In previous work, we showed that telomeres of normal cells are organized within the 3D space of the interphase nucleus in a nonoverlapping and cell cycle-dependent manner. This order is distorted in tumor cell nuclei where telomeres are found in close association forming aggregates of various numbers and sizes. Here we show that c-Myc overexpression induces telomeric aggregations in the interphase nucleus. Directly proportional to the duration of c-Myc deregulation, we observe three or five cycles of telomeric aggregate formation in interphase nuclei. These cycles reflect the onset and propagation of breakage-bridge-fusion cycles that are initiated by end-to-end telomeric fusions of chromosomes. Subsequent to initial chromosomal breakages, new fusions follow and the breakage-bridge-fusion cycles continue. During this time, nonreciprocal translocations are generated. c-Myc-dependent remodeling of the organization of telomeres thus precedes the onset of genomic instability and subsequently leads to chromosomal rearrangements. Our findings reveal that c-Myc possesses the ability to structurally modify chromosomes through telomeric fusions, thereby reorganizing the genetic information.genomic instability ͉ 3D nucleus ͉ breakage-bridge-fusion

Background: Quantitative analysis can be used in combination with fluorescence microscopy. Although the human eye is able to obtain good qualitative results, when analyzing the spatial organization of telomeres in interphase nuclei, there is a need for quantitative results based on image analysis. Methods: We developed a tool for analyzing three-dimensional images of telomeres stained by fluorescence in situ hybridization in interphase nuclei with DNA counterstained with 4 0 ,6-diamidino-2-phenylindole. After deconvolution of the image, we segmented individual telomeres. From the location of the telomeres we derived a distribution parameter r T , which indicated whether the telomeres were in a disk (r T ) 1) or not (r T % 1). We sorted mouse lymphocyte nuclei and measured r T . We also performed a bromodeoxyuridine synchronous cell sorting experiment on live cells and measured r T at several instances.