{"gene":"ATRN","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":1998,"finding":"Attractin (DPPT-L/ATRN) is a 175 kDa serum glycoprotein secreted by activated T lymphocytes that mediates monocyte spreading and the clustering of non-proliferating T lymphocytes around those monocytes, establishing its role in modulating immune cell interactions.","method":"Protein cloning, functional cell adhesion/clustering assays with recombinant protein","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cloning plus functional cell-based assay demonstrating monocyte spreading and T cell clustering, single lab with two orthogonal methods","pmids":["9736737"],"is_preprint":false},{"year":1998,"finding":"Attractin protein contains a putative serine protease catalytic serine, four EGF-like motifs, a CUB domain, a C-type lectin domain, and a domain homologous to the ligand-binding region of the common gamma cytokine chain, defining its domain architecture.","method":"cDNA cloning and sequence analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 3 / Strong — sequence-based domain identification confirmed by cloning; replicated across multiple subsequent papers referencing this architecture","pmids":["9736737"],"is_preprint":false},{"year":1996,"finding":"The 175-kDa serum form of DPPT-L (ATRN) is antigenically and biochemically distinct from the 105-kDa CD26/DPPIV, yet possesses DPPIV enzymatic activity and functions as a co-stimulatory molecule for T-cell responses to recall antigen (tetanus toxoid).","method":"Biochemical characterization, enzymatic activity assay, T-cell co-stimulation functional assay","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — enzymatic activity assay plus functional T-cell costimulation assay, single lab with two orthogonal methods","pmids":["8596018"],"is_preprint":false},{"year":2000,"finding":"Soluble and membrane-bound isoforms of human ATRN arise from alternative splicing: the soluble form uses 25 sequential exons with a terminal LINE-1 retrotransposon-derived exon providing a stop codon and polyadenylation signal, while the membrane form splices over this LINE-1 exon to include five additional exons encoding transmembrane and cytoplasmic domains.","method":"Genomic structure determination, RT-PCR isoform quantification, sequence analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — genomic structure with exon mapping, RT-PCR confirmation of both isoforms, and demonstration of differential regulation in lymphoid tissues; multiple orthogonal methods in one study","pmids":["10811918"],"is_preprint":false},{"year":2000,"finding":"Activation of peripheral blood leukocytes with PHA induces strong surface expression of membrane ATRN followed by its release as soluble ATRN into the medium, establishing the sequential relationship between membrane and secreted isoforms during an inflammatory response.","method":"RT-PCR and functional secretion assay on PHA-activated leukocytes","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct secretion assay combined with isoform expression measurement, single lab two methods","pmids":["10811918"],"is_preprint":false},{"year":2001,"finding":"Loss-of-function mutations in the mouse Atrn (mahogany) gene cause severe spongiform vacuolization of the cerebrum, brainstem, granular layer of cerebellum, and spinal cord, establishing ATRN as required for CNS integrity independent of its coat-color and energy-metabolism roles.","method":"Genetic allelism tests, Northern blot (no Atrn expression), Southern blot (gene deletion), histopathological analysis of three independent Atrn mutant alleles","journal":"Journal of neuropathology and experimental neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — three independent loss-of-function alleles all showing spongiform changes, confirmed by Northern and Southern blot, multiple orthogonal methods","pmids":["11444801"],"is_preprint":false},{"year":2017,"finding":"A homozygous splice-site mutation (c.3068+5G>A) in ATRN causing intronic sequence insertion and premature termination results in hypomyelinating leukodystrophy in humans, confirming that ATRN plays a critical role in central nervous system myelination.","method":"Whole exome sequencing, cDNA analysis of aberrant splicing product in patient samples","journal":"Neurogenetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human loss-of-function confirmed by exome sequencing and cDNA analysis with clear