Fate of Chromatin of Interphase Nuclei Subjected to “Prophasing” in Virus-Fused Cells2

Abstract

The fate of chromatin of interphase nuclei (G1, S, or G2) of cells fused by means of Sendai virus with metaphase cells has been studied in a Chinese hamstercell line (DON). “Prephasing” of such interphase nuclei was differentiated from the metaphase chromosomes by ³H-thymidine labeling of their DNA before cell fusion. After prophasing reached its peak, Colcemid was removed from the culture to permit the binucleate cells to enter a G1 state. Interphase S or G1 chromatin became randomly distributed to daughter cells, when metaphase chromosomes underwent karyokinesis or subsequent cytokinesis, and persisted either as nuclear fragments or micronuclei. In a subsequent nuclear division, Sand G1 chromatin again were subject to prophasing and emerged again as “pulverized” chromatin, an indication of continuousasynchrony with the original metaphase nucleus. This contrasts with the behavior of G2 chromatin. The latter amalgamated with the metaphase chromatin to form a nucleus-like structure. In subsequent mitoses, most G2 chromatin was reorganized as intact metaphase chromosomes among those representative of the original metaphase cell. In this case, the G2 chromatin became synchronized with the original metaphase chromatin. Thus, providing the interphase nucleus is in G2, prophasing in a binucleate cell containing a metaphase set of chromosomes can be followed by events simulating metaphase as well. It is concluded that the metaphase cell contains factors capable of inducing many events of a normal mitosis.