SGO2

SGO2 is a conserved inner-centromere protein that serves as a multifunctional scaffold coordinating cohesin protection, kinetochore–microtubule error correction, and spindle assembly checkpoint (SAC) signaling during cell division. Aurora B kinase phosphorylates SGO2 at distinct sites to separately promote its binding to PP2A, which protects centromeric cohesin, and to MCAK, which corrects erroneous kinetochore attachments and supports chromosome congression; centromeric localization of SGO2 itself requires Mps1 kinase activity, while Bub1-mediated H2A phosphorylation directs SGO2 preferentially to the pericentromere (PMID:20889715, PMID:28947820, PMID:17485487). SGO2 additionally recruits SET/TAF1 to the inner centromere to sustain Aurora B activity by locally inhibiting PP2A, directly binds Mad2 to silence the SAC, and in fission yeast participates in a Mad2-independent APC/C-inhibitory pathway, yet is dispensable for separase inhibition during mouse oocyte meiosis I (PMID:31527146, PMID:24192037, PMID:28178520, PMID:40267054). Beyond mitosis and meiosis, fission yeast Sgo2 relocalizes to subtelomeres during interphase to establish knob chromatin structure in a manner dependent on histone deacetylation and H3-K36 methylation (PMID:40520116).

1. 2007 High

   Establishing that SGO2 is an inner-centromere protein required for MCAK recruitment and kinetochore attachment error correction answered where SGO2 acts and what happens when it is absent — lagging chromosomes and MCAK delocalization.

   Evidence siRNA depletion, immunofluorescence, Co-IP with PP2A, and live-cell imaging in HeLa cells

   PMID:17485487

   Open questions at the time

   • Mechanism by which SGO2 recruits MCAK not resolved
   • Whether PP2A association is functionally required not tested
   • Upstream signals controlling SGO2 centromeric localization unknown
2. 2007 Medium

   Demonstrating that SGO2 colocalizes with centromeric cohesin subunits RAD21 and REC8 and redistributes under tension in mouse meiosis established it as a candidate cohesin protector in mammalian meiosis.

   Evidence Immunofluorescence co-localization in mouse spermatocytes and oocytes

   PMID:17205076

   Open questions at the time

   • No loss-of-function evidence for cohesin protection provided
   • Mechanism of tension-dependent redistribution unknown
3. 2010 High

   Identifying Aurora B as the kinase that phosphorylates SGO2 at separate sites to independently control PP2A binding (cohesin protection) and MCAK binding (error correction) resolved how one scaffold coordinates two distinct centromeric functions through differential phosphorylation.

   Evidence In vitro kinase assay, phosphomutant rescue, Co-IP in HeLa cells

   PMID:20889715

   Open questions at the time

   • Structural basis of phospho-dependent binding switches unknown
   • Whether additional kinases contribute not tested
4. 2010 Medium

   Correlating age-related decline of Sgo2 at centromeres with cohesin loss and chromosome missegregation in aged mouse oocytes provided a physiological context — maternal age-related aneuploidy — for SGO2's cohesin protection function.

   Evidence Immunostaining and quantification in oocytes from young versus aged mice

   PMID:20817533

   Open questions at the time

   • Causal rescue experiment (restoring Sgo2 in aged oocytes) not performed
   • Whether decline is transcriptional or post-translational not determined
5. 2013 High

   Genetic knockout in mouse oocytes demonstrated that Sgol2 simultaneously protects cohesin (via PP2A), silences the SAC (via direct Mad2 binding), promotes congression (via MCAK), and limits bivalent stretching (by inhibiting Aurora C), establishing it as a multi-arm centromeric coordinator during female meiosis.

   Evidence Genetic KO in oocytes, Co-IP for PP2A/Mad2/MCAK, epistasis and functional rescue

   PMID:24192037

   Open questions at the time

   • How SGO2–Mad2 interaction silences the SAC mechanistically is unclear
   • Relative contribution of Aurora C inhibition versus other arms not quantified
6. 2017 High

   Pharmacological and genetic dissection of Mps1 and Bub1 kinase requirements revealed that Mps1 is essential for centromeric SGO2 localization and cohesin protection, while Bub1-mediated H2A phosphorylation directs SGO2 to the pericentromere but is not required for cohesin protection when Mps1 is active.

   Evidence Mps1 inhibitor and Bub1 kinase-dead mutant oocytes with SGO2 immunofluorescence and cohesin protection assay

   PMID:28947820

   Open questions at the time

   • Direct Mps1 substrate on SGO2 or loading factor not identified
   • Whether this hierarchy applies in mitotic cells not tested
7. 2017 Medium

   In fission yeast, identification of a Mad2-independent, Sgo2-dependent APC/C-inhibitory pathway revealed that SGO2 orthologs can delay anaphase onset through a non-canonical checkpoint mechanism when CPC–Klp9 interaction is disrupted.

   Evidence Double-mutant genetic epistasis in S. pombe

   PMID:28178520

   Open questions at the time

   • Whether this pathway operates in mammalian cells is untested
   • Biochemical mechanism of APC/C inhibition by Sgo2 not determined
8. 2019 Medium

   Showing that SET/TAF1 is recruited to the inner centromere through direct interaction with SGO2, where SET sustains Aurora B activity by locally inhibiting PP2A, revealed a positive-feedback loop through which SGO2 balances Aurora B and PP2A at centromeres.

   Evidence Co-IP of SET–SGO2, SET knockdown/overexpression with chromosomal instability readout in HeLa cells

   PMID:31527146

   Open questions at the time

   • Structural basis of SET–SGO2 interaction not resolved
   • How tension regulates SET displacement not mechanistically clear
9. 2025 High

   Biosensor experiments in mouse oocytes established that SGO2 is dispensable for separase inhibition during meiosis I, with securin and cyclin B1–CDK1 each providing sufficient inhibition independently, resolving a long-standing question about whether SGO2 has a direct separase-inhibitory role.

   Evidence Separase biosensor plus genetic perturbation of securin, cyclin B1–CDK1, and SGO2 in mouse oocytes

   PMID:40267054

   Open questions at the time

   • Whether SGO2 contributes to separase regulation in meiosis II or mitosis not addressed
   • Mechanism of SGO2 destruction timing still unexplored
10. 2025 Medium

    Discovery that fission yeast Sgo2 relocalizes from centromeres to subtelomeres during interphase to establish knob chromatin, dependent on histone H4 deacetylation and H3-K36 methylation, revealed an unexpected non-mitotic chromatin-organizing function for SGO2 orthologs.

    Evidence Genetic screen, nts1/set2 deletion, immunofluorescence and histone modification analysis in S. pombe

    PMID:40520116

    Open questions at the time

    • Whether mammalian SGO2 has analogous interphase chromatin roles is unknown
    • Molecular mechanism of knob formation not determined

• Key unresolved questions include the structural basis of SGO2's multi-partner scaffolding (PP2A, MCAK, Mad2, SET), the direct Mps1 substrate or adaptor that loads SGO2 to centromeres, whether the non-canonical SAC-inhibitory pathway operates in mammals, and whether SGO2 has interphase chromatin functions outside yeast.
• No high-resolution structure of SGO2 or its complexes
• Direct Mps1-dependent loading mechanism unresolved
• Mammalian relevance of interphase chromatin role untested