Induction of cortical oscillations in spreading cells by depolymerization of microtubules

Actomyosin-based cortical contractility is a common feature of eukaryotic c ells but the capability to produce rhythmic contractions is found in only a few types such as cardiomyocytes. Mechanisms responsible for the acquisiti on of this capability remain largely unknown. Rhythmic contractility can be induced in non-muscle cells by microtubule depolymerization. Spreading epi thelial cells and fibroblasts in which microtubules were depolymerized with nocodazole or colcemid underwent rhythmic oscillations of the body that la sted for several hours before the cells acquired a stable, flattened shape. By contrast, control cells spread and flattened into discoid shapes in a s mooth and regular manner. Quantitative analysis of the oscillations showed that they have a period of about 50 seconds. The kinase inhibitors, HA 1077 and H7, and the more specific rho-kinase inhibitor, Y 27632, caused the os cillations to immediately cease and the cells to become flat. Transient inc reases in cytoplasmic calcium preceded the contractile phase of the oscilla tions. Wrinkle formation by cells plated on elastic substrata indicated tha t the contractility of colcemid-treated cells increased in comparison to co ntrols but was drastically decreased after HA 1077 addition. These data sug gest that an intact microtubular system normally prevents pulsations by mod erating excessive rho-mediated actin myosin contractility. Possible mechani stic interactions between rho-mediated and calcium activated contractile pa thways that could produce morphological oscillations are discussed. Cell Mo til. (C) 2001 Wiley-Liss, Inc.