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SYCE2

Synaptonemal complex central element protein 2 · UniProt Q6PIF2

Length
218 aa
Mass
24.7 kDa
Annotated
2026-06-10
26 papers in source corpus 12 papers cited in narrative 12 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SYCE2 is a central element protein of the meiotic synaptonemal complex (SC) that drives elongation of the SC backbone along synapsing homologous chromosomes (PMID:17339376). It forms a highly stable constitutive hetero-octameric complex with TEX12 — a SYCE2 tetramer plus two TEX12 dimers — that spontaneously assembles into filamentous structures resembling the SC central element (PMID:22870393); at structural resolution, 2:2 coiled-coil building blocks dimerize into 4:4 hetero-oligomers that interact end-to-end and laterally to build 10-nm fibers, which intertwine into bundled micrometer-long fibers defining the SC midline through a hierarchical assembly mechanism reminiscent of intermediate filaments (PMID:34373646). Its central element localization depends on SYCP1 and on the SYCE1/SYCP1 anchoring network, with SYCE2-TEX12 joining via SYCE1 and being recruited to the remodeled SYCP1 lattice by SYCE3 (PMID:15944401, PMID:16968740, PMID:36635604). Functionally, SYCE2 is required for SC extension beyond initiation foci, and its loss leaves SYCE1/SYCP1 initiation foci unable to elongate, causing impaired meiotic DSB repair, crossover failure, and infertility (PMID:17339376); it physically interacts with the recombinase RAD51, linking SC assembly to recombination (PMID:19247432), and a human SYCE2 variant at a residue required for backbone assembly associates with altered crossover placement and increased pregnancy loss (PMID:38287193). Beyond meiosis, SYCE2 acts in somatic cells where its N-terminal hydrophobic sequence binds the HP1α chromoshadow domain to insulate HP1α from H3K9me3 and potentiate ATM-mediated double-strand break repair (PMID:30456351).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 2005 Medium

    Established SYCE2 as a bona fide central element component of the SC and placed it downstream of the transverse filament protein SYCP1, defining the first node of the central element network.

    Evidence Immunofluorescence localization in mouse spermatocytes and co-immunoprecipitation with SYCP1

    PMID:15944401

    Open questions at the time
    • Direct vs. indirect SYCP1 binding not resolved
    • No structural detail of the interaction
    • Function in SC assembly not yet tested
  2. 2006 High

    Mapped the central element interaction network, showing SYCE2 partners with TEX12 and that this complex joins SYCE1 anchored by SYCP1, defining the molecular architecture of the central element.

    Evidence Reciprocal co-immunoprecipitation, immunofluorescence co-localization, and multiple mouse knockout models

    PMID:16968740

    Open questions at the time
    • Stoichiometry and biophysics of the complex not defined
    • Order of assembly within the network not established
  3. 2007 High

    Demonstrated that SYCE2 is functionally required to extend the SC beyond initiation, separating SC initiation from elongation and linking elongation failure to defective DSB repair, crossover failure, and infertility.

    Evidence Syce2-null mouse with immunofluorescence for SC and DNA repair markers (RAD51, γH2AX) and cytological analysis

    PMID:17339376

    Open questions at the time
    • Molecular basis of elongation not resolved
    • Whether DSB repair defect is direct or secondary to synapsis failure unclear
  4. 2009 Medium

    Connected the central element machinery to the recombination apparatus by showing SYCE2 physically associates with RAD51, hinting that synapsis is coordinated with sites of recombination.

    Evidence Co-immunoprecipitation from Syce1-null mouse meiocytes

    PMID:19247432

    Open questions at the time
    • Single Co-IP without reciprocal validation
    • Direct vs. bridged interaction not established
    • Functional consequence of the interaction not tested
  5. 2012 High

    Defined the molecular building block of SC elongation: SYCE2-TEX12 forms a stable hetero-octamer that self-assembles into central-element-like filaments in vitro, providing a biochemical basis for SC backbone formation.

    Evidence Biochemical reconstitution of recombinant human proteins, analytical ultracentrifugation, size-exclusion chromatography, electron microscopy, and domain mapping

    PMID:22870393

    Open questions at the time
    • Atomic structure not yet determined
    • How in vitro filaments relate to in vivo midline unproven
  6. 2013 Low

    Identified SLX2 as a candidate SYCE2 interactor in germ cells, proposing an additional link to SC formation and recombination.

