{"gene":"SUN5","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":2010,"finding":"SPAG4L (SUN5) and SPAG4L-2 are transmembrane proteins that localize to the inner nuclear membrane, specifically restricted to the apical nuclear region of round spermatids facing the acrosomic vesicle, suggesting involvement in linkage of the acrosomic vesicle to the spermatid nucleus and acrosome biogenesis.","method":"Molecular dissection, cytological and biochemical investigations, immunofluorescence localization","journal":"Molecular human reproduction","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — localization established by immunofluorescence and biochemical fractionation in single lab, functional link proposed but not fully reconstituted","pmids":["21159740"],"is_preprint":false},{"year":2011,"finding":"SPAG4L (SUN5) localizes to the nuclear envelope and endoplasmic reticulum; the transmembrane region and coiled-coil domain (but not the SUN domain) are required for NE/ER localization. It is expressed during meiosis I and II, suggesting a role in NE reconstitution and nuclear migration during spermatocyte division.","method":"GFP-fusion subcellular localization, deletion analysis, Western blot, immunofluorescence with organelle markers","journal":"DNA and cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — deletion mutagenesis with localization readout, single lab, multiple constructs tested","pmids":["21711156"],"is_preprint":false},{"year":2015,"finding":"Sun5 (Spag4l) transits through different cellular compartments during spermatogenesis: in pachytene spermatocytes it is in a membranous compartment distinct from the ER; in round spermatids it progresses to the Golgi and NE; in epididymal sperm it localizes to the tail/head junction. Sun5 is excluded from the NE facing the acrosome (negative result: Sun5 is NOT involved in acrosome attachment to the NE). In Dpy19l2 KO spermatids, upon acrosome detachment, Sun5 relocalizes to the entire NE. Sun5 is glycosylated.","method":"Immunohistochemistry, Western blot, Dpy19l2 knockout mouse model","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO model with defined relocalization phenotype plus negative finding on acrosome attachment, single lab","pmids":["25775128"],"is_preprint":false},{"year":2017,"finding":"Homozygous loss-of-function deletion of SUN5 (frameshift p.Leu143Serfs*30) causes acephalic spermatozoa syndrome; the p.Gly114Arg variant has a strong inhibitory effect on SUN5 mRNA splicing in HeLa cells, establishing that loss of SUN5 function causes the acephalic spermatozoa/head-tail junction defect.","method":"Genomic sequencing, splicing assay in HeLa cells (minigene/splicing reporter)","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function alleles confirmed by sequencing and functional splicing assay, replicated across two independent studies with LOF alleles","pmids":["28541472"],"is_preprint":false},{"year":2018,"finding":"SUN5 interacts with the coupling apparatus protein DNAJB13 during spermatogenesis; SUN domain missense substitutions associated with acephalic spermatozoa syndrome impair this interaction. Mutations also affect secondary structure, protein folding, and cellular localization of SUN5. An intronic mutation causes aberrant splicing yielding a premature stop codon and truncated SUN5.","method":"Co-immunoprecipitation, artificial splicing system, mutagenesis, cellular localization assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — Co-IP of interaction, mutagenesis of SUN domain, splicing assay, multiple orthogonal methods in single rigorous study","pmids":["29298896"],"is_preprint":false},{"year":2018,"finding":"SUN5 truncation mutation (c.381delA; p.V128Sfs*7) decreases SUN5 protein expression and alters the distribution of ODF1 (outer dense fiber 1 protein) in sperm, linking SUN5 to organization of sperm neck structural components.","method":"Western blot, immunofluorescence of ODF1 in patient sperm","journal":"Gene","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single method per observation, patient material only","pmids":["29331481"],"is_preprint":false},{"year":2019,"finding":"SPAG4L (SUN5) and its shorter transcript variant SPAG4Lβ interact with Nesprin2 (a KASH domain protein) to form LINC complexes; these LINC complexes are involved in spermatocyte division during meiosis.","method":"Co-immunoprecipitation, immunofluorescence, northern blot, RT-PCR, in situ hybridization","journal":"Acta biochimica et biophysica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP demonstrating interaction, immunofluorescence localization during meiosis, single lab with multiple orthogonal methods","pmids":["31144711"],"is_preprint":false},{"year":2021,"finding":"Sun5 knockout mice exhibit acephalic spermatozoa syndrome; the head-tail coupling apparatus (HTCA) and centrosome become distant from the nucleus at steps 9–10 of spermatid elongation, and head-tail separation occurs at steps 13–14. SUN5 interacts with Nesprin3 (confirmed by Co-IP) to form a LINC complex required for sperm head-tail connection; loss of Sun5 causes Nesprin3 to lose its localization at the posterior implantation fossa of the nucleus, leading to centrosome detachment. Downregulation of ODF1 and ODF2 also contributes to head-tail linkage damage.","method":"Sun5 knockout mouse generation, Co-immunoprecipitation, immunofluorescence, ultrastructural imaging, isobaric tag quantitative proteomics","journal":"Frontiers in cell and developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse with defined ultrastructural phenotype, reciprocal Co-IP of SUN5-Nesprin3, quantitative proteomics, multiple orthogonal methods","pmids":["34268309"],"is_preprint":false},{"year":2021,"finding":"SUN5, Nesprin3, and ODF1 interact with each other (each pairwise combination confirmed by Co-IP in transfected HEK293T cells), forming a 'triplet' structural complex at the sperm neck; loss of SUN5 disrupts localization of both ODF1 and Nesprin3 in patient sperm, weakening the head-tail junction.","method":"Co-immunoprecipitation in HEK293T cells, immunofluorescence on patient sperm, whole-exome sequencing","journal":"Molecular human reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pairwise Co-IPs in transfected cells confirming trimeric interactions, single lab","pmids":["33848337"],"is_preprint":false},{"year":2022,"finding":"SUN5 promotes colorectal cancer cell proliferation and migration by upregulating phosphorylated ERK1/2 (pERK1/2); this is mediated via Nesprin2 and involves SUN5 interaction with Nup93 to promote nuclear translocation of pERK1/2.","method":"Knockdown/overexpression in CRC cell lines, ERK inhibitor (PD0325901) rescue, xenograft transplantation, Co-IP with Nup93","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional KD/OE with defined signaling readout, inhibitor rescue, Co-IP, single lab","pmids":["36358787"],"is_preprint":false},{"year":2023,"finding":"ARRDC5 affects spermatogenesis by influencing the localization of SUN5 and NDC1; ARRDC5 likely acts through SEC22A-mediated