CEP44

CEP44 is a luminal centriole protein that functions as a structural scaffold coordinating centriole biogenesis and centrosome integrity (PMID:32060285, PMID:31974111). It localizes to the proximal end of both mother and daughter centrioles in ninefold symmetry, binding A-microtubules of the centriole wall and interacting with POC1B to maintain wall structure (PMID:32060285, PMID:37707473). CEP44 acts downstream of CEP295 in a centriole-to-centrosome conversion pathway (CEP295→CEP44→POC1B→TUBE1/TUBD1) that is required for pericentriolar material recruitment; its depletion blocks conversion even when CEP295 still binds centrioles (PMID:32060285). Independently of C-Nap1, LRRC45, and Cep215, CEP44 associates with rootletin and regulates its stability and localization to maintain centrosome cohesion (PMID:31974111). CEP44 also contains intrinsically disordered regions that drive liquid-liquid phase separation into droplets in vitro and in vivo, and it is O-GlcNAcylated by OGT, a modification that promotes droplet fusion and influences its subcellular localization (PMID:40906019).

1. 2020 High

   Established CEP44's molecular role in centriole architecture by placing it within an ordered biogenesis pathway and identifying its physical and structural partners.

   Evidence siRNA depletion, Co-IP, and electron microscopy defining the CEP295→CEP44→POC1B→TUBE1/TUBD1 axis in human cells

   PMID:32060285

   Open questions at the time

   • How CEP44 binding to A-microtubules mechanically stabilizes the wall is not resolved at atomic detail
   • The direct biochemical link between CEP44 and TUBE1/TUBD1 is not demonstrated
   • Whether CEP44 recruits POC1B directly or via intermediates is unclear
2. 2020 Medium

   Extended CEP44's function beyond biogenesis to centrosome cohesion by linking it to rootletin stability, defining a pathway distinct from canonical cohesion factors.

   Evidence siRNA ablation, Co-IP, and centrosome cohesion assays showing CEP44 regulates rootletin independently of C-Nap1, LRRC45, and Cep215

   PMID:31974111

   Open questions at the time

   • Mechanism by which CEP44 stabilizes rootletin is unknown
   • Single-lab finding without reciprocal structural validation
   • Relationship between cohesion role and centriole-wall role not integrated
3. 2023 Medium

   Resolved CEP44's precise spatial organization, confirming a ninefold-symmetric arrangement consistent with direct association with the centriole microtubule wall.

   Evidence Expansion/super-resolution nanoscale imaging of the centrosome

   PMID:37707473

   Open questions at the time

   • Does not establish stoichiometry of CEP44 per centriole
   • Single-lab localization without functional perturbation
4. 2025 Medium

   Revealed a biophysical and regulatory dimension to CEP44 function, showing it phase-separates and that O-GlcNAcylation by OGT modulates its condensate behavior and localization.

   Evidence In vitro/in vivo droplet assays, immunoblotting for O-GlcNAcylation, and immunostaining

   PMID:40906019

   Open questions at the time

   • Functional consequence of CEP44 LLPS for centriole biogenesis or cohesion is not established
   • O-GlcNAcylation sites are not mapped
   • Whether phase separation occurs at the centriole in cells is not shown

• How CEP44's structural scaffolding at the centriole wall, its regulation of centrosome cohesion, and its phase-separation behavior are mechanistically integrated remains unresolved.
• No unified model linking wall stabilization, rootletin regulation, and condensate formation
• No high-resolution structure of CEP44 bound to microtubules or POC1B
• Role of CEP44 LLPS in vivo at the centrosome undefined