CFAP65

CFAP65 is a cilia- and flagella-associated protein essential for spermiogenesis, sperm flagellar assembly, and axonemal central apparatus integrity. In the axoneme, CFAP65 localizes to the C2a projection of the central apparatus, where it forms a complex with FAP70/CFAP70 and FAP147/MYCBPAP (PMID:33988244, PMID:39092789). During mammalian spermiogenesis, CFAP65 is required for acrosome biogenesis, manchette-guided sperm head shaping, and mitochondrial sheath assembly, functioning through a cytoplasmic protein network that includes MNS1, RSPH1, TPPP2, ZPBP1, and SPACA1 (PMID:34231842). Biallelic loss-of-function mutations in CFAP65 cause multiple morphological abnormalities of the sperm flagella (MMAF) and male infertility in humans and mice (PMID:31501240, PMID:31413122).

1. 2017 Medium

   Before CFAP65 was linked to spermatogenesis, an epistasis experiment in gastric cancer cells placed it in a mitochondrial retrograde signaling axis (TFAM→mtDNA→calcium→CFAP65→PCK1), revealing a non-ciliary context for the gene.

   Evidence siRNA knockdown and epistasis ordering in MKN45 gastric cancer cells

   PMID:29259235

   Open questions at the time

   • Single cell line; relevance to physiological CFAP65 function in germ cells or motile cilia unclear
   • Downstream mechanism linking CFAP65 to PCK1 regulation not defined
   • No independent replication in a second cancer model
2. 2019 High

   The first genetic evidence that CFAP65 is essential for sperm structure and motility came from identification of biallelic loss-of-function mutations in MMAF patients and recapitulation by CRISPR-Cas9 knockout in mice, establishing CFAP65 as a male infertility gene.

   Evidence Whole-exome sequencing in multiple MMAF families, Sanger validation, CRISPR-Cas9 Cfap65 KO mouse with sperm phenotyping, transmission electron microscopy of patient spermatozoa

   PMID:31413122 PMID:31501240 PMID:31571197

   Open questions at the time

   • Molecular function of CFAP65 protein was unknown
   • Sub-cellular localization within the flagellar axoneme was not determined
   • Mechanism linking CFAP65 loss to simultaneous acrosome, mitochondrial sheath, and central pair defects was not explained
3. 2021 High

   Cryo-EM and mutant analysis in Chlamydomonas resolved the structural position of FAP65/CFAP65 to the C2a projection of the central apparatus and showed it depends on FAP70 for incorporation, defining its precise axonemal sub-localization.

   Evidence Cryo-electron microscopy, super-resolution SIM, mass spectrometry of fap70-1 mutant axonemes, co-immunoprecipitation with HA-FAP70 in Chlamydomonas

   PMID:33988244

   Open questions at the time

   • Whether mammalian CFAP65 occupies the identical C2a niche was not directly shown structurally
   • Direct structural model of the FAP65-FAP70-FAP147 complex at atomic resolution was not obtained
4. 2021 High

   Detailed mouse knockout analysis revealed that CFAP65 acts at defined spermiogenic stages — required for acrosome maturation from step 9 onward, manchette organization, and mitochondrial sheath assembly — and identified a cytoplasmic interaction network (MNS1, RSPH1, TPPP2, ZPBP1, SPACA1) through which it operates.

   Evidence Cfap65 KO mouse, step-resolved histology and EM of spermatids, endogenous co-immunoprecipitation, quantitative proteomics

   PMID:34231842

   Open questions at the time

   • Co-IP interactions lack reciprocal pulldown or structural validation
   • How CFAP65 coordinates distinct processes (acrosome, manchette, mitochondrial sheath) mechanistically remains unclear
   • Proteomics-inferred pathway disruption needs functional validation of individual downstream targets
5. 2023 Low

   CFAP47 was identified as a physical interactor of CFAP65, and CFAP47 mutations led to reduced CFAP65 protein in patient sperm, suggesting an upstream stability-regulatory relationship.

   Evidence Co-immunoprecipitation and western blot/immunofluorescence in patient spermatozoa

   PMID:37424856

   Open questions at the time

   • Single co-IP without reciprocal validation; interaction directness not confirmed
   • Mechanism of CFAP47-dependent CFAP65 stabilization not determined
   • Only protein-level correlation, not causation, demonstrated for the stability claim
6. 2024 Medium

   MYCBPAP interactome analysis in mouse testes independently confirmed CFAP65 and CFAP70 as binding partners, corroborating the conserved C2a complex from Chlamydomonas in the mammalian sperm flagellum.

   Evidence Endogenous immunoprecipitation–mass spectrometry from MYCBPAP transgenic mouse testes

   PMID:39092789 PMID:39704931

   Open questions at the time

   • No direct structural data confirming mammalian C2a complex architecture
   • Functional consequence of disrupting the CFAP65-MYCBPAP interaction specifically is untested

• The direct biochemical activity of CFAP65 — whether it is a structural scaffold, an enzymatic factor, or a regulatory adaptor within the C2a projection and cytoplasmic spermiogenic network — remains undefined.
• No enzymatic or biochemical activity assigned to CFAP65
• Atomic-resolution structure of CFAP65 alone or in complex is unavailable
• Whether CFAP65 has motile-cilia functions beyond spermatogenesis (e.g. in airway epithelia) is untested in mammalian models