A probabilistic model for the arrangement of a subset of human chromosome territories in WI38 human fibroblasts.

There is growing evidence that chromosome territories have a probabilistic non-random arrangement within the cell nucleus of mammalian cells. Other than their radial positioning, however, our knowledge of the degree and specificity of chromosome territory associations is predominantly limited to studies of pair-wise associations. In this study we have investigated the association profiles of eight human chromosome pairs (numbers 1, 2, 3, 4, 6, 7, 8, 9) in the cell nuclei of G(0)-arrested WI38 diploid lung fibroblasts. Associations between heterologous chromosome combinations ranged from 52% to 78% while the homologous chromosome pairs had much lower levels of association (3-25%). A geometric computational method termed the Generalized Median Graph enabled identification of the most probable arrangement of these eight chromosome pairs. Approximately 41% of the predicted associations are present in any given nucleus. The association levels of several chromosome pairs were very similar in a series of lung fibroblast cell lines but strikingly different in skin and colon derived fibroblast cells. We conclude that a large subset of human chromosomes has a preferred probabilistic arrangement in WI38 cells and that the resulting chromosomal associations show tissue origin specificity.