{"gene":"GDF1","run_date":"2026-04-28T18:06:52","timeline":{"discoveries":[{"year":1990,"finding":"GDF1 was identified as a new member of the TGF-beta superfamily, predicted to be a secreted glycoprotein with a dibasic proteolytic cleavage site. In vitro translation experiments confirmed it is a secreted glycoprotein, and its C-terminus shares the invariant cysteines characteristic of TGF-beta family members.","method":"cDNA cloning, sequence analysis, in vitro translation","journal":"Molecular endocrinology","confidence":"Medium","confidence_rationale":"Tier 1-2 — original biochemical characterization, single lab","pmids":["1704486"],"is_preprint":false},{"year":2000,"finding":"Native GDF1 is not proteolytically processed and therefore inactive, but a chimeric protein containing a heterologous prodomain (BMP2 prodomain fused to GDF1 mature domain) is efficiently processed and signals via Smad2 to induce mesendoderm and axial duplication in Xenopus. Mature GDF1 is sufficient to reverse the left-right axis.","method":"Chimeric protein expression in Xenopus embryos, Smad2 signaling assay, loss-of-function and gain-of-function in vivo","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (chimeric constructs, Smad2 reporter, phenotypic rescue), replicated in later studies","pmids":["11071769"],"is_preprint":false},{"year":2003,"finding":"GDF1 signaling requires EGF-CFC coreceptors and is mediated through Activin receptors. GDF1 binds to and signals through Activin receptors only in the presence of EGF-CFC proteins in Xenopus, establishing that GDF1 converges on Activin receptor/EGF-CFC complexes.","method":"Binding assay, signaling reconstitution in Xenopus, zebrafish epistasis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1-2 — direct binding and signaling reconstitution, replicated in two model organisms, high citation count","pmids":["12514096"],"is_preprint":false},{"year":2006,"finding":"GDF1 signals through type I receptor ALK4 (and ALK7) in receptor reconstitution experiments. Genetic epistasis using compound mutants showed that ALK4, but not ALK7, is responsible for the effects of GDF1 and Nodal during anterior axis development. GDF1 and Nodal converge on ALK4 in the anterior primitive streak.","method":"Receptor reconstitution, compound mutant genetic epistasis, in vivo phenotypic analysis","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 1-2 — receptor reconstitution combined with genetic epistasis, multiple orthogonal methods","pmids":["16564040"],"is_preprint":false},{"year":2007,"finding":"GDF1 functions as a coligand for Nodal rather than as an independent ligand. GDF1 directly interacts with Nodal and greatly increases its specific activity and signaling range. GDF1 is required for long-range Nodal signaling from the lateral plate to the midline in mouse embryos.","method":"Direct protein interaction assay, co-expression in frog embryos, Gdf1 knockout mouse with Nodal introduction experiments","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1-2 — direct interaction demonstrated, multiple in vivo rescue experiments, high citation count","pmids":["18079174"],"is_preprint":false},{"year":2007,"finding":"Native GDF1 precursor is poorly processed when expressed in heterologous cells but its activity can be exposed by co-expression with Furin pro-protein convertase or by using chimeric constructs with heterologous prodomains. Co-expression with Nodal can also activate native GDF1, indicating a novel mode of cooperation. GDF1 signals through ALK4, ActRIIA, ActRIIB, and Cripto to activate Smad-dependent reporters.","method":"Heterologous cell expression, Furin co-expression, chimeric construct analysis, Smad reporter assay","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple biochemical methods in a single study, orthogonal approaches","pmids":["17936261"],"is_preprint":false},{"year":2014,"finding":"Nodal and GDF1 form a heterodimeric complex that copurifies with their cleaved propeptides as a low molecular weight complex. This Nodal·GDF1 heterodimer suppresses serum dependence of Nodal and is required for non-autonomous signaling in Cryptic-expressing cells. GDF1 potentiates Nodal activity by stabilizing a low molecular weight fraction susceptible to neutralization by soluble Acvr2, without increasing direct binding to co-receptors or Activin receptor extracellular domains.","method":"Co-immunoprecipitation, protein co-purification, Activin receptor signaling assay, soluble receptor neutralization assay, human ES cell differentiation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — biochemical co-purification, multiple functional assays, mutagenesis and domain analysis","pmids":["24798330"],"is_preprint":false},{"year":2015,"finding":"GDF1 activates SMAD2/3/4-mediated signaling to exert antiproliferative activity in gastric cells. Epigenetic silencing of GDF1 by promoter hypermethylation abrogates SMAD2/3 phosphorylation, and reactivation of GDF1 restores Smad signaling and transcriptional control of p15, p21, c-Myc cell-cycle regulators and phosphorylation of retinoblastoma protein.","method":"5-aza-dC treatment, genome-wide methylation scanning, Smad phosphorylation western blot, functional characterization in cancer cells","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods in single lab, direct mechanistic link between GDF1 and SMAD2/3 pathway established","pmids":["26212015"],"is_preprint":false},{"year":2015,"finding":"GDF1 acts as a proinflammatory factor in macrophages by inducing IL-6 production and STAT3 activation. Recombinant GDF1 promotes macrophage migration via Smad1/5/8 phosphorylation in a manner sensitive to ALK inhibitors.","method":"Recombinant protein treatment, western blot, ELISA, migration assay, ALK inhibitor pharmacology","journal":"Biochemistry