{"gene":"AKAP4","run_date":"2026-06-09T22:02:43","timeline":{"discoveries":[{"year":1995,"finding":"AKAP4 (Fsc1) encodes the major structural protein of the fibrous sheath in the principal piece of the sperm flagellum; mRNA is expressed exclusively in postmeiotic (round) spermatids and the protein contains 32 cysteine residues and 32 potential phosphorylation sites with no homology to other known cytoskeletal proteins.","method":"cDNA cloning, Northern blot, in situ hybridization, peptide sequencing","journal":"Biology of reproduction","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (peptide sequencing, cDNA cloning, Northern blot, in situ hybridization) establishing primary structure and expression pattern; independently replicated across species in subsequent work","pmids":["7711182"],"is_preprint":false},{"year":1997,"finding":"Pro-AKAP4 (pro-AKAP82) is synthesized in the spermatid cell body, transported down the axoneme, proteolytically cleaved to form mature AKAP4 during fibrous sheath assembly, and becomes insoluble (Triton X-100 resistant) in mature sperm; the RII subunit of PKA co-purifies with AKAP4 in the particulate fraction of sperm, consistent with AKAP4 anchoring PKA to the fibrous sheath.","method":"Immunoelectron microscopy, immunoblotting with phosphatase treatment, Triton X-100 fractionation, antiserum against pro-domain peptide","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal fractionation experiments combined with immunoelectron microscopy, replicated across mouse and human systems","pmids":["9441672"],"is_preprint":false},{"year":1998,"finding":"AKAP4 (FSC1) contains two distinct RIα tethering domains: domain A (residues 219–232) binds both RIα and RII (dual-specificity), and domain B (residues 335–344) specifically binds RIα via an amphipathic helix; site-directed mutagenesis disrupting the amphipathic helix of domain B abolishes RIα binding.","method":"Yeast two-hybrid screening of mouse testis cDNA library, GST-fusion in vitro binding assays, deletion analysis, site-directed mutagenesis, helical wheel projection","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro binding assay with mutagenesis confirming amphipathic helix requirement; multiple orthogonal approaches in one study","pmids":["9852104"],"is_preprint":false},{"year":1998,"finding":"Human AKAP4 (hAKAP82) is encoded by an X-linked gene (Xp11.2), is highly homologous to mouse AKAP82, and its precursor pro-hAKAP82 binds the type II regulatory subunit of PKA through a domain identical to that of the mouse protein; alternative splicing generates at least two distinct transcripts.","method":"cDNA cloning, RII overlay assay, immunofluorescence, chromosomal mapping, sequence analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — RII overlay binding assay plus chromosomal mapping and sequence conservation, replicated across species","pmids":["9822690"],"is_preprint":false},{"year":1999,"finding":"Bovine AKAP82 binds the regulatory subunit of PKA and localizes to the entire principal piece of the sperm flagellum, demonstrating conservation of PKA-anchoring function across mammals.","method":"cDNA cloning, RII binding assay, immunofluorescence, immunoblotting","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RII binding assay plus immunolocalization in a single study, corroborating mouse and human data","pmids":["10411509"],"is_preprint":false},{"year":1999,"finding":"Pro-hAKAP82 and hAKAP82 undergo capacitation-dependent tyrosine phosphorylation in human spermatozoa, but neither the extent of proteolytic processing nor tyrosine phosphorylation of these proteins was found to correlate with differences in sperm motility.","method":"Immunofluorescence, immunoblotting with phosphotyrosine antibodies","journal":"Molecular human reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct detection of capacitation-dependent tyrosine phosphorylation; negative correlation with motility is a defined negative result from a single lab","pmids":["10460219"],"is_preprint":false},{"year":2002,"finding":"Genetic knockout of Akap4 in mice causes failure of fibrous sheath assembly, loss of progressive sperm motility, and male infertility without reducing sperm numbers; fibrous sheath-associated proteins (including signaling and glycolytic enzymes) are absent or substantially reduced, establishing AKAP4 as an essential scaffold for fibrous sheath organization.","method":"Gene targeting (knockout mouse), electron microscopy, immunoblotting, motility analysis","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout with multiple orthogonal phenotypic readouts (motility, ultrastructure, protein localization); widely replicated","pmids":["12167408"],"is_preprint":false},{"year":2004,"finding":"In Akap4-knockout mice, PKA catalytic and regulatory subunits and PI3-kinase lose their normal fibrous sheath subcellular distribution, and PP1γ2 phosphorylation and activity are significantly altered, demonstrating that the fibrous sheath scaffold formed by AKAP4 is required for correct spatial organization and regulation of these kinase/phosphatase signaling components.","method":"Akap4-knockout mouse, subcellular fractionation, immunoblotting, phosphatase activity assay","journal":"Biology of reproduction","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function combined with biochemical fractionation and enzymatic activity assay defining specific downstream signaling consequences","pmids":["15385410"],"is_preprint":false},{"year":2006,"finding":"The pro domain of AKAP4 keeps the precursor in a diffuse cytoplasmic localization in somatic cells; upon removal of the pro domain, mature AKAP4 adopts a punctate distribution dependent on the microtubular cytoskeleton via two domains (T2a and T2b) homologous to the actin-binding T2-tethering domain of AKAP5, suggesting AKAP4 interacts with microtubules to be transported/incorporated into the fibrous sheath.","method":"GFP-fusion protein expression in somatic cell lines, immunofluorescence, cytoskeletal drug treatments (microtubule/actin disruption)","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain-deletion GFP constructs in live cells with cytoskeletal pharmacology; single lab, two orthogonal approaches","pmids":["16687648"],"is_preprint":false},{"year":2005,"finding":"The Akap4 gene produces two alternatively spliced transcripts (Akap82 and Fsc1) differing only in their 5′ UTRs; only the Akap82 transcript is loaded onto polyribosomes and translated in spermatids, while the Fsc1 transcript is not polysomal despite both being deadenylated during spermiogenesis.","method":"Polyribosome fractionation, RT-PCR, reporter assays in vivo and in vitro","journal":"Molecular reproduction and development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — polyribosome fractionation directly demonstrates differential translational loading; single lab","pmids":["15685631"],"is_preprint":false},{"year":2012,"finding":"ERK1/2 phosphorylates proAKAP4 on Thr265 in human spermatozoa in vitro and in vivo; phosphorylation by ERK1/2 (downstream of PKC) causes relocalization of proAKAP4 from the principal piece to the Golgi/mid-piece in a T265-dependent manner; cAMP/PKA attenuates PKC-dependent ERK1/2 activation only in the presence of proAKAP4, and disruption of PKA-RII/AKAP binding (St-HT31) abolishes this inhibitory cross-talk, establishing proAKAP4 as a molecular switch between cAMP/PKA and PKC/ERK1/2 pathways.","method":"In vitro kinase assay, site-directed mutagenesis (T265A), GFP-proAKAP4 transfection in HEK293T, immunofluorescence, phorbol ester stimulation, PKA-AKAP disrupting peptide St-HT31","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro kinase assay plus mutagenesis plus cell-based relocalization assay plus pathway disruption peptide; multiple orthogonal methods in one study","pmids":["27901058"],"is_preprint":false},{"year":2012,"finding":"Porcine oviductal DMBT1 induces tyrosine phosphorylation of proAKAP4 (but not the mature ~80 kDa AKAP4) localized to periacrosomal membranes, independently of calcium, bicarbonate, cAMP analogs, PKA inhibitors, or PKC