Imaging the Nanoscale Distribution of Phosphoinositides in the Cell Plasma Membrane with Single-Molecule Localization Super-Resolution Microscopy.

Phosphoinositides make up only a small fraction of cellular phospholipids yet control cell function in a fundamental manner. Through protein interactions, phosphoinositides define cellular organelle identity and regulate protein function and organization and recruitment at the cytosol-membrane interface. As a result, perturbations on phosphoinositide metabolism alter cell physiology and lead to a wide range of human diseases, including cancer and diabetes. Among seven phosphoinositide members, phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P, also known as PI(4,5)P or PIP) is abundant in the plasma membrane. Besides its role in the second messenger pathway of phospholipase C that cleaves PtdIns(4,5)P to form diacylglycerol and inositol-1,4,5-trisphosphate (IP), PtdIns(4,5)P regulates membrane trafficking and the function of the cytoskeleton, ion channels, and transporters. The nanoscale organization of PtdIns(4,5)P in the plasma membrane becomes essential to understand cellular signaling specificity in time and space. Here, we describe a single-molecule method to visualize the nanoscale distribution of PtdIns(4,5)P in the plasma membrane by using super-resolution microscopy and the dual-color fluorescent probes based on the PLC pleckstrin homology (PH) domain. This approach can be extended to image other phosphoinositides by changing the specific probes.