters allow transcription to be restricted to a defined subset of cells. The second method is to drive expression of a gene from a heat-shock promoter. A gene can then be turned on at a specific point in development by heat shocking the transgenic animal. A more recent inducible technique for ectopic expression relies on site-specific recombination catalyzed by the flp recombinase from Saccharomyces cereuisiae. flp can promote recombination between two flp recombination targets, or FRTs. Advantages of the flp/FRT system are that it is inducible and expression can be activated in any cell in the organism, although dividing cells may be favored. A disadvantage of the method is that, because the clones are generated randomly, ectopic expression varies from animal to animal. The chapter describes protocols for two of the techniques that are currently used to conduct ectopic expression experiments: the heat-shock method and the GAL4 system. © 1994, Elsevier Science Publishers, B.V. All rights reserved.