CFAP300 (formerly C11orf70) is a dynein axonemal assembly factor essential for the cytoplasmic preassembly and intraflagellar transport (IFT)-dependent trafficking of both outer and inner dynein arm complexes into motile cilia and flagella. The protein localizes predominantly to the cytoplasm where it participates in dynein arm assembly, with evidence of IFT-dependent movement along the ciliary axoneme. Loss-of-function mutations cause primary ciliary dyskinesia (PCD) characterized by combined ODA+IDA loss, respiratory disease, laterality defects, and male infertility. CFAP300 interacts with the cytoplasmic ODA/IDA assembly factor DNAAF2 and belongs to the conserved CFAP300 protein family with a DUF4498 domain.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: CFAP300 localizes predominantly to the cytoplasm where it functions in dynein arm preassembly. This is supported by multiple lines of evidence including immunofluorescence studies showing cytoplasmic localization in human airway epithelial cells [PMID:29727692, PMID:29727693] and model organism studies in Paramecium and Chlamydomonas [PMID:29727692]. Reason: Cytoplasmic localization is a core aspect of CFAP300 function, as the protein participates in the cytoplasmic preassembly of dynein arm complexes before their IFT-dependent transport into cilia. UniProt also annotates cytoplasmic localization based on sequence similarity to orthologs (ISS). Supporting Evidence: PMID:29727692 Tagged C11orf70 in Paramecium and Chlamydomonas localizes mainly in the cytoplasm with a small amount in the ciliary component. PMID:29727693 C11orf70 is involved in cytoplasmic assembly of dynein arms. file:human/CFAP300/CFAP300-deep-research-falcon.md CFAP300 localizes predominantly in the cytoplasm of human airway epithelial cells, with additional evidence of transport along the ciliary axoneme |
| GO:0005930 axoneme | IEA GO_REF:0000044 | ACCEPT | Summary: CFAP300 shows IFT-dependent transport into cilia and accumulates at ciliary tips during ciliogenesis [PMID:29727692]. While the protein localizes mainly in the cytoplasm, a fraction is transported into the axoneme via intraflagellar transport. Reason: Although the primary site of CFAP300 function is in the cytoplasm (dynein preassembly), experimental evidence demonstrates IFT-dependent movement of the protein within cilia and accumulation at ciliary tips. This axonemal localization likely reflects the protein's role in IFT-dependent trafficking of assembled dynein complexes. Supporting Evidence: PMID:29727692 IFT139/TTC21B (IFT-A protein) and FLA10 (IFT kinesin) depletion experiments show that its transport within cilia is IFT dependent. During ciliogenesis, C11orf70 accumulates at the ciliary tips in a similar distribution to the IFT-B protein IFT46. file:human/CFAP300/CFAP300-deep-research-falcon.md Model organism data also show cytoplasmic localization and IFT-dependent movement within cilia |
| GO:0005515 protein binding | IPI PMID:29727692 C11orf70 Mutations Disrupting the Intraflagellar Transport-D... | KEEP AS NON CORE | Summary: This annotation is based on the interaction between CFAP300 and DNAAF2, a cytoplasmic ODA/IDA assembly factor [PMID:29727693]. While the interaction is experimentally validated, 'protein binding' is too generic to describe the core function. Reason: The interaction evidence is biologically meaningful and supports CFAP300's role in dynein arm preassembly, but GO:0005515 is too generic to represent the core activity. The focused OpenScientist hypothesis review agreed that no direct biochemical data currently justify replacing it with a specific scaffold, adaptor, chaperone, or dynein-binding molecular function. The dynein assembly biological process annotations better capture the supported function. Supporting Evidence: PMID:29727693 Furthermore, C11orf70 shows an interaction with cytoplasmic ODA/IDA assembly factor DNAAF2, supporting our hypothesis that C11orf70 is a preassembly factor involved in the pathogenesis of PCD. file:human/CFAP300/CFAP300-hypotheses/knowledge-gap-dynein-preassembly-mechanism/openscientist.md The hypothesis correctly identifies this as uninformative, but no experimental evidence supports a more specific MF term. |
| GO:0005737 cytoplasm | ISS GO_REF:0000024 | ACCEPT | Summary: Duplicate annotation of cytoplasmic localization based on sequence similarity to orthologs. This is consistent with experimental data from model organisms and human cells. Reason: This ISS annotation is well-supported by direct experimental evidence in model organisms (Paramecium, Chlamydomonas) and human cells showing cytoplasmic localization. Cytoplasmic localization is essential for CFAP300's role in dynein arm preassembly. Supporting Evidence: PMID:29727692 Tagged C11orf70 in Paramecium and Chlamydomonas localizes mainly in the cytoplasm with a small amount in the ciliary component. |