and biophysics reports","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct recombinant protein application with pathway inhibition, single lab","pmids":["28955827"],"is_preprint":false},{"year":2018,"finding":"Tbx6 transcription factor controls left-right asymmetry through regulation of Gdf1 expression around the node. Gdf1 is a downstream target of Tbx6, and a Gdf1 transgene partially rescues the laterality defect of Tbx6 homozygous mutants.","method":"Genetic epistasis, transgenic rescue, gene expression analysis","journal":"Biology open","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis with transgenic rescue, single lab","pmids":["29650695"],"is_preprint":false},{"year":2019,"finding":"Nkx2.5 transcriptionally activates GDF1 expression by binding to its promoter. Luciferase assay, chromatin immunoprecipitation, and DNA pulldown demonstrated Nkx2.5 binds the GDF1 promoter and transactivates it, placing Nkx2.5 upstream of GDF1.","method":"Luciferase reporter assay, chromatin immunoprecipitation, DNA pulldown assay","journal":"Clinical science","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (ChIP, pulldown, luciferase) in a single lab","pmids":["31171573"],"is_preprint":false},{"year":2020,"finding":"Arsenic suppresses GDF1 expression via ROS-dependent downregulation of Sp1. Sp1 acts as a transcriptional activator of GDF1 by binding to its promoter (shown by ChIP). SIRT1, regulated by Sp1, also modulates GDF1 protein expression through a p66shc/ROS feedback loop.","method":"Chromatin immunoprecipitation, Sp1 overexpression/knockdown, antioxidant rescue, dominant-negative mutant","journal":"Environmental pollution","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP plus gain/loss-of-function experiments, multiple orthogonal approaches in single lab","pmids":["33360347"],"is_preprint":false},{"year":2024,"finding":"GDF1 in the hippocampus activates Akt, which phosphorylates asparagine endopeptidase (AEP) and inhibits AEP-induced synaptic degeneration and amyloid-β production. GDF1 expression is downregulated by the transcription factor C/EBPβ. Knockdown of GDF1 mimics hearing-loss-induced cognitive impairment, while hippocampal overexpression attenuates it.","method":"Knockdown, AAV-mediated overexpression, western blot for Akt/AEP phosphorylation, mouse behavioral testing","journal":"Nature aging","confidence":"Medium","confidence_rationale":"Tier 2 — direct in vivo gain/loss-of-function with defined molecular pathway, single lab","pmids":["38491289"],"is_preprint":false},{"year":2025,"finding":"The Nodal·GDF1 heterodimer is the major signal transducer in vertebrate Nodal signaling and spreads from the left-right organizer through the extracellular space of the paraxial mesoderm to the lateral plate mesoderm in a free-diffusion-like manner, as visualized in live zebrafish using transgenic lines and extracellular trapping (morphotrap).","method":"Transgenic zebrafish live imaging, extracellular morphotrap trapping, fluorescent protein tagging","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — direct in vivo visualization with novel tools, preprint not yet peer-reviewed","pmids":["bio_10.1101_2025.08.13.670121"],"is_preprint":true}],"current_model":"GDF1 is a TGF-beta superfamily member that functions primarily as a coligand for Nodal, forming a heterodimer that requires EGF-CFC coreceptors (Cripto/Cryptic) and signals through ALK4/ActRII Activin receptors via Smad2/3 phosphorylation; GDF1 potentiates Nodal activity and extends its signaling range during left-right patterning, is transcriptionally regulated by Nkx2.5, Tbx6, Sp1, and C/EBPβ, and in neural contexts activates an Akt-asparagine endopeptidase pathway to protect against synaptic degeneration."},"narrative":{"teleology":[{"year":1990,"claim":"Identification of GDF1 as a new TGF-β superfamily member established that the gene encodes a secreted glycoprotein with a predicted dibasic cleavage site and conserved C-terminal cysteine knot, placing it in the BMP/GDF ligand family.","evidence":"cDNA cloning, sequence analysis, and in vitro translation in cell-free system","pmids":["1704486"],"confidence":"Medium","gaps":["No receptor or signaling pathway identified","Biological function unknown","Processing and activation mechanism not tested in vivo"]},{"year":2000,"claim":"Demonstrating that native GDF1 precursor is poorly processed but a chimeric mature domain signals through Smad2 to induce mesendoderm and reverse the left-right axis resolved the paradox of why wild-type GDF1 appeared inactive and identified its signaling pathway.","evidence":"Chimeric BMP2-prodomain/GDF1-mature-domain expression in Xenopus embryos with Smad2 reporter assays and phenotypic analysis","pmids":["11071769"],"confidence":"High","gaps":["Identity of the endogenous activating protease not determined","Receptor identity unknown","Whether GDF1 acts alone or requires a co-ligand unclear"]},{"year":2003,"claim":"Showing that GDF1 requires EGF-CFC coreceptors and signals through Activin receptors defined its receptor complex and explained why GDF1 activity is restricted to cells expressing Cripto or Cryptic.","evidence":"Binding assays and signaling reconstitution in Xenopus; epistasis in zebrafish","pmids":["12514096"],"confidence":"High","gaps":["Specific type I receptor (ALK4 vs ALK7) contribution not resolved","Physical interaction with Nodal not yet tested"]},{"year":2006,"claim":"Receptor reconstitution and compound-mutant epistasis established ALK4 as the physiologically relevant type I receptor for GDF1 and Nodal during anterior axis development, distinguishing it from ALK7.","evidence":"Receptor reconstitution in cell lines and genetic epistasis using ALK4/ALK7/GDF1/Nodal compound mutant mice","pmids":["16564040"],"confidence":"High","gaps":["Role