染色体领域的研究及其进展

间期核中的染色体并不是散乱分布的,而是每条染色体占据了一块特定的核区域,即染色体领域（chromosome territory, CTs）,染色体领域在间期核中的排列与定位是经过严格组织的,并具有一定的动力学特征,染色体领域的这些严格的定位和空间组织与基因的表达调控密切相关。文章综述了这几个方面的研究进展。      

Virtual radiation biophysics: implications of nuclear structure

The non-random positioning of chromosome territories (CTs) in lymphocyte cell nuclei has raised the question whether systematic chromosome-chromosome associations exist which have significant influence on interchange rates. In such a case the spatial proximity of certain CTs or even of clusters of CTs is expected to increase the respective exchange yields significantly, in comparison to a random association of CTs. In the present study we applied computer simulated arrangements of CTs to calculate interchange frequencies between all heterologous CT pairs, assuming a uniform action of the molecular repair machinery. For the positioning of CTs in the virtual nuclear volume we assumed a) a statistical, and b) a gene density-correlated arrangement. The gene density-correlated arrangement regards the more experimentally observed interior localization of gene-rich and the more peripheral positioning of gene-poor CTs. Regarding one-chromosome yields, remarkable differences for single CTs were observed taking into account the gene density-correlated distribution of CTs.     

Dynamic changes of territories 17 and 18 during EBV-infection of human lymphocytes

Interphase chromosomes form distinct spatial domains called chromosome territories (CTs). The arrangement of CTs is non-random and correlated with cellular processes such as differentiation. The purpose of this study is to provide some behavior information of CTs during lymphocyte EBV-infection, which is thought to be a general extra-biological model. Three-dimensional fluorescence in situ hybridization (3D-FISH) was performed on human lymphocytes every 24 h over 96 h periods in EBV-infection. Chromosomes 17 and 18 were selected as target territories for similar size and different gene density. The data indicate that the radial position of territories 17 was altered with time, whereas territories 18 showed relative stable localization. The relative CT volume of CTs 18 to 17 also changed with infection. Our study is the first to examine the timely changes of chromatin positioning and folding in EBV-lymphocyte infection. Dynamic changes in position and folding status of target chromosomes reflected an impact of EBV infection on genome stability.     

Spatial organization of chromosome territories in the interphase nucleus of trisomy 21 cells

In the interphase cell nucleus, chromosomes adopt a conserved and non-random arrangement in subnuclear domains called chromosome territories (CTs). Whereas chromosome translocation can affect CT organization in tumor cell nuclei, little is known about how aneuploidies can impact CT organization. Here, we performed 3D-FISH on control and trisomic 21 nuclei to track the patterning of chromosome territories, focusing on the radial distribution of trisomic HSA21 as well as 11 disomic chromosomes. We have established an experimental design based on cultured chorionic villus cells which keep their original mesenchymal features including a characteristic ellipsoid nuclear morphology and a radial CT distribution that correlates with chromosome size. Our study suggests that in trisomy 21 nuclei, the extra HSA21 induces a shift of HSA1 and HSA3 CTs out toward a more peripheral position in nuclear space and a higher compaction of HSA1 and HSA17 CTs. We posit that the presence of a supernumerary chromosome 21 alters chromosome compaction and results in displacement of other chromosome territories from their usual nuclear position.     

Chromosome territory positioning of conserved homologous chromosomes in different primate species

Interphase chromosomes form distinct spatial domains called chromosome territories (CTs). The position of CTs is known not to be at random and is related to chromosome size and gene density. To elucidate how CTs are arranged in primate proliferating fibroblasts and whether the radial position of CTs has been conserved during primate evolution, several specific CTs corresponding to conserved chromosomes since the Simiiformes (human 6, 12, 13, and 17 homologous CTs) have been studied in 3D preserved interphase nuclei from proliferant cells of two New World monkey species (Lagothrix lagothricha, Saimiri sciureus) and in human by three-dimensional fluorescent in situ hybridization (3D-FISH). Our results indicate that both gene-density and chromosome size influence chromosome territory arrangement in the nucleus. This influence is greater for chromosome-size than for gene-density in the three species studied. A comparison of the radial position of a given CT and its homolog in the species analyzed suggests similar CT distributions for homologous chromosomes. Our statistical analysis using the logit model shows that such homologous positionings cannot, however, be considered identical.Electronic Supplementary Material Supplementary material is available for this article at This paper is dedicated to the memory of Prof. Josep Egozcue, our enthusiast teacher and a good friend.     

Inter- and intra-specific gene-density-correlated radial chromosome territory arrangements are conserved in Old World monkeys

Recently it has been shown that the gene-density correlated radial distribution of human 18 and 19 homologous chromosome territories (CTs) is conserved in higher primates in spite of chromosomal rearrangements that occurred during evolution. However, these observations were limited to apes and New World monkey species. In order to provide further evidence for the evolutionary conservation of gene-density-correlated CT arrangements, we extended our previous study to Old World monkeys. They comprise the remaining species group to be analyzed in order to obtain a comprehensive overview of the nuclear topology of human 18 and 19 homologous CTs in higher primates. In the present study we investigated four lymphoblastoid cell lines from three species of Old World monkeys by three-dimensional fluorescence in situ hybridization (3D-FISH): two individuals of Japanese macaque (Macaca fuscata), crab-eating macaque (Macaca fascicularis), and an interspecies hybrid individual between African green monkey (Cercopithecus aethiops) and Patas monkey (Erythrocebus patas). Our data demonstrate that gene-poor human 18 homologous CTs are located preferentially close to the nuclear periphery, whereas gene-dense human 19 homologous CTs are oriented towards the nuclear center in all cell lines analyzed. The gene-density-correlated positioning of human 18 and 19 homologous CTs is evolutionarily conserved throughout all major higher primate lineages, despite chromosomal inversions, fusions, fissions or reciprocal translocations that occurred in the course of evolution in these species. This remarkable preservation of a gene-density-correlated chromatin arrangement gives further support for a functionally relevant higher-order chromatin architecture.     

