Genetically Encoded Fluorescent Indicators for Organellar Calcium Imaging

Abstract

Optical Ca²⁺ indicators are powerful tools for investigating intracellular Ca²⁺ signals in living cells. Although a variety of Ca²⁺ indicators have been developed, deciphering the physiological functions and spatiotemporal dynamics of Ca²⁺ in intracellular organelles remains challenging. Genetically encoded Ca²⁺ indicators (GECIs) using fluorescent proteins are promising tools for organellar Ca²⁺ imaging, and much effort has been devoted to their development. In this review, we first discuss the key points of organellar Ca²⁺ imaging and summarize the requirements for optimal organellar Ca²⁺ indicators. Then, we highlight some of the recent advances in the engineering of fluorescent GECIs targeted to specific organelles. Finally, we discuss the limitations of currently available GECIs and the requirements for advancing the research on intraorganellar Ca²⁺ signaling.