vesicle trafficking to control transport and localization of SUN5 and other HTCA-related proteins responsible for sperm head-tail attachment.","method":"Arrdc5 knockout mouse, mass spectrometry, immunofluorescence","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse with defined phenotype, MS identification of SUN5 as affected protein, single lab","pmids":["37997706"],"is_preprint":false},{"year":2024,"finding":"SUN5 interacts with LaminB1 (inner nuclear membrane) and with cytoskeletal GTPase Septin12 (and Septin2), forming a LaminB1/SUN5/Septin12 complex at the sperm neck. SUN5 connects the nucleus via LaminB1 and connects the proximal centriole via Septin12; SUN5-Septin12 binding promotes their co-aggregation at the sperm neck. Sun5 knockout disrupts Septin12-proximal centriole attachment to the nucleus, causing head-tail separation.","method":"Immunoprecipitation-mass spectrometry, Co-IP, immunofluorescence, Sun5 knockout mouse","journal":"Molecular human reproduction","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — IP-MS identification followed by Co-IP validation, KO mouse phenotype, multiple partners mapped, single rigorous study with orthogonal methods","pmids":["38870534"],"is_preprint":false},{"year":2024,"finding":"SUN5 is involved in mRNA export in germ cells: in Sun5 KO mice, poly(A)+ RNA accumulates in nuclei of germ cells. SUN5 interacts with mRNA export factor Nxf1 and nucleoporin Nup93; loss of Sun5 reduces the Nxf1–Nup93 interaction and inhibits mRNA export through an Nxf1-dependent (not CRM1-dependent) pathway, contributing to abnormal spermatogenesis.","method":"Sun5 knockout mice, RNA interference in GC-2 cells, Co-IP of SUN5 with Nxf1 and Nup93, poly(A)+ RNA FISH, leptomycin B pharmacological block","journal":"Acta biochimica et biophysica Sinica","confidence":"High","confidence_rationale":"Tier 2 / Moderate — KO mouse with nuclear mRNA accumulation phenotype, Co-IP of multiple interactors, pathway delineation by CRM1 inhibitor, multiple orthogonal methods in single study","pmids":["39108207"],"is_preprint":false},{"year":2025,"finding":"SUN5 interacts with TRIM28 to increase IκBα ubiquitination, activating the NF-κB signaling pathway; this leads to nuclear translocation of phosphorylated P65 and increased transcription of GLUT1 and LDHA, enhancing glycolysis in colorectal cancer cells.","method":"SUN5 overexpression/knockdown in CRC cells, Co-IP of SUN5 with TRIM28, IKK inhibitor (BAY11-7082), glucose uptake and lactate assays, xenograft transplantation","journal":"Acta biochimica et biophysica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, pharmacological inhibition, functional metabolic assays, single lab","pmids":["41311215"],"is_preprint":false},{"year":2026,"finding":"By in situ cryo-electron tomography, SUN5 forms an extensive hexagonal lattice in the nuclear envelope at the base of the sperm head (confirmed in human, mouse, and boar sperm by superresolution fluorescence microscopy). This lattice maintains close apposition between inner and outer nuclear membranes; structural analysis supports a model in which LINC complexes form this lattice by laterally interacting at the outer nuclear membrane.","method":"Superresolution fluorescence microscopy, in situ cryo-electron tomography","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in situ cryo-ET structural determination across multiple species, direct visualization of hexagonal lattice","pmids":["41855266"],"is_preprint":false},{"year":2025,"finding":"In-cell cryo-electron tomography of human spermatozoa reveals the sub-nanometer architecture of the trimeric ~130 kDa SUN5–Nesprin3 LINC complex forming a hexagonal lattice that stitches the nuclear envelope at the sperm base. A unique membrane-anchoring mechanism was identified: a SUN5 KASH-lid β-hairpin and a Nesprin3 amphipathic helix insert into the outer nuclear membrane, driving cooperative nuclear envelope remodeling and flattening of the caudal sperm nucleus.","method":"In-situ electron cryo-tomography, AlphaFold structural predictions, molecular dynamics simulations","journal":"bioRxiv (preprint)","confidence":"High","confidence_rationale":"Tier 1 / Strong — sub-nanometer resolution in-situ cryo-ET with MD simulations and AlphaFold validation, novel structural mechanism described","pmids":["bio_10.1101_2025.08.04.668116"],"is_preprint":true}],"current_model":"SUN5 is a testis-specific inner nuclear membrane protein that forms a hexagonal LINC complex lattice at the sperm head-tail junction by interacting with Nesprin3 (and Nesprin2 during meiosis), LaminB1, and the cytoskeletal GTPase Septin12, physically bridging the nucleus to the proximal centriole/flagellum; loss of SUN5 disrupts this LaminB1/SUN5/Septin12 complex and the correct localization of Nesprin3 and ODF1/ODF2, causing the HTCA and centrosome to detach from the nucleus and producing acephalic spermatozoa syndrome, while SUN5 additionally facilitates mRNA export through an Nxf1/Nup93-dependent pathway in germ cells and, in somatic cancer contexts, promotes ERK signaling and NF-κB–driven glycolysis via interactions with Nesprin2/Nup93 and TRIM28 respectively."},"narrative":{"mechanistic_narrative":"SUN5 is a testis-specific SUN-domain inner nuclear membrane protein that builds the LINC complex anchoring the sperm head to its tail, and its loss causes acephalic spermatozoa syndrome [PMID:28541472, PMID:34268309]. During spermatogenesis SUN5 traffics through distinct compartments — a membranous compartment in spermatocytes, then the Golgi and nuclear envelope in round spermatids, and finally the head-tail junction in mature sperm [PMID:25775128]; its transmembrane and coiled-coil regions, but not the SUN domain, direct nuclear envelope/ER localization [PMID:21711156]. At the sperm neck SUN5 bridges the nucleus to the flagellar apparatus by binding LaminB1 on the nuclear side and the cytoskeletal GTPase Septin12 toward the proximal centriole, forming a LaminB1/SUN5/Septin12 complex whose disruption upon Sun5 loss detaches the centrosome from the nucleus [PMID:38870534]. SUN5 partners with the KASH-domain Nesprins — Nesprin2 during meiotic spermatocyte division [PMID:31144711] and Nesprin3 at the implantation fossa — together with the outer dense fiber proteins ODF1 and ODF2, and loss of SUN5 mislocalizes Nesprin3 and ODF1/ODF2, weakening the head-tail coupling apparatus [PMID:34268309, PMID:33848337]. SUN5 interacts with the coupling-apparatus protein DNAJB13, and acephalic-spermatozoa SUN domain missense substitutions impair this binding and perturb SUN5 folding and localization [PMID:29298896]. In situ cryo-electron tomography shows that the trimeric SUN5–Nesprin3 LINC complex assembles into an extensive hexagonal lattice in the nuclear envelope at the sperm base, maintaining apposition of the inner and outer nuclear membranes across human, mouse, and boar sperm [PMID:41855266]. Beyond its structural role, SUN5 facilitates germ-cell mRNA export via an Nxf1/Nup93-dependent pathway, with Sun5 loss causing nuclear poly(A)+ RNA