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Biomedical subjects

E G Wright

Publications and source records attributed to E G Wright.

At least 37 records · Page 2Linked to original sources
PubMed2000

Absence of delayed chromosomal instability in a normal human fibroblast cell line after 125I iododeoxyuridine.

PURPOSE: To seek the delayed appearance of chromosomal abnormalities in human fibroblasts exposed to the Auger electron emitter 125I. MATERIALS AND METHODS: Normal untransformed human fibroblasts, HF19, were exposed to a concentration of [I125]IUdR, which allowed the survival of 37% of clonogens. Chromosomal analysis using both conventional Giemsa and fluorescence in situ hybridization (FISH) was undertaken on non-clonal bulk cultures from 2 to 39 days after treatment. RESULTS: The data show a declining level of unstable aberrations in the progeny of HF19 fibroblasts exposed to [I125]IUdR, eventually reaching control levels. CONCLUSIONS: The results provide evidence that [125I]IUdR does not induce ongoing chromosomal instability in long-term culture, and gives further support to the use of Auger-electron emitting radionuclides in the treatment and diagnosis of tumours.

Cell Line↗
PubMed1999

An E mu-BCL-2 transgene facilitates leukaemogenesis by ionizing radiation.

Clonogenic murine B cell precursors are normally ultrasensitive to apoptosis following genotoxic exposure in vitro but can be protected by expression of an E mu-BCL-2 transgene. Such exposures are likely to be mutagenic. This in turn suggests that a level of in vivo genotoxic exposure that usually has minimal pathological consequences might become leukaemogenic when damaged cells fail to abort by apoptosis. If this were to be the case, then the cell type that becomes leukaemic and the chromosomal/molecular changes that occur would also be of considerable interest. We tested this possibility by exposing E mu-BCL-2 and wild-type mice of differing ages to a single dose of X-irradiation of 1-4 Gy. Young (approximately 4-6 weeks) transgenic mice developed leukaemia at a high rate following exposure to 2 Gy but adult mice (4-6 months) did not. Exposure to 4 Gy produced leukaemia in both young and adult transgenic mice but at a higher frequency in the former. Leukaemic cell populations showed clonal rearrangements of the IGH gene but in most cases analysed had immunophenotypic features of an early B lympho-myeloid progenitor population which has not previously been recorded in radiation leukaemogenesis. Molecular cytogenetic analysis of leukaemic cells by banded karyotype and FISH revealed a consistent double abnormality: trisomy 15 plus an interstitial deletion of chromosome 4 that was confirmed by LOH analysis.

Animals↗
PubMed1999

Inherited and inducible chromosomal instability: a fragile bridge between genome integrity mechanisms and tumourigenesis.

Cancer is a multi-step process evolving as the result of the accumulation of a number of mutational events. The growing body of evidence implicating genetic instability as a key feature of this evolutionary process and the risk of malignancy associated with chromosomal instability syndromes highlight the importance of understanding the mechanisms that cells use to maintain the integrity of their genomes. Classic examples of inherited chromosomal instability with cancer predisposition are Bloom's syndrome, ataxia telangiectasia, and Fanconi anaemia, although the mechanisms involved are far from understood. Selected features of these inherited disorders are reviewed to provide a background to the more recently discovered inducible chromosomal instability, a phenotype in which apparently normal cells that have survived ionizing radiation and certain chemical insults may produce descendants exhibiting a high frequency of de novo chromosome aberrations and gene mutations. The phenotype is induced at frequencies considerably greater than conventional mutation frequencies but little is understood of the underlying mechanism(s). To date, chromosomal instability induced by ionizing radiation has been the most extensively studied phenotype and it is evident that the expression of inducible instability has a strong dependence on the type of radiation exposure, the cell type irradiated, and the genetic 'predisposition' of the irradiated cell.

Animals↗
PubMed1999

An improved micro-method for obtaining chromosome preparations from individual haemopoietic colonies.

