IFT-20 is the Caenorhabditis elegans ortholog of IFT20, a small (129 aa) coiled-coil subunit of the intraflagellar transport complex B (IFT-B, peripheral IFT-B2 subcomplex). Its gene carries a DAF-19-regulated X-box and is expressed in ciliated sensory neurons. IFT-20::GFP enters sensory cilia and undergoes IFT with the same kinetics as other IFT subunits, and is also seen in dendrites and neuronal cell bodies. Unlike mammalian IFT20, which is anchored at the Golgi by GMAP210, worm IFT-20 has not been detected at the Golgi. ift-20 null mutants position basal bodies and form transition zones but build only short, vestigial axonemes, recruit much less IFT-B (IFT-74) to the ciliary base and into cilia, fail to take up dye, and are defective in osmotic avoidance and male mating.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA to cytoplasm. In worms the non-ciliary pool of IFT-20 is in the cytoplasm of dendrites and cell bodies of ciliated neurons, where IFT particles assemble and are transported. Reason: Not wrong; the cytoplasmic pool is real but is not where IFT-20 does its characteristic work, which is in the cilium and at the ciliary base. Supporting Evidence: PMID:33997658 IFT-74::GFP was readily detectable in dendrites of amphid and phasmid neurons |
| GO:0005813 centrosome | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: IBA to centrosome, propagated from mammalian IFT20 (localizes to the centrosome and Golgi in dividing/ciliated mammalian cells). C. elegans IFT-20 is expressed in postmitotic ciliated sensory neurons, where the relevant centriole-derived structure is the ciliary basal body (separately annotated). Reason: There is no worm evidence for a centrosomal pool of IFT-20, and the IFT-20 functions observed in C. elegans are confined to the ciliary base and cilium of postmitotic neurons. The basal-body/ciliary-base annotations capture the relevant location; the centrosome term adds a mammalian-specific context not supported in the worm. Propagation Review Root cause: PROPAGATION BAD Failure modes: CONTEXT OR TISSUE MISMATCH Sources checked: PANTHER:PTN001278113 · PTN001278113 SUPPORTS SOURCE BUT NOT TARGET Node seeded by mammalian IFT20 centrosome data (MGI:1915585, UniProtKB:Q8IY31); worm IFT-20 acts only in postmitotic ciliated neurons, at the basal body and cilium. Supporting Evidence: PMID:33997658 ift-20 null worms still positioned their basal body normally at the extremity of the dendrite in phasmid neurons |
| GO:0005929 cilium | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping to cilium. Reason: IFT-20::GFP is recruited to cilia and moves by IFT. Supporting Evidence: PMID:33997658 found that the C. elegans IFT20 homolog is also recruited to cilia where it undergoes IFT with similar kinetics to other IFT subunits |
| GO:0005929 cilium | NAS PMID:28479320 Dynein-Driven Retrograde Intraflagellar Transport Is Triphas... | ACCEPT | Summary: NAS from Yi et al. 2017 on IFT-B as a ciliary complex. Reason: Correct. Supporting Evidence: PMID:28479320 Disruption of the dynein-2 tail domain, light intermediate chain, or intraflagellar transport (IFT)-B complex abolishes dynein-2's ciliary localization |
| GO:0030425 dendrite | IDA PMID:23444385 SQL-1, homologue of the Golgi protein GMAP210, modulates int... | KEEP AS NON CORE | Summary: IDA from Broekhuis et al. 2013 (SQL-1 paper), imaging fluorescently tagged IFT proteins in amphid neurons; IFT-20 is visible along dendrites, consistent with dendritic transport of IFT components to the ciliary base. Reason: Plausible and consistent with known dendritic transport of IFT proteins (PMID:10545497), but the dendrite is a transit compartment rather than the site of IFT-20 function. Cache is abstract-only; deferring to the curator on the image. Supporting Evidence: PMID:23444385 Using live imaging of fluorescently tagged IFT proteins, we show that in sql-1 mutants OSM-3 moves faster |
| GO:0030990 intraciliary transport particle | IBA GO_REF:0000033 | ACCEPT | Summary: IBA to the generic IFT particle term. Reason: Correct, if less specific than IFT-B; IFT20 is a conserved IFT-B2 subunit. Supporting Evidence: PMID:33997658 IFT20 is part of the IFT-B complex |
| GO:0030992 intraciliary transport particle B | NAS PMID:28479320 Dynein-Driven Retrograde Intraflagellar Transport Is Triphas... | ACCEPT | Summary: NAS of IFT-B membership from Yi et al. 2017. Reason: Correct; IFT20 is a conserved IFT-B subunit, and worm IFT-20 co-transports with IFT-B. Supporting Evidence: PMID:33997658 IFT20 is part of the IFT-B complex |
| GO:0036064 ciliary basal body | IBA GO_REF:0000033 | ACCEPT | Summary: IBA to ciliary basal body. IFT particles concentrate at the ciliary base; in ift-20 nulls the ciliary-base pool of IFT-74 is strongly reduced, consistent with a role for IFT-20 at the base. Reason: Conserved localization of IFT20 orthologs and consistent with worm data. Supporting Evidence: PMID:16775004 IFT20 subunit of the particle is localized to the Golgi complex in addition to the basal body and cilia |
