Regulation of subcellular contractile actin network by extracellular geometry
Date of Issue2017
School of Materials Science and Engineering
Cells are active materials which can undergo division, shape changes, and migration. The ability to generate force, which is regulated by the actin cytoskeleton in the spatial and temporal dimensions, is essential for these dynamic behaviors. The distribution and localization of force are controlled by actin organization in cells and determined by the biochemical and biophysical properties of ECM. Actomyosin, which is composed of actin filaments, motor proteins, and crosslinkers, constitutes the core machinery for contraction generation. Focal adhesions serve as the mechanical linkage between ECM and the actin cytoskeleton which are responsible for transmitting mechanical forces and regulatory signals. Using high-resolution light microscopy, researchers can determine the location of proteins on actin networks with high spatial and temporal precision. To test how actin binding proteins collaborate to form functional actin structures, a reconstituted system with purified proteins are often used. However, the results obtained from this over-simplified system cannot reflect the real situation inside living cells, for example, the function of focal adhesion and ECM are neglected in this experiment set up. Until now, the formation of actomyosin structure in living cells is still not clearly understood. In this thesis, the primary objective is to study the actin structure in living cells during their migration across discontinuous ECM, by using a pattern which can constrain cells movements directionally. The behaviors of different types of cells when migrating across these discontinuous gaps were then studied. Interestingly, a unique multinodal actin network was discovered for the first time by merely varying the continuous properties of ECM in HUVEC, which provides us a living cell model to study the formation of the actomyosin structure. Using traction force microscopy, it is demonstrated that this subcellular actin structure is contractile. Lastly, the function of a motor protein - myosin II and crosslinker-filamin A in this actin structure was elucidated in detail. The work in this thesis suggests that activities of myosin II and filamin A are controlled by the ECM distribution, which determines the actin architecture.