Fluorescent Protein-Based Indicators for Functional Super-Resolution Imaging of Biomolecular Activities in Living Cells.

Super-resolution light microscopy (SRM) offers a unique opportunity for diffraction-unlimited imaging of biomolecular activities in living cells. To realize such potential, genetically encoded indicators were developed recently from fluorescent proteins (FPs) that exhibit phototransformation behaviors including photoactivation, photoconversion, and photoswitching, etc. Super-resolution observations of biomolecule interactions and biochemical activities have been demonstrated by exploiting the principles of bimolecular fluorescence complementation (BiFC), points accumulation for imaging nanoscale topography (PAINT), and fluorescence fluctuation increase by contact (FLINC), etc. To improve functional nanoscopy with the technology of genetically encoded indicators, it is essential to fully decipher the photo-induced chemistry of FPs and opt for innovative indicator designs that utilize not only fluorescence intensity but also multi-parametric readouts such as phototransformation kinetics. In parallel, technical improvements to both the microscopy optics and image analysis pipeline are promising avenues to increase the sensitivity and versatility of functional SRM.