Mechanochemical pattern formation in the cellular actomyosin cortex

Abstract

Protein patterning is essential for cellular function. From cell division to cell migration, specific positional and temporal arrangement of proteins are requisite to triggering and executing vital cell processes. In the aforementioned examples and many other fundamental cellular activities, biochemical patterns drive or are accompanied by dramatic shape transformations. As mechanical conditions, such as cortical stress and membrane curvature, change in response to spatially arranged and temporally varying forces, the biochemical patterns, too, must evolve with this dynamic environment to enact complex cell movements. While the intricate interplay between protein patterning and cell deformations is important to any cellular function, it is especially paramount to carrying out processes that require large transformations of cell geometry. Yet, how cells rapidly and reliably communicate information between their chemical and mechanical fields is still not fully understood.

In this thesis, I explore the mechanisms of coupling between cell mechanics and biochemical patterns in the actomyosin cortex of Patiria miniata sea star oocytes. This is an ideal biological model system for exploring the interactions between biochemical patterning and mechanical deformations in evolving mechanochemical systems in vivo due to their experimental accessibility and wealth of attainable biochemical patterns. In Chapter 2, I utilize endogenous fluorescent markers embedded in the actomyosin mesh to probe the spatiotemporal surface strain patterns induced by the activity of Rho proteins, a highly conserved regulator of cell contractility, on the oocyte membrane. In Chapter 3, I show how these Rho patterns can be tuned in vivo using dynamic, external geometrical deformations by combining micropipette aspiration with live fluorescence imaging. In Chapter 4, I describe the infrared spectroscopy setup built in the pursuit of uncovering the properties of fluorescent markers. Taken together, the work in this thesis outlines a quantitative approach towards uncovering the coupling between contractility regulating biochemical patterns and cellular deformations in dynamically evolving geometries.