inductor, placing proAKAP4 phosphorylation as an early step in the DMBT1-triggered signal transduction pathway controlling sperm selection.","method":"Mass spectrometry, immunoprecipitation, immunofluorescence, subcellular fractionation, pharmacological inhibitor panel","journal":"Reproduction (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MS identification plus immunoprecipitation plus functional fractionation in a single study; single lab","pmids":["22457434"],"is_preprint":false},{"year":2017,"finding":"AKAP4 knockdown in ovarian cancer cells leads to PKA protein degradation that is rescued by the proteasome inhibitor MG-132, increased ROS and DNA damage, and cell cycle arrest rescued by the ROS quencher NAC, demonstrating that AKAP4 maintains PKA stability and acts through the PKA-CREB signaling axis in cancer cells.","method":"siRNA knockdown, proteasome inhibitor rescue (MG-132), NAC treatment, immunoblotting, flow cytometry, SCID mouse xenograft","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological rescue experiments (MG-132, NAC) identifying PKA degradation mechanism; single lab, two orthogonal rescue approaches","pmids":["28881798"],"is_preprint":false},{"year":2021,"finding":"A hemizygous missense variant (c.1285C>T, p.R429C) in AKAP4 reduces AKAP4 protein expression and its interaction with QRICH2 (demonstrated by co-immunoprecipitation and co-localization), resulting in decreased QRICH2 protein in spermatozoa and dysplastic fibrous sheath leading to male infertility.","method":"Whole-exome sequencing, co-immunoprecipitation, immunofluorescence, HEK-293T cell expression","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP demonstrating interaction plus variant disruption of interaction; single lab","pmids":["34415320"],"is_preprint":false},{"year":2021,"finding":"A missense mutation p.S152P in the pro-domain of AKAP4 causes protein accumulation in the cytoplasm of COS-7 cells (failure to traffic correctly), abolishes mature AKAP4 in spermatozoa, increases ROS/apoptotic markers in GC2-spd cells, decreases PKA/PI3K signaling activity, and disrupts the interaction between AKAP4 and RNASET2.","method":"Sanger sequencing, COS-7 cell transfection with GFP-fusion constructs, immunofluorescence, co-immunoprecipitation, flow cytometry, oxidative stress assays","journal":"Molecular reproduction and development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based mislocalization plus Co-IP interaction disruption plus signaling assay; single lab, multiple readouts","pmids":["34409659"],"is_preprint":false},{"year":2024,"finding":"AKAP4 is a target of SUMO1 modification in porcine sperm under cryopreservation/oxidative stress; SUMO1 modification level increases while AKAP4 protein level decreases under these conditions, but inhibition of SUMO1 modification does not affect AKAP4 degradation, indicating SUMO1 is not involved in AKAP4 proteolysis. However, global inhibition of sperm protein SUMO1 modification reduces sperm motility, ATP content, and DNA integrity.","method":"LC-MS/MS identification of SUMO-modified proteins, SUMO inhibitor treatment, immunoblotting, sperm motility and ATP assays","journal":"Animal reproduction science","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, LC-MS identification of SUMO modification site on AKAP4 but functional rescue specifically for AKAP4 not demonstrated","pmids":["39765132"],"is_preprint":false},{"year":2020,"finding":"Phosphoproteomics of mouse sperm capacitation identified phosphorylation of AKAP4 at Y156 (increased) and Y811 (decreased) during capacitation, with overall upregulated phospho-AKAP4 trends detected by western blot, indicating AKAP4 phosphorylation is dynamically regulated during capacitation.","method":"Label-free quantitative phosphoproteomics, western blotting, IPA pathway analysis","journal":"International journal of molecular sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single phosphoproteomic study without functional follow-up of specific AKAP4 phosphosites; single lab","pmids":["33023073"],"is_preprint":false},{"year":2025,"finding":"SPAG6 modulates testicular AKAP4 levels in mice; in compound Spag6/Spag6l mutants with disorganized fibrous sheath, AKAP4 levels are altered, suggesting SPAG6 acts upstream of AKAP4 in the pathway controlling fibrous sheath assembly.","method":"Double-knockout mouse model, immunoblotting, histological and ultrastructural analysis","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, indirect modulation of AKAP4 levels by SPAG6 without direct mechanistic dissection of the SPAG6-AKAP4 relationship","pmids":["bio_10.1101_2025.07.18.665465"],"is_preprint":true}],"current_model":"AKAP4 is the principal structural scaffold protein of the sperm flagellum fibrous sheath, synthesized as a precursor (proAKAP4) in postmeiotic spermatids, transported along the axoneme, and proteolytically processed into insoluble mature AKAP4 during fibrous sheath assembly; it anchors cAMP-dependent protein kinase (PKA) to the fibrous sheath via dual-specificity (RIα/RII) and RIα-specific amphipathic-helix tethering domains, thereby localizing PKA-dependent phosphorylation to the principal piece to regulate sperm motility; proAKAP4 is additionally phosphorylated on Thr265 by ERK1/2 (downstream of PKC), causing its relocalization and acting as a molecular switch that allows cAMP/PKA to negatively cross-regulate the PKC/ERK1/2 pathway during capacitation and acrosome reaction; AKAP4 also interacts with QRICH2 to maintain fibrous sheath integrity, and its pro-domain controls cytoplasmic retention of the precursor until microtubule-dependent transport delivers it to the assembling sheath."},"narrative":{"mechanistic_narrative":"AKAP4 is the principal structural scaffold protein of the sperm flagellum fibrous sheath in the principal piece, expressed exclusively in postmeiotic spermatids and synthesized as a precursor (proAKAP4) that is transported down the axoneme and proteolytically cleaved into an insoluble, detergent-resistant mature form during fibrous sheath assembly [PMID:7711182, PMID:9441672]. The protein's pro-domain enforces a diffuse cytoplasmic localization of the precursor, and only after its removal does mature AKAP4 acquire a punctate, microtubule-dependent distribution via T2-tethering domains, coupling proteolytic maturation to cytoskeletal delivery into the assembling sheath [PMID:16687648]. Genetic ablation of Akap4 abolishes fibrous sheath assembly, causing loss of progressive motility and male infertility, and mislocalizes the sheath-associated PKA catalytic and regulatory subunits, PI3-kinase, and PP1γ2, establishing AKAP4 as the organizing scaffold that spatially confines kinase/phosphatase signaling to the principal piece [PMID:12167408, PMID:15385410]. AKAP4 anchors PKA through two distinct tethering domains—a dual-specificity domain A (RIα/RII) and an RIα-specific amphipathic-helix domain B—a function conserved across mouse, human, and bovine sperm [PMID:9852104, PMID:9822690, PMID:10411509]. Beyond passive scaffolding, ERK1/2 (downstream of PKC) phosphorylates proAKAP4 on Thr265, relocalizing it and enabling cAMP/PKA to negatively cross-regulate the PKC/ERK1/2 pathway, defining proAKAP4 as a molecular switch between these signaling arms [PMID:27901058]. AKAP4 additionally engages QRICH2 to maintain fibrous sheath integrity, and a hemizygous p.R429C variant that weakens this interaction produces a dysplastic fibrous sheath and male infertility [PMID:34415320]. Outside the male germline, AKAP4 maintains PKA protein stability via the PKA-CREB axis and limits ROS-driven DNA damage in ovarian cancer cells [PMID:28881798].","teleology":[{"year":1995,"claim":"Established the molecular identity of the fibrous sheath's major structural component, defining AKAP4 as a spermatid-specific protein with no homology to known cytoskeletal proteins.","evidence":"cDNA cloning, Northern blot, in situ hybridization, and peptide sequencing of Fsc1/AKAP4","pmids":["7711182"],"confidence":"High","gaps":["No PKA-anchoring activity demonstrated at this stage","Functional requirement in vivo