{"gene":"CD99L2","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2003,"finding":"CD99L2 was identified as a novel paralog of CD99, encoded on the X chromosome, and expressed ubiquitously with particularly high levels in neuronal cells as determined by in situ hybridization. Five putative functional regions were found to be highly conserved between CD99L2 and CD99 by amino acid sequence alignment.","method":"cDNA cloning, genomic organization analysis, in situ hybridization, comparative sequence analysis","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 3 — foundational cloning and expression characterization with direct in situ hybridization, single study","pmids":["12706889"],"is_preprint":false},{"year":2007,"finding":"CD99L2 is expressed at cell borders of transfected cells and on mouse leukocytes and vascular endothelial cells. Transfection of L cell fibroblasts with CD99L2 conferred homophilic cell adhesion in a divalent cation-dependent manner, and anti-CD99L2 antibody blocked neutrophil and monocyte influx into sites of inflammation in vivo.","method":"Transfection of L cell fibroblasts, cell aggregation assay, antibody blockade in vivo inflammation model","journal":"Cell communication & adhesion","confidence":"Medium","confidence_rationale":"Tier 2 — direct functional assay (transfection + aggregation) plus in vivo antibody blockade, single lab","pmids":["18163232"],"is_preprint":false},{"year":2010,"finding":"CD99 and CD99L2 act independently of PECAM-1 during leukocyte extravasation. Blocking CD99 or CD99L2 trapped neutrophils between endothelial cells and the underlying basement membrane in vivo, indicating that both molecules are required for leukocytes to overcome the endothelial basement membrane. CD99 and CD99L2 also cooperate independently of PECAM-1 in TNF-α-stimulated cremaster models.","method":"Blocking antibodies, PECAM-1 gene disruption, electron microscopy, 3D confocal fluorescence microscopy, in vivo cremaster and peritoneum inflammation models","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal in vivo methods (EM, 3D confocal, genetic KO + antibody blockade), replicated across inflammation models","pmids":["20479283"],"is_preprint":false},{"year":2013,"finding":"CD99L2 expression on endothelial cells (but not on myeloid cells) is required for neutrophil extravasation into inflamed tissues. Endothelial-specific conditional gene ablation of CD99L2 impaired neutrophil recruitment into inflamed cremaster and peritoneum and also impaired activated T cell recruitment into inflamed skin, demonstrating that CD99L2 functions as an endothelial molecule and does not require homophilic interaction with leukocyte-expressed CD99L2.","method":"Conditional gene-deficient mice (endothelial- and myeloid-specific Cre drivers), in vivo inflammation models (cremaster, peritoneum, skin)","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific conditional KO with defined cellular phenotype in multiple inflammation models, strong mechanistic placement","pmids":["23293350"],"is_preprint":false},{"year":2013,"finding":"Mouse CD99 physically interacts with CD99L2 through their cytoplasmic domains, forming heterodimers that are more efficiently localized at the plasma membrane than homodimers. CD99 promotes trafficking of CD99L2 to the plasma membrane; surface levels of CD99L2 were markedly reduced on thymocytes, splenic leukocytes, and CTL lines from CD99-deficient mice, and were rescued by reintroduction of wild-type but not cytoplasmic-domain-mutant CD99.","method":"Bimolecular fluorescence complementation, co-immunoprecipitation, FRET assay, flow cytometry, CD99-deficient mice, exogenous rescue with cytoplasmic domain mutants","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal interaction assays plus functional domain mutagenesis and genetic rescue in primary cells","pmids":["24133166"],"is_preprint":false},{"year":2013,"finding":"shRNA-mediated knockdown of mCD99L2 in murine B lymphoma (A20) cells resulted in decreased proliferation, G2 phase prolongation, altered morphology, and upregulation of NF-κB pathway activity, suggesting CD99L2 expression is linked to NF-κB signaling in B lymphoma cells.","method":"shRNA knockdown, MTT assay, flow cytometry, western blot, antibody arrays, NF-κB pathway analysis","journal":"Oncology reports","confidence":"Low","confidence_rationale":"Tier 3 — single lab, indirect pathway inference from western blot, no direct mechanistic link established","pmids":["23338758"],"is_preprint":false},{"year":2015,"finding":"CD99L2-knockout mice show greater than 80% reduction in neutrophil infiltration and near-complete block in monocyte emigration in the thioglycollate peritonitis model. CD99L2 deficiency did not affect circulating leukocyte numbers or expression of ICAM-1, PECAM-1, or CD99 on endothelial cells.","method":"Global CD99L2 knockout mice, thioglycollate peritonitis model, flow cytometry, immunohistochemistry","journal":"Experimental and molecular pathology","confidence":"High","confidence_rationale":"Tier 2 — independent KO mouse line confirming role in leukocyte extravasation with quantified phenotypic readouts","pmids":["26321243"],"is_preprint":false},{"year":2018,"finding":"Tie-2-Cre conditional deletion of CD99L2 inhibits leukocyte entry into the CNS during EAE, reducing perivascular cuffs, inflammatory foci, demyelination, and pro-inflammatory cytokine expression. 