of ALK7 in other contexts not excluded","Whether GDF1 and Nodal signal as a heterodimer not yet tested"]},{"year":2007,"claim":"Discovery that GDF1 physically interacts with Nodal and functions as a coligand rather than an independent signal fundamentally reframed GDF1 biology, explaining its requirement for long-range Nodal signaling from lateral plate to midline.","evidence":"Direct protein interaction assay, co-expression rescue in Xenopus, Gdf1-knockout mouse with ectopic Nodal experiments; parallel biochemical analysis showing Furin-dependent activation and ALK4/ActRII/Cripto-dependent Smad signaling","pmids":["18079174","17936261"],"confidence":"High","gaps":["Stoichiometry and structure of the Nodal·GDF1 heterodimer unknown","Mechanism by which Nodal facilitates GDF1 processing not defined"]},{"year":2014,"claim":"Biochemical isolation of a Nodal·GDF1 heterodimer copurified with cleaved propeptides as a low-molecular-weight complex explained how GDF1 potentiates Nodal: it stabilizes a signaling-competent form that is accessible to receptor neutralization, without increasing direct co-receptor binding.","evidence":"Co-immunoprecipitation, size-exclusion co-purification, soluble Acvr2 neutralization, human ES cell differentiation assay","pmids":["24798330"],"confidence":"High","gaps":["Crystal structure of the heterodimer not determined","Role of propeptide association in diffusion range not tested in vivo"]},{"year":2015,"claim":"Extending GDF1 function beyond embryonic patterning, two studies showed it activates SMAD2/3/4 to suppress proliferation in gastric cells (silenced by promoter methylation in cancer) and induces IL-6/STAT3 and Smad1/5/8 signaling in macrophages, revealing context-dependent pathway usage.","evidence":"Methylation scanning with 5-aza-dC reactivation and Smad phosphorylation western blots in gastric cancer cells; recombinant GDF1 treatment with ALK inhibitor pharmacology in macrophages","pmids":["26212015","28955827"],"confidence":"Medium","gaps":["Smad1/5/8 activation in macrophages is atypical for a Nodal-class ligand — receptor complex mediating this not identified","Tumor-suppressive role based on cell lines without in vivo validation","Whether macrophage effects require Nodal co-expression unknown"]},{"year":2018,"claim":"Identifying Tbx6 as a direct upstream transcriptional regulator of Gdf1 around the node linked somitic transcription factor networks to left-right patterning via GDF1.","evidence":"Genetic epistasis using Tbx6 mutants, transgenic Gdf1 rescue, gene expression analysis in mouse embryos","pmids":["29650695"],"confidence":"Medium","gaps":["Direct promoter binding by Tbx6 not demonstrated by ChIP","Relationship between Tbx6 and other GDF1 regulators (Nkx2.5, Sp1) not addressed"]},{"year":2019,"claim":"Demonstrating that Nkx2.5 binds the GDF1 promoter and transactivates it placed GDF1 downstream of a key cardiac transcription factor, providing a regulatory link between cardiac specification and Nodal signaling.","evidence":"ChIP, DNA pulldown, luciferase reporter assay","pmids":["31171573"],"confidence":"Medium","gaps":["Functional consequence of Nkx2.5-driven GDF1 in cardiac development not shown in vivo","Integration with Tbx6-mediated regulation not examined"]},{"year":2020,"claim":"Sp1 was identified as another direct transcriptional activator of GDF1, with arsenic-induced ROS suppressing GDF1 via Sp1 downregulation, adding an environmental-stress axis to GDF1 regulation.","evidence":"ChIP for Sp1 at GDF1 promoter, Sp1 overexpression/knockdown, antioxidant rescue experiments","pmids":["33360347"],"confidence":"Medium","gaps":["SIRT1/p66shc feedback loop effect on GDF1 protein shown indirectly","Relevance to embryonic versus adult contexts unclear"]},{"year":2024,"claim":"In hippocampal neurons, GDF1 activates Akt to phosphorylate and inhibit asparagine endopeptidase (AEP), suppressing AEP-driven synaptic degeneration and amyloid-β production — a pathway distinct from canonical Smad signaling and regulated by C/EBPβ-mediated transcriptional repression.","evidence":"AAV-mediated GDF1 overexpression/knockdown in mouse hippocampus, western blot for Akt and AEP phosphorylation, behavioral testing","pmids":["38491289"],"confidence":"Medium","gaps":["Receptor mediating Akt activation in neurons not identified","Whether Nodal is a required coligand in this neural context unknown","Single-lab finding not yet independently replicated"]},{"year":null,"claim":"Key unresolved questions include the structural basis of the Nodal·GDF1 heterodimer, how receptor specificity shifts between Smad2/3 and Smad1/5/8 in different cell types, whether GDF1 functions independently of Nodal in adult tissues, and the in vivo transport mechanism of the heterodimer through extracellular space.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No crystal or cryo-EM structure of Nodal·GDF1 complex","Receptor complex mediating non-canonical Smad1/5/8 or Akt signaling unknown","Nodal-independent functions in adult tissues not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[1,2,4,5,6]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,6]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,6]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,2,3,5,6,7,8]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,4,9]}],"complexes":["Nodal·GDF1 heterodimer"],"partners":["NODAL","CRIPTO","CRYPTIC","ALK4","ACVR2A","ACVR2B","SMAD2","FURIN"],"other_free_text":[]},"mechanistic_narrative":"GDF1 is a TGF-β superfamily ligand that functions primarily as a coligand for Nodal, forming a heterodimer that potentiates Nodal signaling range and activity during left-right axis patterning and mesendoderm specification. The Nodal·GDF1 heterodimer signals through ALK4 type I and ActRII type II Activin receptors in an EGF-CFC coreceptor (Cripto/Cryptic)-dependent manner to activate Smad2/3 phosphorylation; native GDF1 precursor is poorly processed and requires Furin-mediated cleavage or co-expression with Nodal for activation [PMID:11071769, PMID:12514096, PMID:16564040, PMID:18079174, PMID:17936261, PMID:24798330]. GDF1 expression is transcriptionally controlled by Nkx2.5, Tbx6, Sp1, and C/EBPβ, linking it to cardiac, somitic, and neural regulatory networks [PMID:29650695, PMID:31171573, PMID:33360347, PMID:38491289]. Beyond embryonic patterning, GDF1 activates SMAD2/3/4 to exert antiproliferative effects in gastric epithelium and engages an Akt–asparagine endopeptidase axis in hippocampal neurons to suppress synaptic degeneration [PMID:26212015, PMID:38491289]."