title: Periodic traction in migrating large amoeba of Physarum polycephalum.
abstract: The slime mould Physarum polycephalum is a giant multinucleated cell exhibiting well-known Ca(2+)-dependent actomyosin contractions of its vein network driving the so-called cytoplasmic shuttle streaming. Its actomyosin network forms both a filamentous cortical layer and large fibrils. In order to understand the role of each structure in the locomotory activity, we performed birefringence observations and traction force microscopy on excised fragments of Physarum. After several hours, these microplasmodia adopt three main morphologies: flat motile amoeba, chain types with round contractile heads connected by tubes and motile hybrid types. Each type exhibits oscillations with a period of about 1.5 min of cell area, traction forces and fibril activity (retardance) when fibrils are present. The amoeboid types show only peripheral forces while the chain types present a never-reported force pattern with contractile rings far from the cell boundary under the spherical heads. Forces are mostly transmitted where the actomyosin cortical layer anchors to the substratum, but fibrils maintain highly invaginated structures and contribute to forces by increasing the length of the anchorage line. Microplasmodia are motile only when there is an asymmetry in the shape and/or the force distribution.
authors: Institut Lumière Matière, UMR5306 Université Lyon 1-CNRS, Université de Lyon, 69622 Villeurbanne cedex, France jean-paul.rieu@univ-lyon1.fr.
authors: Jean-Paul
authors: JP
authors: Rieu
authors: Institut Lumière Matière, UMR5306 Université Lyon 1-CNRS, Université de Lyon, 69622 Villeurbanne cedex, France.
authors: Hélène
authors: H
authors: Delanoë-Ayari
authors: Research Institute for Electronic Science, Hokkaido University, N20W10, Sapporo 060-0806, Japan.
authors: Seiji
authors: S
authors: Takagi
authors: Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.
authors: Yoshimi
authors: Y
authors: Tanaka
authors: Research Institute for Electronic Science, Hokkaido University, N20W10, Sapporo 060-0806, Japan JST, CREST, 5, Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan nakagaki@es.hokudai.ac.jp.
authors: Toshiyuki
authors: T
authors: Nakagaki
mesh_terms: D001683:Biological Clocks / Q000502:physiology*; D002448:Cell Adhesion / Q000502:physiology; D002465:Cell Movement / Q000502:physiology*; D003198:Computer Simulation; D008124:Locomotion / Q000502:physiology*; D008954:Models, Biological; D010507:Periodicity; D016839:Physarum polycephalum / Q000166:cytology* / Q000502:physiology*; D033081:Shear Strength / Q000502:physiology; D062211:Spatio-Temporal Analysis; D013314:Stress, Mechanical
keywords: actomyosin contractility; amoeboid motility; birefringence; physarum; traction force microscopy