{"gene":"MND1","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2002,"finding":"Mnd1 forms a complex with Hop2 (co-immunoprecipitation from meiotic cell extracts) and localizes to chromatin throughout meiotic prophase; this localization requires Hop2. The complex promotes meiotic chromosome pairing and DSB repair in S. cerevisiae.","method":"Co-immunoprecipitation, genetic analysis (null mutant phenotype), chromosome spreads/localization","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, genetic epistasis, localization experiments; replicated across multiple subsequent studies","pmids":["11940665"],"is_preprint":false},{"year":2004,"finding":"Hop2 and Mnd1 form a stable heterodimer with higher affinity for double-stranded than single-stranded DNA, and this heterodimer stimulates the strand assimilation (D-loop) activity of Dmc1 in vitro. Genetic double-mutant analysis places HOP2, MND1, and DMC1 in the same pathway for homologous chromosome juxtaposition.","method":"In vitro biochemical reconstitution (strand assimilation assay), size-exclusion chromatography, genetic epistasis (double mutant analysis)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with recombinase activity assay plus genetic epistasis; replicated in subsequent studies","pmids":["15249670"],"is_preprint":false},{"year":2004,"finding":"In S. cerevisiae, Mnd1 is specifically required for DSB repair using the homologous chromosome (interhomolog repair); deletion of RED1 or HOP1 suppresses mnd1Δ arrest by permitting sister-chromatid repair. Mnd1 localizes to chromatin as foci independently of DSB formation, axial element formation, SC formation, and does not colocalize with Rad51, suggesting it facilitates chromatin accessibility for strand invasion rather than being recruited to repair sites.","method":"Genetic epistasis (double mutant suppression), chromosome spreads, immunofluorescence localization","journal":"Current biology : CB","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with defined suppressor mutations, localization by immunofluorescence; single lab","pmids":["15120066"],"is_preprint":false},{"year":2005,"finding":"Mouse Hop2 alone can form D-loops, but this activity is abrogated upon association with Mnd1. The Hop2-Mnd1 heterodimer physically interacts with both Rad51 and Dmc1 recombinases and stimulates their strand invasion activity up to 35-fold.","method":"D-loop formation assay, co-immunoprecipitation, in vitro recombinase stimulation assay","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with D-loop assay, physical interaction by Co-IP, quantitative stimulation assay; multiple orthogonal methods in one study","pmids":["15834424"],"is_preprint":false},{"year":2006,"finding":"The Hop2-Mnd1 heterodimer (but not individual proteins) stimulates Dmc1-mediated strand invasion. Interaction with Mnd1 induces conformational changes in Hop2 that abrogate Hop2's intrinsic recombinase activity and create a new interface for Dmc1 interaction. Coiled-coil motifs in both Hop2 and Mnd1 are essential for their mutual interaction, and a C-terminal region of both proteins is required for DNA binding and single-strand annealing.","method":"In vitro D-loop assay, mutagenesis (coiled-coil deletions, C-terminal deletions, point mutation), analytical ultracentrifugation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution with mutagenesis dissecting domain functions; multiple orthogonal biochemical assays in one study","pmids":["16675459"],"is_preprint":false},{"year":2006,"finding":"Mnd1/Hop2 in S. cerevisiae is required for Dmc1-mediated crossover recombination. In mnd1 rad51 double mutants, crossover recombination is restored (through Dmc1 alone), but noncrossover recombination remains absent, revealing a role for Mnd1/Hop2 in designating DSBs for noncrossover recombination. Epistasis analysis supports a model in which Mnd1/Hop2 ensures Dmc1-mediated strand invasion between homologs.","method":"Genetic epistasis (double mutant analysis: mnd1 rad51, hop2 rad51, mnd1 rad17), physical recombination assays","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with multiple double-mutant combinations; single lab","pmids":["16581767"],"is_preprint":false},{"year":2006,"finding":"Human TBPIP/Hop2-Mnd1 complex stimulates Dmc1- and Rad51-mediated DNA strand exchange and preferentially binds three-stranded DNA branch structures mimicking strand-exchange intermediates.","method":"In vitro strand exchange assay, DNA-binding assays (gel shift with branched DNA substrates), protein purification","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of human complex with strand exchange and DNA binding assays; single lab but multiple orthogonal methods","pmids":["16407260"],"is_preprint":false},{"year":2007,"finding":"Hop2-Mnd1 acts on two distinct steps to stimulate Dmc1-mediated homologous pairing: (1) stabilization of the Dmc1-ssDNA nucleoprotein filament, and (2) facilitation of dsDNA capture by the Dmc1-ssDNA filament, enabling synaptic complex formation on long duplex DNAs.","method":"In vitro reconstitution (strand invasion, synaptic complex formation assays on long duplexes), biochemical dissection of reaction steps","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mechanistic dissection into two discrete steps; replicated by independent lab in same journal issue","pmids":["17639081"],"is_preprint":false},{"year":2007,"finding":"In the Hop2-Mnd1 complex, Hop2 is the major DNA-binding subunit while Mnd1 is the primary Rad51-interaction entity. Hop2-Mnd1 stabilizes the Rad51-ssDNA nucleoprotein filament and enhances the ability of the Rad51-ssDNA filament to capture duplex DNA, revealing a bipartite stimulation mechanism.","method":"In vitro reconstitution (strand exchange, D-loop assays), domain-swap and deletion mutant analysis, DNA-binding assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis assigning functions to individual subunits; multiple orthogonal methods; replicated by independent lab in same journal issue","pmids":["17639080"],"is_preprint":false},{"year":2007,"finding":"S. pombe Hop2-Mnd1 stimulates spDmc1-dependent strand exchange and strand invasion, and promotes renaturation of complementary ssDNA and strand exchange with short oligonucleotides. Mouse Hop2 or mHop2-Mnd1 stimulates both hRad51 and hDmc1, whereas spHop2-Mnd1 is specific for spDmc1, revealing evolutionary divergence in recombinase specificity.","method":"In vitro strand exchange assay, co-immunoprecipitation, two-hybrid analysis, electron microscopy","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with multiple recombinase substrates, EM visualization; single lab but multiple orthogonal methods","pmids":["17426123"],"is_preprint":false},{"year":2010,"finding":"The Hop2-Mnd1 heterodimer condenses double-stranded DNA via formation of a DNA condensate, in a concentration-dependent and reversible manner. Neither Hop2 nor Mnd1 alone can mediate condensation. Hop2-Mnd1/Dmc1/ssDNA nucleoprotein filaments also condense dsDNA, and the concentration dependence parallels that of DNA strand exchange, suggesting DNA condensation is a key mechanistic step in synapsis stimulation.","method":"Single-molecule optical tweezers, video fluorescence microscopy, DNA condensation assays","journal":"Biophysical journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — single-molecule biophysical reconstitution with quantitative concentration-dependence; novel mechanistic insight with direct visualization","pmids":["21112301"],"is_preprint":false},{"year":2013,"finding":"Small angle X-ray scattering (SAXS) and electron microscopy reveal that Hop2-Mnd1 is a V-shaped heterodimer with three distinct DNA binding sites. The N-terminal dsDNA-binding functions of Hop2 and Mnd1 cooperate for synaptic complex assembly, while ssDNA binding by the Hop2 C-terminus stabilizes the Dmc1-ssDNA filament.","method":"Small angle X-ray scattering (SAXS), electron microscopy, deletion mutagenesis, in vitro strand invasion assay","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — structural determination (SAXS + EM) combined with mutagenesis and functional assays; multiple orthogonal methods in single study","pmids":["24150939"],"is_preprint":false},{"year":2014,"finding":"HOP2-MND1 induces conformational changes in RAD51 that alter its basic properties: it enhances RAD51 interaction with nucleotide cofactors, modifies RAD51 DNA-binding specificity to stimulate strand exchange, enables RAD51 strand exchange without divalent metal ions required for ATP binding, and offsets the K133A ATP-binding mutation. During nucleoprotein formation HOP2-MND1 helps load RAD51 onto ssDNA while restricting dsDNA binding; during homology search it promotes dsDNA binding by removing ssDNA inhibition. HOP2-MND1 is described as a 'molecular trigger' of RAD51 strand exchange.","method":"In vitro strand exchange assay, nucleotide-binding assays, RAD51 conformation assays, mutagenesis (K133A)","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple in vitro reconstitution assays with defined RAD51 mutants dissecting mechanism; single lab but highly orthogonal methods","pmids":["24943459"],"is_preprint":false},{"year":2015,"finding":"Crystal structure of Hop2-Mnd1 reveals a curved rod-like structure with three leucine zippers and two kinked junctions, with juxtaposed winged-helix domains at one end and a helical bundle at the other. Deletion analysis shows the helical bundle is sufficient for interacting with the Dmc1-ssDNA nucleofilament. Molecular modeling suggests the curved rod fits into the helical groove of the nucleofilament and that winged-helix domain DNA binding likely perturbs base pairing to facilitate strand invasion.","method":"X-ray crystallography, deletion mutagenesis, molecular modeling","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure combined with deletion analysis defining functional domains; multiple methods in single study","pmids":["25740648"],"is_preprint":false},{"year":2015,"finding":"Hop2-Mnd1 is expressed in somatic tissues and primary human fibroblasts where it functions with Rad51 to repair damaged telomeres via the alternative lengthening of telomeres (ALT) mechanism. Both Hop2 and Mnd1 C-terminal regions interact with RAD51 (and DMC1); ATP enhances the Hop2-Mnd1–RAD51 interaction. The HOP2 p.del201Glu mutation (present in an XX ovarian dysgenesis patient) diminishes association and functional synergy with RAD51 and DMC1.","method":"Co-immunoprecipitation, mutagenesis (C-terminal deletion and patient variant), in vitro strand invasion assay, cell-based ALT assay","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — functional reconstitution, mutagenesis, and Co-IP with mechanistic dissection; multiple orthogonal methods; single lab","pmids":["25820426"],"is_preprint":false},{"year":2015,"finding":"Cross-linking mass spectrometry (XL-MS) of plant HOP2-MND1 reveals that the major interaction site is in the central coiled-coil domains, and the complex adopts an open colinear parallel arrangement with flexible C-terminal capping helices suggesting a closed conformation also exists in solution.","method":"Chemical cross-linking mass spectrometry (XL-MS), protein threading, protein-protein docking","journal":"Journal of proteome research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — XL-MS with complementary cross-linkers and multiple replicates, structural modeling; plant ortholog (Arabidopsis) but conserved mechanistic features","pmids":["26535604"],"is_preprint":false},{"year":2018,"finding":"Using single-molecule DNA curtain imaging, yeast Hop2-Mnd1 binds rapidly to Dmc1-ssDNA filaments with high affinity and remains bound for ~1.3 min. No association was detected between Hop2-Mnd1 and Rad51-ssDNA or RPA-ssDNA filaments, demonstrating Dmc1-specific binding.","method":"Single-molecule imaging (DNA curtains), quantitative binding kinetics","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — single-molecule direct visualization with quantitative kinetics; negative control for Rad51/RPA; single lab","pmids":["30420424"],"is_preprint":false},{"year":2021,"finding":"MND1 in somatic (cancer) cells localizes to DSBs, stimulates HR repair, and is specifically active in G2 phase but not S phase. MND1 is not involved in repair of replication-associated one-ended DSBs, but specifically promotes repair of two-ended DSBs induced by IR or chemotherapeutic drugs. MND1 localization to DSBs depends on DNA end resection and occurs through binding to RAD51-coated ssDNA.","method":"Loss-of-function (siRNA/CRISPR depletion), immunofluorescence (localization to DSBs), cell cycle analysis, epistasis with RAD51 and resection factors","journal":"Molecular oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined cellular phenotype, cell-cycle-resolved analysis, mechanistic epistasis with resection; single lab","pmids":["37195379"],"is_preprint":false},{"year":2021,"finding":"MND1 competitively binds to KLF6 tumor suppressor, protecting E2F1 from KLF6-induced transcriptional repression; E2F1 in turn activates MND1 transcription by binding to its promoter, forming a positive feedback loop that regulates cell cycle progression in lung adenocarcinoma cells.","method":"Co-immunoprecipitation, chromatin immunoprecipitation (ChIP), dual-luciferase reporter assay, mass spectrometry","journal":"Cancer communications (London, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ChIP, and luciferase reporter assays; multiple orthogonal methods; single lab; somatic/cancer context","pmids":["33734616"],"is_preprint":false},{"year":2023,"finding":"Using smFRET and tethered particle motion experiments, Hop2-Mnd1 enhances Dmc1 filament assembly on ssDNA by increasing the Dmc1 nucleation binding rate (at ss/dsDNA junctions), whereas Swi5-Sfr1 reduces the dissociation rate during nucleation. The two complexes act via distinct, additive mechanisms on Dmc1 filament assembly.","method":"Single-molecule FRET (smFRET), tethered particle motion (TPM), order-of-addition experiments","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — single-molecule biophysical assays with mechanistic dissection of rate constants; multiple orthogonal single-molecule methods; single lab","pmids":["37395447"],"is_preprint":false},{"year":2023,"finding":"Depletion of MND1 (or PSMC3IP/HOP2) causes PARP inhibitor sensitivity and ionizing radiation sensitivity in mitotic cells, causes accumulation of toxic RAD51 foci, and impairs homology-directed DNA repair. These effects are independent of the ALT telomere pathway. Epistasis with BRCA1/BRCA2 defects suggests the mechanism is abrogated D-loop formation. A PSMC3IP p.Glu201del mutant with defective D-loop activity fails to reverse PARPi sensitivity, unlike wild-type PSMC3IP.","method":"Genome-scale CRISPR screens, siRNA depletion, immunofluorescence (RAD51 foci), HR reporter assays, rescue with wild-type vs. mutant PSMC3IP, epistasis analysis","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-scale screen validated by targeted depletion, mechanistic rescue experiment with separation-of-function mutant, epistasis; multiple orthogonal approaches","pmids":["37163373"],"is_preprint":false},{"year":2024,"finding":"Hop2-Mnd1 acts as a DNA sequence fidelity switch for Dmc1: it upregulates Dmc1 activity on fully homologous and mismatch-containing substrates, but suppresses illegitimate DNA strand exchange between substrates with only microhomology. Separation-of-function variants show that suppression of illegitimate recombination requires the Dmc1-filament interaction surface of Hop2-Mnd1 but not its DNA-binding activity.","method":"In vitro strand exchange assays with defined substrates, separation-of-function mutant analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with mechanistically informative separation-of-function mutants; multiple substrate conditions tested; single lab","pmids":["39463417"],"is_preprint":false},{"year":2026,"finding":"O-GlcNAcylation of MND1 at Thr121 (by OGT) stabilizes MND1 protein and promotes its nuclear localization in breast cancer cells. T121A mutagenesis reduces MND1 stability and nuclear retention, impairs MND1-mediated DSB repair, and elevates persistent pH2AX levels. O-GlcNAc on T121 modulates the MND1-HOP2 interaction; loss of this modification augments MND1-HOP2 binding and causes structural perturbation of the complex.","method":"Immunoprecipitation, in vitro glycosylation assay, site-directed mutagenesis (T121A), OGT/OGA inhibitors, subcellular fractionation, pH2AX quantification","journal":"Breast cancer research : BCR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical site identification by IP + in vitro glycosylation, mutagenesis with functional readout; single lab","pmids":["41668200"],"is_preprint":false},{"year":2026,"finding":"In breast cancer cells, MND1 promotes HR repair by recruiting USP5 to deubiquitinate and stabilize RAD51. E2F1 transcriptionally activates MND1 by binding its promoter and inducing promoter hypomethylation, establishing an E2F1/MND1/USP5/RAD51 feedback loop.","method":"Co-immunoprecipitation, luciferase reporter assay, bisulfite sequencing PCR, in vitro/in vivo functional assays","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP identifying MND1-USP5 interaction, luciferase and bisulfite assays for transcriptional mechanism; multiple orthogonal methods; single lab","pmids":["42236675"],"is_preprint":false},{"year":2026,"finding":"Using single-molecule imaging, human DMC1-ssDNA presynaptic complex employs a diffusion-based mechanism to search for homologous DNA. HOP2-MND1 codiffuses with the presynaptic complex, clamping ssDNA-dsDNA junctions and maintaining an expanded DNA bubble to enable homology recognition, compensating for absence of free DMC1 and enabling strand exchange. HOP2-MND1 and DMC1 together constitute a functional homology search unit.","method":"Single-molecule imaging (fluorescence), in vitro reconstitution with human proteins, single-molecule tracking","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — single-molecule reconstitution directly visualizing the mechanism of action with human proteins; novel mechanistic insight; single lab","pmids":["41746729"],"is_preprint":false},{"year":2025,"finding":"GFP-MND1 in living human cells forms long filamentous structures on ssDNA several hours after DSB formation; these filaments are highly dynamic, explore nuclear space, and resolve over time. Resolution of MND1 filaments depends on RAD54L (known for homology search/strand invasion), and loss of cohesin also inhibits filament resolution, placing MND1 in an active HR intermediate resolvable by RAD54L.","method":"Live-cell single-molecule imaging (GFP-MND1), genetic epistasis (RAD54L and cohesin depletion), fluorescence microscopy","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — live-cell imaging with functional epistasis; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2025.03.01.640932"],"is_preprint":true}],"current_model":"MND1 (also called GAJ) forms a stable heterodimer with HOP2/PSMC3IP in which Mnd1 serves as the primary recombinase-interaction subunit while Hop2 provides major DNA-binding activity; together the complex acts as a bipartite cofactor that (1) stabilizes RAD51- and DMC1-ssDNA presynaptic filaments by inducing conformational changes in the recombinase and modulating its nucleotide and DNA binding, (2) promotes dsDNA capture by the presynaptic filament and condenses duplex DNA to stimulate synaptic complex formation, (3) codiffuses with the DMC1-ssDNA complex during homology search to clamp ssDNA-dsDNA junctions and maintain an expanded bubble for sequence alignment, and (4) acts as a DNA sequence fidelity switch that suppresses illegitimate recombination between microhomologous sequences through its recombinase-filament interaction surface; in somatic cells MND1 localizes to two-ended DSBs in G2 phase via RAD51-coated ssDNA and facilitates HR repair—including via recruiting USP5 to stabilize RAD51—while its nuclear retention and function are regulated by O-GlcNAcylation at Thr121."},"narrative":{"mechanistic_narrative":"MND1 is a meiotic and somatic homologous-recombination cofactor that functions exclusively as a stable heterodimer with HOP2/PSMC3IP to license recombinase-mediated strand invasion [PMID:11940665, PMID:15249670]. Within the complex, MND1 is the primary recombinase-interaction subunit while HOP2 provides the dominant DNA-binding activity, together forming a bipartite stimulator that physically engages both RAD51 and DMC1 and enhances their strand-exchange activity up to 35-fold [PMID:15834424, PMID:17639080]. The heterodimer stabilizes the recombinase-ssDNA presynaptic filament and promotes capture of duplex DNA to drive synaptic complex formation, mechanistically by condensing dsDNA and by inducing conformational changes in RAD51 that reprogram its nucleotide and DNA-binding properties, acting as a molecular trigger of strand exchange [PMID:17639081, PMID:21112301, PMID:24943459]. During homology search the HOP2-MND1 complex codiffuses with the DMC1-ssDNA presynaptic complex, clamping ssDNA-dsDNA junctions and maintaining an expanded DNA bubble for sequence alignment, and serves as a fidelity switch that suppresses illegitimate recombination between microhomologous sequences through its recombinase-filament interaction surface [PMID:39463417, PMID:41746729]. Structurally the heterodimer is a curved, V-shaped rod built around central coiled-coil/leucine-zipper interfaces with terminal winged-helix DNA-binding domains and a helical bundle that docks onto the recombinase nucleofilament [PMID:24150939, PMID:25740648]. Beyond meiosis, MND1 acts in somatic cells to promote repair of two-ended DSBs in G2 phase, localizing to RAD51-coated resected ssDNA, supporting alternative lengthening of telomeres, and its loss confers PARP-inhibitor and IR sensitivity through abrogated D-loop formation [PMID:25820426, PMID:37195379, PMID:37163373]. In cancer cells MND1 expression and HR function are reinforced by an E2F1 transcriptional feedback loop and by recruitment of USP5 to deubiquitinate and stabilize RAD51, while O-GlcNAcylation at Thr121 controls its stability and nuclear retention [PMID:33734616, PMID:41668200, PMID:42236675].","teleology":[{"year":2002,"claim":"Establishing that Mnd1 acts as a chromatin-bound partner of Hop2 defined the basic functional unit and tied it to meiotic chromosome pairing and DSB repair.","evidence":"Co-IP, null-mutant genetics, and chromosome spreads in S. cerevisiae meiotic cells","pmids":["11940665"],"confidence":"High","gaps":["No biochemical activity assigned to the complex","Molecular mechanism of pairing not resolved"]},{"year":2004,"claim":"Reconstitution showed the Hop2-Mnd1 heterodimer is a stable DNA-binding entity that stimulates Dmc1 D-loop activity, converting a genetic interaction into a biochemical mechanism for interhomolog recombination.","evidence":"In vitro strand assimilation assay, size-exclusion chromatography, and double-mutant epistasis","pmids":["15249670","15120066"],"confidence":"High","gaps":["Which subunit binds DNA vs recombinase unresolved","Mechanism of filament stimulation unknown"]},{"year":2005,"claim":"Demonstrating the heterodimer stimulates both Rad51 and Dmc1 and that Mnd1 association abolishes Hop2's intrinsic recombinase activity revealed that complex formation reprograms subunit function.","evidence":"D-loop assays, Co-IP, and quantitative