Application of the BrdU/thymidine method to flow cytogenetics: differential quenching/enhancement of Hoechst 33258 fluorescence of late-replicating chromosomes

Discrimination between many types of isolated mammalian chromosomes can be accomplished by dual-beam flow cytometry following DNA staining with Hoechst 33258 (HO) and Chromomycin A3 (CA3). In this report, we show that the bivariate discrimination of selected late-replicating Chinese hamster M3-1 chromosomes can be improved by appropriate treatment of the cells with 5-bromo-2'-deoxyuridine (BrdU) prior to chromosome isolation and staining. Two labeling schemes are reported. In one scheme the chromosomes are collected from cells labeled with BrdU only during late S phase. The Hoechst fluorescence of the 10, 11, M2, and Y chromosomes is substantially quenched by the incorporated BrdU, thus improving their discrimination. In the other scheme, chromosomes are collected from cells labeled with thymidine (dT) during late S phase following 20 h of growth in BrdU-containing medium. The Hoechst fluorescence of the 10, 11, M2, and Y chromosomes is quenched less than the other chromosomes, again improving their discrimination. Y chromosomes from chromosome suspensions of untreated controls, of cells labeled with BrdU during late S phase, and of cells labeled with dT during late S phase following 20 h growth in BrdU were separated by dual-parameter sorting. While the purity of the sorted Y chromosome was 15% in untreated controls, it was 70-75% using the BrdU/dT labeling protocols.

DNA content of cells with generalized chromosome shattering induced by ultraviolet light plus caffeine

Asynchronously growing Chinese hamster cells (M3-1) were UV-irradiated (lambda = 254 nm) and then incubated with/without caffeine (2 mM) for 20 h. Microscopic evaluation of metaphase spreads revealed that after UV-irradiation alone (5.0 J/m2) appearing fragmented and/or pulverized ('GCS-like' cells; GCS, Generalized Chromosome Shattering) was very low while it was high following the combined treatment. Cytogenic and flow cytometric analysis of cells obtained by mechanical shaking cultures treated with UV and caffeine indicated that 'GCS-like' cells have the same DNA content as untreated cells in G2 phase and mitosis.

Induction of chromosome damage by ultraviolet light and caffeine: correlation of cytogenetic evaluation and flow karyotype

Asynchronously growing cells of a M3-1 Chinese hamster line were ultraviolet (UV) irradiated (lambda = 254 nm) with UV fluences up to 7.5 J/m(2). After irradiation cells were incubated with or without 2 mM caffeine for 20 hr, then mitotic cells were selected by mechanical shaking. Their chromosomes were isolated, stained with Hoechst 33258 and chromomycin A3, and measured flow cytometrically. While the fluorescence distributions of chromosomes (flow karyo-types) from cells treated with UV alone or with caffeine alone were very similar to those of untreated controls, the flow karyo-types of UV + caffeine-treated cells showed a debris continuum that increased with increasing UV fluence suggesting an increased number of chromosome fragments. Visual evaluation of metaphase plates revealed that the percentage of cells with chromosome damage also increased steadily with increasing UV fluence. A high degree of correlation was observed between the relative magnitude of the debris level from flow karyotypes and the percentage of cells with chromosome damage and with generalized chromosomes shattering, respectively, as determined from metaphase spreads.

Induction of chromosome shattering by ultraviolet irradiation and caffeine: comparison of whole-cell and partial-cell irradiation

Synchronized and asynchronously growing cells of a V79 sub-line of the Chinese hamster were either whole-cell irradiated ( gamma, 254 nm) or laser-UV-microirradiated ( gamma, 257 nm). Post-incubation with caffeine (1-2 mM) often resulted in chromosome shattering, which was a rare event in the absence of this compound. In experiments with caffeine, the following results were obtained. Shattering of all the chromosomes of a cell (generalized chromosome shattering, GCS) was induced by whole-cell irradiation at the first post-irradiation mitosis when the UV fluence exceeded a "threshold" value in the sensitive phases of the cell cycle (G1 and S). GCS was also induced by laser-UV-microirradiation of a small part of the nucleus in G1 or S whereas microirradiation of cytoplasm beside the nucleus was not effective. An upper limit of the UV fluence in the non-irradiated nuclear part due to scattering of the microbeam was experimentally obtained. This UV fluence was significantly below the threshold fluence necessary to induce GCS in whole-cell irradiation experiments. In other cells, partial nuclear irradiation resulted in shattering of a few chromosomes only, while the majority remained intact (partial chromosome shattering, PCS). G1/early S was the most sensitive phase for induction of GCS by whole-cell and partial nuclear irradiation. The frequency of PCS was observed to increase when partial nuclear irradiation was performed either at lower incident doses or at later stages of S. We suggest that PCS and GCS indicate 2 levels of chromosome damage which can be produced by the synergistic action of UV irradiation and caffeine. PCS may be restricted to microirradiated chromatin whereas GCS involves both irradiated and unirradiated chromosomes in the microirradiated nucleus.