3D analysis revealed accumulation of leukocytes between endothelial cells and the basement membrane, with unaffected luminal docking, indicating CD99L2 mediates leukocyte diapedesis through the endothelial basement membrane at the blood-brain barrier.","method":"Conditional Tie-2-Cre knockout mice, EAE model, 3D confocal analysis of vibratome sections, electron microscopy","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with 3D localization of transmigration block and multiple phenotypic readouts in CNS inflammation model","pmids":["29791026"],"is_preprint":false},{"year":2022,"finding":"Human CD99L2 is constitutively expressed at endothelial cell borders and on leukocyte surfaces. Antibody blockade or genetic knockdown of CD99L2 significantly reduces transmigration of human neutrophils and monocytes across endothelial cells. CD99L2 acts at a specific, sequential step between PECAM and CD99 in transendothelial migration and promotes TEM by recruiting the lateral border recycling compartment (LBRC) to sites of TEM, specifically downstream of PECAM initiation.","method":"Antibody blockade, siRNA knockdown, in vitro transmigration assay with primary human cells, LBRC recruitment assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Ab blockade + genetic KD + LBRC recruitment assay) on primary human cells establishing sequential pathway position","pmids":["35914838"],"is_preprint":false},{"year":2022,"finding":"cd99l2 knockout in zebrafish (via TALEN) reduces recruitment of granulocytes and macrophages to wound sites. Expression of mfap4 was reduced in cd99l2 mutants, potentially contributing to impaired macrophage migration. Neutrophils and macrophages still used interstitial migration to reach wounds, implicating cd99l2 in leukocyte interstitial migration.","method":"TALEN-mediated knockout in zebrafish, caudal fin wounding assay, transgenic fluorescent reporter lines, RNA-seq","journal":"Yi chuan = Hereditas","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with direct imaging readout, but single study with limited mechanistic follow-up","pmids":["36384956"],"is_preprint":false},{"year":2023,"finding":"Porphyromonas gingivalis gingipains downregulate CD99 and CD99L2 expression on endothelial cells and leukocytes through inhibition of the PI3K/Akt pathway, impairing monocyte transendothelial migration despite promoting monocyte adhesion.","method":"In vitro endothelial cell infection assay, TEM assay, western blot, PI3K/Akt pathway inhibitor studies, in vivo mouse model","journal":"Microbiology spectrum","confidence":"Medium","confidence_rationale":"Tier 3 — pathway inhibitor used to infer mechanism, single lab, indirect evidence for PI3K/Akt involvement","pmids":["37199607"],"is_preprint":false},{"year":2025,"finding":"CD99L2 is expressed primarily in neurons and positively regulates neurite outgrowth and excitatory synapse development. CD99L2 inversely regulates immediate-early genes (Arc, Egr1, c-Fos) by inhibiting CREB and SRF transcription factor activity. Neuronal inactivation increases transport of CD99L2 to the cell surface from recycling endosomes. CD99L2 knockout mice exhibit impaired excitatory synaptic transmission and plasticity in the hippocampus, and deficits in spatial memory and contextual fear conditioning.","method":"CD99L2 KO mice, live imaging of recycling endosome trafficking, luciferase reporter assays (CREB/SRF activity), electrophysiology, behavioral tests, neurite outgrowth assays","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods including live imaging, electrophysiology, reporter assays, and behavioral KO phenotyping in a single study","pmids":["39808524"],"is_preprint":false},{"year":2026,"finding":"CD99L2 serves as an activating interactor of the calcium-dependent protease CAPN1. CD99L2 mainly exists in a ubiquitinated form. Ablation of cytoplasmic or extracellular domains of CD99L2 leads to intracellular mislocalization and abrogation of the CD99L2–CAPN1 interaction. Loss-of-function variants in CD99L2 cause X-linked spastic ataxia in humans, with transcriptome analysis in patient fibroblasts revealing synaptic function-specific disturbances.","method":"Exome/genome sequencing (patient cohort), cellular interaction studies (co-IP implied), domain deletion constructs with localization assay, transcriptome analysis in patient fibroblasts","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2–3 — human genetic evidence plus cellular domain-deletion experiments establishing CAPN1 interaction, but interaction methodology not fully detailed","pmids":["41690933"],"is_preprint":false},{"year":2026,"finding":"CD99L2 is transiently induced in primitive erythrocytes by shear stress-activated Piezo1 signaling. CD99L2 binds and anchors β-catenin at the plasma membrane, preventing its nuclear translocation. Loss of CD99L2 leads to aberrant nuclear translocation of β-catenin, activation of Rap1 signaling, and persistent adhesion molecule expression, causing erythrocyte retention and hemolytic anemia. This pathway is conserved in mice and modulated by biomechanical forces.","method":"Zebrafish and mouse models, Piezo1 signaling manipulation, co-immunoprecipitation/binding assays for β-catenin, β-catenin localization imaging, Rap1 signaling assays, loss-of-function models","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1–2 — direct binding assay for CD99L2–β-catenin, mechanistic epistasis (Piezo1→CD99L2→β-catenin/Rap1), replicated in two vertebrate models","pmids":["41915472"],"is_preprint":false}],"current_model":"CD99L2 is a type I transmembrane glycoprotein that functions as an adhesion and signaling molecule with distinct roles in multiple cell types: in endothelial cells, it acts at a specific sequential step (between PECAM-1 and CD99) to recruit the lateral border recycling compartment and mediate leukocyte diapedesis through the endothelial basement membrane; its surface trafficking is regulated by heterodimerization with CD99 via cytoplasmic domain interaction; in erythrocytes, it is induced by Piezo1/shear stress signaling and anchors β-catenin at the membrane to control de-adhesion; in neurons, it promotes excitatory synapse development and inhibits CREB/SRF-mediated immediate-early gene transcription from recycling endosomes; and in the nervous system it activates the protease CAPN1, with loss-of-function causing X-linked spastic ataxia."