Visible light excited ratiometric-GECIs for long-term in-cellulo monitoring of calcium signals

Abstract

Genetically Encoded Calcium Indicators (GECIs) are powerful molecular tools for monitoring calcium (Ca²⁺) signaling in the cytosol and organellar compartments. However, currently available ratiometric indicators that allow measurements of resting Ca²⁺ levels have limitations in long-term Ca²⁺ imaging. They either are ultraviolet (UV)-excited ones with strong photo-toxicity, or have poor performance. To overcome this hurdle, we developed a set of visible light excited ratiometric-GECIs (VR-GECIs) based on existing mono-colored GECIs. With performance comparable to their corresponding mono-color prototypes, this set of VR-GECIs enables long-term measurements of intra-cellular or intra-organellar Ca²⁺ signals. Using these VR-GECIs together with a newly developed off-line analysis tool, we achieved long-term measurements of Ca²⁺ homeostasis of moving or dividing cells. Our tools may find broad applications in decoding Ca²⁺-modulated physiological or pathological processes.