Biomedical subjects

C L Limoli

Publications and source records attributed to C L Limoli.

At least 19 recordsLinked to original sources

PubMed2006

Using superoxide dismutase/catalase mimetics to manipulate the redox environment of neural precursor cells.

Past work has shown that neural precursor cells are predisposed to redox sensitive changes, and that oxidative stress plays a critical role in the acute and persistent changes that occur within the irradiated CNS. Irradiation leads to a marked rise in reactive oxygen species (ROS) that correlates with oxidative endpoints in vivo and reductions in neurogenesis. To better understand the impact of oxidative stress on neural precursor cells, and to determine if radiation-induced oxidative damage and precursor cell loss after irradiation could be reduced, a series of antioxidant compounds (EUK-134, EUK-163, EUK-172, EUK-189) were tested, three of which possess both superoxide dismutase (SOD) and catalase activities and one (EUK-163) whose only significant activity is SOD. Our results show that these SOD/catalase mimetics apparently increase the oxidation of a ROS-sensitive fluorescent indicator dye, particularly after short (12 h) treatments, but that longer treatments (24 h) decrease oxidation attributable to radiation-induced ROS. Similarly, other studies found that cells incubated with CuZnSOD showed some increase in intracellular ROS levels. Subsequent data suggested that the dye-oxidising capabilities of the EUK compounds were linked to differences in their catalase activity and, most likely, their ability to catalyse peroxidative pathways. In unirradiated mice, the EUK-134 analogue induced some decrease of proliferating precursor cells and immature neurons 48 h after radiation, an effect that may be attributable to cytotoxicity and/or inhibition of precursor proliferation. In irradiated mice, a single injection of EUK-134 was not found to be an effective radioprotector at acute times (48 h). The present results support continued development of our in vitro model as a tool for predicting certain in vivo responses, and suggest that in some biological systems the capability to scavenge superoxide but produce excess H(2)O(2), as is known for CuZnSOD, may be potentially deleterious. Our results also show that the ability of catalase mimetics, like true catalases, to catalyse peroxidase reactions can complicate the interpretation of data obtained with certain fluorescent ROS-indicator dyes.

Animals↗

PubMed2006

Redox changes induced in hippocampal precursor cells by heavy ion irradiation.

Hippocampal precursors retain the capacity to proliferate and differentiate throughout life, and their progeny, immature neurons, can undergo neurogenesis, a process believed to be important in maintaining the cognitive health of an organism. A variety of stresses including irradiation have been shown to deplete neural precursor cells, an effect that inhibits neurogenesis and is associated with the onset of cognitive impairments. Our past work has shown that neural precursor cells exposed to X-rays or protons exhibit a prolonged increase in oxidative stress, a factor we hypothesize to be critical in regulating the function of these cells after irradiation and other stresses. Here we report that irradiation of hippocampal precursor cells with high-linear energy transfer (LET) 1 GeV/nucleon 56Fe ions leads to significantly higher levels of oxidative stress when compared to lower LET radiations (X-rays, protons). Irradiation with 1 Gy of 56Fe ions elicits twofold to fivefold higher levels of reactive oxygen species (ROS) compared to unirradiated controls, and at lower doses (<or=1 Gy) neural precursors exhibit a linear dose response 6 h after heavy ion exposure. The use of the antioxidant lipoic acid (LA) was able to reduce ROS levels below background levels when added before or after 56Fe ion irradiation. These results conclusively show that low doses of 56Fe ions can elicit significant levels of oxidative stress in neural precursor cells. Given the prevalence of heavy ions in space and the duration of interplanetary travel, these data suggest that astronauts are at risk for developing cognitive decrements. However, our results also indicate that antioxidants delivered before as radioprotective agents or after as mitigating agents hold promise as effective countermeasures for ameliorating certain adverse effects of heavy ion exposure to the CNS.

Animals↗

PubMed2002

DNA replication arrest in XP variant cells after UV exposure is diverted into an Mre11-dependent recombination pathway by the kinase inhibitor wortmannin.