    Evidence Yeast two-hybrid screening and co-immunoprecipitation

    PMID:23810942

    Open questions at the time
    • Yeast two-hybrid plus single Co-IP, not independently confirmed
    • No functional mutagenesis
    • Physiological relevance untested
  7. 2016 High

    Localized SYCE2 precisely within the bilayered central element and showed it is required, with TEX12, to align opposing SYCP1 N-termini, mechanically explaining its role in central element stabilization.

    Evidence Immunoelectron microscopy with immuno-gold labeling and analysis of SYCE2/TEX12-deficient mice

    PMID:27103161

    Open questions at the time
    • Structural mechanism of SYCP1 N-terminus tethering not at atomic resolution
  8. 2021 High

    Resolved the hierarchical fiber assembly mechanism at near-atomic detail, showing 2:2 coiled coils build up into bundled micrometer-long fibers that define the SC midline, providing the structural logic of synaptic elongation.

    Evidence X-ray crystallography with mutagenesis, biophysics (AUC, MALS), and electron microscopy

    PMID:34373646

    Open questions at the time
    • In vivo regulation of fiber length not addressed
    • How fibers couple to chromosome axes unresolved
  9. 2023 Medium

    Identified SYCE3 as the recruiter that remodels the SYCP1 lattice and brings SYCE2-TEX12 into the central element, placing SYCE2-TEX12 in the assembly order.

    Evidence Biochemical assays, separation-of-function mouse mutagenesis, and protein interaction studies

    PMID:36635604

    Open questions at the time
    • SYCE2-TEX12 is one component of a broader study
    • Direct SYCE3-SYCE2 contact interface not mapped
  10. 2024 Medium

    Tied SYCE2's structural assembly function to human reproductive outcomes by linking a variant in a backbone-assembly residue to altered crossover placement and pregnancy loss.

    Evidence Genome-wide association analysis of 114,761 women with crossover placement analysis

    PMID:38287193

    Open questions at the time
    • Mechanism inferred rather than tested in vitro
    • Causality of the variant not functionally validated
  11. 2025 Medium

    Tested SYCE2 requirement across vertebrates, showing zebrafish syce2 mutants have partial synapsis and reduced DSB repair but remain fertile, revealing species differences in the synapsis checkpoint stringency.

    Evidence Zebrafish loss-of-function genetics with immunofluorescence of SC and DSB markers, fertility and aneuploidy assays

    PMID:40911633

    Open questions at the time
    • Basis for sub-telomeric residual synapsis unclear
    • Why fertility is preserved despite repair defect not resolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • How SYCE2's somatic HP1α-insulating, ATM-potentiating role mechanistically relates to its meiotic SC-elongation function remains unresolved.
  • No unified model connecting somatic chromatin role and meiotic structural role
  • Regulation of SYCE2 expression/function in somatic vs. germ cells unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 3 GO:0008092 cytoskeletal protein binding 2
Localization
GO:0000228 nuclear chromosome 3
Pathway
R-HSA-73894 DNA Repair 3 R-HSA-1474165 Reproduction 2 R-HSA-1640170 Cell Cycle 1
Partners
HP1ΑRAD51SLX2SYCE1SYCE3SYCP1TEX12
Complex memberships
SYCE2-TEX12 hetero-octamersynaptonemal complex central element

