Biomedical subjects

Marion Cremer

Publications and source records attributed to Marion Cremer.

8 recordsLinked to original sources

PubMed2007

Dynamic genome architecture in the nuclear space: regulation of gene expression in three dimensions.

The regulation of gene expression is mediated by interactions between chromatin and protein complexes. The importance of where and when these interactions take place in the nucleus is currently a subject of intense investigation. Increasing evidence indicates that gene activation or silencing is often associated with repositioning of the locus relative to nuclear compartments and other genomic loci. At the same time, however, structural constraints impose limits on chromatin mobility. Understanding how the dynamic nature of the positioning of genetic material in the nuclear space and the higher-order architecture of the nucleus are integrated is therefore essential to our overall understanding of gene regulation.

Biological Transport↗

PubMed2006

Chromatin domains and the interchromatin compartment form structurally defined and functionally interacting nuclear networks.

In spite of strong evidence that the nucleus is a highly organized organelle, a consensus on basic principles of the global nuclear architecture has not so far been achieved. The chromosome territory-interchromatin compartment (CT-IC) model postulates an IC which expands between chromatin domains both in the interior and the periphery of CT. Other models, however, dispute the existence of the IC and claim that numerous chromatin loops expand between and within CTs. The present study was undertaken to resolve these conflicting views. (1) We demonstrate that most chromatin exists in the form of higher-order chromatin domains with a compaction level at least 10 times above the level of extended 30 nm chromatin fibers. A similar compaction level was obtained in a detailed analysis of a particularly gene-dense chromosome region on HSA 11, which often expanded from its CT as a finger-like chromatin protrusion. (2) We further applied an approach which allows the experimental manipulation of both chromatin condensation and the width of IC channels in a fully reversible manner. These experiments, together with electron microscopic observations, demonstrate the existence of the IC as a dynamic, structurally distinct nuclear compartment, which is functionally linked with the chromatin compartment.

Animals↗

PubMed2006

Chromosome territories--a functional nuclear landscape.

Understanding nuclear architecture is indispensable for understanding the cell-type-dependent orchestration of active and silent genes and other nuclear functions, such as RNA splicing, DNA replication and repair. Yet, while it is now generally agreed that chromosomes in the cell nucleus are organized as chromosome territories, present models of chromosome territory architecture differ widely with respect to the possible functional implications of dynamic changes of this architecture during the cell cycle and terminal cell differentiation.

Animals↗

PubMed2005

Histone lysine methylation patterns in human cell types are arranged in distinct three-dimensional nuclear zones.

The impact of histone lysine methylation as an essential epigenetic mechanism for gene regulation has been demonstrated by numerous studies where it was functionally and structurally linked to euchromatin and heterochromatin. Most of these data have been obtained by biochemical and two-dimensional (2D)-microscopic techniques providing little information about the global nuclear arrangement of histone modifications. We investigated the 3D architecture and spatial interrelationships of different histone lysine methylation sites (tri-H3K4, mono-H4K20, mono-H3K9, tri-H3K27, tri-H4K20 and tri-H3K9) in various human cell types. Immunofluorescence and confocal microscopy were used together with a quantitative evaluation of 3D images, to reveal spatial relations of specific methylation sites with either centromeres, nascent RNA or with each other. A close association with centromeres was found only for histone methylation sites previously linked to constitutively repressed chromatin. Differences observed in these sites in relation to the cell cycle emphasize the potential relevance of the dynamic properties of heterochromatin for nuclear functions. Nascent RNA was found associated, though to a different degree, with all histone methylation sites, supporting the increasing evidence that transcription occurs across a wide range of the human genome. Finally we demonstrated by simultaneous visualization of different histone lysine methylation sites that methylation patterns are organized in distinct nuclear zones with little apparent intermingling.

Algorithms↗

PubMed2003

Inheritance of gene density-related higher order chromatin arrangements in normal and tumor cell nuclei.

A gene density-related difference in the radial arrangement of chromosome territories (CTs) was previously described for human lymphocyte nuclei with gene-poor CT #18 located toward the nuclear periphery and gene-dense CT #19 in the nuclear interior (Croft, J.A., J.M. Bridger, S. Boyle, P. Perry, P. Teague, and W.A. Bickmore. 1999. J. Cell Biol. 145:1119-1131). Here, we analyzed the radial distribution of chromosome 18 and 19 chromatin in six normal cell types and in eight tumor cell lines, some of them with imbalances and rearrangements of the two chromosomes. Our findings demonstrate that a significant difference in the radial distribution of #18 and #19 chromatin is a common feature of higher order chromatin architecture in both normal and malignant cell types. However, in seven of eight tumor cell lines, the difference was less pronounced compared with normal cell nuclei due to a higher fraction of nuclei showing an inverted CT position, i.e., a CT #18 located more internally than a CT #19. This observation emphasizes a partial loss of radial chromatin order in tumor cell nuclei.

Cell Line↗

PubMed2003

Chromosome order in HeLa cells changes during mitosis and early G1, but is stably maintained during subsequent interphase stages.

Whether chromosomes maintain their nuclear positions during interphase and from one cell cycle to the next has been controversially discussed. To address this question, we performed long-term live-cell studies using a HeLa cell line with GFP-tagged chromatin. Positional changes of the intensity gravity centers of fluorescently labeled chromosome territories (CTs) on the order of several microm were observed in early G1, suggesting a role of CT mobility in establishing interphase nuclear architecture. Thereafter, the positions were highly constrained within a range of approximately 1 microm until the end of G2. To analyze possible changes of chromosome arrangements from one cell cycle to the next, nuclei were photobleached in G2 maintaining a contiguous zone of unbleached chromatin at one nuclear pole. This zone was stably preserved until the onset of prophase, whereas the contiguity of unbleached chromosome segments was lost to a variable extent, when the metaphase plate was formed. Accordingly, chromatin patterns observed in daughter nuclei differed significantly from the mother cell nucleus. We conclude that CT arrangements were stably maintained from mid G1 to late G2/early prophase, whereas major changes of CT neighborhoods occurred from one cell cycle to the next. The variability of CT neighborhoods during clonal growth was further confirmed by chromosome painting experiments.

Cell Movement↗

PubMed2002

Non-random radial arrangements of interphase chromosome territories: evolutionary considerations and functional implications.

In the nucleus of animal and plant cells individual chromosomes maintain a compartmentalized structure. Chromosome territories (CTs), as these structures were named by Theodor Boveri, are essential components of the higher-order chromatin architecture. Recent studies in mammals and non-mammalian vertebrates indicate that the radial position of a given CT (or segments thereof) is correlated with its size, its gene-density and its replication timing. As a representative case, chicken cell nuclei show highly consistent radial chromatin arrangements: gene-rich, early replicating microchromosomes are clustered within the nuclear interior, while gene-poor, later replicating macrochromosomes are preferentially located at the nuclear periphery. In humans, chromosomes 18 and 19 (HSA18 and 19) territories that are of similar size show a distinctly different position in the cell nuclei of lymphocytes and lymphoblastoid cells: the gene-rich and early replicating HSA19 CTs are typically found close to the nuclear center, while the gene-poor and later replicating HSA18 CTs are preferentially located at the nuclear periphery. Recent comparative maps between human and chicken chromosomes revealed that the chicken macrochromosomes 2 and Z contain the genes homologous to HSA18, while the genes on HSA19 are located onto the chicken microchromosomes. These data lend tentative support to the hypothesis that differences in the radial nuclear positions of gene-rich, early replicating and gene-poor, later replicating chromatin have been evolutionarily conserved during a period of more than 300 million years irrespective of the evolution of highly divergent karyotypes between humans and chicken.

Animals↗

PubMed2002

Evolutionary conservation of chromosome territory arrangements in cell nuclei from higher primates.

We demonstrate that the nuclear topological arrangement of chromosome territories (CTs) has been conserved during primate evolution over a period of about 30 million years. Recent evidence shows that the positioning of chromatin in human lymphocyte nuclei is correlated with gene density. For example, human chromosome 19 territories, which contain mainly gene-dense and early replicating chromatin, are located toward the nuclear center, whereas chromosome 18 territories, which consist mainly of gene-poor and later replicating chromatin, is located close to the nuclear border. In this study, we subjected seven different primate species to comparative analysis of the radial distribution pattern of human chromosome 18- and 19-homologous chromatin by three-dimensional fluorescence in situ hybridization. Our data demonstrate that gene-density-correlated radial chromatin arrangements were conserved during higher-primate genome evolution, irrespective of the major karyotypic rearrangements that occurred in different phylogenetic lineages. The evolutionarily conserved positioning of homologous chromosomes or chromosome segments in related species supports evidence for a functionally relevant higher-order chromatin arrangement that is correlated with gene-density.

Animals↗