Isolation and characterization of two forms of a cytoskeleton.

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Abstract
Isolated petaloid coelomocytes from the sea urchin Strongylocentrotus droebachiensis transform to a filopodial morphology in hypotonic media. Em of negatively stained Triton-insoluble cytoskeletons show that the petaloid form consists of a loose net of microfilaments while the filopodial form consists of paracrystalline bundles of microfilaments. Actin is the major protein of both forms of the cytoskeleton. Additional polypeptides have MW of .apprx. 220,000, 64,000, 57,000 and 27,000 daltons. Relative to actin the filopodial cytoskeletons have an average of 2.5 times as much 57,000 MW polypeptide as the petaloid cytoskeletons. Treatment with 0.25 M NaCl dissociates the filament bundles into individual actin filaments free of the actin-associated polypeptides. One or more of these actin-associated polypeptides may be responsible for crosslinking the actin filaments into bundles and maintaining the 3-dimensional nature of the cytoskeletons.