1,721,023 research outputs found
Bisphenol a effects on mammalian oogenesis and epigenetic integrity of oocytes: A case study exploring risks of endocrine disrupting chemicals
No full textBisphenol A (BPA), originally developed as a synthetic oestrogen, is nowadays extensively used in the production of polymeric plastics. Under harsh conditions, these plastics may release BPA, which then can leach into the environment. Detectable concentrations of BPA have been measured in most analysed samples of human serum, plasma, or urine, as well as in follicular fluid, foetal serum, and amniotic fluid. Here we summarize the evidence about adverse BPA effects on the genetic and epigenetic integrity of mammalian oocytes. We conclude that increasing evidence supports the notion that low BPA concentrations adversely affect the epigenome of mammalian female germ cells, with functional consequences on gene expression, chromosome dynamics in meiosis, and oocyte development. Specific time windows, during which profound chromatin remodelling occurs and maternal imprints are established or protected, appear particularly vulnerable to epigenetic deregulation by BPA. Transgenerational effects have been also observed in the offspring of BPA-treated rodents, although the epigenetic mechanisms of inheritance still need to be clarified. The relevance of these findings for human health protection still needs to be fully assessed, but they warrant further investigation in both experimental models and humans. © 2015 Ursula Eichenlaub-Ritter and Francesca Pacchierotti
The adverse outcome pathway (AOP) for chemical binding to tubulin in oocytes leading to aneuploid offspring
No full textThe Organisation for Economic Co-operation and Development (OECD) has launched the Adverse Outcome Pathway (AOP) Programme to advance knowledge of pathways of toxicity and improve the use of mechanistic information in risk assessment. An AOP links a molecular initiating event (MIE) to an adverse outcome (AO) through intermediate key events (KE). Here, we present the scientific evidence in support of an AOP whereby chemicals that bind to tubulin cause microtubule depolymerization resulting in spindle disorganization followed by altered chromosome alignment and segregation and the generation of aneuploidy in female germ cells, ultimately leading to aneuploidy in the offspring. Aneuploidy, an abnormal number of chromosomes that is not an exact multiple of the haploid number, is a well-known cause of human disease and represents a major cause of infertility, pregnancy failure, and serious genetic disorders in the offspring. Among chemicals that induce aneuploidy in female germ cells, a large majority impairs microtubule dynamics and spindle function. Colchicine, a prototypical chemical that binds to tubulin and causes microtubule depolymerization, is used here to illustrate the AOP. This AOP is specific to female germ cells exposed during the periovulation period. Although the majority of the data come from rodent studies, the available evidence suggests that the MIE and KEs are conserved across species and would occur in human oocytes. The development of AOPs related to mutagenicity in germ cells is expected to aid the identification of potential hazards to germ cell genomic integrity and support regulatory efforts to protect population health. Environ. Mol. Mutagen. 57:87-113, 2016. © 2015 Her Majesty the Queen in Right of Canada
Genomic instability: Crossing pathways at the origin of structural and numerical chromosome changes
No full textGenomic instability leads to a wide spectrum of genetic changes, including single nucleotide mutations, structural chromosome alterations, and numerical chromosome changes. The accepted view on how these events are generated predicts that separate cellular mechanisms and genetic events explain the occurrence of these types of genetic variation. Recently, new findings have shed light on the complexity of the mechanisms leading to structural and numerical chromosome aberrations, their intertwining pathways, and their dynamic evolution, in somatic as well as in germ cells. In this review, we present a critical analysis of these recent discoveries in this area, with the aim to contribute to a deeper knowledge of the molecular networks leading to adverse outcomes in humans following exposure to environmental factors. The review illustrates how several technological advances, including DNA sequencing methods, bioinformatics, and live-cell imaging approaches, have contributed to produce a renewed concept of the mechanisms causing genomic instability. Special attention is also given to the specific pathways causing genomic instability in mammalian germ cells. Remarkably, the same scenario emerged from some pioneering studies published in the 1980s to 1990s, when the evolution of polyploidy, the chromosomal effects of spindle poisons, the fate of micronuclei, were intuitively proposed to share mechanisms and pathways. Thus, an old working hypothesis has eventually found proper validation. © 2015 Wiley Periodicals, Inc