},"prefetch_data":{"uniprot":{"accession":"P27539","full_name":"Embryonic growth/differentiation factor 1","aliases":[],"length_aa":372,"mass_kda":39.5,"function":"May mediate cell differentiation events during embryonic development","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/P27539/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GDF1","classification":"Not Classified","n_dependent_lines":52,"n_total_lines":1208,"dependency_fraction":0.04304635761589404},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GDF1","total_profiled":1310},"omim":[{"mim_id":"616787","title":"CLUSTERIN-ASSOCIATED PROTEIN 1; CLUAP1","url":"https://www.omim.org/entry/616787"},{"mim_id":"613854","title":"CONGENITAL HEART DEFECTS, MULTIPLE TYPES, 6; CHTD6","url":"https://www.omim.org/entry/613854"},{"mim_id":"613702","title":"KLIPPEL-FEIL SYNDROME 3, AUTOSOMAL DOMINANT; KFS3","url":"https://www.omim.org/entry/613702"},{"mim_id":"608808","title":"TRANSPOSITION OF THE GREAT ARTERIES, DEXTRO-LOOPED; DTGA","url":"https://www.omim.org/entry/608808"},{"mim_id":"606919","title":"CERAMIDE SYNTHASE 1; CERS1","url":"https://www.omim.org/entry/606919"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":41.6}],"url":"https://www.proteinatlas.org/search/GDF1"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P27539","domains":[{"cath_id":"2.60.120.970","chopping":"103-115_122-237","consensus_level":"high","plddt":81.8922,"start":103,"end":237}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P27539","model_url":"https://alphafold.ebi.ac.uk/files/AF-P27539-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P27539-F1-predicted_aligned_error_v6.png","plddt_mean":73.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GDF1","jax_strain_url":"https://www.jax.org/strain/search?query=GDF1"},"sequence":{"accession":"P27539","fasta_url":"https://rest.uniprot.org/uniprotkb/P27539.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P27539/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P27539"}},"corpus_meta":[{"pmid":"12514096","id":"PMC_12514096","title":"EGF-CFC proteins are essential coreceptors for the TGF-beta signals Vg1 and GDF1.","date":"2003","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/12514096","citation_count":146,"is_preprint":false},{"pmid":"18079174","id":"PMC_18079174","title":"Long-range action of Nodal requires interaction with GDF1.","date":"2007","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/18079174","citation_count":100,"is_preprint":false},{"pmid":"17924340","id":"PMC_17924340","title":"Loss-of-function mutations in growth differentiation factor-1 (GDF1) are associated with congenital heart defects in humans.","date":"2007","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/17924340","citation_count":92,"is_preprint":false},{"pmid":"1704486","id":"PMC_1704486","title":"Identification of a novel member (GDF-1) of the transforming growth factor-beta superfamily.","date":"1990","source":"Molecular endocrinology (Baltimore, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/1704486","citation_count":87,"is_preprint":false},{"pmid":"16564040","id":"PMC_16564040","title":"Synergistic interaction between Gdf1 and Nodal during anterior axis development.","date":"2006","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/16564040","citation_count":80,"is_preprint":false},{"pmid":"17936261","id":"PMC_17936261","title":"Distinct and cooperative roles of mammalian Vg1 homologs GDF1 and GDF3 during early embryonic development.","date":"2007","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/17936261","citation_count":77,"is_preprint":false},{"pmid":"11071769","id":"PMC_11071769","title":"Mesendoderm induction and reversal of left-right pattern by mouse Gdf1, a Vg1-related gene.","date":"2000","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/11071769","citation_count":60,"is_preprint":false},{"pmid":"24798330","id":"PMC_24798330","title":"Nodal·Gdf1 heterodimers with bound prodomains enable serum-independent nodal signaling and endoderm differentiation.","date":"2014","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24798330","citation_count":36,"is_preprint":false},{"pmid":"20413652","id":"PMC_20413652","title":"Recessively inherited right atrial isomerism caused by mutations in growth/differentiation factor 1 (GDF1).","date":"2010","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20413652","citation_count":35,"is_preprint":false},{"pmid":"22535372","id":"PMC_22535372","title":"mTNF reverse signalling induced by TNFα antagonists involves a GDF-1 dependent pathway: implications for Crohn's disease.","date":"2012","source":"Gut","url":"https://pubmed.ncbi.nlm.nih.gov/22535372","citation_count":27,"is_preprint":false},{"pmid":"26212015","id":"PMC_26212015","title":"Epigenetic silencing of GDF1 disrupts SMAD signaling to reinforce gastric cancer development.","date":"2015","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/26212015","citation_count":20,"is_preprint":false},{"pmid":"33360347","id":"PMC_33360347","title":"Arsenic