CFAP300 (C11orf70; also called DNAAF17) is a conserved accessory factor for the assembly of outer and inner axonemal dynein arms in motile cilia and sperm flagella. It associates with the assembly factor DNAAF2 and is predominantly cytoplasmic, with a smaller ciliary pool. Human biallelic loss-of-function variants cause primary ciliary dyskinesia with dynein-arm defects, impaired ciliary motility and, in some individuals, laterality abnormalities or male infertility. Experiments in Paramecium and Chlamydomonas show that the ciliary distribution of CFAP300 orthologs depends on intraflagellar transport. The precise molecular activity and the division of its contribution between dynein preassembly and delivery remain unresolved.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: Cytoplasmic localization is directly corroborated in human airway epithelial cells. Reason: The UniProt subcellular-location mapping is consistent with the predominant cytoplasmic pool detected by CFAP300 immunostaining in control human nasal epithelial cells (PMID:36246608, Figures 2D and 4); signal is markedly depleted in cells carrying truncating CFAP300 variants. Tagged native orthologs in Paramecium and Chlamydomonas independently show predominantly cytoplasmic localization (PMID:29727692, Figure 3). This localization supports its assembly-factor context without itself establishing a chaperone reaction. |
| GO:0005930 axoneme | IEA GO_REF:0000044 | ACCEPT | Summary: Human airway imaging supports axonemal localization without establishing stable structural incorporation. Reason: GO:0005930 includes proteins associated with the ciliary microtubule core; it does not require a constitutive or detergent-insoluble structural subunit. PMID:36246608, Immunofluorescence Methods, Figure 4 and its Results, directly detects endogenous CFAP300 along alpha-tubulin-marked axonemes in control human nasal epithelial cells using Airyscan imaging, with strongly depleted signal in affected cells. This independently corroborates the preserved UniProt subcellular-location mapping. PMID:29727692, Figure 3C–F, places tagged Chlamydomonas and Paramecium orthologs in a detergent-soluble ciliary membrane/matrix pool. Those organism- and preparation-specific data limit a stable-incorporation claim; they do not negate the human localization or exclude association with axonemal structures. The previous refinement to the already present motile-cilium term applied an unnecessarily strict structural-membership test. Retain the axoneme assertion while leaving residence time, direct microtubule contact and dynamic cargo carriage unresolved. Supporting Evidence: PMID:36246608 CFAP300 was present along the ciliary axoneme file:human/CFAP300/CFAP300-source-evidence.json |
| GO:0005515 protein binding | IPI PMID:29727692 C11orf70 Mutations Disrupting the Intraflagellar Transport-D... | KEEP AS NON CORE | Summary: DNAAF2 association is supported, while the original paper-to-annotation linkage needs clarification. Reason: PMID:29727693, Figure S12 and Table S2, reports a DNAAF2 yeast-two-hybrid result and recovery of tagged DNAAF2 with C11ORF70-HA; the IFT46 and PIH1D3 yeast results were excluded because of autoactivation and were not confirmed by co-immunoprecipitation. The original GOA reference PMID:29727692 is preserved; the read full text and current IntAct target query do not resolve that precise historical IPI linkage. Independent PMID:29727693 supports the binding assertion. No specific dynein-binding, chaperone, motor, or cargo-adaptor activity follows from this partner association. The pinned ClinGen instruction therefore supports retaining generic binding as non-core. Supporting Evidence: PMID:29727693 interaction with cytoplasmic ODA/IDA assembly factor DNAAF2 file:human/CFAP300/CFAP300-source-evidence.json |
| GO:0005737 cytoplasm | ISS GO_REF:0000024 | ACCEPT | Summary: Ortholog-derived cytoplasmic localization agrees with independent human evidence. Reason: Current source comparison resolves the original collapsed ISS assertion into donor accessions A0CY51 (Paramecium tetraurelia) and A8IYS6 (Chlamydomonas reinhardtii), each with direct localization evidence from PMID:29727692. The actual experiments expressed each organism’s own tagged ortholog, not human CFAP300. Human airway immunostaining in PMID:36246608 independently corroborates the same compartment. The historical source object remains unchanged rather than acquiring new donor or qualifier fields. |
| GO:0031514 motile cilium | ISS GO_REF:0000024 | ACCEPT | Summary: A small pool of CFAP300 occurs in motile cilia. Reason: The ISS source is consistent with the tagged ortholog localization and ciliary fractionation in PMID:29727692 and is independently supported by CFAP300 immunostaining along control human airway cilia in PMID:36246608, Figure 4. This is a localization conclusion, not a deduction from the patient motility phenotype. The human antibody imaging is an endpoint assay; it does not visualize transport direction, a moving dynein cargo, or a defined CFAP300 isoform. |
