Development of a novel simplified Q-system with integrated temporal expression control

Bimodal gene expression systems have played a major role in uncovering the function of genes, cells and organ systems during and after development. Employed initially in model systems such as flies and mice, advances in gene technology have vastly expanded the number of species in which these systems can be deployed. One of their limitations is the challenge of imposing temporal expression control. Here, we report the incorporation of temperature-sensitive intein modules with different temperature profiles into QF2, the transcription factor anchoring the Q-system widely used in Drosophila and introduced recently into several insect species and the zebrafish D. rerio. Intein removal from temperature-sensitive QF2_INTts activators in Drosophila larvae and adult flies raised under permissive conditions (18{degrees}C to 25{degrees}C) renders QF2 active and drives strong expression of QUAS reporters. In contrast, raising Drosophila at restrictive temperatures (23{degrees}C to 30{degrees}C) keeps QF2_INTts in a non-functional state unable to bind DNA and therefore, keeping QUAS reporters inactive. We further show that reporter expression can be turned on and off both during development and in flies by changing temperature conditions between restrictive to permissive. Finally, QF2_INTts animals carrying QUAS-Kir2.1 encoding the inward rectifying potassium channel raised under restrictive conditions are fully viable, while raised at or moved as adults to permissive temperature results in embryonic lethality or leads to paralysis. Thus, the intein-based Q-system renders the difficult to employ drug-dependent suppressor QS unnecessary, greatly facilitating temporal regulation of gene expression. Having several advantages over the GAL4 system, the Q system has gained broad acceptance in other insect species and the zebrafish D. rerio, and thus QF2_INTts drivers can be implemented in many other organisms, including disease-transmitting mosquitoes and poikilotherm vertebrate animals much more closely related to humans, to study gene and cell function at any time during or after development.