Ultraviolet (UV) irradiation produces DNA photoproducts that are blocks to DNA replication by normal replicative polymerases. A specialized, damage-specific, distributive polymerase, Pol H or Pol h, that is the product of the hRad30A gene, is required for replication past these photoproducts. This polymerase is absent from XP variant (XP-V) cells that must employ other mechanisms to negotiate blocks to DNA replication. These mechanisms include the use of alternative polymerases or recombination between sister chromatids. Replication forks arrested by UV damage in virus transformed XP-V cells degrade into DNA double strand breaks that are sites for recombination, but in normal cells arrested forks may be protected from degradation by p53 protein. These breaks are sites for binding a protein complex, hMre11/hRad50/Nbs1, that colocalizes with H2AX and PCNA, and can be visualized as immunofluorescent foci. The protein complexes need phosphorylation to activate their DNA binding capacity. Incubation of UV irradiated XP-V cells with the irreversible kinase inhibitor wortmannin, however, increased the yield of Mre11 focus-positive cells. One interpretation of this observation is that two classes of kinases are involved after UV irradiation. One would be a wortmannin-resistant kinase that phosphorylates the Mre11 complex. The other would be a wortmannin-sensitive kinase that phosphorylates and activates the p53/large T in SV40 transformed XP-V cells. The sensitive class corresponds to the PI3-kinases of ATM, ATR, and DNA-PK, but the resistant class remains to be identified. Alternatively, the elevated yield of Mre11 foci positive cells following wortmannin treatment may reflect an overall perturbation to the signaling cascades regulated by wortmannin-sensitive PI3 related kinases. In this scenario, wortmannin could compromise damage inducible-signaling pathways that maintain the stability of stalled forks, resulting in a further destabilization of stalled forks that then degrade, with the formation of DNA double strand breaks.

Androstadienes↗

PubMed2002

Polymerase eta and p53 jointly regulate cell survival, apoptosis and Mre11 recombination during S phase checkpoint arrest after UV irradiation.

Xeroderma pigmentosum variant (XPV) cells lack the damage-specific polymerase eta and undergo a protracted arrest at the S phase checkpoint(s) following UV damage. The S phase checkpoints encompass several qualitatively different processes, and stimulate downstream events that are dependent on the functional state of p53. Primary fibroblasts with wild-type p53 arrest in S, and require a functional polymerase eta (pol eta) to carry out bypass replication, but do not recruit recombination factors for recovery. XPV cells with non-functional p53, as a result of transformation by SV40 or HPV16 (E6/E7), recruit the hMre11/hRad50/Nbs1 complex to arrested replication forks, coincident with PCNA, whereas normal transformed cells preferentially use the pol eta bypass replication pathway. The formation of hMre11 foci implies that arrested replication forks rapidly undergo a collapse involving double strand breakage and rejoining. Apoptosis occurs after UV only in cells transformed by SV40, and not in normal or XPV fibroblasts or HPV16 (E6/E7) transformed cells. Conversely, ultimate cell survival in XPV cells was much less in HPV16 (E6/E7) transformed cells than in SV40 transformed cells, indicating that apoptosis was not a reliable predictor of cell survival. Inhibition of p53 transactivation by pifithrin-alpha or inhibition of protein synthesis by cycloheximide did not induce hMre11 foci or apoptosis in UV damaged fibroblasts. Inhibition of kinase activity with wortmannin did not increase killing by UV, unlike the large increase seen with caffeine. Since HPV16 (E6/E7) transformed XPV cells were highly UV sensitive and not further sensitized by caffeine, it appears likely that caffeine sensitization proceeds through a p53 pathway. The S phase checkpoints are therefore, a complex set of different checkpoints that are coordinated by p53 with the capacity to differentially modulate cell survival, apoptosis, bypass replication and hMre11 recombination.

Acid Anhydride Hydrolases↗

PubMed2001

Attenuation of radiation-induced genomic instability by free radical scavengers and cellular proliferation.

To investigate the mechanisms of radiation-induced chromosomal instability, cells were irradiated in the presence of the free radical scavengers DMSO, glycerol, or cysteamine, in the presence of DMSO while frozen, or held in confluence arrest post-irradiation to permit cells to repair potentially lethal DNA damage. Clones derived from single progenitor cells surviving each treatment were then analyzed for the subsequent development of chromosomal instability. The presence of scavengers (+/- freezing) during irradiation, and the recovery from potentially lethal damage after irradiation led to an increase in cell survival that was accompanied by a decrease in the initial yield of chromosomal rearrangements. Furthermore, analysis of over 400 clones and 80,000 metaphases indicates that these same treatments reduced the incidence of instability at equitoxic doses when compared to controls irradiated in the absence of scavengers at ambient temperature. Results suggest that preventing reactive species from damaging DNA, promoting chemical repair of ionized DNA intermediates, or allowing enzymatic removal of genetic lesions, represent measures that reduce the total burden of DNA damage and reduce the subsequent onset of radiation-induced genomic instability.

