NOVEL FILAMENTOUS BUNDLES IN THE CYTOPLASM OF A UNICELLULAR EUKARYOTE, CRITHIDIA-FASCICULATA

Trypanosomes, an evolutionarily ancient group of unicellular eukaryoti c parasites, appear to lack both microfilaments (actin) and intermedia te filaments (Ifs): the major cytoskeletal component common to all try panosomes consists of a stable microtubular array intimately associate d with the plasma membrane. We pre sent here evidence of bundles of tr ans-cytoplasmic filaments ca. 10 nm in diameter, seen by transmission electron microscopy, that are formed in stationary cultures of an inse ct trypanosome, Crithidia fasciculata. Immunofluorescent labelling wit h an antibody raised against plant fibrillar bundles (AFB) and Western blotting with an antibody that cross-reacts with a broad range of IFs (anti-IFA) as well as with fibrillar bundles, indicates that these fi laments appear to share antigenic determinants common to animal Ifs an d to fibrillar bundles of plant origin.