Signaling clusters in the cell membrane

Abstract

Large-scale molecular assemblies, or signaling clusters, at the cell membrane are emerging as important regulators of cell signaling. Here, we review new findings and describe shared characteristics common to signaling clusters from a diverse set of cellular systems. The well-known T cell receptor cluster serves as our paradigmatic model. Specifically, each cluster initiates recruitment of hundreds of molecules to the membrane, interacts with the actin cytoskeleton, and contains a significant fraction of the entire signaling process. Probed by recent advancements in patterning and microscopy techniques, the signaling clusters display functional outcomes that are not readily predictable from the individual components.

Figure 1. A signaling cluster

Schematic of a T cell receptor microcluster, also called the TCR signalosome, which is densely packed with a diverse set of signaling molecules. Activation of actin assembly initiates centripetal transport. Further details can be found in the text and in references [,–4].

Figure 2. Titration of signaling clusters

(a) Brightfield images of cells off and on the indicated grid pattern size (scale bar = 5 mm). (b) Schematic of TCR microcluster within indicated area in (a) with pMHC bound to activating agonists (stars) and non-activating null (circles) peptides. (c) Corresponding heat maps that display calcium flux for a population of cells on and off the grids, with each cell shown as a horizontal line and >100 cells per heat map.Adapted from reference [27•].

Figure 3. Measuring TCR–actin interactions

(a) Schematic of a T cell on a substrate patterned with diffusion barriers. (b) Left, Time average of a stack of fluorescent actin-GFP. Right, Trace and plots illustrate temporal fluctuations along with time correlation, G(τ). (c) Pixel by pixel image of autocorrelation times reveals regions of high actin volatility and stability.