Roles Of Actin Cytoskeletal Network On Cell Shape Changes During Cytokinesis In Adherent Mammalian Cells

Cytokinesis of animal cells is a mechanical deformation process characterized by a complex coordinated sequence of cytoskeletal changes. The ability to change cellular shape requires that the distribution of different classes of molecules be regulated both spatially and temporally. The actin filament network contributes structure and support for the cells and is the major cytoskeletal system that drives cytokinesis. Analysis the roles of actin cytoskeletal network during cytokinesis not only establishes mechanical-biological relationship among cell shape, cytoskeletal organization and cellular mechanical properties which can help us understand the process and mechanism of active changing cellular shape, but also provide theoretical evidence for revealing the mystery of disease related cytokinesis failure and provide cell mechanical mechanism for replenishment of tissues and organs.In our study, micropipette aspiration technique, local cytoskeletal inhibitors application technique, micro-image dynamic collecting and analysis system, and immunofluorescence method were used to explore the effects of actin network in different phases and different regions during cytokinesis using normal rat kidney epithelial cells (NRK). The investigation analyzed on cells shape changes, defects of cytokinesis, deformability of daughter cells and furrow-thinning dynamics based on the cellular mechanical properpties. The main work and conclusions were as follows:1. Determined on the cellular mechanical properties of cells. Cells treated with cytochalasin D (inhibitor of actin polymerization), colchicine (inhibitor of microtubule polymerization) and blebbistatin (inhibitor of myosinâ…¡ATPase activity). The difference of Elastic modulus and surface tension were tested with by micropipette aspiration technique and its relative theoretical model. The results indicated that disturbance of the process of assembling actin meshwork would cause most dramatic reduction of cellular mechanical. The activity of myosinâ…¡ATPase performed an independent mechanism to influence the mechanical parameters without changing of cytoskeleton, and the interaction between actin and myosinâ…¡acted as an important regulator on cellular mechanical properties.2. Discussed the effects of cytoskeletal disturbing to the process of cell shape changes by releasing cytoskeletal inhibitors in different phases and regions during cytokinesis.Our study released cytoskeletal inhibitors to cells in two different phases during cytokinesis delimited by furrow ingression. In addition, cytoskeltal inhibitors were applied near the polar region of dividing cells. The results showed distinct roles of cytoskeleton in different phases during cytokinesis. Our experiment found that the interaction between actin and myosinâ…¡could diluted the disrupt effects to cytokinesis arousing by abnormal assembling actin. On the other hand, actin-myosinâ…¡interaction determined the higher level deformability of daughter cell, and lower activity of myosinâ…¡ATPase facilitated this process.3. Investigating the dynamic of intercellular bridge and deformation of daughter cells by polar cortical treating with cytoskeletal inhibitors.Our results showed that locally released CD or colchicine at the polar region dramatically influenced the trajectories of intercellular bridge thinning. Disturbing single polar cortical actin induced transformation of the intercellular bridge thinning process, and polar cortical tension controlled deformation time of intercellular bridges.On the other hand, our study analyzed the surface area changes of higher level deformability daughter cells and their intercellular bridge shape. The results showed that bridge morphology parameters D0.5 acted as a dividing point to describe shape changes of daughter cells. Moreover, we adjusted furrow-thinning dynamical parameters based on our experiment. The results indicated that cells had regulated the balance of cortical tension before D0.5.Our study indicated that actin network controlled each step of cell shape changes duiring cytokinesis. Actin acted as the decisive factor in cell mechanical properties and cell shape changes. The interaction between actin and myosinâ…¡undertook the prominent regulator relying on dynamical organization. This interaction controlled mechanical properties of different cellular regions, regulated cortical tension, manipulated the process of cell shape changes.