The role of calcium in amoeboid movement: Results with fluorescent indicator dyes
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Date
2011-02-16
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Abstract
The cytoskeleton of the unicellular organism Amoeba proteus includes a cortical network of filamentous actin directly beneath and attached to the plasma membrane. The contraction of this layer, occurring primarily in the tail, or uroid, region of amoebae, pushes fluid cytoplasm forward and allows for cytoplasmic streaming and pseudopod extension. Actin fibers in this layer are cross-linked into a gel-like structure via a number of actin binding proteins, and this gel must be partially solated in order for contraction to occur. Calcium interacts with several actin-binding proteins, and elevated calcium levels have been shown to promote the solation and contraction of the actin network.
Moving amoebae were injected with fluorescent calcium indicators in order to visualize local intracellular calcium levels. Results indicate high levels of calcium in the uroid region and at the base of pseudopodia, and low levels of calcium in advancing pseudopodia. Much higher fluorescence was seen in the streaming endoplasm of the amoebae compared to the gelled ectoplasm, supporting the hypothesis that calcium is necessary for maintaining the fluidity of the cytoplasm. In addition, evidence suggests that extracellular calcium and intracellular calcium under the control of a phospholipase C pathway are both critical for normal amoeboid movement.
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amoeba, Proteus, calcium, amoeboid, movement, Fluo-4, solation-contraction, coupling