clinical/neuroimaging phenotype, single family","pmids":["28493104"],"is_preprint":false},{"year":2017,"finding":"Zebrafish maternal Atrn depletion causes severe epiboly defects by impairing actomyosin contractile ring formation; Atrn was identified as a binding partner of the demethylase Alkbh4 by yeast two-hybrid assay, and Atrn preferentially interacts with the active form of Alkbh4 to cooperatively regulate actin demethylation and actomyosin formation.","method":"CRISPR/Cas9 maternal mutant generation, morpholino knockdown, immunofluorescence of actin/NMII, yeast two-hybrid interaction assay","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined morphogenetic phenotype plus yeast two-hybrid interaction and biochemical preference for active Alkbh4 form, single lab with multiple orthogonal methods","pmids":["28924386"],"is_preprint":false},{"year":2025,"finding":"Transmembrane ATRN (Attractin) functions as the cell-surface receptor for the bacterial exotoxin Nigritoxin (Ntx) from Vibrio, mediating toxin entry into cells; this ATRN-targeting entry domain is shared by at least two other toxins with unrelated effector domains (Rho-GTPase AMPylation and actin-targeting/proteolysis), establishing ATRN as a common entry receptor for a modular toxin family.","method":"Insect CRISPR screen identifying ATRN as required for toxin entry, functional toxin entry assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR screen plus functional validation across multiple toxins, preprint not yet peer-reviewed; single lab","pmids":["bio_10.1101_2025.10.08.681221"],"is_preprint":true},{"year":2025,"finding":"Transmembrane ATRN acts as an adapter that recruits the E3 ubiquitin ligase MGRN1 (via interaction with MGRN1's RING domain) to melanocortin receptors MC1R and MC4R, enabling MGRN1-dependent ubiquitination and degradation of these receptors at the cell surface; loss of MGRN1 increases surface/ciliary MC4R in fibroblasts and elevates MC1R levels in melanocytes, enhancing eumelanin production.","method":"Co-immunoprecipitation (ATRN–MGRN1 interaction), functional ubiquitination/degradation assays for MC1R and MC4R, receptor surface localization by imaging","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP for interaction plus functional receptor degradation assays and surface localization readout, multiple orthogonal methods in a single preprint lab study","pmids":["bio_10.1101_2025.03.25.645338"],"is_preprint":true}],"current_model":"ATRN (Attractin) is a multifunctional protein expressed as either a secreted or membrane-bound isoform via alternative splicing (regulated by a LINE-1 retrotransposon insertion); the secreted isoform is released by activated T lymphocytes and possesses DPPIV enzymatic activity while mediating monocyte spreading and T cell clustering, the membrane isoform acts as a transmembrane adapter that recruits the E3 ligase MGRN1 to target melanocortin receptors (MC1R, MC4R) for ubiquitination and degradation, and in the CNS ATRN is required for proper myelination—loss-of-function mutations in mice and humans cause severe hypomyelination and spongiform neurodegeneration—while in zebrafish it cooperates with the demethylase Alkbh4 to regulate actin demethylation and actomyosin contractile ring formation during embryonic epiboly, and transmembrane ATRN additionally serves as the cell-surface entry receptor for a family of bacterial exotoxins."},"narrative":{"mechanistic_narrative":"ATRN (Attractin) is a multidomain glycoprotein produced as functionally distinct secreted and membrane-bound isoforms whose roles span immune cell interaction, CNS myelination, and receptor regulation [PMID:10811918, PMID:11444801]. The two isoforms arise by alternative splicing: a soluble form terminating at a LINE-1 retrotransposon-derived exon, and a membrane form that splices over this exon to add transmembrane and cytoplasmic domains [PMID:10811918]; activated leukocytes first display the membrane isoform on the surface and then release the soluble form [PMID:10811918]. The secreted protein, a 175 kDa serum glycoprotein with DPPIV enzymatic activity, is released by activated T lymphocytes and drives monocyte spreading, T cell clustering, and co-stimulation of T-cell antigen responses [PMID:9736737, PMID:8596018]. The membrane isoform acts as a transmembrane adapter, recruiting the E3 ubiquitin ligase MGRN1 through MGRN1's RING domain to the melanocortin receptors MC1R