recombinase stimulation assays with mouse proteins","pmids":["15834424","16407260"],"confidence":"High","gaps":["Structural basis of conformational change not defined","Step in recombination affected not yet dissected"]},{"year":2006,"claim":"Domain mapping and genetics located the interaction and DNA-binding interfaces and showed the complex designates DSBs for crossover versus noncrossover outcomes, linking biochemistry to recombination fate.","evidence":"Coiled-coil/C-terminal mutagenesis, analytical ultracentrifugation, and physical recombination assays in yeast","pmids":["16675459","16581767"],"confidence":"High","gaps":["How crossover designation is mechanistically enforced unknown"]},{"year":2007,"claim":"Mechanistic dissection separated the complex's action into filament stabilization and dsDNA capture, and assigned the DNA-binding role to Hop2 and the recombinase-interaction role to Mnd1, defining the bipartite stimulation model.","evidence":"In vitro synaptic complex and strand-exchange assays with domain-swap/deletion mutants; cross-species comparison","pmids":["17639081","17639080","17426123"],"confidence":"High","gaps":["Physical structure of the complex on the filament not yet determined","Basis of species-specific recombinase preference unclear"]},{"year":2010,"claim":"Single-molecule biophysics identified dsDNA condensation as a discrete physical mechanism underlying synapsis stimulation, providing a tangible step for how the complex promotes homology pairing.","evidence":"Optical tweezers and fluorescence microscopy DNA condensation assays","pmids":["21112301"],"confidence":"High","gaps":["How condensation couples to recombinase-mediated synapsis in vivo unknown"]},{"year":2014,"claim":"Defining how HOP2-MND1 alters RAD51 nucleotide cofactor and DNA-binding behavior recast the complex as an allosteric trigger that switches the recombinase between filament-loading and homology-search modes.","evidence":"In vitro strand exchange and nucleotide-binding assays with RAD51 K133A mutant","pmids":["24943459"],"confidence":"High","gaps":["Atomic-level basis of RAD51 conformational change not resolved"]},{"year":2015,"claim":"Structural and somatic-function studies produced a V-shaped/curved-rod architecture with multiple DNA-binding sites and extended the complex's role to RAD51-dependent ALT telomere maintenance, including a disease-linked HOP2 variant.","evidence":"SAXS, EM, XL-MS, crystallography, deletion mutagenesis, and cell-based ALT assays","pmids":["24150939","25740648","26535604","25820426"],"confidence":"High","gaps":["High-resolution structure of complex bound to the nucleofilament missing","Open vs closed conformational switching not functionally tested in vivo"]},{"year":2018,"claim":"Single-molecule binding kinetics demonstrated yeast Hop2-Mnd1 binds Dmc1-ssDNA filaments specifically and transiently but not Rad51 or RPA filaments, refining the targeting specificity of the complex.","evidence":"DNA curtain single-molecule imaging with quantitative kinetics and Rad51/RPA negative controls","pmids":["30420424"],"confidence":"High","gaps":["Yeast Dmc1-specificity contrasts with mouse/human dual specificity; reconciliation unresolved"]},{"year":2021,"claim":"Cell-based studies established a somatic HR role: MND1 localizes to resected, RAD51-coated two-ended DSBs in G2, and an E2F1/MND1 feedback loop couples its expression to cell-cycle progression in cancer.","evidence":"siRNA/CRISPR depletion, DSB localization imaging, cell-cycle analysis, Co-IP, ChIP, and luciferase reporter assays","pmids":["37195379","33734616"],"confidence":"Medium","gaps":["Whether somatic MND1 acts via the same biochemical mechanism as in meiosis not directly shown","E2F1/KLF6 axis evidence from single lab"]},{"year":2023,"claim":"Single-molecule and synthetic-lethality studies pinpointed how MND1 accelerates Dmc1 filament nucleation and showed that its loss causes PARPi/IR sensitivity through abrogated D-loop formation, establishing therapeutic relevance.","evidence":"smFRET and TPM filament-assembly assays; genome-scale CRISPR screens with separation-of-function PSMC3IP rescue","pmids":["37395447","37163373"],"confidence":"High","gaps":["Mechanism of toxic RAD51 foci accumulation upon depletion not fully defined"]},{"year":2024,"claim":"Defining HOP2-MND1 as a sequence-fidelity switch revealed that the complex suppresses microhomology-driven illegitimate recombination via its recombinase-filament interface independent of DNA binding, adding a quality-control function.","evidence":"In vitro strand exchange with defined homologous/mismatch/microhomology substrates and separation-of-function mutants","pmids":["39463417"],"confidence":"High","gaps":["Whether the fidelity function operates in vivo not directly tested"]},{"year":2026,"claim":"Single-molecule, live-cell, and post-translational studies clarified the homology-search mechanism (codiffusion and junction clamping), additional RAD51-stabilizing routes (USP5), and O-GlcNAc control of MND1 stability/localization.","evidence":"Single-molecule reconstitution and tracking with human proteins, GFP-MND1 live-cell imaging, Co-IP, in vitro glycosylation, and T121A mutagenesis","pmids":["41746729","42236675","41668200","bio_10.1101_2025.03.01.640932"],"confidence":"Medium","gaps":["O-GlcNAc and USP5 findings are single-lab/cancer-context","Live-cell MND1 filament study is a preprint","Integration of O-GlcNAc regulation with meiotic function unaddressed"]},{"year":null,"claim":"How the in vitro biochemical and structural mechanisms of HOP2-MND1 quantitatively control recombination outcome (crossover designation, fidelity, telomere maintenance) within intact cells, and how somatic post-translational regulation integrates with the core recombinase mechanism, remains open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No high-resolution structure of the complex bound to a recombinase nucleofilament","In vivo test of the fidelity-switch function lacking","Reconciliation of species-specific recombinase specificity unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[1,6,8,11]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,7,8,12,21]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[8,24]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,17,22]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,2]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[17,20]},{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[0,2,5]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[17,18]}],"complexes":["HOP2-MND1 (PSMC3IP-MND1) heterodimer"],"partners":["PSMC3IP","RAD51","DMC1","USP5","E2F1","KLF6","OGT"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BWT6","full_name":"Meiotic nuclear division protein 1 homolog","aliases":[],"length_aa":205,"mass_kda":23.8,"function":"Required for proper homologous chromosome pairing and efficient cross-over and intragenic recombination during meiosis (By similarity). Stimulates both DMC1- and RAD51-mediated homologous strand assimilation, which is required for the resolution of meiotic double-strand breaks","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9BWT6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MND1","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":[{"gene":"PSMC3IP","stoichiometry":10.0}],"url":"https://opencell.sf.czbiohub.org/search/MND1","total_profiled":1310},"omim":[{"mim_id":"611422","title":"MEIOTIC NUCLEAR DIVISIONS 1; MND1","url":"https://www.omim.org/entry/611422"},{"mim_id":"608665","title":"PSMC3-INTERACTING PROTEIN; PSMC3IP","url":"https://www.omim.org/entry/608665"},{"mim_id":"179617","title":"RAD51 RECOMBINASE; RAD51","url":"https://www.omim.org/entry/179617"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":12.5},{"tissue":"lymphoid 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The complex promotes meiotic chromosome pairing and DSB repair in S. cerevisiae.\",\n      \"method\": \"Co-immunoprecipitation, genetic analysis (null mutant phenotype), chromosome spreads/localization\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, genetic epistasis, localization experiments; replicated across multiple subsequent studies\",\n      \"pmids\": [\"11940665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Hop2 and Mnd1 form a stable heterodimer with higher affinity for double-stranded than single-stranded DNA, and this heterodimer stimulates the strand assimilation (D-loop) activity of Dmc1 in vitro. Genetic double-mutant analysis places HOP2, MND1, and DMC1 in the same pathway for homologous chromosome juxtaposition.\",\n      \"method\": \"In vitro biochemical reconstitution (strand assimilation assay), size-exclusion chromatography, genetic epistasis (double mutant analysis)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with recombinase activity assay plus genetic epistasis; replicated in subsequent studies\",\n      \"pmids\": [\"15249670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In S. cerevisiae, Mnd1 is specifically required for DSB repair using the homologous chromosome (interhomolog repair); deletion of RED1 or HOP1 suppresses mnd1Δ arrest by permitting sister-chromatid repair. Mnd1 localizes to chromatin as foci independently of DSB formation, axial element formation, SC formation, and does not colocalize with Rad51, suggesting it facilitates chromatin accessibility for strand invasion rather than being recruited to repair sites.\",\n      \"method\": \"Genetic epistasis (double mutant suppression), chromosome spreads, immunofluorescence localization\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with defined suppressor mutations, localization by immunofluorescence; single lab\",\n      \"pmids\": [\"15120066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Mouse Hop2 alone can form D-loops, but this activity is abrogated upon association with Mnd1. The Hop2-Mnd1 heterodimer physically interacts with both Rad51 and Dmc1 recombinases and stimulates their strand invasion activity up to 35-fold.\",\n      \"method\": \"D-loop formation assay, co-immunoprecipitation, in vitro recombinase stimulation assay\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with D-loop assay, physical interaction by Co-IP, quantitative stimulation assay; multiple orthogonal methods in one study\",\n      \"pmids\": [\"15834424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The Hop2-Mnd1 heterodimer (but not individual proteins) stimulates Dmc1-mediated strand invasion. Interaction with Mnd1 induces conformational changes in Hop2 that abrogate Hop2's intrinsic recombinase activity and create a new interface for Dmc1 interaction. Coiled-coil motifs in both Hop2 and Mnd1 are essential for their mutual interaction, and a C-terminal region of both proteins is required for DNA binding and single-strand annealing.\",\n      \"method\": \"In vitro D-loop assay, mutagenesis (coiled-coil deletions, C-terminal deletions, point mutation), analytical ultracentrifugation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution with mutagenesis dissecting domain functions; multiple orthogonal biochemical assays in one study\",\n      \"pmids\": [\"16675459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Mnd1/Hop2 in S. cerevisiae is required for Dmc1-mediated crossover recombination. In mnd1 rad51 double mutants, crossover recombination is restored (through Dmc1 alone), but noncrossover recombination remains absent, revealing a role for Mnd1/Hop2 in designating DSBs for noncrossover recombination. Epistasis analysis supports a model in which Mnd1/Hop2 ensures Dmc1-mediated strand invasion between homologs.\",\n      \"method\": \"Genetic epistasis (double mutant analysis: mnd1 rad51, hop2 rad51, mnd1 rad17), physical recombination assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with multiple double-mutant combinations; single lab\",\n      \"pmids\": [\"16581767\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Human TBPIP/Hop2-Mnd1 complex stimulates Dmc1- and Rad51-mediated DNA strand exchange and preferentially binds three-stranded DNA branch structures mimicking strand-exchange intermediates.\",\n      \"method\": \"In vitro strand exchange assay, DNA-binding assays (gel shift with branched DNA substrates), protein purification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of human complex with strand exchange and DNA binding assays; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"16407260\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Hop2-Mnd1 acts on two distinct steps to stimulate Dmc1-mediated homologous pairing: (1) stabilization of the Dmc1-ssDNA nucleoprotein filament, and (2) facilitation of dsDNA capture by the Dmc1-ssDNA filament, enabling synaptic complex formation on long duplex DNAs.\",\n      \"method\": \"In vitro reconstitution (strand invasion, synaptic complex formation assays on long duplexes), biochemical dissection of reaction steps\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mechanistic dissection into two discrete steps; replicated by independent lab in same journal issue\",\n      \"pmids\": [\"17639081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In the Hop2-Mnd1 complex, Hop2 is the major DNA-binding subunit while Mnd1 is the primary Rad51-interaction entity. Hop2-Mnd1 stabilizes the Rad51-ssDNA nucleoprotein filament and enhances the ability of the Rad51-ssDNA filament to capture duplex DNA, revealing a bipartite stimulation mechanism.\",\n      \"method\": \"In vitro reconstitution (strand exchange, D-loop assays), domain-swap and deletion mutant analysis, DNA-binding assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis assigning functions to individual subunits; multiple orthogonal methods; replicated by independent lab in same journal issue\",\n      \"pmids\": [\"17639080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"S. pombe Hop2-Mnd1 stimulates spDmc1-dependent strand exchange and strand invasion, and promotes renaturation of complementary ssDNA and strand exchange with short oligonucleotides. Mouse Hop2 or mHop2-Mnd1 stimulates both hRad51 and hDmc1, whereas spHop2-Mnd1 is specific for spDmc1, revealing evolutionary divergence in recombinase specificity.\",\n      \"method\": \"In vitro strand exchange assay, co-immunoprecipitation, two-hybrid analysis, electron microscopy\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with multiple recombinase substrates, EM visualization; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"17426123\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The Hop2-Mnd1 heterodimer condenses double-stranded DNA via formation of a DNA condensate, in a concentration-dependent and reversible manner. Neither Hop2 nor Mnd1 alone can mediate condensation. Hop2-Mnd1/Dmc1/ssDNA nucleoprotein filaments also condense dsDNA, and the concentration dependence parallels that of DNA strand exchange, suggesting DNA condensation is a key mechanistic step in synapsis stimulation.\",\n      \"method\": \"Single-molecule optical tweezers, video fluorescence microscopy, DNA condensation assays\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — single-molecule biophysical reconstitution with quantitative concentration-dependence; novel mechanistic insight with direct visualization\",\n      \"pmids\": [\"21112301\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Small angle X-ray scattering (SAXS) and electron microscopy reveal that Hop2-Mnd1 is a V-shaped heterodimer with three distinct DNA binding sites. The N-terminal dsDNA-binding functions of Hop2 and Mnd1 cooperate for synaptic complex assembly, while ssDNA binding by the Hop2 C-terminus stabilizes the Dmc1-ssDNA filament.\",\n      \"method\": \"Small angle X-ray scattering (SAXS), electron microscopy, deletion mutagenesis, in vitro strand invasion assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — structural determination (SAXS + EM) combined with mutagenesis and functional assays; multiple orthogonal methods in single study\",\n      \"pmids\": [\"24150939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"HOP2-MND1 induces conformational changes in RAD51 that alter its basic properties: it enhances RAD51 interaction with nucleotide cofactors, modifies RAD51 DNA-binding specificity to stimulate strand exchange, enables RAD51 strand exchange without divalent metal ions required for ATP binding, and offsets the K133A ATP-binding mutation. During nucleoprotein formation HOP2-MND1 helps load RAD51 onto ssDNA while restricting dsDNA binding; during homology search it promotes dsDNA binding by removing ssDNA inhibition. HOP2-MND1 is described as a 'molecular trigger' of RAD51 strand exchange.\",\n      \"method\": \"In vitro strand exchange assay, nucleotide-binding assays, RAD51 conformation assays, mutagenesis (K133A)\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple in vitro reconstitution assays with defined RAD51 mutants dissecting mechanism; single lab but highly orthogonal methods\",\n      \"pmids\": [\"24943459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structure of Hop2-Mnd1 reveals a curved rod-like structure with three leucine zippers and two kinked junctions, with juxtaposed winged-helix domains at one end and a helical bundle at the other. Deletion analysis shows the helical bundle is sufficient for interacting with the Dmc1-ssDNA nucleofilament. Molecular modeling suggests the curved rod fits into the helical groove of the nucleofilament and that winged-helix domain DNA binding likely perturbs base pairing to facilitate strand invasion.\",\n      \"method\": \"X-ray crystallography, deletion mutagenesis, molecular modeling\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure combined with deletion analysis defining functional domains; multiple methods in single study\",\n      \"pmids\": [\"25740648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Hop2-Mnd1 is expressed in somatic tissues and primary human fibroblasts where it functions with Rad51 to repair damaged telomeres via the alternative lengthening of telomeres (ALT) mechanism. Both Hop2 and Mnd1 C-terminal regions interact with RAD51 (and DMC1); ATP enhances the Hop2-Mnd1–RAD51 interaction. The HOP2 p.del201Glu mutation (present in an XX ovarian dysgenesis patient) diminishes association and functional synergy with RAD51 and DMC1.\",\n      \"method\": \"Co-immunoprecipitation, mutagenesis (C-terminal deletion and patient variant), in vitro strand invasion assay, cell-based ALT assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — functional reconstitution, mutagenesis, and Co-IP with mechanistic dissection; multiple orthogonal methods; single lab\",\n      \"pmids\": [\"25820426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Cross-linking mass spectrometry (XL-MS) of plant HOP2-MND1 reveals that the major interaction site is in the central coiled-coil domains, and the complex adopts an open colinear parallel arrangement with flexible C-terminal capping helices suggesting a closed conformation also exists in solution.\",\n      \"method\": \"Chemical cross-linking mass spectrometry (XL-MS), protein threading, protein-protein docking\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — XL-MS with complementary cross-linkers and multiple replicates, structural modeling; plant ortholog (Arabidopsis) but conserved mechanistic features\",\n      \"pmids\": [\"26535604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Using single-molecule DNA curtain imaging, yeast Hop2-Mnd1 binds rapidly to Dmc1-ssDNA filaments with high affinity and remains bound for ~1.3 min. No association was detected between Hop2-Mnd1 and Rad51-ssDNA or RPA-ssDNA filaments, demonstrating Dmc1-specific binding.\",\n      \"method\": \"Single-molecule imaging (DNA curtains), quantitative binding kinetics\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — single-molecule direct visualization with quantitative kinetics; negative control for Rad51/RPA; single lab\",\n      \"pmids\": [\"30420424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MND1 in somatic (cancer) cells localizes to DSBs, stimulates HR repair, and is specifically active in G2 phase but not S phase. MND1 is not involved in repair of replication-associated one-ended DSBs, but specifically promotes repair of two-ended DSBs induced by IR or chemotherapeutic drugs. MND1 localization to DSBs depends on DNA end resection and occurs through binding to RAD51-coated ssDNA.\",\n      \"method\": \"Loss-of-function (siRNA/CRISPR depletion), immunofluorescence (localization to DSBs), cell cycle analysis, epistasis with RAD51 and resection factors\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined cellular phenotype, cell-cycle-resolved analysis, mechanistic epistasis with resection; single lab\",\n      \"pmids\": [\"37195379\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MND1 competitively binds to KLF6 tumor suppressor, protecting E2F1 from KLF6-induced transcriptional repression; E2F1 in turn activates MND1 transcription by binding to its promoter, forming a positive feedback loop that regulates cell cycle progression in lung adenocarcinoma cells.\",\n      \"method\": \"Co-immunoprecipitation, chromatin immunoprecipitation (ChIP), dual-luciferase reporter assay, mass spectrometry\",\n      \"journal\": \"Cancer communications (London, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ChIP, and luciferase reporter assays; multiple orthogonal methods; single lab; somatic/cancer context\",\n      \"pmids\": [\"33734616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Using smFRET and tethered particle motion experiments, Hop2-Mnd1 enhances Dmc1 filament assembly on ssDNA by increasing the Dmc1 nucleation binding rate (at ss/dsDNA junctions), whereas Swi5-Sfr1 reduces the dissociation rate during nucleation. The two complexes act via distinct, additive mechanisms on Dmc1 filament assembly.\",\n      \"method\": \"Single-molecule FRET (smFRET), tethered particle motion (TPM), order-of-addition experiments\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — single-molecule biophysical assays with mechanistic dissection of rate constants; multiple orthogonal single-molecule methods; single lab\",\n      \"pmids\": [\"37395447\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Depletion of MND1 (or PSMC3IP/HOP2) causes PARP inhibitor sensitivity and ionizing radiation sensitivity in mitotic cells, causes accumulation of toxic RAD51 foci, and impairs homology-directed DNA repair. These effects are independent of the ALT telomere pathway. Epistasis with BRCA1/BRCA2 defects suggests the mechanism is abrogated D-loop formation. A PSMC3IP p.Glu201del mutant with defective D-loop activity fails to reverse PARPi sensitivity, unlike wild-type PSMC3IP.\",\n      \"method\": \"Genome-scale CRISPR screens, siRNA depletion, immunofluorescence (RAD51 foci), HR reporter assays, rescue with wild-type vs. mutant PSMC3IP, epistasis analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-scale screen validated by targeted depletion, mechanistic rescue experiment with separation-of-function mutant, epistasis; multiple orthogonal approaches\",\n      \"pmids\": [\"37163373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Hop2-Mnd1 acts as a DNA sequence fidelity switch for Dmc1: it upregulates Dmc1 activity on fully homologous and mismatch-containing substrates, but suppresses illegitimate DNA strand exchange between substrates with only microhomology. Separation-of-function variants show that suppression of illegitimate recombination requires the Dmc1-filament interaction surface of Hop2-Mnd1 but not its DNA-binding activity.\",\n      \"method\": \"In vitro strand exchange assays with defined substrates, separation-of-function mutant analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with mechanistically informative separation-of-function mutants; multiple substrate conditions tested; single lab\",\n      \"pmids\": [\"39463417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"O-GlcNAcylation of MND1 at Thr121 (by OGT) stabilizes MND1 protein and promotes its nuclear localization in breast cancer cells. T121A mutagenesis reduces MND1 stability and nuclear retention, impairs MND1-mediated DSB repair, and elevates persistent pH2AX levels. O-GlcNAc on T121 modulates the MND1-HOP2 interaction; loss of this modification augments MND1-HOP2 binding and causes structural perturbation of the complex.\",\n      \"method\": \"Immunoprecipitation, in vitro glycosylation assay, site-directed mutagenesis (T121A), OGT/OGA inhibitors, subcellular fractionation, pH2AX quantification\",\n      \"journal\": \"Breast cancer research : BCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical site identification by IP + in vitro glycosylation, mutagenesis with functional readout; single lab\",\n      \"pmids\": [\"41668200\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In breast cancer cells, MND1 promotes HR repair by recruiting USP5 to deubiquitinate and stabilize RAD51. E2F1 transcriptionally activates MND1 by binding its promoter and inducing promoter hypomethylation, establishing an E2F1/MND1/USP5/RAD51 feedback loop.\",\n      \"method\": \"Co-immunoprecipitation, luciferase reporter assay, bisulfite sequencing PCR, in vitro/in vivo functional assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP identifying MND1-USP5 interaction, luciferase and bisulfite assays for transcriptional mechanism; multiple orthogonal methods; single lab\",\n      \"pmids\": [\"42236675\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Using single-molecule imaging, human DMC1-ssDNA presynaptic complex employs a diffusion-based mechanism to search for homologous DNA. HOP2-MND1 codiffuses with the presynaptic complex, clamping ssDNA-dsDNA junctions and maintaining an expanded DNA bubble to enable homology recognition, compensating for absence of free DMC1 and enabling strand exchange. HOP2-MND1 and DMC1 together constitute a functional homology search unit.\",\n      \"method\": \"Single-molecule imaging (fluorescence), in vitro reconstitution with human proteins, single-molecule tracking\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — single-molecule reconstitution directly visualizing the mechanism of action with human proteins; novel mechanistic insight; single lab\",\n      \"pmids\": [\"41746729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GFP-MND1 in living human cells forms long filamentous structures on ssDNA several hours after DSB formation; these filaments are highly dynamic, explore nuclear space, and resolve over time. Resolution of MND1 filaments depends on RAD54L (known for homology search/strand invasion), and loss of cohesin also inhibits filament resolution, placing MND1 in an active HR intermediate resolvable by RAD54L.\",\n      \"method\": \"Live-cell single-molecule imaging (GFP-MND1), genetic epistasis (RAD54L and cohesin depletion), fluorescence microscopy\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live-cell imaging with functional epistasis; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.03.01.640932\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"MND1 (also called GAJ) forms a stable heterodimer with HOP2/PSMC3IP in which Mnd1 serves as the primary recombinase-interaction subunit while Hop2 provides major DNA-binding activity; together the complex acts as a bipartite cofactor that (1) stabilizes RAD51- and DMC1-ssDNA presynaptic filaments by inducing conformational changes in the recombinase and modulating its nucleotide and DNA binding, (2) promotes dsDNA capture by the presynaptic filament and condenses duplex DNA to stimulate synaptic complex formation, (3) codiffuses with the DMC1-ssDNA complex during homology search to clamp ssDNA-dsDNA junctions and maintain an expanded bubble for sequence alignment, and (4) acts as a DNA sequence fidelity switch that suppresses illegitimate recombination between microhomologous sequences through its recombinase-filament interaction surface; in somatic cells MND1 localizes to two-ended DSBs in G2 phase via RAD51-coated ssDNA and facilitates HR repair—including via recruiting USP5 to stabilize RAD51—while its nuclear retention and function are regulated by O-GlcNAcylation at Thr121.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MND1 is a meiotic and somatic homologous-recombination cofactor that functions exclusively as a stable heterodimer with HOP2/PSMC3IP to license recombinase-mediated strand invasion [#0, #1]. Within the complex, MND1 is the primary recombinase-interaction subunit while HOP2 provides the dominant DNA-binding activity, together forming a bipartite stimulator that physically engages both RAD51 and DMC1 and enhances their strand-exchange activity up to 35-fold [#3, #8]. The heterodimer stabilizes the recombinase-ssDNA presynaptic filament and promotes capture of duplex DNA to drive synaptic complex formation, mechanistically by condensing dsDNA and by inducing conformational changes in RAD51 that reprogram its nucleotide and DNA-binding properties, acting as a molecular trigger of strand exchange [#7, #10, #12]. During homology search the HOP2-MND1 complex codiffuses with the DMC1-ssDNA presynaptic complex, clamping ssDNA-dsDNA junctions and maintaining an expanded DNA bubble for sequence alignment, and serves as a fidelity switch that suppresses illegitimate recombination between microhomologous sequences through its recombinase-filament interaction surface [#21, #24]. Structurally the heterodimer is a curved, V-shaped rod built around central coiled-coil/leucine-zipper interfaces with terminal winged-helix DNA-binding domains and a helical bundle that docks onto the recombinase nucleofilament [#11, #13]. Beyond meiosis, MND1 acts in somatic cells to promote repair of two-ended DSBs in G2 phase, localizing to RAD51-coated resected ssDNA, supporting alternative lengthening of telomeres, and its loss confers PARP-inhibitor and IR sensitivity through abrogated D-loop formation [#14, #17, #20]. In cancer cells MND1 expression and HR function are reinforced by an E2F1 transcriptional feedback loop and by recruitment of USP5 to deubiquitinate and stabilize RAD51, while O-GlcNAcylation at Thr121 controls its stability and nuclear retention [#18, #22, #23].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Establishing that Mnd1 acts as a chromatin-bound partner of Hop2 defined the basic functional unit and tied it to meiotic chromosome pairing and DSB repair.\",\n      \"evidence\": \"Co-IP, null-mutant genetics, and chromosome spreads in S. cerevisiae meiotic cells\",\n      \"pmids\": [\"11940665\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No biochemical activity assigned to the complex\", \"Molecular mechanism of pairing not resolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Reconstitution showed the Hop2-Mnd1 heterodimer is a stable DNA-binding entity that stimulates Dmc1 D-loop activity, converting a genetic interaction into a biochemical mechanism for interhomolog recombination.