The Role Of Haspin In The Centromeric Signaling Network And Related Mechanism

The centromere is a special region of chromosome that is necessary for faithful chromosome segregation during mitosis.Many proteins targeting to centromere collaborate together to form a dynamic centromere signaling network,which plays multiple roles into cohesion protection,kinetochore-microtubule attachment,the spinle assembly checkpoint and et al.It’s important to figure out the functions of centomeric proteins and related mechanism.From our study,we found that Haspin is a significant component of the centromere signaling network.Our research revealed the mechanism of Haspin in centromeric cohesion protection and how Haspin cooperates with Bub1 to regulate the activity of centromeric Aurora B.Sister chromatid cohesion,mediated by the multi-subunit cohesin complex,must be precisely regulated to prevent chromosome mis-segregation.In early mitosis,whereas the bulk of cohesin leaves chromosome arms due to the removing activity of its antagonist Wapl,however,centromeric regions retain enough cohesion complex to ensure chromosome biorientation until anaphase onset.It is still not clear how centromeric cohesin is protected against Wapl in mitosis.Here,we show that the interaction of mitotic histone kinase Haspin and the cohesin regulatory subunit Pds5 B,which is mediated by a conserved YGA/R motif in the noncatalytic N terminus of Haspin,is similar to YSR-motif-dependent binding of Wapl to Pds5 B.Haspin depletion or disruption of Haspin-Pds5 B interaction causes centromeric cohesion instability and premature chromatid separation,which can be rescued by inhibiting Wapl dependent cohesin removal.Taken together,these data indicate that the Haspin-Pds5 B interaction,which most likely antagonizes Wapl-mediated cohesin release,is nessesary for centromeric cohesion during mitosis.We further found that the C-terminal kinase domain of Haspin(Haspin-KD)binds and phosphorylates the YSR motif of Wapl(Wapl-YSR),thereby directly inhibiting the YSR motif-dependent interaction of Wapl with Pds5 B.Cells expressing a Wapl-binding deficient mutant of Haspin or treated with Haspin inhibitors show centromeric cohesion defects.Phospho-mimetic mutation in Wapl-YSR prevents Wapl from binding Pds5 B and releasing cohesin.Forced targeting Haspin-KD to centromeres partly bypasses the need for Haspin–Pds5B interaction in cohesion protection.Taken together,these results indicate a kinase-dependent role for Haspin in antagonizing Wapl and protecting centromeric cohesion in mitosis.Previous studies found that Haspin phosphorylates histone H3 at Thr-3 to position CPC at inner centromere.As the catalytic domain of CPC,Aurora B kinase plays an essential role in chromosome bi-orientation.However,it remains largely unclear whether centromere-localized Aurora B is required for faithful chromosome segregation.Here I show that histone H3 Thr-3 phosphorylation(H3pT3)and histone H2 A Thr-120 phosphorylation(H2ApT120)can independently recruit Aurora B.Disrupting H3pT3-mediated localization of Aurora B at the inner centromere impedes the decline in H2ApT120 during metaphase and causes H2ApT120-dependent accumulation of Aurora B at the kinetochore-proximal centromere.Consequently,silencing of the spindle assembly checkpoint(SAC)is delayed,whereas the fidelity of chromosome segregation is negligibly affected.Further eliminating the H2ApT120-dependent pool of Aurora B restores the proper timing for SAC silencing but increases chromosome mis-segregation.Our data indicate that H2ApT120-mediated localization of Aurora B compensates the loss of H3pT3-dependent pool of Aurora B to correct improper kinetochore-microtubule attachments and ensure error-free chromosome segregation.In general,our work dissects the role of Haspin in centromere signaling network and related mechanism.We also provide new insight into how different factors in the complex centromere signaling network are specialized to meet the multiple challenges encountered on the road to accurate chromosome segregation in mitosis...