Chromosome condensation and radiation-induced G2 arrest studied by the induction of premature chromosome condensation following cell fusion.

When mitotic and interphase cells are fused together, the chromosomes of the interphase cell sometimes condense prematurely. The phenomenon of premature chromosome condensation (PCC) was utilized in investigating the problem of whether the chromosomes of cells suffering a radiation-induced G2 delay are capable of condensation. Colcemide-arrested mitotic cells were fused with synchronized G2 cells, and with irradiated cells suffering a G2 delay. The frequency of PCC in mitotic X G2 binucleate cells was determined. This was compared to the PCC frequency in an unirradiated synchronized population rich in G2 cells after fusion with mitotic cells. Flash-labelling with 3HTdR and autoradiography allowed us to eliminate S-phase cells. The frequency of G2 PCCs was not significantly different for the irradiated G2-delayed or unirradiated cells. From these results we conclude that the chromosomes of cells suffering a G2 arrest are capable of condensation, although the involvement of the condensation process in radiation-induced G2 delay cannot be ruled out.