Nanoscale Phosphoinositide Distribution on Cell Membranes of Mouse Cerebellar Neurons

Phosphatidylinositol-4,5-bisphosphate (PI(4,5)P₂) plays an essential role in neuronal activities through interaction with various proteins involved in signaling at membranes. However, the distribution pattern of PI(4,5)P₂ and the association with these proteins on the neuronal cell membranes remain elusive. In this study, we established a method for visualizing PI(4,5)P₂ by SDS-digested freeze-fracture replica labeling (SDS-FRL) to investigate the quantitative nanoscale distribution of PI(4,5)P₂ in cryo-fixed brain. We demonstrate that PI(4,5)P₂ forms tiny clusters with a mean size of ∼1000 nm² rather than randomly distributed in cerebellar neuronal membranes in male C57BL/6J mice. These clusters show preferential accumulation in specific membrane compartments of different cell types, in particular, in Purkinje cell (PC) spines and granule cell (GC) presynaptic active zones. Furthermore, we revealed extensive association of PI(4,5)P₂ with Ca_V2.1 and GIRK3 across different membrane compartments, whereas its association with mGluR1α was compartment specific. These results suggest that our SDS-FRL method provides valuable insights into the physiological functions of PI(4,5)P₂ in neurons.SIGNIFICANCE STATEMENT In this study, we established an electron microscopic method to visualize and analyze the quantitative distribution pattern of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P₂) on cell membranes using cryo-fixed brain tissues and SDS-digested freeze-fracture replica labeling. PI(4,5)P₂ interacts with various ion channels and receptors to regulate membrane signaling but its nanoscale distribution and association with these proteins remain elusive. This method revealed PI(4,5)P₂ clusters preferentially accumulated in specific membrane compartments and its distinct associations with Ca_V2.1, GIRK3, and mGluR1α in the mouse cerebellum. These results demonstrate usefulness of the method for gaining insights into the physiological functions of PI(4,5)P₂.