Shaping centromeres to resist mitotic spindle forces

Abstract

The centromere serves as the binding site for the kinetochore and is essential for the faithful segregation of chromosomes throughout cell division. The point centromere in yeast is encoded by a ∼115 bp specific DNA sequence, whereas regional centromeres range from 6–10 kbp in fission yeast to 5–10 Mbp in humans. Understanding the physical structure of centromere chromatin (pericentromere in yeast), defined as the chromatin between sister kinetochores, will provide fundamental insights into how centromere DNA is woven into a stiff spring that is able to resist microtubule pulling forces during mitosis. One hallmark of the pericentromere is the enrichment of the structural maintenance of chromosome (SMC) proteins cohesin and condensin. Based on studies from population approaches (ChIP-seq and Hi-C) and experimentally obtained images of fluorescent probes of pericentromeric structure, as well as quantitative comparisons between simulations and experimental results, we suggest a mechanism for building tension between sister kinetochores. We propose that the centromere is a chromatin bottlebrush that is organized by the loop-extruding proteins condensin and cohesin. The bottlebrush arrangement provides a biophysical means to transform pericentromeric chromatin into a spring due to the steric repulsion between radial loops. We argue that the bottlebrush is an organizing principle for chromosome organization that has emerged from multiple approaches in the field.

Condensin reorganizes centromeric chromatin during mitotic entry into a bipartite structure stabilized by cohesin

“…A similar loop-based organization has been proposed for yeast centromeres to explain the physico-mechanical properties of the pericentromere and the observed compaction of the centromere in mitosis 44 . Interestingly, and in striking similarity to our Capture-C data, recent Hi-C analysis of yeast pericentromeres revealed a tendency of the regions flanking the core centromere to interact with the pericentromere of the same arm 42 .…”

“…Interestingly, and in striking similarity to our Capture-C data, recent Hi-C analysis of yeast pericentromeres revealed a tendency of the regions flanking the core centromere to interact with the pericentromere of the same arm 42 . Since our modeling indicates that the structure of the pericentromere is a major determinant of core centromere organization, a conserved condensin-driven bottlebrush architecture of the pericentromere 44 can therefore explain why bipartite centromeres are present along regional centromeres of a wide range of vertebrate species. Given observations of a bipartite kinetochore structure in Haemanthus 28, 29 , they may also be present in higher plants.…”

“…To build on the predictions from polymer modeling and our observations of a substantial amount of cohesin at or near the core centromere, we examined a potential role for cohesin in maintaining the architectural integrity of the centromere 42, 44 . Degron-mediated depletion of Sororin 45 , a protector of centromeric cohesin from Wapl-mediated release 46, 47 , produced a pronounced cohesion fatigue phenotype (Supplementary Movie 2), with single chromatids misaligned at spindle poles (arrowheads in +IAA condition in Fig.…”

It’s all in the numbers: Cohesin stoichiometry

“…Centromeres are specialized chromatin regions that adopt an elongated shape composed of a dense array of short loops organized around a central backbone. Cohesin, heavily enriched at pericentromeric regions, is essential for the proper organization of the region that is required for supporting kinetochore binding and generating the opposing spindle force ( Lawrimore et al, 2015 ; Lawrimore et al, 2017 ; Lawrimore and Bloom, 2019 ; Paldi et al, 2020 ; Lawrimore and Bloom, 2022 ). Cohesin removal from the centromeres at anaphase onset relieves the tethering force, and the sister chromatids are pulled to the opposing poles of the dividing cell ( Figure 1C ) ( Michaelis et al, 1997 ; Megee et al, 1999 ; Onn et al, 2008 ).…”

“…The chromosomal localization of cohesin may play a critical role in its tendency to oligomerize. Pericentromeric regions are heavily enriched with cohesin, which is essential for the proper structural organization of the region ( Lawrimore et al, 2015 ; Lawrimore et al, 2017 ; Lawrimore and Bloom, 2019 ; He et al, 2020 ; Lawrimore and Bloom, 2022 ). The high cohesin density can be a critical factor in enhancing oligomerization.…”