RESUMEN
It has been shown that most of Drosophila melanogaster mutant lines obtained as a result of X-rays irradiation (XI) as well as of the combined action of XI and some chemical agents are characterized by decreased indexes of average (7-40 %) and maximal (1-35 %) life span. Insertion-excision processes at the instable genes white and cut are among the reasons of decreased vitality and shortened life span in induced mutants. Collection of neurodegenerative mutants has been obtained under the influence of ENU. Fast dying of flies and decreased vitality correlated with time point of neurodegenerations in brain structure.
Asunto(s)
Drosophila melanogaster , Longevidad , Mutación , Animales , Encéfalo/efectos de los fármacos , Encéfalo/patología , Encéfalo/efectos de la radiación , Cafeína/toxicidad , Drosophila melanogaster/efectos de los fármacos , Drosophila melanogaster/genética , Drosophila melanogaster/crecimiento & desarrollo , Drosophila melanogaster/efectos de la radiación , Etilnitrosourea/toxicidad , Genes de Insecto/efectos de los fármacos , Genes de Insecto/efectos de la radiación , Dosificación Letal Mediana , Longevidad/efectos de los fármacos , Longevidad/genética , Longevidad/efectos de la radiación , Cromosoma X/efectos de los fármacos , Cromosoma X/genética , Cromosoma X/efectos de la radiación , Rayos X/efectos adversosRESUMEN
PURPOSE: Non-random occurrence of induced chromosome breakpoints (BP) has been repeatedly reported. DNA synthesis and chromatin remodeling may influence chromosome BP localization. The CHO9 X chromosome exhibits an early replicating short euchromatic arm (Xpe) and a late replicating long heterochromatic arm (Xqh). We investigated the role played by DNA replication and related chromatin remodeling processes on BP distribution in eu/heterochromatin using the CHO9 X chromosome as a model. MATERIALS AND METHODS: BP induced by etoposide, a topoisomerase II inhibitor, as well as by the S-dependent clastogens ultraviolet-C light (UV-C) and methyl methanesulfonate (MMS) were mapped to CHO9 X chromosome arms. The base analogue 5-bromo-2'-deoxyuridine (BrdUrd) was pulse-added immediately after UV-C irradiation or during etoposide and MMS treatments (40 min) to identify cells in early S-phase (Xpe labeled) or late S-phase (Xqh labeled) after indirect BrdUrd immunodetection in metaphase spreads using primary anti-BrdUrd and secondary fluorochrome-tagged antibodies. RESULTS: During early S-phase, BP induced by etoposide and MMS mapped preferentially to Xpe while BP produced by UV-C localized randomly. BP induced by all agents during late S-phase clustered in Xqh. CONCLUSIONS: Results obtained suggest that replication time of eu/heterochromatin as well as chromatin remodeling may determine BP localization on the CHO9 X chromosome.
Asunto(s)
Aberraciones Cromosómicas/efectos de la radiación , Daño del ADN/genética , Replicación del ADN/fisiología , Replicación del ADN/efectos de la radiación , Cromosoma X/genética , Cromosoma X/efectos de la radiación , Animales , Células CHO , Cricetinae , Cricetulus , Relación Dosis-Respuesta en la Radiación , Dosis de RadiaciónRESUMEN
Cytogenetic analysis of more than 1500 randomly recovered lethal X chromosomes derived from 2000 and 3000 r X-ray exposures of post-meiotic male germ cells has made possible a plot of the distribution in different regions of the X chromosome of: (1) gene mutations associated with cytologically normal chromosomes, (2) mutations associated with chromosomal rearrangement breakpoints, (3) deficiencies, and (4) rearrangement breakpoints whether or not they are associated with mutations. The distribution of point mutations, vital loci and rearrangement breakpoints in different regions of the X chromosome is not proportional to either the number of bands or the relative DNA content. Further, the density of vital loci (those capable of mutating to a lethal allele) is quite different in some regions as compared to others. For example, vital loci in the 3AB region, which has been thoroughly studied by Judd and others, are at least as numerous as bands; whereas, the 3CD region, equally long, has only two vital loci. Other regions densely populated with vital loci include 1B, 1F-2A, 10A, 11A, and 19EF; sparsely populated regions include 6EF and 10B-10E. It seems reasonable to conclude that the recovered X-ray-induced mutants available for analysis do not represent a random sample of those initially induced in the exposed male germ cells.
