Abstract

Development is punctuated by morphogenetic rearrangements of epithelial tissues, including complete detachment of individual motile cells during epithelial-mesenchymal transition (EMT). Dramatic actin rearrangements occur as cell-cell junctions are dismantled and cells become independently motile during EMT. Characterizing dynamic actin rearrangements and identifying actin machinery driving these rearrangements is essential for understanding basic mechanisms of cell-cell junction remodeling; yet, neither the precise series of actin rearrangements at cell-cell junctions that accompany EMT, nor the machinery that controls actin rearrangement during EMT, have been identified. This work represents a detailed study of junctional actin reorganization in cells undergoing EMT, identifies actin regulatory proteins that control this actin reorganization, and defines the specific function of one regulatory protein, zyxin, in EMT. Using immunofluorescence and live cell imaging of HGF induced scattering of MDCK cells, dynamic actin rearrangement events occurring during EMT are characterized. Junctional actin characteristic of cell-cell adherent cells is rearranged into contractile medial actin networks linked to the junctional membrane in the initial steps of cell scattering. This actin rearrangement is accompanied by dynamic redistribution of specific actin regulatory proteins, namely α-actinin and zyxin-VASP complexes. α-Actinin mediates higher order structure of junctional actin. Zyxin-VASP complexes mediate linkage of dynamic medial actin networks to adherens junction membranes. Zyxin regulation of actin-membrane linkage controls whether cell migration during EMT occurs independently in solitary cells or is coordinated through tissues. The functional analysis employed here uses novel, quantitative methods that define specific cellular EMT ‘phenotypes’ to reveal the precise role of zyxin in EMT. Constitutive active zyxin mutants exhibit persistent actin-membrane linkages and a scattering phenotype in which cells migrate without loss of cell-cell adhesion. Zyxin is proposed to regulate EMT progression by regulating disruption or maintenance of actin membrane linkages at cell-cell junctions. Zyxin alters the ability of cells to fully detach and migrate independently during EMT and may be an important regulator of morphogenetic plasticity.

Degree

PhD

College and Department

Life Sciences; Physiology and Developmental Biology

Rights

http://lib.byu.edu/about/copyright/

Date Submitted

2009-08-04

Document Type

Dissertation

Handle

http://hdl.lib.byu.edu/1877/etd3124

Keywords

zyxin, VASP, actin cytoskeleton, epithelial-mesenchymal transition, MDCK, cell-cell adhesion

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