and MC4R, enabling their ubiquitination and degradation [PMID:bio_10.1101_2025.03.25.645338]. Loss-of-function mutations establish ATRN as essential for CNS integrity: mouse mutants develop spongiform vacuolization across the brain and spinal cord [PMID:11444801], and a homozygous human splice-site mutation causes hypomyelinating leukodystrophy [PMID:28493104]. In zebrafish embryos, Atrn binds the demethylase Alkbh4 and is required for actomyosin contractile ring formation during epiboly [PMID:28924386], and transmembrane ATRN additionally serves as a shared cell-surface entry receptor for a modular family of bacterial exotoxins [PMID:bio_10.1101_2025.10.08.681221].","teleology":[{"year":1996,"claim":"Established that the serum 175-kDa DPPT-L species is distinct from CD26/DPPIV yet retains DPPIV enzymatic activity and co-stimulates T-cell responses, defining an immune-modulatory secreted protein.","evidence":"Biochemical characterization, enzymatic assay, and T-cell co-stimulation assay with recall antigen","pmids":["8596018"],"confidence":"Medium","gaps":["Catalytic mechanism and physiological substrates of the DPPIV activity not defined","Receptor/ligand mediating co-stimulation not identified"]},{"year":1998,"claim":"Cloning identified ATRN as a T-cell-secreted glycoprotein that mediates monocyte spreading and T cell clustering, and sequence analysis defined its multidomain architecture (protease serine, EGF, CUB, C-type lectin, gamma-chain-like motifs).","evidence":"Protein/cDNA cloning with cell adhesion/clustering functional assays and sequence-based domain mapping","pmids":["9736737"],"confidence":"Medium","gaps":["Binding partners mediating clustering not identified","Functional contributions of individual domains untested"]},{"year":2000,"claim":"Resolved how a single gene yields opposing forms by showing alternative splicing—gated by a LINE-1-derived exon—produces secreted versus membrane isoforms, with surface membrane ATRN preceding soluble release upon leukocyte activation.","evidence":"Genomic exon mapping, RT-PCR isoform quantification, and secretion assay on PHA-activated leukocytes","pmids":["10811918"],"confidence":"High","gaps":["Mechanism cleaving/releasing the soluble form from membrane ATRN not defined","Regulation of the splicing switch unknown"]},{"year":2001,"claim":"Demonstrated that ATRN is required for CNS integrity independent of its coat-color role, since loss-of-function mouse alleles produce spongiform neurodegeneration.","evidence":"Allelism tests, Northern/Southern blot, and histopathology of three independent mouse Atrn mutant alleles","pmids":["11444801"],"confidence":"High","gaps":["Molecular pathway linking ATRN loss to vacuolization not established","Cell type responsible not pinpointed"]},{"year":2017,"claim":"Confirmed in humans that ATRN loss-of-function causes hypomyelinating leukodystrophy, translating the mouse CNS phenotype to human disease.","evidence":"Whole exome sequencing and patient cDNA analysis of an aberrant splice product (c.3068+5G>A)","pmids":["28493104"],"confidence":"Medium","gaps":["Single family limits genotype-phenotype generalization","Mechanistic role of ATRN in myelin formation not defined"]},{"year":2017,"claim":"Identified a morphogenetic role by showing Atrn binds the demethylase Alkbh4 and is required for actomyosin contractile ring formation during embryonic epiboly.","evidence":"Zebrafish CRISPR maternal mutants and morpholino knockdown, actin/NMII immunofluorescence, and yeast two-hybrid interaction with preference for active Alkbh4","pmids":["28924386"],"confidence":"Medium","gaps":["Whether the Atrn-Alkbh4 axis operates in mammals or CNS unknown","Direct biochemical demethylation mechanism not reconstituted"]},{"year":2025,"claim":"Defined a mechanistic role for membrane ATRN as an adapter that recruits the E3 ligase MGRN1 to drive ubiquitination and degradation of melanocortin receptors MC1R and MC4R, controlling receptor surface levels.","evidence":"Co-IP of ATRN-MGRN1 (RING domain), receptor ubiquitination/degradation assays, and surface/ciliary receptor imaging (preprint)","pmids":["bio_10.1101_2025.03.25.645338"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Whether this pathway underlies the CNS or coat-color phenotypes not tested"]},{"year":2025,"claim":"Established transmembrane ATRN as a shared cell-surface entry receptor for a modular family of bacterial exotoxins with diverse