Search NASA⌕ Search

SEARCH · Search NASA

Results for “Chromosomes, Human, Pair 4/radiation effects”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

4 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Rejoining and misrejoining of radiation-induced chromatin breaks. I. experiments with human lymphocytes

Fluorescence in situ hybridization with a composite probe for human chromosome 4 and a probe that stained all centromeres was used to study gamma-ray induced breakage, rejoining and misrejoining in prematurely condensed chromosomes in human lymphocytes. Dose-response curves for the induction of all types of aberrations in prematurely condensed human chromosomes 4 were determined immediately after irradiation and after 8 h postirradiation incubation. In addition, aberrations were measured after various incubation times from 0 to 18 h after a dose of 7 Gy. Unrejoined chromosome breaks were the most frequent type of aberration observed immediately after irradiation. Approximately 15% of total aberrations observed were chromosome exchanges. After 8 h postirradiation incubation, the frequency of breaks in prematurely condensed chromosomes declined to about 20% of the initial value, and chromosomal exchanges became the most frequent aberration. Results of metaphase analysis were similar to those for prematurely condensed chromosomes after 8 h incubation with the exception that a significantly lower frequency of fragments was observed. Symmetrical and asymmetrical interchanges were found at similar frequencies at all doses. No complex exchanges were observed in lymphocyte chromosomes immediately after exposure. They accounted for about 1% of total exchanges in metaphase chromosomes at doses <3 Gy and about 14% at 7 Gy. Incomplete exchanges amounted to approximately 15% of total exchanges at all doses. The kinetics of break rejoining was exponential, and the frequency of exchanges increased with kinetics similar to that observed for the rejoining of the breaks. This increase in the total exchanges as a function of the time between irradiation and fusion was due to a rapid increase in reciprocal interchanges, and a slower increase in complex exchanges; the frequency of incomplete exchanges increased initially, then decreased with prolonged incubation to the level observed in metaphase. It is concluded that the formation of each kind of chromosome aberrations follows different kinetics.

NASA Discipline Radiation Health↗
NASA NTRS1996

Rejoining and misrejoining of radiation-induced chromatin breaks. II. Biophysical Model

A biophysical model for the kinetics of the formation of radiation-induced chromosome aberrations is developed to account for the recent experimental results obtained with a combination of the premature chromosome condensation (PCC) and fluorescence in situ hybridization (FISH) techniques. In this model, we consider the broken ends of DNA double-strand breaks (DSBs) to be reactant and make use of the interaction distance hypothesis. The repair/misrepair process between broken ends is suggested to consist of two steps; the first step represents the two break ends approaching each other, and the second step represents the enzymatic processes leading to DNA end-to-end rejoining. Only the second step is reflected in the kinetics observed in experiments using PCC. The model appears to be able to fit existing data for human cells. It is shown that the kinetics of the formation of chromosome aberrations can be explained by a single rate that characterizes both rejoining and misrejoining of DSBs, suggesting that repair and misrepair share the same mechanism. Fast repair (completed in minutes) in a subset of DSBs is suggested as an explanation of the complete exchanges observed with PCC in human lymphocytes immediately after irradiation. The fast repair component seems to be absent in human fibroblasts.

NASA Center JSC↗
NASA NTRS1996

Biological dosimetry by interphase chromosome painting

Both fluorescence in situ hybridization of metaphase spreads with whole-chromosome probes and premature chromosome condensation in interphase nuclei have been used in the past to estimate the radiation dose to lymphocytes. We combined these techniques to evaluate the feasibility of using painted interphase chromosomes for biodosimetry. Human peripheral lymphocytes were exposed to gamma rays and fused to mitotic Chinese hamster cells either immediately after irradiation or after 8 h incubation at 37 degrees C. Interphase or metaphase human chromosomes were hybridized with a composite probe specific for human chromosomes 3 and 4. The dose-response curve for fragment induction immediately after irradiation was linear; these results reflected breakage frequency in the total genome in terms of DNA content per chromosome. At 8 h after irradiation, the dose-response curve for chromosome interchanges, the prevalent aberration in interphase chromosomes, was linear-quadratic and similar to that observed for metaphase chromosomes. These results suggest that painting prematurely condensed chromosomes can be useful for biological dosimetry when blood samples are available shortly after the exposure, or when interphase cells are to be scored instead of mitotic cells.

NASA Discipline Radiation Health↗
NASA NTRS1998

The evolution of chromosomal instability in Chinese hamster cells: a changing picture?

PURPOSE: To investigate the kinetics of chromosomal instability induced in clones of Chinese hamster cells following X-irradiation. MATERIALS AND METHODS: X-irradiated clones of GM10115, human-hamster hybrid cells containing a single human chromosome 4 (HC4), have been previously established. These clones were defined as unstable if they contained > or = three subpopulations of cells with unique rearrangements of HC4 as detected by FISH. Stable and unstable clones were analysed by FISH and Giemsa staining at various times post-irradiation. RESULTS: While most of the stable clones continued to show chromosomal stability of HC4 over time, one became marginally unstable at approximately 45 population doublings post-irradiation. Clones exhibiting chromosomal instability had one of several fates. Many of the unstable clones were showed similar levels of instability over time. However, one unstable clone became stable with time in culture, while another became even more unstable over time. Cytogenetic analyses of all clones after Giemsa staining indicated that in some clones the hamster chromosomes were rearranged independent of HC4, demonstrating increased frequencies of chromatid breaks and dicentric chromosomes. The majority of the unstable clones also had higher yields of chromatid gaps. CONCLUSIONS: These data demonstrate the dynamic nature of chromosomal instability as measured by two different cytogenetic assays.

Non-NASA Center↗