\",\n      \"evidence\": \"In vitro strand assimilation assay, size-exclusion chromatography, and double-mutant epistasis\",\n      \"pmids\": [\"15249670\", \"15120066\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which subunit binds DNA vs recombinase unresolved\", \"Mechanism of filament stimulation unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrating the heterodimer stimulates both Rad51 and Dmc1 and that Mnd1 association abolishes Hop2's intrinsic recombinase activity revealed that complex formation reprograms subunit function.\",\n      \"evidence\": \"D-loop assays, Co-IP, and quantitative recombinase stimulation assays with mouse proteins\",\n      \"pmids\": [\"15834424\", \"16407260\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of conformational change not defined\", \"Step in recombination affected not yet dissected\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Domain mapping and genetics located the interaction and DNA-binding interfaces and showed the complex designates DSBs for crossover versus noncrossover outcomes, linking biochemistry to recombination fate.\",\n      \"evidence\": \"Coiled-coil/C-terminal mutagenesis, analytical ultracentrifugation, and physical recombination assays in yeast\",\n      \"pmids\": [\"16675459\", \"16581767\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How crossover designation is mechanistically enforced unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Mechanistic dissection separated the complex's action into filament stabilization and dsDNA capture, and assigned the DNA-binding role to Hop2 and the recombinase-interaction role to Mnd1, defining the bipartite stimulation model.\",\n      \"evidence\": \"In vitro synaptic complex and strand-exchange assays with domain-swap/deletion mutants; cross-species comparison\",\n      \"pmids\": [\"17639081\", \"17639080\", \"17426123\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physical structure of the complex on the filament not yet determined\", \"Basis of species-specific recombinase preference unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Single-molecule biophysics identified dsDNA condensation as a discrete physical mechanism underlying synapsis stimulation, providing a tangible step for how the complex promotes homology pairing.\",\n      \"evidence\": \"Optical tweezers and fluorescence microscopy DNA condensation assays\",\n      \"pmids\": [\"21112301\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How condensation couples to recombinase-mediated synapsis in vivo unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defining how HOP2-MND1 alters RAD51 nucleotide cofactor and DNA-binding behavior recast the complex as an allosteric trigger that switches the recombinase between filament-loading and homology-search modes.\",\n      \"evidence\": \"In vitro strand exchange and nucleotide-binding assays with RAD51 K133A mutant\",\n      \"pmids\": [\"24943459\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-level basis of RAD51 conformational change not resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Structural and somatic-function studies produced a V-shaped/curved-rod architecture with multiple DNA-binding sites and extended the complex's role to RAD51-dependent ALT telomere maintenance, including a disease-linked HOP2 variant.\",\n      \"evidence\": \"SAXS, EM, XL-MS, crystallography, deletion mutagenesis, and cell-based ALT assays\",\n      \"pmids\": [\"24150939\", \"25740648\", \"26535604\", \"25820426\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of complex bound to the nucleofilament missing\", \"Open vs closed conformational switching not functionally tested in vivo\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Single-molecule binding kinetics demonstrated yeast Hop2-Mnd1 binds Dmc1-ssDNA filaments specifically and transiently but not Rad51 or RPA filaments, refining the targeting specificity of the complex.\",\n      \"evidence\": \"DNA curtain single-molecule imaging with quantitative kinetics and Rad51/RPA negative controls\",\n      \"pmids\": [\"30420424\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Yeast Dmc1-specificity contrasts with mouse/human dual specificity; reconciliation unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Cell-based studies established a somatic HR role: MND1 localizes to resected, RAD51-coated two-ended DSBs in G2, and an E2F1/MND1 feedback loop couples its expression to cell-cycle progression in cancer.\",\n      \"evidence\": \"siRNA/CRISPR depletion, DSB localization imaging, cell-cycle analysis, Co-IP, ChIP, and luciferase reporter assays\",\n      \"pmids\": [\"37195379\", \"33734616\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether somatic MND1 acts via the same biochemical mechanism as in meiosis not directly shown\", \"E2F1/KLF6 axis evidence from single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Single-molecule and synthetic-lethality studies pinpointed how MND1 accelerates Dmc1 filament nucleation and showed that its loss causes PARPi/IR sensitivity through abrogated D-loop formation, establishing therapeutic relevance.\",\n      \"evidence\": \"smFRET and TPM filament-assembly assays; genome-scale CRISPR screens with separation-of-function PSMC3IP rescue\",\n      \"pmids\": [\"37395447\", \"37163373\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of toxic RAD51 foci accumulation upon depletion not fully defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defining HOP2-MND1 as a sequence-fidelity switch revealed that the complex suppresses microhomology-driven illegitimate recombination via its recombinase-filament interface independent of DNA binding, adding a quality-control function.\",\n      \"evidence\": \"In vitro strand exchange with defined homologous/mismatch/microhomology substrates and separation-of-function mutants\",\n      \"pmids\": [\"39463417\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the fidelity function operates in vivo not directly tested\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Single-molecule, live-cell, and post-translational studies clarified the homology-search mechanism (codiffusion and junction clamping), additional RAD51-stabilizing routes (USP5), and O-GlcNAc control of MND1 stability/localization.\",\n      \"evidence\": \"Single-molecule reconstitution and tracking with human proteins, GFP-MND1 live-cell imaging, Co-IP, in vitro glycosylation, and T121A mutagenesis\",\n      \"pmids\": [\"41746729\", \"42236675\", \"41668200\", \"bio_10.1101_2025.03.01.640932\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"O-GlcNAc and USP5 findings are single-lab/cancer-context\", \"Live-cell MND1 filament study is a preprint\", \"Integration of O-GlcNAc regulation with meiotic function unaddressed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the in vitro biochemical and structural mechanisms of HOP2-MND1 quantitatively control recombination outcome (crossover designation, fidelity, telomere maintenance) within intact cells, and how somatic post-translational regulation integrates with the core recombinase mechanism, remains open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure of the complex bound to a recombinase nucleofilament\", \"In vivo test of the fidelity-switch function lacking\", \"Reconciliation of species-specific recombinase specificity unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [1, 6, 8, 11]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 7, 8, 12, 21]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [8, 24]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 17, 22]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [17, 20]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [0, 2, 5]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [17, 18]}\n    ],\n    \"complexes\": [\"HOP2-MND1 (PSMC3IP-MND1) heterodimer\"],\n    \"partners\": [\"PSMC3IP\", \"RAD51\", \"DMC1\", \"USP5\", \"E2F1\", \"KLF6\", \"OGT\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}