{"gene":"NDN","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":2003,"finding":"Loss of necdin (Ndn) in mice results in abnormal neuronal activity within the pre-Bötzinger complex (putative respiratory rhythm-generating center), causing unstable respiratory rhythm with prolonged periods of depression, establishing a direct functional role of necdin in central respiratory drive in neonatal neurons.","method":"Targeted gene replacement (lacZ knock-in), neonatal respiratory electrophysiology, loss-of-function phenotypic analysis","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO mouse with defined cellular phenotype (pre-Bötzinger complex dysfunction), single lab but multiple physiological readouts","pmids":["12629158"],"is_preprint":false},{"year":1997,"finding":"The human NDN gene is exclusively expressed from the paternal allele (maternally imprinted), with allele-specific DNA methylation and asynchronous DNA replication as epigenetic marks; expression in brain is restricted to post-mitotic neurons.","method":"Allele-specific expression analysis, DNA methylation assay, replication timing assay, tissue expression analysis","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal epigenetic methods (methylation, replication timing, allele-specific expression), replicated in subsequent studies","pmids":["9354807"],"is_preprint":false},{"year":2001,"finding":"Mouse Ndn acquires a distinctive but unstable maternal methylation pattern in oocytes that persists to the morula stage and is lost by the blastocyst stage; the methylation pattern is substantially remodeled postnatally, suggesting DNA methylation initially preserves a gametic imprint during preimplantation but other epigenetic events maintain imprinting later in development.","method":"Sodium bisulfite sequencing of CpG dinucleotides across the 5' end of Ndn in gametes and preimplantation/adult tissues","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bisulfite sequencing across developmental stages in a single lab, multiple tissue types analyzed","pmids":["11259587"],"is_preprint":false},{"year":2004,"finding":"The human NDN gene promoter CpG island shows maternal allele-specific DNA hypermethylation independent of transcriptional activity; the paternal allele lies in a domain of allele-specific histone hyperacetylation correlating with transcriptional state; histone H3 lysine 4 di- and tri-methylation persists independent of transcription as a stable imprint mark.","method":"Sodium bisulfite sequencing, chromatin immunoprecipitation (ChIP) for histone acetylation and H3K4 methylation","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal methods (bisulfite sequencing + ChIP), single lab","pmids":["15247330"],"is_preprint":false},{"year":2005,"finding":"In vivo DNA footprinting of the NDN promoter revealed allele-specific sites of modified chromatin (DNA-protein interactions) that distinguish parental alleles in NDN-expressing cells and in cells where NDN is not expressed, indicating that layered allele-specific and tissue-specific epigenetic marks control NDN transcription.","method":"In vivo DNA footprinting (ligation-mediated PCR)","journal":"Journal of cellular biochemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single method (in vivo footprinting), single lab, no functional validation of specific footprinted sites","pmids":["15669020"],"is_preprint":false},{"year":2013,"finding":"In the absence of the paternal Ndn allele, the normally silent maternal Ndn allele is expressed at extremely low levels with high non-genetic heterogeneity; this stochastic expression is sex-dependent and shows transgenerational epigenetic inheritance; in ~50% of mutant mice it reduces birth lethality and severity of breathing deficiency, correlated with reduced loss of serotonergic neurons. Competition between non-imprinted Ndn promoters results in monoallelic (paternal or maternal) Ndn expression, suggesting allelic exclusion can occur independent of imprinting.","method":"Quantitative allele-specific expression analysis in wild-type, heterozygous, and homozygous Ndn-deleted mice; multiple mouse models; post-mortem human PWS brain analysis; serotonergic neuron counting","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple mouse genetic models and orthogonal quantitative methods, single lab, functional correlation with neuronal survival","pmids":["24039599"],"is_preprint":false},{"year":2017,"finding":"NDN protein binds to the GN box in the LRP6 promoter to attenuate LRP6 transcription, thereby inhibiting the Wnt signaling pathway; loss of NDN expression promotes CRC cell proliferation by allowing LRP6 upregulation and Wnt pathway activation.","method":"Promoter binding assay (chromatin immunoprecipitation or reporter assay implied), NDN re-expression/knockdown in CRC cell lines, cell cycle