not yet tested"]},{"year":1997,"claim":"Showed how AKAP4 reaches and assembles into the sheath—precursor synthesis, axonemal transport, proteolytic cleavage, and conversion to an insoluble mature form—while co-purification with PKA RII linked the scaffold to kinase anchoring.","evidence":"Immunoelectron microscopy, Triton fractionation, and phosphatase/immunoblot analysis in mouse and human sperm","pmids":["9441672"],"confidence":"High","gaps":["Protease responsible for pro-domain cleavage not identified","Precise tethering domains for PKA not mapped"]},{"year":1998,"claim":"Defined the molecular basis of PKA anchoring by mapping two distinct tethering domains and confirming cross-species conservation of the RII-binding motif in human AKAP4.","evidence":"Yeast two-hybrid, GST in vitro binding with mutagenesis, RII overlay assay, and chromosomal mapping","pmids":["9852104","9822690"],"confidence":"High","gaps":["Functional consequence of dual RIα/RII specificity in vivo unresolved","Whether both domains are simultaneously occupied not addressed"]},{"year":1999,"claim":"Extended PKA-anchoring conservation to bovine sperm and showed AKAP4 undergoes capacitation-dependent tyrosine phosphorylation, though this did not correlate with motility differences.","evidence":"cDNA cloning, RII binding, immunolocalization (bovine); phosphotyrosine immunoblotting (human)","pmids":["10411509","10460219"],"confidence":"Medium","gaps":["Kinase responsible for capacitation-dependent tyrosine phosphorylation not identified","Negative motility correlation from a single lab"]},{"year":2002,"claim":"Demonstrated through genetic knockout that AKAP4 is essential—its loss prevents fibrous sheath assembly, eliminates progressive motility, and causes male infertility, moving AKAP4 from a structural marker to an indispensable scaffold.","evidence":"Akap4-knockout mouse with electron microscopy, motility analysis, and immunoblotting","pmids":["12167408"],"confidence":"High","gaps":["Did not resolve which downstream signaling defects drive immotility","Hierarchy of sheath assembly events not defined"]},{"year":2004,"claim":"Showed the scaffold is required for spatial organization of signaling by demonstrating mislocalization of PKA subunits and PI3-kinase and altered PP1γ2 activity in Akap4-null sperm.","evidence":"Subcellular fractionation, immunoblotting, and phosphatase activity assay in knockout mice","pmids":["15385410"],"confidence":"High","gaps":["Direct binding of PI3K and PP1γ2 to AKAP4 not established","Causal link from mislocalization to motility loss not isolated"]},{"year":2006,"claim":"Explained precursor trafficking control by showing the pro-domain retains AKAP4 in the cytoplasm and that mature AKAP4 uses microtubule-dependent T2 domains for distribution.","evidence":"GFP-fusion constructs in somatic cells with cytoskeletal drug treatments","pmids":["16687648"],"confidence":"Medium","gaps":["Microtubule interaction inferred in somatic cells, not shown directly in spermatids","Transport machinery/motors not identified"]},{"year":2012,"claim":"Revealed AKAP4 as an active signaling hub: ERK1/2 phosphorylates proAKAP4 on Thr265 to relocalize it and enable cAMP/PKA-mediated negative cross-regulation of PKC/ERK1/2, and an independent oviductal DMBT1 pathway induces tyrosine phosphorylation of proAKAP4.","evidence":"In vitro kinase assay, T265A mutagenesis, GFP-proAKAP4 cell relocalization, St-HT31 disruption peptide; mass spectrometry and immunoprecipitation for DMBT1 pathway","pmids":["27901058","22457434"],"confidence":"High","gaps":["In vivo significance of T265 switch during fertilization not quantified","DMBT1-induced kinase identity unknown"]},{"year":2017,"claim":"Identified a non-germline role: AKAP4 maintains PKA protein stability and limits ROS/DNA damage via the PKA-CREB axis in ovarian cancer cells.","evidence":"siRNA knockdown with MG-132 and NAC rescue, immunoblotting, flow cytometry, and xenograft","pmids":["28881798"],"confidence":"Medium","gaps":["Mechanism by which AKAP4 protects PKA from proteasomal degradation undefined","Single lab; relevance beyond ovarian cancer untested"]},{"year":2021,"claim":"Defined disease-causing interaction partners by showing AKAP4 binds QRICH2 (disrupted by p.R429C) and RNASET2 (disrupted by pro-domain p.S152P), with both variants producing dysplastic fibrous sheath and infertility.","evidence":"Whole-exome/Sanger sequencing, reciprocal co-immunoprecipitation, immunofluorescence, and cell expression of variants","pmids":["34415320","34409659"],"confidence":"Medium","gaps":["Direct vs indirect nature of RNASET2 interaction not fully resolved","Variants and Co-IPs from single labs without reconstitution"]},{"year":2024,"claim":"Tested whether SUMO1 modification controls AKAP4 turnover and found AKAP4 is SUMOylated under oxidative/cryopreservation stress but that SUMO1 does not drive its degradation.","evidence":"LC-MS/MS of SUMO-modified proteins with SUMO inhibitor treatment and motility/ATP assays in porcine sperm","pmids":["39765132"],"confidence":"Low","gaps":["AKAP4-specific functional consequence of SUMOylation not isolated from global SUMO effects","Single lab, no rescue specific to AKAP4"]},{"year":2025,"claim":"Positioned SPAG6 upstream of AKAP4 in fibrous sheath assembly by showing AKAP4 levels are altered in Spag6/Spag6l compound mutants.","evidence":"Double-knockout mouse with immunoblotting and ultrastructural analysis (preprint)","pmids":["bio_10.1101_2025.07.18.665465"],"confidence":"Low","gaps":["Indirect level change; no direct SPAG6-AKAP4 mechanism","Preprint, not peer-reviewed"]},{"year":null,"claim":"The protease that cleaves proAKAP4, the molecular machinery delivering it along microtubules, and how dynamic capacitation-stage phosphorylation of specific AKAP4 sites quantitatively tunes motility remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["Identity of the maturation protease unknown","In vivo transport motor not identified","Functional role of individual capacitation phosphosites not dissected"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,6]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,3,7]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[8]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,1,6]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[8,14]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[0,6]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[7,10]}],"complexes":["fibrous sheath"],"partners":["PRKAR2A","PRKAR1A","QRICH2","RNASET2","DMBT1","SPAG6"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5JQC9","full_name":"A-kinase anchor protein 4","aliases":["A-kinase anchor protein 82 kDa","AKAP 82","hAKAP82","Major sperm fibrous sheath protein","HI","Protein kinase A-anchoring protein 4","PRKA4"],"length_aa":854,"mass_kda":94.5,"function":"Major structural component of sperm fibrous sheath (PubMed:9822690). Plays a role in sperm motility (PubMed:34415320, PubMed:9822690)","subcellular_location":"Cell projection, cilium, flagellum","url":"https://www.uniprot.org/uniprotkb/Q5JQC9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/AKAP4","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/AKAP4","total_profiled":1310},"omim":[{"mim_id":"620849","title":"SPERMATOGENIC FAILURE 93; SPGF93","url":"https://www.omim.org/entry/620849"},{"mim_id":"620354","title":"SPERMATOGENIC FAILURE 83; SPGF83","url":"https://www.omim.org/entry/620354"},{"mim_id":"618153","title":"SPERMATOGENIC FAILURE 34; SPGF34","url":"https://www.omim.org/entry/618153"},{"mim_id":"615796","title":"FIBROUS SHEATH-INTERACTING PROTEIN 2; FSIP2","url":"https://www.omim.org/entry/615796"},{"mim_id":"615795","title":"FIBROUS SHEATH-INTERACTING PROTEIN 1; FSIP1","url":"https://www.omim.org/entry/615795"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Principal piece","reliability":"Enhanced"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"testis","ntpm":187.4}],"url":"https://www.proteinatlas.org/search/AKAP4"},"hgnc":{"alias_symbol":["p82","hAKAP82","AKAP82","Fsc1","HI","CT99"],"prev_symbol":[]},"alphafold":{"accession":"Q5JQC9","domains":[{"cath_id":"-","chopping":"19-48_71-140_763-852","consensus_level":"high","plddt":75.7263,"start":19,"end":852}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5JQC9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5JQC9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5JQC9-F1-predicted_aligned_error_v6.png","plddt_mean":53.