A robust method for obtaining chromosome preparations from individual haemopoietic colonies in semi-solid media is described. The accumulation of metaphases and the hypotonic treatment of cells were carried out in the culture dish and individual colonies were transferred onto poly-L-lysine-treated slides and fixed stepwise prior to staining. The technique produced high yields of well-spread metaphases facilitating clonal cytogenetic analysis.

Animals↗
PubMed1999

Identification and characterization of three subtypes of radiation response in normal human urothelial cultures exposed to ionizing radiation.

In an attempt to assess genetic variation underlying the variation in human responses to radiation exposure, measurements of apoptosis, necrosis and induction of key proteins were made in primary explant cultures of human normal urothelium and correlated with growth post- exposure to a range of doses of (60)Co. These data were validated by similar experiments using CBA/H and C57/BL6 mouse strains, known to exhibit genetically determined differences in response to radiation. The data for human tissues show a wide variation in response with three broad categories being identifiable. The commonest had a hypersensitive response involving considerable apoptosis in the low dose region, followed by 'induction' of a survival response at higher doses involving the persistence of abnormal cells. The pattern of gene expression was consistent with suppression of apoptosis. The second category showed no induction of survival and considerable necrosis was seen in the progeny. The rarest category showed an extremely hypersensitive low dose response and despite induction of a survival response, the sensitivity to higher doses was very severe. Considerable apoptosis and necrosis were seen in these cultures. In the mouse experiments, strain CBA/H (mice known to exhibit genetic instability post-irradiation) had lower levels of delayed cell death and apoptosis than C57/BL6 mice (which exhibit significantly less instability). It is concluded that there is a variation in response to radiation between human patient cultures which is detectable in this system and which is consistent with a pattern of radiation- induced delayed death/apoptosis correlating with long-term genomic stability. The mouse experiments demonstrate the importance of genetic factors in determining these responses.

Animals↗
PubMed1998

Chromosomal instability in the descendants of unirradiated surviving cells after alpha-particle irradiation.

We have demonstrated chromosomal instability in the clonal descendants of hemopoietic stem cells after irradiating murine bone marrow with alpha-particles. However, because cells that are irradiated by alpha-particles are defined by a Poisson distribution of individual particle traversals, there is an inevitable proportion of unirradiated cells in the surviving population. The calculated expected proportions of irradiated and nonirradiated cells indicate that the number of clonogenic cells transmitting chromosomal instability is greater than the number expected to be hit and survive. To investigate further this discrepancy, we studied the effects of interposing a grid between the cells and the alpha-particle source so that the surviving population consists predominantly of untraversed stem cells. Comparison with the same irradiation conditions without the grid reveals that the same level of instability is induced. The data confirm that alpha-particles induce chromosomal instability but instability is demonstrated in the progeny of nonirradiated stem cells and must be due to unexpected interactions between irradiated and nonirradiated cells. This untargeted effect has important implications for mechanistic studies of radiation action and for assessment of radiation risk.

Abnormalities, Radiation-Induced↗
PubMed1998

p53-dependent X-ray-induced modulation of cytokine mRNA levels in vivo.

In vitro studies have shown that ionizing radiation can cause increases in some cytokine mRNA levels and activation of the nuclear NF-kappa B and/or AP1 transcription factors which have been implicated in the transcriptional regulation of many cytokine genes. Thus, radiation-induced upregulation of cytokine mRNAs appeared to be in part a direct consequence of transcription factor activation. To test this in vitro model in vivo, the effects of whole-body X-irradiation (0-10 Gy) on cytokine and other gene mRNA levels have been examined in mice. Increases and decreases in cytokine mRNA levels were detected in tissues which underwent an early wave of apoptosis (bone marrow and/or spleen), but not in more radioresistant tissues (kidney, liver, brain, and heart). Some mouse strain-specific differences were observed, but none of the changes in mRNA level was detected in p53-/- mice. As activation of the NF-kappa B and AP1 transcription factors was not detected in early-(spleen) or late-(liver) responding tissues in 10 Gy X-irradiated p53+/+ mice in vivo, it is concluded that the modulation of cytokine gene expression in vivo is p53-dependent and indirectly associated with apoptosis.

