Biomedical subjects

W Martínez-López

Publications and source records attributed to W Martínez-López.

8 recordsLinked to original sources

PubMed2006

Modulation of chromosome damage localization by DNA replication timing.

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.

Animals↗

PubMed2006

Chromatin remodelling and chromosome damage distribution.

Histone acetylation/deacetylation constitute the most relevant chromatin remodelling mechanism to control DNA access to nuclear machinery as well as to mutagenic agents. Thus, these epigenetics mechanisms could be involved in processing DNA lesions into chromosomal aberrations. Although radiation-induced DNA lesions are believed to occur randomly, in most cases chromosome breakpoints appear distributed in a non-random manner. In order to study the distribution of chromosome damage induced by clastogenic agents in relation to chromosome histone acetylation patterns, an experimental model based on treating Chinese hamster cells with endonucleases and ionizing radiations as well as immunolabelling metaphase chromosomes with antibodies to acetylated histone H4 was developed. The analysis of intra- and interchromosome breakpoint distribution has been carried out on G-banded chromosomes, and results obtained were correlated with chromosome acetylated histone H4 profiles. A co-localization of intrachromosomal breakpoints induced by Alu I, Barn HI and DNase I as well as by neutrons and gamma-rays was observed. Radiation- and endonuclease-induced breakpoints tend to cluster in less condensed chromosome regions (G-light bands) that show the highest levels of acetylated histone H4. The analysis of interchromosomal distribution of radiation-induced lesions showed a concentration ofbreakpoints in Chinese hamster chromosomes with particular histone acetylation patterns. The fact that chromosome break-points occur more frequently in transcriptionally competent chromosome regions suggests that chromatin conformation and nuclear architecture could play a role in the distribution of chromosome lesions.

Acetylation↗

PubMed2004

Distribution of breakpoints induced by etoposide and X-rays along the CHO X chromosome.

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.

Animals↗

PubMed2002

Chromosomal aberrations: formation, identification and distribution.

Chromosomal aberrations (CA) are the microscopically visible part of a wide spectrum of DNA changes generated by different repair mechanisms of DNA double strand breaks (DSB). The method of fluorescence in situ hybridisation (FISH) has uncovered unexpected complexities of CA and this will lead to changes in our thinking about the origin of CA. The inter- and intrachromosomal distribution of breakpoints is generally not random. CA breakpoints occur preferentially in active chromatin. Deviations from expected interchromosomal distributions of breakpoints may result from the arrangement of chromosomes in the interphase nucleus and/or from different sensitivities of chromosomes with respect to the formation of CA. Telomeres and interstitial telomere repeat like sequences play an important role in the formation of CA. Subtelomeric regions are hot spots for the formation of symmetrical exchanges between homologous chromatids and cryptic aberrations in these regions are associated with human congenital abnormalities.

Animals↗

PubMed2001

Chromosome regions enriched in hyperacetylated histone H4 are preferred sites for endonuclease- and radiation-induced breakpoints.

Previously, we have shown that breakpoints induced by the endonucleases AluI, BamHI and DNase I in CHO chromosomes are localized mainly in G-light bands. Neutrons and gamma rays produced similar breakpoint clusters to endonucleases in most CHO chromosomes. Here we compare endonuclease- and radiation-induced breakpoint maps with hyperacetylation patterns of histone H4. The H4 acetylation pattern in chromosomes is similar to the pattern of G-light, or R-bands, and breakpoints are clustered in highly acetylated chromosome regions. These findings indicate that chromosomal aberrations occur more frequently in active than in inactive chromatin.

Acetylation↗

PubMed1999

Comparison of AluI-induced frequencies of dicentrics and translocations in human lymphocytes by chromosome painting.

It has been shown repeatedly that following irradiation of human lymphocytes in the G0 stage, more translocations are induced than dicentrics. To check the role of DNA double-strand breaks (DSB) alone for the induction of symmetrical and asymmetrical chromosome aberrations, the frequencies of induced exchange aberrations by the restriction enzyme AluI were analyzed. The enzyme was introduced into cells using the pellet pipetting technique. Frequencies of induced translocations and dicentrics were determined using a chromosome painting assay with chromosome-specific DNA libraries for chromosomes 1, 4 and X (representing 16.8% of the human genome). The number of translocations detected was approximately 3-fold higher than the number of dicentrics, indicating that the increased frequency of translocations compared with dicentrics found in irradiated human lymphocytes does not result from DNA lesions other than DSB but from differential processing of DSB.

Centromere↗

PubMed1998

Localization of chromosome breakpoints: implication of the chromatin structure and nuclear architecture.

Restriction endonucleases and ionizing radiations have been extensively used to study the origin of chromosomal aberrations. Although a non-random distribution of chromosome breakpoints induced by these agents has been claimed by several authors, the significance of the chromatin structure and nuclear architecture in the localization of breakpoints is still not well understood. Breakpoint patterns produced by endonucleases targeted to specific genome sequences or by ionizing radiations could provide additional evidence to clarify this point. Results obtained from the localization of breakpoints induced by AluI, BamHI or DNase I as well as by neutrons or gamma-rays in G-banded Chinese hamster ovary (CHO) chromosomes are presented. AluI and BamHI were electroporated into CHO cells either during the G1 or S-phase of the cell cycle. A co-localization of breakpoints was found with a preferential occurrence in G-light bands independent of the cell cycle stage in which aberration production took place. Since AluI and BamHI recognition sequences are partitioned in the housekeeping and tissue-specific subgenomes respectively, we postulated that nuclease sensitive sites in active chromatin could be the main targets for the induction of breakpoints by these endonucleases. This assumption is supported by the finding that DNase I-induced breakpoint patterns in CHO cells are similar to those produced by AluI and BamHI. Digestion of fixed CHO chromosomes with these endonucleases induced G-banding suggesting a higher sensitivity of G-light chromatin. For comparison purposes, CHO cells were irradiated with neutrons or gamma-rays and breakpoints localized in G-banded chromosome aberrations. A higher occurrence of breakpoints in G-light bands was also observed. We detected seven breakage-prone G-light bands that were preferentially damaged by the three endonucleases and by both types of radiation. These results emphasize the possible implication of the chromatin structure and the nuclear architecture in the localization of chromosome breakpoints induced by endonucleases, neutrons and gamma-rays.

Animals↗

PubMed1998

Intrachromosomal localization of aberration breakpoints induced by neutrons and gamma rays in Chinese hamster ovary cells.

Chromosome breakpoints induced by neutrons or gamma rays in Chinese hamster ovary cells were mapped to Giemsa-light or Giemsa-dark bands or to band junctions. Radiation-induced breakpoints were found to be distributed nonrandomly according to chromosome or band length. More than 60% of the breakpoints were localized in G-light bands. A group of 13 bands which corresponded to only 7% of the total chromosome length contained 22% of the breakpoints produced by neutrons and 14% of those induced by gamma rays. Seven of these 13 bands are also preferentially damaged by AluI, BamHI and DNase I as reported previously. The results indicate that chromatin and nuclear structure may play a role in the distribution of breakpoints produced by ionizing radiation and endonucleases.

Animals↗