In vitro models of tail contraction and cytoplasmic streaming in amoeboid cells.
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 contractions of the tail cortex in many amoeboid cells as defined by the solation-contraction coupling hypothesis (Taylor, D. L., and M. Fechheimer. 1982. Phil. Trans. Soc. Lond. B. 299:185-197). The competing processes of solation and contraction of the gel would appear to be mutually exclusive. However, it is the temporal-spatial balance of the rate and extent of two stages of solation, coupled to contraction, that can explain the conversion of gelled ectoplasm in the tail to a solated endoplasm within the same small volume, generation of a force for the retraction of tails, maintenance of cell polarity, and creation of a positive hydrostatic pressure to push against the newly formed endoplasm. The mechanism of solation-contraction of cortical cytoplasm may be a general component of the normal movement of a variety of amoeboid cells and may also be a component of other contractile events such as cytokinesis.
Janson
L W
LW
Center for Light Microscope Imaging and Biotechnology, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213.
Taylor
D L
DL
D008841:Actin Cytoskeleton / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D000185:Actinin / Q000032:analysis / Q000502:physiology; D000199:Actins / Q000032:analysis / Q000502:physiology; D000656:Amoeba / Q000166:cytology* / Q000502:physiology; D000818:Animals; D002465:Cell Movement / Q000502:physiology*; D003593:Cytoplasm / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D003599:Cytoskeleton / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D018260:Gelsolin; D008854:Microscopy, Electron; D008954:Models, Biological; D009218:Myosins / Q000032:analysis / Q000502:physiology
D000199:Actins; D018260:Gelsolin; D000185:Actinin; D009218:Myosins