Affinage

PCARE

Photoreceptor cilium actin regulator · UniProt A6NGG8

Length
1288 aa
Mass
139.7 kDa
Annotated
2026-06-10
16 papers in source corpus 5 papers cited in narrative 5 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 4/4 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PCARE (C2orf71) is a photoreceptor-enriched, cilium-localized actin-associated protein essential for the development and maintenance of photoreceptor outer segments (PMID:25616964, PMID:32312818). It functions at the base/tip of the outer segment by binding the Arp2/3 complex activator WASF3 and recruiting it to the primary cilium, where co-expression of the two proteins drives actin-polymerization-dependent expansion of the ciliary tip membrane—a process required for outer segment disk formation and abolished by actin-polymerization inhibition or a retinal-dystrophy-associated PCARE mutation (PMID:32312818). Its activity is partitioned across discrete elements: an N-terminal lipid modification within the first three amino acids and a coiled-coil domain direct ciliary targeting, while EVH1 domain-binding linear motifs mediate full WASF3-dependent membrane expansion (PMID:20398886, PMID:35253837). Loss of PCARE in mice causes severe early-onset retinal degeneration with disorganized outer segments, depleted rhodopsin and retinoids, and absent electroretinogram responses, establishing it as causally required for outer segment integrity (PMID:25616964).

Mechanistic history

Synthesis pass · year-by-year structured walk · 5 steps
  1. 2010 Medium

    Established that the uncharacterized C2orf71/PCARE product is a ciliary protein whose integrity and lipid modification matter for photoreceptor function, framing it as a candidate retinal disease gene.

    Evidence Subcellular localization in cultured cells, proteasomal degradation assay of a missense mutant, lipid modification site validation, and morpholino knockdown in zebrafish

    PMID:20398886

    Open questions at the time
    • No molecular partners or biochemical activity identified
    • Connecting-cilium versus outer-segment localization not resolved in photoreceptors
    • Mechanism linking lipid modification to function unknown
  2. 2015 High

    Demonstrated that PCARE is genetically required for photoreceptor outer segment development and maintenance, moving it from a localization candidate to an essential structural/functional gene.

    Evidence Knockout mouse with immunohistochemistry, EM, electroretinography, and retinoid/rhodopsin quantification

    PMID:25616964

    Open questions at the time
    • Molecular mechanism of how loss disorganizes outer segments not defined
    • No interacting proteins identified
    • Inner-segment localization versus site of action unresolved
  3. 2016 Low

    Indicated a genetic interaction between C2orf71 and RP1L1 in photoreceptor and cerebellar development, hinting at a shared pathway.

    Evidence Combinatorial morpholino knockdown of rp1l1 and c2orf71l in zebrafish with eye-size, rhodopsin, and cerebellar readouts

    PMID:27029556

    Open questions at the time
    • Single in vivo knockdown model without rescue or specificity controls
    • No direct physical interaction between PCARE and RP1L1 shown
    • Cerebellar phenotype mechanism unexplained
  4. 2020 High

    Defined the core molecular mechanism: PCARE recruits the Arp2/3 activator WASF3 to the cilium to drive actin-polymerization-dependent ciliary membrane expansion, explaining its role in disk formation.

    Evidence Co-IP, ectopic coexpression in ciliated cells, siRNA and pharmacological actin inhibition, disease-mutant expression, human retinal organoids, and Pcare knockout mouse immunolocalization

    PMID:32312818

    Open questions at the time
    • Direct WASF3-binding interface on PCARE not mapped in this study
    • How membrane expansion is converted into discrete disks unknown
    • Regulation/timing of the expansion cycle not defined
  5. 2022 Medium

    Resolved which PCARE elements drive targeting versus effector activity, separating ciliary localization (coiled coil, lipid modification) from WASF3-dependent expansion (EVH1-binding motifs).

    Evidence Domain-deletion mutagenesis with ciliary localization and tip-expansion measurements upon WASF3 coexpression

    PMID:35253837

    Open questions at the time
    • Functional consequence of the conserved MAK/RP62 kinase binding sites not tested
    • No structural model of the PCARE-WASF3 complex
    • Contribution of each motif in native photoreceptors not validated

Open questions

Synthesis pass · forward-looking unresolved questions
  • How PCARE-driven ciliary membrane expansion is spatially and temporally controlled to generate ordered outer segment disks, and the role of MAK phosphorylation, remains unresolved.
  • No demonstrated regulation of PCARE by MAK kinase
  • Mechanism converting membrane expansion into periodic disks unknown
  • Structure of the PCARE-WASF3-actin assembly undetermined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 2 GO:0008092 cytoskeletal protein binding 1 GO:0060090 molecular adaptor activity 1
Localization
GO:0005929 cilium 3 GO:0005856 cytoskeleton 1
Pathway
R-HSA-1852241 Organelle biogenesis and maintenance 2 R-HSA-1266738 Developmental Biology 1 R-HSA-9709957 Sensory Perception 1
Partners
WASF3

