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PubMed1964

THE FREQUENCY OF SISTER CHROMATID EXCHANGES FOLLOWING EXPOSURE TO VARYING DOSES OF H3-THYMIDINE OR X-RAYS.

In the Chinese hamster cell line CHEF-125, sister chromatid exchanges occurred at a rate of a little higher than one per three chromosomes for each cell cycle. The exchanges were detectable by labeling with H(3)-thymidine and autoradiographic analyses of chromosomes at the second and subsequent metaphases after labeling had occurred. To test the hypothesis that sister chromatid exchanges are caused by radiation, cells were incubated in media with different amounts of H(3)-thymidine. No statistically significant change in the exchange rate was detected over 100-fold range of variation in the amount of incorporated H(3)-thymidine (determined by grain counts of autoradiographs). We have concluded that sister chromatid exchanges are not caused by tritium radiation and therefore are spontaneous events. Cultures were also irradiated with acute doses of x-rays up to 200 r and scored for sister chromatid exchanges. Between zero and 50 r there was a statistically significant increase in the rate of exchanges. This is interpreted as evidence that x-rays can induce some exchanges, although the majority of these events are probably spontaneous.

Animals↗
PubMed1996

Cytogenetic and genetic studies of radiation-induced chromosome damage in mouse oocytes. I. Numerical and structural chromosome anomalies in metaphase II oocytes, pre- and post-implantation embryos.

The incidences of X-ray induced numerical and structural chromosome anomalies were screened in a range of developmental stages from metaphase II oocytes through to post-implantation embryos. Following 1 Gy of acute X-rays to immediately preovulatory stage oocytes, the rate of hyperploidy (chromosome gain) was found to be elevated over levels in unirradiated controls, at metaphase II, in 1-cell and 3.5 day pre-implantation embryos but not in 8.5 day post-implantation foetuses. In the latter, however, the frequency of mosiacism was significantly increased. A similar response of an increase in mosaicism but not in hyperploidy in 8.5 day post-implantation embryos was also found after irradiation of dictyate stage oocytes with 4 Gy of acute X-rays. Significantly elevated frequencies of structural chromosome anomalies were present in metaphase II oocytes and pre-implantation embryonic stages, but could not be detected in block-stained chromosome preparations from 8.5 day post-implantation foetuses. However, analysis of chromosome preparations after G-banding showed that almost 14% of 14.5 day foetuses carried a chromosome rearrangement after 1 Gy of X-rays to immediately preovulatory stage oocytes. Overall, our data indicate that the presence of radiation-induced chromosome gains are incompatible with embryonic survival but that a proportion of embryos with structural chromosome damage develop past mid-gestation. These latter embryos are therefore potentially capable of contributing to the genetic burden of the next generation.

Animals↗
PubMed1964

POLYPLOIDY INDUCED BY X-RAYS IN CHINESE HAMSTER CELLS IN VITRO.

The incidence of polyploidy (specifically, in this case, the doubling of the stemline chromosome number) induced by x-rays in cells cultured in vitro is about the same for both "near-diploid" and "near-tetraploid" sublines of the Chinese hamster. Endoreduplication is a principal cytological mechanism for this form of induced polyploidy.

Animals↗