TEX12

TEX12 is a meiosis-specific structural protein of the synaptonemal complex (SC) central element that is essential for propagation of chromosome synapsis and crossover maturation during meiotic prophase. TEX12 forms a 2:2 coiled-coil heterodimer with SYCE2 that hierarchically assembles through end-to-end and lateral interactions into intermediate-filament-like fibers defining the SC midline; this complex is recruited to the SC lattice through interaction with SYCE3 following SYCE3-mediated remodeling of the SYCP1 transverse filament (PMID:22870393, PMID:34373646, PMID:36635604). PLK1 phosphorylates TEX12 to drive removal of central element proteins from the SC during the prophase-to-metaphase I transition (PMID:22854038). TEX12 also localizes to meiotic centrosomes independently of synapsis, and ectopic somatic expression causes centrosome amplification dependent on phosphorylation of tyrosine 48, providing a mechanistic link to cancer-testis antigen biology (PMID:34880391).

1. 2006 High

   Identifying TEX12 as a central element component that physically associates with SYCE2 established its molecular address within the SC and its partnership hierarchy.

   Evidence Co-immunoprecipitation, immunofluorescence co-localization, and mouse knockout models

   PMID:16968740

   Open questions at the time

   • Stoichiometry and direct binding mode of the TEX12–SYCE2 complex were unknown
   • Whether TEX12 has functions independent of the central element was unaddressed
2. 2008 High

   Genetic ablation showed that TEX12 is not required for synapsis initiation but is essential for its propagation along chromosomes and for crossover maturation, defining its specific functional role within SC assembly.

   Evidence Tex12 knockout mice (male and female), structural analysis of the SC in mutant meiocytes

   PMID:18611960

   Open questions at the time

   • Molecular mechanism by which TEX12 drives synapsis propagation was unclear
   • Whether TEX12 directly participates in recombination or acts indirectly through SC structure was unknown
3. 2012 High

   Biochemical reconstitution revealed that SYCE2 and TEX12 form a stable equimolar hetero-oligomeric complex that self-assembles into filaments resembling the central element, establishing the structural building block of the SC midline.

   Evidence Reconstitution with analytical ultracentrifugation, gel filtration, and electron microscopy of human SYCE2–TEX12

   PMID:22870393

   Open questions at the time

   • Atomic-resolution structure of the SYCE2–TEX12 complex was lacking
   • The assembly hierarchy connecting filament formation to the transverse filament lattice was unknown
4. 2012 High

   Demonstrating that PLK1 directly phosphorylates TEX12 and that PLK activity is required for central element disassembly at meiotic prophase exit revealed the signal controlling SC dismantling.

   Evidence In vitro kinase assays with PLK1–4, PLK inhibitor (BI 2536) treatment of pachytene spermatocytes, okadaic acid–induced prophase exit

   PMID:22854038

   Open questions at the time

   • Specific phosphorylation sites on TEX12 responsible for disassembly were not mapped
   • Whether phosphorylation destabilizes TEX12–SYCE2 filaments directly or acts through additional effectors was untested
5. 2016 High

   Immunoelectron microscopy showed that SYCE2–TEX12 disruption abolishes central alignment of SYCP1 N-termini, establishing that all central element proteins interdependently form the bilayered transverse-filament junction.

   Evidence Immunoelectron microscopy with functional disruption in mouse spermatocytes

   PMID:27103161

   Open questions at the time

   • Exact contact interfaces between SYCE2–TEX12 fibers and SYCP1 N-termini were unresolved
6. 2021 High

   Crystal structures of SYCE2–TEX12 revealed the 2:2 coiled-coil building block and its hierarchical assembly into 10-nm and bundled 40-nm fibers via end-to-end and lateral interactions, analogous to intermediate filament polymerization, providing the atomic-resolution mechanism for SC midline formation.

   Evidence X-ray crystallography, mutagenesis, biophysics, and electron microscopy of human SYCE2–TEX12

   PMID:34373646

   Open questions at the time

   • In vivo validation of assembly-defective mutants in mouse meiosis was not reported
   • How the fiber lattice integrates with other CE components (SYCE1, SYCE3, SIX6OS1) structurally was incomplete
7. 2021 High

   Discovery that TEX12 localizes to meiotic centrosomes independently of synapsis and that ectopic somatic expression drives centrosome amplification dependent on Y48 phosphorylation revealed a SC-independent function relevant to cancer-testis antigen biology.

   Evidence Immunofluorescence, ectopic expression in somatic/cancer cells, Y48 phospho-mutant analysis

   PMID:34880391

   Open questions at the time

   • The kinase responsible for Y48 phosphorylation was not identified
   • Whether centrosomal TEX12 contributes to normal meiotic spindle function was not determined
8. 2021 Medium

   Interaction between TEX11 (Zip4 ortholog) and TEX12 suggested a direct molecular coupling between crossover designation and SC central element assembly.

   Evidence Co-immunoprecipitation in mammalian cells, supported by genetic epistasis in yeast

   PMID:34969823

   Open questions at the time

   • Single Co-IP without reciprocal validation in mammalian system
   • Binding interface and functional consequence of the TEX11–TEX12 interaction were not characterized
9. 2022 High

   Structures of TEX12 alone in multiple conformations showed that its C-terminal tip controls both oligomeric state and fiber-driving capacity, providing a structural basis for potential SYCE2-independent roles such as centrosome function.

   Evidence X-ray crystallography, SAXS, solution light scattering, and C-terminal tip mutagenesis of TEX12

   PMID:36071143

   Open questions at the time

   • Whether the C-terminal tip conformational switch operates in the centrosomal context was untested
   • Functional consequence of TEX12 oligomeric state in vivo was not assessed
10. 2023 High

    Demonstrating that SYCE3 directly interacts with the SYCE2–TEX12 complex and is required for its recruitment to the SC defined the upstream assembly step linking transverse filament remodeling to central element fiber formation.

    Evidence Biochemical interaction assays and separation-of-function mutagenesis in mice

    PMID:36635604

    Open questions at the time

    • Structural basis of the SYCE3–SYCE2/TEX12 interface at atomic resolution was not determined
    • Whether SYCE3-mediated recruitment is the sole pathway or whether redundant recruitment mechanisms exist is unknown

• Key open questions include identifying the kinase and functional role of TEX12 Y48 phosphorylation at centrosomes, mapping the specific PLK1 phosphosites that trigger SC disassembly, and determining whether TEX12's SYCE2-independent oligomeric states serve distinct functions at centrosomes versus chromosomes.
• Kinase for Y48 phosphorylation at centrosomes is unknown
• PLK1 phosphosites on TEX12 are unmapped
• In vivo relevance of TEX12 C-terminal tip conformational switch remains untested