The spindle and kinetochore-associated (Ska) protein complex is required for accurate chromosome segregation during mitosis [1-6] and consists of two copies each of Ska1, Ska2, and Ska3 proteins [4, 7]. The Ska complex contains multiple microtubule-binding elements and promotes kinetochore-microtubule attachment [8-11]. The Ska1 C-terminal domain (CTD) recruits protein phosphatase 1 (PP1) to kinetochores to promote timely anaphase onset [12]. The Ska complex regulates, and is regulated by, Aurora B [13]. Aurora B phosphorylates both Ska1 and Ska3 to inhibit the kinetochore localization of the Ska complex [14]. Despite its multitude of functions at kinetochores, how the Ska complex itself is recruited to kinetochores is unclear. It is unknown whether any mitotic kinases positively regulate the localization of the Ska complex to kinetochores. Here, we show that Cdk1 phosphorylates Ska3 to promote its direct binding to the Ndc80 complex (Ndc80C), a core outer kinetochore component. We also show that this phosphorylation occurs specifically during mitosis and is required for the kinetochore localization of the Ska complex. Ska3 mutants deficient in Cdk1 phosphorylation are defective in kinetochore localization but retain microtubule localization. These mutants support chromosome alignment but delay anaphase onset. We propose that Ska3 phosphorylated by Cdk1 in mitosis binds to Ndc80C and recruits the Ska complex to kinetochores where Ska1 can bind both PP1 and microtubules to promote anaphase onset.

Folic acid-functionalized polymer dots with aggregation induced emission features (AIE Pdots), which show high fluorescence efficiency and little toxicity to living cells, which possess a good capability for targeted HeLa intracellular imaging.

At anaphase onset, Sgo1 function of cohesion protection must be disabled to allow timely chromosome segregation, but how this is achieved is not fully understood. Here, we show that SET, a known PP2A inhibitor, directly binds to a domain in Sgo1 in close proximity to the cohesin-binding motif. The Sgo1–cohesin binding can be disrupted by SET in a dose-dependent manner in vitro as well as by SET overexpression in cells, suggesting that SET is also an inhibitor to the Sgo1–cohesin binding. Furthermore, the SET binding–deficient Sgo1 mutant fully supports centromeric cohesion protection but delays chromosome segregation, suggesting that the SET–Sgo1 binding is required for timely chromosome segregation. Moreover, overexpression of SET WT, not the Sgo1 binding–deficient mutant, exacerbates the occurrence of cohesion fatigue in MG132-arrested cells. Conversely, SET depletion delays it. Thus, we propose that a major function of SET during mitosis is to disrupt the Sgo1–cohesin interaction, thereby promoting centromeric cohesion de-protection and timely chromosome segregation at anaphase onset.

malononitrile) (TPA-AN-TPM) with near-infrared emission was synthesized by coating a disc-like red emission fluorophore with a propeller-shaped AIE fluorophore. The ultrabright red AIE dots TPA-AN-TPM@PS-PVP (TPA-AN-TPM in poly(styrene)-poly(4-vinylpyridine) nanoparticles) with an absolute quantum yield of 12.9% were fabricated by using the AIE molecule TPA-AN-TPM as the core and one biocompatible polymer PS-PVP as the encapsulation matrix. The AIE dots are mono-dispersed with an average diameter of 25 nm, and are stable in an aqueous suspension. In particular, the AIE dots can stain both the cytoplasm and the nuclei with a strong red fluorescence signal, and pose little toxicity to living cells.