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=AKAP4","jax_strain_url":"https://www.jax.org/strain/search?query=AKAP4"},"sequence":{"accession":"Q5JQC9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5JQC9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5JQC9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5JQC9"}},"corpus_meta":[{"pmid":"12167408","id":"PMC_12167408","title":"Targeted disruption of the Akap4 gene causes defects in sperm flagellum and motility.","date":"2002","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/12167408","citation_count":326,"is_preprint":false},{"pmid":"17485482","id":"PMC_17485482","title":"Redundant role of DEAD box proteins p68 (Ddx5) and p72/p82 (Ddx17) in ribosome biogenesis and cell proliferation.","date":"2007","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/17485482","citation_count":131,"is_preprint":false},{"pmid":"9441672","id":"PMC_9441672","title":"Assembly of AKAP82, a protein kinase A anchor protein, into the fibrous sheath of mouse sperm.","date":"1997","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/9441672","citation_count":102,"is_preprint":false},{"pmid":"11229805","id":"PMC_11229805","title":"Molecular genetic analysis of two human sperm fibrous sheath proteins, AKAP4 and AKAP3, in men with dysplasia of the fibrous sheath.","date":"2001","source":"Journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/11229805","citation_count":81,"is_preprint":false},{"pmid":"9852104","id":"PMC_9852104","title":"Identification of tethering domains for protein kinase A type Ialpha regulatory subunits on sperm fibrous sheath protein FSC1.","date":"1998","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9852104","citation_count":79,"is_preprint":false},{"pmid":"7711182","id":"PMC_7711182","title":"Characterization of Fsc1 cDNA for a mouse sperm fibrous sheath component.","date":"1995","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/7711182","citation_count":79,"is_preprint":false},{"pmid":"9822690","id":"PMC_9822690","title":"An X-linked gene encodes a major human sperm fibrous sheath protein, hAKAP82. Genomic organization, protein kinase A-RII binding, and distribution of the precursor in the sperm tail.","date":"1998","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9822690","citation_count":78,"is_preprint":false},{"pmid":"31255637","id":"PMC_31255637","title":"Proteomics and single-cell RNA analysis of Akap4-knockout mice model confirm indispensable role of Akap4 in spermatogenesis.","date":"2019","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/31255637","citation_count":61,"is_preprint":false},{"pmid":"9917064","id":"PMC_9917064","title":"Dual roles of p82, the clam CPEB homolog, in cytoplasmic polyadenylation and translational masking.","date":"1999","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/9917064","citation_count":56,"is_preprint":false},{"pmid":"10460219","id":"PMC_10460219","title":"Relationship between sperm motility and the processing and tyrosine phosphorylation of two human sperm fibrous sheath proteins, pro-hAKAP82 and hAKAP82.","date":"1999","source":"Molecular human reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/10460219","citation_count":55,"is_preprint":false},{"pmid":"30947075","id":"PMC_30947075","title":"Expression, localization, and concentration of A-kinase anchor protein 4 (AKAP4) and its precursor (proAKAP4) in equine semen: Promising marker correlated to the total and progressive motility in thawed spermatozoa.","date":"2019","source":"Theriogenology","url":"https://pubmed.ncbi.nlm.nih.gov/30947075","citation_count":51,"is_preprint":false},{"pmid":"27901058","id":"PMC_27901058","title":"A-Kinase Anchoring Protein 4 (AKAP4) is an ERK1/2 substrate and a switch molecule between cAMP/PKA and PKC/ERK1/2 in human spermatozoa.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/27901058","citation_count":46,"is_preprint":false},{"pmid":"10411509","id":"PMC_10411509","title":"Conservation and function of a bovine sperm A-kinase anchor protein homologous to mouse AKAP82.","date":"1999","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/10411509","citation_count":44,"is_preprint":false},{"pmid":"9917063","id":"PMC_9917063","title":"The clam 3' UTR masking element-binding protein p82 is a member of the CPEB family.","date":"1999","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/9917063","citation_count":43,"is_preprint":false},{"pmid":"21520158","id":"PMC_21520158","title":"Identification of AKAP-4 as a new cancer/testis antigen for detection and immunotherapy of prostate cancer.","date":"2011","source":"The Prostate","url":"https://pubmed.ncbi.nlm.nih.gov/21520158","citation_count":41,"is_preprint":false},{"pmid":"29984477","id":"PMC_29984477","title":"A-kinase anchor protein 4 precursor (pro-AKAP4) in human spermatozoa.","date":"2018","source":"Andrology","url":"https://pubmed.ncbi.nlm.nih.gov/29984477","citation_count":40,"is_preprint":false},{"pmid":"8719244","id":"PMC_8719244","title":"The secretary pathway of plasmodium falciparum regulates transport of p82/RAP1 to the rhoptries.","date":"1995","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/8719244","citation_count":40,"is_preprint":false},{"pmid":"25739119","id":"PMC_25739119","title":"Novel antigens in non-small cell lung cancer: SP17, AKAP4, and PTTG1 are potential immunotherapeutic targets.","date":"2015","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/25739119","citation_count":39,"is_preprint":false},{"pmid":"15385410","id":"PMC_15385410","title":"Changes in intracellular distribution and activity of protein phosphatase PP1gamma2 and its regulating proteins in spermatozoa lacking AKAP4.","date":"2004","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/15385410","citation_count":39,"is_preprint":false},{"pmid":"17712481","id":"PMC_17712481","title":"Localization of AKAP4 and tubulin proteins in sperm with reduced motility.","date":"2007","source":"Asian journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/17712481","citation_count":36,"is_preprint":false},{"pmid":"26590805","id":"PMC_26590805","title":"A-kinase anchor protein 4 (AKAP4) a promising therapeutic target of colorectal cancer.","date":"2015","source":"Journal of experimental & clinical cancer research : CR","url":"https://pubmed.ncbi.nlm.nih.gov/26590805","citation_count":35,"is_preprint":false},{"pmid":"23451156","id":"PMC_23451156","title":"A novel cancer testis antigen, A-kinase anchor protein 4 (AKAP4) is a potential biomarker for breast cancer.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23451156","citation_count":35,"is_preprint":false},{"pmid":"34415320","id":"PMC_34415320","title":"Loss-of-function missense variant of AKAP4 induced male infertility through reduced interaction with QRICH2 during sperm flagella development.","date":"2021","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34415320","citation_count":35,"is_preprint":false},{"pmid":"23762804","id":"PMC_23762804","title":"The novel cancer-testis antigen A-kinase anchor protein 4 (AKAP4) is a potential target for immunotherapy of ovarian serous carcinoma.","date":"2013","source":"Oncoimmunology","url":"https://pubmed.ncbi.nlm.nih.gov/23762804","citation_count":35,"is_preprint":false},{"pmid":"22457434","id":"PMC_22457434","title":"The effect of oviductal deleted in malignant brain tumor 1 over porcine sperm is mediated by a signal transduction pathway that involves pro-AKAP4 phosphorylation.","date":"2012","source":"Reproduction (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/22457434","citation_count":27,"is_preprint":false},{"pmid":"26160834","id":"PMC_26160834","title":"AKAP4 is a circulating biomarker for non-small cell lung