Lamellipodia in Stationary and Fluctuating States

We review recent mathematical models describing the diffusive transport, reaction, and turnover of actin and regulators at the leading edge of motile cells. These models are motivated by experimental results using cells with flat, steady lamellipodia studied by Single Molecule Speckle microscopy. The same cells can also be made to exhibit protruding and retracting lamellipodia, which demonstrate how changes in actin polymerization lead to changes in the rate of protrusion. The second part of this chapter provides a description of these fluctuations as an excitable actin system pushing against the cell membrane by polymerization

Principles driving the spatial organization of Rho GTPase signaling at synapses

The Rho proteins play critical roles in numerous aspects of neuronal development, and mutations in their regulators (GEFs and GAPs) and effectors underlie multiple neurodevelopmental and neurological disorders. How Rho GTPase-mediated signaling can have a hand in regulating so many different neurobiological processes remains a challenging question. An emerging theme is that GAPs and GEFs, through their spatial/temporal regulation and/or through additional protein-protein interactions, cooperate in making connections between upstream signals and the downstream signaling output, engaging distinct effector proteins. This chapter focuses on recent evidence illustrating distinct modes of regulation and specialized roles of Rho regulators particularly in the context of synaptic structure, function, and plasticity, and how their dysregulation affects behavioral processes and contributes to disease. © 2014 Springer-Verlag Wien. All rights reserved