Asunto(s)
Drosophila melanogaster/efectos de la radiación , Cromosomas Sexuales/efectos de la radiación , Cromosoma X/efectos de la radiación , Animales , Aberraciones Cromosómicas , Mapeo Cromosómico , Cruzamientos Genéticos , Femenino , Genes Letales , Genes Recesivos , Prueba de Complementación Genética , Ligamiento Genético , Masculino , MutaciónRESUMEN
We have performed a genetic analysis of the 14C region of the X chromosome of Drosophila melanogaster to isolate loss of function alleles of no-on-transient A (nonA; 14C1-2; 1-52.3). NONA is a nuclear protein common to many cell types, which is present in many puffs on polytene chromosomes. Sequence data suggest that the protein contains a pair of RNA binding motifs (RRM) found in many single-strand nucleic acid binding proteins. Hypomorphic alleles of this gene, which lead to aberrant visual and courtship song behavior, still contain normally distributed nonA RNA and NONA protein in embryos, and in all available alleles NONA protein is present in puffs of third instar larval polytene chromosomes. We find that complete loss of this general nuclear protein is semilethal in hemizygous males and homozygous cell lethal in the female germline. Surviving males show more extreme defects in nervous system function than have been described for the hypomorphic alleles. Five other essential genes that reside within this region have been partially characterized.
Asunto(s)
Proteínas de Drosophila , Drosophila melanogaster/genética , Proteínas Nucleares/genética , Cromosoma X , Alelos , Animales , Animales Modificados Genéticamente , Secuencia de Bases , Mapeo Cromosómico , Cromosomas/ultraestructura , Cruzamientos Genéticos , ADN/química , Cartilla de ADN , Drosophila melanogaster/embriología , Drosophila melanogaster/efectos de la radiación , Embrión no Mamífero/fisiología , Femenino , Genes Letales , Prueba de Complementación Genética , Masculino , Datos de Secuencia Molecular , Mutagénesis , Proteínas Nucleares/fisiología , Especificidad de Órganos , Fenotipo , Reacción en Cadena de la Polimerasa , Cromosoma X/efectos de la radiación , Rayos X , CigotoRESUMEN
A mutator, mu2a, in Drosophila melanogaster potentiates terminal deficiencies. In the female germ line the gamma mutant frequency induced by irradiation of mature oocytes with 5 Gy increases approximately twofold in heterozygotes and 20-fold in homozygotes compared with wild type. The recovery of terminal deficiencies is not limited to breaks close to chromosome ends; high frequencies of deficiencies can be recovered with breakpoints located in centric heterochromatin or near the middle of a chromosome arm. Lesions induced by gamma-rays are repaired slowly in mu2a oocytes, but become "fixed" as terminal deficiencies upon fertilization. A few lesions induced in wild-type females also produce terminal deficiencies. Mutator males do not exhibit an increase in terminal deletions, regardless of the germ cell stage irradiated. In addition, there is no increase in the mutant frequency when mature sperm are irradiated and fertilize eggs produced by mu2a females. The data are consistent with the hypothesis that lesions induced in sperm chromosomes are repaired after fertilization, while lesions induced in oocyte chromosomes are shunted instead to a mechanism that stabilizes broken chromosome ends. We propose that mu2 affects chromosomal structure during oogenesis, thereby modulating DNA repair.