},"narrative":{"teleology":[{"year":2003,"claim":"Establishing CD99L2 as a distinct gene resolved whether the CD99 family had additional members, revealing an X-linked paralog with conserved functional regions and high neuronal expression.","evidence":"cDNA cloning, genomic organization, and in situ hybridization in mouse tissues","pmids":["12706889"],"confidence":"Medium","gaps":["No functional data; expression pattern alone does not establish mechanism","Protein-level validation not shown"]},{"year":2007,"claim":"Demonstrating that CD99L2 mediates homophilic adhesion and that its blockade inhibits inflammation established it as a functional adhesion molecule relevant to leukocyte recruitment.","evidence":"L cell fibroblast transfection/aggregation assay and anti-CD99L2 antibody blockade in vivo","pmids":["18163232"],"confidence":"Medium","gaps":["Single lab; homophilic versus heterophilic binding not fully distinguished","In vivo role could reflect indirect effects of antibody"]},{"year":2010,"claim":"Placing CD99L2 function at the endothelial basement membrane—independent of PECAM-1—resolved where in the multi-step extravasation cascade this molecule acts.","evidence":"Blocking antibodies combined with PECAM-1 KO, electron microscopy, and 3D confocal in murine cremaster and peritoneum models","pmids":["20479283"],"confidence":"High","gaps":["Molecular mechanism of basement membrane traversal not identified","Whether CD99L2 cooperates with or acts redundantly to CD99 at this step unclear"]},{"year":2013,"claim":"Cell-type-specific conditional deletion proved that endothelial—not leukocyte—CD99L2 is the functional pool for extravasation, overturning the homophilic adhesion model, while discovery of CD99–CD99L2 heterodimerization via cytoplasmic domains explained how CD99L2 surface levels are regulated.","evidence":"Endothelial- and myeloid-specific Cre KO mice in multiple inflammation models; BiFC, co-IP, FRET, and cytoplasmic domain mutant rescue in CD99-deficient primary cells","pmids":["23293350","24133166"],"confidence":"High","gaps":["Structural basis of cytoplasmic domain interaction unknown","Whether heterodimer has signaling functions beyond trafficking not tested"]},{"year":2015,"claim":"An independent global CD99L2 KO confirmed the extravasation phenotype with quantified reduction in both neutrophil and monocyte recruitment, strengthening confidence in the non-redundant role.","evidence":"Global CD99L2 knockout mice in thioglycollate peritonitis model with flow cytometry","pmids":["26321243"],"confidence":"High","gaps":["Mechanism downstream of CD99L2 engagement still unresolved","Lymphocyte-specific requirements not tested in this model"]},{"year":2018,"claim":"Extension to the blood–brain barrier showed CD99L2 controls leukocyte entry into the CNS during neuroinflammation, with 3D imaging confirming the same basement-membrane trapping phenotype observed peripherally.","evidence":"Tie-2-Cre conditional KO mice in EAE model with 3D confocal and electron microscopy","pmids":["29791026"],"confidence":"High","gaps":["Whether CD99L2 has additional barrier-specific functions beyond diapedesis not addressed","BBB integrity in the absence of inflammation not assessed"]},{"year":2022,"claim":"Translation to the human system established that CD99L2 recruits the lateral border recycling compartment and defined its precise sequential position between PECAM and CD99 during transendothelial migration.","evidence":"Antibody blockade and siRNA knockdown with LBRC recruitment assay on primary human endothelial cells and leukocytes","pmids":["35914838"],"confidence":"High","gaps":["Molecular mechanism by which CD99L2 recruits the LBRC is unknown","Signaling events coupling CD99L2 engagement to LBRC mobilization not identified"]},{"year":2025,"claim":"Discovery of neuronal functions—promoting excitatory synapse development and suppressing CREB/SRF-driven immediate-early gene transcription from recycling endosomes—revealed a cell-autonomous signaling role entirely distinct from the endothelial adhesion function.","evidence":"CD99L2 KO mice with electrophysiology, live imaging of recycling endosome trafficking, luciferase reporter assays, and behavioral phenotyping","pmids":["39808524"],"confidence":"High","gaps":["Signaling intermediates between CD99L2 and CREB/SRF not identified","Whether recycling endosome localization is required for transcriptional regulation not formally tested"]},{"year":2026,"claim":"Identification of CD99L2 as a CAPN1 activator and of loss-of-function variants causing X-linked spastic ataxia established a direct disease mechanism and linked the neuronal phenotype to a specific protease pathway.","evidence":"Exome/genome sequencing in patient families, domain-deletion constructs with localization and co-IP, transcriptome analysis in patient fibroblasts","pmids":["41690933"],"confidence":"Medium","gaps":["Interaction methodology for CAPN1 not fully detailed; awaits independent validation","Mechanism by which CD99L2 activates CAPN1 unknown","Whether CAPN1 activation accounts for synaptic phenotypes not directly tested"]},{"year":2026,"claim":"The erythrocyte pathway—Piezo1/shear stress → CD99L2 induction → β-catenin membrane anchoring → suppression of Rap1/adhesion—revealed a mechanosensitive de-adhesion function with loss causing hemolytic anemia.","evidence":"Zebrafish and mouse loss-of-function models, co-IP for β-catenin binding, β-catenin localization imaging, Piezo1 signaling manipulation","pmids":["41915472"],"confidence":"High","gaps":["Direct structural basis of CD99L2–β-catenin interaction not resolved","Whether this pathway operates in definitive erythropoiesis not established"]},{"year":null,"claim":"Key unresolved questions include the structural basis for CD99L2's diverse protein interactions (CD99, CAPN1, β-catenin), the signaling mechanism linking CD99L2 to LBRC recruitment during diapedesis, and how the same transmembrane protein exerts distinct functions across endothelial, neuronal, and erythroid contexts.