ACTL7A

ACTL7A is a testis-enriched actin-like protein essential for acrosome biogenesis and sperm head shaping during spermiogenesis (PMID:36734600). It localizes dynamically to the nucleus and subacrosomal space of developing spermatids and later to postacrosomal regions, where it drives formation of subacrosomal filamentous actin and anchors the acrosome to the nucleus via the acroplaxome; its loss abolishes subacrosomal F-actin, causes abnormal acrosomal granule migration, and produces peeling, detached acrosomes (PMID:36734600). ACTL7A operates within a perinuclear theca cytoskeletal network, co-immunoprecipitating with the zona-pellucida-binding protein ZPBP and being stabilized by FNDC8, whose depletion destabilizes ACTL7A and disrupts head morphogenesis (PMID:35921706, PMID:41169243). Disruption of the acrosome-acroplaxome-manchette complex upon ACTL7A loss yields small-headed sperm, accompanied by dysregulation of the PI3K/AKT/mTOR/autophagy axis and PDLIM1 accumulation that impairs manchette development (PMID:37667331). A central downstream consequence of ACTL7A dysfunction is mislocalization, reduced expression, or co-discharge of the sperm-borne oocyte activation factor PLCζ (PLCZ1), which abolishes oocyte calcium oscillations and causes total fertilization failure (PMID:32923619, PMID:35863052). Loss-of-function and missense mutations in ACTL7A cause male infertility through acrosomal and perinuclear theca ultrastructural defects and oocyte activation deficiency, a phenotype rescuable by artificial oocyte activation (PMID:32923619, PMID:34727571).

1. 1999 Medium

   Established ACTL7A's molecular identity by cloning it as an intronless actin-like gene paired head-to-head with ACTL7B, defining the basic gene and protein before any functional role was known.

   Evidence cDNA selection and direct genomic sequencing with multi-tissue expression analysis

   PMID:10373328

   Open questions at the time

   • No protein function or subcellular role defined
   • Testis-specific role not yet identified
2. 2012 Medium

   First linked ACTL7A to sperm physiology by showing PKA-driven upregulation and relocalization during capacitation, and demonstrating that antibody targeting impairs fertilization, framing it as a functionally important and immunologically accessible sperm antigen.

   Evidence Western blot and immunostaining during capacitation; in vitro sperm antibody treatment and active immunization fertility assays in mouse

   PMID:22386842 PMID:23211711

   Open questions at the time

   • Molecular mechanism of relocalization unknown
   • No genetic loss-of-function evidence
   • Direct binding partners not identified
3. 2020 High

   Connected ACTL7A mutation to human infertility by showing a missense variant causes acrosomal defects and PLCζ mislocalization that block oocyte activation, with rescue by artificial oocyte activation establishing the therapeutic and mechanistic link.

   Evidence Whole-exome sequencing, knock-in mouse, TEM, immunofluorescence, western blot, AOA rescue

   PMID:32923619

   Open questions at the time

   • How ACTL7A controls PLCζ localization not resolved
   • Structural basis of the missense effect not defined
4. 2021 Medium

   Confirmed and broadened the disease link by showing biallelic loss-of-function variants reduce ACTL7A and PLCζ and produce perinuclear theca defects, reinforcing oocyte activation deficiency as the core pathology.

   Evidence Whole-exome and Sanger sequencing, TEM, immunofluorescence, western blot in patient sperm

   PMID:34727571

   Open questions at the time

   • No mouse model in this study
   • Mechanistic coupling of PT integrity to PLCζ retention unclear
5. 2022 High

   Defined ACTL7A's physical partnerships and the consequence of mislocalization, showing it complexes with ZPBP and that variant protein fails to attach to the acroplaxome and is discharged with PLCζ, explaining the loss of both proteins from sperm.