Approaches for identifying germ cell mutagens: Report of the 2013 IWGT workshop on germ cell assays(☆)
No full textThis workshop reviewed the current science to inform and recommend the best evidence-based approaches on the use of germ cell genotoxicity tests. The workshop questions and key outcomes were as follows. (1) Do genotoxicity and mutagenicity assays in somatic cells predict germ cell effects? Limited data suggest that somatic cell tests detect most germ cell mutagens, but there are strong concerns that dictate caution in drawing conclusions. (2) Should germ cell tests be done, and when? If there is evidence that a chemical or its metabolite(s) will not reach target germ cells or gonadal tissue, it is not necessary to conduct germ cell tests, notwithstanding somatic outcomes. However, it was recommended that negative somatic cell mutagens with clear evidence for gonadal exposure and evidence of toxicity in germ cells could be considered for germ cell mutagenicity testing. For somatic mutagens that are known to reach the gonadal compartments and expose germ cells, the chemical could be assumed to be a germ cell mutagen without further testing. Nevertheless, germ cell mutagenicity testing would be needed for quantitative risk assessment. (3) What new assays should be implemented and how? There is an immediate need for research on the application of whole genome sequencing in heritable mutation analysis in humans and animals, and integration of germ cell assays with somatic cell genotoxicity tests. Focus should be on environmental exposures that can cause de novo mutations, particularly newly recognized types of genomic changes. Mutational events, which may occur by exposure of germ cells during embryonic development, should also be investigated. Finally, where there are indications of germ cell toxicity in repeat dose or reproductive toxicology tests, consideration should be given to leveraging those studies to inform of possible germ cell genotoxicity. Crown Copyright © 2015. Published by Elsevier B.V. All rights reserved
Environmental Impact on DNA Methylation in the Germline: State of the Art and Gaps of Knowledge
Full text linkThe epigenome consists of chemical changes in DNA and chromatin that without modifying the DNA sequence modulate gene expression and cellular phenotype. The epigenome is highly plastic and reacts to changing external conditions with modifications that can be inherited to daughter cells and across generations. Whereas this innate plasticity allows for adaptation to a changing environment, it also implies the potential of epigenetic derailment leading to so-called epimutations. DNA methylation is the most studied epigenetic mark. DNA methylation changes have been associated with cancer, infertility, cardiovascular, respiratory, metabolic, immunologic, and neurodegenerative pathologies. Experiments in rodents demonstrate that exposure to a variety of chemical stressors, occurring during the prenatal or the adult life, may induce DNA methylation changes in germ cells, which may be transmitted across generations with phenotypic consequences. An increasing number of human biomonitoring studies show environmentally related DNA methylation changes mainly in blood leukocytes, whereas very few data have been so far collected on possible epigenetic changes induced in the germline, even by the analysis of easily accessible sperm. In this paper, we review the state of the art on factors impinging on DNA methylation in the germline, highlight gaps of knowledge, and propose priorities for future studies. © 2015 Francesca Pacchierotti and Marcello Spanò
Environmental Hazard in the Aetiology of Somatic and Germ Cell Aneuploidy
No full textPacchierotti F, Eichenlaub-Ritter U. Environmental Hazard in the Aetiology of Somatic and Germ Cell Aneuploidy. Cytogenetic and Genome Research. 2011;133(2-4):254-268
Analysis of chromosome aberrations in somatic and germ cells of the mouse