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of CD99L2 or its complexes","Signal transduction downstream of CD99L2 engagement at endothelial junctions remains unmapped","Cell-type-specific regulatory mechanisms (transcriptional, post-translational) not systematically defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[1,2,3,6,8]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[11,12,13]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,4,8,13]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[11]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[2,3,6,7,8]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[1,2,8]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[11,12]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[11,13]}],"complexes":[],"partners":["CD99","CAPN1","CTNNB1","PECAM1"],"other_free_text":[]},"mechanistic_narrative":"CD99L2 is an X-linked type I transmembrane glycoprotein that functions as an adhesion and signaling molecule with cell-type-specific roles in leukocyte transendothelial migration, erythrocyte de-adhesion, and neuronal synapse development. In endothelial cells, CD99L2 mediates a discrete sequential step between PECAM-1 and CD99 during leukocyte diapedesis by recruiting the lateral border recycling compartment to transmigration sites, and its endothelial expression—rather than leukocyte expression—is required for neutrophil, monocyte, and T cell passage through the basement membrane [PMID:20479283, PMID:23293350, PMID:35914838]. In neurons, CD99L2 promotes excitatory synapse development and neurite outgrowth while suppressing CREB/SRF-dependent immediate-early gene transcription from recycling endosomes, and it activates the protease CAPN1—with loss-of-function variants in CD99L2 causing X-linked spastic ataxia in humans [PMID:39808524, PMID:41690933]. In primitive erythrocytes, CD99L2 is induced by Piezo1/shear stress signaling and anchors β-catenin at the plasma membrane to prevent Rap1-driven adhesion molecule expression, with its loss causing erythrocyte retention and hemolytic anemia [PMID:41915472]."},"prefetch_data":{"uniprot":{"accession":"Q8TCZ2","full_name":"CD99 antigen-like protein 2","aliases":["MIC2-like protein 1"],"length_aa":262,"mass_kda":28.0,"function":"Plays a role in a late step of leukocyte extravasation helping cells to overcome the endothelial basement membrane. Acts at the same site as, but independently of, PECAM1 (By similarity). Homophilic adhesion molecule, but these interactions may not be required for cell aggregation (By similarity)","subcellular_location":"Cell membrane; Cell junction; Secreted","url":"https://www.uniprot.org/uniprotkb/Q8TCZ2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CD99L2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CD99L2","total_profiled":1310},"omim":[{"mim_id":"313470","title":"CD99 ANTIGEN, X CHROMOSOME; CD99","url":"https://www.omim.org/entry/313470"},{"mim_id":"300846","title":"CD99 ANTIGEN-LIKE 2; CD99L2","url":"https://www.omim.org/entry/300846"},{"mim_id":"173445","title":"PLATELET-ENDOTHELIAL CELL ADHESION MOLECULE 1; PECAM1","url":"https://www.omim.org/entry/173445"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"skeletal muscle","ntpm":170.4}],"url":"https://www.proteinatlas.org/search/CD99L2"},"hgnc":{"alias_symbol":["CD99B"],"prev_symbol":["MIC2L1"]},"alphafold":{"accession":"Q8TCZ2","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TCZ2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TCZ2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TCZ2-F1-predicted_aligned_error_v6.png","plddt_mean":56.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CD99L2","jax_strain_url":"https://www.jax.org/strain/search?query=CD99L2"},"sequence":{"accession":"Q8TCZ2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8TCZ2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8TCZ2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TCZ2"}},"corpus_meta":[{"pmid":"20479283","id":"PMC_20479283","title":"CD99 and CD99L2 act at the same site as, but independently of, PECAM-1 during leukocyte diapedesis.","date":"2010","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/20479283","citation_count":70,"is_preprint":false},{"pmid":"12706889","id":"PMC_12706889","title":"Cloning, genomic organization, alternative transcripts and expression analysis of CD99L2, a novel paralog of human CD99, and identification of evolutionary conserved motifs.","date":"2003","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/12706889","citation_count":51,"is_preprint":false},{"pmid":"18163232","id":"PMC_18163232","title":"The murine CD99-related molecule CD99-like 2 (CD99L2) is an adhesion molecule involved in the inflammatory response.","date":"2007","source":"Cell communication & adhesion","url":"https://pubmed.ncbi.nlm.nih.gov/18163232","citation_count":41,"is_preprint":false},{"pmid":"22681640","id":"PMC_22681640","title":"Immune function genes CD99L2, JARID2 and TPO show association with autism spectrum disorder.","date":"2012","source":"Molecular autism","url":"https://pubmed.ncbi.nlm.nih.gov/22681640","citation_count":34,"is_preprint":false},{"pmid":"23293350","id":"PMC_23293350","title":"Cutting edge: Endothelial-specific gene ablation of CD99L2 impairs leukocyte extravasation in vivo.","date":"2013","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/23293350","citation_count":26,"is_preprint":false},{"pmid":"37199607","id":"PMC_37199607","title":"Porphyromonas gingivalis Gingipains Destroy the Vascular Barrier and Reduce CD99 and CD99L2 Expression To Regulate Transendothelial Migration.","date":"2023","source":"Microbiology spectrum","url":"https://pubmed.ncbi.nlm.nih.gov/37199607","citation_count":13,"is_preprint":false},{"pmid":"24133166","id":"PMC_24133166","title":"Interaction of CD99 with its paralog CD99L2 positively regulates CD99L2 trafficking to cell surfaces.","date":"2013","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/24133166","citation_count":11,"is_preprint":false},{"pmid":"29791026","id":"PMC_29791026","title":"CD99L2 deficiency inhibits leukocyte entry