accumulation [PMID:39108207]. In somatic cancer contexts SUN5 promotes colorectal cancer proliferation and migration through Nesprin2/Nup93-dependent nuclear translocation of phosphorylated ERK1/2 [PMID:36358787] and drives NF-κB-mediated glycolysis via TRIM28 [PMID:41311215].","teleology":[{"year":2010,"claim":"Established where SUN5 acts by localizing it to the inner nuclear membrane of spermatids, defining it as a candidate nuclear-membrane organizer in germ cells.","evidence":"Immunofluorescence and biochemical fractionation of SPAG4L/SUN5 in round spermatids","pmids":["21159740"],"confidence":"Medium","gaps":["Functional role inferred from localization only","Apical/acrosomic association later contradicted"]},{"year":2011,"claim":"Mapped the domains driving SUN5 targeting, showing the transmembrane and coiled-coil regions, not the SUN domain, direct nuclear envelope/ER localization.","evidence":"GFP-fusion deletion analysis with organelle markers in cultured cells","pmids":["21711156"],"confidence":"Medium","gaps":["Binding partners at the NE not identified","Meiotic role proposed but not demonstrated"]},{"year":2015,"claim":"Resolved the dynamic trafficking of SUN5 across spermatogenesis and overturned the early model by showing it is excluded from the acrosome-facing envelope and not involved in acrosome attachment.","evidence":"Immunohistochemistry and Dpy19l2 knockout mouse relocalization analysis","pmids":["25775128"],"confidence":"Medium","gaps":["Trafficking machinery unknown","Final head-tail function not yet mechanistically defined"]},{"year":2017,"claim":"Established SUN5 loss-of-function as the genetic cause of acephalic spermatozoa syndrome, linking the head-tail junction defect to a specific gene.","evidence":"Genomic sequencing of patients and minigene splicing assay in HeLa cells","pmids":["28541472"],"confidence":"High","gaps":["Molecular partners at the junction not yet identified","Mechanism of detachment unresolved"]},{"year":2018,"claim":"Identified DNAJB13 as a SUN5 partner and showed disease-associated SUN domain substitutions impair this interaction and SUN5 folding/localization, providing a molecular basis for pathogenic alleles.","evidence":"Co-IP, SUN-domain mutagenesis, and splicing assay","pmids":["29298896"],"confidence":"High","gaps":["Functional consequence of DNAJB13 binding in vivo not shown","Architecture of the coupling complex unknown"]},{"year":2018,"claim":"Linked SUN5 to organization of sperm neck structural components by showing a truncation allele alters ODF1 distribution.","evidence":"Western blot and ODF1 immunofluorescence in patient sperm","pmids":["29331481"],"confidence":"Low","gaps":["Single method per observation in patient material only","Direct SUN5-ODF1 interaction not tested here"]},{"year":2019,"claim":"Showed SUN5 and a short variant form LINC complexes with the KASH protein Nesprin2 during meiotic spermatocyte division, extending SUN5 function beyond spermatids.","evidence":"Co-IP, immunofluorescence, northern blot and in situ hybridization","pmids":["31144711"],"confidence":"Medium","gaps":["Meiotic LINC requirement not tested by loss of function","Relationship to later Nesprin3 complex unclear"]},{"year":2021,"claim":"Defined the in vivo mechanism of head-tail separation: a Sun5 knockout mouse linked SUN5-Nesprin3 LINC complex loss to Nesprin3 mislocalization, centrosome detachment, and ODF1/ODF2 downregulation.","evidence":"Sun5 knockout mouse, reciprocal Co-IP, ultrastructure, and quantitative proteomics","pmids":["34268309"],"confidence":"High","gaps":["Nuclear-side anchor not yet identified","Order of events in complex assembly unresolved"]},{"year":2021,"claim":"Established a SUN5-Nesprin3-ODF1 triplet complex at the sperm neck, showing SUN5 loss disrupts both ODF1 and Nesprin3 localization in patients.","evidence":"Pairwise Co-IPs in HEK293T cells and patient sperm immunofluorescence","pmids":["33848337"],"confidence":"Medium","gaps":["Pairwise interactions in transfected cells, not native complex","Stoichiometry undefined"]},{"year":2022,"claim":"Revealed a somatic, oncogenic function for SUN5 in colorectal cancer through Nesprin2/Nup93-dependent nuclear translocation of phosphorylated ERK1/2.","evidence":"Knockdown/overexpression in CRC lines, ERK inhibitor rescue, xenografts, Co-IP with Nup93","pmids":["36358787"],"confidence":"Medium","gaps":["Mechanism of pERK nuclear import via Nup93 not structurally defined","Relevance to non-germline tissues unclear"]},{"year":2023,"claim":"Placed SUN5 downstream of vesicle-trafficking control by showing ARRDC5 (via SEC22A) governs SUN5 and NDC1 localization at the HTCA.","evidence":"Arrdc5 knockout mouse, mass spectrometry, immunofluorescence","pmids":["37997706"],"confidence":"Medium","gaps":["Direct ARRDC5-SUN5 relationship not established","Trafficking route of SUN5 not fully mapped"]},{"year":2024,"claim":"Identified the nuclear-side anchor of the complex, showing SUN5 binds LaminB1 and the GTPase Septin12 to bridge nucleus to proximal centriole.","evidence":"IP-MS, Co-IP, immunofluorescence and Sun5 knockout mouse","pmids":["38870534"],"confidence":"High","gaps":["Role of Septin GTPase activity not tested","Integration with Nesprin3 lattice not resolved"]},{"year":2024,"claim":"Uncovered a non-structural role in germ-cell mRNA export, with SUN5 supporting the Nxf1-Nup93 interaction and Sun5 loss causing nuclear poly(A)+ RNA retention.","evidence":"Sun5 knockout mice, GC-2 RNAi, Co-IP with Nxf1/Nup93, poly(A)+ FISH, leptomycin B block","pmids":["39108207"],"confidence":"High","gaps":["Whether export defect contributes to acephaly versus general spermatogenesis unclear","Direct vs indirect role in Nxf1-Nup93 bridging undefined"]},{"year":2025,"claim":"Extended SUN5 cancer signaling to metabolism, showing SUN5-TRIM28 binding activates NF-κB and upregulates glycolytic genes in CRC.","evidence":"OE/KD in CRC cells, Co-IP with TRIM28, IKK inhibitor, metabolic assays, xenografts","pmids":["41311215"],"confidence":"Medium","gaps":["Mechanism by which SUN5 enhances IκBα ubiquitination undefined","Single-lab observation"]},{"year":2025,"claim":"Determined the sub-nanometer architecture of the trimeric SUN5-Nesprin3 LINC complex and a KASH-lid/amphipathic-helix membrane-anchoring mechanism driving nuclear envelope remodeling.","evidence":"In-situ cryo-ET, AlphaFold predictions and molecular dynamics (preprint)","pmids":["bio_10.1101_2025.08.04.668116"],"confidence":"High","gaps":["Preprint, not peer-reviewed","Functional validation of membrane-insertion mutants pending"]},{"year":2026,"claim":"Visualized the higher-order organization, showing SUN5 forms a conserved hexagonal LINC lattice maintaining inner/outer nuclear membrane apposition at the sperm base.","evidence":"Superresolution microscopy and in situ cryo-ET across human, mouse and boar sperm","pmids":["41855266"],"confidence":"High","gaps":["How lattice assembly is initiated and templated is unknown","Link between lattice integrity and force transmission not directly tested"]},{"year":null,"claim":"How the structural LINC-lattice function and the mRNA-export and oncogenic signaling activities of SUN5 are mechanistically related, and whether they share a common biochemical basis, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking structural and signaling roles","Regulation of SUN5 across germline versus somatic contexts undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[7,11,14]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[11,12]}],"localization":[{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[0,1,2,14]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,2]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[3,7,11]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[12]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[9,13]}],"complexes":["SUN5-Nesprin3 LINC complex","LaminB1/SUN5/Septin12 complex","SUN5-Nesprin2 LINC complex"],"partners":["NESPRIN3","NESPRIN2","LMNB1","SEPTIN12","ODF1","DNAJB13","NXF1","NUP93"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8TC36","full_name":"SUN domain-containing protein 5","aliases":["Sad1 and UNC84 domain-containing protein 5","Sperm-associated antigen 4-like protein","Testis and spermatogenesis-related gene 4 protein"],"length_aa":379,"mass_kda":43.1,"function":"Plays an essential role in anchoring sperm head to the tail. Is responsible for the attachment of the coupling apparatus to the sperm nuclear envelope","subcellular_location":"Nucleus inner membrane; Golgi apparatus","url":"https://www.uniprot.org/uniprotkb/Q8TC36/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SUN5","classification":"Not Classified","n_dependent_lines":10,"n_total_lines":1208,"dependency_fraction":0.008278145695364239},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SUN5","total_profiled":1310},"omim":[{"mim_id":"620944","title":"ARRESTIN DOMAIN-CONTAINING PROTEIN 5; ARRDC5","url":"https://www.omim.org/entry/620944"},{"mim_id":"618112","title":"SPERMATOGENIC FAILURE 31; SPGF31","url":"https://www.omim.org/entry/618112"},{"mim_id":"618085","title":"POLYAMINE-MODULATED FACTOR 1-BINDING PROTEIN 1; PMFBP1","url":"https://www.omim.org/entry/618085"},{"mim_id":"617961","title":"SPERMATOGENIC FAILURE 26; SPGF26","url":"https://www.omim.org/entry/617961"},{"mim_id":"617187","title":"SPERMATOGENIC FAILURE 16; SPGF16","url":"https://www.omim.org/entry/617187"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"testis","ntpm":42.8}],"url":"https://www.proteinatlas.org/search/SUN5"},"hgnc":{"alias_symbol":["dJ726C3.1","TSARG4"],"prev_symbol":["SPAG4L"]},"alphafold":{"accession":"Q8TC36","domains":[{"cath_id":"2.60.120.260","chopping":"201-361","consensus_level":"high","plddt":91.5682,"start":201,"end":361},{"cath_id":"4.10.220","chopping":"141-191","consensus_level":"medium","plddt":87.6384,"start":141,"end":191}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TC36","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TC36-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TC36-F1-predicted_aligned_error_v6.png","plddt_mean":75.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SUN5","jax_strain_url":"https://www.jax.org/strain/search?query=SUN5"},"sequence":{"accession":"Q8TC36","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8TC36.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8TC36/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TC36"}},"corpus_meta":[{"pmid":"21159740","id":"PMC_21159740","title":"SPAG4L/SPAG4L-2 are testis-specific SUN domain proteins restricted to the apical nuclear envelope of round spermatids facing the acrosome.","date":"2010","source":"Molecular human reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/21159740","citation_count":69,"is_preprint":false},{"pmid":"28541472","id":"PMC_28541472","title":"Homozygous deletion of SUN5 in three men with decapitated spermatozoa.","date":"2017","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28541472","citation_count":53,"is_preprint":false},{"pmid":"29298896","id":"PMC_29298896","title":"Mechanistic insights into acephalic spermatozoa syndrome-associated mutations in the human SUN5 gene.","date":"2018","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/29298896","citation_count":38,"is_preprint":false},{"pmid":"29329387","id":"PMC_29329387","title":"Patients with acephalic spermatozoa syndrome linked to SUN5 mutations have a favorable pregnancy outcome from ICSI.","date":"2018","source":"Human reproduction (Oxford, England)","url":"https://pubmed.ncbi.nlm.nih.gov/29329387","citation_count":36,"is_preprint":false},{"pmid":"21711156","id":"PMC_21711156","title":"SPAG4L, a novel nuclear envelope protein involved in the meiotic stage of spermatogenesis.","date":"2011","source":"DNA and cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/21711156","citation_count":35,"is_preprint":false},{"pmid":"25775128","id":"PMC_25775128","title":"Dynamics of Sun5 localization during spermatogenesis in wild type and Dpy19l2 knock-out mice indicates that Sun5 is not involved in acrosome attachment to the nuclear envelope.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/25775128","citation_count":34,"is_preprint":false},{"pmid":"29331481","id":"PMC_29331481","title":"Genetic contribution of SUN5 mutations to acephalic spermatozoa in Fujian China.","date":"2018","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/29331481","citation_count":32,"is_preprint":false},{"pmid":"34268309","id":"PMC_34268309","title":"SUN5 Interacting With Nesprin3 Plays an Essential Role in Sperm Head-to-Tail Linkage: Research on Sun5 Gene Knockout Mice.","date":"2021","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/34268309","citation_count":24,"is_preprint":false},{"pmid":"33848337","id":"PMC_33848337","title":"Pathogenesis of acephalic spermatozoa syndrome caused by SUN5 variant.","date":"2021","source":"Molecular human reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/33848337","citation_count":18,"is_preprint":false},{"pmid":"31144711","id":"PMC_31144711","title":"SPAG4L/SPAG4Lβ interacts with Nesprin2 to participate in the meiosis of spermatogenesis.","date":"2019","source":"Acta biochimica et biophysica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/31144711","citation_count":12,"is_preprint":false},{"pmid":"34159570","id":"PMC_34159570","title":"Novel Mutation and Deletion in SUN5 Cause Male Infertility with Acephalic Spermatozoa Syndrome.","date":"2021","source":"Reproductive sciences (Thousand Oaks, Calif.)","url":"https://pubmed.ncbi.nlm.nih.gov/34159570","citation_count":9,"is_preprint":false},{"pmid":"38870534","id":"PMC_38870534","title":"SUN5 interacts with nuclear membrane LaminB1 and cytoskeletal GTPase Septin12 mediating the sperm head-and-tail junction.","date":"2024","source":"Molecular human reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/38870534","citation_count":8,"is_preprint":false},{"pmid":"37997706","id":"PMC_37997706","title":"ARRDC5 deficiency impairs spermatogenesis by affecting SUN5 and