ORP9-PH domain-based fluorescent reporters for visualizing phosphatidylinositol 4-phosphate dynamics in living cells.

Fluorescent reporters that visualize phosphatidylinositol 4-phosphate (PI4P) in living cells are indispensable to elucidate the roles of this fundamental lipid in cell physiology. However, currently available PI4P reporters have limitations, such as Golgi-biased localization and low detection sensitivity. Here, we present a series of fluorescent PI4P reporters based on the pleckstrin homology (PH) domain of oxysterol-binding protein-related protein 9 (ORP9). We show that the green fluorescent protein AcGFP1-tagged ORP9-PH domain can be used as a fluorescent PI4P reporter to detect cellular PI4P across its wide distribution at multiple cellular locations, including the plasma membrane (PM), Golgi, endosomes, and lysosomes with high specificity and contrast. We also developed blue, red, and near-infrared fluorescent PI4P reporters suitable for multicolor fluorescence imaging experiments. Finally, we demonstrate the utility of the ORP9-PH domain-based reporter to visualize dynamic changes in the PI4P distribution and level in living cells upon synthetic ER-PM membrane contact manipulation and GPCR stimulation. This work offers a new set of genetically encoded fluorescent PI4P reporters that are practically useful for the study of PI4P biology.