Chemically Specific Imaging of Lipid Organization in the Cellular Plasma Membrane Using High-Resolution Secondary Ion Mass Spectrometry

Compartmentalization of the plasma membrane into domains of differing composition is required for proper cell function, but the extent and origins of this organization is poorly understood. The non-random distributions of specific membrane proteins have been established through the use of functionalized affinity labels and genetically encoded fluorescent protein constructs. Lateral variations in the abundance of cholesterol and various lipid species are also expected to exist in the plasma membrane and influence its function. Specifically, cholesterol- and sphingolipid-enriched microdomains, which are sometimes called lipid rafts, are postulated to be present in the plasma membrane and mediate cell signaling, virus budding, and many other disease-related biological processes. Biophysically distinct microdomains and cholesterol-dependent nanoclusters within the plasma membranes of living cells have been detected by using advanced high-resolution fluorescence microscopy technique. However a chemically specific and spatially well-resolved imaging technique is required to definitively establish how cholesterol and specific lipid species are organized in the plasma membrane. Imaging secondary ion mass spectrometry (SIMS) is a promising approach for visualizing membrane component distribution in a chemical specific manner. Previously, the lateral distributions of two isotopically labeled lipids within phase-separated model lipid membranes were successfully imaged with 100-nm-lateral resolution by using a high-resolution SIMS approach performed with a Cameca NanoSIMS. Here we extend this approach to intact cells in order to chemically image the distributions of specific lipids within the plasma membrane.