BBS-2 is a core component of the BBSome, a conserved octameric complex essential for ciliary protein trafficking. In C. elegans, BBS-2 is required for proper BBSome assembly and its ciliary localization. The BBSome functions as a scaffold to assemble IFT (intraflagellar transport) particles at both the ciliary base and tip, regulating IFT assembly and turnaround. BBS-2 localizes to the cilium, ciliary basal body, and ciliary axoneme, and is expressed exclusively in ciliated sensory neurons including amphid and phasmid neurons. Loss of BBS-2 function results in defective cilia structure, compromised IFT, and dye-filling defects. BBS-2 is an ortholog of human BBS2, mutations in which cause Bardet-Biedl syndrome, a ciliopathy characterized by retinal dystrophy, obesity, polydactyly, renal malformations, and learning disabilities.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0043005 neuron projection | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation based on phylogenetic inference from mouse and other orthologs. In C. elegans, BBS-2 is expressed in ciliated sensory neurons (PMID:14520415, PMID:15231740). The protein is present in the cilia of amphid and phasmid neurons, which are neuronal projections specialized for sensory function. Reason: BBS-2 localizes to sensory neuron projections (cilia) in C. elegans. This annotation is consistent with direct experimental evidence from PMID:14520415 showing expression in amphid and phasmid neurons. While 'cilium' would be more precise, neuron projection is an accurate parent term for sensory cilia that emerge from neuronal dendrites. Supporting Evidence: PMID:14520415 all available Caenorhabditis elegans BBS homologues are expressed exclusively in ciliated neurons, and contain regulatory elements for RFX, a transcription factor that modulates the expression of genes associated with ciliogenesis and intraflagellar transport file:worm/bbs-2/bbs-2-deep-research-falcon.md model: Edison Scientific Literature |
| GO:0060271 cilium assembly | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation from phylogenetic inference. BBS-2 is required for cilia biogenesis in C. elegans. The BBSome controls IFT assembly and turnaround, which are essential for cilium assembly (PMID:22922713, PMID:15231740). Reason: Direct experimental evidence supports this annotation. PMID:22922713 demonstrates that the BBSome (including BBS-2) is required for assembling IFT particles at both ciliary base and tip, which is essential for cilium assembly. PMID:15231740 shows that loss of BBS proteins results in cilia defects. Supporting Evidence: PMID:22922713 the BBSome is required for assembling IFT particles at both ciliary base and tip PMID:15231740 mutations in the Caenorhabditis elegans bbs-7 and bbs-8 genes cause structural and functional defects in cilia |
| GO:0016020 membrane | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: IBA annotation inferring membrane association. The BBSome functions as a coat complex for sorting membrane proteins to cilia (UniProt annotation by similarity). Reason: While the BBSome is involved in membrane protein trafficking to cilia, this generic 'membrane' annotation is too broad to be informative. The protein is not an integral membrane protein - it is a cytoplasmic protein that associates with membranes transiently during cargo sorting. More specific terms like 'cilium' or 'ciliary basal body' are already captured in other annotations and better describe the relevant membrane compartments. |
| GO:0034464 BBSome | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation indicating BBS-2 is part of the BBSome complex. This is a core identity annotation for the protein, supported by phylogenetic conservation and biochemical evidence (PMID:22922713). Reason: This is the defining annotation for BBS-2. The BBSome complex contains BBS-1, BBS-2, BBS-4, BBS-5, BBS-7, BBS-8, BBS-9, and BBIP10 in C. elegans and is highly conserved. PMID:22922713 provides direct evidence that worm BBS proteins form a complex using BiFC assays. Supporting Evidence: PMID:22922713 In wild-type animals, fluorescence complementation can be observed in BBS-1–BBS-7 and BBS-1–BBS-9 pair, indicative of the coexistence of these three BBS proteins in the same complex |
| GO:0036064 ciliary basal body | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for ciliary basal body localization. BBS-2 localizes to the ciliary basal body where the BBSome assembles IFT particles (PMID:15231740, PMID:22922713). Reason: Direct experimental evidence supports basal body localization. PMID:15231740 states that C. elegans BBS proteins localize predominantly at the base of cilia. PMID:22922713 shows the BBSome assembles at the ciliary base and this is where IFT particle assembly occurs. UniProt annotation also confirms this localization. Supporting Evidence: PMID:15231740 C. elegans BBS proteins localize predominantly at the base of cilia PMID:22922713 the BBSome (refs 3, 4), a group of conserved proteins affected in human Bardet-Biedl syndrome(5) (BBS), assembles IFT complexes at the ciliary base |
| GO:0031514 motile cilium | IBA GO_REF:0000033 | MODIFY | Summary: IBA annotation suggesting motile cilium localization. However, C. elegans sensory neurons contain non-motile (primary/sensory) cilia, not motile cilia. Reason: C. elegans cilia are sensory (non-motile) cilia, not motile cilia. The organism lacks motile cilia entirely - its sensory neurons have non-motile cilia specialized for chemosensation, mechanosensation, and thermosensation. The IBA inference from mouse orthologs (which can be in motile cilia in some contexts) does not apply to worm biology. This annotation should be corrected to non-motile cilium. Proposed replacements: non-motile cilium |
| GO:0005929 cilium | IEA GO_REF:0000044 | ACCEPT | Summary: IEA annotation based on UniProt subcellular location mapping. BBS-2 is localized to cilia in C. elegans sensory neurons (PMID:15231740). Reason: Direct experimental evidence confirms ciliary localization. PMID:15231740 demonstrates that BBS proteins localize to cilia and move bidirectionally along the ciliary axoneme. PMID:22922713 provides additional evidence that BBS-2 localizes to cilia, though with reduced intensity in certain mutant backgrounds. The IEA annotation is consistent with experimental data. Supporting Evidence: PMID:15231740 C. elegans BBS proteins localize predominantly at the base of cilia, and like proteins involved in intraflagellar transport (IFT), a process necessary for cilia biogenesis and maintenance, move bidirectionally along the ciliary axoneme |
| GO:0005930 axoneme | IEA GO_REF:0000044 | ACCEPT | Summary: IEA annotation based on UniProt subcellular location. BBS-2 moves along the ciliary axoneme as part of IFT (PMID:15231740, PMID:22922713). Reason: Direct experimental evidence supports axoneme localization. PMID:15231740 shows that BBS proteins move bidirectionally along the ciliary axoneme. PMID:22922713 demonstrates that BBS-2 shows IFT movement along the axoneme (when not in mutant backgrounds that disrupt BBSome-IFT association). UniProt annotation also confirms axoneme localization. Supporting Evidence: PMID:15231740 like proteins involved in intraflagellar transport (IFT), a process necessary for cilia biogenesis and maintenance, move bidirectionally along the ciliary axoneme |
| GO:0015031 protein transport | IEA GO_REF:0000043 | MODIFY | Summary: IEA annotation from UniProt keyword mapping. The BBSome functions as a coat complex for sorting membrane proteins to cilia (by similarity to human BBS2). Reason: While BBS-2 is involved in protein transport, this term is too general. The BBSome specifically functions in ciliary protein trafficking - sorting membrane proteins to the ciliary membrane and exporting signaling molecules. The more specific process is intraciliary transport, which describes the BBSome's role in IFT assembly and cargo trafficking within cilia. Proposed replacements: intraciliary transport |
| GO:0030030 cell projection organization | IEA GO_REF:0000043 | ACCEPT | Summary: IEA annotation from UniProt keyword mapping. BBS-2 is required for proper cilia structure and function (PMID:22922713, PMID:15231740). Reason: This is an accurate parent term annotation. Cilia are cell projections, and BBS-2 is required for proper cilium organization through its role in IFT assembly. The more specific term 'cilium assembly' is already captured separately, but this broader term correctly captures the overall biological role. Supporting Evidence: PMID:22922713 Our results identify the BBSome as the key player regulating IFT assembly and turnaround in cilia |