effector domains.","evidence":"Insect CRISPR screen and functional toxin entry assays across multiple toxins (preprint)","pmids":["bio_10.1101_2025.10.08.681221"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","ATRN domain mediating toxin binding not mapped","Relevance to mammalian/human ATRN not confirmed"]},{"year":null,"claim":"How ATRN's distinct activities—immune adhesion, MGRN1-mediated receptor degradation, CNS myelination, and actomyosin regulation—are mechanistically connected through its domain architecture remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying molecular mechanism links the immune, neural, and receptor-regulation roles","Functional roles of individual ATRN domains untested","Mechanism by which ATRN loss causes hypomyelination undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[9]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[8]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[2]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3,4,9]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,2,3]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,2]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[9]}],"complexes":[],"partners":["MGRN1","MC1R","MC4R","ALKBH4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O75882","full_name":"Attractin","aliases":["DPPT-L","Mahogany homolog"],"length_aa":1429,"mass_kda":158.5,"function":"Involved in the initial immune cell clustering during inflammatory response and may regulate chemotactic activity of chemokines. May play a role in melanocortin signaling pathways that regulate energy homeostasis and hair color. Low-affinity receptor for agouti (By similarity). Has a critical role in normal myelination in the central nervous system (By similarity)","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/O75882/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ATRN","classification":"Not Classified","n_dependent_lines":31,"n_total_lines":1208,"dependency_fraction":0.02566225165562914},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"ANKRD46","stoichiometry":0.2},{"gene":"CANX","stoichiometry":0.2},{"gene":"HSP90B1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/ATRN","total_profiled":1310},"omim":[{"mim_id":"615197","title":"RESTLESS LEGS SYNDROME, SUSCEPTIBILITY TO, 8; RLS8","url":"https://www.omim.org/entry/615197"},{"mim_id":"612869","title":"ATTRACTIN-LIKE 1; ATRNL1","url":"https://www.omim.org/entry/612869"},{"mim_id":"607559","title":"MAHOGUNIN, RING FINGER 1; MGRN1","url":"https://www.omim.org/entry/607559"},{"mim_id":"606309","title":"PROTOCADHERIN-ALPHA 3; PCDHA3","url":"https://www.omim.org/entry/606309"},{"mim_id":"603130","title":"ATTRACTIN; ATRN","url":"https://www.omim.org/entry/603130"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ATRN"},"hgnc":{"alias_symbol":["DPPT-L","MGCA"],"prev_symbol":[]},"alphafold":{"accession":"O75882","domains":[{"cath_id":"2.60.120.290","chopping":"111-286","consensus_level":"medium","plddt":87.0114,"start":111,"end":286},{"cath_id":"2.10.25,2.10.25","chopping":"289-323","consensus_level":"medium","plddt":88.3166,"start":289,"end":323},{"cath_id":"2.60.120,2.60.120","chopping":"1160-1275","consensus_level":"high","plddt":81.6855,"start":1160,"end":1275}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75882","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75882-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75882-F1-predicted_aligned_error_v6.png","plddt_mean":78.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ATRN","jax_strain_url":"https://www.jax.org/strain/search?query=ATRN"},"sequence":{"accession":"O75882","fasta_url":"https://rest.uniprot.org/uniprotkb/O75882.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75882/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75882"}},"corpus_meta":[{"pmid":"9736737","id":"PMC_9736737","title":"Attractin (DPPT-L), a member of the CUB family of cell adhesion and guidance proteins, is secreted by activated human T lymphocytes and modulates immune cell interactions.","date":"1998","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/9736737","citation_count":132,"is_preprint":false},{"pmid":"21145440","id":"PMC_21145440","title":"Corrosion resistance and surface biocompatibility of a microarc oxidation coating on a Mg-Ca alloy.","date":"2010","source":"Acta biomaterialia","url":"https://pubmed.ncbi.nlm.nih.gov/21145440","citation_count":113,"is_preprint":false},{"pmid":"8596018","id":"PMC_8596018","title":"Serum