[The localization of intermediate filaments in polykaryons in the interphase and mitosis]. / Lokalizatsiia promezhutochnykh filamentov v polikarionakh v interfaze i mitoze.

Localization of vimentin filaments has been investigated in polykaryons formed by cell fusion in culture of Chinese hamster cells (line Ag17). A network of vimentin filaments was observed around each nucleus of the interphase polykaryons. This compartmentalization of the network persists after beginning of mitoses up to metaphase, both in bipolar and multipolar mitotic cells. The picture of localization of intermediate filaments is most clear in polykaryons with mitotic asynchrony of the nuclei at early stages of mitosis. In anaphase, the central part of the network disappears, and in the polykaryon only peripheral part of the network is observed. The compartmentalization of the network of intermediate filaments is disrupted by such a way. In telophase, bright peripheral fluorescence may by the result of the beginning of network reorganization, and this process will be finished in daughter cells. The role of intermediate filaments in distribution of chromosomes and centrioles between daughter cells during mitosis is discussed.

[The centriolar complex of heterophasic homokaryons in the interphase and mitosis]. / Tsentroliarnyi kompleks geterofaznykh gomokarionov v interfaze i mitoze.

Two patterns of heterophasic centrioles occur in interphase polykaryons obtained by cell fusion: in the form of a united complex, or as groups scattered around the cytoplasm. By the start of mitosis, replication of centrioles is finished. There is no cellular center in polykaryons with mitotic asynchrony of nuclei. In these polykaryons pairs of centrioles are situated near each nucleus. In polykaryons with mitotic asynchrony the spindle forms asynchronously and mainly near condensed chromosomes. At metaphase, the spindles display a complicated multipolar organization. Associated by interpolar microtubules, the spindle poles are not always the nearest to each other and therefore kinetochore microtubules may be directed not to the nearest centrioles. Pairs of centrioles are located at the poles. The problem is discussed of the correlation between the centriole number and polykaryon ploidy, as well as of the role of multipolar mitosis in distribution of centrioles and chromosomes between daughter hybrid cells.

[Ultrastructural disorders of the mitotic apparatus during cytochalasin B action]. / Narusheniia ul'trastruktury mitoticheskogo apparata pri deistvii tsitokhalazina B.

A correlation between the number of chromosome sets and the number of centrioles (8n--8 centrioles) was observed in polyploid metaphase cells, during cytochalasin B treatment on the cultured Chinese hamster cells. There is no correlation between the number of chromosome sets and the centriole number after stopping the action of the drug in many cells, but a great variation is observed in maintenance of chromosomes and centrioles (up 6 to 25 n and up 4 to 22 centrioles). In multipolar mitosis, either during the drug action or after its stopping, different numbers of chromosomes are directed towards the poles not depending on the number of centrioles in the poles. During the cytochalasin B treatment, either in bipolar or multipolar metaphases, there are destructions in the ultrastructure of the mitotic apparatus: there are no astral microtubules; in the poles there are diplosomes and duplex of centrioles with fibrillar material around both centrioles; kinetochores are of prometaphase type. After stopping the drug action the astral microtubules appear, but no other patterns of normalization in the mitotic apparatus occur. Desynchronization of three cycles (chromosomal, centriolar and centrosomal) is discussed as a factor of abnormal development of the mitotic apparatus and as a factor of stabilization of aneuploidy in the cell culture.

[Variants of asynchronous DNA synthesis and mitoses in multinucleate cells induced by cytochalasin B]. / Varianty asinkhronnogo sinteza DNK i mitozov v mnogoiadernykh kletkakh, indutsirovannykh tsitokhalazinom B.

Cases of asynchronous progression with separate nuclei of S-period and initial mitotic stages in multinucleate cells were discovered in Chinese hamster cell cultures during a prolonged action of cytochalasin B (7 days) and after its stopping (7 days of cell cultivation without drug). The interphase asynchrony under experimental conditions vary in value corresponding to the level of interphase asynchrony in spontaneous multinucleate cells in control cultures. So, the interphase asynchrony in cytochalasin B-induced multinucleate cells is suggested not to be connected with the drug action. Fusion of heterophase cells and a high level of proliferation activity of multinucleate cells seem to be the main reason of interphase asynchrony both in control cultures and in experimental conditions. Unlike the interphase asynchrony, the appearance of the mitotic asynchrony in multinucleate cells is shown to be connected with the action of cytochalasin B. The high level of the mitotic asynchrony remains after the stopping of drug action. A conclusion is made that mitotic asynchrony of nuclei, along with multipolar mitosis and cytokinesis inhibition, is one more display of the cytotoxic action of cytochalasin B on mitosis.

[Role of multipolar mitoses in the proliferation of multinucleate cells induced by cytochalasin B]. / Issledovanie roli mnogopoliusnykh mitozov v proliferatsii mnogoiadernykh kletok, indutsirovannykh tsitokhalazinom B.

A prolonged action of cytochalasin B results in the formation of numerous multipolar mitoses (26%) in Chinese hamster cell cultures. The transition to multipolar mitoses in the presence of cytochalasin B is not accompanied by K-mitotic delay. It is shown that a multipolar mitosis without cytoplasmic division is one of the main causes of multinucleation development in cytochalasin B-treated cultures. After stopping the drug action the cytochalasin B-induced multinucleate cells continue to divide by multipolar mitosis. In this case it completes with cytokinesis and, probably, leads to a decrease in the number of nuclei per cell. The origin of multipolar mitotic apparatus after the action of cytochalasin B is discussed in addition to the role of multipolar mitosis in formation and proliferation of multinucleate cells.

[Proliferation characteristics of multinucleate cells during prolonged exposure to cytochalasin B]. / Osobennosti proliferatsii mnogoiadernykh kletok pri dlitel'nom vozdeistvii tsitokhalazina B.

The growth of the Chinese hamster cell cultures for 7 days after the stopping of the prolonged cell cultivation with cytochalasin B (5 micrograms/ml, 7 days), on the one hand, results in the decrease in the amount of multinucleate cells from 75 to 25%. On the other hand, it leads to the appearance of a new class of multinucleate cells with more than 7 nuclei. By the 2nd day a rapid increase in the proliferation rate is observed both in uninucleate and multinucleate cells. Then, by the 7th day, the rate of proliferation activity of multinucleate cells decrease more quickly than that of uninucleate ones. It is shown that during a prolonged cell cultivation after the action of cytochalasin B all classes of multinucleate cells are able to DNA reproduction. A question on proliferation abilities of multinucleate cells is discussed.