A charge-dependent phase transition determines interphase chromatin organization

An emerging principle of cellular compartmentalization is that liquid unmixing results in formation of compartments by phase separation. We used electron spectroscopic Imaging (ESI), a transmission electron microscopy technology, to distinguish chromatin and nucleoplasmic phases of mammalian cell lines and their responses towards different environmental changes. We tested the hypothesis that charge-dependent phase separation mediated by the histone N-termini could explain the organization of chromatin. 3D images of nuclear chromatin with electron spectroscopic imaging (ESI) demonstrates that the amount of chromatin proximal to the interchromatin compartment (IC) differs between cell types, reflecting major differences in chromatin organization. These differences were lost when cells were treated overnight with a histone deacetylase inhibitor. We show that drastic, reversible changes in chromatin mixing or unmixing with the nucleoplasm/interchromatin space can be induced by modulating osmolarity of the medium or acetylation status of the chromatin. In vitro phase separation experiments demonstrated that chromatin separated from solution through a phase transition towards a more solid chromatin state.

Identification of DNA and Single Nanoparticles (Qdots) in Muscle Tissue Sections by Low Energy-Loss Electron Spectroscopic Imaging

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Electron Spectroscopic Imaging of DNA Molecules along Carbon Nanotubes by Aberration-Corrected Transmission Electron Microscopy

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.