Evidence

Reading pass · 5 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2010 C2ORF71/PCARE protein localizes to primary cilia in cultured cells, suggesting it localizes to the connecting cilium or outer segment of photoreceptor cells. A missense mutation (p.I201F) within a highly conserved region leads to proteasomal degradation of the protein. Bioinformatic and functional studies identified and validated sites of lipid modification within the first three amino acids of the C2ORF71 protein. Morpholino knockdown of c2orf71 in zebrafish results in visual defects. Subcellular localization in cultured cells, proteasomal degradation assay, lipid modification site validation, morpholino knockdown in zebrafish American journal of human genetics Medium 20398886
2015 Mouse homolog BC027072 (C2orf71/PCARE) protein localizes by immunohistochemistry to the inner segments of photoreceptor cells and outer segments of cone cells. Knockout mice (BC−/−) develop severe early-onset retinal degeneration with disorganized outer segments by 3 weeks and complete loss by 24 weeks, reduced retinoids and rhodopsin levels (<20% of wild-type), and virtually absent electroretinogram responses by 8 weeks, establishing an essential role in outer segment development and maintenance. Custom polyclonal antibody immunohistochemistry, knockout mouse generation, histology, electron microscopy, electroretinography, retinoid/rhodopsin quantification, RNAseq Human molecular genetics High 25616964
2020 PCARE (C2orf71) interacts with the Arp2/3 complex activator WASF3 and efficiently recruits it to the primary cilium. Ectopic coexpression of PCARE and WASF3 in ciliated cells causes remarkable expansion of the ciliary tip membrane, driven by actin polymerization. This process is disrupted by siRNA knockdown of actin regulators, pharmacological inhibition of actin polymerization, or expression of a retinal dystrophy-associated PCARE missense mutation. In human retinal organoids and mouse retina, PCARE and actin colocalize at the base of photoreceptor outer segments, and this process is abrogated in Pcare knockout mice. PCARE is thereby identified as an actin-associated regulator of ciliary membrane expansion during outer segment disk formation. Co-immunoprecipitation/interaction assay, ectopic coexpression in ciliated cells, siRNA knockdown, pharmacological inhibition, disease-associated mutant expression, human retinal organoids, mouse retina immunolocalization, Pcare knockout mouse Proceedings of the National Academy of Sciences of the United States of America High 32312818
2022 PCARE requires specific structural domains for its ciliary function: (1) a predicted helical coiled coil domain is required for ciliary localization — deletion causes failure to localize to cilia; (2) EVH1 domain-binding linear motifs are required for full ciliary tip membrane expansion in coexpression with WASF3 — deletion of these motifs results in smaller ciliary tip expansions; (3) lipid modification on cysteine at amino acid position 3 contributes moderately to ciliary tip expansion size; (4) evolutionary conserved binding sites for photoreceptor kinase MAK (RP62) are present within PCARE. Domain deletion mutagenesis, ciliary localization assay, coexpression with WASF3, ciliary tip expansion measurement Human molecular genetics Medium 35253837
2016 Combined morpholino suppression of rp1l1 and c2orf71l in zebrafish induces reduction of eye size with loss of rhodopsin in photoreceptors and disorganization of the cerebellum, establishing a genetic interaction between C2orf71 and RP1L1 in photoreceptor and cerebellar development. Combinatorial morpholino knockdown in zebrafish, eye size measurement, rhodopsin immunostaining, cerebellar histology Ophthalmic genetics Low 27029556

Source papers

Stage 0 corpus · 16 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2010 Mutations in C2ORF71 cause autosomal-recessive retinitis pigmentosa. American journal of human genetics 78 20398884
2014 A homozygous nonsense CEP250 mutation combined with a heterozygous nonsense C2orf71 mutation is associated with atypical Usher syndrome. Journal of medical genetics 68 24780881
2010 Discovery and functional analysis of a retinitis pigmentosa gene, C2ORF71. American journal of human genetics 66 20398886
2020 PCARE and WASF3 regulate ciliary F-actin assembly that is required for the initiation of photoreceptor outer segment disk formation. Proceedings of the National Academy of Sciences of the United States of America 60 32312818
2012 Late-onset progressive retinal atrophy in the Gordon and Irish Setter breeds is associated with a frameshift mutation in C2orf71. Animal genetics 41 22686255
2011 Novel C2orf71 mutations account for ∼1% of cases in a large French arRP cohort. Human mutation 32 21412943
2016 Putative digenic inheritance of heterozygous RP1L1 and C2orf71 null mutations in syndromic retinal dystrophy. Ophthalmic genetics 24 27029556
2015 Animals deficient in C2Orf71, an autosomal recessive retinitis pigmentosa-associated locus, develop severe early-onset retinal degeneration. Human molecular genetics 18 25616964
2017 C2orf71 Mutations as a Frequent Cause of Autosomal-Recessive Retinitis Pigmentosa: Clinical Analysis and Presentation of 8 Novel Mutations. Investigative ophthalmology & visual science 15 28763557
2011 A survey of DNA variation of C2ORF71 in probands with progressive autosomal recessive retinal degeneration and controls. Investigative ophthalmology & visual science 11 20811058
2023 Clinical and Molecular Aspects of C2orf71/PCARE in Retinal Diseases. International journal of molecular sciences 6 37445847
2019 Novel mutations in c2orf71 causing an early onset form of cone-rod dystrophy: A molecular diagnosis after 20 years of clinical follow-up. Molecular vision 5 31819343
2022 PCARE requires coiled coil, RP62 kinase-binding and EVH1 domain-binding motifs for ciliary expansion. Human molecular genetics 4 35253837
2025 Bilateral macular colobomata: expanded phenotype of PCARE/C2ORF71. Ophthalmic genetics 0 40400237
2024 Mutational Profile and Retinal Phenotypes of PCARE-Related Cone-Rod Dystrophies in a Mexican Cohort. Journal of ophthalmology 0 38468717
2022 [Analysis of C2ORF71 gene variant in a Chinese patient with retinitis pigmentosa]. Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics 0 34964967

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