{"gene":"SPEF2","run_date":"2026-04-28T20:42:08","timeline":{"discoveries":[{"year":1999,"finding":"KPL2 (SPEF2) encodes a novel protein upregulated during ciliogenesis of airway epithelial cells, containing a calponin homology domain, nuclear localization signals, a P-loop, and a proline-rich region; its expression is stage-specific in spermatocytes and round spermatids in the testis and closely parallels axonemal dynein heavy chain expression during ciliated cell differentiation.","method":"Differential display, Northern blot, Southern blot, cDNA cloning and sequencing, immunohistochemistry","journal":"American journal of respiratory cell and molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 — original cloning with domain characterization and expression analysis; single study","pmids":["10100999"],"is_preprint":false},{"year":2006,"finding":"A retrotransposon insertion within an intron of KPL2 (SPEF2) causes aberrant splicing specifically of a testis-expressed exon, leading to frameshifts and premature termination, resulting in defective axoneme development in sperm flagella while cilia in other tissues are unaffected; this demonstrates that SPEF2 is important for correct axoneme development.","method":"Positional cloning, comparative genomic mapping, RT-PCR, sequence analysis, tissue expression analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — positional cloning with molecular validation of splicing defect and tissue-specific phenotype; replicated in subsequent studies","pmids":["16549801"],"is_preprint":false},{"year":2009,"finding":"SPEF2 protein localizes to the Golgi complex, manchette, basal body, and midpiece of the sperm tail during spermatid differentiation, and interacts with the intraflagellar transport protein IFT20 in the testis.","method":"Immunofluorescence microscopy, yeast two-hybrid assay, coimmunoprecipitation","journal":"Biology of reproduction","confidence":"High","confidence_rationale":"Tier 2 — interaction confirmed by both yeast two-hybrid and co-IP, with colocalization; replicated by subsequent studies","pmids":["19889948"],"is_preprint":false},{"year":2011,"finding":"Loss of SPEF2 function in mice (bgh mutation — a nonsense mutation) causes shortened flagella, disorganized axonemal and accessory structures in sperm, and reduced cilia beat frequency in respiratory epithelium (ultrastructurally normal cilia), establishing SPEF2 as required for cilia function and a genetic cause of primary ciliary dyskinesia.","method":"Positional cloning, histopathology, immunofluorescence, electron microscopy, video microscopy, Western blot","journal":"Biology of reproduction","confidence":"High","confidence_rationale":"Tier 1-2 — in vivo loss-of-function mouse model with multiple orthogonal readouts; causative mutation validated by Western blot","pmids":["21715716"],"is_preprint":false},{"year":2017,"finding":"SPEF2 functions in microtubule-mediated protein transport in elongating spermatids via the manchette; it interacts with cytoplasmic dynein 1 and GOLGA3, colocalizes with dynein 1 in the manchette, and is required for IFT20 transport from the Golgi to the manchette. Loss of SPEF2 also causes basal body duplication and defective manchette migration leading to abnormal sperm head shape.","method":"Male germ cell-specific Spef2 knockout mouse, coimmunoprecipitation, immunofluorescence, dynein inhibition assay","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with specific phenotypic readouts combined with reciprocal Co-IP and functional inhibition experiments; multiple orthogonal methods","pmids":["28619825"],"is_preprint":false},{"year":2018,"finding":"SPEF2 is required for osteoblast differentiation and bone formation; Spef2 knockout mice show shorter long bones, reduced bone mineral content, and compromised in vitro osteoblast differentiation.","method":"Spef2 knockout mouse model, X-ray analysis, in vitro osteoblast differentiation assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse with defined cellular phenotype (osteoblast differentiation); single study","pmids":["29339787"],"is_preprint":false},{"year":2019,"finding":"Loss-of-function mutations in SPEF2 in humans cause multiple morphological abnormalities of the sperm flagella (MMAF) with disrupted axonemal structure and mitochondrial sheath defects, and result in significantly decreased SPEF2 protein levels in spermatozoa.","method":"Whole exome sequencing, transmission electron microscopy, Western blot, immunofluorescence","journal":"Journal of medical genetics","confidence":"High","confidence_rationale":"Tier 2 — human loss-of-function validated by multiple orthogonal methods; replicated in independent cohorts across two studies","pmids":["31151990","31048344"],"is_preprint":false},{"year":2019,"finding":"SPEF2 mutations affect the long SPEF2 transcripts expressed in the testis that encode the IFT20-binding domain; deficiency of SPEF2 alters the localization of other axonemal proteins, including CFAP69, in spermatozoa.","method":"Whole exome sequencing, immunofluorescence assay, genetic analysis of isoform specificity","journal":"Journal of medical genetics","confidence":"Medium","confidence_rationale":"Tier 2-3 — isoform-specific effect demonstrated and downstream protein mislocalization shown; single study","pmids":["31048344"],"is_preprint":false},{"year":2020,"finding":"SPEF2 