NDC1.","date":"2023","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/37997706","citation_count":8,"is_preprint":false},{"pmid":"12621555","id":"PMC_12621555","title":"[Cloning of cDNA of TSARG4, a human spermatogenesis related gene].","date":"2003","source":"Sheng wu hua xue yu sheng wu wu li xue bao Acta biochimica et biophysica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/12621555","citation_count":6,"is_preprint":false},{"pmid":"39108207","id":"PMC_39108207","title":"SUN5, a testis-specific nuclear membrane protein, participates in recruitment and export of nuclear mRNA in spermatogenesis.","date":"2024","source":"Acta biochimica et biophysica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/39108207","citation_count":4,"is_preprint":false},{"pmid":"36358787","id":"PMC_36358787","title":"Nuclear Membrane Protein SUN5 Is Highly Expressed and Promotes Proliferation and Migration in Colorectal Cancer by Regulating the ERK Pathway.","date":"2022","source":"Cancers","url":"https://pubmed.ncbi.nlm.nih.gov/36358787","citation_count":4,"is_preprint":false},{"pmid":"28358284","id":"PMC_28358284","title":"Molecular Cloning of Porcine SUN5 Gene and Association between a SNP with Litter Size Trait.","date":"2017","source":"Animal biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/28358284","citation_count":3,"is_preprint":false},{"pmid":"41311215","id":"PMC_41311215","title":"SUN5 interacts with TRIM28, enhancing IκBα ubiquitination to promote glycolysis in colorectal cancer cells.","date":"2025","source":"Acta biochimica et biophysica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/41311215","citation_count":1,"is_preprint":false},{"pmid":"34393249","id":"PMC_34393249","title":"[Genetic analysis of three cases of acephalic spermatozoa syndrome caused by SUN5 mutation and the outcome of assisted reproductive technology].","date":"2021","source":"Beijing da xue xue bao. Yi xue ban = Journal of Peking University. Health sciences","url":"https://pubmed.ncbi.nlm.nih.gov/34393249","citation_count":1,"is_preprint":false},{"pmid":"20855246","id":"PMC_20855246","title":"[Prokaryotic expression and purification of SPAG4L, a novel human testis gene].","date":"2010","source":"Nan fang yi ke da xue xue bao = Journal of Southern Medical University","url":"https://pubmed.ncbi.nlm.nih.gov/20855246","citation_count":0,"is_preprint":false},{"pmid":"40740627","id":"PMC_40740627","title":"Novel SUN5 Mutation Associated with Acephalic Spermatozoa Syndrome: A Cross-sectional Study.","date":"2025","source":"Journal of human reproductive sciences","url":"https://pubmed.ncbi.nlm.nih.gov/40740627","citation_count":0,"is_preprint":false},{"pmid":"24701830","id":"PMC_24701830","title":"[Construction of eukaryotic expression vector of SPAG4L tagged with Myc and His].","date":"2013","source":"Sheng wu gong cheng xue bao = Chinese journal of biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/24701830","citation_count":0,"is_preprint":false},{"pmid":"41855266","id":"PMC_41855266","title":"SUN5 forms a regular protein lattice reinforcing the sperm head-tail junction.","date":"2026","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/41855266","citation_count":0,"is_preprint":false},{"pmid":"19664389","id":"PMC_19664389","title":"[Construction of eukaryotic expression vector of human TSARG4 and establishment of its stable transfected HeLa cell line].","date":"2009","source":"Xi bao yu fen zi mian yi xue za zhi = Chinese journal of cellular and molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/19664389","citation_count":0,"is_preprint":false},{"pmid":"27222178","id":"PMC_27222178","title":"[Preparation of SUN5-specific polyclonal antibody for detection of SUN5 expression in human germ cells].","date":"2016","source":"Nan fang yi ke da xue xue bao = Journal of Southern Medical University","url":"https://pubmed.ncbi.nlm.nih.gov/27222178","citation_count":0,"is_preprint":false},{"pmid":"40977202","id":"PMC_40977202","title":"Whole-exome sequencing reveals a novel mutation in the SUN5 gene causing acephalic spermatozoa syndrome.","date":"2025","source":"Reproduction, fertility, and development","url":"https://pubmed.ncbi.nlm.nih.gov/40977202","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.08.04.668116","title":"<i>In-cell</i>  structure of a LINC complex reveals the molecular basis for membrane remodelling and head-to-tail coupling in sperm cells","date":"2025-08-04","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.04.668116","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15541,"output_tokens":4183,"usd":0.054684,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12066,"output_tokens":4805,"usd":0.090228,"stage2_stop_reason":"end_turn"},"total_usd":0.144912,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"SPAG4L (SUN5) and SPAG4L-2 are transmembrane proteins that localize to the inner nuclear membrane, specifically restricted to the apical nuclear region of round spermatids facing the acrosomic vesicle, suggesting involvement in linkage of the acrosomic vesicle to the spermatid nucleus and acrosome biogenesis.\",\n      \"method\": \"Molecular dissection, cytological and biochemical investigations, immunofluorescence localization\",\n      \"journal\": \"Molecular human reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — localization established by immunofluorescence and biochemical fractionation in single lab, functional link proposed but not fully reconstituted\",\n      \"pmids\": [\"21159740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SPAG4L (SUN5) localizes to the nuclear envelope and endoplasmic reticulum; the transmembrane region and coiled-coil domain (but not the SUN domain) are required for NE/ER localization. It is expressed during meiosis I and II, suggesting a role in NE reconstitution and nuclear migration during spermatocyte division.\",\n      \"method\": \"GFP-fusion subcellular localization, deletion analysis, Western blot, immunofluorescence with organelle markers\",\n      \"journal\": \"DNA and cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — deletion mutagenesis with localization readout, single lab, multiple constructs tested\",\n      \"pmids\": [\"21711156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Sun5 (Spag4l) transits through different cellular compartments during spermatogenesis: in pachytene spermatocytes it is in a membranous compartment distinct from the ER; in round spermatids it progresses to the Golgi and NE; in epididymal sperm it localizes to the tail/head junction. Sun5 is excluded from the NE facing the acrosome (negative result: Sun5 is NOT involved in acrosome attachment to the NE). In Dpy19l2 KO spermatids, upon acrosome detachment, Sun5 relocalizes to the entire NE. Sun5 is glycosylated.\",\n      \"method\": \"Immunohistochemistry, Western blot, Dpy19l2 knockout mouse model\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO model with defined relocalization phenotype plus negative finding on acrosome attachment, single lab\",\n      \"pmids\": [\"25775128\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Homozygous loss-of-function deletion of SUN5 (frameshift p.Leu143Serfs*30) causes acephalic spermatozoa syndrome; the p.Gly114Arg variant has a strong inhibitory effect on SUN5 mRNA splicing in HeLa cells, establishing that loss of SUN5 function causes the acephalic spermatozoa/head-tail junction defect.