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Spatial Association of Homologous Pericentric Regions in Human Lymphocyte Nuclei during Repair

Shamci Monajembashi ^*, Alexander Rapp ^*, Eberhard Schmitt , Heike Dittmar ^*, Karl-Otto Greulich ^* and Michael Hausmann 

^* Department of Single Cell and Single Molecule Techniques and Department of Biocomputing, Institute of Molecular Biotechnology, Jena, Germany; and Institute of Pathology, University Hospital Freiburg, Freiburg, Germany

Correspondence: Address reprint requests to Dr. Shamci Monajembashi, Institute of Molecular Biotechnology, Beutenbergstrasse 11, D-07745 Jena, Germany. Tel.: 49-3641-656-409; Fax: 49-3641-656-410; E-mail: shamci{at}imb-jena.de.

Spatial positioning of pericentric chromosome regions in human lymphocyte cell nuclei was investigated during repair after H₂O₂/L-histidine treatment. Fifteen to three-hundred minutes after treatment, these regions of chromosomes 1, 15, and X were labeled by fluorescence in situ hybridization. The relative locus distances (LL-distances), the relative distances to the nuclear center (LC-distances), and the locus-nuclear center-locus angles (LCL-angles) were measured in 5000 nuclei after two-dimensional microscopy. Experimental frequency histograms were compared to control data from untreated stimulated and quiescent (G₀) nuclei and to a theoretical two-dimensional projection from random points. Based on the frequency distributions of the LL-distances and the LCL-angles, an increase of closely associated labeled regions was found shortly after repair activation. For longer repair times this effect decreased. After 300 min the frequency distribution of the LL-distances was found to be compatible with the random distance distribution again. The LL-distance frequency histograms for quiescent nuclei did not significantly differ from the theoretical random distribution, although this was the case for the stimulated control of chromosomes 15 and X. It may be inferred that, concerning the distances, homologous pericentric regions appear not to be randomly distributed during S-phase, and are subjected to dynamic processes during replication and repair.