| GO:0031514 motile cilium | ISS GO_REF:0000024 | ACCEPT | Summary: CFAP300 is essential for motile cilium function, as its loss leads to immotile respiratory cilia and sperm flagella due to combined ODA+IDA loss [PMID:29727692, PMID:29727693]. The protein is expressed in ciliated respiratory cells and upregulated during ciliogenesis. Reason: CFAP300 is a cilium- and flagellum-specific protein whose function is dedicated to motile cilia assembly. Expression is upregulated during ciliogenesis and the protein shows IFT-dependent transport within cilia. Association with motile cilium is a core aspect of CFAP300 biology. Supporting Evidence: PMID:29727692 Phylogenetic analysis shows C11orf70 is highly conserved, distributed across species similarly to proteins involved in the intraflagellar transport (IFT)-dependant assembly of axonemal dyneins. PMID:29727693 Expression analyses of C11orf70 showed that C11orf70 is expressed in ciliated respiratory cells and that the expression of C11orf70 is upregulated during ciliogenesis, similar to other previously described cytoplasmic dynein-arm assembly factors. |
| GO:0036158 outer dynein arm assembly | IMP PMID:29727692 C11orf70 Mutations Disrupting the Intraflagellar Transport-D... | NEW | Summary: Loss of CFAP300 function causes combined loss of outer dynein arms from the axoneme, demonstrated by TEM and immunofluorescence in human patient cells and model organisms [PMID:29727692, PMID:29727693]. Reason: This is a core biological process for CFAP300. Multiple studies demonstrate that CFAP300 mutations cause loss of outer dynein arms from cilia and flagella. TEM analysis of patient respiratory epithelial cells shows combined ODA+IDA loss, and immunofluorescence confirms absence of ODA markers (DNAH5, DNAI1). Paramecium RNAi knockdown reproduces the phenotype. Supporting Evidence: PMID:29727692 The affected children share a consistent PCD phenotype from early life with laterality defects and immotile respiratory cilia displaying combined loss of inner and outer dynein arms (IDA+ODA). PMID:29727693 Transmission electron microscopy analyses and high-resolution immunofluorescence microscopy demonstrate that loss-of-function mutations in C11orf70 cause immotility of respiratory cilia and sperm flagella, respectively, as a result of the loss of axonemal outer (ODAs) and inner dynein arms (IDAs), indicating that C11orf70 is involved in cytoplasmic assembly of dynein arms. |
| GO:0036159 inner dynein arm assembly | IMP PMID:29727692 C11orf70 Mutations Disrupting the Intraflagellar Transport-D... | NEW | Summary: Loss of CFAP300 function causes combined loss of inner dynein arms from the axoneme, demonstrated by TEM and immunofluorescence in human patient cells and model organisms [PMID:29727692, PMID:29727693]. Reason: This is a core biological process for CFAP300. Loss-of-function mutations cause combined ODA+IDA loss. Immunofluorescence shows loss of IDA marker DNAH7 in patient cells. The defect in both ODA and IDA assembly indicates CFAP300 functions upstream in dynein preassembly affecting multiple dynein arm types. Supporting Evidence: PMID:29727692 Paramecium C11orf70 RNAi knockdown led to combined loss of ciliary IDA+ODA with reduced cilia beating and swim velocity. PMID:29727693 indicating that C11orf70 is involved in cytoplasmic assembly of dynein arms. file:human/CFAP300/CFAP300-deep-research-falcon.md Biallelic CFAP300 variants cause combined loss of outer and inner dynein arms (ODA+IDA) on TEM and loss of ODA/IDA marker staining |
| GO:0070286 axonemal dynein complex assembly | IMP PMID:29727692 C11orf70 Mutations Disrupting the Intraflagellar Transport-D... | NEW | Summary: CFAP300 is required for axonemal dynein complex assembly, specifically for the cytoplasmic preassembly and IFT-dependent trafficking of dynein arm complexes into cilia. Reason: This parent term encompasses both ODA and IDA assembly and appropriately captures CFAP300's role as a dynein axonemal assembly factor. The protein functions in cytoplasmic preassembly of dynein arms and their IFT-dependent transport into the axoneme. Supporting Evidence: PMID:29727692 In summary, C11orf70 is essential for assembly of dynein arms and C11orf70 mutations cause defective cilia motility and PCD. file:human/CFAP300/CFAP300-deep-research-falcon.md CFAP300 is required for cytoplasmic preassembly of axonemal dynein arms and for IFT-dependent trafficking of preassembled dynein complexes into motile cilia |
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Download this section (compressed HTML)Q: What is the precise molecular mechanism by which CFAP300 facilitates dynein arm preassembly? Does it function as a chaperone, scaffold, or adapter protein? Understanding the biochemical activity would enable more precise molecular function annotation. Current evidence shows interaction with DNAAF2 and requirement for dynein assembly, but the mechanism is unclear.
