Multicoloured fluorescent indicators for live-cell and in vivo imaging of inorganic mercury dynamics

Engineered fluorescent indicators for visualizing mercury ion (Hg²⁺) are powerful tools to illustrate the intracellular distribution and serious toxicity of the ion. However, the sensitive and specific detection of Hg²⁺ in living cells and in vivo is challenging. This paper reported the development of fluorescent indicators for Hg²⁺ in green or red color by inserting a circularly permuted fluorescent protein into a highly mercury-specific repressor. These sensors provided a rapid, sensitive, specific, and real-time read-out of Hg²⁺ dynamics in solutions, bacteria, subcellular organelles of mammalian cells, and zebrafish, thereby providing a useful new method for Hg²⁺ detection and bioimaging. In conjunction with the hydrogen peroxide sensor HyPer, we found mercury uptake would trigger subcellular oxidative events at the single-cell level, and provided visual evidence of the causality of mercury and oxidative damage. These sensors would paint the landscape of mercury toxicity to cell functions.