CFAP52

CFAP52 (WDR16/WDRPUH) is a WD40-repeat protein that supports the assembly and motility of motile cilia and sperm flagella across vertebrate germ and ciliated cells (PMID:33139725, PMID:37236356). In male germ cells it localizes to the centrosome/basal body, mitotic spindle poles, the transient manchette, and the sperm flagellum, but is excluded from primary cilia, marking it as a constituent of the basal-body matrix and the sperm tail rather than a general ciliary protein (PMID:32859975). Functionally it acts as a scaffold/stabilizing partner: it binds CFAP45 directly and maintains CFAP45 levels in the flagellum to sustain dynein-ATPase-driven microtubule sliding, placing it within a shared axonemal module containing dynein ATPases and adenylate kinase (AK8) (PMID:33139725, PMID:37236356). It also interacts with the head-tail coupling regulator SPATA6 and is required for SPATA6 protein stability and connecting-piece formation, so that its loss in mice produces acephalic spermatozoa, MMAF, disrupted '9+2' axoneme integrity, and reduced microtubule-inner and radial-spoke protein levels (PMID:38126872). Loss of CFAP52 causes a motile ciliopathy with situs inversus, hydrocephalus, and asthenospermia in animal models and humans (PMID:17394468, PMID:33139725, PMID:37236356). In ependymal ciliogenesis, Cfap52 mRNA is post-transcriptionally stabilized by the RNA-binding protein HuR acting downstream of Foxj1/Rfx, and CFAP52 overexpression rescues HuR-deficient ependymal development (PMID:34815315).

1. 2005 Medium

   Established the first protein interactions of CFAP52, linking it to chaperone machinery and a proliferative role before its ciliary function was known.

   Evidence Co-immunoprecipitation and siRNA knockdown in HCC cells

   PMID:15967112

   Open questions at the time

   • HSP70/CCT1/BRCA2 associations not validated reciprocally or in ciliated cells
   • Relationship between proliferation phenotype and later-defined ciliary roles unresolved
2. 2007 Medium

   Connected CFAP52 to motile-ciliated tissues by showing its ortholog is expressed with kinocilia and that its loss causes hydrocephalus, defining cilia as the relevant context.

   Evidence In situ hybridization, immunohistochemistry and antisense morpholino knockdown in zebrafish

   PMID:17394468

   Open questions at the time

   • Hydrocephalus arises without altered beat frequency, leaving the cellular mechanism unexplained
   • Molecular function of the protein not addressed
3. 2009 Low

   Characterized transcriptional control of the gene, identifying a shared bidirectional promoter with syntaxin 8.

   Evidence Lentiviral reporter and deletion analysis in ependymal primary cultures

   PMID:19191024

   Open questions at the time

   • Foxd1/Sox17/Spz1 sites are computational, not experimentally bound
   • No connection to in vivo regulation demonstrated
4. 2020 Medium

   Defined the subcellular distribution of CFAP52, distinguishing it from primary-cilium proteins and localizing it to basal body, spindle poles, manchette, and flagellum.

   Evidence Immunofluorescence in NIH3T3 and germ cells plus subcellular fractionation

   PMID:32859975

   Open questions at the time

   • Molecular activity at each structure not resolved
   • No interaction partners identified in this study
5. 2020 Medium

   Placed CFAP52 in a defined axonemal adenine-nucleotide homeostasis module with CFAP45, dynein ATPases, and adenylate kinase, explaining its ciliopathy phenotype.

   Evidence Proteomic profiling of CFAP45-deficient cilia and human/mouse genetic epistasis

   PMID:33139725

   Open questions at the time

   • Direct biochemical activity of CFAP52 within the module not measured
   • Order of assembly within the module unresolved
6. 2021 High

   Identified post-transcriptional control of Cfap52 by HuR as a key step in ependymal ciliogenesis, with overexpression rescue establishing it as a downstream effector.

   Evidence Brain-specific HuR conditional knockout, mRNA stability assay, and Cfap52 overexpression rescue in mouse

   PMID:34815315

   Open questions at the time

   • Direct HuR-binding site on Cfap52 mRNA not mapped
   • How CFAP52 levels translate to ciliogenesis at the protein level unresolved
7. 2022 Medium

   Confirmed CFAP52's functional requirement in cilia through a rapid in vivo genetic approach recapitulating null phenotypes.

   Evidence Multiple-guide CRISPR/Cas9 F0 crispant analysis in zebrafish

   PMID:36533556

   Open questions at the time

   • Limited mechanistic resolution beyond phenotype confirmation
   • No molecular partners assessed
8. 2023 High

   Resolved CFAP52's role in dynein-driven motility by showing it binds and stabilizes CFAP45 in the flagellum to enable microtubule sliding.

   Evidence Co-IP, Cfap52 knockout mouse, sperm motility and dynein-driven microtubule sliding assays, TEM

   PMID:37236356

   Open questions at the time

   • Sliding defect occurs without axonemal ultrastructure change, mechanism of force loss not fully defined
   • Stoichiometry of the CFAP52-CFAP45 interaction unknown
9. 2023 High

   Established CFAP52 in sperm head-tail coupling via SPATA6 stabilization, explaining acephalic spermatozoa and MMAF phenotypes.

   Evidence Co-IP, Cfap52 knockout mouse, TEM, and Western blot of downstream axonemal proteins

   PMID:38126872

   Open questions at the time

   • Mechanism by which CFAP52 stabilizes SPATA6 (direct vs scaffolding) not defined
   • Reduction of MIPs and radial spoke proteins is correlative, not mechanistically linked

• How CFAP52 coordinates its distinct roles across basal body, manchette, head-tail junction, and flagellar axoneme through a single WD40 scaffold remains unresolved.
• No structural model of CFAP52 or its complexes
• Unclear whether the CFAP45 and SPATA6 interactions are mutually exclusive or temporally separated
• Biochemical activity beyond protein stabilization not established