cancer.","date":"2015","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/26160834","citation_count":25,"is_preprint":false},{"pmid":"10208752","id":"PMC_10208752","title":"Ca2+ is required for phosphorylation of clam p82/CPEB in vitro: implications for dual and independent roles of MAP and Cdc2 kinases.","date":"1999","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/10208752","citation_count":20,"is_preprint":false},{"pmid":"11476771","id":"PMC_11476771","title":"Molecular evaluation of two major human sperm fibrous sheath proteins, pro-hAKAP82 and hAKAP82, in stump tail sperm.","date":"2001","source":"Fertility and sterility","url":"https://pubmed.ncbi.nlm.nih.gov/11476771","citation_count":19,"is_preprint":false},{"pmid":"27057472","id":"PMC_27057472","title":"A novel cancer testis antigen target A-kinase anchor protein (AKAP4) for the early diagnosis and immunotherapy of colon cancer.","date":"2016","source":"Oncoimmunology","url":"https://pubmed.ncbi.nlm.nih.gov/27057472","citation_count":19,"is_preprint":false},{"pmid":"33486757","id":"PMC_33486757","title":"Decreased expression of AKAP4 and TyrPho proteins in testis, epididymis, and spermatozoa with low sexual performance of mice induced by modified CUMS.","date":"2021","source":"Andrologia","url":"https://pubmed.ncbi.nlm.nih.gov/33486757","citation_count":13,"is_preprint":false},{"pmid":"9349489","id":"PMC_9349489","title":"The gene encoding the capsid protein P82 of the Choristoneura fumiferana multicapsid nucleopolyhedrovirus: sequencing, transcription and characterization by immunoblot analysis.","date":"1997","source":"The Journal of general virology","url":"https://pubmed.ncbi.nlm.nih.gov/9349489","citation_count":13,"is_preprint":false},{"pmid":"28881798","id":"PMC_28881798","title":"Role of A-Kinase anchor protein (AKAP4) in growth and survival of ovarian cancer cells.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/28881798","citation_count":12,"is_preprint":false},{"pmid":"21923911","id":"PMC_21923911","title":"Tracking human multiple myeloma xenografts in NOD-Rag-1/IL-2 receptor gamma chain-null mice with the novel biomarker AKAP-4.","date":"2011","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/21923911","citation_count":12,"is_preprint":false},{"pmid":"37695244","id":"PMC_37695244","title":"Decreased AKAP4/PKA signaling pathway in high DFI sperm affects sperm capacitation.","date":"2023","source":"Asian journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/37695244","citation_count":11,"is_preprint":false},{"pmid":"8573122","id":"PMC_8573122","title":"Dexamethasone inhibits insulin binding to insulin-degrading enzyme and cytosolic insulin-binding protein p82.","date":"1996","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/8573122","citation_count":11,"is_preprint":false},{"pmid":"27158351","id":"PMC_27158351","title":"AKAP4 mediated tumor malignancy in esophageal cancer.","date":"2016","source":"American journal of translational research","url":"https://pubmed.ncbi.nlm.nih.gov/27158351","citation_count":11,"is_preprint":false},{"pmid":"12574244","id":"PMC_12574244","title":"Identification of a specific antigenic region of the P82 protein of Babesia equi and its potential use in serodiagnosis.","date":"2003","source":"Journal of clinical microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/12574244","citation_count":11,"is_preprint":false},{"pmid":"37087050","id":"PMC_37087050","title":"Germ Cell-Specific Proteins AKAP4 and ASPX Facilitate Identification of Rare Spermatozoa in Non-Obstructive Azoospermia.","date":"2023","source":"Molecular & cellular proteomics : MCP","url":"https://pubmed.ncbi.nlm.nih.gov/37087050","citation_count":10,"is_preprint":false},{"pmid":"16687648","id":"PMC_16687648","title":"Protein domains govern the intracellular distribution of mouse sperm AKAP4.","date":"2006","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/16687648","citation_count":10,"is_preprint":false},{"pmid":"33023073","id":"PMC_33023073","title":"Phosphoproteomics and Bioinformatics Analyses Reveal Key Roles of GSK-3 and AKAP4 in Mouse Sperm Capacitation.","date":"2020","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/33023073","citation_count":10,"is_preprint":false},{"pmid":"34409659","id":"PMC_34409659","title":"A new hemizygous missense mutation, c.454T＞C (p.S152P), in AKAP4 gene is associated with asthenozoospermia.","date":"2021","source":"Molecular reproduction and development","url":"https://pubmed.ncbi.nlm.nih.gov/34409659","citation_count":6,"is_preprint":false},{"pmid":"27983916","id":"PMC_27983916","title":"Silencing of A-Kinase Anchor Protein 4 (AKAP4) Inhibits Proliferation and Progression of Thyroid Cancer.","date":"2016","source":"Oncology research","url":"https://pubmed.ncbi.nlm.nih.gov/27983916","citation_count":6,"is_preprint":false},{"pmid":"2258053","id":"PMC_2258053","title":"A binding protein (p82 protein) recognizes specifically the curved heterochromatic DNA in Artemia franciscana.","date":"1990","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/2258053","citation_count":6,"is_preprint":false},{"pmid":"24811938","id":"PMC_24811938","title":"Selective expression and immunogenicity of the cancer/testis antigens SP17, AKAP4 and PTTG1 in non-small cell lung cancer: new candidates for active immunotherapy.","date":"2014","source":"Chest","url":"https://pubmed.ncbi.nlm.nih.gov/24811938","citation_count":6,"is_preprint":false},{"pmid":"15685631","id":"PMC_15685631","title":"Differential RNA expression and polyribosome loading of alternative transcripts of the Akap4 gene in murine spermatids.","date":"2005","source":"Molecular reproduction and development","url":"https://pubmed.ncbi.nlm.nih.gov/15685631","citation_count":4,"is_preprint":false},{"pmid":"35967402","id":"PMC_35967402","title":"Identification of CD8+ T-cell epitope from multiple myeloma-specific antigen AKAP4.","date":"2022","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/35967402","citation_count":3,"is_preprint":false},{"pmid":"30545223","id":"PMC_30545223","title":"Down-regulation of TSGA10, AURKC, OIP5 and AKAP4 genes by Lactobacillus rhamnosus GG and Lactobacillus crispatus SJ-3C-US supernatants in HeLa cell line.","date":"2018","source":"Klinicka onkologie : casopis Ceske a Slovenske onkologicke spolecnosti","url":"https://pubmed.ncbi.nlm.nih.gov/30545223","citation_count":3,"is_preprint":false},{"pmid":"39765132","id":"PMC_39765132","title":"SUMO1 modification reduces oxidative stress and SUMO1ylated AKAP4 degradation affects frozen-thawed boar sperm quality.","date":"2024","source":"Animal reproduction science","url":"https://pubmed.ncbi.nlm.nih.gov/39765132","citation_count":1,"is_preprint":false},{"pmid":"40567906","id":"PMC_40567906","title":"Chrysin's protective effect on the expression of protamine, Tsga10, Dazl, and Akap4 genes against diazinon toxin in male rats: An experimental study.","date":"2025","source":"International journal of reproductive biomedicine","url":"https://pubmed.ncbi.nlm.nih.gov/40567906","citation_count":1,"is_preprint":false},{"pmid":"31969501","id":"PMC_31969501","title":"[Role of outer dense fiber in multiple morphological abnormalities of the sperm flagella in Akap4 gene defect mice].","date":"2019","source":"Zhong nan da xue xue bao. Yi xue ban = Journal of Central South University. Medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/31969501","citation_count":1,"is_preprint":false},{"pmid":"16398361","id":"PMC_16398361","title":"[AKAP82 expression in sperm in asthenospermia].","date":"2005","source":"Zhonghua nan ke xue = National journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/16398361","citation_count":0,"is_preprint":false},{"pmid":"41485432","id":"PMC_41485432","title":"High glucose in the extender impacts the metabolic phosphoproteome and modifies the phosphorylation of AKAP4 in stallion spermatozoa.","date":"2025","source":"Animal reproduction science","url":"https://pubmed.ncbi.nlm.nih.gov/41485432","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.07.18.665465","title":"Two  <i>Spag6</i>  genes control sperm formation and male fertility in mice","date":"2025-07-22","source":"bioRxiv","url":"https://doi.org/10.1101/2025.07.18.665465","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":30359,"output_tokens":4636,"usd":0.080309,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12761,"output_tokens":4158,"usd":0.083877,"stage2_stop_reason":"end_turn"},"total_usd":0.164186,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1995,\n      \"finding\": \"AKAP4 (Fsc1) encodes the major structural protein of the fibrous sheath in the principal piece of the sperm flagellum; mRNA is expressed exclusively in postmeiotic (round) spermatids and the protein contains 32 cysteine residues and 32 potential phosphorylation sites with no homology to other known cytoskeletal proteins.