is a central pair (CP)-associated protein in motile cilia; SPEF2 is absent in HYDIN-mutant cilia, revealing that SPEF2 localization to the central pair depends on functional HYDIN; loss-of-function mutations in SPEF2 itself cause PCD with central pair defects.","method":"Immunofluorescence microscopy on respiratory cells, genetic analysis (whole-exome/next-generation sequencing)","journal":"American journal of respiratory cell and molecular biology","confidence":"High","confidence_rationale":"Tier 2 — IF microscopy on 189 individuals demonstrating SPEF2 dependence on HYDIN; large cohort with genetic confirmation","pmids":["31545650"],"is_preprint":false},{"year":2022,"finding":"SPEF2 interacts with RSPH9 and IFT20 in vitro (in addition to the previously identified IFT20 interaction), and its deficiency leads to reduced expression of proteins related to flagellar assembly including SPAG6, DYNLT1, RSPH1, TOM20, EFHC1, MNS1, and IFT20 in human spermatozoa.","method":"Proteomic analysis, co-immunoprecipitation, Western blot","journal":"Asian journal of andrology","confidence":"Medium","confidence_rationale":"Tier 2-3 — in vitro interaction confirmed by Co-IP; proteomics provides broad view; single study","pmids":["34755699"],"is_preprint":false},{"year":2023,"finding":"SPEF2 and HYDIN interact in sperm flagella; absence of SPEF2 protein in sperm flagella of HYDIN-mutant individuals reveals a dependency relationship between these central pair-associated proteins in sperm flagella (as distinct from respiratory cilia).","method":"Immunofluorescence microscopy on sperm cells, next-generation sequencing","journal":"Frontiers in genetics","confidence":"Medium","confidence_rationale":"Tier 3 — immunofluorescence showing protein interdependency; single study but corroborates respiratory cilia findings","pmids":["36873931"],"is_preprint":false},{"year":2024,"finding":"SPEF2 variants cause absence of the central pair complex in sperm flagella, confirmed by ultrastructural analysis; immunostaining of spermatozoa and respiratory cilia validates pathogenicity of SPEF2 variants in both tissues.","method":"Whole-exome sequencing, electron microscopy, immunofluorescence, in vitro analyses","journal":"Journal of assisted reproduction and genetics","confidence":"Medium","confidence_rationale":"Tier 2 — ultrastructural and immunostaining evidence in multiple patients; single study","pmids":["38568462"],"is_preprint":false}],"current_model":"SPEF2 is a central pair-associated protein essential for motile cilia and sperm flagella assembly: it localizes to the Golgi complex, manchette, basal body, and sperm tail midpiece during spermatogenesis, interacts with IFT20, RSPH9, cytoplasmic dynein 1, and GOLGA3, and functions as a linker for dynein 1-mediated cargo transport along manchette microtubules; its localization at the central pair of cilia depends on functional HYDIN, and loss of SPEF2 disrupts axonemal and accessory structure organization in sperm, reduces cilia beat frequency in respiratory epithelium, and impairs osteoblast differentiation, causing male infertility (MMAF phenotype) and primary ciliary dyskinesia in both animal models and humans."},"narrative":{"teleology":[{"year":1999,"claim":"Identification of SPEF2 (KPL2) as a novel ciliogenesis-associated gene resolved the question of what transcripts accompany ciliated cell differentiation and spermatogenesis, establishing it as a candidate motile cilia gene with a calponin homology domain.","evidence":"Differential display and Northern blot on differentiating airway epithelial cells and testis","pmids":["10100999"],"confidence":"Medium","gaps":["No functional data; domain predictions only","No loss-of-function evidence","Protein localization not determined"]},{"year":2006,"claim":"Positional cloning of a retrotransposon insertion in SPEF2 demonstrated that disruption of a testis-specific exon causes defective sperm axoneme development, establishing SPEF2 as functionally required for flagellar assembly.","evidence":"Positional cloning and RT-PCR in a naturally occurring bovine male-infertility model","pmids":["16549801"],"confidence":"High","gaps":["Mechanism of axoneme disruption unknown","Whether respiratory cilia are affected was untested","No protein interaction data"]},{"year":2009,"claim":"Localization of SPEF2 to the Golgi, manchette, basal body, and sperm tail midpiece, together with its physical interaction with IFT20, revealed that SPEF2 participates in intraflagellar transport-related protein trafficking during spermatid differentiation.","evidence":"Immunofluorescence, yeast two-hybrid, and co-immunoprecipitation in mouse testis","pmids":["19889948"],"confidence":"High","gaps":["Motor protein involvement unknown","Functional consequence of IFT20 interaction not tested in vivo"]},{"year":2011,"claim":"A mouse nonsense mutation in SPEF2 (bgh) proved that SPEF2 is required not only for sperm flagella integrity but also for normal respiratory cilia beat frequency, establishing SPEF2 as a primary ciliary dyskinesia gene.","evidence":"Positional cloning, electron microscopy, video microscopy, and Western blot in bgh mutant mice","pmids":["21715716"],"confidence":"High","gaps":["Respiratory cilia ultrastructure appeared normal despite reduced beat frequency — structural basis unclear","Central pair