{"gene":"GDF6","run_date":"2026-04-28T18:06:52","timeline":{"discoveries":[{"year":1999,"finding":"GDF6 (Xenopus ortholog) directly binds the neural inducer noggin, antagonizing its activity; GDF6 induces epidermis and inhibits neural tissue in dissociated cells, and this activity is blocked by noggin. GDF6 and BMP2 form heterodimers requiring cotranslation in the same cells.","method":"Direct binding assay (GDF6-noggin), dissociated cell fate assays, heterodimer formation by cotranslation","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 1 — direct binding demonstrated, functional rescue/block experiments, mechanistic cotranslation requirement shown","pmids":["10393114"],"is_preprint":false},{"year":2003,"finding":"Gdf6 null mutation in mice causes defects in joint, ligament, and cartilage formation at sites distinct from Gdf5 mutants (wrist, ankle, middle ear, coronal suture); double Gdf5/Gdf6 mutants show additive skeletal defects including loss of limb skeletal elements and scoliosis, establishing non-redundant roles for GDF5/6/7 subgroup members in skeletal boundary formation.","method":"Gene knockout (single and double null mice), skeletal phenotype analysis","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined cellular/skeletal phenotype, double mutant epistasis, replicated across multiple skeletal sites","pmids":["12606286"],"is_preprint":false},{"year":2006,"finding":"Morpholino inhibition of gdf6a in zebrafish recapitulates chorioretinal coloboma, microphthalmia, and anophthalmia, establishing GDF6 as a key regulator of ocular development.","method":"Morpholino knockdown in zebrafish, phenotype analysis","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — morpholino KD with defined ocular phenotype recapitulating human deletion phenotype","pmids":["17236135"],"is_preprint":false},{"year":2006,"finding":"GDF6 knockdown in Xenopus reduces eye size and retinal laminar structure, decreases Smad1/5/8 phosphorylation, reduces Pax6 expression domain, and increases apoptosis along the neural tube and retina, placing GDF6 upstream of canonical BMP/Smad signaling in neural and eye development.","method":"Morpholino knockdown (Xenopus), TUNEL staining, immunostaining for pSmad1/5/8 and Pax6","journal":"BMC developmental biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal readouts (signaling, cell death, gene expression) in loss-of-function model","pmids":["17010201"],"is_preprint":false},{"year":2008,"finding":"GDF6 missense mutation p.Leu289Pro causes Klippel-Feil syndrome; GDF6 knockdown in Xenopus results in anterior axial defects consistent with vertebral segmentation role; GDF6 is expressed at boundaries of developing carpals, tarsals, and vertebrae and in the adult vertebral disc.","method":"Human mutation identification, Xenopus morpholino knockdown, expression analysis","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 — KD phenotype in model organism plus human mutation, single lab","pmids":["18425797"],"is_preprint":false},{"year":2009,"finding":"GDF6 null mutation causes substantially lower tail tendon collagen content (-33%) and 45-50% reduction in tendon material properties in mice, establishing GDF6 as required for tendon matrix modeling.","method":"Gdf6 null mouse, collagen quantification, mechanical testing","journal":"Anatomical record (Hoboken, N.J. : 2007)","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined quantitative phenotype, single lab","pmids":["19248159"],"is_preprint":false},{"year":2009,"finding":"GDF6 heterozygous mutations in patients with ocular and vertebral anomalies were characterized by SOX9-reporter assay and western analysis; Gdf6+/- mice exhibit variable ocular phenotypes; zebrafish morphants show ocular and skeletal (tail, somite marker) defects with altered noggin1/noggin2 expression.","method":"SOX9-reporter assay, western blot, Gdf6+/- mouse, zebrafish morpholino KD, somite marker expression","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods across three model systems plus functional assay in single study","pmids":["19129173"],"is_preprint":false},{"year":2010,"finding":"Adenoviral BMP-13 (GDF6) transduction of C3H10T1/2 mesenchymal progenitor cells induces chondrogenic differentiation (Alcian blue staining, cartilage-specific markers) but fails to support hypertrophic chondrocyte differentiation or endochondral ossification, unlike BMP-2; BMPR-IB/ALK-6 expression is constitutive and not affected by BMP-13.","method":"Adenoviral transduction, RT-PCR, biochemical and histological analysis of differentiation markers, ALP assay","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 1 — in vitro gain-of-function with multiple differentiation readouts, direct comparison to BMP-2","pmids":["14753743"],"is_preprint":false},{"year":2011,"finding":"Recombinant BMP12 (GDF6) and BMP13 bind type I BMPRs (ALK3, ALK6) and type II BMPRs (ACVR2A, ACVR2B, BMPR2) with similar affinities to BMP2, yet BMP12/13 do not activate SMAD1/5/8 signaling in C3H10T1/2 cells and instead dose-dependently induce tendon-specific Thbs4 expression without osteocalcin induction, indicating receptor-binding-independent divergence in downstream signaling.","method":"Receptor binding affinity assays, SMAD signaling assays, gene expression (Thbs4, osteocalcin) in C3H10T1/2 cells","journal":"Growth factors (Chur, Switzerland)","confidence":"High","confidence_rationale":"Tier 1 — direct receptor binding quantification plus downstream signaling assays, mechanistic dissociation of binding from signaling","pmids":["21702718"],"is_preprint":false},{"year":2012,"finding":"Gdf6 is expressed in frontal bone primordia from E10.5-E12.5; Gdf6-/- mice show premature coronal suture fusion due to accelerated differentiation of suture mesenchyme prior to calvarial ossification onset, with increased ALP activity and Runx2 expression in suture mesenchyme, demonstrating that Gdf6 inhibits osteogenic differentiation of coronal suture mesenchyme.","method":"Gdf6 null mouse, ALP activity assay, Runx2 immunostaining, developmental staging","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple molecular readouts and defined cellular mechanism","pmids":["22693558"],"is_preprint":false},{"year":2013,"finding":"Overexpression of Gdf6 induces commitment of pluripotent mesenchymal C3H10T1/2 cells to the adipocyte lineage; this is mediated through type I receptor Bmpr1a and type II receptors Bmpr2 and Acvr2a; both Smad4 and p38 MAPK pathways are required; Runx1t1 is downregulated in committed pre-adipocytes and forced Runx1t1 expression blocks adipocytic commitment.","method":"Overexpression, RNAi silencing of Smad4/p38 MAPK, receptor knockdown, Runx1t1 forced expression","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 2 — multiple pathway components identified by RNAi with specific phenotypic readout in single study","pmids":["23527555"],"is_preprint":false},{"year":2015,"finding":"A GDF6 missense variant (p.Y444N) in the region critical for binding to receptors and the BMP antagonist NOG causes gain-of-function: mutant GDF6 is a more potent stimulator of canonical BMP signaling (SMAD1/5/8) and is resistant to NOG-mediated antagonism, leading to loss of joint formation (multiple synostoses syndrome SYNS4).","method":"Human genetics, BMP signaling reporter assays, NOG antagonism assays, functional comparison of WT vs mutant GDF6","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 1-2 — functional assays in vitro with mutant vs WT comparison, mechanistic explanation of gain-of-function via NOG resistance","pmids":["26643732"],"is_preprint":false},{"year":2016,"finding":"Ror2 is required for local upregulation of gdf6 at the neural plate border in Xenopus; Ror2 morphant embryos fail to activate BMP signaling (spatially restricted) at the neural plate border; Gdf6 is sufficient to rescue neural plate border specification in Ror2 morphants, placing Gdf6 downstream of Ror2/Wnt-PCP signaling and upstream of BMP activation for neural crest induction.","method":"Xenopus morpholino knockdown of Ror2, rescue with Gdf6, pSmad staining, neural plate border marker analysis","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — epistasis established by morpholino + rescue, multiple signaling readouts","pmids":["27578181"],"is_preprint":false},{"year":2020,"finding":"GDF6 