suppresses GDF1 expression via ROS-dependent downregulation of specificity protein 1.","date":"2020","source":"Environmental pollution (Barking, Essex : 1987)","url":"https://pubmed.ncbi.nlm.nih.gov/33360347","citation_count":19,"is_preprint":false},{"pmid":"17364820","id":"PMC_17364820","title":"Cloning and characterization of a LASS1-GDF1 transcript in rat cerebral cortex: conservation of a bicistronic structure.","date":"2007","source":"DNA sequence : the journal of DNA sequencing and mapping","url":"https://pubmed.ncbi.nlm.nih.gov/17364820","citation_count":12,"is_preprint":false},{"pmid":"38491289","id":"PMC_38491289","title":"GDF1 ameliorates cognitive impairment induced by hearing loss.","date":"2024","source":"Nature aging","url":"https://pubmed.ncbi.nlm.nih.gov/38491289","citation_count":11,"is_preprint":false},{"pmid":"26656983","id":"PMC_26656983","title":"Association of GDF1 rs4808863 with fetal congenital heart defects: a case-control study.","date":"2015","source":"BMJ open","url":"https://pubmed.ncbi.nlm.nih.gov/26656983","citation_count":11,"is_preprint":false},{"pmid":"22522086","id":"PMC_22522086","title":"Klippel-Feil syndrome associated with situs inversus: description of a new case and exclusion of GDF1, GDF3 and GDF6 as causal genes.","date":"2012","source":"European journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/22522086","citation_count":11,"is_preprint":false},{"pmid":"31171573","id":"PMC_31171573","title":"Association of functional variant in GDF1 promoter with risk of congenital heart disease and its regulation by Nkx2.5.","date":"2019","source":"Clinical science (London, England : 1979)","url":"https://pubmed.ncbi.nlm.nih.gov/31171573","citation_count":9,"is_preprint":false},{"pmid":"29650695","id":"PMC_29650695","title":"Tbx6 controls left-right asymmetry through regulation of Gdf1.","date":"2018","source":"Biology open","url":"https://pubmed.ncbi.nlm.nih.gov/29650695","citation_count":8,"is_preprint":false},{"pmid":"18615710","id":"PMC_18615710","title":"Generation and characterization of a Gdf1 conditional null allele.","date":"2008","source":"Genesis (New York, N.Y. : 2000)","url":"https://pubmed.ncbi.nlm.nih.gov/18615710","citation_count":6,"is_preprint":false},{"pmid":"32144877","id":"PMC_32144877","title":"A founder truncating variant in GDF1 causes autosomal-recessive right isomerism and associated congenital heart defects in multiplex Arab kindreds.","date":"2020","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/32144877","citation_count":6,"is_preprint":false},{"pmid":"28955827","id":"PMC_28955827","title":"GDF1 is a novel mediator of macrophage infiltration in brown adipose tissue of obese mice.","date":"2015","source":"Biochemistry and biophysics reports","url":"https://pubmed.ncbi.nlm.nih.gov/28955827","citation_count":6,"is_preprint":false},{"pmid":"30206386","id":"PMC_30206386","title":"Phylogenetic evidence for independent origins of GDF1 and GDF3 genes in anurans and mammals.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/30206386","citation_count":5,"is_preprint":false},{"pmid":"35351224","id":"PMC_35351224","title":"Homozygous variants in the GDF1 gene related to recurrent right isomerism and complex CHD in two Indian families.","date":"2022","source":"Cardiology in the young","url":"https://pubmed.ncbi.nlm.nih.gov/35351224","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.08.13.670121","title":"Differential spreading behaviors of Nodal signalling molecules in the extracellular space cooperatively shape left-right asymmetry","date":"2025-08-14","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.13.670121","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12428,"output_tokens":3262,"usd":0.043107},"stage2":{"model":"claude-opus-4-6","input_tokens":6659,"output_tokens":2982,"usd":0.161768},"total_usd":0.204875,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1990,\n      \"finding\": \"GDF1 was identified as a new member of the TGF-beta superfamily, predicted to be a secreted glycoprotein with a dibasic proteolytic cleavage site. In vitro translation experiments confirmed it is a secreted glycoprotein, and its C-terminus shares the invariant cysteines characteristic of TGF-beta family members.\",\n      \"method\": \"cDNA cloning, sequence analysis, in vitro translation\",\n      \"journal\": \"Molecular endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — original biochemical characterization, single lab\",\n      \"pmids\": [\"1704486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Native GDF1 is not proteolytically processed and therefore inactive, but a chimeric protein containing a heterologous prodomain (BMP2 prodomain fused to GDF1 mature domain) is efficiently processed and signals via Smad2 to induce mesendoderm and axial duplication in Xenopus. Mature GDF1 is sufficient to reverse the left-right axis.\",\n      \"method\": \"Chimeric protein expression in Xenopus embryos, Smad2 signaling assay, loss-of-function and gain-of-function in vivo\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (chimeric constructs, Smad2 reporter, phenotypic rescue), replicated in later studies\",\n      \"pmids\": [\"11071769\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"GDF1 signaling requires EGF-CFC coreceptors and is mediated through Activin receptors. GDF1 binds to and signals through Activin receptors only in the presence of EGF-CFC proteins in Xenopus, establishing that GDF1 converges on Activin receptor/EGF-CFC complexes.