Asunto(s)
Drosophila melanogaster/genética , Genes de Insecto , Mutación , Oocitos , Animales , Reparación del ADN/genética , Drosophila melanogaster/efectos de la radiación , Drosophila melanogaster/ultraestructura , Femenino , Heterocromatina/efectos de la radiación , Heterocromatina/ultraestructura , Hibridación in Situ , Masculino , Oocitos/crecimiento & desarrollo , Oocitos/efectos de la radiación , Oocitos/ultraestructura , Espermatozoides/efectos de la radiación , Espermatozoides/ultraestructura , Cromosoma X/genética , Cromosoma X/efectos de la radiación , Cromosoma X/ultraestructuraRESUMEN
We designed a system to determine whether dicentric chromosomes in Drosophila melanogaster break at random or at preferred sites. Sister chromatid exchange in a Ring-X chromosome produced dicentric chromosomes with two bridging arms connecting segregating centromeres as cells divide. This double bridge can break in mitosis. A genetic screen recovered chromosomes that were linearized by breakage in the male germline. Because the screen required viability of males with this X chromosome, the breakpoints in each arm of the double bridge must be closely matched to produce a nearly euploid chromosome. We expected that most linear chromosomes would be broken in heterochromatin because there are no vital genes in heterochromatin, and breakpoint distribution would be relatively unconstrained. Surprisingly, approximately half the breakpoints are found in euchromatin, and the breakpoints are clustered in just a few regions of the chromosome that closely match regions identified as intercalary heterochromatin. The results support the Laird hypothesis that intercalary heterochromatin can explain fragile sites in mitotic chromosomes, including fragile X. Opened rings also were recovered after male larvae were exposed to X-rays. This method was much less efficient and produced chromosomes with a strikingly different array of breakpoints, with almost all located in heterochromatin. A series of circularly permuted linear X chromosomes was generated that may be useful for investigating aspects of chromosome behavior, such as crossover distribution and interference in meiosis, or questions of nuclear organization and function.
Asunto(s)
Centrómero/genética , Aberraciones Cromosómicas/efectos de la radiación , Heterocromatina/genética , Cromosoma X/genética , Animales , Drosophila melanogaster , Heterocromatina/efectos de la radiación , Larva/genética , Larva/efectos de la radiación , Masculino , Meiosis/genética , Mitosis/genética , Cromosoma X/efectos de la radiaciónRESUMEN
SORB (selected observed residual breakpoints) induced by ionizing radiation or endonucleases are often non-randomly distributed in mammalian chromosomes. However, the role played by chromatin structure in the localization of chromosome SORB is not well understood. Anti-topoisomerase drugs such as etoposide are potent clastogens and unlike endonucleases or ionizing radiation, induce DNA double-strand breaks (DSB) by an indirect mechanism. Topoisomerase II (Topo II) is a main component of the nuclear matrix and the chromosome scaffold. Since etoposide leads to DSB by influencing the activity of Topo II, this compound may be a useful tool to study the influence of the chromatin organization on the distribution of induced SORB in mammalian chromosomes. In the present work, we compared the distribution of SORB induced during S-phase by etoposide or X-rays in the short euchromatic and long heterochromatic arms of the CHO9 X chromosome. The S-phase stage (early, mid or late) at which CHO9 cells were exposed to etoposide or X-rays was marked by incorporation of BrdU during treatments and later determined by immunolabeling of metaphase chromosomes with an anti-BrdU FITC-coupled antibody. The majority of treated cells were in late S-phase during treatment either with etoposide or X-rays. SORB induced by etoposide mapped preferentially to Xq but random localization was observed for SORB produced by X-rays. Possible explanations for the uneven distribution of etoposide-induced breakpoints along Xq are discussed.
Asunto(s)
Células CHO/efectos de los fármacos , Células CHO/efectos de la radiación , Rotura Cromosómica , Inhibidores Enzimáticos/toxicidad , Etopósido/toxicidad , Inhibidores de Topoisomerasa II , Cromosoma X/efectos de los fármacos , Cromosoma X/efectos de la radiación , Animales , Células CHO/ultraestructura , Cromátides/efectos de los fármacos , Cromátides/efectos de la radiación , Cromátides/ultraestructura , Aberraciones Cromosómicas , Mapeo Cromosómico , Cricetinae , Cricetulus , ADN/efectos de los fármacos , ADN/efectos de la radiación , Daño del ADN , Femenino , Fase S/efectos de los fármacos , Fase S/efectos de la radiación , Cromosoma X/genética , Cromosoma X/ultraestructuraRESUMEN
Fluorescence in situ hybridization procedures were used to examine the influence of chromosome locus on the frequency and type of chromosome aberrations induced by 60Co gamma rays in the human lymphoblastoid cell line TK6. Aberrations involving the X chromosome were compared to those involving the similarly sized autosome chromosome 7. When corrected for DNA content, acentric fragments were induced with equal frequency in the X and 7 chromosomes. Dose-dependent increases in chromosomal interchanges involving chromosome 7 were noted and the frequencies of balanced translocations and dicentrics produced were approximately equal. Chromosome interchanges involving the X chromosome were rare and showed no apparent dose dependence. Thus, while chromosomes 7 and X are equally sensitive to the induction of chromosome breaks, the X chromosome is much less likely to interact with autosomes than chromosome 7. The noninvolvement of the X chromosome in translocations with autosomes may reflect a more peripheral and separate location for the X chromosome in the mammalian nucleus.
