Synchronization of Events in Fused Interphase-Metaphase Binucleate Cells: Progression of the Telophase-Like Nucleus2

After the initial formation of nuclear envelopes around the metaphase chromosomes and the production of a telophase-like nucleus (TLN) 30 minutes after metaphase- interphase cell fusion, the chromatin of the TLN underwent structural and functional changesthat resembled the progression of a telophase nucleus in the normal cell cycle. To identify the metaphase chromatin, metaphases prelabeled with 3H-thymidine were fused with unlabeled interphase cells. Light microscopy of the TLN, up to 60 minutes after the initial formation, revealed a gradual loss of chromatid structure; by 60 minutes, the chromatin resembled that of interphase. Concomitantly, the number of recognizable TLN's fell, which was matched by an increase in the number of binucleate interphase-interphase cells containing only 1 radiolabeled nucleus. Electron microscopy revealed progressive formation of nucleolilike bodies and, 60 minutes after TLN formation, areas of decondensed chromatin. The ability of the TLN to incorporate 3H-uridine into its chromatin during its progression revealed a temporal pattern similar to that of the metaphase-G1 progression in the normal cell cycle. The progression of the TLN is another example of intracellular synchronization of cell cycle stages in virus-fused cell.