| GO:0042073 intraciliary transport | NAS PMID:28479320 Dynein-Driven Retrograde Intraflagellar Transport Is Triphas... | ACCEPT | Summary: NAS from Yi et al. 2017. Reason: IFT-20::GFP undergoes IFT with the kinetics of other IFT subunits, and loss of IFT-20 reduces ciliary entry of IFT-B; core process. Supporting Evidence: PMID:33997658 found that the C. elegans IFT20 homolog is also recruited to cilia where it undergoes IFT with similar kinetics to other IFT subunits |
| GO:0043025 neuronal cell body | IDA PMID:23444385 SQL-1, homologue of the Golgi protein GMAP210, modulates int... | KEEP AS NON CORE | Summary: IDA from Broekhuis et al. 2013 to neuronal cell body; IFT-20 is visible in amphid neuron cell bodies where it is synthesized. Reason: Synthesis/transit location rather than the site of function. Notably, the same study found no Golgi association for worm IFT-20, unlike mammalian IFT20. Supporting Evidence: PMID:33997658 in contrast to its homolog in mammalian cells, IFT-20 was not detectable at the Golgi and does not seem to interact with the C. elegans homolog of GMAP210 |
| GO:0060271 cilium assembly | IBA GO_REF:0000033 | ACCEPT | Summary: IBA to cilium assembly. ift-20(ok3191) null worms build only severely shortened, vestigial cilia. Reason: Directly supported by worm null phenotype; core process. Supporting Evidence: PMID:33997658 IFT-20 loss leads to a severe defect in ciliary axoneme assembly but does not completely block ciliogenesis in C. elegans |
| GO:0060271 cilium assembly | NAS PMID:28479320 Dynein-Driven Retrograde Intraflagellar Transport Is Triphas... | ACCEPT | Summary: NAS from Yi et al. 2017. Reason: Correct; supported by ift-20 null phenotype. Supporting Evidence: PMID:33997658 IFT-20 is required for ciliogenesis and cilia sensory functions in C. elegans |
| GO:0061512 protein localization to cilium | IBA GO_REF:0000033 | ACCEPT | Summary: IBA to protein localization to cilium. In ift-20 nulls IFT-74::GFP recruitment to the ciliary base and entry into cilia are strongly reduced. Reason: Worm-specific evidence supports a role for IFT-20 in ciliary recruitment and entry of IFT subunits, consistent with the PAINT inference. Supporting Evidence: PMID:33997658 IFT-20 plays a role in the ciliary recruitment and entry of IFT subunits |
| GO:0097546 ciliary base | IBA GO_REF:0000033 | ACCEPT | Summary: IBA to ciliary base. Reason: IFT-20 loss reduces the IFT-B pool at the ciliary base; conserved IFT20 localization. Supporting Evidence: PMID:33997658 the signal intensity of IFT-74::GFP recruited to the ciliary base and inside cilia of phasmid sensory neurons was indeed strongly reduced in ift-20 null worms |
| GO:0097730 non-motile cilium | IBA GO_REF:0000033 | ACCEPT | Summary: IBA to non-motile cilium; the worm gene appears among its own descendant evidence. Reason: All C. elegans cilia are non-motile sensory cilia; IFT-20 enters them. Supporting Evidence: PMID:33997658 found that the C. elegans IFT20 homolog is also recruited to cilia where it undergoes IFT with similar kinetics to other IFT subunits |
| GO:0097730 non-motile cilium | IDA PMID:23444385 SQL-1, homologue of the Golgi protein GMAP210, modulates int... | ACCEPT | Summary: IDA from Broekhuis et al. 2013 (live imaging of tagged IFT proteins in amphid cilia). Reason: Direct imaging; core location. Supporting Evidence: PMID:23444385 some complex A and B proteins move at an intermediate velocity |
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Download this section (compressed HTML)Q: Why can ift-20 null worms still assemble short vestigial cilia, when IFT20 loss blocks ciliogenesis in most mammalian cells? Is there partial redundancy within the worm IFT-B2 subcomplex?
Q: Does worm IFT-20 have any role in delivering ciliary membrane proteins (e.g. receptors or channels) given that it does not associate with the Golgi as in mammals?
Experiment: Image endogenously tagged ciliary membrane proteins (e.g. ODR-10, OSM-9) in ift-20 null neurons to test whether IFT-20 is selectively required for membrane cargo delivery.
Experiment: Test direct binding of IFT-20 to other IFT-B2 subunits (IFT-54/DYF-11, IFT-57/CHE-13) with recombinant worm proteins to define its position in the worm IFT-B complex.
Y110A7A.20 encodes an ortholog of Chlamydomonas and human IFT20;Y110A7A.20 undergoes intraflagellar transport (IFT) in a mannerconsistent with its being a component of the OSM-3-driven IFT-particle Bsubcomplex; Y110A7A.20 is expressed in amphid and phasmid neurons,mechanosensory neurons, and other unidentified head neurons and tailcells; by orthology with human IFT20, Y110A7A.20 may deliver ciliarymembrane proteins from the Golgi complex to the cilium; Y110A7A.20 hasno obvious function in mass RNAi assays.
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