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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 4288

Guy Metenier; Actin in Tetrahymena paravorax: Ultrastructural Localization of HMM-Binding Filaments in Glycerinated Cells. J.Protozool. 31(2):205-215, 1984

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Actin has been identified in the ciliated protozoon Tetrahymena paravorax on the basis of the ultrastructural detection of filaments typically decorated with heavy meromyosin (HMM) in glycerinated microstome cells. These filaments are widely distributed in endoplasmic and cortical regions and can form bundles. They are particularly numerous in elongating cells; HMM-binding filaments run approximately parallel to rib microtubules in the ectoplasm of the right wall of the buccal cavity and seem to extend to the cytopharyngeal region, suggesting some role of actin in maintenance of the crest-trough pattern or ribbed wall and/or in formation of food vacuoles. Extensive actin bundles are observed below some membranellar areas and are thought to follow the course of the microtubular "deep fiber bundle". The "fine filamentous reticulum" underlying the oral ribs and the "apical ring" extending beneath kinetosomes of ciliary couplets display filaments that do not bind HMM and are ~14 nm in diameter. No evidence for actin in these structure was obtained in the present study. The "specialized cytoplasm" of the cytostome-cytopharyngeal region appears as an undecorated reticulum with 20 nm-spaced nodes. Occasionally HMM-binding filaments were found inside the macronucleus, just beneath its envelope. Actin is suggested to be involved in cell shaping and in control of the transport of food vacuoles.