Recombinant biosensors for multiplex and super-resolution imaging of phosphoinositides

Phosphoinositides are a small family of phospholipids, acting as signalling hubs and key regulators of cellular function. Detecting their subcellular distribution is crucial to gain insights into membrane organisation and is most commonly done by over-expression of biosensors. However, this leads to perturbations of phosphoinositide signalling and is challenging in systems that cannot be transfected. Here, we present a toolkit for the reliable, fast, multiplex, and super-resolution detection of all 8 phosphoinositides using a unifying staining approach for fixed cells and tissue, based on recombinant biosensors with self-labelling SNAP tags. These recombinant biosensors are highly specific, and reliably visualise the subcellular distributions of phosphoinositides across scales, ranging from 2D or 3D cell culture to Drosophila tissue. Using stimulated emission depletion (STED) microscopy, we reveal the nanoscale organisation of PI(3)P on endosomes and PI(4)P on the Golgi and confirm the preservation of subcellular membranes. Multiplex staining enables the investigation of phosphoinositide conversions and reveals an unexpected presence of residual PI(3,5)P2 positive membranes in swollen lysosomes following PIKfyve inhibition. This approach enables the versatile, high-resolution visualisation of multiple phosphoinositide species in an unprecedented manner.