analysis, LRP6 expression measurement","journal":"Oncotarget","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, mechanistic detail (GN box binding) asserted but method details sparse in abstract, single cell line (SW480)","pmids":["28521288"],"is_preprint":false},{"year":2016,"finding":"Re-expression of NDN in ovarian cancer cells decreased Bcl-2 levels and induced apoptosis; it also inhibited cell migration by decreasing actin stress fiber and focal adhesion complex formation through deactivation of Src, FAK, and RhoA signaling.","method":"NDN re-expression in ovarian cancer cell lines and xenografts, apoptosis assays, cell migration assays, immunofluorescence for actin/focal adhesions, western blot for Src/FAK/RhoA activity","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal functional assays (apoptosis, migration, signaling pathway components) in cell lines and in vivo xenografts, single lab","pmids":["26689988"],"is_preprint":false}],"current_model":"NDN (necdin) is a paternally expressed imprinted gene whose protein product is restricted to post-mitotic neurons and functions as a transcriptional repressor (binding the LRP6 promoter GN box to suppress Wnt signaling) and a regulator of neuronal survival; loss of necdin disrupts central respiratory rhythmogenesis in the pre-Bötzinger complex, reduces serotonergic neuron survival, and in non-neuronal contexts inhibits apoptosis resistance and cell migration via suppression of Bcl-2, Src/FAK/RhoA, and Wnt/LRP6 pathways; its allele-specific expression is maintained by layered epigenetic marks including maternal promoter DNA hypermethylation, paternal allele histone hyperacetylation, and persistent H3K4 methylation."},"narrative":{"mechanistic_narrative":"NDN (necdin) is a paternally expressed imprinted gene whose product acts as a transcriptional repressor and regulator of neuronal survival and cell behavior [PMID:9354807, PMID:12629158]. In the nervous system, necdin is required for stable central respiratory rhythmogenesis: its loss causes abnormal neuronal activity in the pre-Bötzinger complex and unstable respiratory rhythm in neonatal mice [PMID:12629158], a phenotype that correlates with loss of serotonergic neurons [PMID:24039599]. At the molecular level, necdin functions as a transcriptional repressor, binding the GN box in the LRP6 promoter to attenuate LRP6 transcription and thereby suppress Wnt signaling [PMID:28521288]; in non-neuronal cancer contexts its re-expression also lowers Bcl-2 to induce apoptosis and inhibits cell migration by deactivating Src/FAK/RhoA signaling and reducing actin stress fiber and focal adhesion formation [PMID:26689988]. NDN expression is monoallelic from the paternal allele, restricted to post-mitotic neurons, and maintained by layered epigenetic marks: maternal promoter CpG hypermethylation, paternal allele histone hyperacetylation, and transcription-independent H3K4 methylation [PMID:9354807, PMID:15247330]. The DNA methylation imprint is established as an unstable gametic mark that is remodeled across development, with later epigenetic events sustaining imprinting [PMID:11259587]. In the absence of the paternal allele, the silent maternal allele can be stochastically and heterogeneously reactivated, and this partial expression mitigates breathing deficiency and serotonergic neuron loss [PMID:24039599].","teleology":[{"year":1997,"claim":"Established that NDN is a maternally imprinted, paternally expressed gene with neuron-restricted expression, defining the regulatory logic underlying its dosage in brain.","evidence":"Allele-specific expression, DNA methylation, replication timing, and tissue expression analysis in human","pmids":["9354807"],"confidence":"High","gaps":["Did not define the protein's molecular function","Mechanism linking imprint to neuronal phenotype not addressed"]},{"year":2001,"claim":"Resolved how the imprint is set versus maintained, showing the gametic DNA methylation mark is unstable and remodeled, implying other epigenetic events sustain imprinting later.","evidence":"Bisulfite sequencing across gametes and preimplantation/adult tissues in mouse","pmids":["11259587"],"confidence":"Medium","gaps":["Identity of the maintaining epigenetic events not established","Functional consequence of methylation remodeling untested"]},{"year":2003,"claim":"Provided the first in vivo functional role, showing necdin is required for stable central respiratory rhythm via the pre-Bötzinger complex.","evidence":"lacZ knock-in KO mouse with neonatal respiratory electrophysiology","pmids":["12629158"],"confidence":"Medium","gaps":["Molecular mechanism in respiratory neurons unknown","Single lab; downstream targets not identified"]},{"year":2004,"claim":"Defined the layered chromatin basis of allele-specific control, identifying maternal DNA