Animals↗
PubMed1998

Radiation-induced transmissable chromosomal instability in haemopoietic stem cells.

Heritable radiation-induced genetic alterations have long been assumed to be "fixed" within the first cell division. However, there is a growing body of evidence that a considerable fraction of cells surviving radiation exposure appear normal, but a variety of mutational changes arise in their progeny due to a transmissible genomic instability. In our investigations of G-banded metaphases, non-clonal cytogenetic aberrations, predominantly chromatid-type aberrations, have been observed in the clonal descendants of murine and human haemopoietic stem cells surviving low doses (approximately l track per cell) of alpha-particle irradiations. The data are consistent with a transmissible genetic instability induced in a stem cell resulting in a diversity of chromosomal aberrations in its clonal progeny many cell divisions later. Recent studies have demonstrated that the instability phenotype persists in vivo and that the expression of chromosomal instability has a strong dependence on the genetic characteristics of the irradiated cell. At the time when cytogenetic aberrations are detected, an increased incidence of hprt mutations and apoptotic cells have been observed in the clonal descendants of (alpha-irradiated murine haemopoietic stem cells. Thus, delayed chromosomal abnormalities, delayed cell death by apoptosis and late-arising specific gene mutations may reflect diverse consequences of radiation-induced genomic instability. The relationship, if any, between these effects is not established. Current studies suggest that expression of these delayed heritable effects is determined by the type of radiation exposure, type of cell and a variety of genetic factors.

Alpha Particles↗
PubMed1998

Establishment and characterization of bone marrow stroma-dependent leukemia cell line, HB-1.

Radiation-induced M361 leukemia bearing mice (M361 mice) show characteristics of acute myelogenous leukemia (AML) with granulocytosis. Granulocyte-macrophage colony forming unit (CFU-GM) increased in the bone marrow and spleen and high activity of colony stimulating factor (CSF) was found in the sera of M361 mice. A cell line (HB-1) was established from the spleen cells of M361 mice. Injection of HB-1 cells induced a similar leukemic response as M361 in syngeneic mice. HB-1 cells did not survive in the suspension culture, but proliferated when cultured on hemopoietic supportive stromal cells (MS-10). HB-1 cells appear to be strictly dependent on the hemopoietic supportive bone marrow stroma, which would provide a useful model for the study of cell-cell interactions between hemopoietic cells and marrow stromal cells.

Animals↗
PubMed1998

Tumour induction by methyl-nitroso-urea following preconceptional paternal contamination with plutonium-239.

We have investigated the possibility that transgenerational effects from preconceptional paternal irradiation (PPI) may render offspring more vulnerable to secondary exposure to an unrelated carcinogen. 239Pu (0, 128 or 256 Bq g(-1)) was administered by intravenous injection to male mice, 12 weeks before mating with normal females. Two strains of mouse were used -- CBA/H and BDF1. Haemopoietic spleen colony-forming units (CFU-S) and fibroblastoid colony-forming units (CFU-F), a component of their regulatory microenvironment, were assayed independently in individual offspring at 6, 12 and 19 weeks of age. Bone marrow and spleen from each of these mice were grown in suspension culture for 2 or 7 days for assessment of chromosomal aberrations. Female BDF1 were injected with methyl-nitroso-urea (MNU) as a secondary carcinogen at 10 weeks of age and monitored for onset of leukaemia/lymphoma. Mean values of CFU-S and CFU-F were unaffected by preconceptional paternal plutonium-239 (PP-239Pu), although for CFU-F in particular there was an apparent increase in variation between individual animals. There was significant evidence of an increase in chromosomal aberrations with dose in bone marrow but not in spleen. By 250 days, 68% of MNU-treated control animals (no PPI) had developed thymic lymphoma (62%) or leukaemia (38%). The first case arose 89 days after MNU administration. In the groups with PPI, leukaemia/lymphoma developed from 28 days earlier, rising to 90% by 250 days. Leukaemia (65%) now predominated over lymphoma (35%). This second generation excess of leukaemia appears to be the result of PPI and may be related to inherited changes that affect the development of haemopoietic stem cells.

