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Fanconi anemia (FA) is a chromosome fragility syndrome characterized by bone marrow failure and cancer susceptibility. The central FA protein FANCD2 is known to relocate to chromatin upon DNA damage in a poorly understood process. Here, we have induced subnuclear accumulation of DNA damage to prove that histone H2AX is a novel component of the FA/BRCA pathway in response to stalled replication forks. Analyses of cells from H2AX knockout mice or expressing a nonphosphorylable H2AX (H2AX S136A/S139A ) indicate that phosphorylated H2AX (cH2AX) is required for recruiting FANCD2 to chromatin at stalled replication forks. FANCD2 binding to cH2AX is BRCA1-dependent and cells deficient or depleted of H2AX show an FA-like phenotype, including an excess of chromatid-type chromosomal aberrations and hypersensitivity to MMC. This MMC hypersensitivity of H2AX-deficient cells is not further increased by depleting FANCD2, indicating that H2AX and FANCD2 function in the same pathway in response to DNA damage-induced replication blockage. Consequently, histone H2AX is functionally connected to the FA/BRCA pathway to resolve stalled replication forks and prevent chromosome instability.

Micronucleus (MN) is a biomarker widely used in biomonitoring studies carried out to determine the genetic risk associated to pesticide exposure. Many in vitro and in vivo studies, as well as epidemiological approaches, have demonstrated the ability of certain chemical pesticides to produce genetic effects including cancer and other chronic pathologies in humans; thus, biomonitoring studies have been carried out to characterise the genetic risk associated to pesticide exposure. It must be noted that 'pesticide exposure' is a broad term covering complex mixtures of chemicals and many variables that can reduce or potentiate their risk. In addition, there are large differences in pesticides used in the different parts of the world. Although pesticides constitute a wide group of environmental pollutants, the main focus on their risk has been addressed to people using pesticides in their working places, at the chemical industry or in the crop fields. Here, we present a brief review of biomonitoring studies carried out in people occupationally exposed to pesticides and that use MN in lymphocytes or buccal cells as a target to determine the induction of genotoxic damage. Thus, people working in the chemical industry producing pesticides, people spraying pesticides and people dedicated to floriculture or agricultural works in general are the subject of specific sections. MN is a valuable genotoxic end point when clear exposure conditions exist like in pesticide production workers; nevertheless, better study designs are needed to overcome the uncertainty in exposure, genetic susceptibility and statistical power in the studies of sprayers and floriculture or agricultural workers.

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Health risk assessment of nanomaterials is an emergent field, genotoxicity being an important endpoint to be tested. Since in vivo studies offer many advantages, such as the study of the bioavailability of nanomaterials to sensitive target cells, we propose Drosophila as a useful model for the study of the toxic and genotoxic risks associated with nanoparticle exposure. In this work we have carried out a genotoxic evaluation of silver nanoparticles in Drosophila by using the wing somatic mutation and recombination test. This test is based on the principle that loss of heterozygosis and the corresponding expression of the suitable recessive markers, multiple wing hairs and flare-3, can lead to the formation of mutant clones in larval cells, which are expressed as mutant spots on the wings of adult flies. Silver nanoparticles were supplied to third instar larvae at concentrations ranging from 0.1-10 mM. The results showed that small but significant increases in the frequency of total spots were observed, thus indicating that silver nanoparticles were able to induce genotoxic activity in the wing spot assay of D. melanogaster, mainly via the induction of somatic recombination. These positive results obtained with silver nanoparticles contrast with the negative findings obtained when silver nitrate was tested.

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Fanconi anemia (FA) is a rare genetic disease characterized by chromosome instability, progressive pancytopenia and cancer susceptibility. Telomeres are intimately related to chromosome stability and play an important role in organismal viability at the hematological level. Since previous works suggested an accelerated shortening of telomeres in FA, we have studied several markers of telomere integrity and function in FA patients and age-matched controls to get insights into the mechanisms and consequences of telomere erosion in FA. A higher frequency of extra-chromosomic TTAGGG signals and of chromosome ends with undetectable TTAGGG repeats was observed in FA cells by fluorescence in situ hybridization (FISH), suggesting intensive breakage at telomeric sequences. This was proven by measuring the frequency of excess of telomeric signals per cell, which was 2.8-fold higher in FA. Consistent with previous reports, quantitative FISH analysis showed an accelerated telomere shortening of 0.68 kb in FA, which occurred concurrently in both chromosome arms in a similar magnitude. Our data therefore suggest that the telomere erosion in FA is caused by a higher rate of breakage at TTAGGG sequences in vivo in differentiated cells, in addition to mere replicative shortening during lymphocyte proliferation. Consistent with impaired telomeres in FA patients, we observed a >10-fold increase in chromosome end fusions in FA compared to normal controls. This observation was independent of TRF2, a telomere binding factor that protects human telomeres from end fusions, since immunohistochemistry studies in FA cell lines and corrected counterparts by retrovirus-mediated transfer of FANCA and FANCD2 cDNA showed that a functional FA pathway is not required for telomere binding of TRF2.