Phospho-H2A and Cohesin Specify Distinct Tension-Regulated Sgo1 Pools at Kinetochores and Inner Centromeres

Abstract

Accurate chromosome segregation requires coordination between the dissolution of sister-chromatid cohesion and the establishment of proper kinetochore-microtubule attachment. During mitosis, sister-chromatid cohesion at centromeres enables the biorientation of and tension across sister kinetochores. The complex between shugoshin and protein phosphatase 2A (Sgo1-PP2A) localizes to centromeres in mitosis, binds to cohesin in a reaction requiring Cdk-dependent phosphorylation of Sgo1, dephosphorylates cohesin-bound sororin, and protects a centromeric pool of cohesin from mitotic kinases and the cohesin inhibitor Wapl. Cleavage of centromeric cohesin by separase allows sister chromatids connected to microtubules from opposing poles to be evenly partitioned into daughter cells. The centromeric localization of Sgo1 requires histone H2A phosphorylation at T120 (H2A-pT120) by the kinase Bub1. The exact role of H2A-pT120 in Sgo1 regulation is, however, unclear. Here, we show that cohesin and H2A-pT120 specify two distinct pools of Sgo1-P2A at inner centromeres and kinetochores, respectively, in human cells. Bub1 inactivation delocalizes cohesin-Sgo1 to chromosome arms. Kinetochore tension triggers Sgo1 dephosphorylation and redistributes Sgo1 from inner centromeres to kinetochores. Incomplete Sgo1 redistribution causes chromosome nondisjunction. Our study suggests that Bub1-mediated H2A phosphorylation penetrates kinetochores and that this histone mark contributes to a tension-sensitive Sgo1-based molecular switch for chromosome segregation.

Premature Silencing of the Spindle Assembly Checkpoint Is Prevented by the Bub1-H2A-Sgo1-PP2A Axis in Saccharomyces cerevisiae

“…Cohesin and phosphorylated H2A specify two distinct pools of Sgo1-PP2A at inner centromere and kinetochores, respectively. The tension at kinetochores triggers the redistribution of Sgo1 from inner centromeres to kinetochores (Liu et al 2013). It is unclear if yeast cells have a spatial Sgo1 regulation during mitosis.…”

Tension-dependent removal of pericentromeric shugoshin is an indicator of sister chromosome biorientation

“…Shugoshins are localized to the region surrounding the centromere (the pericentromere) in a manner dependent on the cohesin complex and phosphorylation of histone 2A on residue S121 by the kinetochore-associated kinase Bub1 (Kawashima et al 2010;Liu et al 2013a). Shugoshins are emerging as important pericentromeric ''adaptor'' proteins that integrate multiple functions that contribute to accurate chromosome segregation (Gutié rrez-Caballero et al 2012;Rattani et al 2013;Verzijlbergen et al 2014).…”

Insights into centromeric transcription in mitosis

“…1), to protect the centromeric cohesion in mitosis, thus preventing chromosome missegregation and chromosome instability. [16][17][18][19][20] Our recent immunofluorescence microscopy demonstrated that Sgo1 is sequentially recruited to kinetochores and inner centromeres. 10 The kinetochore and centromeric receptors for Sgo1 are histone H2A phosphor Thr120 (H2A pT120) and cohesin, respectively.…”

“…19,21 I was wondering whether this is also a mechanism to recruit or maintain RNAP II at kinetochores in mitosis. Depletion of Bub1 or pharmacological inhibition of Bub1 kinase activity was sufficient to dislodge RNAP II from kinetochores, which inactivates the transcription at kinetochores.…”

“…10 The kinetochore and centromeric receptors for Sgo1 are histone H2A phosphor Thr120 (H2A pT120) and cohesin, respectively. 19,21 How is Sgo1 installed at inner centromeres after initial kinetochore recruitment? Our data strongly suggests that RNAP II transcription plays an important role in Figure 1.…”