into the central nervous system and ameliorates neuroinflammation.","date":"2018","source":"Journal of leukocyte biology","url":"https://pubmed.ncbi.nlm.nih.gov/29791026","citation_count":11,"is_preprint":false},{"pmid":"26321243","id":"PMC_26321243","title":"CD99-like 2 (CD99L2)-deficient mice are defective in the acute inflammatory response.","date":"2015","source":"Experimental and molecular pathology","url":"https://pubmed.ncbi.nlm.nih.gov/26321243","citation_count":7,"is_preprint":false},{"pmid":"23338758","id":"PMC_23338758","title":"Effect of shRNA targeting mouse CD99L2 gene in a murine B cell lymphoma in vitro and in vivo.","date":"2013","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/23338758","citation_count":6,"is_preprint":false},{"pmid":"35914838","id":"PMC_35914838","title":"Human CD99L2 Regulates a Unique Step in Leukocyte Transmigration.","date":"2022","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/35914838","citation_count":4,"is_preprint":false},{"pmid":"39808524","id":"PMC_39808524","title":"Cd99l2 regulates excitatory synapse development and restrains immediate-early gene activation.","date":"2025","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/39808524","citation_count":3,"is_preprint":false},{"pmid":"41690933","id":"PMC_41690933","title":"Loss-of-function variants in the CAPN1 activator CD99L2 cause X-linked spastic ataxia.","date":"2026","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/41690933","citation_count":0,"is_preprint":false},{"pmid":"36384956","id":"PMC_36384956","title":"The role of the cd99l2 gene on leukocyte interstitial migration in zebrafish.","date":"2022","source":"Yi chuan = Hereditas","url":"https://pubmed.ncbi.nlm.nih.gov/36384956","citation_count":0,"is_preprint":false},{"pmid":"20501370","id":"PMC_20501370","title":"[Preparation of RNA probe for cd99l2 gene of zebrafish labeled with digoxingenin-UTP].","date":"2010","source":"Nan fang yi ke da xue xue bao = Journal of Southern Medical University","url":"https://pubmed.ncbi.nlm.nih.gov/20501370","citation_count":0,"is_preprint":false},{"pmid":"41915472","id":"PMC_41915472","title":"Shear stress-induced Piezo1 activates CD99L2 to facilitate the initiation of blood circulation.","date":"2026","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/41915472","citation_count":0,"is_preprint":false},{"pmid":"40692150","id":"PMC_40692150","title":"Loss of CD99L2 Contributed to Temozolomide Resistance and Glioblastoma Tumorigenesis Based on Genome-scale CRISPR/Cas9 Screening.","date":"2026","source":"Current pharmaceutical design","url":"https://pubmed.ncbi.nlm.nih.gov/40692150","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9454,"output_tokens":3772,"usd":0.042471},"stage2":{"model":"claude-opus-4-6","input_tokens":7212,"output_tokens":2645,"usd":0.153278},"total_usd":0.195749,"stage1_batch_id":"msgbatch_011kfMfE81o6CTcyhVUqumuW","stage2_batch_id":"msgbatch_01DTputS6WNkH745x1nVSoBo","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"CD99L2 was identified as a novel paralog of CD99, encoded on the X chromosome, and expressed ubiquitously with particularly high levels in neuronal cells as determined by in situ hybridization. Five putative functional regions were found to be highly conserved between CD99L2 and CD99 by amino acid sequence alignment.\",\n      \"method\": \"cDNA cloning, genomic organization analysis, in situ hybridization, comparative sequence analysis\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — foundational cloning and expression characterization with direct in situ hybridization, single study\",\n      \"pmids\": [\"12706889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CD99L2 is expressed at cell borders of transfected cells and on mouse leukocytes and vascular endothelial cells. Transfection of L cell fibroblasts with CD99L2 conferred homophilic cell adhesion in a divalent cation-dependent manner, and anti-CD99L2 antibody blocked neutrophil and monocyte influx into sites of inflammation in vivo.\",\n      \"method\": \"Transfection of L cell fibroblasts, cell aggregation assay, antibody blockade in vivo inflammation model\",\n      \"journal\": \"Cell communication & adhesion\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct functional assay (transfection + aggregation) plus in vivo antibody blockade, single lab\",\n      \"pmids\": [\"18163232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CD99 and CD99L2 act independently of PECAM-1 during leukocyte extravasation. Blocking CD99 or CD99L2 trapped neutrophils between endothelial cells and the underlying basement membrane in vivo, indicating that both molecules are required for leukocytes to overcome the endothelial basement membrane. CD99 and CD99L2 also cooperate independently of PECAM-1 in TNF-α-stimulated cremaster models.\",\n      \"method\": \"Blocking antibodies, PECAM-1 gene disruption, electron microscopy, 3D confocal fluorescence microscopy, in vivo cremaster and peritoneum inflammation models\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal in vivo methods (EM, 3D confocal, genetic KO + antibody blockade), replicated across inflammation models\",\n      \"pmids\": [\"20479283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CD99L2 expression on endothelial cells (but not on myeloid cells) is required for neutrophil extravasation into inflamed tissues. Endothelial-specific conditional gene ablation of CD99L2 impaired neutrophil recruitment into inflamed cremaster and peritoneum and also impaired activated T cell recruitment into inflamed skin, demonstrating that CD99L2 functions as an endothelial molecule and does not require homophilic interaction with leukocyte-expressed CD99L2.