title: Topology of Genes in Mammalian Cell Nuclei with Special Emphasis on the MLL Gene and Its Translocation Partners
creator: Murmann, Andrea Eveline
subject: 570
subject: 570 Life sciences
description: Chromosomal translocations are the cause of many forms of leukemia. The mechanisms of how they occur are poorly understood. After a double strand break event, chromosomes are fused generating derivative chromosomes. During the fusion, a chimeric gene can be created and a fusion protein with new functions may be expressed which might cause malignant transformation. One such gene is MLL, which can be fused to a large number of other genes in different types of leukemias. It is believed that the 3D localization of genes, involved in chromosomal translocations in the interphase nucleus of certain hematopoietic tissues, could be a determining factor for a translocation event. This work has analyzed the 3D localization of MLL and some of its major translocation partners in the interphase nucleus of various cells cultured under different conditions, as well as in cell lines carrying translocation involving these genes. An analysis procedure was developed to precisely determine gene positions in the 3D space of the spherical interphase nucleus of hematopoietic cells. The nuclear localization of a gene relative to the nuclear center and the nuclear periphery was determined. To provide a general understanding of the distribution pattern of a given locus within the nucleus, the nuclear volume was divided into five concentric shells in two different ways: 1. shells, of same thickness, which permitted detection of large differences in the position of genes, and 2. shells, whose volume were identical, which permitted a high resolution for genes that were close to the nuclear periphery. Using these tools, the positions of MLL, five of its translocation partners, (AF4, AF6, AF9, ENL and ELL) and four control loci (2q33, 2q35, 7q22 and 8q34) were analyzed in different human cell lines of hematopoietic origin and in primary hematopoietic stem cells. Despite the cell materials’ differences in maturation state, cell lineage, and chromosome number, the localization of each gene and chromosomal locus showed a characteristic distribution pattern in the interphase nucleus in all studied hematopoietic cells, with the extremes being 2q35 having the most peripheral position, and the genes ENL and ELL on 19p13 sharing the most interior nuclear position. The three most common translocation partners of MLL (AF4, AF6 and AF9) were found to be remarkably similar in their localization, which was more peripheral than that of MLL. The position of MLL and AF9 relative to the nuclear surface was independent of the cell cycle and the induction of DSB/apoptosis. Interestingly, despite the differences in distances to the nuclear surface that were characteristic, distance analyses and angle measurements among genes revealed, that their relative positioning to each other is random. The effect of translocations on gene position was also studied in various cell lines carrying well defined translocations involving MLL and its translocation partners AF4, AF6 or AF9. For this study, a designed set of locus specific probes allowed the simultaneous detection of the genes on the normal and the derivative chromosomes. The positions for the normal genes were notably different from the positions of the fusion genes depending on the type of translocation. The analysis of gene density of whole chromosomes and local gene density, within a 2 Mbp window surrounding the locus, revealed a strong correlation between the nuclear position of a locus and its local gene density. In general, genes in areas of high local gene density were found towards the nuclear center, whereas genes in regions of low gene density were detected near the nuclear periphery. The gene density within a 2 Mbp window was determined to be a good predictor for the relative positioning of a locus within the nucleus and could explain the change of position observed after translocation events. Furthermore a correlation between the position of a locus and its position relative to its chromosomal territory seemed to be linked to the gene density. The "2 Mbp prediction" was successfully applied to various examples of nuclear positional studies published in the literature. This work revealed therefore new insight into the nuclear architecture of mammalian cells and has identified principles that determine the 3D position of genes in the nucleus. The results of this work that could help us to better understand the basis for chromosomal translocations that cause leukemia.
date: 2004
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/5373/1/A._Murmann_thesis.pdf
identifier: DOI:10.11588/heidok.00005373
identifier: urn:nbn:de:bsz:16-opus-53732
identifier:   Murmann, Andrea Eveline  (2004) Topology of Genes in Mammalian Cell Nuclei with Special Emphasis on the MLL Gene and Its Translocation Partners.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/5373/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng