The Q system for conditional gene expression is leaky and lacks dynamic range in neurons.

The Q system allows for conditional gene expression in several organisms, including . We aimed to apply this system in neurons to obtain temporally-resolved, tissue-specific expression of a fluorescent reporter. We report that, in our hands, there is undesired expression of the reporter in conditions where expression is supposed to be repressed. In addition, in this setup, the signal‑to‑noise ratio of the Q system is unfavorable. We conclude that the Q system is far from optimal in the nervous system, and advise cautious use.