Showing papers on "Sister chromatid exchange published in 1975"

Cytological detection of mutagen-carcinogen exposure by sister chromatid exchange.

Abstract: A staining technique that detects sister chromatid exchanges (SCEs) has been used to examine the response of chromosomes in cultured Chinese hamster cells to a wide variety of mutagens-carcinogens. The test gives a very sensitive and rapid method for detecting chromosome mutagenicity of chemical agents and provides a powerful new method for detecting environmental mutagens.

Sister chromatid exchanges--a sensitive assay of agents damaging human chromosomes.

Abstract: Sister chromatid exchange frequencies in human lymphocyte chromosomes are greatly increased by alkylating agents, but ionizing radiation has little if any such effect. Scoring these exchanges may provide a useful technique for exploring the mechanisms of chromosome breakage and repair.

Sister chromatid exchange in human chromosomes from normal individuals and patients with ataxia telangiectasia.

Abstract: A new fluorescence plus Giemsa staining technique now makes the detection of sister-chromatid exchange (SCE) a relatively easy matter in cells containing 5-BrdU-substituted DNA. The technique has been

Distribution of sister chromatid exchanges in the euchromatin and heterochromatin of the Indian muntjac.

Abstract: The frequency of sister chromatid exchanges (SCEs) was determined for the chromosomes (except Y2) of the Indian muntjac stained by the fluorescence plus Giemsa (FPG) or harlequin chromosome technique. The relative DNA content of each of the chromosomes was also measured by scanning cytophotometry. After growth in bromodeoxyuridine (BrdU) for two DNA replication cycles, SCEs were distributed according to the Poisson formula in each of the chromosomes. The frequency of SCE in each of the chromosomes was directly proportional to DNA content. A more detailed analysis of SCEs was performed for the three morphologically distinguishable regions of the X-autosome composite chromosome. The SCE frequency in the euchromatic long arm and short arm were proportional to the amount of DNA. In contrast, the constitutive heterochromatin in the neck of this chromosome contained far fewer SCEs than expected on the basis of the amount of DNA in this region. A high frequency of SCE, however, was observed at the point junctions between the euchromatin and heterochromatin.

Sister chromatid exchange in xeroderma pigmentosum cells that are defective in DNA excision repair or post-replication repair.

Abstract: The formation of sister chromatid exchanges has been postulated to depend upon the action of DNA repair enzymes. Our experiments with various human cell lines show that the yield of sister chromatid exchanges is within normal limits in both excision-repair-defective and post-replication-repair-defective cells from the autosomal recessive disease, xeroderma pigmentosum. These results indicate that hypotheses invoking known DNA repair processes to account for the recombination of sister chromatids are inadequate and that the exact enzymatic processes are as yet unknown.

The induction of chromatid deletions in accord with the breakage-and-reunion hypothesis.

Abstract: In the present experiments it has been possible to study large numbers of X-ray induced chromatid deletions, or breads, in Chinese hamster chromosomes and to discern whether or not a sister chromatid exchange also occurs at the point of breadage. Chromatid deletions are only infrequently associated with a sister chromatid exchange. This is contrary to the expectations derived from the exchange hypothesis of Revell. Pn the basis of this hypothesis, in which chromatid deletions are considered to be incomplete exchanges that occur in the necks of little loops in the chromosomes, 40% of the chromatid breaks are expected to be associated with sister chromatid exchanges. The present data are in accord with the conclusions drawn from the earlier autoradiographic experiments of HEDDLE AND BODYCOTE, and show that chromatide breaks can be accounted for on the basis of the breakage-and reunion hypothesis, with the majority being simple breaks and some being incomplete exchanges between two such breaks.

Sister chromatid exchange and chromosome organization based on a bromodeoxyuridine Giemsa-C-banding technique (TC-banding).

Abstract: Hoechst 33258 fluorescent staining of bromodeoxyuridine substituted chromosomes provided a high resolution technique for following the segregation of replicated chromosomal DNA (Latt, 1973) Modifications have produced the same results after Giemsa staining (Wolff and Perry, 1975) Since this does not necessarily require Hoechst (Korenberg and Freedlander, 1975), we call this bromodeoxyuridine-Giemsa banding (BG-banding) We here describe a further modification which allows one to follow the T-rich strand of the AT-rich satellite DNA of C-band heterochromatin We call this TC-banding This technique was used to examine metacentric marker chromosomes found in mouse L-cells that contain many interstitial blocks of centromeric-type heterochromatin in each arm plus the usual two blocks of centromeric heterochromatin One of the advantages of this technique for such chromosomes is that it is possible to distinguish first from second cell cycle sister chromatid exchange and unambiguously detect centromeric sister chromatid exchange We found some chromosomes to have high rates of centromeric sister chromatid exchange After one cycle in bromodeoxyuridine we could examine the satellite polarity of the heterochromatic DNA Since there was no change in satellite polarity in any of the heterochromatic blocks, marker chromosomes could not have been formed by paracentric inversions, inverted insertions or inverted translocations These results allow the formulation of several rules of chromosome organization

Implications of somatic recombination and sister chromatid exchange in Bloom's syndrome and cells treated with mitomycin C.

Abstract: It is suggested that the somatic recombination observed in Bloom's syndrome and cells treated with mitomycin C may be the result of selection for recombination events that can occur only between homologous segments of DNA, rather than a result of somatic pairing in the nucleus.

Centromeric asymmetry and induction of translocations and sister chromatid exchanges in mouse chromosomes

Abstract: THE mechanisms involved in chromosome rejoining are not understood. We showed that chromosome rejoining in Robertsonian centric fusion can be studied cytologically1 with a staining technique based on the quenching by 5-bromodeoxyuridine (BrdU) of the fluorescence of the dye 33258 Hoechst2. When mouse cells were grown for one generation in the presence of BrdU and stained with 33258 Hoechst, there was a brightly fluorescent spot appearing over half of the centromeric region in every autosome3. (This asymmetry presumably reflects the unequal distribution of thymidine (45% compared with 22%) between the two chains of mouse satellite DNA4, the fluorescent spot representing the old thymidine-rich chain of satellite DNA.) The arrangement of fluorescent spots in metacentric chromosomes resulting from Robertsonian fusion suggested that the thymidine-rich chain of satellite DNA in the centromeric region is associated with the same DNA chain (in terms of polarity) in every mouse autosome1. We have used the centromeric asymmetry in mouse chromosomes as a marker for DNA polarity in studies on radiation and drug-induced chromosomal translocation and sister chromatid exchange (SCE).