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We developed an advanced optical microscope for the simultaneous visualization of membrane fluidity and morphology to define cell adhesion signatures. This microscope combines ratiometric spectral imaging of membrane fluidity and interferometric imaging of membrane morphology. As a preliminary demonstration, we simultaneously visualized the interface between a giant unilamellar vesicle (GUV) and a glass substrate at different temperatures. We identified more fluid regions of the membrane and membrane adhesion sites (conversely, low-fluidic, ordered membrane domains correlate with nonadhered regions). This microscopic system was applied to human breast cancer cell lines with different malignancies; then, we identified adhesion signature of cancer cells: 1) low-fluidic, ordered membrane domains at the cell periphery and 2) large fluidic deviation at the nonadhered region. Inhibition of the cholesterol synthesis pathway suppresses the ordered membrane domains at the cancer cell periphery; thus, high level of cholesterol supports the appearance. Furthermore, an inhibitor of the unsaturated lipid synthesis pathway suppressed the large fluidic deviation at the nonadhered region; variation of unsaturated lipids contributes to heterogeneity of the cancer membrane. Therefore, our advanced optical microscopy enables us to couple membrane physical properties with cell adhesion, leading to definition of adhesion signatures of broad cell types, not just for cancer cells, that regulate life phenomena. [ABSTRACT FROM AUTHOR]

Using Onsager׳s variational principle, we derive in the Monge gauge the equations describing the dynamics of almost planar bilayer membranes. All dissipations sources are taken into account: intermonolayer friction, solvent viscosity and monolayer viscosity. We recover and extend the results of Seifert and Langer and we discuss in detail the effect of membrane tension on the relaxation rates. Above a threshold tension, the avoided crossing of the relaxation rates disappears and the long-time dynamics is controlled by intermonolayer friction at all scales. The flow within the solvent and the monolayers is calculated both for the relaxation of a sinusoidal membrane shape and a Gaussian bud. The two vortices localized on the membrane split into four vortices at very small scales due to the monolayers slip. We discuss, depending on the scale, the legitimacy to neglect some of the dissipation sources, proposing an approximation scheme that allows to retain only the intermonolayer friction at small scales. [ABSTRACT FROM AUTHOR]

Cells are populated by a vast array of membrane-binding proteins that execute critical functions. Functions, like signaling and intracellular transport, require the abilities to bind to highly curved membranes and to trigger membrane deformation. Among these proteins is amphiphysin 1, implicated in clathrin-mediated endocytosis. It contains a Bin-Amphiphysin-Rvs membrane-binding domain with an N-terminal amphipathic helix that senses and generates membrane curvature. However, an understanding of the parameters distinguishing these two functions is missing. By pulling a highly curved nanotube of controlled radius from a giant vesicle in a solution containing amphiphysin, we observed that the action of the protein depends directly on its density on the membrane. At low densities of protein on the nearly flat vesicle. the distribution of proteins and the mechanical effects induced are described by a model based on spontaneous curvature induction. The tube radius and force are modified by protein binding but still depend on membrane tension. In the dilute limit, when practically no proteins were present on the vesicle, no mechanical effects were detected, but strong protein enrichment proportional to curvature was seen on the tube. At high densities, the radius is independent of tension and vesicle protein density, resulting from the formation of a scaffold around the tube. As a consequence, the scaling of the force with tension is modified. For the entire density range, protein was enriched on the tube as compared to the vesicle. Our approach shows that the strength of curvature sensing and mechanical effects on the tube depends on the protein density. [ABSTRACT FROM AUTHOR]