MBI PhD Oral Defense

Time: 10:15am
Date: Thursday, 10 May 2018
Venue: MBI, level 5 meeting rooms

Supervisors:  Prof Virgile Viasnoff (Main supervisor), Prof Alexander Bershadsky (Co-supervisor)

Actin cytoskeleton self-organization in epithelial cells

by Salma JALAL, Bershadsky Group

In this project I have systematically investigated the principles of actin cytoskeleton self-organization in epithelial cells by confining isolated cells on isotropic adhesive islands of varying size, and compared the actin cytoskeleton self-organization in these cells with that in fibroblasts. In fibroblasts, our lab has previously described that an initially circular pattern of circumferential actin dynamically evolves into a radial pattern of actin bundles. The radial fibres in this pattern spontaneously tilt in one direction to form the chiral pattern, before finally producing parallel linear stress fibres. We have since found that progression from circular to chiral actin patterns depends on cell-projected area and rarely occurs on small islands. Epithelial cells on the other hand, did not exhibit succession through all the actin patterns described above even on large islands. Upon confinement, the actin cytoskeleton in non-keratinocyte epithelial cells is arrested at the circular stage, while in keratinocytes it can progress as far as the radial pattern but still cannot break symmetry. Epithelial-mesenchymal transition pushed actin cytoskeleton development from circular towards radial patterns but remains insufficient to cause chirality. Surprisingly, small doses of G-actin sequestering drug, latrunculin A, induced chiral swirling in keratinocytes. During this swirling, keratin filaments follow actin and also demonstrate chiral swirling movement. In spite of this dynamic interplay between the actin and keratin cytoskeleton, depletion of the keratin network did not change the pattern of actin organization in keratinocytes. In order to examine the role of cell-matrix and cell-cell adhesions in directing actin cytoskeleton-self organization, actin cytoskeleton development was compared between cells plated on cadherin, fibronectin, collagen and poly-D-lysine coated adhesive islands. The actin cytoskeleton self-organization is severely disrupted when adhesion is mediated only by electrostatic attraction. On the other hand, it is globally similar when attachment to the substrate is changed from integrin- to cadherin-mediated adhesions.

**Please note the examination following the seminar is closed-door**