Chromatin plates in the interphase nucleus

Abstract

Early results showed the emanation of chromatin fibers from mitotic chromosomes and nuclei swollen with water. In contrast, under metaphase ionic conditions, it was found that chromatin from mitotic chromosomes is planar and forms multilayered plates. Here, we show that in buffers containing interphase cation concentrations, the chromatin emanated from disrupted nuclei also has a planar morphology. Furthermore, the chromatin fragments produced by micrococcal nuclease digestion of nuclei form the typical beads‐on‐a‐string fibers in the absence of cations, but they self‐assemble into plate‐like structures in buffers containing magnesium. The plates from interphase nuclei do not form the thick multilayered structures observed in metaphase chromosomes, suggesting that they are more exposed to the medium to facilitate DNA replication and gene expression.

Supramolecular multilayer organization of chromosomes: possible functional roles of planar chromatin in gene expression and DNA replication and repair

“…(bottom) represents schematically these two compaction states of planar chromatin; it shows part of a chromosome that is compacted (all layers are tightly stacked; panel D) in mitosis and early G1 phase, and more extended with few contacts between layers in late G1, S and G2 phases (panel E). This model is consistent with EM results indicating that the chromatin plates in interphase have a lower tendency to form stacked multilayer structures than chromatin from metaphase chromosomes .…”

“…Chromatin emanated from disrupted nuclei suspended in buffers containing the cation concentrations found during interphase [18] also showed a laminar morphology [23]. Furthermore, chromatin fragments obtained from nuclei in G1, S and G2 cell cycle phases associate to form plate-like structures [23] in buffers containing physiological concentrations of monovalent cations and Mg 2+ (Fig. 1G, H).…”

“…The maintenance of the transverse orientation of chromosome bands after their mechanical splitting is also consistent with these observations. Since as indicated in the Introduction, there are evidences showing that chromatin plates do not disappear in interphase , these topological advantages are probably maintained throughout the cell cycle. In agreement with this, cytogenetic experiments using microdissection‐based multicolour banding showed that the band organization of chromosomes is essentially maintained during all the stages of the interphase (Fig.…”

“…1G, H). The planar structures observed in interphase are not so well defined as the plates from metaphase chromosomes and show a low tendency to stack together [23].…”

“…Chromatin plates emanate from soft‐denatured metaphase chromosomes and interphase nuclei , and they can be self‐assembled from chromatin fragments in the presence of physiological concentrations of Mg 2+ . Figures reproduced with permission from the indicated references.…”