hypermethylation, paternal histone hyperacetylation, and transcription-independent H3K4 methylation as the imprint marks.","evidence":"Bisulfite sequencing and ChIP for histone acetylation and H3K4 methylation on human NDN","pmids":["15247330"],"confidence":"Medium","gaps":["Causal hierarchy among marks not established","Mechanism establishing the marks unknown"]},{"year":2005,"claim":"Mapped allele- and tissue-specific DNA-protein interactions at the NDN promoter, indicating bound factors distinguish parental alleles and expression states.","evidence":"In vivo DNA footprinting by ligation-mediated PCR","pmids":["15669020"],"confidence":"Low","gaps":["Single method with no functional validation of footprinted sites","Identity of bound proteins not determined"]},{"year":2016,"claim":"Established a non-neuronal cell-biological function, showing necdin promotes apoptosis and suppresses migration by lowering Bcl-2 and deactivating Src/FAK/RhoA signaling.","evidence":"NDN re-expression in ovarian cancer cells and xenografts with apoptosis, migration, immunofluorescence, and western blot assays","pmids":["26689988"],"confidence":"Medium","gaps":["Direct versus indirect regulation of Src/FAK/RhoA unresolved","Relevance to neuronal phenotypes not established"]},{"year":2017,"claim":"Identified a direct transcriptional repressor activity, showing necdin binds the LRP6 promoter GN box to attenuate LRP6 and suppress Wnt signaling.","evidence":"Promoter binding/reporter assay plus NDN re-expression/knockdown and proliferation analysis in CRC cells","pmids":["28521288"],"confidence":"Low","gaps":["Single cell line (SW480) with sparse mechanistic detail","Direct DNA binding not rigorously demonstrated","Generality across tissues untested"]},{"year":2013,"claim":"Demonstrated that the silent maternal allele can be stochastically reactivated independent of imprinting and that this partial expression mitigates breathing and serotonergic neuron deficits.","evidence":"Quantitative allele-specific expression across multiple mouse models, human PWS brain analysis, serotonergic neuron counting","pmids":["24039599"],"confidence":"Medium","gaps":["Mechanism of stochastic maternal reactivation unclear","Basis of sex-dependence and transgenerational inheritance not defined"]},{"year":null,"claim":"How necdin's transcriptional repressor activity mechanistically links to its neuronal survival and respiratory functions remains unresolved.","evidence":"No timeline discovery connects the LRP6/Wnt or Src/FAK/RhoA mechanisms to the pre-Bötzinger or serotonergic neuron phenotypes","pmids":[],"confidence":"Low","gaps":["No identified neuronal target genes of necdin repression","No structural model of necdin DNA binding","Direct physical partners in neurons uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[6]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[6]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[6]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,7]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[7]}],"complexes":[],"partners":[],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q99608","full_name":"Necdin","aliases":[],"length_aa":321,"mass_kda":36.1,"function":"Growth suppressor that facilitates the entry of the cell into cell cycle arrest. Functionally similar to the retinoblastoma protein it binds to and represses the activity of cell-cycle-promoting proteins such as SV40 large T antigen, adenovirus E1A, and the transcription factor E2F. Necdin also interacts with p53 and works in an additive manner to inhibit cell growth. Also functions as a transcription factor and directly binds to specific guanosine-rich DNA sequences (By similarity)","subcellular_location":"Perikaryon; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q99608/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NDN","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NDN","total_profiled":1310},"omim":[{"mim_id":"615547","title":"SCHAAF-YANG SYNDROME; SHFYNG","url":"https://www.omim.org/entry/615547"},{"mim_id":"608243","title":"NSE3 HOMOLOG, SMC5-SMC6 COMPLEX COMPONENT; NSMCE3","url":"https://www.omim.org/entry/608243"},{"mim_id":"605283","title":"MAGE-LIKE 2; MAGEL2","url":"https://www.omim.org/entry/605283"},{"mim_id":"602117","title":"NECDIN; NDN","url":"https://www.omim.org/entry/602117"},{"mim_id":"601623","title":"UBIQUITIN-PROTEIN LIGASE E3A; UBE3A","url":"https://www.omim.org/entry/601623"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/NDN"},"hgnc":{"alias_symbol":["HsT16328","PWCR"],"prev_symbol":[]},"alphafold":{"accession":"Q99608","domains":[{"cath_id":"1.10.10.1200","chopping":"94-176","consensus_level":"high","plddt":83.4639,"start":94,"end":176},{"cath_id":"1.10.10.1210","chopping":"185-270","consensus_level":"high","plddt":84.9719,"start":185,"end":270}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99608","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q99608-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q99608-F1-predicted_aligned_error_v6.png","plddt_mean":66.