Deciphering Intracellular Signaling Regulating Directed Cell Migration
Embargo until
2015-05-01
Date
2013-10-18
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Publisher
Johns Hopkins University
Abstract
Directed cell migration is a ubiquitous phenomenon with implications in development, wound healing, immunity, and metastasis. The ability of cells to orient their migration is dependent on the presence of external cues, the components to detect them and the intracellular networks to process them. This dissertation explores how the regulation of core intracellular components can shape directional migration responses and the mechanisms in which cells decode single and multiple external guidance cues. Given the complexity and redundancy in migratory signaling pathways, we develop a new technique to generate an intracellular gradient of protein activity without receptor activation. We demonstrate the utility of this technique by imposing gradients of different values of the active form of one of the core mediators of directed migration, a Rho GTPase, Rac. We find that shallow gradients of Rac alone are sufficient to direct the polarity and movement of cells, recapitulating phenotypes of chemoattractant induced migration and demonstrating synthetic chemotaxis in mammalian cells. These results reveal that cell polarity can be defined starting from a downstream node, Rac. Furthermore, we present a new refined mathematical model of cell chemotaxis and suggest a novel role for an upstream kinase, PI3K, in sensitizing cells to Rac activation. Next, we explore how cells process multiple guidance inputs, chemotaxis and contact inhibition of locomotion (CIL), and the resulting implications for directed cell migration. We find that chemotaxis and CIL do not act independently, as the resulting migration phenotypes when both cues are presented in conjunction are altered when they are presented individually. The balance between these cues is dynamic; modulating the strength of the cues through external inputs or molecular interventions can influence the resulting directed migration outcomes. We further investigate the mechanistic basis of this dependency by enumerating the molecular mediators of these cues and finding where they might crosstalk. In this study, we develop several new techniques at the interface between engineering and the life sciences and present their applications. We anticipate that similar multidisciplinary approaches will help unravel mysteries in directed cell migration and in general biology.
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Keywords
directed migration, microfluidics
cell biology, chemotaxis, cell migration, imaging