| GO:0034464 BBSome | IEA GO_REF:0000002 | ACCEPT | Summary: IEA annotation from InterPro domain mapping. BBS-2 is part of the BBSome complex. Reason: This is a duplicate of the IBA annotation for BBSome membership, both are correct. The InterPro domain (IPR016616, Bardet-Biedl syndrome 2 protein) correctly predicts BBSome membership, which is experimentally validated. |
| GO:1905515 non-motile cilium assembly | IEA GO_REF:0000002 | ACCEPT | Summary: IEA annotation from InterPro mapping. BBS-2 is required for assembly of sensory (non-motile) cilia in C. elegans. Reason: This is the most precise cilium assembly term for C. elegans BBS-2. All cilia in C. elegans are non-motile sensory cilia. The BBSome is required for their assembly through its role in IFT particle organization. This is more specific than the general 'cilium assembly' term and accurately reflects the worm biology. Supporting Evidence: PMID:14520415 all available Caenorhabditis elegans BBS homologues are expressed exclusively in ciliated neurons |
| GO:0005929 cilium | NAS PMID:22922713 The BBSome controls IFT assembly and turnaround in cilia. | ACCEPT | Summary: NAS annotation from ComplexPortal based on PMID:22922713. This study provides direct evidence for BBS-2 ciliary localization in C. elegans. Reason: PMID:22922713 directly demonstrates that BBS-2 localizes to cilia in C. elegans. The paper shows GFP-tagged BBS-2 in cilia and that various BBS proteins (including BBS-2) show dim but detectable ciliary staining even in mutant backgrounds. Supporting Evidence: PMID:22922713 the others (BBS-2, -5, -7, -8, -9) only showed very dim ciliary staining when compared to wild-type animals |
| GO:0060271 cilium assembly | NAS PMID:22922713 The BBSome controls IFT assembly and turnaround in cilia. | ACCEPT | Summary: NAS annotation from ComplexPortal. PMID:22922713 demonstrates the BBSome is required for IFT assembly, which is essential for cilium assembly. Reason: This is a duplicate of the IBA annotation but with different evidence. PMID:22922713 provides the key mechanistic insight that the BBSome controls IFT assembly at both ciliary base and tip, which is essential for ciliogenesis. Supporting Evidence: PMID:22922713 Our results identify the BBSome as the key player regulating IFT assembly and turnaround in cilia |
| GO:0036064 ciliary basal body | IDA PMID:22922713 The BBSome controls IFT assembly and turnaround in cilia. | ACCEPT | Summary: IDA annotation based on direct localization studies. PMID:22922713 shows BBS-2 localization at the ciliary base through GFP tagging and BiFC experiments. Reason: PMID:22922713 provides direct experimental evidence for BBS-2 basal body localization. The study shows that BBS proteins accumulate at the ciliary base, particularly in mutant backgrounds where BBSome-IFT coupling is disrupted. This is where the BBSome assembles IFT particles before they enter the cilium. Supporting Evidence: PMID:22922713 all BBSome proteins strongly accumulate around the ciliary base and show no IFT movement in bbs-1(jhu598) |
| GO:0043005 neuron projection | IDA PMID:14520415 Basal body dysfunction is a likely cause of pleiotropic Bard... | ACCEPT | Summary: IDA annotation from PMID:14520415. This landmark BBS study demonstrated that all C. elegans BBS homologs are expressed exclusively in ciliated sensory neurons. Reason: PMID:14520415 provides direct experimental evidence that BBS genes (including bbs-2) are expressed exclusively in ciliated neurons in C. elegans. The paper used GFP reporter constructs to demonstrate neuron-specific expression. Sensory cilia are neuronal projections from these neurons. Supporting Evidence: PMID:14520415 all available Caenorhabditis elegans BBS homologues are expressed exclusively in ciliated neurons, and contain regulatory elements for RFX, a transcription factor that modulates the expression of genes associated with ciliogenesis and intraflagellar transport |
