| Accurate cell proliferation is an important event during its whole life span,and the fidelity of cell proliferation is essential to reproduction of biological organisms.As cells proliferate,chromosomes with duplicated genetic information migrate during the whole process to achieve an accurate separation.During mitotic progression,dynamic growth or shrinking of kinetochore microtubules(kMTs)drive chromosome alignment and oscillation around spindle equator.However,how kMT dynamics is regulated remains largely unknown.Here,we report that CSPP1 is a novel kinetochore(KT)protein whose localization depends on Aurora B kinase activity.Inhibition of Aurora B kinase prevents KT residence of CSPP1.We also show that CSPP1 interacts with CENP-H,which is basis of KT localization of CSPP1.Suppression of CSPP1 impairs chromosome compaction at spindle equator and leads to mitotic arrest.The arrestment is spindle assembly checkpoint(SAC)mediated,as BubRl and Mad2 persist on metaphase KTs in CSPP1 depleted cells.Chromosome oscillation is greatly dampened by CSPP1 depletion.However,velocity of KT movement increases,without obvious defect on KT-MT attachment,which suggest an enhancement of kMT dynamics.Compared with normal cells,the dynamics of kMTs is highly elevated in CSPP1 inhibited cells,and the dynamics is greatly reduced when over-expressing CSPP1,implying that CSPP1 is an inhibitor of kMT dynamics.Indeed,CSPP1 forms a complex with MT depolymerase MCAK and inhibits its ATPase activity.Interestingly,we also found that CSPP1 asymmetrically localizes at sister KTs,as does CENP-H.Taken together,we propose that different tension on moving sister KTs allows Aurora B to recruit more CSPP1 on trailing KT,thus inhibiting MCAK activity to make sure of MT growth;while less CSPP1 on leading KT allows MTs to depolymerize,achieving a coordination between MTs on sister KTs.Auorora B,Mpsl and Bubl play important roles in localization of KT components.However,the underlying mechanism remains elusive.We found a new KT protein,Bubin.Inhibition of Bubin leads to mitotic arrest,defect of KT-MT attachment,failure of chrosome cohesion and so on.We also demonstrate that Bubin interacts with Bub1 and enhances its kinase activity.The KT residences of Bubin and Bubl rely on each other.Further,we found that Bubin also interactes with Incenp,a component of Chrosomal Passenger Complex(CPC).Bubin is required for KT targeting of CPC,and vice versa.Taken together,we propose that Bubin functions in regulating Aurora B-Mpsl-Bubl loop,thus faciliating assembly of functional KT.Taken together,my research on MT associated protein CSPP1 provides a mechanism for regulation of chromosome movement during mitosis and a potential conformation-function relationship.Besides,I identified a new binding partner of Bub1/BubR1 which we name it as Bubin.It is sure that further investigation of Bub1/BubR1-Bubin signaling would benefit our understanding of mechanisms underlying chromosome stability maintenance,thus providing a theoretical/technological basis for interference of human diseases. |
