TECTB

TECTB (β-tectorin) is a secreted glycoprotein that serves as an essential structural component of the tectorial membrane (TM), the acellular extracellular matrix overlying the organ of Corti, where it shapes the cochlear mechanics underlying frequency selectivity and sensitivity (PMID:20981024). Its incorporation into the striated-sheet matrix of the TM depends on direct interaction with α-tectorin (TECTA): a TECTA mutation that abolishes TECTA–TECTB binding yields a TM deficient in TECTB that lacks the striated-sheet matrix and detaches from the organ of Corti (PMID:18452040). CEACAM16 stabilizes the TECTA–TECTB association, since loss of CEACAM16 reduces TM TECTB levels and abolishes striated-sheet matrix and Hensen's stripe formation (PMID:25080593), and proper deposition of TECTB further requires the proteolytic activity of the serine protease hepsin (TMPRSS1), as catalytically active but not protease-dead hepsin restores TECTB incorporation (PMID:39437584). Functionally, TECTB confers anisotropic mechanical properties on the TM, selectively contributing to shear and transverse stiffness without affecting stiffness along the collagen-fiber axis (PMID:30665694); through this, it sets the spatial extent and propagation velocity of TM travelling waves, tuning the trade-off between frequency selectivity and sensitivity (PMID:20981024). The integrity of the conserved cysteines within TECTB's zona pellucida (ZP) domain is required for TM matrix assembly: a ZP-domain missense variant (p.Cys225Tyr) causes autosomal dominant non-syndromic hearing loss, with disrupted TM morphology and heightened susceptibility to noise-induced hearing loss (PMID:40832383).

1. 2008 Medium

   Established that TECTB does not assemble into the TM autonomously but requires a physical interaction with TECTA, defining the molecular basis of striated-sheet matrix formation.

   Evidence Spontaneous Tecta A349D missense knock-in mouse with TM immunohistochemistry and electron microscopy

   PMID:18452040

   Open questions at the time

   • Does not map the TECTA–TECTB interaction interface or domains
   • Interaction inferred from co-deficiency rather than direct binding assay
2. 2010 High

   Linked TECTB's structural role to a defined mechanical function, showing it governs TM travelling-wave spread and velocity that tune the selectivity–sensitivity trade-off in the cochlea.

   Evidence Tectb knockout mouse with TM travelling-wave measurements and auditory functional testing

   PMID:20981024

   Open questions at the time

   • Does not resolve which biophysical TM property mediates the wave change
   • Molecular contribution of TECTB to matrix architecture not directly visualized here
3. 2014 Medium

   Identified CEACAM16 as a stabilizer of the TECTA–TECTB association, explaining how the striated-sheet matrix and Hensen's stripe are maintained.

   Evidence Ceacam16 null mouse with protein interaction readout, immunohistochemistry, and electron microscopy

   PMID:25080593

   Open questions at the time

   • Direct ternary complex of TECTA/TECTB/CEACAM16 not biochemically reconstituted
   • Stoichiometry and binding sites unknown
4. 2019 Medium

   Resolved the specific mechanical contribution of TECTB, demonstrating it provides shear and transverse stiffness and sets TM anisotropy rather than overall stiffness.

   Evidence Isolated TM biophysical measurements with harmonic radial excitation and anisotropic finite-element modeling in Tectb−/− vs. wild-type

   PMID:30665694

   Open questions at the time

   • