Affinage

C2CD3

C2 domain-containing protein 3 · UniProt Q4AC94

Length
2353 aa
Mass
260.4 kDa
Annotated
2026-04-28
12 papers in source corpus 9 papers cited in narrative 9 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

C2CD3 is a centriolar scaffold protein that organizes the distal lumen of centrioles and is essential for ciliogenesis, centriole appendage assembly, and Hedgehog signal transduction. It adopts a 9-fold radially symmetric arrangement forming a ~100 nm luminal ring composed of C2CD3, SFI1, centrin-2, CEP135, and NA14, with its N-terminal hook-like domain attaching to A-microtubules and its C-terminal region anchoring the luminal ring; depletion disrupts this network, abolishes DISCO complex (MNR/CEP90/OFD1) recruitment via direct interaction with MNR, and prevents distal appendage formation (PMID:41364719). C2CD3 promotes centriole elongation in opposition to OFD1, and its loss yields short centrioles lacking subdistal and distal appendages, while its overexpression drives centriole hyperelongation; CEP120 is required for proper C2CD3 recruitment to the distal centriole (PMID:24997988, PMID:30988386). Loss-of-function mutations in C2CD3 cause ciliopathy phenotypes including defective Gli3 processing and impaired Hedgehog signaling, and hypomorphic patient variants reduce ciliation frequency and SHH pathway output in rescue experiments (PMID:19004860, PMID:39690811).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2008 High

    A forward genetic screen established that C2cd3 is required for ciliogenesis and acts as an intracellular component of Hedgehog signal transduction, resolving whether the gene functions in cilia formation versus signaling per se by showing loss of both cilia and Gli3 processing.

    Evidence Forward genetic screen with multiple mutant alleles in mouse, epistasis with Hedgehog pathway components

    PMID:19004860

    Open questions at the time
    • Molecular mechanism by which C2cd3 supports ciliogenesis was unknown
    • Direct localization within the centriole substructure was not resolved
    • No interacting partners were identified
  2. 2014 High

    C2CD3 was placed at the distal end of centrioles and shown to physically associate with OFD1 in an antagonistic regulatory axis controlling centriole length, establishing that centriole elongation is actively balanced by opposing activities.

    Evidence Reciprocal co-immunoprecipitation, overexpression and loss-of-function in human cells, patient mutation analysis

    PMID:24997988

    Open questions at the time
    • How C2CD3 mechanistically drives centriole elongation was not determined
    • Structural organization of C2CD3 at the distal centriole was unresolved
    • Relationship to appendage assembly beyond marker loss was unclear
  3. 2016 Medium

    Patient fibroblast analysis showed that C2CD3 loss impairs basal body maturation even when the distal appendage protein CEP164 is still recruited, separating C2CD3 function from simple appendage protein targeting.

    Evidence Patient-derived fibroblast immunofluorescence and ciliation assay

    PMID:27094867

    Open questions at the time
    • Single-lab patient cell study; not replicated independently
    • Which step of basal body maturation requires C2CD3 was not defined
    • Whether CEP164 at appendages is fully functional in C2CD3-deficient cells was untested
  4. 2019 High

    CEP120 was identified as a physical partner required for C2CD3 recruitment to distal centrioles, and a disease-associated CEP120 mutation reduced C2CD3 binding, establishing a recruitment hierarchy upstream of C2CD3.

    Evidence Reciprocal co-IP, CRISPR KO in RPE1 cells, disease mutant binding assay

    PMID:30988386

    Open questions at the time
    • Whether CEP120 directly deposits C2CD3 or acts indirectly was not resolved
    • Domains of C2CD3 mediating CEP120 interaction were not mapped
  5. 2021 Medium

    Domain-specific conditional alleles in mouse revealed that the N-terminal C2 domain of C2cd3 is critical for early embryonic and craniofacial development, establishing that C2CD3 has separable domain-specific functions in vivo.

    Evidence Conditional allelic series with tissue-specific phenotyping in mouse

    PMID:34211969

    Open questions at the time
    • Single-lab study; molecular partners of each domain were not identified
    • How N-terminal versus C-terminal domains relate to centriolar substructures was unknown
  6. 2025 High

    Cryo-ET and expansion microscopy resolved C2CD3's 9-fold radially symmetric architecture in the distal centriolar lumen, showed its N-terminus forms a hook attaching to A-microtubules while its C-terminus anchors a luminal ring with SFI1/centrin-2/CEP135/NA14, and demonstrated that C2CD3 directly binds MNR to recruit the DISCO complex for appendage initiation—unifying its roles in centriole structure, elongation, and appendage assembly.

