Increased sister chromatid exchange events in the human late replicating X

Sister chromatid exchange in the goat (Capra hircus)

Lymphocyte cells from 30 Maltese and Syrian derivative goats (13 males and 17 females) reared in southern Italy underwent sister chromatid exchange (SCE) test. For the 902 cells we studied, the SCE-mean values were 6.6 +/- 3.0 per cell for both breeds. The SCE-frequency did not follow a Poisson distribution. The simultaneous visualization of SCEs and G-bands in the lightly stained chromatid allowed the study of SCE-distribution in chromosomes 1 and X. The number of SCEs in chromosome 1 was significantly higher (P > 0.001) than expected from relative chromosome length. No statistical differences between the numbers of SCEs in the active (early-replicating) and inactive (late-replicating) X-chromosomes of female cells were found.

Sister-chromatid exchange rates in XX and XY cells of ten chimeric Callithrix jacchus individuals

In order to ascertain whether or not sister-chromatid exchange (SCE) differs in relation to sex, SCE rates in XX and XY cells from 10 specimens of marmoset (Callithrix jacchus) were examined. The choice of this primate is particularly suitable for three reasons: most individuals have a chimeric constitution, the X chromosome is quite large and the Y chromosome is particularly small. Therefore, the influence of possible differences in their exposure to the external environment can be eliminated. The results obtained did not reveal any significant difference between SCE rates in male and female cells in any of the examined individuals.

Non-uniform distribution of sister chromatid exchanges in human lymphocytes

To test whether sister chromatid exchange (SCE) scores on human chromosomes have a uniform distribution, simulated SCE scores were generated and compared with observed scores using log-linear models. The analysis was performed at the level of the chromosome groups. Using this method we first tested whether the number of SCEs was distributed uniformly, i.e. proportional to the relative length of the chromosomes. Refinements of this hypothesis were made by considering a variable region around a first SCE to be inert for other SCEs and by making the occurrence of an SCE on a chromosome dependent on the occurrence of another SCE on the same chromosome. In further analyses it was tested whether the number of SCEs was proportional to the number of G bands on a chromosome, or to the DNA content of the chromosomes. None of the tested hypotheses fitted the observed data, establishing the non-uniform distribution of these events.

Increased sister chromatid exchanges in human cell lines characterized by monosomy X or structural abnormalities of the X chromosome

In the present investigation we test the hypothesis that deficiencies of the X chromosome affect sister chromatid exchange (SCE) frequencies in human fibroblast cell lines. Our results show increased mean SCE frequencies in cell lines with abnormalities of the X chromosome: 45,X; 46,X,del(X) (q13), 46,X,del(X)(p11), and 46,X,i(Xq); control cell lines were 46,XX. In only one abnormal line [46,X,del(X)(p11)] was the increase not significant after correcting for multiple comparisons. If SCE formation is replication-dependent, the increased SCE frequencies might merely reflect the prolonged cell cycle we reported previously in cell lines with X chromosome abnormalities (Simpson and LeBeau 1981). Other explanations for differences between cell lines are possible, e.g., that deleted loci on the X chromosome affect cellular uptake of bromodeoxyuridine (BrDU). However, specific mechanisms were not explored directly.

Selective differential staining of sister chromatids of the facultative heterochromatic X chromosome in the female mouse

Selective differential staining of sister chromatids for the facultative heterochromatic X chromosome in the female mouse has been achieved by the combination of two differential staining techniques; one for the heterochromatic X chromosome and the other for sister chromatids. Thermal hypotonic treatment moderately destroyed the chromosome structure except for the heterochromatic X in BrdU labelled metaphase cells, resulting in the selective sister chromatid differentiation of this X with Giemsa stain. This technique enables us to know the exact frequency of th spontaneous sister chromatid exchanges in the heterochromatic X without using 3H-TdR labelling for detecting the late DNA replication. The results indicate that the sister chromatid exchange frequency of the heterochromatic X chromosome is not affected by its late DNA replication during S phase, or by the genetic inactivation and the resulting heterochromatinization.

Sister chromatid exchanges in human leukocyte chromosomes: spontaneous and induced frequencies in early- and late-proliferating cells in vitro

Human leukocyte cultures were pulse-treated with the trifunctional alkylating mutagen trenimon in a final concentration of 10(-7) M for 15--20 h after culture start, i.e., in the G1 phase of the cell cycle. At 24 h after culture start bromodeoxyuridine (BUdR) was added to the trenimon-treated cultures and to several untreated cultures running in parallel. The series treated with BUdR only and the series treated with BUdR+trenimon were each used to prepare two cultures at different culture times. Mitoses were collected during consecutive intervals of 12 h from 30 h up to 102 h after culture initiation by colcemid. For all preparation times (42 h, 54 h, 66 h, 78 h, 90 h, and 102 h) the frequencies of first, second, and third and further mitoses were determined in the BUdR- and in the BUdR+trenimon-treated series. In the trenimon-treated series a clear cell cycle delay was detected as compared with the normal distribution of different types of mitoses found in series treated with BUdR only. Spontaneous and trenimon-induced sister chromatid exchange (SCE) frequencies were determined in second mitoses occurring at 66 h, 78 h, 90 h, and 102 h after culture start. For all these preparation times about six SCE per metaphase were consistently found in BUdR-treated, and about 19 SCE per metaphase in BUdR+-trenimon-treated series, indicating a homogeneous sensitivity of early- and late-proliferating cells with respect to the induction of SCE.

Sister chromatid exchange in chromosomes of cattle (Bos taurus)

Lymhocytes from clinically healthy Holstein animals (8 males and 23 females) were cultured in media containing 5-bromodeoxyuridine (10 microgram/ml) for two cycles of deoxyribonucleic acid replication (48 h). The exchange of sister chromatids per cell varied from 1 to 16 with a mean of 5.4 and a standard deviation of 2.1 in 603 differentially stained metaphase chromosome spreads. The major fraction of exchanges in the X chromosome were located in the region of the subcentromeric G negative bands q1 and q2. When the cells were pulse labeled with tritium labeled thymidine (1 muCi/ml) for the last 6 h of the cell cycle, the rate of exchange was higher in the late replicating X chromosome (facultative heterochromatin) in comparison to its homologue (active X). This study characterizes the yield of sister chromatid exchange in lymphocytes exposed to a given amount of 5-bromodeoxyuridine in a population of normal individuals so that it may be used as a standard for 1) a diagnostic tool in pathological conditions and 2) as an assay of chromosome stability in relation to environmental hazards.

Sister chromatid exchanges in balanced translocation carriers and in patients with unbalanced karyotypes

Sister chromatid exchanges (SCEs) were studied in peripheral human leukocytes from 16 patients with balanced translocations or with unbalanced karyotypes, and from 4 controls. No difference was seen between these two groups of people in the mean number of SCEs per cell, or in the total number of SCEs observed for each pair of autosomes involved in the translocations studied. With this last number no difference from the expected number of SCEs, if one supposes that SCEs follow a random distribution, was seen.