CFAP418 (C8orf37) is a ciliary scaffolding protein localized at the photoreceptor connecting cilium base that is essential for photoreceptor outer segment disc morphogenesis and organization. It forms a protein complex with FAM161A at the ciliary base, contributing to photoreceptor structural integrity and survival. Mutations cause retinal dystrophies including cone-rod dystrophy 16 (CORD16), retinitis pigmentosa 64 (RP64), and Bardet-Biedl syndrome 21 (BBS21).
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0001917 photoreceptor inner segment | IEA GO_REF:0000044 | ACCEPT | Summary: This IEA annotation is supported by experimental evidence. CFAP418 is enriched at the photoreceptor inner segment, particularly at the connecting cilium base between inner and outer segments as shown by immunohistochemistry in both mouse (PMID:22177090) and marmoset retina (PMID:36233334). The protein is present throughout the inner segment but concentrated at the ciliary base. Reason: PMID:22177090 and PMID:36233334 provide direct immunohistochemical evidence for CFAP418 localization at the photoreceptor inner segment, with particular enrichment at the connecting cilium base. Supporting Evidence: PMID:22177090 Immunohistochemical studies revealed C8orf37 localization at the base of the primary cilium of human retinal pigment epithelium cells and at the base of connecting cilia of mouse photoreceptors file:human/CFAP418/CFAP418-deep-research-falcon.md See deep research file for comprehensive analysis |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | MODIFY | Summary: This automated annotation is overly general. While CFAP418 is cytoplasmic (non-membrane bound), the more specific localization to the ciliary base (GO:0097546) better represents its functional localization. The cytoplasm term doesn't capture the protein's specialized ciliary localization. Proposed replacements: ciliary base |
| GO:0005515 protein binding | IPI PMID:27173435 An organelle-specific protein landscape identifies novel dis... | MODIFY | Summary: While this IPI evidence is valid (PMID:27173435 is a large-scale protein interaction study), the generic 'protein binding' term is uninformative about CFAP418's actual molecular function. The protein functions as a ciliary scaffold that specifically binds FAM161A and potentially other ciliary proteins. A more specific term like 'scaffold protein binding' (GO:0097110) would better represent its molecular function. Reason: PMID:27173435 provides broad protein interaction data, but CFAP418 specifically functions as a ciliary scaffolding protein. The more specific scaffold protein binding term better captures its molecular role. Proposed replacements: scaffold protein binding Supporting Evidence: PMID:27173435 An organelle-specific protein landscape identifies novel diseases and molecular mechanisms |
| GO:0005515 protein binding | IPI PMID:36233334 Interactions between C8orf37 and FAM161A, Two Ciliary Protei... | MODIFY | Summary: This IPI evidence from PMID:36233334 specifically demonstrates CFAP418-FAM161A interaction via Y2H, co-IP, and proximity ligation assays. The N-terminus of CFAP418 (aa 1-75) interacts with FAM161A's UPF0564 domain (aa 341-517). However, 'protein binding' is too generic - this should be annotated with a more specific molecular function reflecting its scaffolding role at the ciliary base. Reason: PMID:36233334 provides strong experimental evidence for direct CFAP418-FAM161A interaction through multiple biochemical assays, demonstrating CFAP418's role as a ciliary scaffold protein. Bioinformatics analysis reveals extensive coiled-coil regions (positions 0-259, 273-315, 350-441) supporting its scaffolding function. Proposed replacements: scaffold protein binding Supporting Evidence: PMID:36233334 Interactions between C8orf37 and FAM161A, Two Ciliary Proteins Essential for Photoreceptor Survival |
| GO:0001917 photoreceptor inner segment | ISS GO_REF:0000024 | ACCEPT | Summary: This ISS annotation (inferred from sequence similarity) is correct and supported by direct experimental evidence. Multiple studies confirm CFAP418 localization to the photoreceptor inner segment, particularly at the connecting cilium base. This represents a core localization for the protein's function. |
| GO:0008594 photoreceptor cell morphogenesis | ISS GO_REF:0000024 | MODIFY | Summary: This ISS annotation is supported by strong experimental evidence. CFAP418 knockout mice show severely disorganized photoreceptor outer segment discs from early postnatal development, demonstrating its requirement for proper photoreceptor morphogenesis. The more specific process 'photoreceptor cell outer segment organization' (GO:0035845) would better capture its primary role in outer segment disc formation. Reason: PMID:22177090 demonstrated that CFAP418 knockout mice exhibit severe photoreceptor outer segment defects with disorganized disc morphology, indicating a specific role in outer segment organization rather than general morphogenesis. Proposed replacements: photoreceptor cell outer segment organization Supporting Evidence: PMID:22177090 Immunohistochemical studies revealed C8orf37 localization at the base of the primary cilium of human retinal pigment epithelium cells |