prodomain (not the BMP domain) is a ligand for CD99; GDF6 prodomain binding to CD99 extracellular domain recruits CSK (C-terminal Src kinase) to the YQKKK motif in CD99 intracellular domain, inhibiting Src activity; GDF6 silencing causes Src hyperactivation and p21-dependent growth arrest in Ewing sarcoma; two GDF6 prodomain mutants linked to Klippel-Feil syndrome are hyperactive in CD99-Src signaling.","method":"siRNA knockdown, Co-IP/pulldown (GDF6 prodomain-CD99), domain mapping, CSK recruitment assay, Src activity assay, growth arrest assay","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1-2 — ligand-receptor binding demonstrated, intracellular motif mapped, downstream kinase activity quantified, multiple orthogonal methods","pmids":["33147457"],"is_preprint":false},{"year":2020,"finding":"GDF6 signals through SMAD1/5/8 and ERK1/2 phosphorylation in human nucleus pulposus cells; recombinant GDF6 treatment induces anabolic response (increased matrix/NP-phenotypic markers, glycosaminoglycan production) in degenerate NP cells; blocking studies confirm both SMAD-dependent and SMAD-independent (ERK1/2) mechanisms.","method":"Recombinant GDF6 treatment, pSmad1/5/8 and pERK1/2 western blot, pathway inhibitor blocking studies, GAG assay, gene expression","journal":"International journal of molecular sciences","confidence":"High","confidence_rationale":"Tier 1-2 — pathway identified by signaling assays and validated by blocking studies with multiple readouts","pmids":["32992671"],"is_preprint":false},{"year":2020,"finding":"High BMPR2 expression in adipose-derived stem cells correlates with enhanced SMAD1/5/8 signaling and greater GDF6 responsiveness; SMAD1/5/8 signaling is required for rhGDF6-induced NP-like differentiation, while ERK1/2 contributes to critical NP gene expression and aggrecan/type II collagen production.","method":"Receptor expression profiling, rhGDF6 treatment, SMAD1/5/8 and ERK1/2 inhibitor studies, NP marker gene expression and matrix production","journal":"Journal of tissue engineering","confidence":"Medium","confidence_rationale":"Tier 2 — inhibitor studies defining pathway requirements, single lab, multiple cell types compared","pmids":["32489577"],"is_preprint":false},{"year":2020,"finding":"Knockout of Gdf6 in mice causes cochlear aplasia; long-range cis-regulatory elements located ~350 kb downstream of GDF6 are required for its expression in the cochlea, as human deletions of this noncoding region cause reduced GDF6 expression (shown in patient iPSC-derived otic lineage cells) and cochlear aplasia.","method":"Gdf6 mouse knockout, iPSC-derived otic cells with GDF6 expression analysis, human genomic deletion mapping","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined phenotype, functional regulatory element validated in human cells","pmids":["32369452"],"is_preprint":false},{"year":2021,"finding":"SCDAL lncRNA induces GDF6 expression via direct interaction with SNF5 at the GDF6 promoter; secreted GDF6 promotes endothelial angiogenesis via non-canonical VEGFR2 activation.","method":"lncRNA knockdown/overexpression, ChIP/interaction assays at GDF6 promoter, tube formation assay, VEGFR2 signaling analysis","journal":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","confidence":"Medium","confidence_rationale":"Tier 2 — direct SNF5-promoter interaction shown, non-canonical receptor pathway identified, single lab","pmids":["34319658"],"is_preprint":false},{"year":2023,"finding":"Overloading-induced PIEZO1 activation upregulates miR-155-5p, which suppresses GDF6 mRNA (and downstream SMAD2/3 signaling), causing chondrocyte senescence and OA; miR-155-5p inhibition or recombinant GDF6 rescues joint homeostasis and attenuates OA in vivo.","method":"Mouse OA models, PIEZO1 activation, miR-155-5p mimic/inhibitor, GDF6 supplementation, SMAD2/3 signaling assays, in vivo intra-articular injection","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 — pathway epistasis established in vitro and in vivo with rescue experiments, single lab","pmids":["38508350"],"is_preprint":false},{"year":2023,"finding":"METTL3-mediated m6A methylation stabilizes GDF6 mRNA in dental pulp stem cells; METTL3 knockdown impairs dentinogenesis differentiation while overexpression promotes it, and this is linked to increased GDF6 (and STC1) mRNA stability.","method":"MeRIP-seq, lentiviral METTL3 KD/OE, RNA stability assay (actinomycin D), ALP/alizarin red staining, direct pulp capping model","journal":"BMC oral health","confidence":"Medium","confidence_rationale":"Tier 2 — m6A writer identified, mRNA stability directly measured, functional consequence in vitro and in vivo, single lab","pmids":["37041485"],"is_preprint":false},{"year":2023,"finding":"GDF6 gain-of-function knock-in mice (p.Tyr443Asn, orthologous to human p.Tyr444Asn) recapitulate SYNS4 joint fusion; embryonic analysis shows joint interzone formation defects and excess chondrogenesis; RNA sequencing reveals enhanced BMP signaling and bone formation pathways, confirming that increased GDF6/BMP activity disrupts joint morphogenesis.","method":"CRISPR knock-in mouse, skeletal phenotype analysis, embryonic forelimb joint interzone analysis, RNA sequencing of forelimb buds","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 1-2 — precise knock-in mouse with transcriptomic and phenotypic characterization, mechanistic pathway confirmation","pmids":["36744814"],"is_preprint":false},{"year":2024,"finding":"FTO-mediated m6A demethylation destabilizes GDF6 mRNA; depletion of FTO stabilizes GDF6 mRNA and enhances type I interferon production while reducing pro-inflammatory factors in RSV-infected cells; IGF2BP1 (m6A reader) binding is required for GDF6 mRNA stability and downstream IFN production.","method":"FTO KD, IGF2BP1 KD, m6A-seq, mRNA stability assays, IFN and cytokine measurement","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 — m6A eraser (FTO) and reader (IGF2BP1) identified with functional consequence on GDF6 mRNA and downstream signaling, single lab","pmids":["39474078"],"is_preprint":false},{"year":2024,"finding":"GDF6 overexpression in gastric cancer cells promotes EMT via the TGF-β/SMAD3 signaling pathway (upregulating phospho-SMAD3, N-cadherin, vimentin; downregulating E-cadherin); GDF6 silencing reverses these effects.","method":"GDF6 siRNA KD and overexpression, western blot for pSMAD3 and EMT markers, CCK-8, scratch, Transwell assays","journal":"Pathology, research and practice","confidence":"Medium","confidence_rationale":"Tier 2 — gain- and loss-of-function with defined signaling pathway, single lab","pmids":["38850874"],"is_preprint":false},{"year":2025,"finding":"GDF6 activates AMPKα through the cAMP/Epac1 pathway to exert anti-hypertrophic cardioprotective effects; GDF6 KD aggravates and GDF6 OE attenuates pressure overload-induced cardiac hypertrophy in mice; AMPKα inhibition or Epac1 KD abolishes GDF6's protective effects.","method":"AAV9-mediated cardiac GDF6 OE/KD, TAC mouse model, pharmacological AMPKα inhibition, Epac1 KD, echocardiography, molecular signaling assays, NRVM in vitro","journal":"Biomedicines","confidence":"Medium","confidence_rationale":"Tier 2 — pathway epistasis validated by both genetic and pharmacological inhibition in vivo and in vitro, single lab","pmids":["41462947"],"is_preprint":false},{"year":2020,"finding":"miR-155-5p from M1-polarized macrophage-derived exosomes directly binds the 3' UTR of GDF6 mRNA to suppress GDF6 protein expression, impairing HUVEC migration and tube formation; miR-155-5p antagomiR promotes angiogenesis and wound healing in diabetic mice by enhancing GDF6.","method":"Exosome isolation, high-throughput miRNA sequencing, dual-luciferase 3'UTR reporter assay, HUVEC functional assays, in vivo diabetic wound model","journal":"Molecular therapy. Nucleic acids","confidence":"High","confidence_rationale":"Tier 1-2 — 3'UTR binding validated by luciferase assay, functional rescue in vitro and in vivo","pmids":["38074896"],"is_preprint":false},{"year":2020,"finding":"miR-98 directly binds GDF6 (and FAPP2) mRNA 3'-UTR to negatively regulate their expression; miR-98 suppresses proliferation, viability, and migration of trophoblast cells; GDF6 knockdown inhibits miR-98-mediated trophoblast proliferation.","method":"Dual-luciferase 3'UTR reporter assay, western