CEP44

CEP44 is a luminal centriole protein that localizes in ninefold symmetry at the proximal end of both mother and daughter centrioles, where it binds A-microtubules and interacts with POC1B to maintain centriole wall integrity and enable centriole-to-centrosome conversion through a CEP295→CEP44→POC1B→TUBE1/TUBD1 pathway required for pericentriolar material recruitment (PMID:32060285, PMID:37707473). Independently of its role in centriole biogenesis, CEP44 associates with rootletin to stabilize the centrosome linker and maintain centrosome cohesion; its depletion causes premature centrosome separation without affecting C-Nap1 or LRRC45 levels (PMID:31974111). CEP44 contains intrinsically disordered regions that drive liquid–liquid phase separation, and O-GlcNAcylation by OGT promotes CEP44 droplet fusion and modulates its centrosomal localization (PMID:40906019).

1. 2020 High

   Establishing that CEP44 functions as a luminal centriole structural component acting downstream of CEP295 to recruit POC1B, maintain centriole wall integrity, and enable centriole-to-centrosome conversion resolved where CEP44 fits in the centriole biogenesis hierarchy.

   Evidence siRNA depletion with electron microscopy, co-immunoprecipitation, epistasis analysis, and immunofluorescence in human cells

   PMID:32060285

   Open questions at the time

   • Direct binding interface between CEP44 and A-microtubules not structurally resolved
   • Whether CEP44 has catalytic activity or acts purely as a scaffold is unknown
   • Mechanism by which CEP44 loss prevents PCM recruitment despite CEP295 presence is unclear
2. 2020 High

   Demonstrating that CEP44 associates with rootletin and is required for centrosome linker stability and cohesion revealed a second, distinct function for CEP44 at the proximal centriole end, separable from its centriole biogenesis role.

   Evidence siRNA depletion, reciprocal co-immunoprecipitation, centrosome cohesion assays, and immunofluorescence in human cells

   PMID:31974111

   Open questions at the time

   • Whether the rootletin-binding and POC1B-binding functions of CEP44 are mediated by distinct domains is unknown
   • How CEP44 stabilizes rootletin at a molecular level has not been determined
3. 2023 Medium

   Super-resolution mapping of CEP44 in ninefold symmetry at centrioles provided a precise nanoscale framework for its structural role, distinguishing it from outer centriole components like CEP152.

   Evidence Expansion microscopy and super-resolution fluorescence imaging in human cells

   PMID:37707473

   Open questions at the time

   • No functional perturbation of CEP44 was performed in this study
   • Whether the ninefold pattern reflects direct microtubule attachment stoichiometry is unresolved
4. 2025 Medium

   Discovery that CEP44 undergoes liquid–liquid phase separation via intrinsically disordered regions and that OGT-mediated O-GlcNAcylation promotes droplet fusion and modulates centrosomal localization introduced a post-translational regulatory layer to CEP44 function.

   Evidence In vitro and in vivo droplet formation assays, co-immunoprecipitation with OGT, immunoblotting for O-GlcNAc, immunostaining, and PTM prediction analysis

   PMID:40906019

   Open questions at the time

   • Specific O-GlcNAcylation sites on CEP44 have not been mapped by mutagenesis
   • Functional consequence of LLPS for centriole biogenesis or centrosome cohesion not tested
   • Interplay between O-GlcNAcylation and phosphorylation is based on prediction, not direct experimental validation

• The relationship between CEP44 phase separation properties and its two established functions — centriole-to-centrosome conversion and centrosome linker maintenance — remains unconnected, as does the structural basis of its interactions with POC1B and rootletin.
• No high-resolution structure of CEP44 or its complexes exists
• Whether LLPS contributes to PCM recruitment or linker assembly is untested
• In vivo relevance of CEP44 loss in animal models has not been reported