\",\n      \"method\": \"Binding assay, signaling reconstitution in Xenopus, zebrafish epistasis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct binding and signaling reconstitution, replicated in two model organisms, high citation count\",\n      \"pmids\": [\"12514096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"GDF1 signals through type I receptor ALK4 (and ALK7) in receptor reconstitution experiments. Genetic epistasis using compound mutants showed that ALK4, but not ALK7, is responsible for the effects of GDF1 and Nodal during anterior axis development. GDF1 and Nodal converge on ALK4 in the anterior primitive streak.\",\n      \"method\": \"Receptor reconstitution, compound mutant genetic epistasis, in vivo phenotypic analysis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — receptor reconstitution combined with genetic epistasis, multiple orthogonal methods\",\n      \"pmids\": [\"16564040\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GDF1 functions as a coligand for Nodal rather than as an independent ligand. GDF1 directly interacts with Nodal and greatly increases its specific activity and signaling range. GDF1 is required for long-range Nodal signaling from the lateral plate to the midline in mouse embryos.\",\n      \"method\": \"Direct protein interaction assay, co-expression in frog embryos, Gdf1 knockout mouse with Nodal introduction experiments\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct interaction demonstrated, multiple in vivo rescue experiments, high citation count\",\n      \"pmids\": [\"18079174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Native GDF1 precursor is poorly processed when expressed in heterologous cells but its activity can be exposed by co-expression with Furin pro-protein convertase or by using chimeric constructs with heterologous prodomains. Co-expression with Nodal can also activate native GDF1, indicating a novel mode of cooperation. GDF1 signals through ALK4, ActRIIA, ActRIIB, and Cripto to activate Smad-dependent reporters.\",\n      \"method\": \"Heterologous cell expression, Furin co-expression, chimeric construct analysis, Smad reporter assay\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple biochemical methods in a single study, orthogonal approaches\",\n      \"pmids\": [\"17936261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Nodal and GDF1 form a heterodimeric complex that copurifies with their cleaved propeptides as a low molecular weight complex. This Nodal·GDF1 heterodimer suppresses serum dependence of Nodal and is required for non-autonomous signaling in Cryptic-expressing cells. GDF1 potentiates Nodal activity by stabilizing a low molecular weight fraction susceptible to neutralization by soluble Acvr2, without increasing direct binding to co-receptors or Activin receptor extracellular domains.\",\n      \"method\": \"Co-immunoprecipitation, protein co-purification, Activin receptor signaling assay, soluble receptor neutralization assay, human ES cell differentiation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biochemical co-purification, multiple functional assays, mutagenesis and domain analysis\",\n      \"pmids\": [\"24798330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"GDF1 activates SMAD2/3/4-mediated signaling to exert antiproliferative activity in gastric cells. Epigenetic silencing of GDF1 by promoter hypermethylation abrogates SMAD2/3 phosphorylation, and reactivation of GDF1 restores Smad signaling and transcriptional control of p15, p21, c-Myc cell-cycle regulators and phosphorylation of retinoblastoma protein.\",\n      \"method\": \"5-aza-dC treatment, genome-wide methylation scanning, Smad phosphorylation western blot, functional characterization in cancer cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods in single lab, direct mechanistic link between GDF1 and SMAD2/3 pathway established\",\n      \"pmids\": [\"26212015\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"GDF1 acts as a proinflammatory factor in macrophages by inducing IL-6 production and STAT3 activation. Recombinant GDF1 promotes macrophage migration via Smad1/5/8 phosphorylation in a manner sensitive to ALK inhibitors.\",\n      \"method\": \"Recombinant protein treatment, western blot, ELISA, migration assay, ALK inhibitor pharmacology\",\n      \"journal\": \"Biochemistry and biophysics reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct recombinant protein application with pathway inhibition, single lab\",\n      \"pmids\": [\"28955827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Tbx6 transcription factor controls left-right asymmetry through regulation of Gdf1 expression around the node. Gdf1 is a downstream target of Tbx6, and a Gdf1 transgene partially rescues the laterality defect of Tbx6 homozygous mutants.\",\n      \"method\": \"Genetic epistasis, transgenic rescue, gene expression analysis\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with transgenic rescue, single lab\",\n      \"pmids\": [\"29650695\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Nkx2.5 transcriptionally activates GDF1 expression by binding to its promoter. Luciferase assay, chromatin immunoprecipitation, and DNA pulldown demonstrated Nkx2.5 binds the GDF1 promoter and transactivates it, placing Nkx2.5 upstream of GDF1.\",\n      \"method\": \"Luciferase reporter assay, chromatin immunoprecipitation, DNA pulldown assay\",\n      \"journal\": \"Clinical science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (ChIP, pulldown, luciferase) in a single lab\",\n      \"pmids\": [\"31171573\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Arsenic suppresses GDF1 expression via ROS-dependent downregulation of Sp1. Sp1 acts as a transcriptional activator of GDF1 by binding to its promoter (shown by ChIP). SIRT1, regulated by Sp1, also modulates GDF1 protein expression through a p66shc/ROS feedback loop.