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NDN","jax_strain_url":"https://www.jax.org/strain/search?query=NDN"},"sequence":{"accession":"Q99608","fasta_url":"https://rest.uniprot.org/uniprotkb/Q99608.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q99608/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99608"}},"corpus_meta":[{"pmid":"9354807","id":"PMC_9354807","title":"The human necdin gene, NDN, is maternally imprinted and located in the Prader-Willi syndrome chromosomal region.","date":"1997","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/9354807","citation_count":207,"is_preprint":false},{"pmid":"19066619","id":"PMC_19066619","title":"A paternal deletion of MKRN3, MAGEL2 and NDN does not result in Prader-Willi syndrome.","date":"2008","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/19066619","citation_count":100,"is_preprint":false},{"pmid":"12629158","id":"PMC_12629158","title":"Absence of Ndn, encoding the Prader-Willi syndrome-deleted gene necdin, results in congenital deficiency of central respiratory drive in neonatal mice.","date":"2003","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/12629158","citation_count":94,"is_preprint":false},{"pmid":"8220172","id":"PMC_8220172","title":"Nonsynaptic diffusion neurotransmission (NDN) in the brain.","date":"1993","source":"Neurochemistry international","url":"https://pubmed.ncbi.nlm.nih.gov/8220172","citation_count":56,"is_preprint":false},{"pmid":"11259587","id":"PMC_11259587","title":"Establishment and maintenance of DNA methylation patterns in mouse Ndn: implications for maintenance of imprinting in target genes of the imprinting center.","date":"2001","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/11259587","citation_count":43,"is_preprint":false},{"pmid":"15247330","id":"PMC_15247330","title":"Tissue-specific and imprinted epigenetic modifications of the human NDN gene.","date":"2004","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/15247330","citation_count":42,"is_preprint":false},{"pmid":"24039599","id":"PMC_24039599","title":"Stochastic loss of silencing of the imprinted Ndn/NDN allele, in a mouse model and humans with prader-willi syndrome, has functional consequences.","date":"2013","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24039599","citation_count":30,"is_preprint":false},{"pmid":"14579385","id":"PMC_14579385","title":"A MAGE/NDN-like gene in zebrafish.","date":"2003","source":"Developmental dynamics : an official publication of the American Association of Anatomists","url":"https://pubmed.ncbi.nlm.nih.gov/14579385","citation_count":18,"is_preprint":false},{"pmid":"28521288","id":"PMC_28521288","title":"Hypermethylation of NDN promotes cell proliferation by activating the Wnt signaling pathway in colorectal cancer.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/28521288","citation_count":14,"is_preprint":false},{"pmid":"26689988","id":"PMC_26689988","title":"NDN is an imprinted tumor suppressor gene that is downregulated in ovarian cancers through genetic and epigenetic mechanisms.","date":"2016","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/26689988","citation_count":13,"is_preprint":false},{"pmid":"34359112","id":"PMC_34359112","title":"Conservation of Imprinting and Methylation of MKRN3, MAGEL2 and NDN Genes in Cattle.","date":"2021","source":"Animals : an open access journal from MDPI","url":"https://pubmed.ncbi.nlm.nih.gov/34359112","citation_count":7,"is_preprint":false},{"pmid":"11439287","id":"PMC_11439287","title":"Systematic screening for mutations in the human necdin gene (NDN): identification of two naturally occurring polymorphisms and association analysis in body weight regulation.","date":"2001","source":"International journal of obesity and related metabolic disorders : journal of the International Association for the Study of Obesity","url":"https://pubmed.ncbi.nlm.nih.gov/11439287","citation_count":6,"is_preprint":false},{"pmid":"31007492","id":"PMC_31007492","title":"Is prone sleeping dangerous for neonates? Polysomnographic characteristics and NDN gene analysis.","date":"2019","source":"Tzu chi medical journal","url":"https://pubmed.ncbi.nlm.nih.gov/31007492","citation_count":4,"is_preprint":false},{"pmid":"15669020","id":"PMC_15669020","title":"Chromatin modification of the human imprinted NDN (necdin) gene detected by in vivo footprinting.","date":"2005","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15669020","citation_count":4,"is_preprint":false},{"pmid":"41397315","id":"PMC_41397315","title":"Machine learning and multi-omics-based identification of hub paternal