\",\n      \"method\": \"Genomic sequencing, splicing assay in HeLa cells (minigene/splicing reporter)\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function alleles confirmed by sequencing and functional splicing assay, replicated across two independent studies with LOF alleles\",\n      \"pmids\": [\"28541472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SUN5 interacts with the coupling apparatus protein DNAJB13 during spermatogenesis; SUN domain missense substitutions associated with acephalic spermatozoa syndrome impair this interaction. Mutations also affect secondary structure, protein folding, and cellular localization of SUN5. An intronic mutation causes aberrant splicing yielding a premature stop codon and truncated SUN5.\",\n      \"method\": \"Co-immunoprecipitation, artificial splicing system, mutagenesis, cellular localization assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP of interaction, mutagenesis of SUN domain, splicing assay, multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"29298896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SUN5 truncation mutation (c.381delA; p.V128Sfs*7) decreases SUN5 protein expression and alters the distribution of ODF1 (outer dense fiber 1 protein) in sperm, linking SUN5 to organization of sperm neck structural components.\",\n      \"method\": \"Western blot, immunofluorescence of ODF1 in patient sperm\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method per observation, patient material only\",\n      \"pmids\": [\"29331481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SPAG4L (SUN5) and its shorter transcript variant SPAG4Lβ interact with Nesprin2 (a KASH domain protein) to form LINC complexes; these LINC complexes are involved in spermatocyte division during meiosis.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence, northern blot, RT-PCR, in situ hybridization\",\n      \"journal\": \"Acta biochimica et biophysica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP demonstrating interaction, immunofluorescence localization during meiosis, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"31144711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Sun5 knockout mice exhibit acephalic spermatozoa syndrome; the head-tail coupling apparatus (HTCA) and centrosome become distant from the nucleus at steps 9–10 of spermatid elongation, and head-tail separation occurs at steps 13–14. SUN5 interacts with Nesprin3 (confirmed by Co-IP) to form a LINC complex required for sperm head-tail connection; loss of Sun5 causes Nesprin3 to lose its localization at the posterior implantation fossa of the nucleus, leading to centrosome detachment. Downregulation of ODF1 and ODF2 also contributes to head-tail linkage damage.\",\n      \"method\": \"Sun5 knockout mouse generation, Co-immunoprecipitation, immunofluorescence, ultrastructural imaging, isobaric tag quantitative proteomics\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse with defined ultrastructural phenotype, reciprocal Co-IP of SUN5-Nesprin3, quantitative proteomics, multiple orthogonal methods\",\n      \"pmids\": [\"34268309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SUN5, Nesprin3, and ODF1 interact with each other (each pairwise combination confirmed by Co-IP in transfected HEK293T cells), forming a 'triplet' structural complex at the sperm neck; loss of SUN5 disrupts localization of both ODF1 and Nesprin3 in patient sperm, weakening the head-tail junction.\",\n      \"method\": \"Co-immunoprecipitation in HEK293T cells, immunofluorescence on patient sperm, whole-exome sequencing\",\n      \"journal\": \"Molecular human reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pairwise Co-IPs in transfected cells confirming trimeric interactions, single lab\",\n      \"pmids\": [\"33848337\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SUN5 promotes colorectal cancer cell proliferation and migration by upregulating phosphorylated ERK1/2 (pERK1/2); this is mediated via Nesprin2 and involves SUN5 interaction with Nup93 to promote nuclear translocation of pERK1/2.\",\n      \"method\": \"Knockdown/overexpression in CRC cell lines, ERK inhibitor (PD0325901) rescue, xenograft transplantation, Co-IP with Nup93\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional KD/OE with defined signaling readout, inhibitor rescue, Co-IP, single lab\",\n      \"pmids\": [\"36358787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ARRDC5 affects spermatogenesis by influencing the localization of SUN5 and NDC1; ARRDC5 likely acts through SEC22A-mediated vesicle trafficking to control transport and localization of SUN5 and other HTCA-related proteins responsible for sperm head-tail attachment.\",\n      \"method\": \"Arrdc5 knockout mouse, mass spectrometry, immunofluorescence\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with defined phenotype, MS identification of SUN5 as affected protein, single lab\",\n      \"pmids\": [\"37997706\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SUN5 interacts with LaminB1 (inner nuclear membrane) and with cytoskeletal GTPase Septin12 (and Septin2), forming a LaminB1/SUN5/Septin12 complex at the sperm neck. SUN5 connects the nucleus via LaminB1 and connects the proximal centriole via Septin12; SUN5-Septin12 binding promotes their co-aggregation at the sperm neck. Sun5 knockout disrupts Septin12-proximal centriole attachment to the nucleus, causing head-tail separation.\",\n      \"method\": \"Immunoprecipitation-mass spectrometry, Co-IP, immunofluorescence, Sun5 knockout mouse\",\n      \"journal\": \"Molecular human reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — IP-MS identification followed by Co-IP validation, KO mouse phenotype, multiple partners mapped, single rigorous study with orthogonal methods\",\n      \"pmids\": [\"38870534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SUN5 is involved in mRNA export in germ cells: in Sun5 KO mice, poly(A)+ RNA accumulates in nuclei of germ cells. SUN5 interacts with mRNA export factor Nxf1 and nucleoporin Nup93; loss of Sun5 reduces the Nxf1–Nup93 interaction and inhibits mRNA export through an Nxf1-dependent (not CRM1-dependent) pathway, contributing to abnormal spermatogenesis.\",\n      \"method\": \"Sun5 knockout mice, RNA interference in GC-2 cells, Co-IP of SUN5 with Nxf1 and Nup93, poly(A)+ RNA FISH, leptomycin B pharmacological block\",\n      \"journal\": \"Acta biochimica et biophysica Sinica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with nuclear mRNA accumulation phenotype, Co-IP of multiple interactors, pathway delineation by CRM1 inhibitor, multiple orthogonal methods in single study\",\n      \"pmids\": [\"39108207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SUN5 interacts with TRIM28 to increase IκBα ubiquitination, activating the NF-κB signaling pathway; this leads to nuclear translocation of phosphorylated P65 and increased transcription of GLUT1 and LDHA, enhancing glycolysis in colorectal cancer cells.