A conditional tissue-specific transgene expression system using inducible GAL4

TLDR

The GAL4/UAS system is the most widely used method for spatially restricted transgene expression in Drosophila. The authors aimed to add temporal control to this system by testing a RU486‑dependent GeneSwitch GAL4 protein in flies. They expressed GeneSwitch under tissue‑specific promoters (elav for neurons, mhc for muscles) and showed that its transcriptional activity in larvae is induced by RU486, as demonstrated with UAS‑reporter lines. RU486‑dependent expression was detectable within 5 h, was dose‑responsive, had minimal background, and enabled manipulation of larval muscle physiology, proving GeneSwitch’s utility for conditional tissue‑specific expression in Drosophila.

Abstract

In Drosophila , the most widely used system for generating spatially restricted transgene expression is based on the yeast GAL4 protein and its target upstream activating sequence (UAS). To permit temporal as well as spatial control over UAS-transgene expression, we have explored the use of a conditional RU486-dependent GAL4 protein (GeneSwitch) in Drosophila . By using cloned promoter fragments of the embryonic lethal abnormal vision gene or the myosin heavy chain gene, we have expressed GeneSwitch specifically in neurons or muscles and show that its transcriptional activity within the target tissues depends on the presence of the activator RU486 (mifepristone). We used available UAS-reporter lines to demonstrate RU486-dependent tissue-specific transgene expression in larvae. Reporter protein expression could be detected 5 h after systemic application of RU486 by either feeding or “larval bathing.” Transgene expression levels were dose-dependent on RU486 concentration in larval food, with low background expression in the absence of RU486. By using genetically altered ion channels as reporters, we were able to change the physiological properties of larval bodywall muscles in an RU486-dependent fashion. We demonstrate here the applicability of GeneSwitch for conditional tissue-specific expression in Drosophila , and we provide tools to control pre- and postsynaptic expression of transgenes at the larval neuromuscular junction during postembryonic life.