Animals↗
PubMed1998

Radiation-induced genomic instability in haemopoietic cells.

PURPOSE: To review studies of radiation-induced genomic instability in haemopoietic cells. MAJOR FINDINGS: Studies have demonstrated a high frequency of non-clonal, cytogenetic abnormalities in the clonal descendants of alpha-particle-irradiated (approximately one track per cell) primary murine and human haemopoietic stem cells in vitro. The induction of this phenomenon has a strong dependence on the genetic characteristics of the cells and is transmissible in vivo following transplantation of alpha-irradiated mouse bone marrow. In clonogenic cell cultures of alpha-irradiated haemopoietic cells, there is also an increased incidence of hprt mutations and an increased incidence of apoptosis. These effects may be regarded as the consequences of a destabilization of the genome collectively termed radiation-induced genomic instability. Instability is induced at very high frequencies suggesting that epigenetic changes may be a common underlying mechanism. Consistent with this suggestion is the finding of an enhanced and persisting oxy-radical activity in the descendants of irradiated stem cells, which is consistent with oxidative stress being an important feature of the mechanism(s) underlying the persistence of instability in haemopoietic cells. Recent studies have revealed that more clonogenic cells than are actually traversed by an alpha-particle are able to express the instability phenotype. These data are consistent with unexpected interactions between irradiated and non-irradiated cells but the mechanism of initiation of instability is not understood.

Alpha Particles↗
PubMed1998

Induction of lympho-haemopoietic malignancy: impact of preconception paternal irradiation.

PURPOSE: To investigate the effects of preconception paternal irradiation (PPI) from injected 239Pu on the susceptibility to induction of lympho-haemopoietic malignancy by subsequent irradiation or exposure to a chemical carcinogen. MATERIALS AND METHODS: The male CBA/H and DBA2 mouse was injected with 0, 128 or 256 Bqg(-1) 239Pu 12 weeks before mating with the normal CBA/H and C57B1 female respectively. CBA/H offspring were exposed to 3.3 Gy gamma-rays total body irradiation: BDF1 offspring were injected with 50 mg kg(-1) methyl nitrosourea (MNU). The offspring were assayed for changes in bone marrow progenitor cell numbers and chromosome aberrations and were followed up for subsequent induction of neoplasia. RESULTS: While the untreated mouse showed a normal distribution for cellularity, spleen colony-forming units (CFU-S) and fibroblastoid colony-forming units (CFU-F), significant numbers of PPI offspring presented levels outside the normal range. There was a tendency for them also to show increased, dose-related, levels of chromosomal aberrations. Offspring treated with irradiation or MNU developed an increased incidence of lympho-haemopoietic malignancies. CONCLUSIONS: These studies have shown that PPI results in offspring that are more susceptible to the induction of lymphohaemopoietic malignancy on encountering a secondary carcinogenic insult. This may be linked to inherited chromosomal instability and abnormal kinetics of haemopoiesis. The experiments indicate a potential mechanism by which an increased incidence of leukaemia may be linked to PPI.

Animals↗
PubMed1998

Radiation-induced chromosomal instability in human fibroblasts: temporal effects and the influence of radiation quality.

PURPOSE: To determine whether chromosomal instability is induced in human diploid fibroblasts by ionizing radiation and to investigate the effects of radiation quality by comparing X-rays, neutrons and alpha-particles. MATERIALS AND METHODS: Cells from two human diploid fibroblast lines, HF12 and HF19, were irradiated and analysed cytogenetically at 3, 20 and 35 population doublings post-irradiation. RESULTS: Exposure of HF19 cells to neutrons and alpha-particles resulted in a consistently increased frequency of unstable aberrations, particularly chromatid-type aberrations, compared to control cultures. Aberration frequency after X-irradiation was not significantly greater than controls at 20 population doublings but was significantly increased after 35 population doublings, although not to the same level as that following neutron or alpha-irradiation. No chromosomal instability was demonstrated in the progeny of HF12 cells after X-, neutron or alpha-particle irradiation. CONCLUSIONS: The data are consistent with the progeny of irradiated HF19 cells expressing chromosomal instability. All three radiations are effective in inducing instability, but the expression of the phenotype is influenced by radiation quality. The absence of radiation-induced chromosomal instability in HF12 cells may reflect the influence of genetic factors.