\",\n      \"method\": \"SUN5 overexpression/knockdown in CRC cells, Co-IP of SUN5 with TRIM28, IKK inhibitor (BAY11-7082), glucose uptake and lactate assays, xenograft transplantation\",\n      \"journal\": \"Acta biochimica et biophysica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, pharmacological inhibition, functional metabolic assays, single lab\",\n      \"pmids\": [\"41311215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"By in situ cryo-electron tomography, SUN5 forms an extensive hexagonal lattice in the nuclear envelope at the base of the sperm head (confirmed in human, mouse, and boar sperm by superresolution fluorescence microscopy). This lattice maintains close apposition between inner and outer nuclear membranes; structural analysis supports a model in which LINC complexes form this lattice by laterally interacting at the outer nuclear membrane.\",\n      \"method\": \"Superresolution fluorescence microscopy, in situ cryo-electron tomography\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in situ cryo-ET structural determination across multiple species, direct visualization of hexagonal lattice\",\n      \"pmids\": [\"41855266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In-cell cryo-electron tomography of human spermatozoa reveals the sub-nanometer architecture of the trimeric ~130 kDa SUN5–Nesprin3 LINC complex forming a hexagonal lattice that stitches the nuclear envelope at the sperm base. A unique membrane-anchoring mechanism was identified: a SUN5 KASH-lid β-hairpin and a Nesprin3 amphipathic helix insert into the outer nuclear membrane, driving cooperative nuclear envelope remodeling and flattening of the caudal sperm nucleus.\",\n      \"method\": \"In-situ electron cryo-tomography, AlphaFold structural predictions, molecular dynamics simulations\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — sub-nanometer resolution in-situ cryo-ET with MD simulations and AlphaFold validation, novel structural mechanism described\",\n      \"pmids\": [\"bio_10.1101_2025.08.04.668116\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"SUN5 is a testis-specific inner nuclear membrane protein that forms a hexagonal LINC complex lattice at the sperm head-tail junction by interacting with Nesprin3 (and Nesprin2 during meiosis), LaminB1, and the cytoskeletal GTPase Septin12, physically bridging the nucleus to the proximal centriole/flagellum; loss of SUN5 disrupts this LaminB1/SUN5/Septin12 complex and the correct localization of Nesprin3 and ODF1/ODF2, causing the HTCA and centrosome to detach from the nucleus and producing acephalic spermatozoa syndrome, while SUN5 additionally facilitates mRNA export through an Nxf1/Nup93-dependent pathway in germ cells and, in somatic cancer contexts, promotes ERK signaling and NF-κB–driven glycolysis via interactions with Nesprin2/Nup93 and TRIM28 respectively.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SUN5 is a testis-specific SUN-domain inner nuclear membrane protein that builds the LINC complex anchoring the sperm head to its tail, and its loss causes acephalic spermatozoa syndrome [#3, #7]. During spermatogenesis SUN5 traffics through distinct compartments — a membranous compartment in spermatocytes, then the Golgi and nuclear envelope in round spermatids, and finally the head-tail junction in mature sperm [#2]; its transmembrane and coiled-coil regions, but not the SUN domain, direct nuclear envelope/ER localization [#1]. At the sperm neck SUN5 bridges the nucleus to the flagellar apparatus by binding LaminB1 on the nuclear side and the cytoskeletal GTPase Septin12 toward the proximal centriole, forming a LaminB1/SUN5/Septin12 complex whose disruption upon Sun5 loss detaches the centrosome from the nucleus [#11]. SUN5 partners with the KASH-domain Nesprins — Nesprin2 during meiotic spermatocyte division [#6] and Nesprin3 at the implantation fossa — together with the outer dense fiber proteins ODF1 and ODF2, and loss of SUN5 mislocalizes Nesprin3 and ODF1/ODF2, weakening the head-tail coupling apparatus [#7, #8]. SUN5 interacts with the coupling-apparatus protein DNAJB13, and acephalic-spermatozoa SUN domain missense substitutions impair this binding and perturb SUN5 folding and localization [#4]. In situ cryo-electron tomography shows that the trimeric SUN5–Nesprin3 LINC complex assembles into an extensive hexagonal lattice in the nuclear envelope at the sperm base, maintaining apposition of the inner and outer nuclear membranes across human, mouse, and boar sperm [#14]. Beyond its structural role, SUN5 facilitates germ-cell mRNA export via an Nxf1/Nup93-dependent pathway, with Sun5 loss causing nuclear poly(A)+ RNA accumulation [#12]. In somatic cancer contexts SUN5 promotes colorectal cancer proliferation and migration through Nesprin2/Nup93-dependent nuclear translocation of phosphorylated ERK1/2 [#9] and drives NF-\\u03baB-mediated glycolysis via TRIM28 [#13].\",\n  \"teleology\": [\n    {\n      \"year\": 2010,\n      \"claim\": \"Established where SUN5 acts by localizing it to the inner nuclear membrane of spermatids, defining it as a candidate nuclear-membrane organizer in germ cells.\",\n      \"evidence\": \"Immunofluorescence and biochemical fractionation of SPAG4L/SUN5 in round spermatids\",\n      \"pmids\": [\"21159740\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role inferred from localization only\", \"Apical/acrosomic association later contradicted\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Mapped the domains driving SUN5 targeting, showing the transmembrane and coiled-coil regions, not the SUN domain, direct nuclear envelope/ER localization.\",\n      \"evidence\": \"GFP-fusion deletion analysis with organelle markers in cultured cells\",\n      \"pmids\": [\"21711156\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding partners at the NE not identified\", \"Meiotic role proposed but not demonstrated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Resolved the dynamic trafficking of SUN5 across spermatogenesis and overturned the early model by showing it is excluded from the acrosome-facing envelope and not involved in acrosome attachment.\",\n      \"evidence\": \"Immunohistochemistry and Dpy19l2 knockout mouse relocalization analysis\",\n      \"pmids\": [\"25775128\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trafficking machinery unknown\", \"Final head-tail function not yet mechanistically defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established SUN5 loss-of-function as the genetic cause of acephalic spermatozoa syndrome, linking the head-tail junction defect to a specific gene.