\",\n      \"method\": \"cDNA cloning, Northern blot, in situ hybridization, peptide sequencing\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (peptide sequencing, cDNA cloning, Northern blot, in situ hybridization) establishing primary structure and expression pattern; independently replicated across species in subsequent work\",\n      \"pmids\": [\"7711182\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Pro-AKAP4 (pro-AKAP82) is synthesized in the spermatid cell body, transported down the axoneme, proteolytically cleaved to form mature AKAP4 during fibrous sheath assembly, and becomes insoluble (Triton X-100 resistant) in mature sperm; the RII subunit of PKA co-purifies with AKAP4 in the particulate fraction of sperm, consistent with AKAP4 anchoring PKA to the fibrous sheath.\",\n      \"method\": \"Immunoelectron microscopy, immunoblotting with phosphatase treatment, Triton X-100 fractionation, antiserum against pro-domain peptide\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal fractionation experiments combined with immunoelectron microscopy, replicated across mouse and human systems\",\n      \"pmids\": [\"9441672\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"AKAP4 (FSC1) contains two distinct RIα tethering domains: domain A (residues 219–232) binds both RIα and RII (dual-specificity), and domain B (residues 335–344) specifically binds RIα via an amphipathic helix; site-directed mutagenesis disrupting the amphipathic helix of domain B abolishes RIα binding.\",\n      \"method\": \"Yeast two-hybrid screening of mouse testis cDNA library, GST-fusion in vitro binding assays, deletion analysis, site-directed mutagenesis, helical wheel projection\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro binding assay with mutagenesis confirming amphipathic helix requirement; multiple orthogonal approaches in one study\",\n      \"pmids\": [\"9852104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Human AKAP4 (hAKAP82) is encoded by an X-linked gene (Xp11.2), is highly homologous to mouse AKAP82, and its precursor pro-hAKAP82 binds the type II regulatory subunit of PKA through a domain identical to that of the mouse protein; alternative splicing generates at least two distinct transcripts.\",\n      \"method\": \"cDNA cloning, RII overlay assay, immunofluorescence, chromosomal mapping, sequence analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — RII overlay binding assay plus chromosomal mapping and sequence conservation, replicated across species\",\n      \"pmids\": [\"9822690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Bovine AKAP82 binds the regulatory subunit of PKA and localizes to the entire principal piece of the sperm flagellum, demonstrating conservation of PKA-anchoring function across mammals.\",\n      \"method\": \"cDNA cloning, RII binding assay, immunofluorescence, immunoblotting\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RII binding assay plus immunolocalization in a single study, corroborating mouse and human data\",\n      \"pmids\": [\"10411509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Pro-hAKAP82 and hAKAP82 undergo capacitation-dependent tyrosine phosphorylation in human spermatozoa, but neither the extent of proteolytic processing nor tyrosine phosphorylation of these proteins was found to correlate with differences in sperm motility.\",\n      \"method\": \"Immunofluorescence, immunoblotting with phosphotyrosine antibodies\",\n      \"journal\": \"Molecular human reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct detection of capacitation-dependent tyrosine phosphorylation; negative correlation with motility is a defined negative result from a single lab\",\n      \"pmids\": [\"10460219\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Genetic knockout of Akap4 in mice causes failure of fibrous sheath assembly, loss of progressive sperm motility, and male infertility without reducing sperm numbers; fibrous sheath-associated proteins (including signaling and glycolytic enzymes) are absent or substantially reduced, establishing AKAP4 as an essential scaffold for fibrous sheath organization.\",\n      \"method\": \"Gene targeting (knockout mouse), electron microscopy, immunoblotting, motility analysis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout with multiple orthogonal phenotypic readouts (motility, ultrastructure, protein localization); widely replicated\",\n      \"pmids\": [\"12167408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In Akap4-knockout mice, PKA catalytic and regulatory subunits and PI3-kinase lose their normal fibrous sheath subcellular distribution, and PP1γ2 phosphorylation and activity are significantly altered, demonstrating that the fibrous sheath scaffold formed by AKAP4 is required for correct spatial organization and regulation of these kinase/phosphatase signaling components.\",\n      \"method\": \"Akap4-knockout mouse, subcellular fractionation, immunoblotting, phosphatase activity assay\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function combined with biochemical fractionation and enzymatic activity assay defining specific downstream signaling consequences\",\n      \"pmids\": [\"15385410\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The pro domain of AKAP4 keeps the precursor in a diffuse cytoplasmic localization in somatic cells; upon removal of the pro domain, mature AKAP4 adopts a punctate distribution dependent on the microtubular cytoskeleton via two domains (T2a and T2b) homologous to the actin-binding T2-tethering domain of AKAP5, suggesting AKAP4 interacts with microtubules to be transported/incorporated into the fibrous sheath.\",\n      \"method\": \"GFP-fusion protein expression in somatic cell lines, immunofluorescence, cytoskeletal drug treatments (microtubule/actin disruption)\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain-deletion GFP constructs in live cells with cytoskeletal pharmacology; single lab, two orthogonal approaches\",\n      \"pmids\": [\"16687648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The Akap4 gene produces two alternatively spliced transcripts (Akap82 and Fsc1) differing only in their 5′ UTRs; only the Akap82 transcript is loaded onto polyribosomes and translated in spermatids, while the Fsc1 transcript is not polysomal despite both being deadenylated during spermiogenesis.\",\n      \"method\": \"Polyribosome fractionation, RT-PCR, reporter assays in vivo and in vitro\",\n      \"journal\": \"Molecular reproduction and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — polyribosome fractionation directly demonstrates differential translational loading; single lab\",\n      \"pmids\": [\"15685631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ERK1/2 phosphorylates proAKAP4 on Thr265 in human spermatozoa in vitro and in vivo; phosphorylation by ERK1/2 (downstream of PKC) causes relocalization of proAKAP4 from the principal piece to the Golgi/mid-piece in a T265-dependent manner; cAMP/PKA attenuates PKC-dependent ERK1/2 activation only in the presence of proAKAP4, and disruption of PKA-RII/AKAP binding (St-HT31) abolishes this inhibitory cross-talk, establishing proAKAP4 as a molecular switch between cAMP/PKA and PKC/ERK1/2 pathways.