| During cell division it is essential that each daughter cell receives a full copy of the genome. The mitotic spindle apparatus, composed of microtubules and chromatin, faithfully segregates the duplicated genome equally between daughter cells. Microtubules bind to sister chromatids and exert extensional forces towards opposite poles. The pericentric chromatin surrounding the attachment site resists the microtubule forces with contractile spring-like prosperities. Tension generated from these opposing forces silences the spindle checkpoint to ensure accurate segregation. Using budding yeast as a model system we find that the chromatin spring is composed of the intramolecular pericentromere loop along with SMC protein complexes cohesin and condensin. Simulations of the pericentric chromatin as a non-linear spring accurately recapitulate in vivo spindle and chromatin dynamics. This is contrary to the dogma that the chromatin spring is linear. In addition, we find that the pericentromeres of the 16 different chromosomes in yeast physically interact and behave as an ensemble. The interlinked network of attachment sites in the yeast spindle provides insight as to how multiple attachments sites function in a mammalian kinetochore. Cohesin, condensin and the pericentromere compose an interlinked network of chromatin springs that equalizes tension over multiple dynamic attachment sites to aid the faithful segregation of the genome in mitosis. |
