Affinage

SYCE2

Synaptonemal complex central element protein 2 · UniProt Q6PIF2

Length
218 aa
Mass
24.7 kDa
Annotated
2026-04-28
25 papers in source corpus 13 papers cited in narrative 13 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SYCE2 is an essential structural component of the synaptonemal complex (SC) central element that drives meiotic chromosome synapsis, DNA double-strand break repair, and crossover formation. SYCE2 forms a constitutive hetero-oligomeric complex with TEX12 in which 2:2 coiled-coil building blocks assemble into 4:4 units that polymerize end-to-end and laterally into micrometer-long fibers structurally analogous to intermediate filaments, defining the SC midline (PMID:22870393, PMID:34373646). Recruitment of SYCE2-TEX12 into the SC depends on SYCE3-mediated remodeling of the SYCP1 transverse filament lattice, and loss of SYCE2 permits initiation but not elongation of synapsis, blocking DSB repair and crossover completion (PMID:17339376, PMID:36635604). A human SYCE2 missense variant at a structurally critical assembly residue alters crossover distribution across chromosomes and increases pregnancy loss risk, and in somatic cells SYCE2 additionally promotes ATM-dependent DSB repair by dissociating HP1α from H3K9me3 through its N-terminal hydrophobic sequence (PMID:38287193, PMID:30456351).

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 2005 High

    Identifying SYCE2 as a central element-specific protein recruited by SYCP1 established the first molecular handle for dissecting SC central element composition beyond the transverse filaments.

    Evidence Immunofluorescence and co-localization in mouse meiocytes

    PMID:15944401

    Open questions at the time
    • No biochemical interaction assay with SYCP1
    • Functional requirement not yet tested
  2. 2006 High

    Demonstrating that SYCE2 forms a stable complex with TEX12 by co-immunoprecipitation revealed a discrete sub-module within the central element distinct from the SYCE1-SYCP1 sub-complex.

    Evidence Reciprocal co-IP and immunofluorescence co-localization in mouse testis

    PMID:16968740

    Open questions at the time
    • Stoichiometry and higher-order assembly unknown
    • No structural data
  3. 2007 High

    Syce2-null mice showed axis formation without synaptic elongation, retained DSB markers, and impaired crossover, placing SYCE2 downstream of SYCP1/SYCE1 and establishing it as essential for SC extension and meiotic recombination.

    Evidence Mouse knockout with cytological analysis of meiotic chromosomes

    PMID:17339376

    Open questions at the time
    • Molecular mechanism of elongation failure unknown
    • Whether SYCE2 acts directly in DSB repair versus indirectly through synapsis defects was unresolved
  4. 2009 Medium

    Detection of a SYCE2–RAD51 physical interaction in a synapsis-deficient background suggested SYCE2 may bridge recombination intermediates and synapsis initiation sites.

    Evidence Co-immunoprecipitation from Syce1-null mouse testis

    PMID:19247432

    Open questions at the time
    • Single Co-IP in a mutant background without reciprocal validation
    • Functional consequence of the interaction not tested
    • Directness of binding not established
  5. 2012 High

    Biochemical reconstitution showed SYCE2-TEX12 spontaneously forms a hetero-octameric complex that assembles into filaments, providing the first structural basis for how central element fibers are built.

    Evidence Analytical ultracentrifugation, SEC, and electron microscopy of recombinant human proteins

    PMID:22870393

    Open questions at the time
    • Atomic-resolution structure lacking
    • Mechanism of filament elongation and bundling unknown
  6. 2016 High

    Immuno-EM localization of SYCE2 between the two bilayers of the central element, together with the observation that SYCE2 loss disrupts SYCP1 N-terminal alignment, defined the ultrastructural position of SYCE2 within the SC architecture.

    Evidence Immunoelectron microscopy with gold-particle mapping in mouse spermatocytes

    PMID:27103161

    Open questions at the time
    • Molecular contacts between SYCE2-TEX12 fibers and SYCP1 N-termini uncharacterized
  7. 2018 Medium

    Discovery that SYCE2 displaces HP1α from H3K9me3 via its N-terminal hydrophobic sequence to promote ATM-dependent DSB repair in somatic cells revealed an unexpected extrasynaptonemal function.

    Evidence Co-IP, domain mutagenesis, chromatin fractionation, and DSB repair assays in somatic cell lines

    PMID:30456351

    Open questions at the time
    • Physiological relevance in somatic tissues in vivo not established
    • Whether this function operates during meiosis untested
    • Single-lab finding
  8. 2021 High

    Crystal structures of SYCE2-TEX12 revealed a hierarchical assembly from 2:2 coiled coils to 4:4 units to 10-nm and then 40-nm fibers, establishing an intermediate-filament-like polymerization mechanism for SC midline formation.

    Evidence X-ray crystallography, SAXS, AUC, and electron microscopy of human recombinant complexes

    PMID:34373646

    Open questions at the time
    • How lateral bundling is regulated in vivo unknown
    • No in vivo mutagenesis of fiber-assembly interfaces at that time
  9. 2022 High

    Structural analysis of TEX12 mutants showed that TEX12's C-terminal tip controls the oligomeric state and conformational switch that initiates SYCE2-TEX12 fiber assembly, identifying a regulatory mechanism within the complex.