   Evidence Knockout and knock-in mouse models, Co-IP, IP-LC/MS interactome, TEM, immunofluorescence, IVF/ICSI

   PMID:35863052 PMID:35921706

   Open questions at the time

   • Stoichiometry and direct vs indirect nature of interactions not resolved
   • How acroplaxome attachment is molecularly mediated unknown
6. 2022 Medium

   Provided structural rationale for a pathogenic missense allele, showing p.D75A destabilizes ACTL7A via loss of a hydrogen bond and helix-to-coil transition, linking protein folding to PT/acrosome defects and PLCZ1 dysregulation.

   Evidence Whole-exome sequencing, in silico 3D structural modeling, immunofluorescence, TEM, western blot

   PMID:36574082

   Open questions at the time

   • Structural prediction not experimentally validated
   • Degradation pathway not identified
7. 2023 High

   Identified the core cell-biological function as subacrosomal F-actin formation and acroplaxome-mediated acrosomal anchoring, the mechanistic basis for acrosome attachment that earlier mutation studies implicated indirectly.

   Evidence Actl7a knockout mouse, phalloidin F-actin staining, dynamic-localization immunofluorescence, TEM

   PMID:36734600

   Open questions at the time

   • Biochemical mechanism of F-actin nucleation/organization by ACTL7A unknown
   • Whether ACTL7A polymerizes or scaffolds conventional actin unresolved
8. 2023 Medium

   Placed ACTL7A within a broader head-shaping program, linking its loss to acrosome-acroplaxome-manchette disruption and to PI3K/AKT/mTOR-mediated autophagy inhibition and PDLIM1 accumulation that impairs the manchette.

   Evidence Actl7a knockout mouse, TMT quantitative proteomics, immunofluorescence, TEM, western blot

   PMID:37667331

   Open questions at the time

   • Causality between ACTL7A loss and pathway activation not directly tested
   • Direct vs secondary effect on manchette unclear
9. 2023 Medium

   Extended the human genetic spectrum to actin-domain variants, confirming absent sperm ACTL7A, near-absent PLCζ, and impaired acrosomal PNA staining as a reproducible patient phenotype.

   Evidence Whole-exome sequencing, immunofluorescence, western blot, bioinformatic structural prediction in patients

   PMID:37991128

   Open questions at the time

   • No functional model in this cohort
   • Genotype-phenotype correlation across variants incomplete
10. 2025 Medium

    Defined a perinuclear theca complex by showing FNDC8 interacts with and stabilizes ACTL7A, providing a mechanism for maintaining ACTL7A protein levels needed for head morphogenesis.

    Evidence Co-immunoprecipitation and Fndc8 knockout mouse, immunofluorescence, western blot

    PMID:41169243

    Open questions at the time

    • Whether stabilization is direct or via complex assembly unknown
    • Other PT partners maintaining ACTL7A not fully mapped
11. 2025 Low

    Began mapping a wider PT cytoskeletal network by Co-IP of ACTL7A with ACTRT1/ACTRT2/ARPM1 and ZPBP, and proposed a nuclear chromatin-regulatory role via HDAC1/HDAC3 association and putative ARP subunit swapping in remodeler complexes.

    Evidence Co-IP in Arpm1-deficient context (preprint); Actl7a/Actl7b knockout mice with HDAC1/HDAC3 immunofluorescence, transcriptomics, in silico modeling (preprint)

    PMID:38464253 PMID:bio_10.1101_2025.03.27.645694

    Open questions at the time

    • Single Co-IP without reciprocal validation; ACTL7A not the primary subject
    • Nucleosome-remodeler interactions are in silico predictions only, not biochemically validated
    • Nuclear/chromatin function not connected to the cytoplasmic acrosomal role

• The biochemical mechanism by which ACTL7A nucleates or organizes subacrosomal F-actin, and how this physically retains PLCζ in the perinuclear theca, remains unresolved.
• No in vitro reconstitution of ACTL7A actin activity
• Direct ACTL7A-PLCζ interaction not demonstrated
• Structural model of ACTL7A in the acroplaxome lacking