involvement not yet identified"]},{"year":2017,"claim":"Conditional knockout and interaction studies established SPEF2 as a molecular linker between cytoplasmic dynein 1 and cargo (including IFT20) along manchette microtubules, explaining how it coordinates protein transport and head shaping during spermiogenesis.","evidence":"Male germ cell-specific Spef2 knockout, co-immunoprecipitation with dynein 1 and GOLGA3, dynein inhibition assay","pmids":["28619825"],"confidence":"High","gaps":["Direct binding domains for dynein 1 and GOLGA3 not mapped","Structural basis of SPEF2 bridging function unknown"]},{"year":2018,"claim":"Discovery that Spef2 knockout mice exhibit impaired osteoblast differentiation and reduced bone formation extended SPEF2 function beyond cilia/flagella to skeletal development.","evidence":"Spef2 knockout mouse with X-ray analysis and in vitro osteoblast differentiation assay","pmids":["29339787"],"confidence":"Medium","gaps":["Mechanism linking SPEF2 to osteoblast differentiation unknown","Whether this is cilia-dependent or cilia-independent is unresolved","Single study without independent replication"]},{"year":2019,"claim":"Identification of loss-of-function SPEF2 mutations in human infertile men confirmed SPEF2 as a causal gene for MMAF with axonemal and mitochondrial sheath defects, and demonstrated that disease-causing mutations selectively affect the long testis-expressed isoform encoding the IFT20-binding domain.","evidence":"Whole-exome sequencing, transmission electron microscopy, Western blot, and immunofluorescence in independent human cohorts","pmids":["31151990","31048344"],"confidence":"High","gaps":["Genotype-phenotype correlations across different mutation types incomplete","Isoform-specific rescue not performed"]},{"year":2020,"claim":"Demonstration that SPEF2 is a central pair-associated protein whose localization depends on HYDIN identified its precise axonemal substructure and placed it within the HYDIN-dependent central pair assembly pathway, linking SPEF2 mutations to PCD with central pair defects.","evidence":"Immunofluorescence on respiratory cells from 189 individuals including HYDIN-mutant patients, with whole-exome sequencing","pmids":["31545650"],"confidence":"High","gaps":["Whether SPEF2 is a structural component or regulatory factor at the central pair is unclear","Direct SPEF2–HYDIN binding not demonstrated"]},{"year":2022,"claim":"Proteomic and interaction studies expanded the SPEF2 interactome to include RSPH9 and revealed that SPEF2 deficiency broadly reduces levels of flagellar assembly proteins, indicating SPEF2 acts upstream in flagellar protein homeostasis.","evidence":"Co-immunoprecipitation and proteomic analysis of human spermatozoa","pmids":["34755699"],"confidence":"Medium","gaps":["Whether reduced protein levels reflect transcriptional, transport, or stability defects is unknown","RSPH9 interaction awaits in vivo validation"]},{"year":2023,"claim":"The SPEF2–HYDIN dependency was confirmed in sperm flagella (extending the respiratory cilia finding), establishing that central pair integrity in both cilia and flagella requires coordinated SPEF2–HYDIN interaction.","evidence":"Immunofluorescence on sperm from HYDIN-mutant individuals","pmids":["36873931"],"confidence":"Medium","gaps":["Direct physical interaction between SPEF2 and HYDIN not biochemically confirmed","Single study"]},{"year":null,"claim":"Key unresolved questions include the structural basis of SPEF2 at the central pair, the molecular domains mediating its interactions with dynein 1 and HYDIN, the mechanism connecting SPEF2 to osteoblast differentiation, and whether short SPEF2 isoforms have distinct ciliary functions.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structural data for SPEF2 or its complexes","Cilia-independent vs cilia-dependent roles in bone not delineated","No reconstituted in vitro transport assay with purified SPEF2"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[2,4]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[2,4]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[2,4]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[8,11]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[1,3,4,8]},{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[1,4,6]}],"complexes":[],"partners":["IFT20","GOLGA3","RSPH9","HYDIN","DYNC1H1"],"other_free_text":[]},"mechanistic_narrative":"SPEF2 is a central pair-associated protein essential for the assembly and function of motile cilia and sperm flagella. It contains a calponin homology domain and functions as a linker for cytoplasmic dynein 1-mediated cargo transport along manchette microtubules during spermiogenesis, interacting with IFT20, GOLGA3, RSPH9, and HYDIN to coordinate intraflagellar transport and axonemal organization [PMID:19889948, PMID:28619825, PMID:34755699, PMID:31545650]. Loss of SPEF2 disrupts axonemal central pair formation, accessory structure assembly, and mitochondrial sheath integrity in sperm, and reduces ciliary beat frequency in respiratory epithelium, causing multiple morphological abnormalities of the sperm flagella (MMAF) and primary ciliary dyskinesia in humans [PMID:31151990, PMID:31545650, PMID:38568462, PMID:21715716]. SPEF2 localization to the central pair depends on functional HYDIN, and its deficiency additionally impairs osteoblast differentiation and bone formation [PMID:31545650, PMID:29339787]."