high molecular weight dipeptidyl peptidase IV (CD26) is similar to a novel antigen DPPT-L released from activated T cells.","date":"1996","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/8596018","citation_count":74,"is_preprint":false},{"pmid":"10811918","id":"PMC_10811918","title":"Secreted and membrane attractin result from alternative splicing of the human ATRN gene.","date":"2000","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/10811918","citation_count":70,"is_preprint":false},{"pmid":"19966381","id":"PMC_19966381","title":"Influence of artificial biological fluid composition on the biocorrosion of potential orthopedic Mg-Ca, AZ31, AZ91 alloys.","date":"2009","source":"Biomedical materials (Bristol, England)","url":"https://pubmed.ncbi.nlm.nih.gov/19966381","citation_count":48,"is_preprint":false},{"pmid":"19815098","id":"PMC_19815098","title":"In vitro degradation and cytotoxicity of Mg/Ca composites produced by powder metallurgy.","date":"2009","source":"Acta biomaterialia","url":"https://pubmed.ncbi.nlm.nih.gov/19815098","citation_count":41,"is_preprint":false},{"pmid":"11444801","id":"PMC_11444801","title":"Mice with mutations in the mahogany gene Atrn have cerebral spongiform changes.","date":"2001","source":"Journal of neuropathology and experimental neurology","url":"https://pubmed.ncbi.nlm.nih.gov/11444801","citation_count":29,"is_preprint":false},{"pmid":"26459213","id":"PMC_26459213","title":"Anion inhibition studies of the dandruff-producing fungus Malassezia globosa β-carbonic anhydrase MgCA.","date":"2015","source":"Bioorganic & medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/26459213","citation_count":26,"is_preprint":false},{"pmid":"30026104","id":"PMC_30026104","title":"Characterization of unusual MgCa particles involved in the formation of foraminifera shells using a novel quantitative cryo SEM/EDS protocol.","date":"2018","source":"Acta biomaterialia","url":"https://pubmed.ncbi.nlm.nih.gov/30026104","citation_count":24,"is_preprint":false},{"pmid":"31546411","id":"PMC_31546411","title":"PEO coatings design for Mg-Ca alloy for cardiovascular stent and bone regeneration applications.","date":"2019","source":"Materials science & engineering. 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adapters","date":"2025-03-26","source":"bioRxiv","url":"https://doi.org/10.1101/2025.03.25.645338","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15146,"output_tokens":2612,"usd":0.042309,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9803,"output_tokens":3115,"usd":0.063445,"stage2_stop_reason":"end_turn"},"total_usd":0.105754,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"Attractin (DPPT-L/ATRN) is a 175 kDa serum glycoprotein secreted by activated T lymphocytes that mediates monocyte spreading and the clustering of non-proliferating T lymphocytes around those monocytes, establishing its role in modulating immune cell interactions.\",\n      \"method\": \"Protein cloning, functional cell adhesion/clustering assays with recombinant protein\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cloning plus functional cell-based assay demonstrating monocyte spreading and T cell clustering, single lab with two orthogonal methods\",\n      \"pmids\": [\"9736737\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Attractin protein contains a putative serine protease catalytic serine, four EGF-like motifs, a CUB domain, a C-type lectin domain, and a domain homologous to the ligand-binding region of the common gamma cytokine chain, defining its domain architecture.\",\n      \"method\": \"cDNA cloning and sequence analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Strong — sequence-based domain identification confirmed by cloning; replicated across multiple subsequent papers referencing this architecture\",\n      \"pmids\": [\"9736737\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The 175-kDa serum form of DPPT-L (ATRN) is antigenically and biochemically distinct from the 105-kDa CD26/DPPIV, yet possesses DPPIV enzymatic activity and functions as a co-stimulatory molecule for T-cell responses to recall antigen (tetanus toxoid).