blot, RT-PCR, trophoblast cell functional assays (EdU, MTT, Transwell)","journal":"Reproduction (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 — direct 3'UTR binding validated, functional epistasis in trophoblast cells, single lab","pmids":["32045359"],"is_preprint":false},{"year":2020,"finding":"CRISPR/Cas9 knockout of Gdf6 attenuates migration of murine IMCD3 cells; this effect is rescued by wild-type but not mutant GDF6, establishing GDF6 as required for normal cell migration with variant-specific functional impairment.","method":"CRISPR/Cas9 KO, cell migration assay, rescue with WT vs mutant GDF6","journal":"European journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 — CRISPR KO with rescue distinguishing WT from mutant, single lab","pmids":["32737436"],"is_preprint":false}],"current_model":"GDF6 is a secreted BMP-family ligand that signals canonically through BMPR1A/ALK3, ALK6 and type II receptors (BMPR2, ACVR2A/B) to activate SMAD1/5/8 (and non-canonically ERK1/2) to regulate joint boundary formation, skeletal patterning, ocular development, tendon/cartilage matrix maintenance, and neural plate border specification; its activity is antagonized by noggin (direct binding), modulated by miR-155-5p and miR-98 targeting its 3' UTR, stabilized by METTL3-mediated m6A methylation and destabilized by FTO, and its prodomain additionally functions as a CD99 ligand that recruits CSK to suppress Src activity; gain-of-function mutations conferring noggin resistance drive hyperactive BMP/SMAD signaling causing multiple synostoses, while loss of function disrupts joint interzone formation, coronal suture patency, cochlear development, and cell migration."},"narrative":{"teleology":[{"year":1999,"claim":"The question of how GDF6 relates to BMP antagonism was resolved by showing that GDF6 directly binds noggin, which blocks its epidermal-inducing activity, and that GDF6 can form heterodimers with BMP2 only through cotranslation—establishing GDF6 as a noggin-regulated BMP ligand.","evidence":"Direct binding assay (GDF6–noggin), dissociated Xenopus cell fate assays, heterodimer cotranslation experiments","pmids":["10393114"],"confidence":"High","gaps":["Affinity constants for GDF6–noggin vs other BMP–noggin pairs not determined","Heterodimer signaling properties not characterized"]},{"year":2003,"claim":"The in vivo requirement of GDF6 for skeletal patterning was established when Gdf6-null mice exhibited joint, ligament, cartilage, and coronal suture defects at sites distinct from Gdf5 mutants, and double mutants showed additive phenotypes, proving non-redundant roles within the GDF5/6/7 subgroup.","evidence":"Single and double Gdf5/Gdf6 knockout mice with skeletal phenotype analysis","pmids":["12606286"],"confidence":"High","gaps":["Downstream transcriptional targets in joint interzone not identified","Mechanism distinguishing GDF5 vs GDF6 site specificity unknown"]},{"year":2006,"claim":"GDF6 was placed upstream of canonical SMAD1/5/8 signaling in ocular and neural development: its knockdown in zebrafish and Xenopus caused microphthalmia/coloboma, reduced pSMAD1/5/8, decreased Pax6 expression, and increased apoptosis, establishing GDF6 as essential for eye formation.","evidence":"Morpholino knockdown in zebrafish and Xenopus, pSmad1/5/8 immunostaining, TUNEL, Pax6 expression analysis","pmids":["17236135","17010201"],"confidence":"High","gaps":["Direct receptor engagement in retinal progenitors not defined","Whether GDF6 acts cell-autonomously in retina versus via a relay not resolved"]},{"year":2008,"claim":"Identification of a GDF6 missense mutation causing Klippel-Feil syndrome extended the skeletal boundary-formation role to human vertebral segmentation, supported by Xenopus knockdown recapitulating anterior axial defects.","evidence":"Human mutation identification (p.Leu289Pro), Xenopus morpholino knockdown, expression analysis","pmids":["18425797"],"confidence":"Medium","gaps":["Functional consequence of p.Leu289Pro on receptor binding or signaling not biochemically tested","Limited patient numbers"]},{"year":2009,"claim":"The requirement of GDF6 for connective tissue integrity was quantified: Gdf6-null mice had 33% lower tail tendon collagen and 45–50% reduced mechanical properties, establishing GDF6 as a regulator of tendon matrix modeling.","evidence":"Gdf6-null mouse, collagen quantification, biomechanical testing","pmids":["19248159"],"confidence":"Medium","gaps":["Whether GDF6 acts directly on tenocytes or via paracrine signaling not resolved","Single anatomical site analyzed"]},{"year":2010,"claim":"GDF6 was shown to promote chondrogenic but not hypertrophic/osteogenic differentiation of mesenchymal progenitors, distinguishing its downstream program from BMP-2 and explaining its joint-preserving rather than bone-forming role.","evidence":"Adenoviral GDF6 transduction of C3H10T1/2 cells, differentiation marker profiling, comparison with BMP-2","pmids":["14753743"],"confidence":"High","gaps":["Receptor-level basis for divergent signaling relative to BMP-2 not defined"]},{"year":2011,"claim":"A paradox was identified: GDF6 binds type I (ALK3, ALK6) and type II (ACVR2A, ACVR2B, BMPR2) receptors with affinities comparable to BMP-2 yet fails to activate SMAD1/5/8 in the same cells, instead inducing tendon-specific genes—revealing receptor-binding-independent divergence in signaling output.","evidence":"Quantitative receptor binding affinity assays, SMAD signaling assays, Thbs4/osteocalcin gene expression in C3H10T1/2 cells","pmids":["21702718"],"confidence":"High","gaps":["Co-receptor or intracellular scaffolding differences not identified","Context-dependency of SMAD activation across cell types not systematically explored"]},{"year":2012,"claim":"The mechanism by which GDF6 maintains cranial suture patency was clarified: Gdf6-null mice showed premature coronal suture fusion via accelerated osteogenic differentiation (elevated ALP, Runx2) of suture mesenchyme, positioning GDF6 as an inhibitor of osteoblast commitment at suture boundaries.","evidence":"Gdf6-null mouse, ALP activity, Runx2 immunostaining, developmental staging of suture fusion","pmids":["22693558"],"confidence":"High","gaps":["Whether GDF6 acts cell-autonomously on suture mesenchyme not shown","Interaction with other craniosynostosis-associated pathways (FGF, Wnt) not tested"]},{"year":2013,"claim":"GDF6 was found to direct adipocyte lineage commitment through BMPR1A and BMPR2/ACVR2A, requiring both SMAD4 and p38 MAPK, with Runx1t1 acting as a downstream transcriptional switch—broadening GDF6 function beyond skeletal boundaries to adipogenesis.","evidence":"GDF6 overexpression and RNAi of Smad4, p38 MAPK, receptors, and Runx1t1 in C3H10T1/2 cells","pmids":["23527555"],"confidence":"High","gaps":["In vivo adipogenic role of GDF6 not validated","Whether p38 activation is direct or indirect not resolved"]},{"year":2015,"claim":"The gain-of-function mechanism for GDF6 p.Y444N was defined: this mutation renders GDF6 resistant to noggin antagonism and enhances SMAD1/5/8 signaling, causing multiple synostoses syndrome (SYNS4)—proving that the noggin–GDF6 balance is the critical rheostat for joint formation.","evidence":"BMP signaling reporter assays, noggin antagonism assays comparing WT and mutant GDF6, human genetic data","pmids":["26643732"],"confidence":"High","gaps":["Structural basis for noggin resistance not determined","Whether other BMP antagonists (e.g. gremlin) are similarly affected not tested"]},{"year":2016,"claim":"GDF6 was placed downstream of Ror2/Wnt-PCP signaling in neural plate border specification: Ror2 depletion abolished local GDF6 upregulation and BMP activity at the neural plate border, and GDF6 was sufficient to rescue neural crest induction in Ror2 morphants.","evidence":"Xenopus Ror2 morpholino knockdown, GDF6 rescue, pSmad staining, neural plate border marker analysis","pmids":["27578181"],"confidence":"High","gaps":["Direct transcriptional regulation of GDF6 by Ror2/PCP pathway not demonstrated","Mammalian conservation not tested"]},{"year":2020,"claim":"Multiple advances defined GDF6 signaling in disc biology and its post-transcriptional regulation: in nucleus pulposus cells GDF6 activates both SMAD1/5/8 and ERK1/2 for anabolic responses; miR-155-5p and miR-98 were validated as direct suppressors of GDF6 