Induction of endoreduplication by hydrazine in Chinese hamster V 79 cells and reduced incidence of sister chromatid exchanges in endoreduplicated mitoses

Hydrazine in high concentrations very effectively induces endoreduplication in Chinese hamster V 79 cells. The addition of 5-bromodeoxyuridine (BrdU) for the duration of one cell cycle prior to the induction of endoreduplication produces diplochromosomes with sister chromatid differentiation (SCD) after differential chromatid staining. The fact that diplochromosomes with complete SCD are obtained shows that endoreduplication was induced in cells that were in G2-phase. The analysis of sister chromatid exchanges (SCEs) showed that hydrazine treatment rarely led to increased SCE frequencies in mitoses after endoreduplication, but that it caused a strong SCE induction in diploid second division metaphases in the same culture. Neither catalase nor cysteine had an effect on the induction of endoreduplication or the incidence of SCEs. Treatment of the cells with mitomycin C prior to addition of BrdU led to increased SCE frequencies. Compared with the normal mitoses from the same preparation, the mitoses after endoreduplication showed a significantly reduced induction of SCEs. In contrast to these findings, SCE induction was not reduced in the common tetraploid V 79 cells after colcemid-induced polyploidization.