imprinted genes PEG11/RTL1, PEG9/DLK1, PEG6/NDN, and PEG5/NNAT in sperm of couples experiencing idiopathic recurrent pregnancy loss.","date":"2025","source":"Computers in biology and medicine","url":"https://pubmed.ncbi.nlm.nih.gov/41397315","citation_count":3,"is_preprint":false},{"pmid":"38252343","id":"PMC_38252343","title":"Cloning, tissue expression and imprinting status analysis of the NDN gene in Dolang sheep.","date":"2024","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/38252343","citation_count":1,"is_preprint":false},{"pmid":"40231584","id":"PMC_40231584","title":"A Case of Prader-Willi Syndrome With a Deletion Including MAGEL2 , NDN , and MKRN3 , but Excluding SNRPN and SNORD116.","date":"2025","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/40231584","citation_count":1,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.10.24.684371","title":"The Preclinical Animal Network (PCAN): Integrative high-throughput phenotyping of standardized mouse models for Prader-Willi syndrome","date":"2025-10-26","source":"bioRxiv","url":"https://doi.org/10.1101/2025.10.24.684371","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10009,"output_tokens":2020,"usd":0.030163,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9084,"output_tokens":2654,"usd":0.055885,"stage2_stop_reason":"end_turn"},"total_usd":0.086048,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"Loss of necdin (Ndn) in mice results in abnormal neuronal activity within the pre-Bötzinger complex (putative respiratory rhythm-generating center), causing unstable respiratory rhythm with prolonged periods of depression, establishing a direct functional role of necdin in central respiratory drive in neonatal neurons.\",\n      \"method\": \"Targeted gene replacement (lacZ knock-in), neonatal respiratory electrophysiology, loss-of-function phenotypic analysis\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO mouse with defined cellular phenotype (pre-Bötzinger complex dysfunction), single lab but multiple physiological readouts\",\n      \"pmids\": [\"12629158\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The human NDN gene is exclusively expressed from the paternal allele (maternally imprinted), with allele-specific DNA methylation and asynchronous DNA replication as epigenetic marks; expression in brain is restricted to post-mitotic neurons.\",\n      \"method\": \"Allele-specific expression analysis, DNA methylation assay, replication timing assay, tissue expression analysis\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal epigenetic methods (methylation, replication timing, allele-specific expression), replicated in subsequent studies\",\n      \"pmids\": [\"9354807\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Mouse Ndn acquires a distinctive but unstable maternal methylation pattern in oocytes that persists to the morula stage and is lost by the blastocyst stage; the methylation pattern is substantially remodeled postnatally, suggesting DNA methylation initially preserves a gametic imprint during preimplantation but other epigenetic events maintain imprinting later in development.\",\n      \"method\": \"Sodium bisulfite sequencing of CpG dinucleotides across the 5' end of Ndn in gametes and preimplantation/adult tissues\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bisulfite sequencing across developmental stages in a single lab, multiple tissue types analyzed\",\n      \"pmids\": [\"11259587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The human NDN gene promoter CpG island shows maternal allele-specific DNA hypermethylation independent of transcriptional activity; the paternal allele lies in a domain of allele-specific histone hyperacetylation correlating with transcriptional state; histone H3 lysine 4 di- and tri-methylation persists independent of transcription as a stable imprint mark.\",\n      \"method\": \"Sodium bisulfite sequencing, chromatin immunoprecipitation (ChIP) for histone acetylation and H3K4 methylation\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal methods (bisulfite sequencing + ChIP), single lab\",\n      \"pmids\": [\"15247330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In vivo DNA footprinting of the NDN promoter revealed allele-specific sites of modified chromatin (DNA-protein interactions) that distinguish parental alleles in NDN-expressing cells and in cells where NDN is not expressed, indicating that layered allele-specific and tissue-specific epigenetic marks control NDN transcription.