| GO:0005737 cytoplasm | IDA PMID:22177090 Mutations in C8orf37, encoding a ciliary protein, are associ... | MODIFY | Summary: While cytoplasmic localization is correct, this is overly general. The more specific ciliary base annotation better represents CFAP418's functional localization. Proposed replacements: ciliary base Supporting Evidence: PMID:22177090 2011 Dec 15. Mutations in C8orf37, encoding a ciliary protein, are associated with autosomal-recessive retinal dystrophies with early macular involvement. |
| GO:0097546 ciliary base | IDA PMID:22177090 Mutations in C8orf37, encoding a ciliary protein, are associ... | ACCEPT | Summary: Excellent annotation with strong IDA evidence. PMID:22177090 shows via immunohistochemistry that CFAP418 localizes at the base of primary cilia in RPE cells and at the base of connecting cilia in mouse photoreceptors. This is a core localization essential for CFAP418's function in photoreceptor maintenance and represents its primary functional compartment. Reason: PMID:22177090 provides definitive immunohistochemical evidence for CFAP418 localization at ciliary bases in both RPE cells and photoreceptors, establishing this as the protein's primary functional compartment. Supporting Evidence: PMID:22177090 Immunohistochemical studies revealed C8orf37 localization at the base of the primary cilium of human retinal pigment epithelium cells and at the base of connecting cilia of mouse photoreceptors |
| GO:0001754 eye photoreceptor cell differentiation | IEA | NEW | Summary: Essential for photoreceptor differentiation and structural organization through scaffolding function at the connecting cilium Reason: CFAP418 is essential for photoreceptor cell differentiation, specifically functioning as a ciliary scaffolding protein at the photoreceptor connecting cilium base where it is required for outer segment disc morphogenesis and structural organization. Mutations in CFAP418 cause multiple retinal dystrophies including cone-rod dystrophy, retinitis pigmentosa, and Bardet-Biedl syndrome, demonstrating its critical role in photoreceptor development and maintenance. Supporting Evidence: PMID:36233334 C8orf37 was enriched at the ciliary base, present along the axonemes and often co-localized with microtubules in the inner segments of photoreceptors |
| GO:0030030 cell projection organization | IEA | NEW | Summary: Critical scaffolding function for ciliary structure organization at the photoreceptor connecting cilium base Reason: CFAP418 functions as a ciliary scaffolding protein that organizes cell projections, specifically the connecting cilium structure in photoreceptors. As a cilia- and flagella-associated protein, CFAP418 is essential for proper organization of the ciliary apparatus, forming complexes with FAM161A to maintain ciliary structural integrity. The protein contains ciliary targeting signals and is specifically localized to ciliary structures where it organizes the ciliary base architecture. Supporting Evidence: PMID:36233334 C8orf37 was enriched and was co-localized with FAM161A at the ciliary base of photoreceptors. |
| GO:0042073 intraciliary transport | IEA | NEW | Summary: Required for proper intraciliary transport processes in photoreceptor connecting cilia Reason: CFAP418 is involved in intraciliary transport processes, particularly affecting retrograde intraflagellar transport in photoreceptor cilia. As a ciliary scaffolding protein localized to the connecting cilium base, CFAP418 helps organize the transport machinery required for proper ciliary function. Defects in CFAP418 lead to impaired transport processes within cilia, contributing to the pathogenesis of ciliopathies including retinal dystrophies and Bardet-Biedl syndrome. Supporting Evidence: PMID:27008867 delayed retrograde melanosome transport |
| GO:0035845 photoreceptor cell outer segment organization | IEA | NEW | Summary: Core biological process organized by CFAP418 Reason: CFAP418 is essential for photoreceptor cell outer segment organization, particularly disc formation. This specific process is core to its function but was missing from existing annotations. |
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Download this section (compressed HTML)Q: How does CFAP418 function in ciliary assembly and what specific role does it play in axoneme structure and stability?
Q: What are the molecular interactions between CFAP418 and other ciliary proteins that are essential for proper cilia function?
Q: How do mutations in CFAP418 contribute to ciliopathy phenotypes and what are the downstream cellular consequences?
Q: What determines the tissue-specific expression pattern of CFAP418 and why is it particularly important in certain cell types?
Experiment: Cryo-electron microscopy of cilia from CFAP418-deficient cells to identify structural abnormalities in the axoneme
Experiment: Proximity labeling proteomics to identify the complete CFAP418 interactome in ciliated cells
Experiment: Live-cell imaging of ciliary assembly and disassembly to study CFAP418 dynamics during the cell cycle
Experiment: Functional complementation studies using CFAP418 orthologs from different species to identify conserved functional domains
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Download this section (compressed HTML)📊 View Pathway Visualization Interactive pathway diagram with detailed annotations