\",\n      \"method\": \"In vitro kinase assay, site-directed mutagenesis (T265A), GFP-proAKAP4 transfection in HEK293T, immunofluorescence, phorbol ester stimulation, PKA-AKAP disrupting peptide St-HT31\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro kinase assay plus mutagenesis plus cell-based relocalization assay plus pathway disruption peptide; multiple orthogonal methods in one study\",\n      \"pmids\": [\"27901058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Porcine oviductal DMBT1 induces tyrosine phosphorylation of proAKAP4 (but not the mature ~80 kDa AKAP4) localized to periacrosomal membranes, independently of calcium, bicarbonate, cAMP analogs, PKA inhibitors, or PKC inductor, placing proAKAP4 phosphorylation as an early step in the DMBT1-triggered signal transduction pathway controlling sperm selection.\",\n      \"method\": \"Mass spectrometry, immunoprecipitation, immunofluorescence, subcellular fractionation, pharmacological inhibitor panel\",\n      \"journal\": \"Reproduction (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS identification plus immunoprecipitation plus functional fractionation in a single study; single lab\",\n      \"pmids\": [\"22457434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"AKAP4 knockdown in ovarian cancer cells leads to PKA protein degradation that is rescued by the proteasome inhibitor MG-132, increased ROS and DNA damage, and cell cycle arrest rescued by the ROS quencher NAC, demonstrating that AKAP4 maintains PKA stability and acts through the PKA-CREB signaling axis in cancer cells.\",\n      \"method\": \"siRNA knockdown, proteasome inhibitor rescue (MG-132), NAC treatment, immunoblotting, flow cytometry, SCID mouse xenograft\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological rescue experiments (MG-132, NAC) identifying PKA degradation mechanism; single lab, two orthogonal rescue approaches\",\n      \"pmids\": [\"28881798\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A hemizygous missense variant (c.1285C>T, p.R429C) in AKAP4 reduces AKAP4 protein expression and its interaction with QRICH2 (demonstrated by co-immunoprecipitation and co-localization), resulting in decreased QRICH2 protein in spermatozoa and dysplastic fibrous sheath leading to male infertility.\",\n      \"method\": \"Whole-exome sequencing, co-immunoprecipitation, immunofluorescence, HEK-293T cell expression\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP demonstrating interaction plus variant disruption of interaction; single lab\",\n      \"pmids\": [\"34415320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A missense mutation p.S152P in the pro-domain of AKAP4 causes protein accumulation in the cytoplasm of COS-7 cells (failure to traffic correctly), abolishes mature AKAP4 in spermatozoa, increases ROS/apoptotic markers in GC2-spd cells, decreases PKA/PI3K signaling activity, and disrupts the interaction between AKAP4 and RNASET2.\",\n      \"method\": \"Sanger sequencing, COS-7 cell transfection with GFP-fusion constructs, immunofluorescence, co-immunoprecipitation, flow cytometry, oxidative stress assays\",\n      \"journal\": \"Molecular reproduction and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based mislocalization plus Co-IP interaction disruption plus signaling assay; single lab, multiple readouts\",\n      \"pmids\": [\"34409659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"AKAP4 is a target of SUMO1 modification in porcine sperm under cryopreservation/oxidative stress; SUMO1 modification level increases while AKAP4 protein level decreases under these conditions, but inhibition of SUMO1 modification does not affect AKAP4 degradation, indicating SUMO1 is not involved in AKAP4 proteolysis. However, global inhibition of sperm protein SUMO1 modification reduces sperm motility, ATP content, and DNA integrity.\",\n      \"method\": \"LC-MS/MS identification of SUMO-modified proteins, SUMO inhibitor treatment, immunoblotting, sperm motility and ATP assays\",\n      \"journal\": \"Animal reproduction science\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, LC-MS identification of SUMO modification site on AKAP4 but functional rescue specifically for AKAP4 not demonstrated\",\n      \"pmids\": [\"39765132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Phosphoproteomics of mouse sperm capacitation identified phosphorylation of AKAP4 at Y156 (increased) and Y811 (decreased) during capacitation, with overall upregulated phospho-AKAP4 trends detected by western blot, indicating AKAP4 phosphorylation is dynamically regulated during capacitation.\",\n      \"method\": \"Label-free quantitative phosphoproteomics, western blotting, IPA pathway analysis\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single phosphoproteomic study without functional follow-up of specific AKAP4 phosphosites; single lab\",\n      \"pmids\": [\"33023073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SPAG6 modulates testicular AKAP4 levels in mice; in compound Spag6/Spag6l mutants with disorganized fibrous sheath, AKAP4 levels are altered, suggesting SPAG6 acts upstream of AKAP4 in the pathway controlling fibrous sheath assembly.\",\n      \"method\": \"Double-knockout mouse model, immunoblotting, histological and ultrastructural analysis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, indirect modulation of AKAP4 levels by SPAG6 without direct mechanistic dissection of the SPAG6-AKAP4 relationship\",\n      \"pmids\": [\"bio_10.1101_2025.07.18.665465\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"AKAP4 is the principal structural scaffold protein of the sperm flagellum fibrous sheath, synthesized as a precursor (proAKAP4) in postmeiotic spermatids, transported along the axoneme, and proteolytically processed into insoluble mature AKAP4 during fibrous sheath assembly; it anchors cAMP-dependent protein kinase (PKA) to the fibrous sheath via dual-specificity (RIα/RII) and RIα-specific amphipathic-helix tethering domains, thereby localizing PKA-dependent phosphorylation to the principal piece to regulate sperm motility; proAKAP4 is additionally phosphorylated on Thr265 by ERK1/2 (downstream of PKC), causing its relocalization and acting as a molecular switch that allows cAMP/PKA to negatively cross-regulate the PKC/ERK1/2 pathway during capacitation and acrosome reaction; AKAP4 also interacts with QRICH2 to maintain fibrous sheath integrity, and its pro-domain controls cytoplasmic retention of the precursor until microtubule-dependent transport delivers it to the assembling sheath.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"AKAP4 is the principal structural scaffold protein of the sperm flagellum fibrous sheath in the principal piece, expressed exclusively in postmeiotic spermatids and synthesized as a precursor (proAKAP4) that is transported down the axoneme and proteolytically cleaved into an insoluble, detergent-resistant mature form during fibrous sheath assembly [#0, #1]. The protein's pro-domain enforces a diffuse cytoplasmic localization of the precursor, and only after its removal does mature AKAP4 acquire a punctate, microtubule-dependent distribution via T2-tethering domains, coupling proteolytic maturation to cytoskeletal delivery into the assembling sheath [#8]. Genetic ablation of Akap4 abolishes fibrous sheath assembly, causing loss of progressive motility and male infertility, and mislocalizes the sheath-associated PKA catalytic and regulatory subunits, PI3-kinase, and PP1\\u03b32, establishing AKAP4 as the organizing scaffold that spatially confines kinase/phosphatase signaling to the principal piece [#6, #7]. AKAP4 anchors PKA through two distinct tethering domains\\u2014a dual-specificity domain A (RI\\u03b1/RII) and an RI\\u03b1-specific amphipathic-helix domain B\\u2014a function conserved across mouse, human, and bovine sperm [#2, #3, #4]. Beyond passive scaffolding, ERK1/2 (downstream of PKC) phosphorylates proAKAP4 on Thr265, relocalizing it and enabling cAMP/PKA to negatively cross-regulate the PKC/ERK1/2 pathway, defining proAKAP4 as a molecular switch between these signaling arms [#10]. AKAP4 additionally engages QRICH2 to maintain fibrous sheath integrity, and a hemizygous p.R429C variant that weakens this interaction produces a dysplastic fibrous sheath and male infertility [#13]. Outside the male germline, AKAP4 maintains PKA protein stability via the PKA-CREB axis and limits ROS-driven DNA damage in ovarian cancer cells [#12].