No full textChromosome aberration tests are used to evaluate the clastogenicity of chemical and physical agents, that is, the capacity of these agents to cause breaks in chromosomes and produce microscopically visible fragments or structural rearrangements. Aberrations are scored in metaphase chromosomes of dividing cells. In the mouse, bone marrow progenitors of erythrocytes and leukocytes provide abundant metaphases to study the effects on somatic cells, whereas the response of male germ cells to clastogenic agents can be visualized on metaphases of spermatogonia and primary spermatocytes. The techniques to prepare the slides for analyses are well standardized and internationally harmonized protocols for tests in bone marrow and spermatogonia provide the guidance necessary to obtain meaningful results. It is advisable to adhere as much as possible to these recommendations. Not all tests are suitable to score the same kind of aberrations. Here an overview of the application domains of these tests is provided with warnings on the scoring criteria and statistical analysis. © Springer Science+Business Media, New York 2013
Critical issues in genotoxicity assessment of TiO2 nanoparticles by human peripheral blood mononuclear cells
No full textIn the last years, a number of in vitro studies have been performed to assess the genotoxic activity of titanium dioxide (TiO2). To resolve the contradictory results, in this study, we investigated the genotoxic activity of commercial TiO2 nanoparticles (NPs) and microparticles of different forms (anatase, rutile and mix of both). We evaluated micronucleus formation in stimulated lymphocytes, as well as DNA strand breaks and 8-oxo-7,8-dihydro-2′-deoxyguanosine in peripheral blood mononuclear cells (PBMCs), a mixed population of lymphocytes and monocytes. Different responses to TiO2 exposure were obtained depending on the assay. Both TiO2 NPs and microparticles and all the crystalline forms elicited a significant increase in 8-oxo-7,8-dihydro-2′-deoxyguanosine and DNA strand breaks in the whole PBMC population, without a concurrent increase of micronuclei in proliferating lymphocytes. The distribution of DNA damage in PBMCs, detected by the comet assay, that measures DNA damage at level of single cells, indicated the presence of a more susceptible cell subpopulation. The measurement of side scatter signals by flow cytometry highlighted the preferential physical interaction of TiO2 particles with monocytes that also displayed higher reactive oxygen species generation, providing a mechanistic explanation for the different responses observed in genotoxicity assays with PBMCs and lymphocytes. This study confirmed the suitability of human PBMCs as multi-cell model to investigate NP-induced DNA damage, but suggested some caution in the use of stimulated lymphocytes for the assessment of NP clastogenicity. Copyright © 2018 John Wiley & Sons, Ltd
Rad54/Rad54B deficiency is associated to increased chromosome breakage in mouse spermatocytes
No full textRad54 protein is a key player of the homologous recombination pathway, required for deposition and stabilisation of Rad51 foci at double strand breaks. Its role at the meiotic prophase, when double strand breaks are physiologically introduced to allow recombination, is well described. However, the hypothesis that Rad54 deficiency affect chromosome integrity of germ cells in unirradiated and irradiated animals has not been tested yet. In this study, the occurrence of spontaneous and X-ray-induced chromosome aberrations was assessed by analysis of spermatocyte MI spreads or by application of micronucleus assay in early spermatids isolated from wild type and Rad54/Rad54B knockout (KO) mice. In Rad54/Rad54B KO mice, the spontaneous chromosome aberration frequency detected at MI was >10-fold higher than in wild type animals. In addition, after exposure to 1 Gy X-rays at the radiosensitive stage of diplotene, an enhanced response to radiation was observed in Rad54-deficient animals, corresponding to a 2-3 sensitivity factor in comparison to wild type mice. Also the spontaneous frequency of micronucleated round spermatids was on the average 10-fold higher in KO than in wild type mice, indicating that Rad54/Rad54B KO spermatocytes carrying chromosome aberrations are able to pass through the meiotic divisions and to continue the spermatogenesis process. Our results provide the first evidence of the role of Rad54/Rad54B in the maintenance of a stable karyotype during male meiosis, and suggest that Rad54/Rad54B deficiency may impact on the DNA integrity of developing mouse gametes. © 2018 The Author(s)
- …