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 SYCE2 (originally named CESC1) was identified as a central element protein of the mammalian synaptonemal complex that interacts with the transverse filament protein SYCP1 and requires SYCP1 for its localization to the central element. Microarray expression profiling (identification), immunofluorescence localization in mouse spermatocytes, co-immunoprecipitation with SYCP1 Journal of cell science Medium 15944401
2006 SYCE2 co-localizes with TEX12 in a punctate pattern at the central element, and TEX12 specifically co-immunoprecipitates with SYCE2, indicating they form a complex. SYCE2 localization to the central element depends on SYCP1. SYCE1 interacts with SYCP1 and anchors the central element, while the TEX12-SYCE2 complex interacts with SYCE1, forming a molecular network within the central element. Immunofluorescence co-localization, co-immunoprecipitation, analysis of multiple mouse knockout models Journal of cell science High 16968740
2007 SYCE2 is required for synaptonemal complex assembly: in Syce2-null mice, SC initiation occurs at SYCE1/SYCP1 foci but cannot extend, demonstrating that SYCP1, SYCE1, and SYCE2 are all required sequentially for SC assembly. Loss of SYCE2 also causes retention of DNA break and repair markers (impaired DSB repair) and failure of crossover, resulting in infertility in both sexes. Mouse knockout (null mutation), immunofluorescence for SC markers, markers of DNA breakage/repair (RAD51, γH2AX), cytological analysis The Journal of cell biology High 17339376
2009 SYCE2 physically interacts with the DNA repair protein RAD51, as demonstrated by co-immunoprecipitation in Syce1-null mouse meiocytes; this interaction may promote homologous synapsis from sites of recombination. Co-immunoprecipitation from mouse meiotic cells (Syce1 null background) PLoS genetics Medium 19247432
2012 Human SYCE2 and TEX12 form a highly stable constitutive hetero-octameric complex (SYCE2 tetramer + two TEX12 dimers) that spontaneously assembles into filamentous structures resembling the SC central element, as revealed by biophysical analysis and electron microscopy. The regions responsible for homotypic (SYCE2-SYCE2, TEX12-TEX12) and heterotypic (SYCE2-TEX12) interactions were defined. Biochemical reconstitution, biophysical analysis (analytical ultracentrifugation, size-exclusion chromatography), electron microscopy of recombinant complexes, domain-mapping Open biology High 22870393
2013 SLX2 (SYCP3-like X-linked 2) interacts with SYCE2 in meiotic germ cells, as demonstrated by yeast two-hybrid screening and co-immunoprecipitation, suggesting SLX2 involvement in SC formation and DNA recombination through SYCE2. Yeast two-hybrid screening, co-immunoprecipitation Gene Low 23810942
2016 Within the SC central region, SYCE2 localizes between the two layers of a bilayered central element junction structure. Disruption of SYCE2 and TEX12 localization abolishes central alignment of the N-terminal region of SYCP1, demonstrating that SYCE2 (with TEX12) contributes in an interdependent manner to stabilization of opposing SYCP1 N-termini. Immunoelectron microscopy with immuno-gold labeling in mouse spermatocytes, protein interaction data, analysis of mutant mice lacking SYCE2/TEX12 Journal of cell science High 27103161
2018 In somatic cells, SYCE2 insulates HP1α from trimethylated histone H3K9 (H3K9me3) by interacting with the chromoshadow domain of HP1α through its N-terminal hydrophobic sequence (not through canonical PXVXL motifs). This reduces HP1α-H3K9me3 binding without affecting H3K9me3 levels and potentiates ATM-mediated DNA double-strand break repair. Co-immunoprecipitation, chromatin immunoprecipitation, cell-based DSB repair assays, domain mapping/mutagenesis, knockdown and overexpression experiments in somatic cells Life science alliance Medium 30456351
2021 X-ray crystal structures of human SYCE2-TEX12 reveal that building blocks are 2:2 coiled coils that dimerize into 4:4 hetero-oligomers, which interact end-to-end and laterally to form 10-nm fibers that intertwine into 40-nm bundled micrometer-long fibers defining the SC midline. This hierarchical fiber assembly mechanism resembles intermediate filament proteins and underpins synaptic elongation. X-ray crystallography, mutagenesis, biophysics (analytical ultracentrifugation, multi-angle light scattering), electron microscopy Nature structural & molecular biology High 34373646
2023 SYCE3 interacts with the SYCE2-TEX12 complex, providing a mechanism for its recruitment to the SYCP1 lattice during SC assembly. Specifically, SYCE3 remodels the SYCP1 lattice and establishes new SYCP1 dimer-tethering interactions, then recruits CE complexes including SYCE2-TEX12. Biochemical assays, separation-of-function mutagenesis in mice, protein interaction studies Nature structural & molecular biology Medium 36635604
2024 A missense variant in a key residue of SYCE2 required for SC backbone assembly associates with altered crossover placement (more random crossover distribution) and increased pregnancy loss, linking SYCE2's structural role in SC assembly to recombination quality and reproductive outcomes. Genome-wide association analysis (114,761 women), crossover placement analysis using population genetic data Nature structural & molecular biology Medium 38287193
2025 In zebrafish syce2 mutants, chromosomes show partial synapsis (primarily at sub-telomeric regions) and reduced efficiency of meiotic DSB repair compared to wild type. Unlike mouse Syce2 mutants, zebrafish syce2 mutant females and males are fertile, indicating a less stringent synapsis checkpoint in zebrafish. Zebrafish loss-of-function genetics, immunofluorescence of SC components and DSB markers, fertility assays, progeny aneuploidy analysis PLoS genetics Medium 40911633