Alpha Particles↗
PubMed1997

Haemopoietic stem cells: their heterogeneity and regulation.

The maintenance of the various blood cell populations in mammals is achieved by the proliferation and differentiation of precursor cells located primarily in the bone marrow. These precursor cells are all derived from a common haemopoietic stem cell population that is established during embryogenesis and functions for the lifetime of the organism. An overview is given of the various assay systems for haemopoietic stem cells, how these assays have contributed to understanding the considerable heterogeneity within the stem cell compartment, the regulation of stem cells and the development of the haemopoietic system.

Animals↗
PubMed1997

Genetic factors influencing alpha-particle-induced chromosomal instability.

Alpha-particle-induced chromosomal instability in haemopoietic cells obtained from the CBA/H, DBA/2 and C57BL/6 inbred strains of mouse has been demonstrated at frequencies dependent on genotype. The CBA/H and DBA/2 strains may be regarded as 'sensitive' and the C57BL/6 strain as 'resistant'; resistance was dominant in cells from F1 hybrids. Previously, in cultures where we demonstrated radiation-induced chromosomal instability we also demonstrated an enhanced and persisting oxyradical activity. Quantitative differences in superoxide generation have now been correlated with genetically determined differences in the expression of chromosomal instability. Our findings demonstrate an important influence of genetic factors in alpha-particle-induced chromosomal instability.

Alpha Particles↗
PubMed1997

Delayed appearance of radiation-induced mutations at the Hprt locus in murine hemopoietic cells.

Earlier work in this laboratory identified high levels of non-clonal chromatid aberrations in the clonal descendants of murine hemopoietic stem cells after many cell divisions postirradiation with densely-ionizing, high linear energy transfer (LET) alpha-particles, but not with sparsely ionizing low LET X-rays. Using the Hprt locus as a marker, we have now demonstrated genomic instability in murine hemopoietic stem cells for greater than 20 cell divisions following both high and low LET irradiation. The increase in Hprt-deficient variants demonstrated following X- as well as alpha-particle and neutron irradiation indicates that there is a difference in the LET-dependence of delayed gene mutations and higher-order cytogenetic effects. Over 90% of the mutations identified arose in the expanding colonies after more than 12 cell divisions postirradiation and therefore cannot be attributed to the initial DNA damage. Such a high frequency of delayed mutations has important implications for mechanistic studies of radiation mutagenesis and for risk estimation.

Alpha Particles↗
PubMed1996

The p53 response to ionising radiation in adult and developing murine tissues.

The induction of the p53 response to ionising radiation has been studied during murine development and in the adult animal. The response has been assessed by precise quantitative assay of p53 protein levels in tissues and by immunohistochemistry. Newly developed transgenic mice in which a lacZ transgene is driven by a p53 response element have also been used to directly assess the transcriptional activity of the induced protein. There is striking developmental control of the p53 response so that in early development all tissues accumulate high levels of p53 following radiation and indeed p53 is present at elevated levels in some unirradiated tissues. Later in development clear heterogeneity of the p53 response becomes apparent, both in terms of the responses of individual tissues and of cell populations, within those tissues. The study of lacZ transgene expression and the occurrence of apoptosis in different tissues that accumulate p53 protein point to a further level of control regulating the nature and degree of the downstream response to elevated levels of p53 in cells. These findings have important implications for the susceptibility of different tissue types to carcinogenic and other insults. The early expression of the p53 response is consistent with novel models of p53 function that suggest it may have evolved principally as a defense against teratogenic insult that permits plasticity of development.

Age Factors↗