    Evidence U-ExM, cryo-ET, C2CD3 depletion with multi-marker IF, direct MNR interaction assay

    PMID:41364719

    Open questions at the time
    • Atomic-resolution structure of C2CD3 or its domain interfaces is not available
    • How the luminal ring contributes to centriole elongation mechanistically is unclear
    • Whether the 9-fold ring is dynamically remodeled during the cell cycle is unknown
  7. 2025 Medium

    Hypomorphic patient variants were shown to reduce C2CD3 basal body localization, shorten cilia, and attenuate SHH signaling output, directly linking variant severity to functional deficits via rescue in KO cells.

    Evidence Patient fibroblast and renal epithelial cell assays, C2CD3 KO RPE-1 rescue, qRT-PCR for GLI1/GLI3

    PMID:39690811

    Open questions at the time
    • Single-lab study with limited variant panel
    • Whether reduced localization reflects folding defects or impaired CEP120 interaction is untested
  8. 2025 Medium

    Cross-species studies in C. elegans (SAS-1) and human cells placed C2CD3 upstream of SSNA1 and LRRCC1 in the distal luminal hierarchy, establishing a conserved epistatic relationship for centriole integrity.

    Evidence Null allele epistasis in C. elegans with U-Ex-STED, KO super-resolution imaging in human cells (preprints)

    PMID:bio_10.1101_2025.04.22.650004 PMID:bio_10.1101_2025.04.28.648957

    Open questions at the time
    • Both studies are preprints awaiting peer review
    • Whether C2CD3–SSNA1 interaction is direct or mediated by the luminal ring is unresolved
    • Functional consequence of SSNA1 loss downstream of C2CD3 in ciliogenesis not fully characterized

Open questions

Synthesis pass · forward-looking unresolved questions
  • The atomic structure of C2CD3, the mechanism by which it promotes centriole elongation, and the dynamic regulation of the luminal ring during centriole maturation and the cell cycle remain unresolved.
  • No high-resolution structure of C2CD3 or its individual domains is available
  • How the C2CD3–OFD1 antagonism is biochemically regulated is unknown
  • Whether C2CD3 has enzymatic activity through its C2 domains or acts purely as a scaffold is untested

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 2 GO:0008092 cytoskeletal protein binding 1
Localization
GO:0005815 microtubule organizing center 4
Pathway
R-HSA-162582 Signal Transduction 2 R-HSA-1852241 Organelle biogenesis and maintenance 2
Partners
CEP120CEP135CETN2MNROFD1SFI1SSNA1
Complex memberships
C2CD3/SFI1/centrin-2/CEP135/NA14 luminal ring

