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Title: Regulation of junction configuration by cell tension
Author: Sri Ranjan, Kyasha
ISNI:       0000 0004 7427 6667
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2016
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The maintenance of cell-cell contacts is essential for tissue cohesion and a variety of different physiological processes in morphogenesis and homeostasis. Adherens junctions are protein complexes that mediate cell-cell contacts in epithelial cells and E-cadherin receptors are their main component. During junction formation, thin bundles of actin localise towards cell-cell contacts in the characteristic cytoskeletal organization of epithelia. Tension at the underlying cortex and thin bundle compaction help form tight, straight junctions and maintain cadherin receptors in place. However, how these epithelia-specific structures are formed and remodelled lacks in-depth understanding. In this study, I have addressed how contractile forces modulate junction configuration and molecular composition (adhesion receptors and actin cytoskeleton). Micropatterning was used to precisely confine the geometry of cells, control cortical forces and provide a permissive, simplistic way in which cells are allowed to interact. Three different shapes, namely squares, triangles and circles were patterned to study biophysical and junction properties. Although the average cell heights and volumes are similar between different geometries, cortical stiffness (i.e. Young’s modulus) is two-fold higher in cells grown in geometries that impose higher contractility: squares and triangles. Doublets seeded on these shapes also position their nuclei further apart and exhibit preferences in junction orientation. A majority of cells cultured on triangular and square geometries have shorter and straighter junctions with a clear presence of thin bundles parallel to the cell-cell interface. Localisation of phosphorylated myosin light chain to thin bundles reinforce the notion that these are the main contractile pool instead of the junctional actin at contacts. Counter-intuitively, E-cadherin and F-actin density are also reduced with increased contractility and tension. Taken together, higher levels of contractility and cortical tension imposed by the square and triangle geometric shapes, are necessary to properly generate the epithelial cellular architecture, configuration of junctions and their molecular makeup. This suggests that tensional constraints play an important role in regulating the stability of junctions and the organization of underlying actin filaments that support the characteristic epithelial cell shape.
Supervisor: Braga, Vania ; Stevens, Molly Sponsor: British Heart Foundation ; Imperial College London
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral