{"gene":"REEP1","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":2010,"finding":"REEP1 is structurally related to the DP1/Yop1p family of ER-shaping proteins and localizes to the tubular ER in neurons. REEP1 forms protein complexes with atlastin-1 and spastin within the tubular ER, interactions requiring hydrophobic hairpin domains in each protein. REEP1 also binds microtubules directly and promotes ER alignment along the microtubule cytoskeleton. A SPG31 mutant REEP1 lacking the C-terminal cytoplasmic region failed to interact with microtubules and disrupted the ER network. REEP proteins were required for ER network formation in vitro.","method":"Co-immunoprecipitation in COS7 cells, overexpression/domain-deletion analysis, in vitro ER network formation assay, immunofluorescence colocalization in rat cortical neurons","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (Co-IP, in vitro reconstitution, domain mutagenesis, live imaging), replicated across cell types and conditions in a single rigorous study","pmids":["20200447"],"is_preprint":false},{"year":2006,"finding":"REEP1 was initially reported to localize to mitochondria based on cellular fractionation/localization experiments in the study identifying it as the SPG31 disease gene.","method":"Subcellular fractionation and localization assays in transfected cells","journal":"American journal of human genetics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single localization method; later work showed REEP1 is primarily an ER protein at ER-mitochondria contacts, reducing confidence in pure mitochondrial assignment","pmids":["16826527"],"is_preprint":false},{"year":2013,"finding":"REEP1 is a neuron-specific, membrane-binding, and membrane curvature-inducing protein residing in the ER. In REEP1-deficient mice (homozygous exon 2 deletion), cortical motor neurons showed reduced complexity of the peripheral ER by ultrastructural analysis, connecting proper neuronal ER architecture to long-term axon survival.","method":"Mouse knockout model (heterozygous and homozygous exon 2 deletion), electron microscopy ultrastructural analysis, behavioral gait analysis","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO mouse with defined cellular phenotype (ER morphology by EM) plus behavioral readout; replicated across heterozygous and homozygous models","pmids":["24051375"],"is_preprint":false},{"year":2015,"finding":"REEP1 is present at the ER-mitochondria interface, containing subdomains for both mitochondrial and ER localization. REEP1 facilitates ER-mitochondria interactions (measured by split-RLuc8 assay), and disease-associated REEP1 mutations diminish this function. Knockdown of Reep1 and expression of pathological mutations caused neuritic growth defects and degeneration in mouse cortical neurons.","method":"Cellular imaging (immunofluorescence/confocal), biochemical fractionation, novel split-RLuc8 bioluminescence complementation assay for ER-mitochondria contacts, neuritic growth/degeneration assays in mouse cortical culture","journal":"Annals of neurology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (fractionation, split-RLuc8 assay, neuronal KD phenotype), single lab but rigorous functional validation with disease mutations","pmids":["26201691"],"is_preprint":false},{"year":2016,"finding":"REEP1 is involved in lipid droplet biology: Reep1-null mice show partial lipoatrophy, and Reep1-/- embryonic fibroblasts and cortical neurons show lipid droplet abnormalities. REEP1 co-immunoprecipitates with seipin (BSCL2) in cells, linking ER morphogenesis to lipid droplet regulation.","method":"Reep1 knockout mouse (null allele), lipid droplet staining in fibroblasts and neurons, co-immunoprecipitation of REEP1 with seipin, MRI of mice","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO mouse with multiple cellular phenotypes plus reciprocal Co-IP identifying seipin as binding partner; multiple orthogonal methods","pmids":["27638887"],"is_preprint":false},{"year":2014,"finding":"The N-terminus of REEP1 is necessary for proper targeting to and/or retention in the ER. HSP-associated missense variants at the N-terminus abolish ER targeting and cause accumulation at lipid droplets. Co-overexpression of REEP1 with atlastins increases lipid droplet size synergistically, whereas REEP1 alone does not.","method":"Overexpression of wild-type and mutant REEP1 constructs in cell lines, immunofluorescence localization, lipid droplet size measurement, N-terminal deletion/tagging experiments","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple constructs and orthogonal imaging/biochemical approaches in a single lab; functional ER-targeting mechanism defined by mutagenesis","pmids":["24478229"],"is_preprint":false},{"year":2012,"finding":"A dHMN-associated internally shortened REEP1 variant (p.102_139del) shows a subcellular localization defect distinct from the HSP-associated missense mutation (p.Ala20Glu). The p.102_139del variant also recruits atlastin-1 (a REEP1 binding partner) to the altered sites of localization, whereas p.Ala20Glu does not, suggesting distinct pathogenic mechanisms for HSP vs. dHMN.","method":"Exogenous overexpression in cell lines, immunofluorescence localization, minigene splice assay confirming mRNA consequence","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, cell-based localization and atlastin-1 co-recruitment assay; two orthogonal approaches supporting distinct mechanisms","pmids":["22703882"],"is_preprint":false},{"year":2017,"finding":"In SPG31 patient fibroblasts, mitochondrial morphology is highly tubular due to hyperphosphorylation of DRP1 at serine 637, which inhibits mitochondrial fission. This hyperphosphorylation is caused by impaired interaction between REEP1 and the mitochondrial phosphatase PGAM5. Genetic or pharmacological reduction of DRP1-S637 phosphorylation restores mitochondrial morphology. Pathological REEP1 mutations expressed in neurons target REEP1 to mitochondria and sequester mitochondria to the perinuclear region, impairing axonal mitochondrial transport.","method":"Primary fibroblasts from SPG31 patients, immunofluorescence/confocal mitochondrial morphology analysis, phospho-DRP1 biochemical assays, REEP1-PGAM5 interaction assay, primary neuronal culture with mutant REEP1 overexpression and mitochondrial transport imaging","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient cells plus neuronal culture, biochemical phosphorylation assays, and rescue experiments; single lab with multiple orthogonal methods","pmids":["28007911"],"is_preprint":false},{"year":2017,"finding":"A nonstop variant in REEP1 produces a C-terminally extended protein whose extension triggers self-aggregation of REEP1 and of reporter proteins, demonstrating a toxic gain-of-function mechanism distinct from the loss-of-function seen in HSP. This aggregation-prone behavior maps to a 3'UTR-encoded cryptic amyloidogenic element.","method":"Expression of nonstop variant protein in cells, aggregation assays with REEP1 and reporter fusions, mRNA/protein analysis","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional aggregation assays with multiple reporters in a single lab; mechanistically distinct from prior loss-of-function findings","pmids":["29124833"],"is_preprint":false},{"year":2014,"finding":"In a Drosophila model, downregulation of the REEP1 homolog enhanced Tau toxicity and increased formation of insoluble Tau aggregates, while overexpression of either Drosophila or human REEP1 reversed these phenotypes and promoted neuronal resistance to ER stress, identifying a role for REEP1 in preventing Tau aggregation and in ER stress resistance.","method":"Drosophila RNAi screen, Tau toxicity assays, Tau solubility/aggregation biochemistry, REEP1 overexpression rescue experiments in fly model","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo Drosophila model with loss- and gain-of-function, biochemical Tau aggregation readout; single lab","pmids":["25096240"],"is_preprint":false},{"year":2022,"finding":"REEP1 associates with NDUFA4 and plays an important role in preserving the integrity of mitochondrial complex IV. Forced REEP1 expression in the spinal cord of SOD1G93A mice extended lifespan, decelerated symptom progression, improved motor performance, and alleviated neuromuscular synaptic loss and motor neuron loss through augmentation of mitochondrial function.","method":"Co-immunoprecipitation of REEP1 with NDUFA4, OXPHOS complex IV activity assays, in vivo AAV-mediated REEP1 overexpression in SOD1G93A mice with behavioral and histological readouts","journal":"Neuroscience bulletin","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus in vivo rescue with functional mitochondrial assay; single lab, multiple orthogonal methods","pmids":["36520405"],"is_preprint":false},{"year":2023,"finding":"The fission yeast ortholog of human REEP1-4 (Yep1/Hva22/Rop1) is essential for autophagosomal enclosure of ER-phagy and nucleophagy cargos but not bulk autophagy. This function relies on Yep1's ability to self-interact and shape membranes, requiring its C-terminal amphipathic helices. Human REEP1-4 can functionally substitute for Yep1 in ER-phagy, confirming functional conservation.","method":"Imaging-based screen in S. pombe, yeast genetics (deletion mutants), complementation assays with human REEP1-4, domain mutagenesis (amphipathic helix deletion), fluorescence microscopy of autophagy intermediates","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — genetic screen plus domain mutagenesis plus cross-species complementation; multiple orthogonal methods demonstrating mechanistic conservation of REEP1 in membrane shaping for selective autophagy","pmids":["37939137"],"is_preprint":false},{"year":2024,"finding":"REEP1 enhances MAM (mitochondria-associated ER membrane) formation and interacts with NDPK-D at mitochondria; increased REEP1 levels at mitochondria reduce cardiolipin (CL) externalization via the REEP1-NDPK-D interaction, thereby promoting autophagosome biogenesis.","method":"Fluorescent staining for ER-mitochondria co-localization, cardiolipin probe assay in MAM fractions, co-localization/interaction assays of REEP1 with NDPK-D, monodansylcadaverine staining for autophagosomes in SH-SY5Y cells, in vivo A53T-αSyn mouse model with behavioral tests","journal":"Phytomedicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, pharmacological intervention study; REEP1-NDPK-D interaction supported by co-localization but binding assay details limited in abstract","pmids":["39178680"],"is_preprint":false},{"year":2020,"finding":"REEP1-null mice exhibit increased ER stress markers alongside progressive motor deficits and axonal degeneration; treatment with salubrinal (an ER stress inhibitor) increased nerve-muscle connections and enhanced motor functions, implicating ER stress as a downstream mechanism of REEP1 deficiency.","method":"REEP1 knockout mouse model, ER stress marker quantification, salubrinal pharmacological treatment, neuromuscular junction innervation analysis, behavioral motor testing","journal":"Biology open","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO mouse with pharmacological rescue and multiple readouts; single lab","pmids":["32878877"],"is_preprint":false}],"current_model":"REEP1 is a hydrophobic hairpin-containing ER-shaping protein of the DP1/Yop1p family that resides at the tubular ER and ER-mitochondria contact sites in neurons; it physically interacts with atlastin-1 and spastin via hydrophobic domains to coordinate tubular ER network formation, directly binds microtubules through its C-terminal cytoplasmic region to align ER along the cytoskeleton, associates with seipin to regulate lipid droplet homeostasis, interacts with PGAM5 to control DRP1-S637 phosphorylation and mitochondrial fission dynamics, associates with NDUFA4 to support mitochondrial complex IV integrity, and—based on yeast ortholog studies—uses self-interaction and C-terminal amphipathic helices to facilitate autophagosomal enclosure of ER-phagy cargos; loss-of-function causes ER stress, reduced peripheral ER complexity in motor neurons, impaired mitochondrial transport, and progressive axonal degeneration underlying hereditary spastic paraplegia (SPG31)."},"narrative":{"mechanistic_narrative":"REEP1 is a neuron-enriched, membrane curvature-inducing protein of the DP1/Yop1p family that shapes the tubular endoplasmic reticulum and governs ER contacts with the cytoskeleton and with mitochondria [PMID:20200447, PMID:24051375]. Through hydrophobic hairpin domains it assembles into complexes with the ER-shaping machinery atlastin-1 and spastin, while its C-terminal cytoplasmic region binds microtubules directly to align the ER along the cytoskeleton; loss of this C-terminal region disrupts the ER network [PMID:20200447]. REEP1 also resides at the ER–mitochondria interface, where it carries distinct ER- and mitochondria-targeting subdomains and promotes ER–mitochondria contact formation [PMID:26201691], and it couples ER morphogenesis to lipid droplet homeostasis through interaction with seipin (BSCL2) [PMID:27638887]. At mitochondria, REEP1 interacts with the phosphatase PGAM5 to keep DRP1-serine 637 dephosphorylated and thereby permit mitochondrial fission, and it associates with NDUFA4 to preserve complex IV integrity [PMID:28007911, PMID:36520405]. Proper N-terminal targeting is required for ER residence, and disease variants that abolish it redirect REEP1 to lipid droplets or mitochondria [PMID:24478229, PMID:28007911]. Loss of REEP1 reduces peripheral ER complexity in motor neurons, triggers ER stress, and causes progressive axonal degeneration; REEP1 mutations cause the hereditary spastic paraplegia SPG31 [PMID:16826527, PMID:24051375, PMID:32878877]. A conserved membrane-shaping function supports selective autophagy: the fission yeast ortholog is essential for autophagosomal enclosure of ER-phagy cargos via C-terminal amphipathic helices, a function human REEP1-4 can substitute for [PMID:37939137].","teleology":[{"year":2006,"claim":"Establishing REEP1 as the SPG31 disease gene and assigning an initial subcellular location framed the first hypotheses about where it acts.","evidence":"Subcellular fractionation and localization in