CFAP47

CFAP47 is a structural scaffolding protein of the motile cilium and sperm flagellum, essential for connecting the central pair microtubules of the axoneme and for proper flagellar assembly. In situ cryo-electron tomography of mouse sperm reveals that CFAP47 is a core component of the central apparatus (CA) bridge: its N-terminal ASH domains bind the C1 microtubule, its central ring domain interacts with HYDIN, and its C-terminal region anchors to C2, thereby tethering C1 and C2; knockout of Cfap47 produces a hollowed bridge and severely reduced sperm motility (PMID:40473901). CFAP47 also physically interacts with WDR87 in the flagellar midpiece and is required for WDR87 localization during sperm tail biogenesis (PMID:36571501). Loss-of-function hemizygous variants in CFAP47 cause X-linked multiple morphological abnormalities of the flagella (MMAF) and asthenozoospermia in men, with additional ciliary defects observed in renal tubular epithelium and respiratory epithelium consistent with a broader ciliopathy (PMID:33472045, PMID:39698362, PMID:37723893).

1. 2021 High

   Establishing that CFAP47 is required for sperm flagellar integrity and motility resolved the gene's primary physiological function: hemizygous loss-of-function variants in men caused MMAF, and a Cfap47-mutant mouse model phenocopied the defect with rescue by ICSI, proving a flagella-specific role.

   Evidence Whole-exome sequencing in multiple MMAF probands, Cfap47-mutant mouse sperm phenotyping and ICSI rescue

   PMID:33472045

   Open questions at the time

   • Molecular mechanism by which CFAP47 supports flagellar structure was unknown
   • Whether CFAP47 functions in cilia outside sperm was untested
   • Direct protein interaction partners were uncharacterized
2. 2022 Medium

   Identification of a CFAP47–WDR87 physical complex in the flagellar midpiece, with WDR87 mislocalization upon CFAP47 loss, established that CFAP47 has a cargo-transport or scaffolding role during sperm tail assembly beyond simple structural integrity.

   Evidence Co-immunoprecipitation and immunofluorescence in CFAP47-mutant human spermatozoa

   PMID:36571501

   Open questions at the time

   • Interaction demonstrated by single Co-IP without reciprocal pull-down
   • Whether WDR87 mislocalization is a direct or indirect consequence of CFAP47 loss was not resolved
   • The domain of CFAP47 mediating the WDR87 interaction was not mapped
3. 2023 Medium

   Discovery that CFAP47 variants reduce ciliary cell numbers and basal bodies in respiratory epithelium of PCD patients broadened the gene's role from sperm-only to a general motile cilia function.

   Evidence Immunofluorescence and TEM of respiratory epithelial cells from two independent patients with CFAP47 missense variants

   PMID:37723893

   Open questions at the time

   • Whether the respiratory phenotype reflects a direct structural role of CFAP47 in airway cilia or a ciliogenesis defect was not distinguished
   • Full PCD clinical characterization (situs inversus, mucociliary clearance) was limited
4. 2024 Medium

   Demonstration that CFAP47 localizes to primary cilia of renal tubules and that Cfap47-knockout mice develop tubular vacuolation and dilation extended the gene's functional scope to primary (non-motile) cilia and implicated it in renal ciliopathy.

   Evidence Immunohistology of human kidney, Cfap47-KO mouse renal histology

   PMID:39698362

   Open questions at the time

   • Whether the renal phenotype is due to structural disruption of primary cilia or a signaling defect was not resolved
   • Progression to cystic kidney disease was not longitudinally assessed
5. 2025 High

   Sub-nanometer cryo-ET combined with AlphaFold2 modeling resolved the molecular architecture of CFAP47 within the central apparatus bridge, showing that its N-terminal ASH domains bind C1, a central ring contacts HYDIN, and the C-terminus anchors to C2 — providing the first atomic-level explanation for how the central pair is tethered.

   Evidence In situ cryo-electron tomography of mouse sperm with AlphaFold2 atomic fitting; Cfap47-KO mouse validation showing hollowed CA bridge and reduced motility

   PMID:40473901

   Open questions at the time

   • Whether the same bridge architecture exists in airway motile cilia or primary cilia was not tested
   • How loss of the bridge mechanistically propagates to outer doublet dynein regulation is unknown
   • Post-translational modifications regulating CFAP47 incorporation into the bridge were not examined

• How CFAP47's dual roles — as a central apparatus bridge component in motile cilia and as a factor in primary cilia of kidney and possibly other tissues — relate mechanistically remains unresolved; whether CFAP47 serves a structural versus signaling scaffold function in primary cilia is an open question.
• No structural data for CFAP47 in primary cilia
• Genotype–phenotype correlation across tissues (sperm, airway, kidney) not systematically established
• Whether CFAP47 participates in dynein-arm regulatory signaling through the CA remains untested