},"prefetch_data":{"uniprot":{"accession":"Q9C093","full_name":"Sperm flagellar protein 2","aliases":["Protein KPL2"],"length_aa":1822,"mass_kda":209.8,"function":"Required for correct axoneme development in spermatozoa. Important for normal development of the manchette and sperm head morphology. Essential for male fertility. Plays a role in localization of the intraflagellar transport protein IFT20 to the manchette, suggesting function as an adapter for dynein-mediated protein transport during spermatogenesis (PubMed:31048344, PubMed:31151990, PubMed:31278745). Also plays a role in bone growth where it seems to be required for normal osteoblast differentiation (By similarity)","subcellular_location":"Cell projection, cilium, flagellum; Cytoplasm; Golgi apparatus","url":"https://www.uniprot.org/uniprotkb/Q9C093/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SPEF2","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SPEF2","total_profiled":1310},"omim":[{"mim_id":"621121","title":"CILIA- AND FLAGELLA-ASSOCIATED PROTEIN 54; CFAP54","url":"https://www.omim.org/entry/621121"},{"mim_id":"619712","title":"SPERMATOGENIC FAILURE 65; SPGF65","url":"https://www.omim.org/entry/619712"},{"mim_id":"619144","title":"SPERMATOGENIC FAILURE 49; SPGF49","url":"https://www.omim.org/entry/619144"},{"mim_id":"618751","title":"SPERMATOGENIC FAILURE 43; SPGF43","url":"https://www.omim.org/entry/618751"},{"mim_id":"618704","title":"CILIA- AND FLAGELLA-ASSOCIATED PROTEIN 221; CFAP221","url":"https://www.omim.org/entry/618704"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Primary cilium","reliability":"Supported"},{"location":"Flagellar centriole","reliability":"Supported"},{"location":"Nuclear bodies","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"},{"location":"Mid piece","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SPEF2"},"hgnc":{"alias_symbol":["KPL2","FLJ23577","CT122"],"prev_symbol":[]},"alphafold":{"accession":"Q9C093","domains":[{"cath_id":"1.10.418.10","chopping":"2-145","consensus_level":"high","plddt":81.091,"start":2,"end":145},{"cath_id":"-","chopping":"517-546_1016-1076_1112-1198_1209-1216_1239-1282_1336-1411","consensus_level":"medium","plddt":84.9504,"start":517,"end":1411},{"cath_id":"-","chopping":"1462-1524","consensus_level":"medium","plddt":81.973,"start":1462,"end":1524}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9C093","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9C093-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9C093-F1-predicted_aligned_error_v6.png","plddt_mean":70.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SPEF2","jax_strain_url":"https://www.jax.org/strain/search?query=SPEF2"},"sequence":{"accession":"Q9C093","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9C093.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9C093/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9C093"}},"corpus_meta":[{"pmid":"21715716","id":"PMC_21715716","title":"Loss of SPEF2 function in mice results in spermatogenesis defects and primary ciliary dyskinesia.","date":"2011","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/21715716","citation_count":105,"is_preprint":false},{"pmid":"18713476","id":"PMC_18713476","title":"Partial duplication of the PRLR and SPEF2 genes at the late feathering locus in chicken.","date":"2008","source":"BMC genomics","url":"https://pubmed.ncbi.nlm.nih.gov/18713476","citation_count":79,"is_preprint":false},{"pmid":"16549801","id":"PMC_16549801","title":"An intronic insertion in KPL2 results in aberrant splicing and causes the immotile short-tail sperm defect in the pig.","date":"2006","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/16549801","citation_count":76,"is_preprint":false},{"pmid":"19889948","id":"PMC_19889948","title":"Expression of SPEF2 during mouse spermatogenesis and identification of IFT20 as an interacting protein.","date":"2009","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/19889948","citation_count":75,"is_preprint":false},{"pmid":"31151990","id":"PMC_31151990","title":"Loss-of-function mutations in SPEF2 cause multiple morphological abnormalities of the sperm flagella (MMAF).","date":"2019","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/31151990","citation_count":64,"is_preprint":false},{"pmid":"31048344","id":"PMC_31048344","title":"Homozygous mutations in SPEF2 induce multiple morphological abnormalities of the sperm flagella and male infertility.","date":"2019","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/31048344","citation_count":60,"is_preprint":false},{"pmid":"28619825","id":"PMC_28619825","title":"SPEF2 functions in microtubule-mediated transport in elongating spermatids to ensure proper male germ cell differentiation.","date":"2017","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/28619825","citation_count":57,"is_preprint":false},{"pmid":"31545650","id":"PMC_31545650","title":"SPEF2- and HYDIN-Mutant Cilia Lack the Central Pair-associated Protein SPEF2, Aiding Primary Ciliary Dyskinesia Diagnostics.","date":"2020","source":"American journal of respiratory cell and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/31545650","citation_count":57,"is_preprint":false},{"pmid":"10100999","id":"PMC_10100999","title":"Cloning and characterization of KPL2, a novel gene induced during ciliogenesis of tracheal epithelial cells.","date":"1999","source":"American journal of respiratory cell and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/10100999","citation_count":41,"is_preprint":false},{"pmid":"29339787","id":"PMC_29339787","title":"Cilia-related protein SPEF2 regulates osteoblast differentiation.