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2014 C2CD3 localizes to the distal end of centrioles and physically associates with OFD1; C2CD3 acts as a positive regulator of centriole elongation while OFD1 antagonizes C2CD3 activity as a negative regulator. Loss of C2CD3 results in short centrioles lacking subdistal and distal appendages, whereas C2CD3 overexpression triggers centriole hyperelongation. Co-immunoprecipitation, immunofluorescence colocalization, overexpression and loss-of-function in human cells, patient mutation analysis Nature genetics High 24997988
2008 C2cd3 (mouse ortholog) is required for ciliogenesis and Hedgehog signal transduction; loss of C2cd3 disrupts cilia formation, prevents proteolytic processing of Gli3, and impairs intracellular transduction of the Hedgehog signal. C2cd3 protein localizes to the basal body, consistent with its role in ciliogenesis. Forward genetic screen, genetic mapping, second allele characterization, target gene expression analysis, double-mutant epistasis, immunofluorescence localization Development (Cambridge, England) High 19004860
2019 CEP120 interacts with C2CD3 and is required for proper recruitment of C2CD3 to the distal ends of centrioles; a disease-associated CEP120 mutant (I975S) has reduced affinity for C2CD3 binding. Loss of CEP120 results in impaired C2CD3 recruitment, failed centriole appendage assembly, and defective ciliogenesis. Co-immunoprecipitation, CRISPR/Cas9 knockout in RPE1 cells, immunofluorescence, disease mutant binding assay Scientific reports High 30988386
2016 Loss of C2CD3 function in human patient-derived fibroblasts reduces the ability to form cilia and impairs basal body maturation; however, distal appendage protein CEP164 is still recruited, indicating CEP164 recruitment is not sufficient for efficient basal body maturation in C2CD3-defective backgrounds. Patient fibroblast culture analysis, immunofluorescence for basal body and appendage markers, ciliation assay Scientific reports Medium 27094867
2021 Conditional deletion of the C-terminal PKC-C2 domains or the N-terminal C2CD3N-C2 domain of C2cd3 in mice reveals that the N-terminal C2CD3N-C2 domain is critical for early embryonic development and a craniofacial-specific role, indicating domain-specific functional requirements. Conditional allelic series in mouse, tissue-specific isoform analysis, phenotypic characterization Frontiers in cell and developmental biology Medium 34211969
2025 C2CD3 adopts a radially symmetric 9-fold organization within the centriole's distal lumen, forming a ~100 nm luminal ring structure (~27 nodes). The C-terminal region localizes near the luminal ring, while the N-terminal region localizes near a hook-like structure that attaches to the A-microtubule and is adjacent to the DISCO complex (MNR/CEP90/OFD1). C2CD3 depletion disrupts DISCO complex recruitment via direct interaction with MNR, destabilizes the luminal ring network (C2CD3/SFI1/centrin-2/CEP135/NA14), and impairs the distal microtubule tip protein CEP162, functioning as an architectural scaffold for distal centriole assembly and appendage formation. Ultrastructure Expansion Microscopy (U-ExM), iterative U-ExM, in situ cryo-electron tomography (cryo-ET), C2CD3 depletion with immunofluorescence for multiple markers, direct interaction assay with MNR PLoS biology High 41364719
2025 C2CD3 acts upstream of SSNA1 and LRRCC1 in a hierarchical targeting network in the distal centriolar lumen; C2CD3 is required for SSNA1 localization to the distal lumen of centrioles. Knockout cell lines, super-resolution imaging with expansion microscopy, epistasis analysis bioRxivpreprint Medium bio_10.1101_2025.04.28.648957
2025 Hypomorphic missense variants in C2CD3 reduce C2CD3 localization to the basal body, shorten cilia length, reduce ciliation frequency (especially in kidney epithelial cells), and dysregulate SHH signaling (reduced GLI3 activator and GLI1 mRNA); rescue experiments in C2CD3 KO RPE-1 cells confirm these variants have a reduced capacity to restore ciliogenesis. Patient-derived fibroblast and urinary renal epithelial cell assays, C2CD3 KO RPE-1 rescue experiments, immunofluorescence, qRT-PCR for GLI1 and GLI3 Human molecular genetics Medium 39690811
2025 C. elegans SAS-1 (homolog of human C2CD3) is essential for centriole integrity during oogenesis, spermatogenesis, and early embryogenesis, and is required for SSNA-1 localization to centrioles; SAS-1 epistasis places it upstream of SSNA-1 in centriole organization. Null allele generation, U-Ex-STED microscopy, molecular epistasis with null alleles, heterologous human cell recruitment assay bioRxivpreprint Medium bio_10.1101_2025.04.22.650004

Source papers

Stage 0 corpus · 12 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2014 The oral-facial-digital syndrome gene C2CD3 encodes a positive regulator of centriole elongation. Nature genetics 115 24997988
2008 C2cd3 is required for cilia formation and Hedgehog signaling in mouse. Development (Cambridge, England) 85 19004860
2019 CEP120 interacts with C2CD3 and Talpid3 and is required for centriole appendage assembly and ciliogenesis. Scientific reports 34 30988386
2016 Mutations in human C2CD3 cause skeletal dysplasia and provide new insights into phenotypic and cellular consequences of altered C2CD3 function. Scientific reports 30 27094867
2018 Characterization of three ciliopathy pedigrees expands the phenotype associated with biallelic C2CD3 variants. European journal of human genetics : EJHG 22 30097616
2021 Centriolar Protein C2cd3 Is Required for Craniofacial Development. Frontiers in cell and developmental biology 6 34211969
2021 Mutation in the Ciliary Protein C2CD3 Reveals Organ-Specific Mechanisms of Hedgehog Signal Transduction in Avian Embryos. Journal of developmental biology 5 33805906
2025 The Luminal Ring Protein C2CD3 Acts as a Radial In-to-Out Organizer of the Distal Centriole and Appendages. bioRxiv : the preprint server for biology 4 40667239
2025 The luminal ring protein C2CD3 acts as a radial in-to-out organizer of the distal centriole and appendages. PLoS biology 1 41364719
2024 The ciliary protein C2cd3 is required for mandibular musculoskeletal tissue patterning. Differentiation; research in biological diversity 1 38810379
2024 Multiple Fibrolipomas of the Tongue: A Rare Case Report of a Pediatric Patient With Whole Exome Sequencing of the C2CD3 Gene. Case reports in dentistry 1 39734585
2025 Use of patient-derived cell models for characterization of compound heterozygous hypomorphic C2CD3 variants in a patient with isolated nephronophthisis. Human molecular genetics 0 39690811