The irradiation of dividing cells. I. The effects of x-ray on prophase chromosomes

Anaphase-telophase analysis of chromosomal damage induced by chemicals

Three main aspects involved in the chemical induction of anaphase-telophase aberrations in the first mitosis after treatment were analyzed: 1) the relationship between the frequency of anaphase-telophase aberrations and the time of fixation after treatment; 2) the dose-response relationships; and 3) the proliferative rate of cells exposed to chemicals which interact with DNA by different mechanisms. Experiments were carried out using Chinese hamster ovary (CHO) cells. The compounds examined were adriamycin (ADR) and mitomycin C (MMC). The frequency of cells with chromatin bridges or with lagging chromosomes as well as the mitotic index was determined in each experiment. The results obtained showed that 1) chromatin bridges and lagging chromosomes are apparently induced during the S period of the previous interphase; 2) the increase in the cytotoxicity index (inferred from the mitotic index) and the frequency of cells with chromatin bridges and lagging chromosomes were proportional to the treatment lapse and to the dose employed; and 3) the effect of ADR on cell growth differs from the effect of MMC. While ADR decreased the mitotic activity of cells in logarithmic growth phase, MMC induced mitotic delay. In accordance with these results, the occurrence of chromatin bridges in anaphase-telophase could be explained by the induction of chromosome stickiness and, to a lesser extent, by the induction of exchange-type aberrations. On the other hand, lagging chromosomes seem to be the result of chromatid or chromosome breaks because the lagging chromosomes observed were primarily, if not all, fragments and not whole chromosomes. Our evaluation of the anaphase-telophase test indicates that it is very sensitive method for the detection of chemical clastogens, but other factors, such as mitotic depression, must be taken into account to avoid false-negative results.

Enhancement by caffeine of the frequency of anaphase-telophase chromatin bridges induced by triethylenemelamine (TEM)

Treatment of BHK cells for 8 h with triethylenemelamine (TEM) followed by caffeine for 4 or 8 h, increased the frequency of anaphase-telophase chromatin bridges in relation to controls and TEM-treated cells. These results indicate that TEM-induced chromosome lesions detected as chromatin bridges at anaphase-telophase could be potentiated by caffeine.

Half-chromatid aberrations and chromosome strandedness

If cells are irradiated during prophase, at anaphase they may show a side-arm bridge type of configuration. These have usually been interpreted as half-chromatid aberrations and they have been used as evidence that chromosomes are multistranded. It is the purpose of this paper to emphasize that such a configuration may just as easily arise on the basis of a single-stranded chromosome, and that the data on the type of aberrations found at the next mitosis (M2) suggest that chromosomes are single-stranded.

The strandedness of chromosomes: evidence from chromosomal aberrations

If cells are irradiated late in the mitotic cycle (late G2or early prophase), at the following anaphase they frequently exhibit characteristic chromosomal configurations known as sidearm bridges. These are often interpreted as sub-chromatid aberrations and are taken as evidence that chromosomes are multi-stranded. This interpretation, although recently challenged, is supported by experiments based upon the normal replication that converts chromatids to full chromosomes. The rationale is that aberrations involving only one chromatid of a chromosome are converted by replication to chromosome aberrations involving both chromatids. After replication, therefore, there should be no chromatid aberrations remaining unless the initial aberration involved less than a full chromatid. The results show that chromatid aberrations do appear after chromosomal replication: at the second mitosis after irradiation. Another experiment shows that most such chromatid aberrations are not the result of errors in the replication of previous chromatid aberrations.