    Evidence Crystal structures of TEX12 variants with light-scattering and SAXS validation

    PMID:36071143

    Open questions at the time
    • What triggers the conformational switch in vivo is unknown
    • Whether post-translational modifications regulate assembly untested
  10. 2023 High

    Reconstitution and mouse mutagenesis demonstrated that SYCE3 remodels SYCP1 tetramers into 2:1 SYCP1-SYCE3 heterotrimers, creating new lattice interfaces that recruit SYCE2-TEX12, solving the long-standing question of how central element proteins are integrated into the transverse filament scaffold.

    Evidence Biochemical reconstitution, separation-of-function mutagenesis in mice, biophysical assays

    PMID:36635604

    Open questions at the time
    • Order of SYCE2-TEX12 versus SYCE1-SIX6OS1 recruitment not fully resolved
    • In vivo dynamics of lattice remodeling unknown
  11. 2024 Medium

    A GWAS-identified SYCE2 missense variant at a structurally validated assembly-critical residue was shown to alter crossover distribution and increase pregnancy loss, directly linking SYCE2 fiber assembly to crossover patterning and reproductive fitness in humans.

    Evidence GWAS of 114,761 women with structural annotation from prior crystal structures

    PMID:38287193

    Open questions at the time
    • Functional impact of the variant not validated by in vitro assembly assay or animal model
    • Mechanism by which assembly perturbation alters crossover placement unclear
  12. 2025 Medium

    Zebrafish syce2 mutants showed partial sub-telomeric synapsis and reduced DSB repair efficiency but retained fertility, revealing that the stringency of SC-dependent meiotic checkpoints varies across vertebrates.

    Evidence Loss-of-function zebrafish mutant with cytological and fertility analysis

    PMID:40911633

    Open questions at the time
    • Whether partial synapsis in zebrafish reflects distinct SC architecture versus checkpoint differences is unresolved
    • Crossover distribution not analyzed

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key remaining questions include: what triggers the TEX12 conformational switch that initiates SYCE2-TEX12 fiber assembly in vivo; whether SYCE2's somatic HP1α-displacing function is physiologically relevant during meiotic DSB repair; and how SYCE2 fiber integrity mechanistically influences crossover positioning.
  • No regulatory signal (post-translational modification or binding event) for assembly initiation identified
  • SYCE2-RAD51 interaction not validated by orthogonal methods
  • No complete structural model of an assembled SC central element

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:0005694 chromosome 3 GO:0005634 nucleus 2
Pathway
R-HSA-1474165 Reproduction 3 R-HSA-1640170 Cell Cycle 3 R-HSA-73894 DNA Repair 2
Partners
HP1Α (CBX5)RAD51SYCE1SYCE3SYCP1TEX12
Complex memberships
SYCE2-TEX12 central element complex