\",\n      \"method\": \"Biochemical characterization, enzymatic activity assay, T-cell co-stimulation functional assay\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — enzymatic activity assay plus functional T-cell costimulation assay, single lab with two orthogonal methods\",\n      \"pmids\": [\"8596018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Soluble and membrane-bound isoforms of human ATRN arise from alternative splicing: the soluble form uses 25 sequential exons with a terminal LINE-1 retrotransposon-derived exon providing a stop codon and polyadenylation signal, while the membrane form splices over this LINE-1 exon to include five additional exons encoding transmembrane and cytoplasmic domains.\",\n      \"method\": \"Genomic structure determination, RT-PCR isoform quantification, sequence analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — genomic structure with exon mapping, RT-PCR confirmation of both isoforms, and demonstration of differential regulation in lymphoid tissues; multiple orthogonal methods in one study\",\n      \"pmids\": [\"10811918\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Activation of peripheral blood leukocytes with PHA induces strong surface expression of membrane ATRN followed by its release as soluble ATRN into the medium, establishing the sequential relationship between membrane and secreted isoforms during an inflammatory response.\",\n      \"method\": \"RT-PCR and functional secretion assay on PHA-activated leukocytes\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct secretion assay combined with isoform expression measurement, single lab two methods\",\n      \"pmids\": [\"10811918\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Loss-of-function mutations in the mouse Atrn (mahogany) gene cause severe spongiform vacuolization of the cerebrum, brainstem, granular layer of cerebellum, and spinal cord, establishing ATRN as required for CNS integrity independent of its coat-color and energy-metabolism roles.\",\n      \"method\": \"Genetic allelism tests, Northern blot (no Atrn expression), Southern blot (gene deletion), histopathological analysis of three independent Atrn mutant alleles\",\n      \"journal\": \"Journal of neuropathology and experimental neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — three independent loss-of-function alleles all showing spongiform changes, confirmed by Northern and Southern blot, multiple orthogonal methods\",\n      \"pmids\": [\"11444801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A homozygous splice-site mutation (c.3068+5G>A) in ATRN causing intronic sequence insertion and premature termination results in hypomyelinating leukodystrophy in humans, confirming that ATRN plays a critical role in central nervous system myelination.\",\n      \"method\": \"Whole exome sequencing, cDNA analysis of aberrant splicing product in patient samples\",\n      \"journal\": \"Neurogenetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human loss-of-function confirmed by exome sequencing and cDNA analysis with clear clinical/neuroimaging phenotype, single family\",\n      \"pmids\": [\"28493104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Zebrafish maternal Atrn depletion causes severe epiboly defects by impairing actomyosin contractile ring formation; Atrn was identified as a binding partner of the demethylase Alkbh4 by yeast two-hybrid assay, and Atrn preferentially interacts with the active form of Alkbh4 to cooperatively regulate actin demethylation and actomyosin formation.\",\n      \"method\": \"CRISPR/Cas9 maternal mutant generation, morpholino knockdown, immunofluorescence of actin/NMII, yeast two-hybrid interaction assay\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined morphogenetic phenotype plus yeast two-hybrid interaction and biochemical preference for active Alkbh4 form, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"28924386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Transmembrane ATRN (Attractin) functions as the cell-surface receptor for the bacterial exotoxin Nigritoxin (Ntx) from Vibrio, mediating toxin entry into cells; this ATRN-targeting entry domain is shared by at least two other toxins with unrelated effector domains (Rho-GTPase AMPylation and actin-targeting/proteolysis), establishing ATRN as a common entry receptor for a modular toxin family.