Condensation-decondensation of the γ-tubulin containing material in the absence of a structurally visible organelle during the cell cycle of Physarum plasmodia

• Published in: Biology of the cell 1999-05, Vol.91 (4), p.393-406
• Main Authors: Rotaru, Victor, Lajoie-Mazenc, Isabelle, Tollon, Yvette, Raynaud-Messina, Brigitte, Jean, Catherine, Détraves, Claire, Julian, Monique, Moisand, André, Wright, Michel
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Antibodies, Monoclonal; Benzimidazoles - pharmacology; Carbamates; cell cycle; Cell Cycle - drug effects; Cell Cycle - physiology; Cell Nucleolus - chemistry; Cell Nucleolus - physiology; Epitopes - chemistry; Epitopes - physiology; Fluorescent Antibody Technique; gamma-tubulin; Interphase - drug effects; Interphase - physiology; Microscopy, Electron; mitosis; Mitosis - drug effects; Mitosis - physiology; Molecular Sequence Data; MTOC; Mutagens - pharmacology; Physarum; Physarum - growth & development; Physarum - physiology; Protozoan Proteins - immunology; Spindle Apparatus - chemistry; Spindle Apparatus - immunology; Spindle Apparatus - ultrastructure; spindle pole; Tubulin - chemistry; Tubulin - immunology; Tubulin - metabolism
• ISSN: 0248-4900; 1768-322X
• DOI: 10.1016/S0248-4900(99)80099-9

Genetic evidence has shown the presence of a common spindle pole organiser in Physarum amoebae and plasmodia. But the typical centrosome and mitosis observed in amoebae are replaced in plasmodia by an intranuclear mitosis devoid of any structurally defined organelle. The fate of γ-tubulin and of another component (TPH17) of the centrosome of Physarum amoebae was investigated in the nuclei of synchronous plasmodia. These two amoebal centrosomal elements were present in the nuclear compartment during the entire cell cycle and exhibited similar relocalisation from metaphase to telophase. Three preparation methods showed that γ-tubulin containing material was dispersed in the nucleoplasm during interphase. It constituted an intranuclear thread-like structure. In contrast, the TPH17 epitope exhibited a localisation close to the nucleolus. In late G2-phase, the γ-tubulin containing elements condensed in a single organelle which further divided. Intranuclear microtubules appeared before the condensation of the γ-tubulin material and treatment with microtubule poisons suggested that microtubules were required in this process. The TPH17 epitope relocalised in the intranuclear spindle later than the γ-tubulin containing material suggesting a maturation process of the mitotic poles. The decondensation of the γ-tubulin material and of the material containing the TPH17 epitope occurred immediately after telophase. Hence in the absence of a structurally defined centrosome homologue, the microtubule nucleating material undergoes a cycle of condensation and decondensation during the cell cycle.