Membrane Dynamics Correlate with Formation of Signaling Clusters during Cell Spreading

Abstract

The morphology and duration of contacts between cells and adhesive surfaces play a key role in several biological processes, such as cell migration, cell differentiation, and the immune response. The interaction of receptors on the cell membrane with ligands on the adhesive surface leads to triggering of signaling pathways, which allow cytoskeletal rearrangement, and large-scale deformation of the cell membrane, which allows the cell to spread over the substrate. Despite numerous studies of cell spreading, the nanometer-scale dynamics of the membrane during formation of contacts, spreading, and initiation of signaling are not well understood. Using interference reflection microscopy, we study the kinetics of cell spreading at the micron scale, as well as the topography and fluctuations of the membrane at the nanometer scale during spreading of Jurkat T cells on antibody-coated substrates. We observed two modes of spreading, which were characterized by dramatic differences in membrane dynamics and topography. Formation of signaling clusters was closely related to the movement and morphology of the membrane in contact with the activating surface. Our results suggest that cell membrane morphology may be a critical constraint on signaling at the cell-substrate interface.

Adhesion‐dependent modulation of actin dynamics in Jurkat T cells

“…Taken together, these observations suggest that the observed waves are a mixture of coupled actin‐membrane waves as well as actin density waves traveling on a planar membrane surface. This is consistent with our previous observations using IRM that the membrane topography at the cell substrate interface is not entirely flat, rather it has vertical undulations on the order of 25–50 nm that are about a micron in length [Lam Hui et al, ].…”

“…Cell boundaries were extracted using techniques detailed earlier [Lam Hui et al, ]. An active contour (snake algorithm) was applied to perform curvature‐driven smoothing of the perimeter of the binary image and any self‐intersections were removed.…”

Mechanosensing in the immune response

“…Further evidence for active formation of microclusters comes from a recent study which used high-resolution light sheet microscopy to show that dynamic microvilli on T cells drive the formation of close contacts on the APC surface, which are colocalized with TCR microclusters [89]. This is consistent with earlier work showing the correlation between microclusters and regions of reduced membrane fluctuations [84]. These findings suggest that active forces, potentially generated by the cytoskeleton, may enhance the efficacy of TCR triggering by enabling and stabilizing contacts between the T cell membrane and APC.…”

“…Upon receptor engagement, TCR assemble into signaling microclusters at sites of close adhesion [54, 84]. Signaling microclusters are the sites of early signaling.…”

Existence of and decay to equilibrium of the filament end density along the leading edge of the lamellipodium

“…2007), mouse fibroblasts (Symons and Mitchison 1991) or T cells (Hui et al. 2012). It is important to note, that even in a situation where the cell is not moving, the lamellipodium is still very dynamic and filaments are being constantly turned over (Yam et al.…”