\",\n      \"evidence\": \"Genomic sequencing of patients and minigene splicing assay in HeLa cells\",\n      \"pmids\": [\"28541472\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular partners at the junction not yet identified\", \"Mechanism of detachment unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified DNAJB13 as a SUN5 partner and showed disease-associated SUN domain substitutions impair this interaction and SUN5 folding/localization, providing a molecular basis for pathogenic alleles.\",\n      \"evidence\": \"Co-IP, SUN-domain mutagenesis, and splicing assay\",\n      \"pmids\": [\"29298896\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of DNAJB13 binding in vivo not shown\", \"Architecture of the coupling complex unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linked SUN5 to organization of sperm neck structural components by showing a truncation allele alters ODF1 distribution.\",\n      \"evidence\": \"Western blot and ODF1 immunofluorescence in patient sperm\",\n      \"pmids\": [\"29331481\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single method per observation in patient material only\", \"Direct SUN5-ODF1 interaction not tested here\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showed SUN5 and a short variant form LINC complexes with the KASH protein Nesprin2 during meiotic spermatocyte division, extending SUN5 function beyond spermatids.\",\n      \"evidence\": \"Co-IP, immunofluorescence, northern blot and in situ hybridization\",\n      \"pmids\": [\"31144711\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Meiotic LINC requirement not tested by loss of function\", \"Relationship to later Nesprin3 complex unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined the in vivo mechanism of head-tail separation: a Sun5 knockout mouse linked SUN5-Nesprin3 LINC complex loss to Nesprin3 mislocalization, centrosome detachment, and ODF1/ODF2 downregulation.\",\n      \"evidence\": \"Sun5 knockout mouse, reciprocal Co-IP, ultrastructure, and quantitative proteomics\",\n      \"pmids\": [\"34268309\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nuclear-side anchor not yet identified\", \"Order of events in complex assembly unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established a SUN5-Nesprin3-ODF1 triplet complex at the sperm neck, showing SUN5 loss disrupts both ODF1 and Nesprin3 localization in patients.\",\n      \"evidence\": \"Pairwise Co-IPs in HEK293T cells and patient sperm immunofluorescence\",\n      \"pmids\": [\"33848337\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Pairwise interactions in transfected cells, not native complex\", \"Stoichiometry undefined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealed a somatic, oncogenic function for SUN5 in colorectal cancer through Nesprin2/Nup93-dependent nuclear translocation of phosphorylated ERK1/2.\",\n      \"evidence\": \"Knockdown/overexpression in CRC lines, ERK inhibitor rescue, xenografts, Co-IP with Nup93\",\n      \"pmids\": [\"36358787\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of pERK nuclear import via Nup93 not structurally defined\", \"Relevance to non-germline tissues unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Placed SUN5 downstream of vesicle-trafficking control by showing ARRDC5 (via SEC22A) governs SUN5 and NDC1 localization at the HTCA.\",\n      \"evidence\": \"Arrdc5 knockout mouse, mass spectrometry, immunofluorescence\",\n      \"pmids\": [\"37997706\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ARRDC5-SUN5 relationship not established\", \"Trafficking route of SUN5 not fully mapped\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified the nuclear-side anchor of the complex, showing SUN5 binds LaminB1 and the GTPase Septin12 to bridge nucleus to proximal centriole.\",\n      \"evidence\": \"IP-MS, Co-IP, immunofluorescence and Sun5 knockout mouse\",\n      \"pmids\": [\"38870534\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Role of Septin GTPase activity not tested\", \"Integration with Nesprin3 lattice not resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Uncovered a non-structural role in germ-cell mRNA export, with SUN5 supporting the Nxf1-Nup93 interaction and Sun5 loss causing nuclear poly(A)+ RNA retention.\",\n      \"evidence\": \"Sun5 knockout mice, GC-2 RNAi, Co-IP with Nxf1/Nup93, poly(A)+ FISH, leptomycin B block\",\n      \"pmids\": [\"39108207\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether export defect contributes to acephaly versus general spermatogenesis unclear\", \"Direct vs indirect role in Nxf1-Nup93 bridging undefined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended SUN5 cancer signaling to metabolism, showing SUN5-TRIM28 binding activates NF-\\u03baB and upregulates glycolytic genes in CRC.\",\n      \"evidence\": \"OE/KD in CRC cells, Co-IP with TRIM28, IKK inhibitor, metabolic assays, xenografts\",\n      \"pmids\": [\"41311215\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which SUN5 enhances IκBα ubiquitination undefined\", \"Single-lab observation\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Determined the sub-nanometer architecture of the trimeric SUN5-Nesprin3 LINC complex and a KASH-lid/amphipathic-helix membrane-anchoring mechanism driving nuclear envelope remodeling.\",\n      \"evidence\": \"In-situ cryo-ET, AlphaFold predictions and molecular dynamics (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.08.04.668116\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Functional validation of membrane-insertion mutants pending\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Visualized the higher-order organization, showing SUN5 forms a conserved hexagonal LINC lattice maintaining inner/outer nuclear membrane apposition at the sperm base.\",\n      \"evidence\": \"Superresolution microscopy and in situ cryo-ET across human, mouse and boar sperm\",\n      \"pmids\": [\"41855266\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How lattice assembly is initiated and templated is unknown\", \"Link between lattice integrity and force transmission not directly tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the structural LINC-lattice function and the mRNA-export and oncogenic signaling activities of SUN5 are mechanistically related, and whether they share a common biochemical basis, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking structural and signaling roles\", \"Regulation of SUN5 across germline versus somatic contexts undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [7, 11, 14]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [11, 12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [0, 1, 2, 14]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [3, 7, 11]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [9, 13]}\n    ],\n    \"complexes\": [\n      \"SUN5-Nesprin3 LINC complex\",\n      \"LaminB1/SUN5/Septin12 complex\",\n      \"SUN5-Nesprin2 LINC complex\"\n    ],\n    \"partners\": [\n      \"NESPRIN3\",\n      \"NESPRIN2\",\n      \"LMNB1\",\n      \"SEPTIN12\",\n      \"ODF1\",\n      \"DNAJB13\",\n      \"NXF1\",\n      \"NUP93\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}