A three-dimensional approach to mitotic chromosome structure: evidence for a complex hierarchical organization.
We describe findings on the architecture of Drosophila melanogaster mitotic chromosomes, made using a three-dimensional-oriented structural approach. Using high-voltage and conventional transmission electron microscopy combined with axial tomography and digital contrast-enhancement techniques, we have for the first time visualized significant structural detail within minimally perturbed mitotic chromosomes. Chromosomes prepared by several different preparative procedures showed a consistent size hierarchy of discrete chromatin structural domains with cross-sectional diameters of 120, 240, 400-500, and 800-1,000 A. In fully condensed, metaphase-arrested chromosomes, there is evidence for even larger-scale structural organization in the range of 1,300-3,000-A size. The observed intrachromosomal arrangements of these higher-order structural domains show that both the radial loop and sequential helical coiling models of chromosome structure are over-simplifications of the true situation. Finally, our results suggest that the pathway of chromatin condensation through mitosis consists of concurrent changes occurring at several levels of chromatin organization, rather than a strictly sequential folding process.
D000818:Animals; D002843:Chromatin / Q000648:ultrastructure; D002875:Chromosomes / Q000648:ultrastructure*; D004331:Drosophila melanogaster / Q000196:embryology / Q000648:ultrastructure; D007091:Image Processing, Computer-Assisted; D008677:Metaphase; D008854:Microscopy, Electron; D008954:Models, Biological; D014054:Tomography
D002843:Chromatin