Q: Does CFAP300 have distinct roles in ODA versus IDA assembly, or does it function at a common step upstream of both? Both ODA and IDA are affected by CFAP300 loss, suggesting either a very upstream role or involvement in multiple parallel pathways.
Q: Does CFAP300 directly bind defined dynein subunits or complexes, or does it act indirectly through DNAAF2-associated preassembly machinery and IFT139-linked transport? This distinction is required before assigning a specific dynein-binding or adaptor molecular function.
Q: Does CFAP300 localize to dynein axonemal particle (DynAP) condensates in multiciliated cells, or is its relationship to DynAPs only inferred from DNAAF2 interaction and sequence features?
Experiment: Proximity labeling (BioID/APEX) in human ciliated cells to identify the full interactome of CFAP300 in the dynein preassembly pathway. This would clarify CFAP300's position in the assembly hierarchy and identify additional interaction partners beyond DNAAF2.
Hypothesis: CFAP300 interacts with multiple components of the dynein preassembly machinery in addition to DNAAF2.
Experiment: Time-course imaging of tagged CFAP300 during ciliogenesis to characterize the dynamics of cytoplasmic preassembly versus axonemal transport. This would provide insight into whether CFAP300 primarily functions in cytoplasmic preassembly, IFT-dependent transport, or both.
Hypothesis: CFAP300 shows dynamic localization during ciliogenesis, with initial cytoplasmic accumulation followed by IFT-dependent transport into the axoneme.
Experiment: Assay dynein heavy-chain and intermediate-chain abundance in CFAP300-mutant differentiated airway epithelial cells, comparing cytoplasmic pools with axonemal incorporation. Reduced cytoplasmic dynein levels would support a preassembly or stability defect, whereas normal cytoplasmic levels with failed ciliary import would support a transport-coupling model.
Hypothesis: CFAP300 is required either for dynein subunit stability during preassembly or for transfer of preassembled dynein arms to the IFT-dependent import pathway.
Experiment: Perform BioID or TurboID proximity labeling with tagged CFAP300 in differentiated human airway epithelial cells to define native proximal partners, including DNAAFs, IFT components, and dynein arm subunits.
Hypothesis: The CFAP300 proximal interactome will distinguish a scaffold/adaptor mechanism with multiple assembly and transport partners from a narrower chaperone or client-specific binding role.
Experiment: Test CFAP300 co-localization with DynAP markers in multiciliated cells and measure condensate exchange dynamics by FRAP.
Hypothesis: If CFAP300 partitions into DynAP condensates, it should co-localize with established DynAP markers and show condensate-like recovery dynamics.
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The biochemical activity of CFAP300 is unknown. It is unresolved whether it acts as a chaperone/co-chaperone, a scaffold, or an adaptor; what its client/substrate is; and whether it acts at one common step upstream of both dynein arm types or in parallel ODA- and IDA-specific steps.
OPEN BIOLOGYONTOLOGY MF_DARK
What is known: Loss-of-function causes primary ciliary dyskinesia with combined outer and inner dynein arm (ODA+IDA) loss; CFAP300 is required for cytoplasmic preassembly of axonemal dyneins and their IFT-dependent delivery into the axoneme, localizes mainly to the cytoplasm, moves into cilia by IFT, and interacts with the preassembly factor DNAAF2. Its sole domain is DUF4498, a domain of unknown function.
Significance: This is the assembly step whose failure removes all axonemal dynein motors — mechanistically central to motile ciliopathy. Even "a dynein-preassembly factor" has no adequate GO molecular-function term, which is why the gene reads as MF-dark.
What would resolve it: Proximity/affinity proteomics of the CFAP300–DNAAF2 module; in vitro reconstitution of dynein assembly intermediates; structural characterization of DUF4498.
Provenance (the field's own admissions):
Proposed term (ontology gap):
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