mRNA via 3′-UTR binding; and GDF6 knockout caused cochlear aplasia linked to distant cis-regulatory elements.","evidence":"Pathway inhibitor blocking studies in NP cells, dual-luciferase 3′UTR reporter assays for miR-155-5p and miR-98, Gdf6-null mouse cochlear phenotype, iPSC-derived otic cell expression analysis","pmids":["32992671","38074896","32045359","32369452"],"confidence":"High","gaps":["Identity of m6A vs miRNA regulatory hierarchy on GDF6 mRNA not integrated","Long-range enhancer–promoter looping mechanism not structurally resolved"]},{"year":2020,"claim":"An entirely novel signaling modality was discovered: the GDF6 prodomain (not the mature BMP ligand) binds CD99 and recruits CSK to suppress Src activity; Klippel-Feil-associated prodomain mutations are hyperactive in this axis, revealing a BMP-independent signaling function for the GDF6 precursor.","evidence":"Co-IP/pulldown of GDF6 prodomain–CD99, CSK recruitment assay, Src activity measurement, growth arrest assay in Ewing sarcoma cells","pmids":["33147457"],"confidence":"High","gaps":["Whether prodomain–CD99 signaling operates in skeletal tissues not tested","Stoichiometry and structural basis of prodomain–CD99 interaction unknown","Relationship between prodomain processing and dual signaling modes undefined"]},{"year":2023,"claim":"GDF6 mRNA was shown to be epitranscriptomically regulated: METTL3-mediated m6A methylation stabilizes GDF6 mRNA during dentinogenesis, and gain-of-function knock-in mice (p.Tyr443Asn) confirmed that enhanced GDF6/BMP signaling disrupts joint interzone formation at the transcriptomic level.","evidence":"MeRIP-seq and actinomycin-D stability assays in dental pulp stem cells; CRISPR knock-in mouse with RNA-seq of limb buds","pmids":["37041485","36744814"],"confidence":"High","gaps":["Which m6A sites on GDF6 mRNA are functionally critical not mapped at nucleotide resolution","Transcriptomic changes in knock-in mice not validated at the protein level for all targets"]},{"year":2024,"claim":"The m6A regulatory circuit was extended: FTO demethylation destabilizes GDF6 mRNA, while IGF2BP1 acts as the m6A reader stabilizing it; FTO depletion increases GDF6 and type I interferon output in RSV-infected cells, linking GDF6 to innate immune regulation.","evidence":"FTO and IGF2BP1 knockdown, m6A-seq, mRNA stability assays, IFN and cytokine measurement in RSV-infected cells","pmids":["39474078"],"confidence":"Medium","gaps":["Whether GDF6 directly drives IFN production or acts indirectly not resolved","Relevance of GDF6-IFN axis beyond RSV infection unknown"]},{"year":2025,"claim":"GDF6 was shown to exert cardioprotective anti-hypertrophic effects through a non-canonical cAMP/Epac1/AMPKα pathway, distinct from its classical BMP receptor signaling.","evidence":"AAV9-mediated cardiac GDF6 overexpression/knockdown in TAC mouse model, pharmacological AMPKα inhibition, Epac1 knockdown, neonatal rat ventricular myocytes","pmids":["41462947"],"confidence":"Medium","gaps":["Receptor mediating cAMP/Epac1 activation by GDF6 in cardiomyocytes not identified","Single lab, awaits independent confirmation"]},{"year":null,"claim":"Key unresolved questions include the structural basis for GDF6's divergent signaling through the same receptors as BMP-2, the physiological contexts in which prodomain–CD99 versus mature-ligand–BMPR signaling predominate, and how m6A-dependent mRNA stabilization integrates with miRNA-mediated repression to set GDF6 protein levels in specific tissues.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal structure of GDF6–receptor complex available","Prodomain cleavage regulation and tissue-specific processing not characterized","Integrated quantitative model of epitranscriptomic and miRNA regulation of GDF6 mRNA absent"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,8,11,14]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[13]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,8,14,24]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,10,11,14,20,23]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,2,3,9,12,16]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[19,21]}],"complexes":[],"partners":["NOG","BMPR1A","BMPR2","ACVR2A","ACVR2B","CD99","CSK","IGF2BP1"],"other_free_text":[]},"mechanistic_narrative":"GDF6 is a secreted BMP-family ligand that patterns skeletal boundaries, maintains connective tissue matrices, and directs cell fate specification across multiple organ systems. It signals through type I receptors BMPR1A/ALK3 and ALK6 and type II receptors BMPR2, ACVR2A, and ACVR2B to activate canonical SMAD1/5/8 and non-canonical ERK1/2 pathways, driving chondrogenic and NP-like differentiation while inhibiting hypertrophic and osteogenic programs [PMID:14753743, PMID:32992671, PMID:23527555]; its activity is antagonized by direct binding to noggin, and gain-of-function mutations conferring noggin resistance cause multiple synostoses syndrome (SYNS4) through hyperactive BMP/SMAD signaling and joint interzone disruption [PMID:26643732, PMID:36744814]. Beyond classical BMP signaling, the GDF6 prodomain functions as a ligand for CD99, recruiting CSK to suppress Src kinase activity independently of the mature BMP domain [PMID:33147457]. GDF6 mRNA stability is regulated by m6A epitranscriptomic machinery—stabilized by METTL3/IGF2BP1 and destabilized by FTO—and is post-transcriptionally repressed by miR-155-5p and miR-98 targeting its 3′ UTR [PMID:37041485, PMID:39474078, PMID:38074896, PMID:32045359]."},"prefetch_data":{"uniprot":{"accession":"Q6KF10","full_name":"Growth/differentiation factor 6","aliases":["Bone morphogenetic protein 13","BMP-13","Growth/differentiation factor 16"],"length_aa":455,"mass_kda":50.7,"function":"Growth factor that controls proliferation and cellular differentiation in the retina and bone formation. Plays a key role in regulating apoptosis during retinal development. Establishes dorsal-ventral positional information in the retina and controls the formation of the retinotectal map (PubMed:23307924). Required for normal formation of bones and joints in the limbs, skull, digits and axial skeleton. Plays a key role in establishing boundaries between skeletal elements during development. Regulation of GDF6 expression seems to be a mechanism for evolving species-specific changes in skeletal structures. Seems to positively regulate differentiation of chondrogenic tissue through the growth factor receptors subunits BMPR1A, BMPR1B, BMPR2 and ACVR2A, leading to the activation of SMAD1-SMAD5-SMAD8 complex. The regulation of chondrogenic differentiation is inhibited by NOG (PubMed:26643732). Also involved in the induction of adipogenesis from mesenchymal stem cells. This mechanism acts through the growth factor receptors subunits BMPR1A, BMPR2 and ACVR2A and the activation of SMAD1-SMAD5-SMAD8 complex and MAPK14/p38 (By similarity)","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q6KF10/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GDF6","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GDF6","total_profiled":1310},"omim":[{"mim_id":"619553","title":"DEAFNESS, AUTOSOMAL RECESSIVE 118, WITH COCHLEAR APLASIA; DFNB118","url":"https://www.omim.org/entry/619553"},{"mim_id":"617898","title":"MULTIPLE SYNOSTOSES SYNDROME 4; SYNS4","url":"https://www.omim.org/entry/617898"},{"mim_id":"615360","title":"LEBER CONGENITAL AMAUROSIS 17; LCA17","url":"https://www.omim.org/entry/615360"},{"mim_id":"613703","title":"MICROPHTHALMIA/COLOBOMA 6; MCOPCB6","url":"https://www.omim.org/entry/613703"},{"mim_id":"613094","title":"MICROPHTHALMIA, ISOLATED 4; MCOP4","url":"https://www.omim.org/entry/613094"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Nuclear membrane","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"placenta","ntpm":10.2}],"url":"https://www.proteinatlas.org/search/GDF6"},"hgnc":{"alias_symbol":["BMP13","KFS","KFS1"],"prev_symbol":["SGM1"]},"alphafold":{"accession":"Q6KF10","domains":[{"cath_id":"2.60.120","chopping":"124-241_255-282","consensus_level":"high","plddt":82.4461,"start":124,"end":282},{"cath_id":"2.10.90.10","chopping":"289-296_352-455","consensus_level":"medium","plddt":91.1495,"start":289,"end":455}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6KF10","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6KF10-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6KF10-F1-predicted_aligned_error_v6.png","plddt_mean":70.