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 SYCE2 (then called CESC1) localizes exclusively to the central element of the mammalian synaptonemal complex and its localization to the central element depends on recruitment by the transverse filament protein SYCP1. Immunofluorescence localization, microarray expression profiling, co-localization studies in mouse meiocytes Journal of cell science High 15944401
2006 SYCE2 forms a complex with TEX12 within the synaptonemal complex central element, as demonstrated by co-immunoprecipitation; TEX12 exactly co-localizes with SYCE2 in a punctate pattern, and SYCE1 co-localizes with SYCP1 in a more continuous pattern, suggesting a molecular network in which TEX12-SYCE2 forms a sub-complex that interacts with SYCE1. Co-immunoprecipitation, immunofluorescence co-localization, mouse knockout models Journal of cell science High 16968740
2007 SYCE2 is required for synaptonemal complex assembly, double-strand break repair, and homologous recombination; in Syce2-null mice, chromosome axes form but do not synapse, markers of DNA breakage and repair are retained on the axes, and crossover is impaired. SC assembly can initiate at SYCE1/SYCP1 sites but cannot extend without SYCE2, placing SYCE2 downstream of SYCP1 and SYCE1 in assembly. Mouse knockout (Syce2 null), immunofluorescence, cytological analysis of meiotic chromosomes 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 mice where synapsis is disrupted, suggesting SYCE2 promotes homologous synapsis from sites of recombination. Co-immunoprecipitation from Syce1-null mouse testis extracts PLoS genetics Medium 19247432
2012 Human SYCE2 and TEX12 form a highly stable, constitutive hetero-octameric complex (equimolar SYCE2 tetramer plus two TEX12 dimers), and this complex spontaneously assembles into filamentous structures resembling the SC central element, providing a structural basis for SC assembly driven by SYCE2-TEX12 higher-order structures. Biochemical reconstitution, biophysical analysis (analytical ultracentrifugation, size-exclusion chromatography), electron microscopy, domain-mapping interaction assays Open biology High 22870393
2013 SLX2 interacts with SYCE2 as demonstrated by yeast two-hybrid screening and co-immunoprecipitation assays, suggesting SLX2 involvement in synaptonemal complex formation and DNA recombination via SYCE2. Yeast two-hybrid, co-immunoprecipitation Gene Low 23810942
2016 SYCE2 localizes between the two bilayers of the SC central element in mouse spermatocytes, and disruption of SYCE2 (and TEX12) localization abolishes central alignment of the N-terminal region of SYCP1, showing that SYCE2 contributes to stabilization of the bilayered transverse-filament-central-element junction structure. Immunoelectron microscopy, gold particle distribution analysis, protein interaction data Journal of cell science High 27103161
2018 In somatic cells, SYCE2 interacts with the chromoshadow domain of HP1α through its N-terminal hydrophobic sequence (not via canonical PXVXL motifs), dissociates HP1α from H3K9me3, and promotes ATM-mediated DNA double-strand break repair, even in the absence of exogenous DNA damage. Co-immunoprecipitation, domain-mapping mutagenesis, chromatin fractionation, DSB repair assays in somatic cells Life science alliance Medium 30456351
2021 X-ray crystal structures of human SYCE2-TEX12 reveal that individual 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 bundle into 40-nm micrometer-long fibers defining the SC midline. This hierarchical fibrous assembly mechanism resembles intermediate filament proteins (vimentin, lamin, keratin) and structurally underpins synaptic elongation along meiotic chromosomes. X-ray crystallography, mutagenesis, biophysical analysis (SAXS, AUC), electron microscopy Nature structural & molecular biology High 34373646
2022 TEX12's C-terminal tip sequence drives SYCE2-TEX12 fibrous assembly within the SC and also controls the oligomeric state and conformation of isolated TEX12; crystal structures of TEX12 mutants reveal three distinct conformations, establishing that SYCE2-TEX12 complex assembly is regulated by conformational changes in TEX12. X-ray crystallography of TEX12 mutants, solution light scattering, X-ray scattering (SAXS) Communications biology High 36071143
2023 SYCE3 interacts with the SYCE2-TEX12 complex (as well as SYCE1-SIX6OS1), providing a mechanism for SYCE2-TEX12 recruitment into the SC. SYCE3 binding causes SYCP1 tetramers to undergo conformational change into 2:1 heterotrimers, disrupting the SYCP1 lattice assembly interfaces and establishing a new SYCP1-SYCE3 lattice that integrates CE complexes for long-range synapsis. Biochemical reconstitution, separation-of-function mutagenesis in mice, biophysical interaction assays Nature structural & molecular biology High 36635604
2024 A missense variant in SYCE2 at a key residue for synaptonemal complex backbone assembly associates with more random crossover placement and altered recombination rates across chromosomes, and increases risk of pregnancy loss, demonstrating that SYCE2 assembly function directly influences crossover distribution and reproductive outcomes. Genome-wide association analysis (114,761 women), functional annotation of variant as disrupting SC assembly at a structurally validated residue Nature structural & molecular biology Medium 38287193
2025 In zebrafish syce2 mutants, chromosomes exhibit partial synapsis primarily at sub-telomeric regions and show reduced efficiency in repairing meiotic DSBs, but syce2 mutant females and males remain fertile, indicating a less stringent meiotic checkpoint for synapsis errors in zebrafish than in mice. Loss-of-function mutation in zebrafish, cytological analysis of synapsis and DSB markers, fertility assays, progeny aneuploidy assessment PLoS genetics Medium 40911633

Source papers

Stage 0 corpus · 25 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 163 15944401
2007 SYCE2 is required for synaptonemal complex assembly, double strand break repair, and homologous recombination. The Journal of cell biology 154 17339376
2006 Characterization of a novel meiosis-specific protein within the central element of the synaptonemal complex. Journal of cell science 126 16968740
2013 Reconstruction of an integrated genome-scale co-expression network reveals key modules involved in lung adenocarcinoma. PloS one 89 23874428
2008 Corona is required for higher-order assembly of transverse filaments into full-length synaptonemal complex in Drosophila oocytes. PLoS genetics 63 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 49 22870393
2019 Molecular structure of human synaptonemal complex protein SYCE1. Chromosoma 35 30607510
2016 The central element of the synaptonemal complex in mice is organized as a bilayered junction structure. Journal of cell science 33 27103161
2021 Structural basis of meiotic chromosome synaptic elongation through hierarchical fibrous assembly of SYCE2-TEX12. Nature structural & molecular biology 31 34373646
2019 A molecular model for self-assembly of the synaptonemal complex protein SYCE3. The Journal of biological chemistry 28 31023827
2021 Synaptonemal complex proteins modulate the level of genome integrity in cancers. Cancer science 23 33382503
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 Structural maturation of SYCP1-mediated meiotic chromosome synapsis by SYCE3. Nature structural & molecular biology 19 36635604
2023 SRSF1-mediated alternative splicing is required for spermatogenesis. International journal of biological sciences 14 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 7 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
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