Asunto(s)
Rayos gamma , Translocación Genética , Cromosoma X/efectos de la radiación , Línea Celular , Cromosomas Humanos Par 7/efectos de la radiación , Radioisótopos de Cobalto , Humanos , Hibridación Fluorescente in SituRESUMEN
Ionizing radiation is a well-known risk factor for sarcoma development. To investigate whether radiation-associated sarcomas are characterized by chromosome aberrations that distinguish them from de novo sarcomas, we identified those patients in our series of more than 500 cytogenetically abnormal sarcomas that fulfilled the following criteria: (1) each patient should have been irradiated for another malignancy at least 3 years prior to the sarcoma diagnosis, and (2) the sarcoma should have developed within the field of radiation. Ten patients fulfilling these criteria could be retrieved (median age at sarcoma diagnosis was 55 years, range 17-79; median latency period between primary tumor and radiation-associated sarcoma was 9 years, range 4-30). The diagnoses were typical for radiation-associated sarcomas: 2 each of malignant fibrous histiocytoma, leiomyosarcoma, and pleomorphic sarcoma, and 1 each of osteosarcoma, fibrosarcoma, myxofibrosarcoma, and spindle cell sarcoma. All 10 cases had relatively complex karyotypes with multiple, mostly unbalanced, structural rearrangements, similar to what has been reported in de novo sarcomas of the corresponding histologic subtypes. The only cytogenetic features that were unusually frequent among the radiation-associated sarcomas were the finding of unrelated clones in 3 cases, and loss of material from chromosome arm 3p, in particular 3p21-3pter, in 8 cases. Loss of the same chromosome segment has been described in 4 of the 8 previously published cases of radiation-associated sarcomas that have been analyzed after short-term culturing, which makes this imbalance significantly (P < 0.001) more frequent among radiation-associated sarcomas (12 of 18 cases) than among unselected cases of the corresponding histologic subtypes (74 of 282 cases). In contrast to the cytogenetic results, no 3p deletions were detected among the 6 cases of the present series that could be analyzed by comparative genomic hybridization (CGH). The most frequent imbalance detected by CGH was gain of 15cen-q15 (3 cases), followed by loss of chromosome 13 and gain of 5p, and 7cen-q22, each detected in 2 cases.
Asunto(s)
Aberraciones Cromosómicas/genética , Cromosomas Humanos Par 3/efectos de la radiación , Neoplasias Inducidas por Radiación/genética , Sarcoma/genética , Adolescente , Adulto , Anciano , Trastornos de los Cromosomas , Cromosomas Humanos Par 1/genética , Cromosomas Humanos Par 1/efectos de la radiación , Cromosomas Humanos Par 3/genética , Femenino , Humanos , Hibridación Fluorescente in Situ , Cariotipificación , Masculino , Persona de Mediana Edad , Hibridación de Ácido Nucleico , Cromosoma X/genética , Cromosoma X/efectos de la radiaciónRESUMEN
The induction of chromosome exchanges was investigated in SW-1573 human lung tumour cells radiosensitized with iododeoxyuridine (IdUrd) and irradiated with gamma-rays. Following treatment chromosome 2 and X were analyzed using fluorescence in situ hybridization (FISH) with chromosome-specific DNA libraries. The yield of chromosome exchanges involving chromosome 2 was higher than those involving chromosome-X. On the basis of the DNA content the relative involvement of the X-chromosome in exchange frequencies after 2 Gy was much higher than of chromosome 2. After 4 Gy the relative involvement of both chromosomes in exchanges is approximately equal. After radiosensitization, increased chromosome exchange frequencies are observed in both studied chromosomes. For the total chromosome exchange frequencies the sensitizer enhancement ratio (SER) at 2 Gy is 1.8 and 1.3 for chromosome 2 and X respectively. The SER at 4 Gy for total exchange frequencies is 1.6 and 1.9 chromosome 2 and X respectively. For reciprocal exchanges at 2 Gy higher SER values and at 4 Gy lower SER values were observed for both chromosomes.
Asunto(s)
Carcinoma de Células Escamosas/patología , Cromosomas Humanos Par 2/efectos de la radiación , Rayos gamma , Idoxuridina/farmacología , Neoplasias Pulmonares/patología , Fármacos Sensibilizantes a Radiaciones/farmacología , Translocación Genética/efectos de la radiación , Cromosoma X/efectos de la radiación , Aberraciones Cromosómicas , Cromosomas Humanos Par 2/efectos de los fármacos , Daño del ADN , Reparación del ADN , Relación Dosis-Respuesta en la Radiación , Humanos , Hibridación Fluorescente in Situ , Translocación Genética/efectos de los fármacos , Células Tumorales Cultivadas/efectos de los fármacos , Células Tumorales Cultivadas/efectos de la radiación , Cromosoma X/efectos de los fármacosRESUMEN
PURPOSE: To study the frequencies and distribution of X-ray-induced chromosomal aberrations in different arms as well as different regions of the long arms of Chinese hamster X chromosomes by fluorescence in situ hybridization (FISH). MATERIAL AND METHODS: Female embryonic primary cells of Chinese hamster were exposed to 1 and 4 Gy X-rays during the G1 stage and metaphases were collected 20 h later with colcemid-blocking. Induced aberrations involving different arms as well as different regions of the long arm of the X chromosomes were analysed by three-colour FISH using arm-specific painting probes. Distributions of aberrations in the arms were statistically analysed by chi2-test, with the hypothesis that aberrations are proportionally distributed on the basis of their relative lengths of the arms. RESULTS: The long arms of the X chromosomes were frequently involved in breaks than was the short arm. The result of the chi2-test indicates a non-proportional distribution of breaks between the arms, while exchanges (dicentrics and translocations) involving the arms were proportionally distributed. Differential involvement of regions of the long arm, i.e. Xq1 and Xq2, in breaks was also observed. Xq21, a known common fragile site in the X chromosome, was often involved in terminal deletions. CONCLUSION: Arm-specific probes of Chinese hamster chromosomes are useful for the detailed study of X-ray-induced aberrations in the X chromosome. The heterogeneity of the Chinese hamster X chromosome in response to X-ray-induced aberrations exists not only between the short (euchromatin) and the long (heterochromatin) arms, but also between different heterochromatic regions of the long arm of the X chromosome.
Asunto(s)
Aberraciones Cromosómicas , Heterocromatina/efectos de la radiación , Cromosoma X/efectos de la radiación , Animales , Células Cultivadas , Cricetinae , Cricetulus , Relación Dosis-Respuesta en la Radiación , Embrión de Mamíferos , Femenino , Heterocromatina/genética , Hibridación Fluorescente in Situ , Rayos XRESUMEN
A total of 255 chromosomal aberrations induced by X-rays in G1 phase of the cell cycle were scored in 600 G-banded metaphases prepared from Chinese hamster female cells. On the basis of a detailed analysis of these aberrations a total of 441 chromosomal breakpoints were mapped to the individual Chinese hamster chromosomes and their bands. More breakpoints were mapped to G-light (80.5%) than to G-dark (19.5%) bands. Chromosomal distribution of breakpoints revealed that chromosomes 5 and 8 had significantly more exchange breakpoints than expected on the basis of chromosomal length, whereas the X chromosome had significantly more terminal deletion breakpoints than expected. At the same time chromosomes 5 and 8 had a deficiency of terminal deletions, whereas the X chromosome had significant deficiency of exchange breakpoints. These results indicate that radiation-induced exchange and terminal deletion breakpoints, as observed in the first postirradiation metaphase, have different patterns of distribution in Chinese hamster chromosomes. Clustering of terminal deletions in the long arms of X chromosomes, which are entirely occupied by heterochromatin, suggests that chromosomal repair mechanisms responsible for rejoining of chromosomal breaks are less effective in heterochromatic than in other genomic regions.
Asunto(s)
Aberraciones Cromosómicas , Bandeo Cromosómico , Interfase/efectos de la radiación , Cromosoma X/efectos de la radiación , Animales , División Celular , Línea Celular , Deleción Cromosómica , Inversión Cromosómica , Cricetinae , Femenino , Translocación GenéticaRESUMEN
The effects of a low dose (0.1-20 mGy) preirradiation with X-rays followed by a higher dose (2 Gy) of the same radiation on the recovery of the genetic damage induced as dominant lethals in mature oocytes (stage 14) of different strains of Drosophila melanogaster were investigated. The response was shown to be dependent on the genotype of the flies tested, since lower frequencies of dominant lethals (DL) were only obtained in strains carrying the white mutation. Based on these observations experiments to locate the genetic factor responsible for the adaptive response (AR) were performed. This factor was found to be in a specific region of the X-chromosome. Additional experiments were carried out to give information on the minimal dose required to induce the AR. The results showed that the lowest dose needed is 0.2 mGy. Increasing the conditioning X-ray dose had no influence on the response.
