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The inner centromere is a biomolecular condensate scaffolded by the chromosomal passenger complex.

ABSTRACT: The inner centromere is a region on every mitotic chromosome that enables specific biochemical reactions that underlie properties, such as the maintenance of cohesion, the regulation of kinetochores and the assembly of specialized chromatin, that can resist microtubule pulling forces. The chromosomal passenger complex (CPC) is abundantly localized to the inner centromeres and it is unclear whether it is involved in non-kinase activities that contribute to the generation of these unique chromatin properties. We find that the borealin subunit of the CPC drives phase separation of the CPC in vitro at concentrations that are below those found on the inner centromere. We also provide strong evidence that the CPC exists in a phase-separated state at the inner centromere. CPC phase separation is required for its inner-centromere localization and function during mitosis. We suggest that the CPC combines phase separation, kinase and histone code-reading activities to enable the formation of a chromatin body with unique biochemical activities at the inner centromere.

SUBMITTER: Trivedi P

PROVIDER: S-EPMC7341897 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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The inner centromere is a biomolecular condensate scaffolded by the chromosomal passenger complex.

Trivedi Prasad P Palomba Francesco F Niedzialkowska Ewa E Digman Michelle A MA Gratton Enrico E Stukenberg P Todd PT

Nature cell biology 20190903 9

The inner centromere is a region on every mitotic chromosome that enables specific biochemical reactions that underlie properties, such as the maintenance of cohesion, the regulation of kinetochores and the assembly of specialized chromatin, that can resist microtubule pulling forces. The chromosomal passenger complex (CPC) is abundantly localized to the inner centromeres and it is unclear whether it is involved in non-kinase activities that contribute to the generation of these unique chromatin ...[more]

PMID: 31481798

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Project description:DEAD-box helicases are important regulators of biomolecular condensates. However, the mechanisms through which these enzymes affect the dynamics of biomolecular condensates have not been systematically explored. Here, we demonstrate the mechanism by which mutation of a DEAD-box helicaseâ€™s catalytic core alters ribonucleoprotein condensate dynamics in the presence of ATP. Through altering RNA length within the system, we are able to attribute the altered biomolecular dynamics and material properties to physical crosslinking of RNA facilitated by the mutant helicase. These results suggest the mutant condensates approach a gel transition when RNA length is increased to lengths comparable to eukaryotic mRNA. Lastly, we show that this crosslinking effect is tunable with ATP concentration, uncovering a system whose RNA mobility and material properties vary with enzyme activity. More generally, these findings point to a fundamental mechanism for modulating condensate dynamics and emergent material properties through nonequilibrium, molecular-scale interactions.SignificanceBiomolecular condensates are membraneless organelles which organize cellular biochemistry. These structures have a diversity of material properties and dynamics which are crucial to their function. How condensate properties are determined by biomolecular interactions and enzyme activity remain open questions. DEAD-box helicases have been identified as central regulators of many protein-RNA condensates, though their specific mechanistic roles are ill-defined. In this work, we demonstrate that a DEAD-box helicase mutation crosslinks condensate RNA in an ATP-dependent fashion via protein-RNA clamping. Protein and RNA diffusion can be tuned with ATP concentration, corresponding to an order of magnitude change in condensate viscosity. These findings expand our understanding of control points for cellular biomolecular condensates that have implications for medicine and bioengineering.

Project description:A single inner centromere protein (INCENP) found throughout eukaryotes modulates Aurora B kinase activity and chromosomal passenger complex (CPC) localization, which is essential for timely mitotic progression. It has been proposed that INCENP might act as a rheostat to regulate Aurora B activity through mitosis, with successively higher activity threshold levels for chromosome alignment, the spindle checkpoint, anaphase spindle transfer and finally spindle elongation and cytokinesis. It remains mechanistically unclear how this would be achieved. Here, we reveal that the urochordate, Oikopleura dioica, possesses two INCENP paralogs, which display distinct localizations and subfunctionalization in order to complete M-phase. INCENPa was localized on chromosome arms and centromeres by prometaphase, and modulated Aurora B activity to mediate H3S10/S28 phosphorylation, chromosome condensation, spindle assembly and transfer of the CPC to the central spindle. Polo-like kinase (Plk1) recruitment to CDK1 phosphorylated INCENPa was crucial for INCENPa-Aurora B enrichment on centromeres. The second paralog, INCENPb was enriched on centromeres from prometaphase, and relocated to the central spindle at anaphase onset. In the absence of INCENPa, meiotic spindles failed to form, and homologous chromosomes did not segregate. INCENPb was not required for early to mid M-phase events but became essential for the activity and localization of Aurora B on the central spindle and midbody during cytokinesis in order to allow abscission to occur. Together, our results demonstrate that INCENP paralog switching on centromeres modulates Aurora B kinase localization, thus chronologically regulating CPC functions during fast embryonic divisions in the urochordate O. dioica. Abbreviations: CCAN: constitutive centromere-associated network; CENPs: centromere proteins; cmRNA: capped messenger RNA; CPC: chromosomal passenger complex; INCENP: inner centromere protein; Plk1: polo-like kinase 1; PP1: protein phosphatase 1; PP2A: protein phosphatase 2A; SAC: spindle assembly checkpoint; SAH: single α-helix domain.

Dataset Information

The inner centromere is a biomolecular condensate scaffolded by the chromosomal passenger complex.

Publications

The inner centromere is a biomolecular condensate scaffolded by the chromosomal passenger complex.

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