Frozen‐hydrated chromatin from metaphase chromosomes has an interdigitated multilayer structure. (4th January 2019)

• Record Type: Journal Article
• Authors: Chicano, Andrea; Crosas, Eva; Otón, Joaquín; Melero, Roberto; Engel, Benjamin D; Daban, Joan‐Ramon
• Is Part Of: EMBO journal. Volume 38:Number 7(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2019-01-04
• Subjects: chromatin higher‐order structure -- cryo‐electron tomography -- DNA packaging -- metaphase chromosome structure -- small‐angle X‐ray scattering; Molecular biology -- Periodicals; 572.805
• DOI: 10.15252/embj.201899769
• Languages: English
• ISSNs: 0261-4189

Abstract

Abstract: Cryo‐electron tomography and small‐angle X‐ray scattering were used to investigate the chromatin folding in metaphase chromosomes. The tomographic 3D reconstructions show that frozen‐hydrated chromatin emanated from chromosomes is planar and forms multilayered plates. The layer thickness was measured accounting for the contrast transfer function fringes at the plate edges, yielding a width of ~ 7.5 nm, which is compatible with the dimensions of a monolayer of nucleosomes slightly tilted with respect to the layer surface. Individual nucleosomes are visible decorating distorted plates, but typical plates are very dense and nucleosomes are not identifiable as individual units, indicating that they are tightly packed. Two layers in contact are ~ 13 nm thick, which is thinner than the sum of two independent layers, suggesting that nucleosomes in the layers interdigitate. X‐ray scattering of whole chromosomes shows a main scattering peak at ~ 6 nm, which can be correlated with the distance between layers and between interdigitating nucleosomes interacting through their faces. These observations support a model where compact chromosomes are composed of many chromatin layers stacked along the chromosome axis. Synopsis: Cryo‐electron tomography (ET) reveals that the long chromatin filaments in human metaphase chromosomes are folded to form multilaminar structures, which are probably stacked along the chromosome axis. This compact organization of chromatin may be useful for the protecting genomic DNA during cell division. Frozen‐hydrated (unsupported, uncrosslinked, and unstained) chromatin emanated from metaphase chromosomes is planar and forms multilayered plates. Cryo‐tomograms show large multilayered plates with widths similar to the diameter of human chromatids. Thickness measurements suggest that plates are formed by mononucleosome layers, interdigitated with each other in compact multilayered plates. SAXS of chromosomes shows a dominant peak at ˜ 6 nm, which can be correlated with the distance between layers and between nucleosomes interacting through their faces. Abstract : Cryo‐electron tomography of non‐crosslinked, non‐surface‐absorbed samples implicates stacked planar layers of mononucleosome width in 3D‐assembly of compact mitotic chromatin.