Constrained, random, and independent motion of texas-red-labeled chromatin in living interphase PtK2 cells

Abstract

In this study, we observed and analyzed the sub-micron motion of interphase chromosomes in living cells, labeled with the fluorescent thymidine analogue, Texas-Red dUTP. Our approach has an advantage in that chromosomes can be analyzed with regard to the nuclear architecture. We calibrated the observed motion of fluorescence-labeled chromatin by eliminating the rotational and translational movement of living nuclei that could significantly affect chromatin motion. Mathematical analyses of chromatin motion showed that: (1) interphase chromatin in living nuclei moves randomly, and the motion is limited within a small sub-region; (2) chromatin near the nuclear envelope moves in a more limited area than does centrally located chromatin; and (3) closely situated chromatin domains move independently of each other. Random and constrained chromatin motion in living nuclei supports the concept that interphase chromatin fibers are loose, flexible and floating in the nuclear matrix, and that chromatin anchors to the backbone of chromosomes. Moreover, that the random motions of DNA domains are independent of each other suggests that interphase chromatin arranges without structurally rigid continuity. This active motion of chromatin is consistent with dynamic biological processes, requiring chromosome motility and interactions. Additionally, the dynamic properties of interphase chromosomes may be significant in the interpretation of acquired chromosomal aberrations.