\",\n      \"method\": \"Conditional gene-deficient mice (endothelial- and myeloid-specific Cre drivers), in vivo inflammation models (cremaster, peritoneum, skin)\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific conditional KO with defined cellular phenotype in multiple inflammation models, strong mechanistic placement\",\n      \"pmids\": [\"23293350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Mouse CD99 physically interacts with CD99L2 through their cytoplasmic domains, forming heterodimers that are more efficiently localized at the plasma membrane than homodimers. CD99 promotes trafficking of CD99L2 to the plasma membrane; surface levels of CD99L2 were markedly reduced on thymocytes, splenic leukocytes, and CTL lines from CD99-deficient mice, and were rescued by reintroduction of wild-type but not cytoplasmic-domain-mutant CD99.\",\n      \"method\": \"Bimolecular fluorescence complementation, co-immunoprecipitation, FRET assay, flow cytometry, CD99-deficient mice, exogenous rescue with cytoplasmic domain mutants\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal interaction assays plus functional domain mutagenesis and genetic rescue in primary cells\",\n      \"pmids\": [\"24133166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"shRNA-mediated knockdown of mCD99L2 in murine B lymphoma (A20) cells resulted in decreased proliferation, G2 phase prolongation, altered morphology, and upregulation of NF-κB pathway activity, suggesting CD99L2 expression is linked to NF-κB signaling in B lymphoma cells.\",\n      \"method\": \"shRNA knockdown, MTT assay, flow cytometry, western blot, antibody arrays, NF-κB pathway analysis\",\n      \"journal\": \"Oncology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, indirect pathway inference from western blot, no direct mechanistic link established\",\n      \"pmids\": [\"23338758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CD99L2-knockout mice show greater than 80% reduction in neutrophil infiltration and near-complete block in monocyte emigration in the thioglycollate peritonitis model. CD99L2 deficiency did not affect circulating leukocyte numbers or expression of ICAM-1, PECAM-1, or CD99 on endothelial cells.\",\n      \"method\": \"Global CD99L2 knockout mice, thioglycollate peritonitis model, flow cytometry, immunohistochemistry\",\n      \"journal\": \"Experimental and molecular pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — independent KO mouse line confirming role in leukocyte extravasation with quantified phenotypic readouts\",\n      \"pmids\": [\"26321243\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Tie-2-Cre conditional deletion of CD99L2 inhibits leukocyte entry into the CNS during EAE, reducing perivascular cuffs, inflammatory foci, demyelination, and pro-inflammatory cytokine expression. 3D analysis revealed accumulation of leukocytes between endothelial cells and the basement membrane, with unaffected luminal docking, indicating CD99L2 mediates leukocyte diapedesis through the endothelial basement membrane at the blood-brain barrier.\",\n      \"method\": \"Conditional Tie-2-Cre knockout mice, EAE model, 3D confocal analysis of vibratome sections, electron microscopy\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with 3D localization of transmigration block and multiple phenotypic readouts in CNS inflammation model\",\n      \"pmids\": [\"29791026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Human CD99L2 is constitutively expressed at endothelial cell borders and on leukocyte surfaces. Antibody blockade or genetic knockdown of CD99L2 significantly reduces transmigration of human neutrophils and monocytes across endothelial cells. CD99L2 acts at a specific, sequential step between PECAM and CD99 in transendothelial migration and promotes TEM by recruiting the lateral border recycling compartment (LBRC) to sites of TEM, specifically downstream of PECAM initiation.\",\n      \"method\": \"Antibody blockade, siRNA knockdown, in vitro transmigration assay with primary human cells, LBRC recruitment assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Ab blockade + genetic KD + LBRC recruitment assay) on primary human cells establishing sequential pathway position\",\n      \"pmids\": [\"35914838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"cd99l2 knockout in zebrafish (via TALEN) reduces recruitment of granulocytes and macrophages to wound sites. Expression of mfap4 was reduced in cd99l2 mutants, potentially contributing to impaired macrophage migration. Neutrophils and macrophages still used interstitial migration to reach wounds, implicating cd99l2 in leukocyte interstitial migration.\",\n      \"method\": \"TALEN-mediated knockout in zebrafish, caudal fin wounding assay, transgenic fluorescent reporter lines, RNA-seq\",\n      \"journal\": \"Yi chuan = Hereditas\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with direct imaging readout, but single study with limited mechanistic follow-up\",\n      \"pmids\": [\"36384956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Porphyromonas gingivalis gingipains downregulate CD99 and CD99L2 expression on endothelial cells and leukocytes through inhibition of the PI3K/Akt pathway, impairing monocyte transendothelial migration despite promoting monocyte adhesion.\",\n      \"method\": \"In vitro endothelial cell infection assay, TEM assay, western blot, PI3K/Akt pathway inhibitor studies, in vivo mouse model\",\n      \"journal\": \"Microbiology spectrum\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — pathway inhibitor used to infer mechanism, single lab, indirect evidence for PI3K/Akt involvement\",\n      \"pmids\": [\"37199607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CD99L2 is expressed primarily in neurons and positively regulates neurite outgrowth and excitatory synapse development. CD99L2 inversely regulates immediate-early genes (Arc, Egr1, c-Fos) by inhibiting CREB and SRF transcription factor activity. Neuronal inactivation increases transport of CD99L2 to the cell surface from recycling endosomes. CD99L2 knockout mice exhibit impaired excitatory synaptic transmission and plasticity in the hippocampus, and deficits in spatial memory and contextual fear conditioning.