CFAP300

CFAP300 is a cytoplasmic dynein arm preassembly factor (DNAAF) essential for the assembly and intraflagellar transport of both outer and inner dynein arms in motile cilia and sperm flagella. CFAP300 localizes predominantly to the cytoplasm where it interacts with DNAAF2 and is required for dynein arm preassembly; it is also transported within cilia in an IFT-dependent manner, accumulating at ciliary tips during ciliogenesis (PMID:29727692, PMID:29727693, PMID:36246608). Loss-of-function mutations in CFAP300 cause primary ciliary dyskinesia characterized by complete absence of both ODA and IDA from respiratory cilia and sperm flagella, resulting in cilia immotility, reduced flagellar length, acrosomal malformation, and male infertility (PMID:29727693, PMID:33635866, PMID:40898687, PMID:40806783). Tissue-specific differences in ODA retention between respiratory cilia and sperm flagella of CFAP300 mutants reflect distinct ODA type compositions along the proximal–distal axis of the axoneme (PMID:33635866).

1. 2018 High

   Identification of CFAP300 as a DNAAF resolved how loss of a single gene abolishes both ODA and IDA: CFAP300 mutations cause complete absence of both dynein arm types from cilia and flagella, establishing it as a cytoplasmic dynein arm preassembly factor.

   Evidence TEM, immunofluorescence, and high-speed video microscopy of respiratory cilia and sperm flagella from patients with CFAP300 loss-of-function mutations across multiple independent cohorts; RNAi in Paramecium and Chlamydomonas

   PMID:29727692 PMID:29727693

   Open questions at the time

   • Precise step in the dynein preassembly cascade at which CFAP300 acts is undefined
   • No structural information on CFAP300 or its complexes
   • Whether CFAP300 acts on ODA and IDA through the same or distinct mechanisms is unknown
2. 2018 High

   Demonstrating IFT-dependent ciliary transport of CFAP300 revealed it is not solely a cytoplasmic factor but also participates in dynein arm delivery within cilia, bridging preassembly and axonemal incorporation.

   Evidence Tagged protein localization in Paramecium and Chlamydomonas combined with IFT-A (IFT139/TTC21B) and IFT-B (FLA10) depletion experiments

   PMID:29727692

   Open questions at the time

   • Identity of the IFT adaptor linking CFAP300 to the IFT machinery is unknown
   • Whether ciliary CFAP300 is cargo-bound or travels independently has not been determined
3. 2018 Medium

   The physical interaction between CFAP300 and DNAAF2 placed CFAP300 within the known DNAAF network and suggested it functions as part of a preassembly complex rather than alone.

   Evidence Co-immunoprecipitation of C11orf70 with DNAAF2

   PMID:29727693

   Open questions at the time

   • Interaction detected by single Co-IP without reciprocal pull-down or in vitro reconstitution
   • Other components of the CFAP300-containing preassembly complex have not been identified
   • Functional consequence of disrupting the CFAP300–DNAAF2 interaction has not been tested
4. 2019 Medium

   Disparate localization of ODA and IDA markers in CFAP300-mutant cilia revealed that outer and inner dynein arms use distinct trafficking routes to the axoneme, deepening understanding of dynein arm delivery beyond cytoplasmic preassembly.

   Evidence Immunofluorescence of DNAH5 (ODA) and DNALI1 (IDA) in respiratory epithelial cells from CFAP300-mutant patients

   PMID:30916986

   Open questions at the time

   • Molecular basis for differential ODA vs. IDA trafficking not characterized
   • Whether residual proximal ODA reflects a CFAP300-independent assembly pathway is unresolved
5. 2021 High

   Comparative analysis of sperm versus respiratory cilia in CFAP300 mutants explained tissue-specific phenotypic severity: sperm flagella (single ODA type) lose all ODAs, while respiratory cilia can retain proximal ODAs, reflecting distinct ODA type compositions along the axoneme.

   Evidence Systematic IF, TEM, and high-speed video microscopy comparing sperm flagella and respiratory cilia across multiple DNAAF mutant individuals

   PMID:33635866

   Open questions at the time

   • Which specific ODA heavy chain isoforms are affected versus spared in different compartments is not fully resolved
   • Whether flagellar length reduction is a direct consequence of dynein loss or an independent CFAP300 function is unclear
6. 2022 Medium

   Super-resolution imaging in human airway epithelial cells confirmed intraciliary transport of CFAP300, extending the IFT-dependent transport finding from model organisms to human cells.

   Evidence Super-resolution microscopy of CFAP300 in normal human airway epithelial cells

   PMID:36246608

   Open questions at the time

   • Dynamics and directionality of CFAP300 transport within human cilia have not been measured
   • Whether CFAP300 returns retrogradely or is incorporated at the distal tip is unknown
7. 2025 Medium

   ALI-cultured patient airway cells confirmed complete cilia immotility and dynein arm absence in a controlled in vitro system, and proteomics of CFAP300-mutant sperm revealed broader defects including acrosomal malformation and altered mitochondrial and autophagy protein levels.

   Evidence ALI cultures with TEM, IF, and high-speed video microscopy; TMT-based quantitative proteomics of patient sperm

   PMID:40806783 PMID:40898687

   Open questions at the time

   • Whether acrosomal and mitochondrial defects are secondary to dynein loss or reflect independent CFAP300 functions is unresolved
   • Proteomic changes identified in a single patient cohort await independent validation
   • ALI rescue experiments with wild-type CFAP300 have not been performed

• The precise biochemical activity of CFAP300 in the dynein preassembly cascade — whether it acts as a chaperone, scaffold, or adaptor — remains unknown, and its full interaction network and structural basis have not been determined.
• No enzymatic or chaperone activity has been assigned to CFAP300
• No crystal or cryo-EM structure is available
• Complete set of direct CFAP300 binding partners is not defined
• Mechanism by which CFAP300 facilitates handoff of preassembled dynein complexes to IFT is unknown