Asunto(s)
Adaptación Fisiológica/genética , Adaptación Fisiológica/efectos de la radiación , Daño del ADN/genética , Drosophila melanogaster/genética , Drosophila melanogaster/efectos de la radiación , Animales , Muerte Celular/efectos de la radiación , Relación Dosis-Respuesta en la Radiación , Drosophila melanogaster/fisiología , Femenino , Variación Genética , Genotipo , Masculino , Oocitos/fisiología , Oocitos/efectos de la radiación , Fenotipo , Cromosoma X/fisiología , Cromosoma X/efectos de la radiaciónRESUMEN
PURPOSE: It is generally accepted that chromosome exchanges in irradiated cells are formed through interactions between separate DNA double-strand breaks (DSB). Here we tested whether non-irradiated DNA participates in the formation of chromosome aberrations when complex DNA DSB are induced elsewhere in the nucleus. MATERIALS AND METHODS: Synchronized Chinese hamster cells containing an X chromosome with a late replicating q arm (X(q) domain) were labelled with 125I-iododeoxyuridine (125IdUrd) in a period of S-phase when the vast majority of the X(q) domain was not replicating. DNA damage from 125I decay was accumulated at the G1/S border while the cells were stored in liquid nitrogen. Decay of 125I induced DSB in the immediate vicinity of the 125I atom. Chromosome aberrations involving what is essentially the 125I-free X domain were scored at the first mitosis after cell thawing. As a positive control, cells were treated with 125IdUrd at a later period in S-phase when the X(q) domain replicates, yielding a labelled X(q) domain. RESULTS: The 125I-free X(q) domain exhibited chromosome aberrations (exchanges and fragments). The frequency of these aberrations was linearly dependent on the number of 125I decays elsewhere in the cell nucleus. The efficiency of formation of chromosome aberrations by the 125I-free X(q) domain was approximately half of that observed in the 125I-labelled X(q) domain. CONCLUSIONS: The involvement of the 125I-free X(q) domain in chromosome aberrations suggests that DNA not damaged by the decay of incorporated 125I can interact with damaged DNA, indicating the existence of an alternative pathway for the formation of chromosome aberrations.
Asunto(s)
Núcleo Celular/genética , Núcleo Celular/efectos de la radiación , Cromatina/genética , Aberraciones Cromosómicas/efectos de la radiación , Animales , Línea Celular , Núcleo Celular/metabolismo , Cromatina/metabolismo , Cricetinae , Daño del ADN , Idoxuridina/metabolismo , Hibridación Fluorescente in Situ , Radioisótopos de Yodo , Modelos Genéticos , Cromosoma X/genética , Cromosoma X/metabolismo , Cromosoma X/efectos de la radiaciónRESUMEN
PURPOSE: To study the relationship between cell reproductive death and exchange frequency in SW-1573 human lung tumour cells with and without incorporated iodo-deoxyuridine (IdUrd) following irradiation of plateau-phase cultures with y-rays. METHOD: Linear-quadratic (LQ) analysis was performed for the data on clonogenic survival and on the frequency of chromosomal exchanges studied with fluorescence in situ hybridization in chromosomes X and 2. RESULTS: Differences in the LQ parameters alpha and beta of both non-sensitized and sensitized chromosomes were found. In both chromosomes an increase in the number of chromosomal exchanges in IdUrd-radiosensitized cells compared with non-sensitized cells was observed. The alpha-enhancement factors of 1.7 and 1.9 for the X-chromosome and for chromosome 2, respectively, are similar. For the X-chromosome, the beta coefficient increased by a factor of 3.9 and for chromosome 2 by a factor of 1.4. After correction to a full genome equivalence, no significant difference in alpha was found between chromosomes X and 2 for both control and sensitized cells. In contrast, an almost 2.8 times higher beta was found for the sensitized X-chromosome compared to this value for chromosome 2. CONCLUSIONS: It can be concluded that the linear-quadratic analysis of dose-response relationships offers insights into the correlation between cell survival and induction of exchanges in non-sensitized and radiosensitized cells.
