CFAP300

CFAP300 (C11orf70/DNAAF17) is a cytoplasmic dynein arm preassembly factor required for the assembly of both outer (ODA) and inner (IDA) dynein arms in motile ciliary and flagellar axonemes (PMID:29727692, PMID:29727693). It localizes predominantly to the cytoplasm with a smaller pool transported into the ciliary compartment by an IFT-dependent mechanism, accumulating at ciliary tips in a distribution resembling the IFT-B protein IFT46 (PMID:29727692), and it is also detected moving along the length of cilia, consistent with a role in both cytoplasmic preassembly and trafficking of dynein complexes into the axoneme (PMID:36246608). Mechanistically it acts as a dynein preassembly factor through physical interaction with the assembly factor DNAAF2 (PMID:29727693). Loss-of-function mutations abolish CFAP300 protein and cause combined ODA+IDA deficiency with immotile cilia and absent ciliary beating in patient respiratory epithelium, and complete dynein arm loss with shortened, immotile sperm flagella, identifying it as a cause of primary ciliary dyskinesia and male infertility (PMID:36246608, PMID:40806783, PMID:33635866); in sperm, loss additionally produces acrosomal malformation and altered abundance of spermatogenesis and mitochondrial ATP-synthesis proteins (PMID:40898687). Beyond its conserved axonemal role, in zebrafish Cfap300 operates in a Cfap300-Hnf1ba-Cdh17 pathway governing epithelial-to-endocrine transdifferentiation in the pronephros (PMID:42067934).

1. 2018 High

   Established the core molecular function of CFAP300 as a cytoplasmic factor required for assembly of both dynein arm types, distinguishing it from axonemal structural components.

   Evidence RNAi knockdown, tagged localization, and IFT-component depletion epistasis in Paramecium and Chlamydomonas with TEM

   PMID:29727692

   Open questions at the time

   • Molecular step in the preassembly chain not resolved
   • Direct substrate or dynein subunit binding not biochemically defined
2. 2018 Medium

   Connected CFAP300 to the known DNAAF preassembly machinery and to human disease by demonstrating a physical interaction with DNAAF2 and disease-causing loss-of-function alleles.

   Evidence Co-immunoprecipitation with DNAAF2, TEM, immunofluorescence, and ciliogenesis expression analysis in patient material

   PMID:29727693

   Open questions at the time

   • Single lab; interaction interface and stoichiometry with DNAAF2 unknown
   • Whether interaction is direct or bridged by other DNAAFs not established
3. 2019 Medium

   Showed that outer versus inner dynein arm trafficking to the axoneme may follow distinct routes, refining how preassembled complexes reach their destination.

   Evidence Immunofluorescence of DNAH5 (ODA) and DNALI1 (IDA) in patient respiratory cells plus ortholog silencing in Schmidtea mediterranea

   PMID:30916986

   Open questions at the time

   • Mechanism producing disparate ODA/IDA localization not defined
   • Single lab
4. 2021 Medium

   Revealed tissue-specific consequences of CFAP300 loss, with complete dynein loss in sperm but partial proximal ODA retention in some respiratory cilia, linked to differing dynein arm composition between tissues.

   Evidence High-speed video microscopy, TEM, and comparative immunofluorescence of sperm flagella versus respiratory cilia with flagellar length analysis

   PMID:33635866

   Open questions at the time

   • Basis for tissue-specific differential requirement unresolved
   • Single study
5. 2022 Medium

   Provided direct evidence that CFAP300 is transported within cilia, extending its role from cytoplasmic preassembly to intraciliary dynein delivery.

   Evidence Super-resolution microscopy in normal human airway epithelial cells plus patient loss-of-function confirmation by IF and TEM

   PMID:36246608

   Open questions at the time

   • Cargo carried during transport not directly identified
   • Single lab
6. 2025 Medium

   Extended CFAP300's role in spermatogenesis beyond flagellar dynein to acrosome formation and altered abundance of spermatogenesis and mitochondrial proteins.

   Evidence TEM, immunofluorescence, histology, and TMT quantitative proteomics of patient versus control sperm

   PMID:40898687

   Open questions at the time

   • Single patient; causal link between CFAP300 loss and acrosome defect not mechanistically dissected
   • Whether proteomic changes are direct or secondary to immotility is unknown
7. 2025 Medium

   Uncovered a cilia-associated developmental signaling role in which Cfap300 loss derepresses hnf1ba to drive cdh17 and block endocrine transdifferentiation.

   Evidence TALEN zebrafish knockout with in situ hybridization, RT-qPCR/digital PCR, and two-step genetic epistasis rescue

   PMID:42067934

   Open questions at the time

   • Mechanism linking ciliary CFAP300 function to hnf1ba regulation unknown
   • Conservation of this pathway in mammals not tested
   • Single lab
8. 2025 Medium

   Confirmed in a physiological airway model that a recurrent loss-of-function allele abolishes CFAP300 protein, eliminates both dynein arms, and arrests ciliary beating.

   Evidence Air-liquid interface patient cultures with high-speed video microscopy, TEM, and immunofluorescence

   PMID:40806783

   Open questions at the time

   • Does not add new molecular mechanism beyond confirming null phenotype
   • Single lab

• How CFAP300 mechanistically loads dynein complexes onto IFT for axonemal delivery, and whether its developmental signaling role reflects cilia-dependent or independent functions, remain unresolved.
• No structure of CFAP300 or its DNAAF2 complex
• Dynein cargo handed off during intraciliary transport not identified
• Mammalian relevance of the Hnf1ba-Cdh17 pathway untested