INCENP2

TgINCENP2 is an essential subunit of the Toxoplasma gondii chromosomal passenger complex (CPC), which it forms together with Aurora kinase 1 (TgArk1) and TgINCENP1 (PMID:30051161). Within this complex, TgINCENP2 is required for translocation of TgArk1 to the nucleus, since loss of TgINCENP2 function prevents the Aurora kinase from reaching its nuclear compartment (PMID:30051161). Functionally, TgINCENP2 is indispensable for faithful cell division and parasite growth—its interference produces pronounced division and growth defects, whereas TgINCENP1 is dispensable (PMID:30051161). Beyond its role in CPC assembly and TgArk1 targeting during endodyogeny, no further mechanistic detail has been characterized in the available corpus.

1. 2018 Medium

   Establishing whether TgINCENP2 is a bona fide component of the Toxoplasma CPC answered how the parasite organizes an Aurora-kinase-based mitotic machinery, placing TgINCENP2 alongside TgArk1 and TgINCENP1.

   Evidence Co-immunoprecipitation / interaction assays showing TgArk1 binds both TgINCENPs

   PMID:30051161

   Open questions at the time

   • Complex membership inferred from Co-IP in a single lab without independent replication
   • Stoichiometry and direct versus indirect binding within the complex not resolved
   • No structural model of the TgINCENP2-TgArk1 interface
2. 2018 Medium

   Determining that TgINCENP2 is required for nuclear delivery of TgArk1 clarified a functional hierarchy within the CPC, showing TgINCENP2 acts upstream of the kinase's subcellular targeting.

   Evidence Loss-of-function mutant analysis with fluorescence localization of TgArk1

   PMID:30051161

   Open questions at the time

   • Molecular mechanism of TgArk1 nuclear import via TgINCENP2 unknown
   • Whether TgINCENP1 contributes to TgArk1 targeting not distinguished
3. 2018 Medium

   Testing the requirement of each INCENP for viability showed TgINCENP2, but not TgINCENP1, is essential for division and growth, defining TgINCENP2 as the functionally critical CPC subunit.

   Evidence Genetic loss-of-function interference with division and growth phenotypic readouts

   PMID:30051161

   Open questions at the time

   • Molecular basis for the differential essentiality of TgINCENP1 versus TgINCENP2 not defined
   • Specific division step (spindle assembly, segregation, budding) that fails unresolved
4. 2018 Low

   Cell cycle-staged imaging showed the CPC displays dynamic localization consistent with organizing the mitotic spindle during endodyogeny, linking TgINCENP2 to spindle-associated events.

   Evidence Fluorescence microscopy across cell cycle stages

   PMID:30051161

   Open questions at the time

   • Dynamic localization described without functional dissection of the pattern
   • Direct role of TgINCENP2 in spindle organization not mechanistically demonstrated

• How TgINCENP2 mediates TgArk1 nuclear import at the molecular level and what spindle or chromosomal substrates the CPC acts on during endodyogeny remain unknown.
• No structural or biochemical characterization of the TgINCENP2-TgArk1 interaction
• Substrates phosphorylated by the TgArk1/TgINCENP2 complex unidentified
• Mechanism of the dynamic cell cycle-dependent localization not defined