Molecular mechanism of cutokinesis

点击翻译按钮获取中文摘要

The purpose of this research project has been to clarify the mechanism of cytokinesis at a molecular level. The first approach we used was to study the formation of the contractile ring. As a result, we found following seven actin-modulating proteins and characterized them. (1) 45K protein-actin complex which is able to modulate both the rate of polymerization of actin and the end-to-end interactions of actin filaments by binding to the barbed end of the actin filament. (2) Alpha-actinin which crosslinks actin filaments in the absence of calcium ions to form filament bundles. (3) 100K protein which severs actin filaments in the presence of calcium ions. (4) 250K protein which crosslinks actin filaments in a Ca-independent manner. (5) 20K protein-actin complex which has prpperties similar to the 45K protein-actin complex. This protein was thought to attach to the inner surface of the plasma membrane and link actin filaments to the membrane. (6) Spectrin which crosslinks actin fialments in a Ca-independent manner. (7) A Ca-binding 15K protein which inhibits the rate of actin polymerization as well as microtubule assembly. Among these proteins, alpha-actinin was labeled with a fluorescent reagent and microinjected into living egg and pursued its movement in the cell. It was concentrated in the cleavage furrow region at cytokinesis. Therefore, this protein may be relevant to cytokinesis.The second approach was to study the mechanism of contraction of the cleavage furrow using cleavage furrow isolated from newt egg. By using electron microscopy we demonstrated that the parallel actin filaments in the contractile arc were crosslinked by various actin-crosslinking proteins. We also demonstrated that the contraction could be induced in the isolated furrow in vitro and it was inhibited by actin inhibitors.