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Polykaryocytosis was induced in human cells (Lu 106 cell line) grown on coverslips after treatment with high titer materials of the Edmonston strain of the measles virus. The nuclei in polykaryocytes exhibited cytopathic effects and were usually in contact with each other. Nuclear membranes at points of contact sometimes disappeared, resulting in fusions between nuclei. Nuclear division in polykaryocytes was partially or completely synchronized. The occasional presence of successive mitotic stages in sequence, possibly denotes a transfer of the mitotic trigger in a certain direction within the syncytium. The mitotic figures were mainly multipolar appearing as tripolar, quadripolar or star-shaped equatorial plates in small rounded polykaryocytes, or as more complex configurations with equatorial plates at angles to each other in large flat syncytia. In some of these configurations, individual spindles were at different planes. Regular anaphases and successful cytokinesis were observed especially in simple multipolar mitoses. Mono- and multinucleate origins of multipolar mitosis, mechanisms for induction and synchronism of mitosis, as well as chromosomal constitutions of segregant cells were discussed. Orientation of chromosomes at the poles in virus-induced polykaryocytes and in three-group metaphases found in control cells, largely denotes a prometaphase condition. Frequently diplochromosomes and less commonly undivided metaphase chromosomes were found in the treated material. The virus also induced chromosome pulverizations. Different chromosomal groups in syncytia, also chromosomes within a mitotic figure, may be differentially damaged. |
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