Reconstruction of Active Regular Motion in Amoeba Extract: Dynamic Cooperation between Sol and Gel States

Abstract

Amoeboid locomotion is one of the typical modes of biological cell migration. Cytoplasmic sol–gel conversion of an actomyosin system is thought to play an important role in locomotion. However, the mechanisms underlying sol–gel conversion, including trigger, signal, and regulating factors, remain unclear. We developed a novel model system in which an actomyosin fraction moves like an amoeba in a cytoplasmic extract. Rheological study of this model system revealed that the actomyosin fraction exhibits shear banding: the sol–gel state of actomyosin can be regulated by shear rate or mechanical force. Furthermore, study of the living cell indicated that the shear-banding property also causes sol–gel conversion with the same order of magnitude as that of shear rate. Our results suggest that the inherent sol–gel transition property plays an essential role in the self-regulation of autonomous translational motion in amoeba.

Non-periodic oscillatory deformation of an actomyosin microdroplet encapsulated within a lipid interface

“…Since the myosin concentration in the present study, 6 mg/ml, is much higher than the critical assembling concentration, ~0.5 μM ( e.g. , 0.11 mg/ml of skeletal muscle myosin), myosin thick filaments emerge in the present condition, which were previously confirmed by electron micrograph 30 . To make clear the contribution of ATP depletion in the present system, we checked the behavior in the presence of ATP regeneration system (0 mM, 10 mM, and 30 mM in phosphocreatine concentration) ( Fig.…”

“…All the following preparations were performed at 2 °C to avoid disfunction of actin and myosin proteins. The actomyosin fraction was prepared by modifying a previously described method 30 . A portion of A. proteus (10 g) suspended in a cell washing solution (2 mM O , O′ -Bis(2-aminoethyl)ethyleneglycol- N , N , N′ , N′ -tetraacetic acid (EGTA), 2 mM MgCl 2 , and 20 mM Piperazine-1,4-bis(2-ethanesulphonic acid) (PIPES)-KOH, pH 7.0) was first centrifuged at 6,000 × g for 2 min.…”

Wrinkling of a spherical lipid interface induced by actomyosin cortex

“…The actomyosin fraction was prepared by modifying a previously described method [24]. All procedures were performed at 2…”

Multiblock copolymers exhibiting spatio-temporal structure with autonomous viscosity oscillation

“…Not only limited to the static spatial structure, microscopic temporal structures such as rhythm and oscillation are also known to influence macro dynamic processes in living organisms. These include energy transport and/or signal transduction via periodic formation of synaptic vesicles at nerve terminals 9 , periodic structural oscillation of fibroblast cells 10 , pulsation of cardiac muscle cells, amoeboid locomotion 11 12 13 14 15 , etc. In the straightforward movement of an amoeba, rhythmic sol-gel conversion occurs based on the hierarchical actin polymerization/depolymerization beneath the plasma membrane 13 14 15 .…”