\",\n      \"method\": \"In vivo DNA footprinting (ligation-mediated PCR)\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single method (in vivo footprinting), single lab, no functional validation of specific footprinted sites\",\n      \"pmids\": [\"15669020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In the absence of the paternal Ndn allele, the normally silent maternal Ndn allele is expressed at extremely low levels with high non-genetic heterogeneity; this stochastic expression is sex-dependent and shows transgenerational epigenetic inheritance; in ~50% of mutant mice it reduces birth lethality and severity of breathing deficiency, correlated with reduced loss of serotonergic neurons. Competition between non-imprinted Ndn promoters results in monoallelic (paternal or maternal) Ndn expression, suggesting allelic exclusion can occur independent of imprinting.\",\n      \"method\": \"Quantitative allele-specific expression analysis in wild-type, heterozygous, and homozygous Ndn-deleted mice; multiple mouse models; post-mortem human PWS brain analysis; serotonergic neuron counting\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple mouse genetic models and orthogonal quantitative methods, single lab, functional correlation with neuronal survival\",\n      \"pmids\": [\"24039599\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"NDN protein binds to the GN box in the LRP6 promoter to attenuate LRP6 transcription, thereby inhibiting the Wnt signaling pathway; loss of NDN expression promotes CRC cell proliferation by allowing LRP6 upregulation and Wnt pathway activation.\",\n      \"method\": \"Promoter binding assay (chromatin immunoprecipitation or reporter assay implied), NDN re-expression/knockdown in CRC cell lines, cell cycle analysis, LRP6 expression measurement\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, mechanistic detail (GN box binding) asserted but method details sparse in abstract, single cell line (SW480)\",\n      \"pmids\": [\"28521288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Re-expression of NDN in ovarian cancer cells decreased Bcl-2 levels and induced apoptosis; it also inhibited cell migration by decreasing actin stress fiber and focal adhesion complex formation through deactivation of Src, FAK, and RhoA signaling.\",\n      \"method\": \"NDN re-expression in ovarian cancer cell lines and xenografts, apoptosis assays, cell migration assays, immunofluorescence for actin/focal adhesions, western blot for Src/FAK/RhoA activity\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal functional assays (apoptosis, migration, signaling pathway components) in cell lines and in vivo xenografts, single lab\",\n      \"pmids\": [\"26689988\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NDN (necdin) is a paternally expressed imprinted gene whose protein product is restricted to post-mitotic neurons and functions as a transcriptional repressor (binding the LRP6 promoter GN box to suppress Wnt signaling) and a regulator of neuronal survival; loss of necdin disrupts central respiratory rhythmogenesis in the pre-Bötzinger complex, reduces serotonergic neuron survival, and in non-neuronal contexts inhibits apoptosis resistance and cell migration via suppression of Bcl-2, Src/FAK/RhoA, and Wnt/LRP6 pathways; its allele-specific expression is maintained by layered epigenetic marks including maternal promoter DNA hypermethylation, paternal allele histone hyperacetylation, and persistent H3K4 methylation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"NDN (necdin) is a paternally expressed imprinted gene whose product acts as a transcriptional repressor and regulator of neuronal survival and cell behavior [#1, #0]. In the nervous system, necdin is required for stable central respiratory rhythmogenesis: its loss causes abnormal neuronal activity in the pre-Bötzinger complex and unstable respiratory rhythm in neonatal mice [#0], a phenotype that correlates with loss of serotonergic neurons [#5]. At the molecular level, necdin functions as a transcriptional repressor, binding the GN box in the LRP6 promoter to attenuate LRP6 transcription and thereby suppress Wnt signaling [#6]; in non-neuronal cancer contexts its re-expression also lowers Bcl-2 to induce apoptosis and inhibits cell migration by deactivating Src/FAK/RhoA signaling and reducing actin stress fiber and focal adhesion formation [#7]. NDN expression is monoallelic from the paternal allele, restricted to post-mitotic neurons, and maintained by layered epigenetic marks: maternal promoter CpG hypermethylation, paternal allele histone hyperacetylation, and transcription-independent H3K4 methylation [#1, #3]. The DNA methylation imprint is established as an unstable gametic mark that is remodeled across development, with later epigenetic events sustaining imprinting [#2]. In the absence of the paternal allele, the silent maternal allele can be stochastically and heterogeneously reactivated, and this partial expression mitigates breathing deficiency and serotonergic neuron loss [#5].