Cell Cycle Studies on a Temperature-sensitive Cell Division Mutant of Mammalian Cells

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Abstract
A temperature-sensitive mutant (ts2) of murine leukemic L5178Y cells accumulates aberrant mitotic cells and subsequently, multinucleate cells upon exposure to a restrictive temperature. Temperature-shift experiments using synchronized cell populations demonstrate that the execution point of ts2 cells is located between the early and mid S phase in the cell cycle. Mutant cells can achieve cell division when they are shifted down by the time of karyokinetic stage. Multinucleate cells, once formed, are unable to undergo cytokinesis even though transferred to a permissive temperature. Cytofluorometric analysis indicates that unequal chromosome distribution among daughter nuclei takes place during multinucleation. The mechanism of defective karyokinesis and cytokinesis in ts2 cells is discussed.