UCSF

This thesis presents work toward understanding the spatial organization of key molecules during cell morphogenesis and migration. Cell migration is essential for many processes including developmental morphogenesis, axon guidance, and immune responses. Chemotaxis, or directed migration guided by chemical cues, requires the spatial and temporal coordination of a multitude of molecules that pattern the force-generating actin cytoskeleton to build plasma membrane protrusions and power cell motility. This work focuses on identifying novel chemotaxis effectors, dissecting their molecular signaling logic, and exploring how key molecules spatially organize to enable the large-scale, self-organization of cell shape and movement.

In the first project, we identified and characterized a novel signaling effector of neutrophil chemotaxis (Chapter 2). From a mass spectrometry pulldown screen, we identified Homer3 as a Gαi2 interacting protein. With biochemical and cell biology techniques, we report that Homer3 is necessary for efficient chemotaxis by regulating the polarized spatial organization, rather than the magnitude and kinetics, of key signaling molecules. Overall, our work characterized how Homer3 functions as a scaffold to spatially organize polarity signaling and actin assembly.

In the second project, we studied the spatial organization of the WAVE complex, which is a key effector of cell shape and migration across eukaryotes (Chapter 3). Using quantitative, live-cell super-resolution microscopy, we discovered how the WAVE complex spatially assembles into nanometer scale ring structures at sites of saddle membrane curvature in the absence of actin polymerization. This geometric association for the WAVE complex could explain emergent cell behaviors, such as expanding and self-straightening lamellipodia as well as the ability of endothelial cells to recognize and seal transcellular holes.

In the third project, I describe my pilot work using nanotopography to physically manipulate cell geometry to assay curvature sensation (Chapter 4). The interdisciplinary nature of this experiment, which spans nano-engineering, cell biology, and high-resolution microscopy, highlights a combination of expertise that will undoubtedly unveil exciting insights.