Animals↗

PubMed2001

Nucleotide excision repair "a legacy of creativity".

The first half of the 20th century has seen an enormous growth in our knowledge of DNA repair, in no small part due to the work of Dirk Bootsma, Philip Hanawalt and Bryn Bridges; those honored by this issue. For the new millennium, we have asked three general questions: (A) Do we know all possible strategies of nucleotide excision repair (NER) in all organisms? (B) How is NER integrated and regulated in cells and tissues? (C) Does DNA replication represent a new frontier in the roles of DNA repair? We make some suggestions for the kinds of answers the next generation may provide. The kingdom of archea represents an untapped field for investigation of DNA repair in organisms with extreme lifestyles. NER appears to involve a similar strategy to the other kingdoms of prokaryotes and eukaryotes, but subtle differences suggest that individual components of the system may differ. NER appears to be regulated by several major factors, especially p53 and Rb which interact with transcription coupled repair and global genomic repair, respectively. Examples can be found of major regulatory changes in repair in testicular tissue and melanoma cells. Our understanding of replication of damaged DNA has undergone a revolution in recent years, with the discovery of multiple low-fidelity DNA polymerases that facilitate replicative bypass. A secondary mechanism of replication in the absence of NER or of one or more of these polymerases involves sister chromatid exchange and recombination (hMre11/hRad50/Nbs1). The relative importance of bypass and recombination is determined by the action of p53. We hypothesise that these polymerases may be involved in resolution of complex DNA structures during completion of replication and sister chromatid resolution. With these fascinating problems to investigate, the field of DNA repair will surely not disappoint the next generation.

Animals↗

PubMed2001

DNA polymerase eta undergoes alternative splicing, protects against UV sensitivity and apoptosis, and suppresses Mre11-dependent recombination.

Polymerase eta (pol eta) is a low-fidelity DNA polymerase that is the product of the gene, POLH, associated with the human XP variant disorder in which there is an extremely high level of solar-induced skin carcinogenesis. The complete human genomic sequence spans about 40 kb containing 10 coding exons and a cDNA of 2.14 kb; exon I is untranslated and is 6 kb upstream from the first coding exon. Using bacterial artificial chromosomes (BACs), the gene was mapped to human chromosome band 6p21 and mouse band 17D. The gene is expressed in most tissues, except for very low or undetectable levels in peripheral lymphocytes, fetal spleen, and adult muscle; exon II, however, is frequently spliced out in normal cells and in almost half the transcripts in the testis and fetal liver. Expression of POLH in a multicopy episomal vector proved nonviable, suggesting that overexpression is toxic. Expression from chromosomally integrated linear copies using either an EF1-alpha or CMV promoter was functional, resulting in cell lines with low or high levels of pol eta protein, respectively. Point mutations in the center of the gene and in a C-terminal cysteine and deletion of exon II resulted in inactivation, but addition of a terminal 3 amino acid C-terminal tag, or an N- or C-terminal green fluorescent protein, had no effect on function. A low level of expression of pol eta eliminated hMre11 recombination and partially restored UV survival, but did not prevent UV-induced apoptosis, which required higher levels of expression. Polymerase eta is therefore involved in S-phase checkpoint and signal transduction pathways that lead to arrest in S, apoptosis, and recombination. In normal cells, the predominant mechanism of replication of UV damage involves pol eta-dependent bypass, and Mre11-dependent recombination that acts is a secondary, backup mechanism when cells are severely depleted of pol eta.

Alternative Splicing↗

PubMed2001

A role for chromosomal instability in the development of and selection for radioresistant cell variants.

