Journal Article

ChromEMT

Deerinck, Thomas J., Ou, Horng D., Phan, Sébastien, Ellisman, Mark H., Thor, Andrea, O’Shea, Clodagh C.

2017

Overview

The nuclei of human cells contain 2 meters of genomic DNA. How does it all fit? Compaction starts with the DNA wrapping around histone octamers to form nucleosomes, but it is unclear how these further compress into mitotic chromosomes. Ou et al. describe a DNA-labeling method that allows them to visualize chromatin organization in human cells (see the Perspective by Larson and Misteli). They show that chromatin forms flexible chains with diameters between 5 and 24 nm. In mitotic chromosomes, chains bend back on themselves to pack at high density, whereas during interphase, the chromatin chains are more extended. Science , this issue p. eaag0025 ; see also p. 354 A new technique reveals that chromatin is a disordered 5- to 24-nanometer chain that is packed at different concentration densities according to the cell cycle. The chromatin structure of DNA determines genome compaction and activity in the nucleus. On the basis of in vitro structures and electron microscopy (EM) studies, the hierarchical model is that 11-nanometer DNA-nucleosome polymers fold into 30- and subsequently into 120- and 300- to 700-nanometer fibers and mitotic chromosomes. To visualize chromatin in situ, we identified a fluorescent dye that stains DNA with an osmiophilic polymer and selectively enhances its contrast in EM. Using ChromEMT (ChromEM tomography), we reveal the ultrastructure and three-dimensional (3D) organization of individual chromatin polymers, megabase domains, and mitotic chromosomes. We show that chromatin is a disordered 5- to 24-nanometer-diameter curvilinear chain that is packed together at different 3D concentration distributions in interphase and mitosis. Chromatin chains have many different particle arrangements and bend at various lengths to achieve structural compaction and high packing densities.

• Publisher: American Association for the Advancement of Science,The American Association for the Advancement of Science
• Subject: 3,3'-Diaminobenzidine - chemistry / Amino acid sequence / Anthraquinones - chemistry / Cell division / Cell fate / Cell Nucleus - ultrastructure / Chromatids / Chromatin / Chromatin - chemistry / Chromatin - ultrastructure / Chromosomes / Compaction / Deoxyribonucleic acid / Diameters / Distribution patterns / DNA / DNA - chemistry / DNA - ultrastructure / DNA structure / Dyes / Electron microscopy / Epigenetics / Erythrocytes / Fibers / Fluorescent dyes / Fluorescent Dyes - chemistry / Fluorescent indicators / Folding / Gene mapping / Gene sequencing / Genomes / Heredity / Heterochromatin / High density / Histones / Humans / Interphase / Labeling / Magnesium chloride / Microscopy / Microscopy, Electron - methods / Mitosis / Nuclei / Nuclei (cytology) / Nucleosomes / Nucleosomes - ultrastructure / Nucleotide sequence / Oxidation-Reduction / Packaging / Polymers / RESEARCH ARTICLE SUMMARY / Spatial distribution / Spherical coordinates / Staining and Labeling - methods / Tomography / Ultrastructure