In vitro models of tail contraction and cytoplasmic streaming in amoeboid cells.

Abstract

Abstract. We have developed a reconstituted gel-sol and contractile model system that mimics the structure and dynamics found at the ectoplasm/endoplasm interface in the tails of many amoeboid cells. We tested the role of gel-sol transformations of the actin-based cytoskeleton in the regulation of contraction and in the generation of endoplasm from ectoplasm. In a model system with fully phosphorylated myosin II, we demonstrated that either decreasing the actin filament length distribution or decreasing the extent of actin filament cross-linking initiated both a weakening of the gel strength and contraction. However, streaming of the solated gel components occurred only under conditions where the length distribution of actin was decreased, causing a self-destruct process of continued solation and contraction of the gel. These results offer significant support that gel strength plays an important role in the regulation of actin/myosin II-based contrac-

Keratocytes Generate Traction Forces in Two Phases

“…Actin and myosin monomers must be recycled forward from more posterior regions for filament assembly to occur at the leading edge (Bereiter- Hahn et al, 1981;Kolega et al, 1991;Janson and Taylor, 1993;Post et al, 1995;Anderson et al, 1996;DeBiasio et al, 1996). In keratocytes, fibers were observed by Svitkina et al (1997) to disassemble under the cell body, analogous to earlier observations of stress fiber dissolution in the cell bodies of fibroblasts Kolega et al, 1991) and reduced assembly of actin and myosin in the cell body relative to the lamellum (Kolega and Taylor, 1993;Giuliano and Taylor, 1994).…”

“…As they noted, this type of mechanism, whereby movement in response to contractile force is increased by reducing cytoskeletal stiffness, has been outlined in the solation-contraction coupling hypothesis (Taylor and Fechheimer, 1982). This process has been demonstrated in in vitro models (Taylor et al, 1973;Janson and Taylor, 1993).…”

Optical micromanipulation

“…All cells survived after all three manipulation approaches (data not shown). However, some living cells generate membrane blebs during manipulations, which usually indicates that cells cannot retain 14 their cortical tension and are unhealthy [42][43][44]. A representative cell with a membrane bleb is shown in fig.…”

Acto-myosin reorganization and PAR polarity inC. elegans

“…The result of cortical contraction is regions of high acto-myosin density surrounded by holes in the network (Kane, 1983). Modifications of cortical contractility can result in both reorganization of the cell and remodeling of the cortex (Hellewell and Taylor, 1979;Janson et al, 1991;Janson and Taylor, 1993;Stendahl and Stossel, 1980;Taylor and Fechheimer, 1982), both of which are essential aspects of domain formation.…”