Cytokinesis in Tetrahymena: Determination of division plane and organization of contractile ring

A protein, Tetrahymena p85, is localized to the presumptive division plane before the formation of the contractile ring, p85 directly interacts with T etrahymena calmodulin (CaM) in a Ca2+-dependent manner, and p85 and CaM col ocalize in the division furrow. A Ca2+/CaM. inhibitor N-(6-Aminohexyl)-5-ch loro-1-naphthalenesulfonamide HCl (W7) inhibits the direct interaction betw een p85 and Ca2+/CaM. W7 also inhibits the localization of p85 and CaM to t he division plane, and the formation of the contractile ring and division f urrow. Tetrahymena fimbrin and elongation factor-1a (EF-1 alpha), which ind uce bundling of Tetrahymena F-actin, are also localized to the division fur row during cytokinesis. The Tetrahymena fimbrin has two actin-binding domai ns, but lacks the EF-hand Ca2+-binding motif, suggesting that Tetrahymena f imbrin probably crosslinks actin filaments in a Ca2+- insensitive manner du ring cytokinesis. The evidence also indicates that Ca2+/CaM inhibits the F- actin-bundling activity of EF-1 alpha; and EF-l alpha and CaM colocalize in the division furrow. In this review, we propose that the Ca2+/CaM signal a nd its target protein p85 cooperatively regulate the determination of the d ivision plane, and that a Ca2+-insensitive actin-bundling protein. Tetrahym ena fimbrin, and a Ca2+/CaM-sensitive actin-bundling protein, EF-1 alpha, p lay pivotal roles in regulating the organization of the contractile ring mi crofilaments. Microsc. Res. Tech. 49:127-135, 2000. (C) 2000 Wiley-Liss, In c.