Suppressive effects of flavonoids on dioxin toxicity

Dioxin type chemicals such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) cause a variety of toxicity. Most of the toxicity of TCDD has been attributed to a mechanism by which TCDD is bound to aryl hydrocarbon receptor (AhR) and transforms the receptor. Thus, suppression of the AhR transformation by food factors can suppress the dioxin toxicity. In this study, flavonoids at various concentrations were treated to a rat cytosolic fraction containing AhR before adding 1 nM TCDD. The transformed AhR was detected by an electrophoretic mobility shift assay with a DNA oligonucleotide consensus to dioxin response element. As the results, flavones and flavonols at dietary levels act as the antagonists for AhR and suppress the transformation. The antagonistic IC50 values were in a range between 0.14 and 10 microM, which are close to the physiological levels in human. These results suggest that a plant-based diet can prevent the dioxin toxicity.     

Conservation of relative chromosome positioning in normal and cancer cells

Chromosomes exist in the interphase nucleus as individual chromosome territories. It is unclear to what extent chromosome territories occupy particular positions with respect to each other and how structural rearrangements, such as translocations, affect chromosome organization within the cell nucleus. Here we analyze the relative interphase positioning of chromosomes in mouse lymphoma cells compared to normal splenocytes. We show that in a lymphoma cell line derived from an ATM(-/-) mouse, two translocated chromosomes are preferentially positioned in close proximity to each other. The relative position of the chromosomes involved in these translocations is conserved in normal splenocytes. Relative positioning of chromosomes in normal splenocytes is not due to their random distribution in the interphase nucleus and persists during mitosis. These observations demonstrate that the relative arrangement of chromosomes in the interphase nucleus can be conserved between normal and cancer cells and our data support the notion that physical proximity facilitates rearrangements between chromosomes.     

Aryl hydrocarbon receptor-dependent induction of apoptosis by 2,3,7,8-tetrachlorodibenzo-p-dioxin in cerebellar granule cells from mouse

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a prototypical environmental contaminant with neurotoxic properties that alters neurodevelopment and behavior. TCDD is a ligand of the aryl hydrocarbon receptor (AhR), which is a key signaling molecule to fully understand the toxic and carcinogenic properties of dioxin. Much effort is underway to unravel the molecular mechanisms and the signaling pathways involved in TCDD-induced neurotoxicity, and to define its molecular targets in neurons. We have used cerebellar granule cells (CGC) from wild-type (AhR+/+) and AhR-null (AhR-/-) mice to characterize the cell death that takes place in neurons after TCDD toxicity. TCDD induced cell death in CGC cultures from wild-type mice with an EC(50) of 127±21 nM. On the contrary, when CGC neurons from AhR-null mice were treated with TCDD no significant cell death was observed. The role of AhR in TCDD-induced death was further assessed by using the antagonists resveratrol and α-naphtoflavone, which readily protected against TCDD toxicity in AhR+/+ CGC cultures. AhR+/+ CGC cultures treated with TCDD showed nuclear fragmentation, DNA laddering, and increased caspase 3 activity, similarly to what was found by the use of staurosporine, a well-established inducer of apoptosis. Finally, the AhR pathway was active in CGC because TCDD could induce the expression of the target gene cytochrome P450 1A2 in AhR+/+ CGC cultures. All together these results support the hypothesis that TCDD toxicity in CGC neurons involves the AhR and that it takes place mainly through an apoptotic process. AhR could be then considered a novel target in neurotoxicity and neurodegeneration whose down-modulation could block certain xenobiotic-related adverse effects in CNS.     

Molecular targets that link dioxin exposure to toxicity phenotypes

Many toxicology studies have elucidated health effects associated with exposure to various chemicals, but few have identified the molecular targets that cause specific endpoints of toxicity. Our understanding of the toxicity of dioxins, a group of chemicals capable of causing toxicity at environmentally relevant levels of exposure, is no exception. Dioxins are unique compared to most chemicals that we are exposed to in the environment because they activate a high affinity receptor, aryl hydrocarbon receptor (AhR), that was identified more than three decades ago. In recent years, several lines of experimental evidence have provided clues for opening the "black box" that contains the molecular mechanisms of dioxin action. These clues have emerged by toxicologists beginning to identify the molecular targets that link AhR signaling to tissue-specific toxicity phenotypes. Endpoints of dioxin toxicity for which downstream molecular targets have begun to be elucidated are observed in developmental or tissue regeneration processes, and include impaired prostate development and hydronephrosis in mouse fetuses and pups, reduced midbrain blood flow and jaw malformation in zebrafish embryos, and impaired fin regeneration in larval and adult zebrafish. Significant progress in identifying molecular targets for dioxin-induced hepatotoxicity in adult mice also has occurred. Misregulation of AhR downstream pathways, such as conversion of arachidonic acid to prostanoids via cyclooxygenase-2, and altered Wnt/β-catenin signaling downregulating Sox9, and signaling by receptors for inflammatory cytokines have been implicated in tissue-specific endpoints of dioxin toxicity. These findings may not only begin to clarify the molecular targets of dioxin action but shed light on new molecular events associated with development and disease.