Definition and Morphologic Features of Chromosome Pulverization: A Hypothesis to Explain the Phenomenon<xref ref-type="fn" rid="FN2">2</xref>

Abstract

The chromosome pulverization phenomenon and cell fusion were studied in a Chinese hamster cell line, Don, during the initial period of Sendai virus treatment. Pulverized nuclei in the G2 phase or prophase were characterized by variety in morphologic appearance. These phases were recognized by the presence of paired chromatin particles in the pulverized nuclei. Pulverized nuclei in the S phase of the cell cycle had a relatively constant morphologic picture consisting of fine particles or threads. These observations were confirmed by the autoradiographic behavior of the pulverized nuclei. More difficult to define were pulverizations in the G1 phase. It was concluded that the morphology of chromosome pulverization basically depended on the cellular phase at which exposure to the virus and fusion occurred. Metaphase chromosomes are extremely resistant to pulverization, with cells becoming less resistant in the anaphasic, telophasic, and interphasic parts of the cycle in the order cited. The nuclei of interphase cells fused with anaphase or telophase cells undergo pulverization less frequently than when fusion occurs with metaphase cells. The chromosome pulverization phenomenon is defined as a total loss of nuclear architectural integrity in fused, multinucleate cells in which the presence of an intact, mitotic nucleus is a prerequisite for the induction of the phenomenon. A hypothesis is advanced that implicates the system responsible for nuclear membrane lysis in the mitotic cell in the induction of chromosome pulverization. This hypothesis is explained in terms of morphologic features observed in experiments with Sendai-virus-induced cellular fusions containing chromosome pulverizations.