\",\n      \"method\": \"Chromatin immunoprecipitation, Sp1 overexpression/knockdown, antioxidant rescue, dominant-negative mutant\",\n      \"journal\": \"Environmental pollution\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP plus gain/loss-of-function experiments, multiple orthogonal approaches in single lab\",\n      \"pmids\": [\"33360347\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GDF1 in the hippocampus activates Akt, which phosphorylates asparagine endopeptidase (AEP) and inhibits AEP-induced synaptic degeneration and amyloid-β production. GDF1 expression is downregulated by the transcription factor C/EBPβ. Knockdown of GDF1 mimics hearing-loss-induced cognitive impairment, while hippocampal overexpression attenuates it.\",\n      \"method\": \"Knockdown, AAV-mediated overexpression, western blot for Akt/AEP phosphorylation, mouse behavioral testing\",\n      \"journal\": \"Nature aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct in vivo gain/loss-of-function with defined molecular pathway, single lab\",\n      \"pmids\": [\"38491289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The Nodal·GDF1 heterodimer is the major signal transducer in vertebrate Nodal signaling and spreads from the left-right organizer through the extracellular space of the paraxial mesoderm to the lateral plate mesoderm in a free-diffusion-like manner, as visualized in live zebrafish using transgenic lines and extracellular trapping (morphotrap).\",\n      \"method\": \"Transgenic zebrafish live imaging, extracellular morphotrap trapping, fluorescent protein tagging\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct in vivo visualization with novel tools, preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.08.13.670121\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"GDF1 is a TGF-beta superfamily member that functions primarily as a coligand for Nodal, forming a heterodimer that requires EGF-CFC coreceptors (Cripto/Cryptic) and signals through ALK4/ActRII Activin receptors via Smad2/3 phosphorylation; GDF1 potentiates Nodal activity and extends its signaling range during left-right patterning, is transcriptionally regulated by Nkx2.5, Tbx6, Sp1, and C/EBPβ, and in neural contexts activates an Akt-asparagine endopeptidase pathway to protect against synaptic degeneration.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"GDF1 is a TGF-β superfamily ligand that functions primarily as a coligand for Nodal, forming a heterodimer that potentiates Nodal signaling range and activity during left-right axis patterning and mesendoderm specification. The Nodal·GDF1 heterodimer signals through ALK4 type I and ActRII type II Activin receptors in an EGF-CFC coreceptor (Cripto/Cryptic)-dependent manner to activate Smad2/3 phosphorylation; native GDF1 precursor is poorly processed and requires Furin-mediated cleavage or co-expression with Nodal for activation [PMID:11071769, PMID:12514096, PMID:16564040, PMID:18079174, PMID:17936261, PMID:24798330]. GDF1 expression is transcriptionally controlled by Nkx2.5, Tbx6, Sp1, and C/EBPβ, linking it to cardiac, somitic, and neural regulatory networks [PMID:29650695, PMID:31171573, PMID:33360347, PMID:38491289]. Beyond embryonic patterning, GDF1 activates SMAD2/3/4 to exert antiproliferative effects in gastric epithelium and engages an Akt–asparagine endopeptidase axis in hippocampal neurons to suppress synaptic degeneration [PMID:26212015, PMID:38491289].\",\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Identification of GDF1 as a new TGF-β superfamily member established that the gene encodes a secreted glycoprotein with a predicted dibasic cleavage site and conserved C-terminal cysteine knot, placing it in the BMP/GDF ligand family.\",\n      \"evidence\": \"cDNA cloning, sequence analysis, and in vitro translation in cell-free system\",\n      \"pmids\": [\"1704486\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No receptor or signaling pathway identified\", \"Biological function unknown\", \"Processing and activation mechanism not tested in vivo\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Demonstrating that native GDF1 precursor is poorly processed but a chimeric mature domain signals through Smad2 to induce mesendoderm and reverse the left-right axis resolved the paradox of why wild-type GDF1 appeared inactive and identified its signaling pathway.\",\n      \"evidence\": \"Chimeric BMP2-prodomain/GDF1-mature-domain expression in Xenopus embryos with Smad2 reporter assays and phenotypic analysis\",\n      \"pmids\": [\"11071769\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the endogenous activating protease not determined\", \"Receptor identity unknown\", \"Whether GDF1 acts alone or requires a co-ligand unclear\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showing that GDF1 requires EGF-CFC coreceptors and signals through Activin receptors defined its receptor complex and explained why GDF1 activity is restricted to cells expressing Cripto or Cryptic.\",\n      \"evidence\": \"Binding assays and signaling reconstitution in Xenopus; epistasis in zebrafish\",\n      \"pmids\": [\"12514096\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific type I receptor (ALK4 vs ALK7) contribution not resolved\", \"Physical interaction with Nodal not yet tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Receptor reconstitution and compound-mutant epistasis established ALK4 as the physiologically relevant type I receptor for GDF1 and Nodal during anterior axis development, distinguishing it from ALK7.\",\n      \"evidence\": \"Receptor reconstitution in cell lines and genetic epistasis using ALK4/ALK7/GDF1/Nodal compound mutant mice\",\n      \"pmids\": [\"16564040\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Role of ALK7 in other contexts not excluded\", \"Whether GDF1 and Nodal signal as a heterodimer not yet tested\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Discovery that GDF1 physically interacts with Nodal and functions as a coligand rather than an independent signal fundamentally reframed GDF1 biology, explaining its requirement for long-range Nodal signaling from lateral plate to midline.