Induction of cortical oscillations in spreading cells by depolymerization of microtubules

Abstract

Actomyosin-based cortical contractility is a common feature of eukaryotic cells but the capability to produce rhythmic contractions is found in only a few types such as cardiomyocytes. Mechanisms responsible for the acquisition of this capability remain largely unknown. Rhythmic contractility can be induced in non-muscle cells by microtubule depolymerization. Spreading epithelial cells and fibroblasts in which microtubules were depolymerized with nocodazole or colcemid underwent rhythmic oscillations of the body that lasted for several hours before the cells acquired a stable, flattened shape. By contrast, control cells spread and flattened into discoid shapes in a smooth 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 oscillations to immediately cease and the cells to become flat. Transient increases in cytoplasmic calcium preceded the contractile phase of the oscillations. Wrinkle formation by cells plated on elastic substrata indicated that the contractility of colcemid-treated cells increased in comparison to controls but was drastically decreased after HA 1077 addition. These data suggest that an intact microtubular system normally prevents pulsations by moderating excessive rho-mediated actin myosin contractility. Possible mechanistic interactions between rho-mediated and calcium activated contractile pathways that could produce morphological oscillations are discussed.