\",\n      \"method\": \"CD99L2 KO mice, live imaging of recycling endosome trafficking, luciferase reporter assays (CREB/SRF activity), electrophysiology, behavioral tests, neurite outgrowth assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including live imaging, electrophysiology, reporter assays, and behavioral KO phenotyping in a single study\",\n      \"pmids\": [\"39808524\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"CD99L2 serves as an activating interactor of the calcium-dependent protease CAPN1. CD99L2 mainly exists in a ubiquitinated form. Ablation of cytoplasmic or extracellular domains of CD99L2 leads to intracellular mislocalization and abrogation of the CD99L2–CAPN1 interaction. Loss-of-function variants in CD99L2 cause X-linked spastic ataxia in humans, with transcriptome analysis in patient fibroblasts revealing synaptic function-specific disturbances.\",\n      \"method\": \"Exome/genome sequencing (patient cohort), cellular interaction studies (co-IP implied), domain deletion constructs with localization assay, transcriptome analysis in patient fibroblasts\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — human genetic evidence plus cellular domain-deletion experiments establishing CAPN1 interaction, but interaction methodology not fully detailed\",\n      \"pmids\": [\"41690933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"CD99L2 is transiently induced in primitive erythrocytes by shear stress-activated Piezo1 signaling. CD99L2 binds and anchors β-catenin at the plasma membrane, preventing its nuclear translocation. Loss of CD99L2 leads to aberrant nuclear translocation of β-catenin, activation of Rap1 signaling, and persistent adhesion molecule expression, causing erythrocyte retention and hemolytic anemia. This pathway is conserved in mice and modulated by biomechanical forces.\",\n      \"method\": \"Zebrafish and mouse models, Piezo1 signaling manipulation, co-immunoprecipitation/binding assays for β-catenin, β-catenin localization imaging, Rap1 signaling assays, loss-of-function models\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct binding assay for CD99L2–β-catenin, mechanistic epistasis (Piezo1→CD99L2→β-catenin/Rap1), replicated in two vertebrate models\",\n      \"pmids\": [\"41915472\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD99L2 is a type I transmembrane glycoprotein that functions as an adhesion and signaling molecule with distinct roles in multiple cell types: in endothelial cells, it acts at a specific sequential step (between PECAM-1 and CD99) to recruit the lateral border recycling compartment and mediate leukocyte diapedesis through the endothelial basement membrane; its surface trafficking is regulated by heterodimerization with CD99 via cytoplasmic domain interaction; in erythrocytes, it is induced by Piezo1/shear stress signaling and anchors β-catenin at the membrane to control de-adhesion; in neurons, it promotes excitatory synapse development and inhibits CREB/SRF-mediated immediate-early gene transcription from recycling endosomes; and in the nervous system it activates the protease CAPN1, with loss-of-function causing X-linked spastic ataxia.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CD99L2 is an X-linked type I transmembrane glycoprotein that functions as an adhesion and signaling molecule with cell-type-specific roles in leukocyte transendothelial migration, erythrocyte de-adhesion, and neuronal synapse development. In endothelial cells, CD99L2 mediates a discrete sequential step between PECAM-1 and CD99 during leukocyte diapedesis by recruiting the lateral border recycling compartment to transmigration sites, and its endothelial expression—rather than leukocyte expression—is required for neutrophil, monocyte, and T cell passage through the basement membrane [PMID:20479283, PMID:23293350, PMID:35914838]. In neurons, CD99L2 promotes excitatory synapse development and neurite outgrowth while suppressing CREB/SRF-dependent immediate-early gene transcription from recycling endosomes, and it activates the protease CAPN1—with loss-of-function variants in CD99L2 causing X-linked spastic ataxia in humans [PMID:39808524, PMID:41690933]. In primitive erythrocytes, CD99L2 is induced by Piezo1/shear stress signaling and anchors β-catenin at the plasma membrane to prevent Rap1-driven adhesion molecule expression, with its loss causing erythrocyte retention and hemolytic anemia [PMID:41915472].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Establishing CD99L2 as a distinct gene resolved whether the CD99 family had additional members, revealing an X-linked paralog with conserved functional regions and high neuronal expression.\",\n      \"evidence\": \"cDNA cloning, genomic organization, and in situ hybridization in mouse tissues\",\n      \"pmids\": [\"12706889\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional data; expression pattern alone does not establish mechanism\", \"Protein-level validation not shown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrating that CD99L2 mediates homophilic adhesion and that its blockade inhibits inflammation established it as a functional adhesion molecule relevant to leukocyte recruitment.\",\n      \"evidence\": \"L cell fibroblast transfection/aggregation assay and anti-CD99L2 antibody blockade in vivo\",\n      \"pmids\": [\"18163232\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; homophilic versus heterophilic binding not fully distinguished\", \"In vivo role could reflect indirect effects of antibody\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Placing CD99L2 function at the endothelial basement membrane—independent of PECAM-1—resolved where in the multi-step extravasation cascade this molecule acts.