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/29339787","citation_count":24,"is_preprint":false},{"pmid":"36873931","id":"PMC_36873931","title":"Pathogenic gene variants in CCDC39, CCDC40, RSPH1, RSPH9, HYDIN, and SPEF2 cause defects of sperm flagella composition and male infertility.","date":"2023","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/36873931","citation_count":24,"is_preprint":false},{"pmid":"22394230","id":"PMC_22394230","title":"L1 insertion within SPEF2 gene is associated with increased litter size in the Finnish Yorkshire population.","date":"2011","source":"Journal of animal breeding and genetics = Zeitschrift fur Tierzuchtung und Zuchtungsbiologie","url":"https://pubmed.ncbi.nlm.nih.gov/22394230","citation_count":21,"is_preprint":false},{"pmid":"34755699","id":"PMC_34755699","title":"Sperm flagellar 2 (SPEF2) is essential for sperm flagellar assembly in humans.","date":"2022","source":"Asian journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/34755699","citation_count":18,"is_preprint":false},{"pmid":"17610085","id":"PMC_17610085","title":"Infertile Finnish Yorkshire boars carry a full-length LINE-1 retrotransposon within the KPL2 gene.","date":"2007","source":"Molecular genetics and genomics : MGG","url":"https://pubmed.ncbi.nlm.nih.gov/17610085","citation_count":16,"is_preprint":false},{"pmid":"37801226","id":"PMC_37801226","title":"circ_SPEF2 Regulates the Balance of Treg Cells by Regulating miR-16-5p/BACH2 in Lymphoma and Participates in the Immune Response.","date":"2023","source":"Tissue engineering and regenerative medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37801226","citation_count":9,"is_preprint":false},{"pmid":"36615117","id":"PMC_36615117","title":"Novel SPEF2 Variant in a Japanese Patient with Primary Ciliary Dyskinesia: A Case Report and Literature Review.","date":"2022","source":"Journal of clinical medicine","url":"https://pubmed.ncbi.nlm.nih.gov/36615117","citation_count":6,"is_preprint":false},{"pmid":"24712415","id":"PMC_24712415","title":"A recent L1 insertion within SPEF2 gene is associated with changes in PRLR expression in sow reproductive organs.","date":"2014","source":"Animal genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24712415","citation_count":5,"is_preprint":false},{"pmid":"34679903","id":"PMC_34679903","title":"Search for Associations of FSHR, INHA, INHAB, PRL, TNP2 and SPEF2 Genes Polymorphisms with Semen Quality in Russian Holstein Bulls (Pilot Study).","date":"2021","source":"Animals : an open access journal from MDPI","url":"https://pubmed.ncbi.nlm.nih.gov/34679903","citation_count":4,"is_preprint":false},{"pmid":"35965828","id":"PMC_35965828","title":"The ciliary protein Spef2 stimulates acinar Ampkα/Sirt1 signaling and ameliorates acute pancreatitis and associated lung injury.","date":"2022","source":"Annals of translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/35965828","citation_count":3,"is_preprint":false},{"pmid":"39753944","id":"PMC_39753944","title":"Novel variants of FSIP2 and SPEF2 cause varying degrees of spermatozoa damage in MMAF patients and favorable ART outcomes.","date":"2025","source":"Journal of assisted reproduction and genetics","url":"https://pubmed.ncbi.nlm.nih.gov/39753944","citation_count":2,"is_preprint":false},{"pmid":"38568462","id":"PMC_38568462","title":"Novel SPEF2 variants cause male infertility and likely primary ciliary dyskinesia.","date":"2024","source":"Journal of assisted reproduction and genetics","url":"https://pubmed.ncbi.nlm.nih.gov/38568462","citation_count":1,"is_preprint":false},{"pmid":"40949679","id":"PMC_40949679","title":"Retraction: The ciliary protein Spef2 stimulates acinar Ampkα/Sirt1 signaling and ameliorates acute pancreatitis and associated lung injury.","date":"2024","source":"Annals of translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40949679","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12534,"output_tokens":2705,"usd":0.039088},"stage2":{"model":"claude-opus-4-6","input_tokens":6054,"output_tokens":2466,"usd":0.13788},"total_usd":0.176968,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1999,\n      \"finding\": \"KPL2 (SPEF2) encodes a novel protein upregulated during ciliogenesis of airway epithelial cells, containing a calponin homology domain, nuclear localization signals, a P-loop, and a proline-rich region; its expression is stage-specific in spermatocytes and round spermatids in the testis and closely parallels axonemal dynein heavy chain expression during ciliated cell differentiation.\",\n      \"method\": \"Differential display, Northern blot, Southern blot, cDNA cloning and sequencing, immunohistochemistry\",\n      \"journal\": \"American journal of respiratory cell and molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — original cloning with domain characterization and expression analysis; single study\",\n      \"pmids\": [\"10100999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"A retrotransposon insertion within an intron of KPL2 (SPEF2) causes aberrant splicing specifically of a testis-expressed exon, leading to frameshifts and premature termination, resulting in defective axoneme development in sperm flagella while cilia in other tissues are unaffected; this demonstrates that SPEF2 is important for correct axoneme development.