\",\n      \"evidence\": \"Direct protein interaction assay, co-expression rescue in Xenopus, Gdf1-knockout mouse with ectopic Nodal experiments; parallel biochemical analysis showing Furin-dependent activation and ALK4/ActRII/Cripto-dependent Smad signaling\",\n      \"pmids\": [\"18079174\", \"17936261\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and structure of the Nodal·GDF1 heterodimer unknown\", \"Mechanism by which Nodal facilitates GDF1 processing not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Biochemical isolation of a Nodal·GDF1 heterodimer copurified with cleaved propeptides as a low-molecular-weight complex explained how GDF1 potentiates Nodal: it stabilizes a signaling-competent form that is accessible to receptor neutralization, without increasing direct co-receptor binding.\",\n      \"evidence\": \"Co-immunoprecipitation, size-exclusion co-purification, soluble Acvr2 neutralization, human ES cell differentiation assay\",\n      \"pmids\": [\"24798330\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystal structure of the heterodimer not determined\", \"Role of propeptide association in diffusion range not tested in vivo\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Extending GDF1 function beyond embryonic patterning, two studies showed it activates SMAD2/3/4 to suppress proliferation in gastric cells (silenced by promoter methylation in cancer) and induces IL-6/STAT3 and Smad1/5/8 signaling in macrophages, revealing context-dependent pathway usage.\",\n      \"evidence\": \"Methylation scanning with 5-aza-dC reactivation and Smad phosphorylation western blots in gastric cancer cells; recombinant GDF1 treatment with ALK inhibitor pharmacology in macrophages\",\n      \"pmids\": [\"26212015\", \"28955827\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Smad1/5/8 activation in macrophages is atypical for a Nodal-class ligand — receptor complex mediating this not identified\", \"Tumor-suppressive role based on cell lines without in vivo validation\", \"Whether macrophage effects require Nodal co-expression unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identifying Tbx6 as a direct upstream transcriptional regulator of Gdf1 around the node linked somitic transcription factor networks to left-right patterning via GDF1.\",\n      \"evidence\": \"Genetic epistasis using Tbx6 mutants, transgenic Gdf1 rescue, gene expression analysis in mouse embryos\",\n      \"pmids\": [\"29650695\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct promoter binding by Tbx6 not demonstrated by ChIP\", \"Relationship between Tbx6 and other GDF1 regulators (Nkx2.5, Sp1) not addressed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrating that Nkx2.5 binds the GDF1 promoter and transactivates it placed GDF1 downstream of a key cardiac transcription factor, providing a regulatory link between cardiac specification and Nodal signaling.\",\n      \"evidence\": \"ChIP, DNA pulldown, luciferase reporter assay\",\n      \"pmids\": [\"31171573\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of Nkx2.5-driven GDF1 in cardiac development not shown in vivo\", \"Integration with Tbx6-mediated regulation not examined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Sp1 was identified as another direct transcriptional activator of GDF1, with arsenic-induced ROS suppressing GDF1 via Sp1 downregulation, adding an environmental-stress axis to GDF1 regulation.\",\n      \"evidence\": \"ChIP for Sp1 at GDF1 promoter, Sp1 overexpression/knockdown, antioxidant rescue experiments\",\n      \"pmids\": [\"33360347\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"SIRT1/p66shc feedback loop effect on GDF1 protein shown indirectly\", \"Relevance to embryonic versus adult contexts unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"In hippocampal neurons, GDF1 activates Akt to phosphorylate and inhibit asparagine endopeptidase (AEP), suppressing AEP-driven synaptic degeneration and amyloid-β production — a pathway distinct from canonical Smad signaling and regulated by C/EBPβ-mediated transcriptional repression.\",\n      \"evidence\": \"AAV-mediated GDF1 overexpression/knockdown in mouse hippocampus, western blot for Akt and AEP phosphorylation, behavioral testing\",\n      \"pmids\": [\"38491289\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor mediating Akt activation in neurons not identified\", \"Whether Nodal is a required coligand in this neural context unknown\", \"Single-lab finding not yet independently replicated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of the Nodal·GDF1 heterodimer, how receptor specificity shifts between Smad2/3 and Smad1/5/8 in different cell types, whether GDF1 functions independently of Nodal in adult tissues, and the in vivo transport mechanism of the heterodimer through extracellular space.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No crystal or cryo-EM structure of Nodal·GDF1 complex\", \"Receptor complex mediating non-canonical Smad1/5/8 or Akt signaling unknown\", \"Nodal-independent functions in adult tissues not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [1, 2, 4, 5, 6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 2, 3, 5, 6, 7, 8]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 4, 9]}\n    ],\n    \"complexes\": [\n      \"Nodal·GDF1 heterodimer\"\n    ],\n    \"partners\": [\n      \"NODAL\",\n      \"CRIPTO\",\n      \"CRYPTIC\",\n      \"ALK4\",\n      \"ACVR2A\",\n      \"ACVR2B\",\n      \"SMAD2\",\n      \"FURIN\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}