Asunto(s)
Carcinoma de Células Escamosas/patología , Aberraciones Cromosómicas , Cromosomas Humanos Par 2/efectos de la radiación , Idoxuridina/farmacología , Neoplasias Pulmonares/patología , Inhibidores de la Síntesis del Ácido Nucleico/farmacología , Fármacos Sensibilizantes a Radiaciones/farmacología , Cromosoma X/efectos de la radiación , Carcinoma de Células Escamosas/radioterapia , Carcinoma de Células Escamosas/ultraestructura , Muerte Celular/efectos de la radiación , División Celular/efectos de la radiación , Supervivencia Celular/efectos de los fármacos , Supervivencia Celular/efectos de la radiación , Terapia Combinada , Relación Dosis-Respuesta a Droga , Humanos , Idoxuridina/metabolismo , Hibridación Fluorescente in Situ , Neoplasias Pulmonares/radioterapia , Neoplasias Pulmonares/ultraestructura , Inhibidores de la Síntesis del Ácido Nucleico/metabolismo , Fármacos Sensibilizantes a Radiaciones/metabolismo , Timidina/metabolismo , Células Tumorales Cultivadas/efectos de los fármacos , Células Tumorales Cultivadas/efectos de la radiaciónRESUMEN
The pattern of titrated thymidine (3H-TdR), a direct precursor of DNA, induced aberrations on the X chromosome of Gryllotalpa fossor was examined. 3H-TdR produced aberrations randomly distributed over the entire length of the X chromosome; breaks were observed in both the eu- and the heterochromatic arms of the X chromosome in both the sexes. Since the eu- and the heterochromatic arms cannot be distinguished cytologically in this insect, the presence of aberrations on both arms of the same X chromosome in the male and damage to both X chromosomes in the female indicate that both euchromatic and heterochromatic regions (facultative or constitutive) are equally liable to aberrations induced by H-TdR. This is in contrast to the non-random induction of aberrations by 3H-UdR, which causes chromosome damage due to the proximity of the labeled RNA to the DNA template during transcription.
Asunto(s)
Aberraciones Cromosómicas , Mutagénesis , Timidina/toxicidad , Tritio/toxicidad , Cromosoma X/efectos de la radiación , Animales , Femenino , Masculino , OrtópterosRESUMEN
This paper describes the genetic analysis of X-ray-induced mutations at several visible loci (yellow, white, Notch, vermilion and forked) located on the X-chromosome of Drosophila melanogaster after recovery in excision repair-deficient condition (mus-201). A total of 118 mutations observed in 83636 F1 females were analyzed. The white mutations in particular have been investigated at the molecular level. The results show that: (1) the frequency of recovered whole-body mutations is similar or slightly lower in repair-deficient than in repair-proficient condition (respectively 1.5 x 10(-4)/locus/15 Gy and 2.3 x 10(-4)/locus/15 Gy); (2) the frequency of observed mosaic mutations is significantly higher in the repair-deficient condition than in the proficient condition (respectively 2.7 x 10(-4)/locus/15 Gy and 0.9 x 10(-4)/locus/15 Gy); (3) the analysis of F2 male lethal mutations and the cytological analysis of the recovered mutations in the excision repair-deficient condition indicate a decrease in mutations associated with gross chromosomal aberrations (including multilocus deletions); (4) at the molecular level, the spectrum of recovered intragenic mutations is similar after excision-deficient and -proficient repair. These results indicate that excision repair is involved in X-ray-induced DNA damage that is repaired efficiently in the normal repair condition, but bypassed in the excision repair-deficient condition, leading to mosaic mutations. In addition, lesions that apparently cannot be bypassed by DNA replication lead to a decrease in the fraction of mutations due to gross chromosomal aberrations among the whole-body mutations.