transfected cells in the gene-identification study","pmids":["16826527"],"confidence":"Low","gaps":["Single localization method later superseded by ER assignment","No mechanism linking localization to disease","Mitochondrial-only assignment not reconciled with ER residence"]},{"year":2010,"claim":"Placing REEP1 in the DP1/Yop1p family and showing it complexes with atlastin-1 and spastin and binds microtubules defined its core function as a tubular ER-shaping and ER–cytoskeleton-coupling protein.","evidence":"Co-IP in COS7, domain-deletion mutagenesis, in vitro ER network formation, and neuronal colocalization","pmids":["20200447"],"confidence":"High","gaps":["Stoichiometry and architecture of the REEP1–atlastin–spastin complex unresolved","Microtubule-binding motif within the C-terminus not mapped at residue level"]},{"year":2013,"claim":"A knockout mouse connected loss of REEP1 to reduced peripheral ER complexity in motor neurons, tying neuronal ER architecture to long-term axon survival.","evidence":"Reep1 exon-2 deletion mice with EM ultrastructure and gait analysis","pmids":["24051375"],"confidence":"High","gaps":["Causal chain from ER morphology to axon degeneration not delineated","Cell-autonomous vs non-autonomous contribution unclear"]},{"year":2014,"claim":"Mapping an N-terminal ER-targeting requirement and a synergistic effect on lipid droplet size with atlastins clarified how missense variants mislocalize REEP1 and connected it to lipid droplet biology.","evidence":"Overexpression of WT/mutant constructs, immunofluorescence, lipid droplet sizing, N-terminal deletion/tagging","pmids":["24478229"],"confidence":"Medium","gaps":["Targeting signal not defined at sequence level","Mechanism of lipid droplet size synergy with atlastins unknown"]},{"year":2014,"claim":"A Drosophila model revealed that REEP1 confers resistance to ER stress and suppresses Tau aggregation, extending its relevance beyond ER shaping to proteostasis.","evidence":"Drosophila RNAi/overexpression, Tau solubility biochemistry, cross-species rescue","pmids":["25096240"],"confidence":"Medium","gaps":["Molecular link between REEP1 and Tau aggregation not defined","Relevance to mammalian neurons not established here"]},{"year":2012,"claim":"Comparing an HSP missense variant against a dHMN truncation variant showed divergent mislocalization and atlastin-1 recruitment, indicating distinct pathogenic mechanisms across REEP1-linked disorders.","evidence":"Overexpression localization, atlastin-1 co-recruitment, minigene splice assay","pmids":["22703882"],"confidence":"Medium","gaps":["Endogenous-level validation lacking","Functional consequence of altered atlastin-1 recruitment unmeasured"]},{"year":2015,"claim":"Demonstrating REEP1 subdomains for both ER and mitochondrial localization and a measurable role in ER–mitochondria contact formation established it as a membrane contact-site organizer disrupted by disease mutations.","evidence":"Fractionation, split-RLuc8 contact-site assay, neuronal knockdown growth/degeneration assays","pmids":["26201691"],"confidence":"High","gaps":["Tethering partners at the contact site not identified","Quantitative contribution to organelle communication unknown"]},{"year":2016,"claim":"Identifying seipin as a REEP1 binding partner and documenting lipoatrophy and lipid droplet defects in null mice linked REEP1-dependent ER morphogenesis to lipid droplet regulation.","evidence":"Reep1-null mice, lipid droplet staining, reciprocal Co-IP with seipin, MRI","pmids":["27638887"],"confidence":"High","gaps":["Functional consequence of REEP1–seipin interaction on droplet biogenesis not mechanistically resolved","Tissue specificity of lipoatrophy phenotype unexplained"]},{"year":2017,"claim":"Showing that impaired REEP1–PGAM5 interaction causes DRP1-S637 hyperphosphorylation and excessively tubular mitochondria, reversible by reducing that phosphorylation, defined a mitochondrial fission control pathway in SPG31.","evidence":"SPG31 patient fibroblasts, phospho-DRP1 assays, REEP1–PGAM5 interaction, neuronal mitochondrial transport imaging, rescue","pmids":["28007911"],"confidence":"Medium","gaps":["Direct biochemical reconstitution of REEP1–PGAM5–DRP1 axis lacking","Whether mutant mitochondrial mislocalization is cause or consequence not resolved"]},{"year":2017,"claim":"A nonstop variant producing a C-terminally extended, self-aggregating protein revealed a toxic gain-of-function mechanism distinct from HSP loss-of-function.","evidence":"Expression of nonstop variant, aggregation assays with REEP1 and reporter fusions, mRNA/protein analysis","pmids":["29124833"],"confidence":"Medium","gaps":["In vivo relevance of the aggregation phenotype not tested","Cellular toxicity pathway downstream of aggregation undefined"]},{"year":2020,"claim":"Demonstrating elevated ER stress markers in REEP1-null mice and rescue by salubrinal placed ER stress downstream of REEP1 deficiency as a tractable degeneration mechanism.","evidence":"REEP1 KO mice, ER stress marker quantification, salubrinal treatment, NMJ and motor readouts","pmids":["32878877"],"confidence":"Medium","gaps":["Molecular trigger linking ER shape loss to the unfolded protein response unclear","Durability and translational relevance of pharmacological rescue untested"]},{"year":2022,"claim":"Identifying a REEP1–NDUFA4 association needed for complex IV integrity, and showing REEP1 overexpression is neuroprotective in SOD1G93A mice, extended REEP1's mitochondrial role to oxidative phosphorylation and broader motor neuron disease.","evidence":"Co-IP with NDUFA4, complex IV activity assays, AAV REEP1 overexpression in SOD1G93A mice","pmids":["36520405"],"confidence":"Medium","gaps":["Mechanism by which REEP1 supports complex IV assembly/stability unknown","Whether benefit is via complex IV or general mitochondrial support unresolved"]},{"year":2023,"claim":"Cross-species work showed the REEP1 ortholog is essential for autophagosomal enclosure of ER-phagy cargos via C-terminal amphipathic helices, with human REEP1-4 rescuing the yeast defect, establishing a conserved membrane-shaping role in selective autophagy.","evidence":"S. pombe imaging screen, deletion mutants, domain mutagenesis, human REEP1-4 complementation","pmids":["37939137"],"confidence":"High","gaps":["Direct demonstration of ER-phagy enclosure function for human REEP1 in mammalian neurons lacking","How membrane shaping mechanistically drives enclosure not resolved"]},{"year":2024,"claim":"Linking REEP1 to MAM formation and an NDPK-D interaction that limits cardiolipin externalization tied REEP1 to autophagosome biogenesis in a neurodegeneration model.","evidence":"ER-mitochondria co-localization, cardiolipin probe in MAM fractions, REEP1–NDPK-D interaction, autophagosome staining, A53T-αSyn mice","pmids":["39178680"],"confidence":"Low","gaps":["REEP1–NDPK-D binding supported only by co-localization, no rigorous binding assay","Single pharmacological-intervention study, not independently confirmed"]},{"year":null,"claim":"How REEP1's single membrane-shaping activity is mechanistically partitioned across its multiple contexts—tubular ER, ER–mitochondria contacts, lipid droplet regulation, mitochondrial fission/complex IV, and selective autophagy—and which functions are most relevant to SPG31 axonal degeneration remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model integrating curvature induction with partner binding","Relative contribution of ER vs mitochondrial defects to motor neuron loss undefined","Endogenous interactome at neuronal contact sites not comprehensively mapped"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[2]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,2,11]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,2,3,5]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[3,7,10]},{"term_id":"GO:0005811","term_label":"lipid droplet","supporting_discovery_ids":[4,5]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[0,2]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[11]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[13]}],"complexes":[],"partners":["ATL1","SPAST","BSCL2","PGAM5","NDUFA4","NME4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9H902","full_name":"Receptor expression-enhancing protein 1","aliases":["Spastic paraplegia 31 protein"],"length_aa":201,"mass_kda":22.3,"function":"Required for endoplasmic reticulum (ER) network formation, shaping and remodeling; it links ER tubules to the cytoskeleton. May also enhance the cell surface expression of odorant receptors (PubMed:20200447). May play a role in long-term axonal maintenance (PubMed:24478229)","subcellular_location":"Membrane; Mitochondrion membrane; Endoplasmic reticulum","url":"https://www.uniprot.org/uniprotkb/Q9H902/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/REEP1","classification":"Not Classified","n_dependent_lines":25,"n_total_lines":1208,"dependency_fraction":0.020695364238410598},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/REEP1","total_profiled":1310},"omim":[{"mim_id":"620011","title":"NEURONOPATHY, DISTAL HEREDITARY MOTOR, AUTOSOMAL RECESSIVE 6; HMNR6","url":"https://www.omim.org/entry/620011"},{"mim_id":"614751","title":"NEURONOPATHY, DISTAL HEREDITARY MOTOR, AUTOSOMAL DOMINANT 12; HMND12","url":"https://www.omim.org/entry/614751"},{"mim_id":"613564","title":"CHROMOSOME 2p12-p11.2 DELETION SYNDROME","url":"https://www.omim.org/entry/613564"},{"mim_id":"610250","title":"SPASTIC PARAPLEGIA 31, AUTOSOMAL DOMINANT; SPG31","url":"https://www.omim.org/entry/610250"},{"mim_id":"610243","title":"ZINC FINGER FYVE DOMAIN-CONTAINING PROTEIN 27; ZFYVE27","url":"https://www.omim.org/entry/610243"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"testis","ntpm":42.3}],"url":"https://www.proteinatlas.org/search/REEP1"},"hgnc":{"alias_symbol":["FLJ13110","SPG31","Yip2a"],"prev_symbol":["C2orf23"]},"alphafold":{"accession":"Q9H902","domains":[{"cath_id":"-","chopping":"1-80","consensus_level":"medium","plddt":70.4655,"start":1,"end":80}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H902","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H902-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H902-F1-predicted_aligned_error_v6.png","plddt_mean":67.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=REEP1","jax_strain_url":"https://www.jax.org/strain/search?query=REEP1"},"sequence":{"accession":"Q9H902","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H902.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H902/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H902"}},"corpus_meta":[{"pmid":"20200447","id":"PMC_20200447","title":"Hereditary spastic paraplegia proteins REEP1, spastin, and atlastin-1 coordinate microtubule interactions with the tubular ER network.","date":"2010","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/20200447","citation_count":318,"is_preprint":false},{"pmid":"16826527","id":"PMC_16826527","title":"Mutations in the novel mitochondrial protein REEP1 cause hereditary spastic paraplegia type 31.","date":"2006","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/16826527","citation_count":190,"is_preprint":false},{"pmid":"18321925","id":"PMC_18321925","title":"REEP1 mutation spectrum and genotype/phenotype correlation in hereditary spastic paraplegia type 31.","date":"2008","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/18321925","citation_count":146,"is_preprint":false},{"pmid":"26201691","id":"PMC_26201691","title":"Hereditary spastic paraplegia-linked REEP1 modulates endoplasmic reticulum/mitochondria contacts.","date":"2015","source":"Annals of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/26201691","citation_count":85,"is_preprint":false},{"pmid":"27638887","id":"PMC_27638887","title":"Reep1 null mice reveal a converging role for hereditary spastic paraplegia proteins in lipid droplet regulation.","date":"2016","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/27638887","citation_count":82,"is_preprint":false},{"pmid":"21618648","id":"PMC_21618648","title":"REEP1 mutations in SPG31: frequency, mutational spectrum, and potential association with mitochondrial morpho-functional dysfunction.","date":"2011","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/21618648","citation_count":79,"is_preprint":false},{"pmid":"22703882","id":"PMC_22703882","title":"Exome sequencing identifies a REEP1 mutation involved in distal hereditary motor neuropathy type V.","date":"2012","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/22703882","citation_count":77,"is_preprint":false},{"pmid":"24051375","id":"PMC_24051375","title":"A spastic paraplegia mouse model reveals REEP1-dependent ER shaping.","date":"2013","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/24051375","citation_count":76,"is_preprint":false},{"pmid":"24478229","id":"PMC_24478229","title":"Functional mutation analysis provides evidence for a role of REEP1 in lipid droplet biology.","date":"2014","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/24478229","citation_count":51,"is_preprint":false},{"pmid":"20718791","id":"PMC_20718791","title":"Mutation screening of spastin, atlastin, and REEP1 in hereditary spastic paraplegia.","date":"2011","source":"Clinical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20718791","citation_count":45,"is_preprint":false},{"pmid":"19034539","id":"PMC_19034539","title":"New pedigrees and novel mutation expand the phenotype of REEP1-associated hereditary spastic paraplegia (HSP).","date":"2008","source":"Neurogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/19034539","citation_count":38,"is_preprint":false},{"pmid":"28007911","id":"PMC_28007911","title":"Mitochondrial morphology and cellular distribution are altered in SPG31 patients and are linked to DRP1 hyperphosphorylation.","date":"2017","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28007911","citation_count":35,"is_preprint":false},{"pmid":"18644145","id":"PMC_18644145","title":"Autosomal dominant hereditary spastic paraplegia: novel mutations in the REEP1 gene (SPG31).","date":"2008","source":"BMC medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/18644145","citation_count":35,"is_preprint":false},{"pmid":"24355597","id":"PMC_24355597","title":"REEP1 and REEP2 proteins are preferentially expressed in neuronal and neuronal-like exocytotic tissues.","date":"2013","source":"Brain 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REEP1-4 is required for autophagosomal enclosure of ER-phagy/nucleophagy cargos in fission yeast.","date":"2023","source":"PLoS biology","url":"https://pubmed.ncbi.nlm.nih.gov/37939137","citation_count":13,"is_preprint":false},{"pmid":"25096240","id":"PMC_25096240","title":"Functional screening in Drosophila reveals the conserved role of REEP1 in promoting stress resistance and preventing the formation of Tau aggregates.","date":"2014","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25096240","citation_count":13,"is_preprint":false},{"pmid":"32878877","id":"PMC_32878877","title":"Inhibition of ER stress improves progressive motor deficits in a REEP1-null mouse model of hereditary spastic paraplegia.","date":"2020","source":"Biology open","url":"https://pubmed.ncbi.nlm.nih.gov/32878877","citation_count":12,"is_preprint":false},{"pmid":"39178680","id":"PMC_39178680","title":"Phillyrin promotes autophagosome formation in A53T-αSyn-induced Parkinson's disease model via modulation of REEP1.","date":"2024","source":"Phytomedicine : international journal of phytotherapy and phytopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/39178680","citation_count":11,"is_preprint":false},{"pmid":"19072839","id":"PMC_19072839","title":"Clinical and genetic study of a novel mutation in the REEP1 gene.","date":"2009","source":"Synapse (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/19072839","citation_count":11,"is_preprint":false},{"pmid":"29107646","id":"PMC_29107646","title":"Spastic paraplegia type 31: A novel REEP1 splice site donor variant and expansion of the phenotype variability.","date":"2017","source":"Parkinsonism & related disorders","url":"https://pubmed.ncbi.nlm.nih.gov/29107646","citation_count":11,"is_preprint":false},{"pmid":"31913854","id":"PMC_31913854","title":"A complete overview of REEP1: old and new insights on its role in hereditary spastic paraplegia and neurodegeneration.","date":"2020","source":"Reviews in the 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sciences","url":"https://pubmed.ncbi.nlm.nih.gov/36834939","citation_count":7,"is_preprint":false},{"pmid":"28099355","id":"PMC_28099355","title":"Hereditary spastic paraplegia due to a novel mutation of the REEP1 gene: Case report and literature review.","date":"2017","source":"Medicine","url":"https://pubmed.ncbi.nlm.nih.gov/28099355","citation_count":7,"is_preprint":false},{"pmid":"32655478","id":"PMC_32655478","title":"Screening for REEP1 Mutations in 31 Chinese Hereditary Spastic Paraplegia Families.","date":"2020","source":"Frontiers in neurology","url":"https://pubmed.ncbi.nlm.nih.gov/32655478","citation_count":5,"is_preprint":false},{"pmid":"38889632","id":"PMC_38889632","title":"Generation of a human induced pluripotent stem cell line (FSMi001-A) from fibroblasts of a patient carrying heterozygous mutation in the REEP1 gene.","date":"2024","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/38889632","citation_count":3,"is_preprint":false},{"pmid":"35132160","id":"PMC_35132160","title":"A clinical and genetic study of SPG31 in Japan.","date":"2022","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35132160","citation_count":2,"is_preprint":false},{"pmid":"38479332","id":"PMC_38479332","title":"Generation of homozygous and heterozygous REEP1 knockout induced pluripotent stem cell lines by CRISPR/Cas9 gene editing.","date":"2024","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/38479332","citation_count":1,"is_preprint":false},{"pmid":"31055810","id":"PMC_31055810","title":"[Deletional variant of REEP1 gene in a pedigree affected with spastic paraplegia type 31].","date":"2019","source":"Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/31055810","citation_count":1,"is_preprint":false},{"pmid":"41018230","id":"PMC_41018230","title":"Double gene mutations of LRSAM1 and REEP1 and a new REEP1 mutation site found in a patient with amyotrophic lateral sclerosis with subjective paresthesia: A case report.","date":"2023","source":"Ibrain","url":"https://pubmed.ncbi.nlm.nih.gov/41018230","citation_count":0,"is_preprint":false},{"pmid":"38525447","id":"PMC_38525447","title":"Phenotypic variability in a large kindred with spastic paraplegia associated with a novel REEP1 variant.","date":"2024","source":"eNeurologicalSci","url":"https://pubmed.ncbi.nlm.nih.gov/38525447","citation_count":0,"is_preprint":false},{"pmid":"32905827","id":"PMC_32905827","title":"A novel REEP1 splicing mutation with broad clinical variability in a family with hereditary spastic paraplegia.","date":"2020","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/32905827","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":19348,"output_tokens":3986,"usd":0.058917,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11766,"output_tokens":4636,"usd":0.087365,"stage2_stop_reason":"end_turn"},"total_usd":0.146282,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"REEP1 is structurally related to the DP1/Yop1p family of ER-shaping proteins and localizes to the tubular ER in neurons. REEP1 forms protein complexes with atlastin-1 and spastin within the tubular ER, interactions requiring hydrophobic hairpin domains in each protein. REEP1 also binds microtubules directly and promotes ER alignment along the microtubule cytoskeleton. A SPG31 mutant REEP1 lacking the C-terminal cytoplasmic region failed to interact with microtubules and disrupted the ER network. REEP proteins were required for ER network formation in vitro.\",\n      \"method\": \"Co-immunoprecipitation in COS7 cells, overexpression/domain-deletion analysis, in vitro ER network formation assay, immunofluorescence colocalization in rat cortical neurons\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (Co-IP, in vitro reconstitution, domain mutagenesis, live imaging), replicated across cell types and conditions in a single rigorous study\",\n      \"pmids\": [\"20200447\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"REEP1 was initially reported to localize to mitochondria based on cellular fractionation/localization experiments in the study identifying it as the SPG31 disease gene.\",\n      \"method\": \"Subcellular fractionation and localization assays in transfected cells\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single localization method; later work showed REEP1 is primarily an ER protein at ER-mitochondria contacts, reducing confidence in pure mitochondrial assignment\",\n      \"pmids\": [\"16826527\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"REEP1 is a neuron-specific, membrane-binding, and membrane curvature-inducing protein residing in the ER. In REEP1-deficient mice (homozygous exon 2 deletion), cortical motor neurons showed reduced complexity of the peripheral ER by ultrastructural analysis, connecting proper neuronal ER architecture to long-term axon survival.\",\n      \"method\": \"Mouse knockout model (heterozygous and homozygous exon 2 deletion), electron microscopy ultrastructural analysis, behavioral gait analysis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO mouse with defined cellular phenotype (ER morphology by EM) plus behavioral readout; replicated across heterozygous and homozygous models\",\n      \"pmids\": [\"24051375\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"REEP1 is present at the ER-mitochondria interface, containing subdomains for both mitochondrial and ER localization. REEP1 facilitates ER-mitochondria interactions (measured by split-RLuc8 assay), and disease-associated REEP1 mutations diminish this function. Knockdown of Reep1 and expression of pathological mutations caused neuritic growth defects and degeneration in mouse cortical neurons.\",\n      \"method\": \"Cellular imaging (immunofluorescence/confocal), biochemical fractionation, novel split-RLuc8 bioluminescence complementation assay for ER-mitochondria contacts, neuritic growth/degeneration assays in mouse cortical culture\",\n      \"journal\": \"Annals of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (fractionation, split-RLuc8 assay, neuronal KD phenotype), single lab but rigorous functional validation with disease mutations\",\n      \"pmids\": [\"26201691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"REEP1 is involved in lipid droplet biology: Reep1-null mice show partial lipoatrophy, and Reep1-/- embryonic fibroblasts and cortical neurons show lipid droplet abnormalities. REEP1 co-immunoprecipitates with seipin (BSCL2) in cells, linking ER morphogenesis to lipid droplet regulation.\",\n      \"method\": \"Reep1 knockout mouse (null allele), lipid droplet staining in fibroblasts and neurons, co-immunoprecipitation of REEP1 with seipin, MRI of mice\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO mouse with multiple cellular phenotypes plus reciprocal Co-IP identifying seipin as binding partner; multiple orthogonal methods\",\n      \"pmids\": [\"27638887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The N-terminus of REEP1 is necessary for proper targeting to and/or retention in the ER. HSP-associated missense variants at the N-terminus abolish ER targeting and cause accumulation at lipid droplets. Co-overexpression of REEP1 with atlastins increases lipid droplet size synergistically, whereas REEP1 alone does not.\",\n      \"method\": \"Overexpression of wild-type and mutant REEP1 constructs in cell lines, immunofluorescence localization, lipid droplet size measurement, N-terminal deletion/tagging experiments\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple constructs and orthogonal imaging/biochemical approaches in a single lab; functional ER-targeting mechanism defined by mutagenesis\",\n      \"pmids\": [\"24478229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"A dHMN-associated internally shortened REEP1 variant (p.102_139del) shows a subcellular localization defect distinct from the HSP-associated missense mutation (p.Ala20Glu). The p.102_139del variant also recruits atlastin-1 (a REEP1 binding partner) to the altered sites of localization, whereas p.Ala20Glu does not, suggesting distinct pathogenic mechanisms for HSP vs. dHMN.\",\n      \"method\": \"Exogenous overexpression in cell lines, immunofluorescence localization, minigene splice assay confirming mRNA consequence\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, cell-based localization and atlastin-1 co-recruitment assay; two orthogonal approaches supporting distinct mechanisms\",\n      \"pmids\": [\"22703882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In SPG31 patient fibroblasts, mitochondrial morphology is highly tubular due to hyperphosphorylation of DRP1 at serine 637, which inhibits mitochondrial fission. This hyperphosphorylation is caused by impaired interaction between REEP1 and the mitochondrial phosphatase PGAM5. Genetic or pharmacological reduction of DRP1-S637 phosphorylation restores mitochondrial morphology. Pathological REEP1 mutations expressed in neurons target REEP1 to mitochondria and sequester mitochondria to the perinuclear region, impairing axonal mitochondrial transport.\",\n      \"method\": \"Primary fibroblasts from SPG31 patients, immunofluorescence/confocal mitochondrial morphology analysis, phospho-DRP1 biochemical assays, REEP1-PGAM5 interaction assay, primary neuronal culture with mutant REEP1 overexpression and mitochondrial transport imaging\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient cells plus neuronal culture, biochemical phosphorylation assays, and rescue experiments; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"28007911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A nonstop variant in REEP1 produces a C-terminally extended protein whose extension triggers self-aggregation of REEP1 and of reporter proteins, demonstrating a toxic gain-of-function mechanism distinct from the loss-of-function seen in HSP. This aggregation-prone behavior maps to a 3'UTR-encoded cryptic amyloidogenic element.\",\n      \"method\": \"Expression of nonstop variant protein in cells, aggregation assays with REEP1 and reporter fusions, mRNA/protein analysis\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional aggregation assays with multiple reporters in a single lab; mechanistically distinct from prior loss-of-function findings\",\n      \"pmids\": [\"29124833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In a Drosophila model, downregulation of the REEP1 homolog enhanced Tau toxicity and increased formation of insoluble Tau aggregates, while overexpression of either Drosophila or human REEP1 reversed these phenotypes and promoted neuronal resistance to ER stress, identifying a role for REEP1 in preventing Tau aggregation and in ER stress resistance.\",\n      \"method\": \"Drosophila RNAi screen, Tau toxicity assays, Tau solubility/aggregation biochemistry, REEP1 overexpression rescue experiments in fly model\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo Drosophila model with loss- and gain-of-function, biochemical Tau aggregation readout; single lab\",\n      \"pmids\": [\"25096240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"REEP1 associates with NDUFA4 and plays an important role in preserving the integrity of mitochondrial complex IV. Forced REEP1 expression in the spinal cord of SOD1G93A mice extended lifespan, decelerated symptom progression, improved motor performance, and alleviated neuromuscular synaptic loss and motor neuron loss through augmentation of mitochondrial function.\",\n      \"method\": \"Co-immunoprecipitation of REEP1 with NDUFA4, OXPHOS complex IV activity assays, in vivo AAV-mediated REEP1 overexpression in SOD1G93A mice with behavioral and histological readouts\",\n      \"journal\": \"Neuroscience bulletin\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus in vivo rescue with functional mitochondrial assay; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"36520405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The fission yeast ortholog of human REEP1-4 (Yep1/Hva22/Rop1) is essential for autophagosomal enclosure of ER-phagy and nucleophagy cargos but not bulk autophagy. This function relies on Yep1's ability to self-interact and shape membranes, requiring its C-terminal amphipathic helices. Human REEP1-4 can functionally substitute for Yep1 in ER-phagy, confirming functional conservation.\",\n      \"method\": \"Imaging-based screen in S. pombe, yeast genetics (deletion mutants), complementation assays with human REEP1-4, domain mutagenesis (amphipathic helix deletion), fluorescence microscopy of autophagy intermediates\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — genetic screen plus domain mutagenesis plus cross-species complementation; multiple orthogonal methods demonstrating mechanistic conservation of REEP1 in membrane shaping for selective autophagy\",\n      \"pmids\": [\"37939137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"REEP1 enhances MAM (mitochondria-associated ER membrane) formation and interacts with NDPK-D at mitochondria; increased REEP1 levels at mitochondria reduce cardiolipin (CL) externalization via the REEP1-NDPK-D interaction, thereby promoting autophagosome biogenesis.\",\n      \"method\": \"Fluorescent staining for ER-mitochondria co-localization, cardiolipin probe assay in MAM fractions, co-localization/interaction assays of REEP1 with NDPK-D, monodansylcadaverine staining for autophagosomes in SH-SY5Y cells, in vivo A53T-αSyn mouse model with behavioral tests\",\n      \"journal\": \"Phytomedicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, pharmacological intervention study; REEP1-NDPK-D interaction supported by co-localization but binding assay details limited in abstract\",\n      \"pmids\": [\"39178680\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"REEP1-null mice exhibit increased ER stress markers alongside progressive motor deficits and axonal degeneration; treatment with salubrinal (an ER stress inhibitor) increased nerve-muscle connections and enhanced motor functions, implicating ER stress as a downstream mechanism of REEP1 deficiency.\",\n      \"method\": \"REEP1 knockout mouse model, ER stress marker quantification, salubrinal pharmacological treatment, neuromuscular junction innervation analysis, behavioral motor testing\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO mouse with pharmacological rescue and multiple readouts; single lab\",\n      \"pmids\": [\"32878877\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"REEP1 is a hydrophobic hairpin-containing ER-shaping protein of the DP1/Yop1p family that resides at the tubular ER and ER-mitochondria contact sites in neurons; it physically interacts with atlastin-1 and spastin via hydrophobic domains to coordinate tubular ER network formation, directly binds microtubules through its C-terminal cytoplasmic region to align ER along the cytoskeleton, associates with seipin to regulate lipid droplet homeostasis, interacts with PGAM5 to control DRP1-S637 phosphorylation and mitochondrial fission dynamics, associates with NDUFA4 to support mitochondrial complex IV integrity, and—based on yeast ortholog studies—uses self-interaction and C-terminal amphipathic helices to facilitate autophagosomal enclosure of ER-phagy cargos; loss-of-function causes ER stress, reduced peripheral ER complexity in motor neurons, impaired mitochondrial transport, and progressive axonal degeneration underlying hereditary spastic paraplegia (SPG31).\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"REEP1 is a neuron-enriched, membrane curvature-inducing protein of the DP1/Yop1p family that shapes the tubular endoplasmic reticulum and governs ER contacts with the cytoskeleton and with mitochondria [#0, #2]. Through hydrophobic hairpin domains it assembles into complexes with the ER-shaping machinery atlastin-1 and spastin, while its C-terminal cytoplasmic region binds microtubules directly to align the ER along the cytoskeleton; loss of this C-terminal region disrupts the ER network [#0]. REEP1 also resides at the ER\\u2013mitochondria interface, where it carries distinct ER- and mitochondria-targeting subdomains and promotes ER\\u2013mitochondria contact formation [#3], and it couples ER morphogenesis to lipid droplet homeostasis through interaction with seipin (BSCL2) [#4]. At mitochondria, REEP1 interacts with the phosphatase PGAM5 to keep DRP1-serine 637 dephosphorylated and thereby permit mitochondrial fission, and it associates with NDUFA4 to preserve complex IV integrity [#7, #10]. Proper N-terminal targeting is required for ER residence, and disease variants that abolish it redirect REEP1 to lipid droplets or mitochondria [#5, #7]. Loss of REEP1 reduces peripheral ER complexity in motor neurons, triggers ER stress, and causes progressive axonal degeneration; REEP1 mutations cause the hereditary spastic paraplegia SPG31 [#1, #2, #13]. A conserved membrane-shaping function supports selective autophagy: the fission yeast ortholog is essential for autophagosomal enclosure of ER-phagy cargos via C-terminal amphipathic helices, a function human REEP1-4 can substitute for [#11].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Establishing REEP1 as the SPG31 disease gene and assigning an initial subcellular location framed the first hypotheses about where it acts.\",\n      \"evidence\": \"Subcellular fractionation and localization in transfected cells in the gene-identification study\",\n      \"pmids\": [\"16826527\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single localization method later superseded by ER assignment\", \"No mechanism linking localization to disease\", \"Mitochondrial-only assignment not reconciled with ER residence\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Placing REEP1 in the DP1/Yop1p family and showing it complexes with atlastin-1 and spastin and binds microtubules defined its core function as a tubular ER-shaping and ER\\u2013cytoskeleton-coupling protein.\",\n      \"evidence\": \"Co-IP in COS7, domain-deletion mutagenesis, in vitro ER network formation, and neuronal colocalization\",\n      \"pmids\": [\"20200447\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and architecture of the REEP1\\u2013atlastin\\u2013spastin complex unresolved\", \"Microtubule-binding motif within the C-terminus not mapped at residue level\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A knockout mouse connected loss of REEP1 to reduced peripheral ER complexity in motor neurons, tying neuronal ER architecture to long-term axon survival.\",\n      \"evidence\": \"Reep1 exon-2 deletion mice with EM ultrastructure and gait analysis\",\n      \"pmids\": [\"24051375\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal chain from ER morphology to axon degeneration not delineated\", \"Cell-autonomous vs non-autonomous contribution unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Mapping an N-terminal ER-targeting requirement and a synergistic effect on lipid droplet size with atlastins clarified how missense variants mislocalize REEP1 and connected it to lipid droplet biology.