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GDF6","jax_strain_url":"https://www.jax.org/strain/search?query=GDF6"},"sequence":{"accession":"Q6KF10","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6KF10.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6KF10/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6KF10"}},"corpus_meta":[{"pmid":"12606286","id":"PMC_12606286","title":"Multiple 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interfaces","date":"2024-10-03","source":"bioRxiv","url":"https://doi.org/10.1101/2024.10.03.616126","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":31034,"output_tokens":6461,"usd":0.095008},"stage2":{"model":"claude-opus-4-6","input_tokens":10091,"output_tokens":4182,"usd":0.232508},"total_usd":0.327516,"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\": 1999,\n      \"finding\": \"GDF6 (Xenopus ortholog) directly binds the neural inducer noggin, antagonizing its activity; GDF6 induces epidermis and inhibits neural tissue in dissociated cells, and this activity is blocked by noggin. GDF6 and BMP2 form heterodimers requiring cotranslation in the same cells.\",\n      \"method\": \"Direct binding assay (GDF6-noggin), dissociated cell fate assays, heterodimer formation by cotranslation\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct binding demonstrated, functional rescue/block experiments, mechanistic cotranslation requirement shown\",\n      \"pmids\": [\"10393114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Gdf6 null mutation in mice causes defects in joint, ligament, and cartilage formation at sites distinct from Gdf5 mutants (wrist, ankle, middle ear, coronal suture); double Gdf5/Gdf6 mutants show additive skeletal defects including loss of limb skeletal elements and scoliosis, establishing non-redundant roles for GDF5/6/7 subgroup members in skeletal boundary formation.\",\n      \"method\": \"Gene knockout (single and double null mice), skeletal phenotype analysis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular/skeletal phenotype, double mutant epistasis, replicated across multiple skeletal sites\",\n      \"pmids\": [\"12606286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Morpholino inhibition of gdf6a in zebrafish recapitulates chorioretinal coloboma, microphthalmia, and anophthalmia, establishing GDF6 as a key regulator of ocular development.\",\n      \"method\": \"Morpholino knockdown in zebrafish, phenotype analysis\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — morpholino KD with defined ocular phenotype recapitulating human deletion phenotype\",\n      \"pmids\": [\"17236135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"GDF6 knockdown in Xenopus reduces eye size and retinal laminar structure, decreases Smad1/5/8 phosphorylation, reduces Pax6 expression domain, and increases apoptosis along the neural tube and retina, placing GDF6 upstream of canonical BMP/Smad signaling in neural and eye development.\",\n      \"method\": \"Morpholino knockdown (Xenopus), TUNEL staining, immunostaining for pSmad1/5/8 and Pax6\",\n      \"journal\": \"BMC developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal readouts (signaling, cell death, gene expression) in loss-of-function model\",\n      \"pmids\": [\"17010201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GDF6 missense mutation p.Leu289Pro causes Klippel-Feil syndrome; GDF6 knockdown in Xenopus results in anterior axial defects consistent with vertebral segmentation role; GDF6 is expressed at boundaries of developing carpals, tarsals, and vertebrae and in the adult vertebral disc.\",\n      \"method\": \"Human mutation identification, Xenopus morpholino knockdown, expression analysis\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KD phenotype in model organism plus human mutation, single lab\",\n      \"pmids\": [\"18425797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GDF6 null mutation causes substantially lower tail tendon collagen content (-33%) and 45-50% reduction in tendon material properties in mice, establishing GDF6 as required for tendon matrix modeling.\",\n      \"method\": \"Gdf6 null mouse, collagen quantification, mechanical testing\",\n      \"journal\": \"Anatomical record (Hoboken, N.J. : 2007)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined quantitative phenotype, single lab\",\n      \"pmids\": [\"19248159\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GDF6 heterozygous mutations in patients with ocular and vertebral anomalies were characterized by SOX9-reporter assay and western analysis; Gdf6+/- mice exhibit variable ocular phenotypes; zebrafish morphants show ocular and skeletal (tail, somite marker) defects with altered noggin1/noggin2 expression.\",\n      \"method\": \"SOX9-reporter assay, western blot, Gdf6+/- mouse, zebrafish morpholino KD, somite marker expression\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods across three model systems plus functional assay in single study\",\n      \"pmids\": [\"19129173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Adenoviral BMP-13 (GDF6) transduction of C3H10T1/2 mesenchymal progenitor cells induces chondrogenic differentiation (Alcian blue staining, cartilage-specific markers) but fails to support hypertrophic chondrocyte differentiation or endochondral ossification, unlike BMP-2; BMPR-IB/ALK-6 expression is constitutive and not affected by BMP-13.\",\n      \"method\": \"Adenoviral transduction, RT-PCR, biochemical and histological analysis of differentiation markers, ALP assay\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro gain-of-function with multiple differentiation readouts, direct comparison to BMP-2\",\n      \"pmids\": [\"14753743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Recombinant BMP12 (GDF6) and BMP13 bind type I BMPRs (ALK3, ALK6) and type II BMPRs (ACVR2A, ACVR2B, BMPR2) with similar affinities to BMP2, yet BMP12/13 do not activate SMAD1/5/8 signaling in C3H10T1/2 cells and instead dose-dependently induce tendon-specific Thbs4 expression without osteocalcin induction, indicating receptor-binding-independent divergence in downstream signaling.\",\n      \"method\": \"Receptor binding affinity assays, SMAD signaling assays, gene expression (Thbs4, osteocalcin) in C3H10T1/2 cells\",\n      \"journal\": \"Growth factors (Chur, Switzerland)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct receptor binding quantification plus downstream signaling assays, mechanistic dissociation of binding from signaling\",\n      \"pmids\": [\"21702718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Gdf6 is expressed in frontal bone primordia from E10.5-E12.5; Gdf6-/- mice show premature coronal suture fusion due to accelerated differentiation of suture mesenchyme prior to calvarial ossification onset, with increased ALP activity and Runx2 expression in suture mesenchyme, demonstrating that Gdf6 inhibits osteogenic differentiation of coronal suture mesenchyme.\",\n      \"method\": \"Gdf6 null mouse, ALP activity assay, Runx2 immunostaining, developmental staging\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple molecular readouts and defined cellular mechanism\",\n      \"pmids\": [\"22693558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Overexpression of Gdf6 induces commitment of pluripotent mesenchymal C3H10T1/2 cells to the adipocyte lineage; this is mediated through type I receptor Bmpr1a and type II receptors Bmpr2 and Acvr2a; both Smad4 and p38 MAPK pathways are required; Runx1t1 is downregulated in committed pre-adipocytes and forced Runx1t1 expression blocks adipocytic commitment.\",\n      \"method\": \"Overexpression, RNAi silencing of Smad4/p38 MAPK, receptor knockdown, Runx1t1 forced expression\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple pathway components identified by RNAi with specific phenotypic readout in single study\",\n      \"pmids\": [\"23527555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"A GDF6 missense variant (p.Y444N) in the region critical for binding to receptors and the BMP antagonist NOG causes gain-of-function: mutant GDF6 is a more potent stimulator of canonical BMP signaling (SMAD1/5/8) and is resistant to NOG-mediated antagonism, leading to loss of joint formation (multiple synostoses syndrome SYNS4).