ABSTRACT
The structure of chromatin at the nucleosome level inside cells is mysterious. Here we present in situ cryo-ET analyses of chromatin in both G1 and metaphase RPE-1 cells. G1 nucleosomes are concentrated in globular chromatin domains and metaphase nucleosomes are concentrated in the chromatids. Classification analysis reveals that canonical mononucleosomes, ordered stacked dinucleosomes, and mononucleosomes with a disordered gyre-proximal density are abundant in both cell-cycle states. Class averages that have more than two stacked nucleosomes or that have side-by-side dinucleosomes are not detected, suggesting that groups of more than two nucleosomes are heterogeneous. Large multi-megadalton structures are abundant in G1 nucleoplasm, but not found in G1 chromatin domains and metaphase chromatin. The macromolecular phenotypes studied here represent a starting point for the comparative analysis of condensation in normal and unhealthy human cells, in other cell-cycle states, other organisms, and in vitro chromatin assemblies.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
New terms: Dense irregular bodies
Abbreviations used
- cryo-ET
- electron cryotomography / cryo-electron cryotomography
- Megacomplex
- multi-megadalton globular complexes