Asunto(s)
Reparación del ADN , Drosophila melanogaster/genética , Mutación , Cromosoma X/efectos de la radiación , Animales , Secuencia de Bases , Femenino , Masculino , Datos de Secuencia Molecular , Mapeo RestrictivoRESUMEN
The X-ray induction of recessive visible specific locus mutations at 14 X-chromsome loci was studied in Drosophila melanogaster using the "Maxy" technique. The X-ray exposure was 3000 R to 5-day-old males and the sampling of germ cells was restricted to mature spermatozoa. Presumptive mutant females recovered in the F1 generation were tested for transmission, allelism, fertility and viability in males. A total of 128 mutations (115 completes and 13 mosaics including those that were male viable as well as male-lethal) recovered among 38 898 female progeny were found to be transmitted. On the basis of the above frequency, the average mutation rate can be estimated as 7.8 X 10(-8)/locus/R; for mutations that were viable and fertile in males, the rate is 3.0 X 10(-5)/locus/R (49 mutations among 38 898 progeny). The frequency of mutations at the different loci encompassed a wide range: while no mutations were recovered at the raspberry and carnation loci, at others, the numbers ranged from 1 at echinus to 31 at garnet; in addition, the proportion of mutations that was male-viable was also different, depending on the locus. Schalet's extensive data on spontaneous mutations at 13 (of the 14 loci employed in the present study) loci permit an estimate of the spontaneous rate which is 6.1 X 10(-6)/locus (a total of39 mutations among 490 000 progeny); for mutations that were viable and fertile in males, the rate is 3.0 X 10(-6)/locus (19 mutations among 490 000 progeny). The mutability of the different loci varied over a 9-fold range. When the different loci are ranked depending on their relative mutability (for spontaneous and induced mutations) it is found that in general, loci that mutate spontaneously relatively more frequently are also those at which more mutations have been recovered in the radiation experiments and likewise, those that are less mutable spontaneously are also those that mutate less after irradiation. Since the data are limited, it is concluded that the above finding is not inconsistent with the assumption of proportionality between spontaneous and induction rates of mutations. On the basis of the above results, a doubling dose of 100 R can be calculated for the X-ray induction of specific-locus mutations in Drosophila spermatozoa.
Asunto(s)
Drosophila melanogaster/genética , Mutación , Cromosomas Sexuales , Cromosoma X , Animales , Relación Dosis-Respuesta en la Radiación , Femenino , Genes Recesivos , Masculino , Cromosomas Sexuales/efectos de la radiación , Cromosoma X/efectos de la radiación , Rayos XRESUMEN
A total X-ray dose of 50 Gy was applied to the nematode Panagrellus redivivus using dose-rates ranging from 0.23 Gy/min to 10.49 Gy/min, and the frequency of lethal X-chromosomes was determined. This frequency ranged from approximately 1.6% at the lower dose-rate to 4.3% at the highest dose-rate, indicating a dose-rate dependency of mutation frequency in the spermatogonia and oogonia of this organism.
Asunto(s)
Mutación , Nematodos/efectos de la radiación , Cromosoma X/efectos de la radiación , Animales , Cruzamientos Genéticos , Relación Dosis-Respuesta en la Radiación , Femenino , Frecuencia de los Genes , Genes Letales/efectos de la radiación , Masculino , Nematodos/genética , Rayos XRESUMEN
A series of X-irradiation experiments was carried out using Drosophila melanogaster females homozygous for a third chromosome mutator gene and females which had a similar genetic background except that the mutator-bearing third chromosomes were substituted by normal wild-type chromosomes. The mutator females had been previously shown by Gold and Green to manifest a higher level of radiation-induced mutability (as measured by the X-ray-induction of sex-linked recessive lethals) in their pre-meiotic germ cells compared to normal females at an exposure of 100 R. In the presence work, the sensitivity of the pre-meiotic germ cells of mutator and normal females to the X-ray induction (2000 R) of sex-linked recessive lethals was studied. In addition, experiments were conducted to examine the sensitivity of the immature (stage 7; prophase I of meiosis) oocytes of both kinds of females to the induction of dominant lethals, X-linked recessive lethals and X-chromosome losses. The result show that in pre-meiotic germ cells, the frequencies of radiation-induced recessive lethals are similar in both kinds of females. However, the proportion of these mutations that occur in clusters of size 3 and higher, is higher in mutator than in normal females. In stage-7 oocytes, the frequencies of radiation-induced dominant lethals and sex-linked recessive lethals were similar in both kinds of females. The X-loss frequencies however, were consistently higher in mutator females although statistical significance was obtained only at higher exposures (3000 and 3750 R) and not at lower ones (750-2250 R). Possible reasons for the discrepancy between the present results and those of Gold and Green with respect to pre-meiotic germ cells are discussed.