\",\n      \"method\": \"Human genetics, BMP signaling reporter assays, NOG antagonism assays, functional comparison of WT vs mutant GDF6\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — functional assays in vitro with mutant vs WT comparison, mechanistic explanation of gain-of-function via NOG resistance\",\n      \"pmids\": [\"26643732\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Ror2 is required for local upregulation of gdf6 at the neural plate border in Xenopus; Ror2 morphant embryos fail to activate BMP signaling (spatially restricted) at the neural plate border; Gdf6 is sufficient to rescue neural plate border specification in Ror2 morphants, placing Gdf6 downstream of Ror2/Wnt-PCP signaling and upstream of BMP activation for neural crest induction.\",\n      \"method\": \"Xenopus morpholino knockdown of Ror2, rescue with Gdf6, pSmad staining, neural plate border marker analysis\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis established by morpholino + rescue, multiple signaling readouts\",\n      \"pmids\": [\"27578181\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"GDF6 prodomain (not the BMP domain) is a ligand for CD99; GDF6 prodomain binding to CD99 extracellular domain recruits CSK (C-terminal Src kinase) to the YQKKK motif in CD99 intracellular domain, inhibiting Src activity; GDF6 silencing causes Src hyperactivation and p21-dependent growth arrest in Ewing sarcoma; two GDF6 prodomain mutants linked to Klippel-Feil syndrome are hyperactive in CD99-Src signaling.\",\n      \"method\": \"siRNA knockdown, Co-IP/pulldown (GDF6 prodomain-CD99), domain mapping, CSK recruitment assay, Src activity assay, growth arrest assay\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ligand-receptor binding demonstrated, intracellular motif mapped, downstream kinase activity quantified, multiple orthogonal methods\",\n      \"pmids\": [\"33147457\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"GDF6 signals through SMAD1/5/8 and ERK1/2 phosphorylation in human nucleus pulposus cells; recombinant GDF6 treatment induces anabolic response (increased matrix/NP-phenotypic markers, glycosaminoglycan production) in degenerate NP cells; blocking studies confirm both SMAD-dependent and SMAD-independent (ERK1/2) mechanisms.\",\n      \"method\": \"Recombinant GDF6 treatment, pSmad1/5/8 and pERK1/2 western blot, pathway inhibitor blocking studies, GAG assay, gene expression\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — pathway identified by signaling assays and validated by blocking studies with multiple readouts\",\n      \"pmids\": [\"32992671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"High BMPR2 expression in adipose-derived stem cells correlates with enhanced SMAD1/5/8 signaling and greater GDF6 responsiveness; SMAD1/5/8 signaling is required for rhGDF6-induced NP-like differentiation, while ERK1/2 contributes to critical NP gene expression and aggrecan/type II collagen production.\",\n      \"method\": \"Receptor expression profiling, rhGDF6 treatment, SMAD1/5/8 and ERK1/2 inhibitor studies, NP marker gene expression and matrix production\",\n      \"journal\": \"Journal of tissue engineering\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — inhibitor studies defining pathway requirements, single lab, multiple cell types compared\",\n      \"pmids\": [\"32489577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Knockout of Gdf6 in mice causes cochlear aplasia; long-range cis-regulatory elements located ~350 kb downstream of GDF6 are required for its expression in the cochlea, as human deletions of this noncoding region cause reduced GDF6 expression (shown in patient iPSC-derived otic lineage cells) and cochlear aplasia.\",\n      \"method\": \"Gdf6 mouse knockout, iPSC-derived otic cells with GDF6 expression analysis, human genomic deletion mapping\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined phenotype, functional regulatory element validated in human cells\",\n      \"pmids\": [\"32369452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SCDAL lncRNA induces GDF6 expression via direct interaction with SNF5 at the GDF6 promoter; secreted GDF6 promotes endothelial angiogenesis via non-canonical VEGFR2 activation.\",\n      \"method\": \"lncRNA knockdown/overexpression, ChIP/interaction assays at GDF6 promoter, tube formation assay, VEGFR2 signaling analysis\",\n      \"journal\": \"Advanced science (Weinheim, Baden-Wurttemberg, Germany)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct SNF5-promoter interaction shown, non-canonical receptor pathway identified, single lab\",\n      \"pmids\": [\"34319658\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Overloading-induced PIEZO1 activation upregulates miR-155-5p, which suppresses GDF6 mRNA (and downstream SMAD2/3 signaling), causing chondrocyte senescence and OA; miR-155-5p inhibition or recombinant GDF6 rescues joint homeostasis and attenuates OA in vivo.\",\n      \"method\": \"Mouse OA models, PIEZO1 activation, miR-155-5p mimic/inhibitor, GDF6 supplementation, SMAD2/3 signaling assays, in vivo intra-articular injection\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway epistasis established in vitro and in vivo with rescue experiments, single lab\",\n      \"pmids\": [\"38508350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"METTL3-mediated m6A methylation stabilizes GDF6 mRNA in dental pulp stem cells; METTL3 knockdown impairs dentinogenesis differentiation while overexpression promotes it, and this is linked to increased GDF6 (and STC1) mRNA stability.\",\n      \"method\": \"MeRIP-seq, lentiviral METTL3 KD/OE, RNA stability assay (actinomycin D), ALP/alizarin red staining, direct pulp capping model\",\n      \"journal\": \"BMC oral health\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — m6A writer identified, mRNA stability directly measured, functional consequence in vitro and in vivo, single lab\",\n      \"pmids\": [\"37041485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GDF6 gain-of-function knock-in mice (p.Tyr443Asn, orthologous to human p.Tyr444Asn) recapitulate SYNS4 joint fusion; embryonic analysis shows joint interzone formation defects and excess chondrogenesis; RNA sequencing reveals enhanced BMP signaling and bone formation pathways, confirming that increased GDF6/BMP activity disrupts joint morphogenesis.\",\n      \"method\": \"CRISPR knock-in mouse, skeletal phenotype analysis, embryonic forelimb joint interzone analysis, RNA sequencing of forelimb buds\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — precise knock-in mouse with transcriptomic and phenotypic characterization, mechanistic pathway confirmation\",\n      \"pmids\": [\"36744814\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FTO-mediated m6A demethylation destabilizes GDF6 mRNA; depletion of FTO stabilizes GDF6 mRNA and enhances type I interferon production while reducing pro-inflammatory factors in RSV-infected cells; IGF2BP1 (m6A reader) binding is required for GDF6 mRNA stability and downstream IFN production.\",\n      \"method\": \"FTO KD, IGF2BP1 KD, m6A-seq, mRNA stability assays, IFN and cytokine measurement\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — m6A eraser (FTO) and reader (IGF2BP1) identified with functional consequence on GDF6 mRNA and downstream signaling, single lab\",\n      \"pmids\": [\"39474078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GDF6 overexpression in gastric cancer cells promotes EMT via the TGF-β/SMAD3 signaling pathway (upregulating phospho-SMAD3, N-cadherin, vimentin; downregulating E-cadherin); GDF6 silencing reverses these effects.\",\n      \"method\": \"GDF6 siRNA KD and overexpression, western blot for pSMAD3 and EMT markers, CCK-8, scratch, Transwell assays\",\n      \"journal\": \"Pathology, research and practice\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function with defined signaling pathway, single lab\",\n      \"pmids\": [\"38850874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GDF6 activates AMPKα through the cAMP/Epac1 pathway to exert anti-hypertrophic cardioprotective effects; GDF6 KD aggravates and GDF6 OE attenuates pressure overload-induced cardiac hypertrophy in mice; AMPKα inhibition or Epac1 KD abolishes GDF6's protective effects.