Genetically encoded single circularly permuted fluorescent protein-based intensity indicators

Fluorescent protein (FP)-based genetically encoded indicators are valuable tools for reporting signaling activities with high spatial-temporal resolution in living cells and animal models. Thereinto, single circularly permuted FP-based intensity sensors (cpFP sensors or cpFP-based sensors, unless otherwise specified) are of particular interest due to their unprecedented high sensitivity and fast kinetics. In this review, we summarized the recent progress with cpFP sensors, focusing on the practical considerations in sensor development and usage, and categorization of cpFP sensors. We also discuss future directions in improvement of existing sensors, development of new sensors, and functional super-resolution imaging with cpFP sensors.