CATSPER4

CATSPER4 is an essential pore-forming subunit of the sperm-specific CatSper calcium channel, required for flagellar calcium influx, hyperactivated motility, and male fertility. It contains a single voltage-sensor-like channel domain with a conserved TxDxW pore-loop sequence and a C-terminal coiled-coil domain that mediates assembly into a heterotetrameric complex with CATSPER1–3 (PMID:12932298, PMID:17227845). Targeted disruption of CatSper4 in mice abolishes the alkalinization-activated ICatSper current and causes complete male infertility without affecting spermatogenesis, demonstrating that CATSPER4 is indispensable for channel function (PMID:17227845, PMID:17344468). Channel assembly in the sperm flagellum depends on the scaffold protein CATSPERθ (Tmem249), which directly interfaces with CATSPER4 at CatSper dimer junctions, while reciprocally, intact CATSPER4 is required for CATSPERθ protein stability (PMID:37725640).

1. 2003 Medium

   Identification of CATSPER4 as a fourth CatSper family member with a single channel-forming domain and predicted coiled-coil interaction motif established the molecular basis for a heterotetrameric channel model.

   Evidence In silico gene identification, domain/sequence analysis, testis expression profiling

   PMID:12932298

   Open questions at the time

   • No functional reconstitution of the predicted channel
   • Stoichiometry and subunit arrangement within the tetramer not determined
   • No protein-level validation of domain assignments
2. 2007 High

   Gene knockout demonstrated that CATSPER4 is essential for the sperm ICatSper calcium current, hyperactivated motility, and male fertility, resolving whether all four CatSper subunits are individually required for channel function.

   Evidence Targeted gene disruption in mice, patch-clamp electrophysiology of sperm ICatSper, co-immunoprecipitation, computer-assisted sperm motility analysis, fertility assays

   PMID:17227845 PMID:17344468

   Open questions at the time

   • Channel gating mechanism and individual subunit contribution to pore conductance unknown
   • No structural data for the assembled CatSper complex
   • Human genetic confirmation of CATSPER4 loss-of-function causing infertility not yet reported
3. 2023 High

   Discovery that CATSPERθ scaffolds CATSPER4 during channel assembly and that reciprocal dependence exists between pore subunits and CATSPERθ revealed a quality-control checkpoint for CatSper trafficking to flagella.

   Evidence CATSPERθ knockout mice, co-immunoprecipitation, immunofluorescence localization, Western blot in spermatids from multiple CatSper-subunit KO lines

   PMID:37725640

   Open questions at the time

   • Direct binding interface between CATSPERθ and CATSPER4 not structurally resolved
   • Trafficking route from spermatid ER to flagellar membrane not mapped
   • Whether auxiliary subunits (β, γ, δ) also depend on CATSPERθ for assembly is unclear
4. 2026 Medium

   Identification of a functional CRE in the CatSper4 promoter bound by CREMτ in spermatids established a transcriptional mechanism controlling CatSper4 expression during spermiogenesis.

   Evidence Promoter-reporter deletion analysis, EMSA, ChIP in mouse testis

   PMID:41680579

   Open questions at the time

   • Single-lab study; independent replication pending
   • Whether CREMτ-dependent regulation extends to other CatSper subunit genes not tested
   • In vivo consequences of CRE mutation on CatSper4 protein levels and fertility not assessed

• The atomic structure of the CatSper heterotetrameric pore, the specific contribution of CATSPER4 to ion selectivity and gating, and the relevance of CATSPER4 mutations to human infertility remain unresolved.
• No high-resolution structure of the assembled CatSper channel
• No human genetic studies directly linking CATSPER4 variants to male infertility
• Mechanism by which alkalinization gates ICatSper through CATSPER4 is unknown