| GO:1905515 non-motile cilium assembly | IEP PMID:14520415 Basal body dysfunction is a likely cause of pleiotropic Bard... | ACCEPT | Summary: IEP annotation based on expression pattern from PMID:14520415. The gene is expressed specifically in ciliated sensory neurons during developmental stages when cilia are being assembled. Reason: The expression pattern evidence (IEP) appropriately supports involvement in non-motile cilium assembly. PMID:14520415 shows BBS gene expression specifically in ciliated neurons containing RFX regulatory elements. C. elegans cilia are exclusively non-motile sensory cilia, so expression in ciliated cells during ciliogenesis supports this annotation. Supporting Evidence: PMID:14520415 all available Caenorhabditis elegans BBS homologues are expressed exclusively in ciliated neurons, and contain regulatory elements for RFX, a transcription factor that modulates the expression of genes associated with ciliogenesis |
| GO:0042073 intraciliary transport | IDA PMID:22922713 The BBSome controls IFT assembly and turnaround in cilia. | NEW | Summary: The BBSome (including BBS-2) is required for IFT particle assembly and turnaround at both the ciliary base and tip. BBS proteins move bidirectionally along cilia as IFT cargo (PMID:22922713, PMID:15231740). Reason: This is a core function annotation that should be added. PMID:22922713 provides definitive evidence that the BBSome controls IFT assembly and turnaround. The paper shows that BBS proteins associate with moving IFT particles and are required for proper IFT particle reassembly at the ciliary tip for retrograde transport. Supporting Evidence: PMID:22922713 After IFT particles are assembled at the ciliary base, the BBSome binds to the IFT particle like a cargo but not a structural component PMID:15231740 like proteins involved in intraflagellar transport (IFT), a process necessary for cilia biogenesis and maintenance, move bidirectionally along the ciliary axoneme |
| GO:0035735 intraciliary transport involved in cilium assembly | IMP PMID:22922713 The BBSome controls IFT assembly and turnaround in cilia. | NEW | Summary: Loss of BBSome function results in disrupted IFT and defective ciliogenesis. The BBSome-mediated IFT assembly is required for cilium biogenesis. Reason: This annotation links the BBSome's IFT function directly to cilium assembly. PMID:22922713 demonstrates that disruption of BBSome-IFT coupling leads to IFT-B accumulation at ciliary tips and compromised cilia formation. This is a more precise annotation than the general 'cilium assembly' term. Supporting Evidence: PMID:22922713 The absence of the BBSome at the cilia tip leads to the defective recycling of IFT complex |
| GO:0005198 structural molecule activity | IDA PMID:22922713 The BBSome controls IFT assembly and turnaround in cilia. | NEW | Summary: BBS-2 contributes to the structural integrity of the BBSome complex, acting as a scaffold for IFT particle assembly. Reason: BBS-2 is a core structural component of the BBSome complex. PMID:22922713 demonstrates that BBS proteins form a complex using BiFC assays. The BBSome functions as a scaffold organizing IFT-A, IFT-B, and cargo molecules, with BBS-2 being essential for complex integrity. Supporting Evidence: PMID:22922713 In wild-type animals, fluorescence complementation can be observed in BBS-1–BBS-7 and BBS-1–BBS-9 pair, indicative of the coexistence of these three BBS proteins in the same complex |
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Download this section (compressed HTML)Q: What is the precise stoichiometry of the C. elegans BBSome complex compared to vertebrate orthologs?
Q: Does BBS-2 have any BBSome-independent functions in C. elegans?
Q: How does the BBSome recognize and select specific cargo for ciliary transport?
Experiment: Proteomics analysis of BBSome interactors in C. elegans to identify cargo molecules specifically dependent on BBS-2
Experiment: Live imaging of BBS-2::GFP to quantify IFT dynamics in various sensory neuron subtypes
Experiment: Tissue-specific rescue experiments to determine which neuronal functions require BBS-2
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