Chromosome instability is a common occurrence in tumour cells. We examined the hypothesis that the elevated rate of mutation formation in unstable cells can lead to the development of clones of cells that are resistant to the cancer therapy. To test this hypothesis, we compared chromosome instability to radiation sensitivity in 30 independently isolated clones of GM10115 human-hamster hybrid cells. There was a broader distribution of radiosensitivity and a higher mean SF(2)in chromosomally unstable clones. Cytogenetic and DNA double-strand break rejoining assays suggest that sensitivity was a function of DNA repair efficiency. In the unstable population, the more radioresistant clones also had significantly lower plating efficiencies. These observations suggest that chromosome instability in GM10115 cells can lead to the development of cell variants that are more resistant to radiation. In addition, these results suggest that the process of chromosome breakage and recombination that accompanies chromosome instability might provide some selective pressure for more radioresistant variants.

Animals↗

PubMed2001

DNA strand break yields after post-high LET irradiation incubation with endonuclease-III and evidence for hydroxyl radical clustering.

PURPOSE: To determine the increase in single- (SSB) and double-strand break (DSB) yields after post-high LET irradiation incubation of plasmid DNA with the endonuclease-III (endo-III) of Escherichia coli. MATERIALS AND METHODS: Plasmid DNA in aerobic aqueous solution was irradiated with one of five radiation types: 137Cs gamma-rays (LET approximately 0.3keV microm(-1)), 244Cm alpha-particles (140-190 keV microm(-1)), 4He ions (97 keV microm(-1)), 56Fe ions (143 keV microm(-1)) or 197Au ions (1,440 keV microm(-1)). The irradiated samples were then incubated with endo-III. SSB and DSB yields were quantified by agarose gel electrophoresis. RESULTS: Endo-III incubation produced an increase in the SSB and DSB yields. The increases were in general lower after the high LET irradiation than after gamma-irradiation. This may reflect inhibition of the activity of endo-III by the nearby DNA damage expected from high LET radiation. It can be shown that even if the activity of endo remains unchanged, significantly lower increases in SSB and DSB yields would still be expected. CONCLUSION: The results provide evidence for clustered DNA damage after high LET irradiation.

Cesium Radioisotopes↗

PubMed2000

Polymerase eta deficiency in the xeroderma pigmentosum variant uncovers an overlap between the S phase checkpoint and double-strand break repair.

The xeroderma pigmentosum variant (XPV) is a genetic disease involving high levels of solar-induced cancer that has normal excision repair but shows defective DNA replication after UV irradiation because of mutations in the damage-specific polymerase hRAD30. We previously found that the induction of sister chromatid exchanges by UV irradiation was greatly enhanced in transformed XPV cells, indicating the activation of a recombination pathway. We now have identified that XPV cells make use of a homologous recombination pathway involving the hMre11/hRad50/Nbs1 protein complex, but not the Rad51 recombination pathway. The hMre11 complexes form at arrested replication forks, in association with proliferating cell nuclear antigen. In x-ray-damaged cells, in contrast, there is no association between hMre11 and proliferating cell nuclear antigen. This recombination pathway assumes greater importance in transformed XPV cells that lack a functional p53 pathway and can be detected at lower frequencies in excision-defective XPA fibroblasts and normal cells. DNA replication arrest after UV damage, and the associated S phase checkpoint, is therefore a complex process that can recruit a recombination pathway that has a primary role in repair of double-strand breaks from x-rays. The symptoms of elevated solar carcinogenesis in XPV patients therefore may be associated with increased genomic rearrangements that result from double-strand breakage and rejoining in cells of the skin in which p53 is inactivated by UV-induced mutations.

Acid Anhydride Hydrolases↗

PubMed2000

Genomic instability induced by high and low LET ionizing radiation.

Genomic instability is the increased rate of acquisition of alterations in the mammalian genome, and includes such diverse biological endpoints as chromosomal destabilization, aneuploidy, micronucleus formation, sister chromatid exchange, gene mutation and amplification, variations in colony size, reduced plating efficiency, and cellular transformation. Because these multiple endpoints persist long after initial radiation exposure, genomic instability has been proposed to operate as a driving force contributing to genetic plasticity and carcinogenic potential. Many of these radiation-induced endpoints depend qualitatively and quantitatively on genetic background, dose and LET. Differences in the frequency and temporal expression of chromosomal instability depend on all three of the foregoing factors. On the other hand, many of these endpoints appear independent of dose and show bystander effects, implicating non-nuclear targets and epigenetic regulatory mechanisms. The present work will survey results concerning the LET dependence of genomic instability and the role of epigenetic mechanisms, with a particular emphasis on the endpoint of chromosomal instability.