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established the molecular identity of the fibrous sheath's major structural component, defining AKAP4 as a spermatid-specific protein with no homology to known cytoskeletal proteins.\",\n      \"evidence\": \"cDNA cloning, Northern blot, in situ hybridization, and peptide sequencing of Fsc1/AKAP4\",\n      \"pmids\": [\"7711182\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No PKA-anchoring activity demonstrated at this stage\", \"Functional requirement in vivo not yet tested\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Showed how AKAP4 reaches and assembles into the sheath\\u2014precursor synthesis, axonemal transport, proteolytic cleavage, and conversion to an insoluble mature form\\u2014while co-purification with PKA RII linked the scaffold to kinase anchoring.\",\n      \"evidence\": \"Immunoelectron microscopy, Triton fractionation, and phosphatase/immunoblot analysis in mouse and human sperm\",\n      \"pmids\": [\"9441672\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Protease responsible for pro-domain cleavage not identified\", \"Precise tethering domains for PKA not mapped\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defined the molecular basis of PKA anchoring by mapping two distinct tethering domains and confirming cross-species conservation of the RII-binding motif in human AKAP4.\",\n      \"evidence\": \"Yeast two-hybrid, GST in vitro binding with mutagenesis, RII overlay assay, and chromosomal mapping\",\n      \"pmids\": [\"9852104\", \"9822690\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of dual RI\\u03b1/RII specificity in vivo unresolved\", \"Whether both domains are simultaneously occupied not addressed\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Extended PKA-anchoring conservation to bovine sperm and showed AKAP4 undergoes capacitation-dependent tyrosine phosphorylation, though this did not correlate with motility differences.\",\n      \"evidence\": \"cDNA cloning, RII binding, immunolocalization (bovine); phosphotyrosine immunoblotting (human)\",\n      \"pmids\": [\"10411509\", \"10460219\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Kinase responsible for capacitation-dependent tyrosine phosphorylation not identified\", \"Negative motility correlation from a single lab\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrated through genetic knockout that AKAP4 is essential\\u2014its loss prevents fibrous sheath assembly, eliminates progressive motility, and causes male infertility, moving AKAP4 from a structural marker to an indispensable scaffold.\",\n      \"evidence\": \"Akap4-knockout mouse with electron microscopy, motility analysis, and immunoblotting\",\n      \"pmids\": [\"12167408\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve which downstream signaling defects drive immotility\", \"Hierarchy of sheath assembly events not defined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showed the scaffold is required for spatial organization of signaling by demonstrating mislocalization of PKA subunits and PI3-kinase and altered PP1\\u03b32 activity in Akap4-null sperm.\",\n      \"evidence\": \"Subcellular fractionation, immunoblotting, and phosphatase activity assay in knockout mice\",\n      \"pmids\": [\"15385410\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct binding of PI3K and PP1\\u03b32 to AKAP4 not established\", \"Causal link from mislocalization to motility loss not isolated\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Explained precursor trafficking control by showing the pro-domain retains AKAP4 in the cytoplasm and that mature AKAP4 uses microtubule-dependent T2 domains for distribution.\",\n      \"evidence\": \"GFP-fusion constructs in somatic cells with cytoskeletal drug treatments\",\n      \"pmids\": [\"16687648\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Microtubule interaction inferred in somatic cells, not shown directly in spermatids\", \"Transport machinery/motors not identified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Revealed AKAP4 as an active signaling hub: ERK1/2 phosphorylates proAKAP4 on Thr265 to relocalize it and enable cAMP/PKA-mediated negative cross-regulation of PKC/ERK1/2, and an independent oviductal DMBT1 pathway induces tyrosine phosphorylation of proAKAP4.\",\n      \"evidence\": \"In vitro kinase assay, T265A mutagenesis, GFP-proAKAP4 cell relocalization, St-HT31 disruption peptide; mass spectrometry and immunoprecipitation for DMBT1 pathway\",\n      \"pmids\": [\"27901058\", \"22457434\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo significance of T265 switch during fertilization not quantified\", \"DMBT1-induced kinase identity unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified a non-germline role: AKAP4 maintains PKA protein stability and limits ROS/DNA damage via the PKA-CREB axis in ovarian cancer cells.\",\n      \"evidence\": \"siRNA knockdown with MG-132 and NAC rescue, immunoblotting, flow cytometry, and xenograft\",\n      \"pmids\": [\"28881798\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which AKAP4 protects PKA from proteasomal degradation undefined\", \"Single lab; relevance beyond ovarian cancer untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined disease-causing interaction partners by showing AKAP4 binds QRICH2 (disrupted by p.R429C) and RNASET2 (disrupted by pro-domain p.S152P), with both variants producing dysplastic fibrous sheath and infertility.\",\n      \"evidence\": \"Whole-exome/Sanger sequencing, reciprocal co-immunoprecipitation, immunofluorescence, and cell expression of variants\",\n      \"pmids\": [\"34415320\", \"34409659\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect nature of RNASET2 interaction not fully resolved\", \"Variants and Co-IPs from single labs without reconstitution\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Tested whether SUMO1 modification controls AKAP4 turnover and found AKAP4 is SUMOylated under oxidative/cryopreservation stress but that SUMO1 does not drive its degradation.\",\n      \"evidence\": \"LC-MS/MS of SUMO-modified proteins with SUMO inhibitor treatment and motility/ATP assays in porcine sperm\",\n      \"pmids\": [\"39765132\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"AKAP4-specific functional consequence of SUMOylation not isolated from global SUMO effects\", \"Single lab, no rescue specific to AKAP4\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Positioned SPAG6 upstream of AKAP4 in fibrous sheath assembly by showing AKAP4 levels are altered in Spag6/Spag6l compound mutants.\",\n      \"evidence\": \"Double-knockout mouse with immunoblotting and ultrastructural analysis (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.07.18.665465\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Indirect level change; no direct SPAG6-AKAP4 mechanism\", \"Preprint, not peer-reviewed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The protease that cleaves proAKAP4, the molecular machinery delivering it along microtubules, and how dynamic capacitation-stage phosphorylation of specific AKAP4 sites quantitatively tunes motility remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Identity of the maturation protease unknown\", \"In vivo transport motor not identified\", \"Functional role of individual capacitation phosphosites not dissected\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 3, 7]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 1, 6]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [8, 14]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [7, 10]}\n    ],\n    \"complexes\": [\"fibrous sheath\"],\n    \"partners\": [\"PRKAR2A\", \"PRKAR1A\", \"QRICH2\", \"RNASET2\", \"DMBT1\", \"SPAG6\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":7,"faith_pct":71.42857142857143}}