\",\n      \"method\": \"AAV9-mediated cardiac GDF6 OE/KD, TAC mouse model, pharmacological AMPKα inhibition, Epac1 KD, echocardiography, molecular signaling assays, NRVM in vitro\",\n      \"journal\": \"Biomedicines\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway epistasis validated by both genetic and pharmacological inhibition in vivo and in vitro, single lab\",\n      \"pmids\": [\"41462947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"miR-155-5p from M1-polarized macrophage-derived exosomes directly binds the 3' UTR of GDF6 mRNA to suppress GDF6 protein expression, impairing HUVEC migration and tube formation; miR-155-5p antagomiR promotes angiogenesis and wound healing in diabetic mice by enhancing GDF6.\",\n      \"method\": \"Exosome isolation, high-throughput miRNA sequencing, dual-luciferase 3'UTR reporter assay, HUVEC functional assays, in vivo diabetic wound model\",\n      \"journal\": \"Molecular therapy. Nucleic acids\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — 3'UTR binding validated by luciferase assay, functional rescue in vitro and in vivo\",\n      \"pmids\": [\"38074896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"miR-98 directly binds GDF6 (and FAPP2) mRNA 3'-UTR to negatively regulate their expression; miR-98 suppresses proliferation, viability, and migration of trophoblast cells; GDF6 knockdown inhibits miR-98-mediated trophoblast proliferation.\",\n      \"method\": \"Dual-luciferase 3'UTR reporter assay, western blot, RT-PCR, trophoblast cell functional assays (EdU, MTT, Transwell)\",\n      \"journal\": \"Reproduction (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct 3'UTR binding validated, functional epistasis in trophoblast cells, single lab\",\n      \"pmids\": [\"32045359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CRISPR/Cas9 knockout of Gdf6 attenuates migration of murine IMCD3 cells; this effect is rescued by wild-type but not mutant GDF6, establishing GDF6 as required for normal cell migration with variant-specific functional impairment.\",\n      \"method\": \"CRISPR/Cas9 KO, cell migration assay, rescue with WT vs mutant GDF6\",\n      \"journal\": \"European journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — CRISPR KO with rescue distinguishing WT from mutant, single lab\",\n      \"pmids\": [\"32737436\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GDF6 is a secreted BMP-family ligand that signals canonically through BMPR1A/ALK3, ALK6 and type II receptors (BMPR2, ACVR2A/B) to activate SMAD1/5/8 (and non-canonically ERK1/2) to regulate joint boundary formation, skeletal patterning, ocular development, tendon/cartilage matrix maintenance, and neural plate border specification; its activity is antagonized by noggin (direct binding), modulated by miR-155-5p and miR-98 targeting its 3' UTR, stabilized by METTL3-mediated m6A methylation and destabilized by FTO, and its prodomain additionally functions as a CD99 ligand that recruits CSK to suppress Src activity; gain-of-function mutations conferring noggin resistance drive hyperactive BMP/SMAD signaling causing multiple synostoses, while loss of function disrupts joint interzone formation, coronal suture patency, cochlear development, and cell migration.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"GDF6 is a secreted BMP-family ligand that patterns skeletal boundaries, maintains connective tissue matrices, and directs cell fate specification across multiple organ systems. It signals through type I receptors BMPR1A/ALK3 and ALK6 and type II receptors BMPR2, ACVR2A, and ACVR2B to activate canonical SMAD1/5/8 and non-canonical ERK1/2 pathways, driving chondrogenic and NP-like differentiation while inhibiting hypertrophic and osteogenic programs [PMID:14753743, PMID:32992671, PMID:23527555]; its activity is antagonized by direct binding to noggin, and gain-of-function mutations conferring noggin resistance cause multiple synostoses syndrome (SYNS4) through hyperactive BMP/SMAD signaling and joint interzone disruption [PMID:26643732, PMID:36744814]. Beyond classical BMP signaling, the GDF6 prodomain functions as a ligand for CD99, recruiting CSK to suppress Src kinase activity independently of the mature BMP domain [PMID:33147457]. GDF6 mRNA stability is regulated by m6A epitranscriptomic machinery—stabilized by METTL3/IGF2BP1 and destabilized by FTO—and is post-transcriptionally repressed by miR-155-5p and miR-98 targeting its 3′ UTR [PMID:37041485, PMID:39474078, PMID:38074896, PMID:32045359].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"The question of how GDF6 relates to BMP antagonism was resolved by showing that GDF6 directly binds noggin, which blocks its epidermal-inducing activity, and that GDF6 can form heterodimers with BMP2 only through cotranslation—establishing GDF6 as a noggin-regulated BMP ligand.\",\n      \"evidence\": \"Direct binding assay (GDF6–noggin), dissociated Xenopus cell fate assays, heterodimer cotranslation experiments\",\n      \"pmids\": [\"10393114\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Affinity constants for GDF6–noggin vs other BMP–noggin pairs not determined\", \"Heterodimer signaling properties not characterized\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The in vivo requirement of GDF6 for skeletal patterning was established when Gdf6-null mice exhibited joint, ligament, cartilage, and coronal suture defects at sites distinct from Gdf5 mutants, and double mutants showed additive phenotypes, proving non-redundant roles within the GDF5/6/7 subgroup.\",\n      \"evidence\": \"Single and double Gdf5/Gdf6 knockout mice with skeletal phenotype analysis\",\n      \"pmids\": [\"12606286\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream transcriptional targets in joint interzone not identified\", \"Mechanism distinguishing GDF5 vs GDF6 site specificity unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"GDF6 was placed upstream of canonical SMAD1/5/8 signaling in ocular and neural development: its knockdown in zebrafish and Xenopus caused microphthalmia/coloboma, reduced pSMAD1/5/8, decreased Pax6 expression, and increased apoptosis, establishing GDF6 as essential for eye formation.\",\n      \"evidence\": \"Morpholino knockdown in zebrafish and Xenopus, pSmad1/5/8 immunostaining, TUNEL, Pax6 expression analysis\",\n      \"pmids\": [\"17236135\", \"17010201\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct receptor engagement in retinal progenitors not defined\", \"Whether GDF6 acts cell-autonomously in retina versus via a relay not resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identification of a GDF6 missense mutation causing Klippel-Feil syndrome extended the skeletal boundary-formation role to human vertebral segmentation, supported by Xenopus knockdown recapitulating anterior axial defects.\",\n      \"evidence\": \"Human mutation identification (p.Leu289Pro), Xenopus morpholino knockdown, expression analysis\",\n      \"pmids\": [\"18425797\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of p.Leu289Pro on receptor binding or signaling not biochemically tested\", \"Limited patient numbers\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The requirement of GDF6 for connective tissue integrity was quantified: Gdf6-null mice had 33% lower tail tendon collagen and 45–50% reduced mechanical properties, establishing GDF6 as a regulator of tendon matrix modeling.\",\n      \"evidence\": \"Gdf6-null mouse, collagen quantification, biomechanical testing\",\n      \"pmids\": [\"19248159\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether GDF6 acts directly on tenocytes or via paracrine signaling not resolved\", \"Single anatomical site analyzed\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"GDF6 was shown to promote chondrogenic but not hypertrophic/osteogenic differentiation of mesenchymal progenitors, distinguishing its downstream program from BMP-2 and explaining its joint-preserving rather than bone-forming role.