Detection of laser--UV microirradiation-induced DNA photolesions by immunofluorescent staining

A low-power laser-UV microbeam of wavelength 257 nm was used for microirradiation of a small part of the nucleus of Chinese hamster cells. Following fixation in interphase or in the subsequent metaphase indirect immunofluorescent staining was performed with antiserum to photoproducts of DNA treated with far UV light. The results show that antibodies specific for UV-irradiated DNA can be used for a direct detection of laser-UV microirradiation-induced DNA photolesions. The potential usefulness of this method for investigation of the spatial arrangement of chromosomes in the interphase nucleus is discussed.

Induction of chromosome shattering and micronuclei by ultraviolet light and caffeine. I. Temporal relationship and antagonistic effects of the four deoxyribonucleosides

It is known that nucleosides may have antimutagenic and anticlastogenic effects. Here, we have investigated the influence of nucleosides on the induction of shattered chromosomes (fragmentation and/or pulverization of chromosomes of a mitotic cell) and of micronuclei by ultraviolet (UV) light and caffeine. Asynchronous cell cultures of a V79 subline of the Chinese hamster were irradiated at wavelength 254 nm using fluences up to 5.2 joules/m2. Following irradiation, the cells were postincubated either with 1.0 mM or 2.0 mM caffeine alone or with caffeine plus the four deoxyribonucleosides (dXs) (concentration 0.1 mM each). After different incubation times (three to 24 hours), chromosome preparations were performed. In other experiments, synchronized cells were used. The percentage of metaphase spreads with shattered chromosomes and the percentage of cells with micronuclei were determined. Post-treatment with caffeine alone resulted in shattered chromosomes in a high percentage of cells at the first post-irradiation mitosis as described previously. Formation of cells with micronuclei was observed only afer the appearance of mitotic cells with shattered chromosomes, the maximum percentage of cells with micronuclei being smaller than the maximum percentage of cells with shattered chromosomes. The strong potentiating effect of UV-light plus caffeine was significantly reduced, however, if the post-treatment was performed with caffeine plus nucleosides. A significant reduction was also observed in the percentage of micronuclei. An evaluation of the mitotic indices and of cell-cycle parameters indicates that the effect of nucleosides was not due to enhanced interphase death.

Considerations on a laser-scanning-microscope with high resolution and depth of field

In conventional light microscopy, the depth of focus is severely limited. This limitation might be overcome by a light optical scanning procedure. In this procedure, the specimen surface is scanned point for point by a focused laser beam. The image of the specimen surface is generated by an electronic system, similar to the procedure used in the scanning electron microscope. Possibilities to develop a "laser-scanning-microscope" on the basis of available techniques (laser microirradiation, miniprocessors, light detecting systems, automatic focusing, holographic focusing etc.) are discussed. On account of its possibility to form images of high resolution and depth of focus, a laser-scanning-microscope might become a valuable tool in addition to conventional light microscopy and scanning electron microscopy.

Results of reflex photometric determinations of vasoconstriction after topical steroid application. Tachyphylaxis, relative and absolute refractory phase after single and multiple application of steroid

After a repeated intensive topical application (4-h rhythm), there it is phase already after 28 h in which the cutaneous vessels are insensitive (refractory) to constrictor stimuli due to steroids. This refractory phase lasts for at least 68 h. A single local application of steroid likewise leads to a diminished vasoreactivity for a limited time. The relative refractory phase is limited to 96 h under the given experimental conditions.

Laser UV microirradiation of interphase nuclei and post-treatment with caffeine. A new approach to establish the arrangement of interphase chromosomes

Laser UV microirradiation of Chinese hamster interphase cells combined with caffeine post-treatment produced different patterns of chromosome damage in mitosis following irradiation of a small area of the nucleus that may be classified in three categories: I)intact metaphase figures, II)chromosome damage confined to a small area of the metaphase spread, III)mitotic figures with damage on all chromosomes. Category III might be the consequence of a non-localized distortion of nuclear metabolism. By contrast, category II may reflect localized DNA damage induced by microirradiation, which could not be efficiently repaired due to the effect of caffeine. If this interpretation is right, in metaphase figures of category II chromosome damage should occur only at the irradiation site. The effect might then be used to investigate neighbourhood relationships of individual chromosomes in the interphase nucleus.