Animals↗

PubMed2000

Chromosomal instability induced by heavy ion irradiation.

PURPOSE: To establish the dose-response relationship for the induction of chromosomal instability in GM10115 cells exposed to high-energy iron ions (1 GeV/nucleon, mean LET 146 keV/microm) and gold ions (11 GeV/nucleon, mean LET 1450 keV/microm). Past work has established that sparsely ionizing X-rays can induce a long-lived destabilization of chromosomes in a dose-dependent manner at an incidence of approximately 3% per gray. The present investigation assesses the capacity of High-Z and High-energy (HZE) particles to elicit this same endpoint. MATERIALS AND METHODS: Clonal populations derived from single progenitor cells surviving heavy-ion irradiation were analyzed cytogenetically to identify those clones showing a persistent destablization of chromosomes. RESULTS: Dose-response data, with a particular emphasis at low dose (< 1.0 Gy), indicate a frequency of approximately 4% per gray for the induction of chromosomal instability in clones derived from single progenitor cells surviving exposure to iron ions. The induction of chromosomal instability by gold ions was, however, less responsive to applied dose, as the observed incidence of this phenotype varied from 0 to 10% over 1-8 Gy. Both iron and gold ions gave dose-dependent increases in the yield of chromosomal aberrations (both chromosome- and chromatid-type) measured at the first mitosis following irradiation, as well as shoulderless survival curves having D0=0.87 and 1.1 Gy respectively. CONCLUSIONS: Based on the present dose-response data, the relative biological effectiveness of iron ions is 1.3 for the induction of chromosomal instability, and this indicates that heavy ions are only slightly more efficient than X-rays at eliciting this delayed phenotype.

Animals↗

PubMed1999

Critical target and dose and dose-rate responses for the induction of chromosomal instability by ionizing radiation.

To investigate the critical target, dose response and dose-rate response for the induction of chromosomal instability by ionizing radiation, bromodeoxyuridine (BrdU)-substituted and unsubstituted GM10115 cells were exposed to a range of doses (0.1-10 Gy) and different dose rates (0.092-17.45 Gy min(-1)). The status of chromosomal stability was determined by fluorescence in situ hybridization approximately 20 generations after irradiation in clonal populations derived from single progenitor cells surviving acute exposure. Overall, nearly 700 individual clones representing over 140,000 metaphases were analyzed. In cells unsubstituted with BrdU, a dose response was found, where the probability of observing delayed chromosomal instability in any given clone was 3% per gray of X rays. For cells substituted with 25-66% BrdU, however, a dose response was observed only at low doses (<1.0 Gy); at higher doses (>1.0 Gy), the incidence of chromosomal instability leveled off. There was an increase in the frequency and complexity of chromosomal instability per unit dose compared to cells unsubstituted with BrdU. The frequency of chromosomal instability appeared to saturate around approximately 30%, an effect which occurred at much lower doses in the presence of BrdU. Changing the gamma-ray dose rate by a factor of 190 (0.092 to 17.45 Gy min(-1)) produced no significant differences in the frequency of chromosomal instability. The enhancement of chromosomal instability promoted by the presence of the BrdU argues that DNA comprises at least one of the critical targets important for the induction of this end point of genomic instability.

Animals↗

PubMed1998

Apoptosis, reproductive failure, and oxidative stress in Chinese hamster ovary cells with compromised genomic integrity.

Chromosomal instability and persistent reproductive cell death show a significant correlation after cells are exposed to ionizing radiation. To examine the possible role of apoptosis in persistent reproductive cell death, we analyzed subsets of chromosomally stable and unstable clones for relationships between chromosome stability, reproductive integrity, and apoptosis. All clones were generated from the GM10115 cell line and derived from single progenitor cells surviving 10 Gy of X-rays, and all measurements were made approximately 60-80 generations after irradiation. The incidence of apoptosis, as measured by both annexin V binding of phosphatidylserine residues and terminal deoxynucleotidyl transferase labeling of DNA strand breaks, was significantly higher in chromosomally unstable clones than it was in chromosomally stable clones (P < 0.05; ANOVA and Student's t test). Furthermore, statistical analyses of the biological end points of persistent reproductive cell death and apoptosis were consistent, showing R2 values of 0.78 and 0.76, respectively. These results suggest that persistent reproductive cell death can, in part, be explained by the predisposition of a fraction of the clonal population to undergo apoptosis or necrosis. Immunological blot analyses of protein levels and DNA bandshift assays confirmed the mutant status of p53 in the host cell line, implying an apoptotic pathway that is independent of p53. Induction of apoptosis by agents such as actinomycin D, etoposide, and staurosporine and induction of necrosis by sodium azide were accompanied by an increase in the level of intracellular peroxy radicals and lipid peroxidation products, two independent end points that are typically associated with oxidative stress. Similar findings were observed in several subclones showing persistent apoptosis. These results suggest that the elevated levels of free radical damage that we detected were derived from the fraction of cells dying by apoptotic or necrotic processes. Possible mechanisms whereby oxidative stress may contribute indirectly to the perpetuation of chromosomal instability are discussed.