\",\n      \"method\": \"Insect CRISPR screen identifying ATRN as required for toxin entry, functional toxin entry assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR screen plus functional validation across multiple toxins, preprint not yet peer-reviewed; single lab\",\n      \"pmids\": [\"bio_10.1101_2025.10.08.681221\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Transmembrane ATRN acts as an adapter that recruits the E3 ubiquitin ligase MGRN1 (via interaction with MGRN1's RING domain) to melanocortin receptors MC1R and MC4R, enabling MGRN1-dependent ubiquitination and degradation of these receptors at the cell surface; loss of MGRN1 increases surface/ciliary MC4R in fibroblasts and elevates MC1R levels in melanocytes, enhancing eumelanin production.\",\n      \"method\": \"Co-immunoprecipitation (ATRN–MGRN1 interaction), functional ubiquitination/degradation assays for MC1R and MC4R, receptor surface localization by imaging\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP for interaction plus functional receptor degradation assays and surface localization readout, multiple orthogonal methods in a single preprint lab study\",\n      \"pmids\": [\"bio_10.1101_2025.03.25.645338\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"ATRN (Attractin) is a multifunctional protein expressed as either a secreted or membrane-bound isoform via alternative splicing (regulated by a LINE-1 retrotransposon insertion); the secreted isoform is released by activated T lymphocytes and possesses DPPIV enzymatic activity while mediating monocyte spreading and T cell clustering, the membrane isoform acts as a transmembrane adapter that recruits the E3 ligase MGRN1 to target melanocortin receptors (MC1R, MC4R) for ubiquitination and degradation, and in the CNS ATRN is required for proper myelination—loss-of-function mutations in mice and humans cause severe hypomyelination and spongiform neurodegeneration—while in zebrafish it cooperates with the demethylase Alkbh4 to regulate actin demethylation and actomyosin contractile ring formation during embryonic epiboly, and transmembrane ATRN additionally serves as the cell-surface entry receptor for a family of bacterial exotoxins.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ATRN (Attractin) is a multidomain glycoprotein produced as functionally distinct secreted and membrane-bound isoforms whose roles span immune cell interaction, CNS myelination, and receptor regulation [#3, #5]. The two isoforms arise by alternative splicing: a soluble form terminating at a LINE-1 retrotransposon-derived exon, and a membrane form that splices over this exon to add transmembrane and cytoplasmic domains [#3]; activated leukocytes first display the membrane isoform on the surface and then release the soluble form [#4]. The secreted protein, a 175 kDa serum glycoprotein with DPPIV enzymatic activity, is released by activated T lymphocytes and drives monocyte spreading, T cell clustering, and co-stimulation of T-cell antigen responses [#0, #2]. The membrane isoform acts as a transmembrane adapter, recruiting the E3 ubiquitin ligase MGRN1 through MGRN1's RING domain to the melanocortin receptors MC1R and MC4R, enabling their ubiquitination and degradation [#9]. Loss-of-function mutations establish ATRN as essential for CNS integrity: mouse mutants develop spongiform vacuolization across the brain and spinal cord [#5], and a homozygous human splice-site mutation causes hypomyelinating leukodystrophy [#6]. In zebrafish embryos, Atrn binds the demethylase Alkbh4 and is required for actomyosin contractile ring formation during epiboly [#7], and transmembrane ATRN additionally serves as a shared cell-surface entry receptor for a modular family of bacterial exotoxins [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established that the serum 175-kDa DPPT-L species is distinct from CD26/DPPIV yet retains DPPIV enzymatic activity and co-stimulates T-cell responses, defining an immune-modulatory secreted protein.\",\n      \"evidence\": \"Biochemical characterization, enzymatic assay, and T-cell co-stimulation assay with recall antigen\",\n      \"pmids\": [\"8596018\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Catalytic mechanism and physiological substrates of the DPPIV activity not defined\", \"Receptor/ligand mediating co-stimulation not identified\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Cloning identified ATRN as a T-cell-secreted glycoprotein that mediates monocyte spreading and T cell clustering, and sequence analysis defined its multidomain architecture (protease serine, EGF, CUB, C-type lectin, gamma-chain-like motifs).