Fig. 2.

Graphical scheme of the available genetic systems to ectopically express human transgenes in Drosophila. Drosophila modeling allows spreading the expression of a transgene exclusively within a specific tissue, thanks to different transgenesis programs. a The bipartite Gal4-UAS system is characterized by the use of two lines of flies: the first one carrying the yeast transcription factor GAL4 under the control of a tissue-specific (or stadium-specific) promoter, and the second one carrying the transgene downstream the UAS domain (the GAL4 binding site). By crossing these two lines, a progeny (F1) expressing the transgenic protein only in the tissues where the GAL4 is active will be generated. b The temporal and regional gene expression targeting (TARGET) system permits a fine-tuned temporal control of the expression, in a more precise manner than Gal4/UAS. The ubiquitous tubulin promoter spreads the expression of a temperature-sensitive Gal80 that, at 18 °C, binds the Gal4 and blocks the transgene transcription. Shifting the temperature at 29 °C determines the Gal4 deliverance and its interaction with UAS sequences, thus allowing the transgene production. c The Gene Switch system is characterized by a hormone-inducible Gal4: feeding flies with a nutritional medium supplemented with RU486 (mifepristone) determines the Gal4 activation and consequently the initiation of the transcriptional process