| GO:0036158 outer dynein arm assembly | IMP PMID:29727692 C11orf70 Mutations Disrupting the Intraflagellar Transport-D... | NEW | Summary: Retain the prior outer-dynein-arm assembly proposal with a bounded accessory-factor mechanism. Reason: Human CFAP300 variants selectively disrupt outer dynein arms and their axonemal markers in PMID:29727692 and PMID:29727693. This necessity evidence is joined by the direct DNAAF2 interaction assays in PMID:29727693, positioning CFAP300 as an accessory component of the assembly machinery rather than merely an assembled motor substrate. The assignment is a combined inference of assembly-factor participation, not purified catalytic activity or proof of dynein cargo carriage. Same-role DNAAF1, DNAAF2 and DNAAF3 carry assembly annotations; current typed parents and the fixed-main GO-CAM index reveal no convention excluding this role or conflicting CFAP300 model. Retain the specific outer-arm proposal and withdraw the redundant authored parent GO:0070286. Supporting Evidence: PMID:29727692 combined loss of inner and outer dynein arms file:human/CFAP300/CFAP300-source-evidence.json |
| GO:0036159 inner dynein arm assembly | IMP PMID:29727692 C11orf70 Mutations Disrupting the Intraflagellar Transport-D... | NEW | Summary: Retain the prior inner-dynein-arm assembly proposal with the same accessory-factor scope. Reason: Patient respiratory cilia lose inner-arm markers, including DNALI1, and PMID:29727693 additionally assays DNAH6-containing IDA groups and sperm flagella. Paramecium CFAP300 depletion similarly reduces inner arms. Combined with the DNAAF2 interaction, these findings support CFAP300 participation as an assembly accessory factor; they do not identify a catalytic step or demonstrate that all inner-arm types require it. This sibling of the outer-arm proposal adds distinct coverage. The redundant authored GO:0070286 parent is withdrawn; the current comparator, hierarchy and GO-CAM checks are recorded in the source evidence artifact. Supporting Evidence: PMID:29727692 assembly of dynein arms file:human/CFAP300/CFAP300-source-evidence.json |
Loading supporting content…
Download this section (compressed HTML)Q: Does CFAP300 stabilize or assemble a defined dynein intermediate, or mainly enable its subsequent delivery? Existing association and localization assays do not separate these roles.
Q: Do the three human CFAP300 products differ in dynein-intermediate association, cytoplasmic assembly-site residence or ciliary entry, and which differences are required for motile-cilium function?
Q: Does endogenous CFAP300 participate in cytoplasmic dynein-assembly particles (DynAPs), and does its interaction with DNAAF2 alter client assembly or residence rather than merely sharing the same compartment?
Experiment: Measure dynein intermediate composition and ciliary entry separately in CFAP300-deficient human airway cultures rescued with defined CFAP300 products and DNAAF2-interaction mutants.
Hypothesis: CFAP300-dependent assembly or stabilization can be separated from a later delivery defect.
Experiment: Test purified CFAP300 and DNAAF2 with defined dynein clients and appropriate binary-binding controls, then compare rescue activity in cells.
Hypothesis: A defined client or cofactor activity can explain the assembly phenotype without assuming a generic scaffold or chaperone mechanism.
Experiment: Test whether endogenously tagged CFAP300 is enriched with DNAAF2 and dynein clients in cytoplasmic dynein-assembly particles (DynAPs) in differentiated human airway cultures. Compare wild-type and interaction-disrupting rescue constructs, measuring local residence dynamics, dynein intermediate composition and subsequent ciliary entry separately.
Hypothesis: If CFAP300 performs an assembly-site cofactor role, its interaction with DNAAF2 should affect a defined client intermediate or residence behavior; colocalization alone would not establish that activity.
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: Which molecular activity does CFAP300 perform within the DNAAF2-associated assembly pathway, and at which step does it act?
OPEN BIOLOGY MF_DARK
What is known: Human and model-organism perturbations cause selective outer/inner dynein-arm defects; DNAAF2 association is directly supported. Human imaging and tagged ortholog fractionation establish predominantly cytoplasmic localization with a small ciliary pool. These data support an accessory assembly role but do not distinguish a chaperone, scaffold, other cofactor, or delivery mechanism. No reconstituted dynein-cargo bridge or universal requirement for every axonemal motor is established. MF_DARK here records biological uncertainty about the performed molecular activity, not an established activity for which GO is known to lack a term. DNAAF2 association does not by itself demonstrate selective bridging of two clients, protein-folding assistance or a preassembly-specific reaction.
Significance: Identifying the molecular step would determine whether an existing MF applies or an ontology proposal is warranted. An assembly-factor process role alone does not establish a missing MF, and the unresolved preassembly-versus-delivery distinction prevents defining a preassembly-specific activity for CFAP300.
What would resolve it: Combine defined CFAP300–DNAAF2 and dynein-subunit assays with separation-of-function rescue in differentiated human airway cells; measure soluble assembly intermediates and ciliary entry independently.
Provenance (the field's own admissions):
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)