Taxol affects both the microtubular arrays of heliozoan axonemes and their microtubule-organizing center.
Short and long-term effects of the antitumor drug taxol on the microtubular axonemes and on the microtubule-organizing centroplast of the centrolhelidian Heterophrys marina have been investigated. Short-term treatment reveals that general aspects of cell structure remain substantially unaffected and that additional microtubule (MT) assembly in individual axonemes is accompanied by disassembly in others. However, the interaction between MTs, via cross-bridging associated proteins, is seriously affected as indicated by the numerous softly-bent axopods with disturbed arrays of the normally hexagonal pattern. Stabilization of MTs becomes evident by the reexpansion of axopods during low temperature incubation and also by the rapid inhibition of the saltatory movement of the extrusive organelles. Rapidly reexpanding axonemes of cells incubated at higher temperatures and in high taxol concentrations arise asymmetrically from the microtubule-organizing centrosomal structure (centroplast) and form a single thick and thorn-like axopodium, indicating a certain disarrangement of the centrally located microtubule-organizing center (MTOC), which obviously is severely damaged after long-term treatment. With increasing disorganization of the centroplast's structure, these cells reveal themselves unable to sustain their regular microtubular axonemal cytoskeleton. Paradoxically, polymerization of free microtubules from the tubulin pool does not take place. Instead, paracrystalline arrays of twisted filaments appear within the cytoplasm. It is concluded that heliozoan MTs can only persist if stabilized by additional factors, such as permanent interaction with the intact centroplast, and that even in the presence of taxol, MTs unattached to such an MTOC will be intrinsically unstable.
D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D003593:Cytoplasm / Q000187:drug effects / Q000648:ultrastructure; D003599:Cytoskeleton / Q000648:ultrastructure*; D056890:Eukaryota / Q000187:drug effects* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008870:Microtubules / Q000187:drug effects*; D017239:Paclitaxel; D013997:Time Factors
D000470:Alkaloids; D017239:Paclitaxel