Effects of altering histone posttranslational modifications on mitotic chromosome structure and mechanics

Abstract

During cell division, chromatin is compacted into mitotic chromosomes to aid faithful segregation of the genome between two daughter cells. Posttranslational modifications (PTMs) of histones alter compaction of interphase chromatin, but it remains poorly understood how these modifications affect mitotic chromosome stiffness and structure. Using micropipette-based force measurements and epigenetic drugs, we probed the influence of canonical histone PTMs that dictate interphase euchromatin (acetylation) and heterochromatin (methylation) on mitotic chromosome stiffness. By measuring chromosome doubling force (the force required to double chromosome length), we find that histone methylation, but not acetylation, contributes to mitotic structure and stiffness. We discuss our findings in the context of chromatin gel modeling of the large-scale organization of mitotic chromosomes.

Force-induced gene up-regulation does not follow the weak power law but depends on H3K9 demethylation

“…Since heterochromatin domains at the nuclear membrane are packed chromatins and, thus, experience less deformation under force than euchromatin at the nuclear interior (35), it is possible that those genes at the nuclear interior are mechanoresponsive because they experience greater deformation than the genes at the nuclear periphery. Our results are consistent with this notion and are in line with a recent finding that hypermethylation of H3K9me2/3 results in an increase in mitotic chromosome stiffness (36). However, hypermethylation at H3K9me3 still experiences enough stretching that should have been sufficient to unpack chromatin domains to initiate transcription.…”

Mesoscale Phase Separation of Chromatin in the Nucleus

“…For example, nucleoplasmic lamin A can act to "crosslink" two chromatin regions in vivo [29][30][31]. Other studies have indeed considered chromatin to act as a polymer gel cross-linked by non-histone protein complexes [32,33].…”

Nucleus-Cytoskeleton Crosstalk During Mitotic Entry

“…Taken together, these observations implicate the NL in the mechanical stability of the nucleus and highlight the need for its depolymerization during prophase ( Georgatos et al, 1997 ), to facilitate microtubule-dependent nuclear permeabilization ( Beaudouin et al, 2002 ; Salina et al, 2002 ). At the same time, mitotic chromosomes condense, altering their structure and stiffness ( Stephens et al, 2017 ; Sun et al, 2018 ; Biggs et al, 2019 ). Evidence from metaphase chromosomes isolated from HeLa cells showed this process to be largely dependent on condensins ( Sun et al, 2018 ), although histone post-translational modifications also play an important role ( Biggs et al, 2019 ).…”

“…At the same time, mitotic chromosomes condense, altering their structure and stiffness ( Stephens et al, 2017 ; Sun et al, 2018 ; Biggs et al, 2019 ). Evidence from metaphase chromosomes isolated from HeLa cells showed this process to be largely dependent on condensins ( Sun et al, 2018 ), although histone post-translational modifications also play an important role ( Biggs et al, 2019 ). Finally, the actin cytoskeleton, which is connected to the nucleus through the LINC complex ( Versaevel et al, 2014 ), is remodeled to assemble a mitotic cortex ( Ramkumar and Baum, 2016 ).…”