Animals↗

PubMed1998

DNA double-strand breaks, chromosomal rearrangements, and genomic instability.

DNA double-strand breaks can lead to chromosomal rearrangements at the first mitosis after exposure to the DNA strand-breaking agent. The evidence suggests a number of different pathways for DNA double-strand break rejoining in mammalian cells, but it is unclear what factors determine the fate of the induced break and whether or not it will lead to chromosomal rearrangement. If a cell does survive and proliferate after DNA cleavage, delayed chromosomal instability can be observed in the clonal descendants of the exposed cell. Most, but not all DNA double-strand breaking agents are effective at inducing this delayed chromosomal instability. In this paper, we review the evidence for the role of the DNA double-strand break in directly induced and delayed chromosomal rearrangements.

Animals↗

PubMed1998

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.

Animals↗

PubMed1998

Recombination involving interstitial telomere repeat-like sequences promotes chromosomal instability in Chinese hamster cells.

The physical termini of mammalian chromosomes are capped with tandem repeats of the telomere sequence (TTAGGG)n. After fluorescence in situ hybridization with a labeled (TTAGGG)n probe, telomere-repeat-like sequences are seen as discrete bands at distinct intrachromosomal sites in a variety of vertebrate species. There is increasing evidence that these sites may be hot-spots for chromosomal rearrangements, fragility and neoplasia. We have investigated whether the interstitial telomere bands found in hamster chromosomes from a human hamster hybrid cell line are hot-spots for chromosome rearrangements induced by DNA-damaging agents. Our data indicate that the interstitial telomere bands are involved in chromosomal rearrangements observed at the first mitosis after G1 exposure of cells to X-rays or restriction endonucleases at a four- to fivefold higher frequency than expected based on their size. In addition, we have extended these observations to demonstrate for the first time that these interstitial telomere-repeat-like sequences participate in the delayed chromosomal instability observed in the progeny of cells surviving X-ray-exposure at multiple generations after irradiation. In two highly unstable clones showing multiple populations of rearranged chromosomes, interstitial telomere bands were observed at the site of recombination between the human and hamster chromosomes at a five- to sixfold higher frequency than expected. There were also rearrangement and amplification of the interstitial telomere bands within the hamster chromosomes. These rearrangements occur during clonal expansion of cells surviving treatment with DNA-damaging agents and suggest a role for the interstitial telomere band in driving chromosomal instability. We conclude from the observed data that interstitial telomere bands function as recombinational hot-spots that participate in generating the diverse chromosome rearrangements observed both immediately and as a delayed effect of cellular exposure to DNA damaging agents.

Animals↗

PubMed1998

Induction of chromosome aberrations and delayed genomic instability by photochemical processes.

Exponentially growing cells cultured in medium containing bromodeoxyuridine, then exposed to UVA light in the presence of the dye Hoechst 33258, show significant levels of DNA strand breaks and base damage. This dye-bromodeoxyuridine-UVA photolysis treatment is markedly cytotoxic. We now demonstrate that exposure of cells to the agents used in photolysis leads directly to the formation of chromosome aberrations. Furthermore, we demonstrate that this photochemical treatment induces delayed chromosomal instability in clonal populations derived from single progenitor cells surviving photolysis. These results suggest that photolysis-induced DNA damage leads to chromosome rearrangements that could account for the observed cytotoxicity. Furthermore, in those cells surviving photolysis, the delayed effects of this treatment can be observed several generations after exposure and are manifested as compromised genomic integrity.

Animals↗