\",\n      \"evidence\": \"Overexpression of WT/mutant constructs, immunofluorescence, lipid droplet sizing, N-terminal deletion/tagging\",\n      \"pmids\": [\"24478229\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Targeting signal not defined at sequence level\", \"Mechanism of lipid droplet size synergy with atlastins unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"A Drosophila model revealed that REEP1 confers resistance to ER stress and suppresses Tau aggregation, extending its relevance beyond ER shaping to proteostasis.\",\n      \"evidence\": \"Drosophila RNAi/overexpression, Tau solubility biochemistry, cross-species rescue\",\n      \"pmids\": [\"25096240\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular link between REEP1 and Tau aggregation not defined\", \"Relevance to mammalian neurons not established here\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Comparing an HSP missense variant against a dHMN truncation variant showed divergent mislocalization and atlastin-1 recruitment, indicating distinct pathogenic mechanisms across REEP1-linked disorders.\",\n      \"evidence\": \"Overexpression localization, atlastin-1 co-recruitment, minigene splice assay\",\n      \"pmids\": [\"22703882\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endogenous-level validation lacking\", \"Functional consequence of altered atlastin-1 recruitment unmeasured\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrating REEP1 subdomains for both ER and mitochondrial localization and a measurable role in ER\\u2013mitochondria contact formation established it as a membrane contact-site organizer disrupted by disease mutations.\",\n      \"evidence\": \"Fractionation, split-RLuc8 contact-site assay, neuronal knockdown growth/degeneration assays\",\n      \"pmids\": [\"26201691\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tethering partners at the contact site not identified\", \"Quantitative contribution to organelle communication unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identifying seipin as a REEP1 binding partner and documenting lipoatrophy and lipid droplet defects in null mice linked REEP1-dependent ER morphogenesis to lipid droplet regulation.\",\n      \"evidence\": \"Reep1-null mice, lipid droplet staining, reciprocal Co-IP with seipin, MRI\",\n      \"pmids\": [\"27638887\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of REEP1\\u2013seipin interaction on droplet biogenesis not mechanistically resolved\", \"Tissue specificity of lipoatrophy phenotype unexplained\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showing that impaired REEP1\\u2013PGAM5 interaction causes DRP1-S637 hyperphosphorylation and excessively tubular mitochondria, reversible by reducing that phosphorylation, defined a mitochondrial fission control pathway in SPG31.\",\n      \"evidence\": \"SPG31 patient fibroblasts, phospho-DRP1 assays, REEP1\\u2013PGAM5 interaction, neuronal mitochondrial transport imaging, rescue\",\n      \"pmids\": [\"28007911\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemical reconstitution of REEP1\\u2013PGAM5\\u2013DRP1 axis lacking\", \"Whether mutant mitochondrial mislocalization is cause or consequence not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"A nonstop variant producing a C-terminally extended, self-aggregating protein revealed a toxic gain-of-function mechanism distinct from HSP loss-of-function.\",\n      \"evidence\": \"Expression of nonstop variant, aggregation assays with REEP1 and reporter fusions, mRNA/protein analysis\",\n      \"pmids\": [\"29124833\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance of the aggregation phenotype not tested\", \"Cellular toxicity pathway downstream of aggregation undefined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating elevated ER stress markers in REEP1-null mice and rescue by salubrinal placed ER stress downstream of REEP1 deficiency as a tractable degeneration mechanism.\",\n      \"evidence\": \"REEP1 KO mice, ER stress marker quantification, salubrinal treatment, NMJ and motor readouts\",\n      \"pmids\": [\"32878877\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular trigger linking ER shape loss to the unfolded protein response unclear\", \"Durability and translational relevance of pharmacological rescue untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identifying a REEP1\\u2013NDUFA4 association needed for complex IV integrity, and showing REEP1 overexpression is neuroprotective in SOD1G93A mice, extended REEP1's mitochondrial role to oxidative phosphorylation and broader motor neuron disease.\",\n      \"evidence\": \"Co-IP with NDUFA4, complex IV activity assays, AAV REEP1 overexpression in SOD1G93A mice\",\n      \"pmids\": [\"36520405\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which REEP1 supports complex IV assembly/stability unknown\", \"Whether benefit is via complex IV or general mitochondrial support unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Cross-species work showed the REEP1 ortholog is essential for autophagosomal enclosure of ER-phagy cargos via C-terminal amphipathic helices, with human REEP1-4 rescuing the yeast defect, establishing a conserved membrane-shaping role in selective autophagy.\",\n      \"evidence\": \"S. pombe imaging screen, deletion mutants, domain mutagenesis, human REEP1-4 complementation\",\n      \"pmids\": [\"37939137\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct demonstration of ER-phagy enclosure function for human REEP1 in mammalian neurons lacking\", \"How membrane shaping mechanistically drives enclosure not resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linking REEP1 to MAM formation and an NDPK-D interaction that limits cardiolipin externalization tied REEP1 to autophagosome biogenesis in a neurodegeneration model.\",\n      \"evidence\": \"ER-mitochondria co-localization, cardiolipin probe in MAM fractions, REEP1\\u2013NDPK-D interaction, autophagosome staining, A53T-\\u03b1Syn mice\",\n      \"pmids\": [\"39178680\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"REEP1\\u2013NDPK-D binding supported only by co-localization, no rigorous binding assay\", \"Single pharmacological-intervention study, not independently confirmed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How REEP1's single membrane-shaping activity is mechanistically partitioned across its multiple contexts\\u2014tubular ER, ER\\u2013mitochondria contacts, lipid droplet regulation, mitochondrial fission/complex IV, and selective autophagy\\u2014and which functions are most relevant to SPG31 axonal degeneration remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model integrating curvature induction with partner binding\", \"Relative contribution of ER vs mitochondrial defects to motor neuron loss undefined\", \"Endogenous interactome at neuronal contact sites not comprehensively mapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 2, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 2, 3, 5]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [3, 7, 10]},\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ATL1\", \"SPAST\", \"BSCL2\", \"PGAM5\", \"NDUFA4\", \"NME4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}