ACTIN-BINDING PROTEINS IN CELL MOTILITY

This chapter focuses on the actin-binding proteins (ABP) in cell motility. Many actin-binding proteins (ABP) have been isolated from nonmuscle cells and are classified into several groups based on specific properties which are characterized in vitro. These ABPs play key roles in the dynamic behavior of the actin cytoskeleton in nonmuscle cells. Two types of actin-myosin-based cell motility have been studied. 1. Streaming of the cytoplasmic sol on the inner surface of the cortical gel layer. The typical cytoplasmic streaming is seen in internodal cells of Characeae. The sol continuously slides on bundles of actin filaments located on the cortical gel layer. These bundles of actin filaments are stable structures and show no appreciable structural changes during cytoplasmic streaming. 2. Passive flow of the cytoplasmic sol within the cortical gel layer. This type of cytoplasmic streaming is seen in plasmodium of an acellular slime mold, Physarum polycephalum, and in a giant ameba, Chaos chaos. The contractile apparatuses are constructed in cell regions when they contract, and disintegrate after the contraction. Therefore it is a complex problem to determine where and when the contractile apparatuses are constructed, in addition to how they work in these cells. The ABPs are the key to solving these problems. The chapter discusses passive cytoplasmic streaming in Physarum plasmodium, and also includes ameboid movements of other cells. © 1994, Academic Press Inc.