The Synergy between Topography and Lipid Domains in the Plasma Membrane of Mast Cells Controls the Localization of Signaling Proteins and Facilitates their Coordinated Activation.

Similar to T cells and B cells, mast cell surfaces are dominated by microvilli, and like these other immune cells we showed with microvillar cartography (MC) that key signaling proteins for RBL mast cells localize to these topographical features. Although stabilization of ordered lipid nanodomains around antigen-crosslinked IgE-FcεRI is known to facilitate necessary coupling with Lyn tyrosine kinase to initiate transmembrane signaling in these mast cells, the relationship of ordered-lipid nanodomains to membrane topography had not been determined. With nanoscale resolution provided by MC, SEM and co-localization probability (CP) analysis, we found that FcεRI and Lyn kinase are positioned exclusively on the microvilli of resting mast cells in separate nano-assemblies, and upon antigen-activation they merge into overlapping populations together with the LAT scaffold protein, accompanied by elongation and merger of microvilli into ridge-like ruffles.