\",\n      \"method\": \"Positional cloning, comparative genomic mapping, RT-PCR, sequence analysis, tissue expression analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — positional cloning with molecular validation of splicing defect and tissue-specific phenotype; replicated in subsequent studies\",\n      \"pmids\": [\"16549801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SPEF2 protein localizes to the Golgi complex, manchette, basal body, and midpiece of the sperm tail during spermatid differentiation, and interacts with the intraflagellar transport protein IFT20 in the testis.\",\n      \"method\": \"Immunofluorescence microscopy, yeast two-hybrid assay, coimmunoprecipitation\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — interaction confirmed by both yeast two-hybrid and co-IP, with colocalization; replicated by subsequent studies\",\n      \"pmids\": [\"19889948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Loss of SPEF2 function in mice (bgh mutation — a nonsense mutation) causes shortened flagella, disorganized axonemal and accessory structures in sperm, and reduced cilia beat frequency in respiratory epithelium (ultrastructurally normal cilia), establishing SPEF2 as required for cilia function and a genetic cause of primary ciliary dyskinesia.\",\n      \"method\": \"Positional cloning, histopathology, immunofluorescence, electron microscopy, video microscopy, Western blot\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vivo loss-of-function mouse model with multiple orthogonal readouts; causative mutation validated by Western blot\",\n      \"pmids\": [\"21715716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SPEF2 functions in microtubule-mediated protein transport in elongating spermatids via the manchette; it interacts with cytoplasmic dynein 1 and GOLGA3, colocalizes with dynein 1 in the manchette, and is required for IFT20 transport from the Golgi to the manchette. Loss of SPEF2 also causes basal body duplication and defective manchette migration leading to abnormal sperm head shape.\",\n      \"method\": \"Male germ cell-specific Spef2 knockout mouse, coimmunoprecipitation, immunofluorescence, dynein inhibition assay\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with specific phenotypic readouts combined with reciprocal Co-IP and functional inhibition experiments; multiple orthogonal methods\",\n      \"pmids\": [\"28619825\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SPEF2 is required for osteoblast differentiation and bone formation; Spef2 knockout mice show shorter long bones, reduced bone mineral content, and compromised in vitro osteoblast differentiation.\",\n      \"method\": \"Spef2 knockout mouse model, X-ray analysis, in vitro osteoblast differentiation assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse with defined cellular phenotype (osteoblast differentiation); single study\",\n      \"pmids\": [\"29339787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Loss-of-function mutations in SPEF2 in humans cause multiple morphological abnormalities of the sperm flagella (MMAF) with disrupted axonemal structure and mitochondrial sheath defects, and result in significantly decreased SPEF2 protein levels in spermatozoa.\",\n      \"method\": \"Whole exome sequencing, transmission electron microscopy, Western blot, immunofluorescence\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — human loss-of-function validated by multiple orthogonal methods; replicated in independent cohorts across two studies\",\n      \"pmids\": [\"31151990\", \"31048344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SPEF2 mutations affect the long SPEF2 transcripts expressed in the testis that encode the IFT20-binding domain; deficiency of SPEF2 alters the localization of other axonemal proteins, including CFAP69, in spermatozoa.\",\n      \"method\": \"Whole exome sequencing, immunofluorescence assay, genetic analysis of isoform specificity\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — isoform-specific effect demonstrated and downstream protein mislocalization shown; single study\",\n      \"pmids\": [\"31048344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SPEF2 is a central pair (CP)-associated protein in motile cilia; SPEF2 is absent in HYDIN-mutant cilia, revealing that SPEF2 localization to the central pair depends on functional HYDIN; loss-of-function mutations in SPEF2 itself cause PCD with central pair defects.\",\n      \"method\": \"Immunofluorescence microscopy on respiratory cells, genetic analysis (whole-exome/next-generation sequencing)\",\n      \"journal\": \"American journal of respiratory cell and molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — IF microscopy on 189 individuals demonstrating SPEF2 dependence on HYDIN; large cohort with genetic confirmation\",\n      \"pmids\": [\"31545650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SPEF2 interacts with RSPH9 and IFT20 in vitro (in addition to the previously identified IFT20 interaction), and its deficiency leads to reduced expression of proteins related to flagellar assembly including SPAG6, DYNLT1, RSPH1, TOM20, EFHC1, MNS1, and IFT20 in human spermatozoa.