Topography of chromosome territories - evidence for a structural memory of nuclear architecture
Understanding nuclear architecture is indispensable to understand the cell type dependent orchestration of active and silent genes and other nuclear functions, such as RNA-splicing, DNA-replication and repair1. The topography of chromosome territories (CTs) and the interchromatin compartment (IC) was analyzed in human cells with emphasis a) on the relative contribution of large and small chromatin loops to CT architecture and b) on the dynamics of CT and IC arrangements during interphase2. We demonstrate that most chromatin is present in compact domains with a DNA content from about one to few Mb. Occasional giant loops that expand from the periphery of CTs showed a chromatin compaction of about 1 : 300 or more. This finding argues against a major contribution of expanded 10 or 30 nm chromatin fibers. In interphase nuclei of living cells we induced chromatin condensation - decondensation cycles by the transient increase of osmolarity in the medium (290 - 570 - 290 mOsm/l). Within one minute following exposure of cells to hyperosmolar medium we observed a contiguous network of hyper-condensed chromatin (HCC) bundles with diameters of several hundred nanometers, side by side with a network of expanded IC channels and lacunas. Exposure of living interphase cells to repeated cycles revealed strikingly preserved global chromatin arrangements demonstrating a "memory" of higher order chromatin organization.
1 T. Cremer, M. Cremer, S. Dietzel, S. Müller, I. Solovei, S. Fakan. Role of chromosome territories in the functional nuclear landscape. Ms submitted.
2 H. Albiez, L. Schermelleh, C. Tiberi, L. Vecchio, T. Thormeyer, I. Solovei, B. Joffe, M. Cremer, S. Dittrich, S. Yang, K. Rohr, H. Leonhardt, J. von Hase, C. Cremer, S. Fakan, T. Cremer. Evidence for a structural memory of nuclear architecture. Ms submitted.