Helical metaphase chromatid coiling is conserved

Abstract

The higher-order metaphase chromosome organization has been under controversial discussion already for 140 years. Classical light and electron microscopy proposed chromatids to be composed of helically organized chromatin fibers, so-called chromonemata. More recently also non-helical models were suggested. We studied the chromosome organization in barley by interdisciplinary cutting-edge approaches, such as chromosome sorting, chromosome conformation capture, oligonucleotide-fluorescence in situ hybridization, base analog incorporation, super-resolution microscopy, and polymer simulation to elucidate the arrangement of chromatids of large mitotic metaphase chromosomes. Our data provide cumulative evidence for the presence of a helically arranged 400 nm chromatin fiber representing the chromonema within the chromatid arms. The number of turns is positively correlated with the arm length. Turn size and chromatin density decrease towards the telomeres. Due to the specialized functions of centromeres and nucleolus-organizing regions, the helical organization is interrupted at these regions, which display several thinners and straight chromatin fibers. Based on our findings and re-analyzing previously published data from other plant and non-plant species we conclude that the helical turning of metaphase chromatid arms is a conserved feature of large eukaryotic chromosomes.

Single-Molecule Micromanipulation and Super-Resolution Imaging Resolve Nanodomains Underlying Chromatin Folding in Mitotic Chromosomes

“…Thus, we reasoned that imaging the DNA should be the most direct method to interrogate the native structure. We imaged mitotic chromosomes in metaphase-arrested HeLa cells using 3D-SIM with the cyanine dye, YOYO-1, which has a high affinity for DNA and bright fluorescence with a low background (Figure A). , We note that it is believed that the metaphase chromosome higher-order structure is quite similar among mammalian cells, , and so these results from HeLa cells should be applicable to mammalian cells in general. These images revealed easily appreciable granular domains (that we call compact granules (CGs)) more or less homogeneously distributed throughout each chromosome (Figure A and Figure S1A).…”

The Czech Plant Nucleus Workshop 2021

“…A complex study of the higherorder 3D structure of both metaphase and interphase chromosomes was presented by H. Šimková (IEB). By a combination of Hi-C and chromosome painting techniques, she demonstrated that sister chromatids of barley metaphase chromosomes have a helical structure, where one turn contains 20 -38 Mbp chromatin-packed DNA, depending on the position on the chromosome arm (Kubalová et al 2021a). Microscopy is a classical technique to study cell nuclei and chromosomes.…”

FISH Going Meso-Scale: A Microscopic Search for Chromatin Domains

“…For these reasons, Oligopaints are widely applied to assess the organization of TADs, A/B compartments and other chromatin domains in different model organisms ( Boettiger and Murphy, 2020 ; Hu and Wang, 2021 ). Moreover, this type of FISH-probe is used to address questions of chromatin fiber organization within highly compacted metaphase chromosomes ( Kubalová et al, 2021 ). In further sections, we briefly review major insights from FISH-imaging, which together with 3C-based methods aided pieces to the puzzle of spatial organization of chromatin domains in human, mouse, Drosophila and other model genomes.…”