\",\n      \"evidence\": \"Adenoviral GDF6 transduction of C3H10T1/2 cells, differentiation marker profiling, comparison with BMP-2\",\n      \"pmids\": [\"14753743\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor-level basis for divergent signaling relative to BMP-2 not defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"A paradox was identified: GDF6 binds type I (ALK3, ALK6) and type II (ACVR2A, ACVR2B, BMPR2) receptors with affinities comparable to BMP-2 yet fails to activate SMAD1/5/8 in the same cells, instead inducing tendon-specific genes—revealing receptor-binding-independent divergence in signaling output.\",\n      \"evidence\": \"Quantitative receptor binding affinity assays, SMAD signaling assays, Thbs4/osteocalcin gene expression in C3H10T1/2 cells\",\n      \"pmids\": [\"21702718\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Co-receptor or intracellular scaffolding differences not identified\", \"Context-dependency of SMAD activation across cell types not systematically explored\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The mechanism by which GDF6 maintains cranial suture patency was clarified: Gdf6-null mice showed premature coronal suture fusion via accelerated osteogenic differentiation (elevated ALP, Runx2) of suture mesenchyme, positioning GDF6 as an inhibitor of osteoblast commitment at suture boundaries.\",\n      \"evidence\": \"Gdf6-null mouse, ALP activity, Runx2 immunostaining, developmental staging of suture fusion\",\n      \"pmids\": [\"22693558\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether GDF6 acts cell-autonomously on suture mesenchyme not shown\", \"Interaction with other craniosynostosis-associated pathways (FGF, Wnt) not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"GDF6 was found to direct adipocyte lineage commitment through BMPR1A and BMPR2/ACVR2A, requiring both SMAD4 and p38 MAPK, with Runx1t1 acting as a downstream transcriptional switch—broadening GDF6 function beyond skeletal boundaries to adipogenesis.\",\n      \"evidence\": \"GDF6 overexpression and RNAi of Smad4, p38 MAPK, receptors, and Runx1t1 in C3H10T1/2 cells\",\n      \"pmids\": [\"23527555\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo adipogenic role of GDF6 not validated\", \"Whether p38 activation is direct or indirect not resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The gain-of-function mechanism for GDF6 p.Y444N was defined: this mutation renders GDF6 resistant to noggin antagonism and enhances SMAD1/5/8 signaling, causing multiple synostoses syndrome (SYNS4)—proving that the noggin–GDF6 balance is the critical rheostat for joint formation.\",\n      \"evidence\": \"BMP signaling reporter assays, noggin antagonism assays comparing WT and mutant GDF6, human genetic data\",\n      \"pmids\": [\"26643732\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for noggin resistance not determined\", \"Whether other BMP antagonists (e.g. gremlin) are similarly affected not tested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"GDF6 was placed downstream of Ror2/Wnt-PCP signaling in neural plate border specification: Ror2 depletion abolished local GDF6 upregulation and BMP activity at the neural plate border, and GDF6 was sufficient to rescue neural crest induction in Ror2 morphants.\",\n      \"evidence\": \"Xenopus Ror2 morpholino knockdown, GDF6 rescue, pSmad staining, neural plate border marker analysis\",\n      \"pmids\": [\"27578181\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct transcriptional regulation of GDF6 by Ror2/PCP pathway not demonstrated\", \"Mammalian conservation not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Multiple advances defined GDF6 signaling in disc biology and its post-transcriptional regulation: in nucleus pulposus cells GDF6 activates both SMAD1/5/8 and ERK1/2 for anabolic responses; miR-155-5p and miR-98 were validated as direct suppressors of GDF6 mRNA via 3′-UTR binding; and GDF6 knockout caused cochlear aplasia linked to distant cis-regulatory elements.\",\n      \"evidence\": \"Pathway inhibitor blocking studies in NP cells, dual-luciferase 3′UTR reporter assays for miR-155-5p and miR-98, Gdf6-null mouse cochlear phenotype, iPSC-derived otic cell expression analysis\",\n      \"pmids\": [\"32992671\", \"38074896\", \"32045359\", \"32369452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of m6A vs miRNA regulatory hierarchy on GDF6 mRNA not integrated\", \"Long-range enhancer–promoter looping mechanism not structurally resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"An entirely novel signaling modality was discovered: the GDF6 prodomain (not the mature BMP ligand) binds CD99 and recruits CSK to suppress Src activity; Klippel-Feil-associated prodomain mutations are hyperactive in this axis, revealing a BMP-independent signaling function for the GDF6 precursor.\",\n      \"evidence\": \"Co-IP/pulldown of GDF6 prodomain–CD99, CSK recruitment assay, Src activity measurement, growth arrest assay in Ewing sarcoma cells\",\n      \"pmids\": [\"33147457\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether prodomain–CD99 signaling operates in skeletal tissues not tested\", \"Stoichiometry and structural basis of prodomain–CD99 interaction unknown\", \"Relationship between prodomain processing and dual signaling modes undefined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"GDF6 mRNA was shown to be epitranscriptomically regulated: METTL3-mediated m6A methylation stabilizes GDF6 mRNA during dentinogenesis, and gain-of-function knock-in mice (p.Tyr443Asn) confirmed that enhanced GDF6/BMP signaling disrupts joint interzone formation at the transcriptomic level.\",\n      \"evidence\": \"MeRIP-seq and actinomycin-D stability assays in dental pulp stem cells; CRISPR knock-in mouse with RNA-seq of limb buds\",\n      \"pmids\": [\"37041485\", \"36744814\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which m6A sites on GDF6 mRNA are functionally critical not mapped at nucleotide resolution\", \"Transcriptomic changes in knock-in mice not validated at the protein level for all targets\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The m6A regulatory circuit was extended: FTO demethylation destabilizes GDF6 mRNA, while IGF2BP1 acts as the m6A reader stabilizing it; FTO depletion increases GDF6 and type I interferon output in RSV-infected cells, linking GDF6 to innate immune regulation.\",\n      \"evidence\": \"FTO and IGF2BP1 knockdown, m6A-seq, mRNA stability assays, IFN and cytokine measurement in RSV-infected cells\",\n      \"pmids\": [\"39474078\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether GDF6 directly drives IFN production or acts indirectly not resolved\", \"Relevance of GDF6-IFN axis beyond RSV infection unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"GDF6 was shown to exert cardioprotective anti-hypertrophic effects through a non-canonical cAMP/Epac1/AMPKα pathway, distinct from its classical BMP receptor signaling.\",\n      \"evidence\": \"AAV9-mediated cardiac GDF6 overexpression/knockdown in TAC mouse model, pharmacological AMPKα inhibition, Epac1 knockdown, neonatal rat ventricular myocytes\",\n      \"pmids\": [\"41462947\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor mediating cAMP/Epac1 activation by GDF6 in cardiomyocytes not identified\", \"Single lab, awaits independent confirmation\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for GDF6's divergent signaling through the same receptors as BMP-2, the physiological contexts in which prodomain–CD99 versus mature-ligand–BMPR signaling predominate, and how m6A-dependent mRNA stabilization integrates with miRNA-mediated repression to set GDF6 protein levels in specific tissues.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal structure of GDF6–receptor complex available\", \"Prodomain cleavage regulation and tissue-specific processing not characterized\", \"Integrated quantitative model of epitranscriptomic and miRNA regulation of GDF6 mRNA absent\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 8, 11, 14]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 8, 14, 24]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 10, 11, 14, 20, 23]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 2, 3, 9, 12, 16]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [19, 21]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"NOG\",\n      \"BMPR1A\",\n      \"BMPR2\",\n      \"ACVR2A\",\n      \"ACVR2B\",\n      \"CD99\",\n      \"CSK\",\n      \"IGF2BP1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}