\",\n      \"method\": \"Proteomic analysis, co-immunoprecipitation, Western blot\",\n      \"journal\": \"Asian journal of andrology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — in vitro interaction confirmed by Co-IP; proteomics provides broad view; single study\",\n      \"pmids\": [\"34755699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SPEF2 and HYDIN interact in sperm flagella; absence of SPEF2 protein in sperm flagella of HYDIN-mutant individuals reveals a dependency relationship between these central pair-associated proteins in sperm flagella (as distinct from respiratory cilia).\",\n      \"method\": \"Immunofluorescence microscopy on sperm cells, next-generation sequencing\",\n      \"journal\": \"Frontiers in genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — immunofluorescence showing protein interdependency; single study but corroborates respiratory cilia findings\",\n      \"pmids\": [\"36873931\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SPEF2 variants cause absence of the central pair complex in sperm flagella, confirmed by ultrastructural analysis; immunostaining of spermatozoa and respiratory cilia validates pathogenicity of SPEF2 variants in both tissues.\",\n      \"method\": \"Whole-exome sequencing, electron microscopy, immunofluorescence, in vitro analyses\",\n      \"journal\": \"Journal of assisted reproduction and genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ultrastructural and immunostaining evidence in multiple patients; single study\",\n      \"pmids\": [\"38568462\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SPEF2 is a central pair-associated protein essential for motile cilia and sperm flagella assembly: it localizes to the Golgi complex, manchette, basal body, and sperm tail midpiece during spermatogenesis, interacts with IFT20, RSPH9, cytoplasmic dynein 1, and GOLGA3, and functions as a linker for dynein 1-mediated cargo transport along manchette microtubules; its localization at the central pair of cilia depends on functional HYDIN, and loss of SPEF2 disrupts axonemal and accessory structure organization in sperm, reduces cilia beat frequency in respiratory epithelium, and impairs osteoblast differentiation, causing male infertility (MMAF phenotype) and primary ciliary dyskinesia in both animal models and humans.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SPEF2 is a central pair-associated protein essential for the assembly and function of motile cilia and sperm flagella. It contains a calponin homology domain and functions as a linker for cytoplasmic dynein 1-mediated cargo transport along manchette microtubules during spermiogenesis, interacting with IFT20, GOLGA3, RSPH9, and HYDIN to coordinate intraflagellar transport and axonemal organization [PMID:19889948, PMID:28619825, PMID:34755699, PMID:31545650]. Loss of SPEF2 disrupts axonemal central pair formation, accessory structure assembly, and mitochondrial sheath integrity in sperm, and reduces ciliary beat frequency in respiratory epithelium, causing multiple morphological abnormalities of the sperm flagella (MMAF) and primary ciliary dyskinesia in humans [PMID:31151990, PMID:31545650, PMID:38568462, PMID:21715716]. SPEF2 localization to the central pair depends on functional HYDIN, and its deficiency additionally impairs osteoblast differentiation and bone formation [PMID:31545650, PMID:29339787].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of SPEF2 (KPL2) as a novel ciliogenesis-associated gene resolved the question of what transcripts accompany ciliated cell differentiation and spermatogenesis, establishing it as a candidate motile cilia gene with a calponin homology domain.\",\n      \"evidence\": \"Differential display and Northern blot on differentiating airway epithelial cells and testis\",\n      \"pmids\": [\"10100999\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional data; domain predictions only\", \"No loss-of-function evidence\", \"Protein localization not determined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Positional cloning of a retrotransposon insertion in SPEF2 demonstrated that disruption of a testis-specific exon causes defective sperm axoneme development, establishing SPEF2 as functionally required for flagellar assembly.\",\n      \"evidence\": \"Positional cloning and RT-PCR in a naturally occurring bovine male-infertility model\",\n      \"pmids\": [\"16549801\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of axoneme disruption unknown\", \"Whether respiratory cilia are affected was untested\", \"No protein interaction data\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Localization of SPEF2 to the Golgi, manchette, basal body, and sperm tail midpiece, together with its physical interaction with IFT20, revealed that SPEF2 participates in intraflagellar transport-related protein trafficking during spermatid differentiation.