CENPO

CENPO is a constitutive kinetochore protein that assembles into the CENP-O complex with CENP-P, CENP-Q, CENP-U (CENP-50), and CENP-R, functioning in faithful mitotic chromosome segregation and recovery from spindle damage (PMID:18094054). The four core subunits (CENP-O, -P, -Q, -U) form a stable complex whose kinetochore localization is interdependent, with CENP-R associating peripherally and localizing independently of the others (PMID:18094054); CENP-U serves as the master scaffold, since its loss removes all CENP-O complex members from kinetochores while leaving other kinetochore proteins intact (PMID:24481920). Architecturally, a defined region of CENP-U together with the CENP-Q C-terminus forms the CENP-U/Q heterocomplex that bridges to the CENP-O/P sub-complex, and CENP-R is tethered through interactions with CENP-U and CENP-Q rather than CENP-O/P (PMID:33660361). Functionally, the complex is required for recovery from spindle damage, preventing premature sister chromatid separation in a manner dependent on CENP-U phosphorylation and reversible by proteasome inhibition (PMID:18094054), and it acts in parallel with BUB1 to recruit threshold levels of PLK1 to mitotic kinetochores, such that loss of one pathway sensitizes cells to loss of the other (PMID:33596090).

1. 2007 High

   Established that CENP-O is a subunit of a discrete, stably assembled kinetochore complex rather than an isolated factor, defining its physical context.

   Evidence Bacterial coexpression reconstitution and DT40 knockout localization analysis

   PMID:18094054

   Open questions at the time

   • Did not resolve subunit stoichiometry or atomic architecture
   • CENP-R's mode of association left only partially defined
2. 2007 High

   Linked the complex to a cellular function — recovery from spindle damage — and identified CENP-U phosphorylation and proteasome regulation as control points for preventing premature sister chromatid separation.

   Evidence DT40 knockouts with nocodazole block/release and MG132 rescue

   PMID:18094054

   Open questions at the time

   • Kinase responsible for CENP-U phosphorylation not identified
   • Proteasome substrate driving premature separation not defined
   • CENP-O-specific contribution versus other subunits not isolated
3. 2014 High

   Resolved the assembly hierarchy by showing CENP-U is the master scaffold whose loss collapses kinetochore localization of all CENP-O complex members.

   Evidence Conditional knockout mouse ES cells with immunofluorescence of kinetochore proteins

   PMID:24481920

   Open questions at the time

   • Receptor at the kinetochore that recruits CENP-U not identified
   • Does not establish CENP-O's specific structural role within the complex
4. 2021 High

   Placed the complex in a defined molecular pathway by showing it acts in parallel with BUB1 to set threshold PLK1 levels at kinetochores, explaining synthetic genetic vulnerabilities.

   Evidence Genome-wide essentiality screens and genetic perturbation with PLK1 kinetochore localization readout

   PMID:33596090

   Open questions at the time

   • Molecular bridge connecting the complex to PLK1 not mapped
   • Specific CENP-O subunit mediating PLK1 recruitment not pinpointed
5. 2021 Medium

   Mapped the internal interaction architecture, defining the CENP-U/Q heterocomplex and how it bridges CENP-O/P and tethers CENP-R.

   Evidence In vitro binding assays with defined protein fragments

   PMID:33660361

   Open questions at the time

   • Single-lab domain mapping without full structural validation
   • No high-resolution structure of the assembled complex
   • Quantitative affinities of interactions not determined

• How CENP-U phosphorylation, proteasome activity, and PLK1 recruitment are mechanistically coupled to spindle-damage recovery remains unresolved.
• No identified kinase/phosphatase circuit controlling CENP-U
• No structural model of the complex bound to its kinetochore receptor or to PLK1