Characteristics of chromosomes in polarized normal human bronchial cells provide a blueprint for nuclear organization

In normal human terminally differentiated and polarized bronchial cells, the fluorescent "painting" technique (FISH) for all chromosomes (except Y) documented that each homologue of each chromosome occupies a distinct, separate domain within the nucleus. The homologues are distributed along the nuclear membrane. In most cells and chromosomes studied, the two homologues were not identical: one was usually more "compact" than the other which was more "open," displaying fiber-shaped extensions. The differences between the territories of homologues 1 and 7 were shown to be statistically valid (P < 0.0001 by Wilcoxon sign rank test), as has been previously documented for the two X chromosomes (Eils et al., 1996). In some parallel arrays of bronchial cells, the position of the chromosomes in the nuclei was either identical or formed a mirror image, suggesting that the position of the chromosomes in polarized nuclei may be constant. To confirm this observation, the angles formed by the two homologues in the polarized oval nuclei were measured for chromosomes 1, X, and 7. The measurements disclosed that, in about two-thirds of the nuclei, the two homologues formed angles of 150 degrees, 157 degrees and 148 degrees, nearly identical to those formed by the same three chromosomes in prometaphase rosettes of cultured diploid human fibroblasts (Nagele et al., 1995). In about one third of the nuclei, the same homologues formed angles of 89 degrees, 72 degrees, and 94 degrees, and occasionally an angle of 180 degrees. A three-dimensional computer reconstruction of the nuclei was performed using the data for the X chromosomes. By cinematographic technique, it could be documented that the angles separating the two homologues depended on the rotation of the nucleus along the axes X, Y, and Z. The cause of the rotation is speculative at this time. Because of the concordance of these data in terminally differentiated epithelial cells with prior observations on prometaphases of human diploid fibroblasts, it is suggested that the position of chromosomes in all human cells is constant throughout the cell cycle. The possible significance of these observations is discussed.