Source papers

Stage 0 corpus · 26 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2009 Mutation of the mouse Syce1 gene disrupts synapsis and suggests a link between synaptonemal complex structural components and DNA repair. PLoS genetics 166 19247432
2005 Two novel proteins recruited by synaptonemal complex protein 1 (SYCP1) are at the centre of meiosis. Journal of cell science 164 15944401
2007 SYCE2 is required for synaptonemal complex assembly, double strand break repair, and homologous recombination. The Journal of cell biology 156 17339376
2006 Characterization of a novel meiosis-specific protein within the central element of the synaptonemal complex. Journal of cell science 129 16968740
2013 Reconstruction of an integrated genome-scale co-expression network reveals key modules involved in lung adenocarcinoma. PloS one 90 23874428
2008 Corona is required for higher-order assembly of transverse filaments into full-length synaptonemal complex in Drosophila oocytes. PLoS genetics 64 18802461
2016 Type 2 Deiodinase Disruption in Astrocytes Results in Anxiety-Depressive-Like Behavior in Male Mice. Endocrinology 51 27501182
2012 Structural analysis of the human SYCE2-TEX12 complex provides molecular insights into synaptonemal complex assembly. Open biology 50 22870393
2019 Molecular structure of human synaptonemal complex protein SYCE1. Chromosoma 37 30607510
2016 The central element of the synaptonemal complex in mice is organized as a bilayered junction structure. Journal of cell science 35 27103161
2021 Structural basis of meiotic chromosome synaptic elongation through hierarchical fibrous assembly of SYCE2-TEX12. Nature structural & molecular biology 33 34373646
2019 A molecular model for self-assembly of the synaptonemal complex protein SYCE3. The Journal of biological chemistry 29 31023827
2021 Synaptonemal complex proteins modulate the level of genome integrity in cancers. Cancer science 23 33382503
2023 Structural maturation of SYCP1-mediated meiotic chromosome synapsis by SYCE3. Nature structural & molecular biology 22 36635604
2013 SYCP3-like X-linked 2 is expressed in meiotic germ cells and interacts with synaptonemal complex central element protein 2 and histone acetyltransferase TIP60. Gene 20 23810942
2023 SRSF1-mediated alternative splicing is required for spermatogenesis. International journal of biological sciences 17 37781512
2015 Protein SYCP2 is an ancient component of the metazoan synaptonemal complex. Cytogenetic and genome research 14 25831978
2024 Variant in the synaptonemal complex protein SYCE2 associates with pregnancy loss through effect on recombination. Nature structural & molecular biology 8 38287193
2022 Coiled-coil structure of meiosis protein TEX12 and conformational regulation by its C-terminal tip. Communications biology 6 36071143
2018 Somatic role of SYCE2: an insulator that dissociates HP1α from H3K9me3 and potentiates DNA repair. Life science alliance 4 30456351
2025 Distinct cellular and reproductive consequences of meiotic chromosome synapsis defects in syce2 and sycp1 mutant zebrafish. PLoS genetics 1 40911633
2018 Cryo-electron tomography of SYCP3 fibers under native conditions. Methods in cell biology 1 29957214
2026 The synaptonemal complex: structure, function, and clinical implications†. Biology of reproduction 0 42059593
2025 Cell cycle-related biomarker lineage promotes the malignant progression of recurrent IDH wild-type glioma. Discover oncology 0 41364265
2025 SOX30 Governs Synaptonemal Complex Assembly and Homologous Recombination in Male Meiosis. Cell proliferation 0 41467312
2025 Synaptonemal complex assembly in yeast depends on a 2:2 Ecm11-Gmc2 heterocomplex. Open biology 0 41537827

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