SEPTIN14

SEPTIN14 is a GTP-binding septin that assembles into heteromeric septin filaments and organizes actin- and microtubule-based cytoskeletal structures required for sperm morphogenesis and cortical neuronal migration (PMID:39982757, PMID:20181826). During spermiogenesis it localizes to the acroplaxome, manchette, neck, and annulus, where it interacts and co-localizes with microtubules and actin during manchette formation and assembles into annular septin filaments through defined domain contacts—its GTP-binding domain (GBD) binds the GBD of SEPT2 and its C-terminus binds the GBD of SEPT7 (PMID:39982757). SEPT14 also associates with SEPT9 and additional septins, consistent with incorporation into broader heteromeric septin complexes (PMID:17922164). In sperm-head morphogenesis SEPT14 binds the actin-binding protein ACTN4 and recruits it to the perinuclear and manchette regions; polymerization-disrupting missense mutations (p.Ala123Thr and p.Ile333Thr) impair filament assembly, mislocalize and fragment ACTN4, and produce malformed sperm heads with abnormal chromatin packaging and DNA fragmentation (PMID:31450874, PMID:33228246). Loss of SEPT14 in mice causes subfertility with irregular acrosomes, DNA damage, disorganized mitochondria, displaced annuli, and impaired motility and capacitation (PMID:39982757). In a parallel role, SEPT14 uses its C-terminal coiled-coil region to bind SEPT4, an interaction required for leading-process formation and cortical migration of neurons (PMID:20181826).

1. 2007 Medium

   Establishing SEPT14 as a bona fide septin required showing it physically associates with known septins; this defined it as a member of heteromeric septin assemblies rather than an isolated protein.

   Evidence Yeast two-hybrid plus reciprocal co-immunoprecipitation in cell lines and rat testes, with co-localization

   PMID:17922164

   Open questions at the time

   • Stoichiometry and architecture of the SEPT14-containing complex not resolved
   • Functional consequence of the SEPT9 interaction not tested
   • Y2H hits with nine additional septins not validated biochemically
2. 2010 High

   It was unknown whether SEPT14 had a role outside the testis; mapping a SEPT4-binding C-terminal coiled-coil and showing its requirement in vivo established a function in cortical neuronal migration.

   Evidence In utero electroporation knockdown with wild-type and C-terminal deletion rescue, plus co-immunoprecipitation

   PMID:20181826

   Open questions at the time

   • Molecular mechanism linking SEPT14-SEPT4 to leading-process cytoskeleton not defined
   • Whether SEPT14 acts in the same complex with other neuronal septins not addressed
3. 2019 Medium

   Linking SEPT14 to human male infertility required disease alleles; two missense mutations that impair polymerization were tied to severe sperm-head and chromatin defects, establishing polymerization as functionally critical.

   Evidence In vitro polymerization assays of mutant vs wild-type protein, with TEM, Toluidine blue, and comet assay on patient sperm

   PMID:31450874

   Open questions at the time

   • Causality in humans is associative, not genetically proven by rescue
   • How impaired polymerization mechanistically produces chromatin/DNA defects not shown
4. 2020 Medium

   The downstream effector through which SEPT14 shapes the sperm head was unknown; identifying ACTN4 as a partner mislocalized by polymerization-defective SEPT14 connected SEPT14 filaments to actin organization at the manchette.

   Evidence Co-immunoprecipitation with nano-LC-MS/MS, immunostaining, and mutant SEPT14 cell model; complemented by immunocytochemical mapping of SEPT14 to the sperm head-to-tail region

   PMID:32249155 PMID:33228246

   Open questions at the time

   • Direct vs indirect SEPT14-ACTN4 binding not distinguished
   • Localization study alone provides no functional readout
5. 2025 High

   A definitive loss-of-function model and domain-level interaction map were missing; knockout mice with multi-compartment defects plus GBD/C-terminus mapping established SEPT14 as an architectural organizer of septin filaments across spermiogenesis structures.

   Evidence Sept14 knockout mice with sperm functional assays, immunofluorescence, and domain-specific co-IP mapping of SEPT2/SEPT7/SEPT9 interactions

   PMID:39982757

   Open questions at the time

   • Structural basis of GBD-GBD and C-terminus-GBD contacts not solved
   • How the same protein coordinates manchette microtubules and annulus filaments not mechanistically separated

• How SEPT14 GTP binding/hydrolysis regulates filament assembly and effector recruitment, and whether its neuronal and germ-cell roles share a common mechanism, remain open.
• No structure of SEPT14 or its complexes
• GTPase cycle not directly characterized
• Unified model across spermiogenesis and cortical migration absent