\",\n      \"evidence\": \"Immunofluorescence, yeast two-hybrid, and co-immunoprecipitation in mouse testis\",\n      \"pmids\": [\"19889948\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Motor protein involvement unknown\", \"Functional consequence of IFT20 interaction not tested in vivo\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"A mouse nonsense mutation in SPEF2 (bgh) proved that SPEF2 is required not only for sperm flagella integrity but also for normal respiratory cilia beat frequency, establishing SPEF2 as a primary ciliary dyskinesia gene.\",\n      \"evidence\": \"Positional cloning, electron microscopy, video microscopy, and Western blot in bgh mutant mice\",\n      \"pmids\": [\"21715716\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Respiratory cilia ultrastructure appeared normal despite reduced beat frequency — structural basis unclear\", \"Central pair involvement not yet identified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Conditional knockout and interaction studies established SPEF2 as a molecular linker between cytoplasmic dynein 1 and cargo (including IFT20) along manchette microtubules, explaining how it coordinates protein transport and head shaping during spermiogenesis.\",\n      \"evidence\": \"Male germ cell-specific Spef2 knockout, co-immunoprecipitation with dynein 1 and GOLGA3, dynein inhibition assay\",\n      \"pmids\": [\"28619825\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct binding domains for dynein 1 and GOLGA3 not mapped\", \"Structural basis of SPEF2 bridging function unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Discovery that Spef2 knockout mice exhibit impaired osteoblast differentiation and reduced bone formation extended SPEF2 function beyond cilia/flagella to skeletal development.\",\n      \"evidence\": \"Spef2 knockout mouse with X-ray analysis and in vitro osteoblast differentiation assay\",\n      \"pmids\": [\"29339787\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking SPEF2 to osteoblast differentiation unknown\", \"Whether this is cilia-dependent or cilia-independent is unresolved\", \"Single study without independent replication\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identification of loss-of-function SPEF2 mutations in human infertile men confirmed SPEF2 as a causal gene for MMAF with axonemal and mitochondrial sheath defects, and demonstrated that disease-causing mutations selectively affect the long testis-expressed isoform encoding the IFT20-binding domain.\",\n      \"evidence\": \"Whole-exome sequencing, transmission electron microscopy, Western blot, and immunofluorescence in independent human cohorts\",\n      \"pmids\": [\"31151990\", \"31048344\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genotype-phenotype correlations across different mutation types incomplete\", \"Isoform-specific rescue not performed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstration that SPEF2 is a central pair-associated protein whose localization depends on HYDIN identified its precise axonemal substructure and placed it within the HYDIN-dependent central pair assembly pathway, linking SPEF2 mutations to PCD with central pair defects.\",\n      \"evidence\": \"Immunofluorescence on respiratory cells from 189 individuals including HYDIN-mutant patients, with whole-exome sequencing\",\n      \"pmids\": [\"31545650\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SPEF2 is a structural component or regulatory factor at the central pair is unclear\", \"Direct SPEF2–HYDIN binding not demonstrated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Proteomic and interaction studies expanded the SPEF2 interactome to include RSPH9 and revealed that SPEF2 deficiency broadly reduces levels of flagellar assembly proteins, indicating SPEF2 acts upstream in flagellar protein homeostasis.\",\n      \"evidence\": \"Co-immunoprecipitation and proteomic analysis of human spermatozoa\",\n      \"pmids\": [\"34755699\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether reduced protein levels reflect transcriptional, transport, or stability defects is unknown\", \"RSPH9 interaction awaits in vivo validation\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The SPEF2–HYDIN dependency was confirmed in sperm flagella (extending the respiratory cilia finding), establishing that central pair integrity in both cilia and flagella requires coordinated SPEF2–HYDIN interaction.\",\n      \"evidence\": \"Immunofluorescence on sperm from HYDIN-mutant individuals\",\n      \"pmids\": [\"36873931\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct physical interaction between SPEF2 and HYDIN not biochemically confirmed\", \"Single study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of SPEF2 at the central pair, the molecular domains mediating its interactions with dynein 1 and HYDIN, the mechanism connecting SPEF2 to osteoblast differentiation, and whether short SPEF2 isoforms have distinct ciliary functions.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structural data for SPEF2 or its complexes\", \"Cilia-independent vs cilia-dependent roles in bone not delineated\", \"No reconstituted in vitro transport assay with purified SPEF2\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [8, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [1, 3, 4, 8]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [1, 4, 6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"IFT20\", \"GOLGA3\", \"RSPH9\", \"HYDIN\", \"DYNC1H1\"],\n    \"other_free_text\": []\n  }\n}\n```"}