This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Inside the cell nucleus, DNA is wrapped around histone proteins to form nucleosomes, which are further organized into chromatin. Chromatin has traditionally been divided into transcriptionally active euchromatin and relatively inactive heterochromatin.
However, chromatin is not a fixed structure. Nucleosomes continuously move within the nucleus, and this motion is closely related to the physical organization and function of the genome. Previous studies have shown that transcription can influence chromatin motion, but whether this effect is the same throughout the nucleus has remained unclear.
An international research team led by Kazuhiro Maeshima at the National Institute of Genetics and SOKENDAI has now investigated how different transcription systems affect the motion of distinct chromatin regions in living human cells. The work is published in the journal Cell Reports. The researchers combined two technologies.
The first was Repli-Histo labeling, a method previously developed by the group that distinguishes four chromatin classes, ranging from euchromatin (Classes IA and IB) to heterochromatin (Classes II and III). They further developed a machine-learning classifier to identify these chromatin classes objectively. The second technique was single-nucleosome imaging, which allowed the team to directly track the movement of individual nucleosomes in living cells.
This combination revealed that nucleosome motion becomes progressively more constrained from euchromatin toward heterochromatin. The researchers found that transcription does not constrain chromatin uniformly throughout the nucleus. When RNA polymerase II (Pol II), which transcribes most protein-coding genes, was inhibited using three different inhibitors, nucleosome motion increased in euchromatin (Classes IA and IB).
Surprisingly, increased motion was also observed in heterochromatin around nucleoli. In contrast, heterochromatin at the nuclear periphery showed little change. The team then examined RNA polymerase I (Pol I), which produces the major ribosomal RNAs inside nucleoli.
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