A Tubulin promoter drives expression of the C-terminal part of cic (contains the C2 and C1 domains, but lacks the DNA-binding domain), tagged at the N-terminal end with a nuclear localization signal, and at the C-terminal end (via a GGGSGGGS linker) with mCherry. This transgene can be used as a sensor for quantitative measurements of endogenous levels of rl (ERK) activity; nuclear accumulation of the protein occurs upon rl downregulation and exclusion from the nucleus occurs upon rl activation.