\",\n      \"evidence\": \"Blocking antibodies combined with PECAM-1 KO, electron microscopy, and 3D confocal in murine cremaster and peritoneum models\",\n      \"pmids\": [\"20479283\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of basement membrane traversal not identified\", \"Whether CD99L2 cooperates with or acts redundantly to CD99 at this step unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Cell-type-specific conditional deletion proved that endothelial—not leukocyte—CD99L2 is the functional pool for extravasation, overturning the homophilic adhesion model, while discovery of CD99–CD99L2 heterodimerization via cytoplasmic domains explained how CD99L2 surface levels are regulated.\",\n      \"evidence\": \"Endothelial- and myeloid-specific Cre KO mice in multiple inflammation models; BiFC, co-IP, FRET, and cytoplasmic domain mutant rescue in CD99-deficient primary cells\",\n      \"pmids\": [\"23293350\", \"24133166\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of cytoplasmic domain interaction unknown\", \"Whether heterodimer has signaling functions beyond trafficking not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"An independent global CD99L2 KO confirmed the extravasation phenotype with quantified reduction in both neutrophil and monocyte recruitment, strengthening confidence in the non-redundant role.\",\n      \"evidence\": \"Global CD99L2 knockout mice in thioglycollate peritonitis model with flow cytometry\",\n      \"pmids\": [\"26321243\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism downstream of CD99L2 engagement still unresolved\", \"Lymphocyte-specific requirements not tested in this model\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Extension to the blood–brain barrier showed CD99L2 controls leukocyte entry into the CNS during neuroinflammation, with 3D imaging confirming the same basement-membrane trapping phenotype observed peripherally.\",\n      \"evidence\": \"Tie-2-Cre conditional KO mice in EAE model with 3D confocal and electron microscopy\",\n      \"pmids\": [\"29791026\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CD99L2 has additional barrier-specific functions beyond diapedesis not addressed\", \"BBB integrity in the absence of inflammation not assessed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Translation to the human system established that CD99L2 recruits the lateral border recycling compartment and defined its precise sequential position between PECAM and CD99 during transendothelial migration.\",\n      \"evidence\": \"Antibody blockade and siRNA knockdown with LBRC recruitment assay on primary human endothelial cells and leukocytes\",\n      \"pmids\": [\"35914838\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which CD99L2 recruits the LBRC is unknown\", \"Signaling events coupling CD99L2 engagement to LBRC mobilization not identified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Discovery of neuronal functions—promoting excitatory synapse development and suppressing CREB/SRF-driven immediate-early gene transcription from recycling endosomes—revealed a cell-autonomous signaling role entirely distinct from the endothelial adhesion function.\",\n      \"evidence\": \"CD99L2 KO mice with electrophysiology, live imaging of recycling endosome trafficking, luciferase reporter assays, and behavioral phenotyping\",\n      \"pmids\": [\"39808524\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling intermediates between CD99L2 and CREB/SRF not identified\", \"Whether recycling endosome localization is required for transcriptional regulation not formally tested\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identification of CD99L2 as a CAPN1 activator and of loss-of-function variants causing X-linked spastic ataxia established a direct disease mechanism and linked the neuronal phenotype to a specific protease pathway.\",\n      \"evidence\": \"Exome/genome sequencing in patient families, domain-deletion constructs with localization and co-IP, transcriptome analysis in patient fibroblasts\",\n      \"pmids\": [\"41690933\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Interaction methodology for CAPN1 not fully detailed; awaits independent validation\", \"Mechanism by which CD99L2 activates CAPN1 unknown\", \"Whether CAPN1 activation accounts for synaptic phenotypes not directly tested\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"The erythrocyte pathway—Piezo1/shear stress → CD99L2 induction → β-catenin membrane anchoring → suppression of Rap1/adhesion—revealed a mechanosensitive de-adhesion function with loss causing hemolytic anemia.\",\n      \"evidence\": \"Zebrafish and mouse loss-of-function models, co-IP for β-catenin binding, β-catenin localization imaging, Piezo1 signaling manipulation\",\n      \"pmids\": [\"41915472\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct structural basis of CD99L2–β-catenin interaction not resolved\", \"Whether this pathway operates in definitive erythropoiesis not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for CD99L2's diverse protein interactions (CD99, CAPN1, β-catenin), the signaling mechanism linking CD99L2 to LBRC recruitment during diapedesis, and how the same transmembrane protein exerts distinct functions across endothelial, neuronal, and erythroid contexts.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of CD99L2 or its complexes\", \"Signal transduction downstream of CD99L2 engagement at endothelial junctions remains unmapped\", \"Cell-type-specific regulatory mechanisms (transcriptional, post-translational) not systematically defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [1, 2, 3, 6, 8]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [11, 12, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 4, 8, 13]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [2, 3, 6, 7, 8]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [1, 2, 8]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [11, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [11, 13]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CD99\",\n      \"CAPN1\",\n      \"CTNNB1\",\n      \"PECAM1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}