The splitting of human chromosomes into chromatids in the absence of either DNA or protein synthesis

Micronuclei and 3AB index in X-irradiated human lymphocytes in G0 and G1 phases

We applied the cytokines-block micronucleus assay to observe the radiobiological response of human lymphocytes after X-ray treatment in the G0 and G1 phases. In addition, we used 3-aminobenzamide (3AB) to measure the 3AB index in the two phases. The experimental results show that at 2 Gy the MN yield and the 3AB index are dependent on the cell phase and show considerable inter-individual variability. The radiation-induced MN frequency obtained for 33 subjects is 0.470 +/- 0.063 for the G0 phase and 0.689 +/- 0.139 for the G1 phase; the 3AB index values are 0.326 +/- 0.144 and 0.067 +/- 0.058 for G0 and G1 phases, respectively. At the individual level, the 3AB index for the G1 phase correlates inversely with the cytogenetic effects observed in that phase. We discuss the possibility of applying the MN test combined with the 3AB index to lymphocytes at different phases to study the individual response to radiation (individual radiosensitivity).

Cytogenetic effect of some anti-tuberculosis drugs in vitro

The comparative cytogenetic effects of some widely used anti-tuberculosis drugs (PAS Na, PRA, RMA) were estimated depending on the in vitro administered concentrations, in human peripheral blood cultures. The structural chromosomal lesions were randomly distributed between the different chromosome groups of the human karyotype; nearly 10 to 30% of affected cells had more than one lesion per metaphase. In the treatements with PAS Na and PRA the analysis of the frequencies of the cell carring chromosomal aberrations and of the chromosomal lesion types indicated a dose-response correlation. The significance of the results obtained in vitro on the chromosome-breaking effects of anti-tuberculosis agents and the genetic peril is pointed out.

X-ray induction of chromosome and chromatid aberrations in the same cells after treatment with hydroxyurea

Vicia faba root meristem cells treated for 24 h with 1.25 mM hydroxyurea and then X-irradiated contained a large number of cells with both chromosome and chromatid aberrations. X-irradiation 4 h after release from the hydroxyurea block yielded cells with almost exclusively chromatid aberrations.

Radiation induced DNA double strand breaks and chromosome aberrations

This paper presents arguments which favour an alternative approach to the interpretation of radiation induced chromosome aberrations. Starting from the modern concept that a chromosome has a DNA double stranded helix backbone and that the induction of DNA double strand breaks has a quadratic dose relationship, it is concluded that most chromosome aberrations arise from only one chromosome break. The direct correlation between chromosome aberrations and cell death derived from the model is demonstrated by the analysis of experimental results. The effect of dose rate, LET and the occurrence of chromatid aberrations after irradiation in G1 are all logically explained by the theoretical model.

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.