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established that NDN is a maternally imprinted, paternally expressed gene with neuron-restricted expression, defining the regulatory logic underlying its dosage in brain.\",\n      \"evidence\": \"Allele-specific expression, DNA methylation, replication timing, and tissue expression analysis in human\",\n      \"pmids\": [\"9354807\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the protein's molecular function\", \"Mechanism linking imprint to neuronal phenotype not addressed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Resolved how the imprint is set versus maintained, showing the gametic DNA methylation mark is unstable and remodeled, implying other epigenetic events sustain imprinting later.\",\n      \"evidence\": \"Bisulfite sequencing across gametes and preimplantation/adult tissues in mouse\",\n      \"pmids\": [\"11259587\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the maintaining epigenetic events not established\", \"Functional consequence of methylation remodeling untested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Provided the first in vivo functional role, showing necdin is required for stable central respiratory rhythm via the pre-Bötzinger complex.\",\n      \"evidence\": \"lacZ knock-in KO mouse with neonatal respiratory electrophysiology\",\n      \"pmids\": [\"12629158\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism in respiratory neurons unknown\", \"Single lab; downstream targets not identified\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined the layered chromatin basis of allele-specific control, identifying maternal DNA hypermethylation, paternal histone hyperacetylation, and transcription-independent H3K4 methylation as the imprint marks.\",\n      \"evidence\": \"Bisulfite sequencing and ChIP for histone acetylation and H3K4 methylation on human NDN\",\n      \"pmids\": [\"15247330\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal hierarchy among marks not established\", \"Mechanism establishing the marks unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Mapped allele- and tissue-specific DNA-protein interactions at the NDN promoter, indicating bound factors distinguish parental alleles and expression states.\",\n      \"evidence\": \"In vivo DNA footprinting by ligation-mediated PCR\",\n      \"pmids\": [\"15669020\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single method with no functional validation of footprinted sites\", \"Identity of bound proteins not determined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established a non-neuronal cell-biological function, showing necdin promotes apoptosis and suppresses migration by lowering Bcl-2 and deactivating Src/FAK/RhoA signaling.\",\n      \"evidence\": \"NDN re-expression in ovarian cancer cells and xenografts with apoptosis, migration, immunofluorescence, and western blot assays\",\n      \"pmids\": [\"26689988\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect regulation of Src/FAK/RhoA unresolved\", \"Relevance to neuronal phenotypes not established\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified a direct transcriptional repressor activity, showing necdin binds the LRP6 promoter GN box to attenuate LRP6 and suppress Wnt signaling.\",\n      \"evidence\": \"Promoter binding/reporter assay plus NDN re-expression/knockdown and proliferation analysis in CRC cells\",\n      \"pmids\": [\"28521288\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single cell line (SW480) with sparse mechanistic detail\", \"Direct DNA binding not rigorously demonstrated\", \"Generality across tissues untested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrated that the silent maternal allele can be stochastically reactivated independent of imprinting and that this partial expression mitigates breathing and serotonergic neuron deficits.\",\n      \"evidence\": \"Quantitative allele-specific expression across multiple mouse models, human PWS brain analysis, serotonergic neuron counting\",\n      \"pmids\": [\"24039599\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of stochastic maternal reactivation unclear\", \"Basis of sex-dependence and transgenerational inheritance not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How necdin's transcriptional repressor activity mechanistically links to its neuronal survival and respiratory functions remains unresolved.\",\n      \"evidence\": \"No timeline discovery connects the LRP6/Wnt or Src/FAK/RhoA mechanisms to the pre-Bötzinger or serotonergic neuron phenotypes\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No identified neuronal target genes of necdin repression\", \"No structural model of necdin DNA binding\", \"Direct physical partners in neurons uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}\n```","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}