\",\n      \"evidence\": \"Protein/cDNA cloning with cell adhesion/clustering functional assays and sequence-based domain mapping\",\n      \"pmids\": [\"9736737\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Binding partners mediating clustering not identified\", \"Functional contributions of individual domains untested\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Resolved how a single gene yields opposing forms by showing alternative splicing—gated by a LINE-1-derived exon—produces secreted versus membrane isoforms, with surface membrane ATRN preceding soluble release upon leukocyte activation.\",\n      \"evidence\": \"Genomic exon mapping, RT-PCR isoform quantification, and secretion assay on PHA-activated leukocytes\",\n      \"pmids\": [\"10811918\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Mechanism cleaving/releasing the soluble form from membrane ATRN not defined\", \"Regulation of the splicing switch unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstrated that ATRN is required for CNS integrity independent of its coat-color role, since loss-of-function mouse alleles produce spongiform neurodegeneration.\",\n      \"evidence\": \"Allelism tests, Northern/Southern blot, and histopathology of three independent mouse Atrn mutant alleles\",\n      \"pmids\": [\"11444801\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Molecular pathway linking ATRN loss to vacuolization not established\", \"Cell type responsible not pinpointed\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Confirmed in humans that ATRN loss-of-function causes hypomyelinating leukodystrophy, translating the mouse CNS phenotype to human disease.\",\n      \"evidence\": \"Whole exome sequencing and patient cDNA analysis of an aberrant splice product (c.3068+5G>A)\",\n      \"pmids\": [\"28493104\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Single family limits genotype-phenotype generalization\", \"Mechanistic role of ATRN in myelin formation not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified a morphogenetic role by showing Atrn binds the demethylase Alkbh4 and is required for actomyosin contractile ring formation during embryonic epiboly.\",\n      \"evidence\": \"Zebrafish CRISPR maternal mutants and morpholino knockdown, actin/NMII immunofluorescence, and yeast two-hybrid interaction with preference for active Alkbh4\",\n      \"pmids\": [\"28924386\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Whether the Atrn-Alkbh4 axis operates in mammals or CNS unknown\", \"Direct biochemical demethylation mechanism not reconstituted\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined a mechanistic role for membrane ATRN as an adapter that recruits the E3 ligase MGRN1 to drive ubiquitination and degradation of melanocortin receptors MC1R and MC4R, controlling receptor surface levels.\",\n      \"evidence\": \"Co-IP of ATRN-MGRN1 (RING domain), receptor ubiquitination/degradation assays, and surface/ciliary receptor imaging (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.03.25.645338\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Whether this pathway underlies the CNS or coat-color phenotypes not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established transmembrane ATRN as a shared cell-surface entry receptor for a modular family of bacterial exotoxins with diverse effector domains.\",\n      \"evidence\": \"Insect CRISPR screen and functional toxin entry assays across multiple toxins (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.10.08.681221\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"ATRN domain mediating toxin binding not mapped\", \"Relevance to mammalian/human ATRN not confirmed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ATRN's distinct activities—immune adhesion, MGRN1-mediated receptor degradation, CNS myelination, and actomyosin regulation—are mechanistically connected through its domain architecture remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No unifying molecular mechanism links the immune, neural, and receptor-regulation roles\", \"Functional roles of individual ATRN domains untested\", \"Mechanism by which ATRN loss causes hypomyelination undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3, 4, 9]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 2, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"MGRN1\", \"MC1R\", \"MC4R\", \"ALKBH4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":5,"faith_pct":80.0}}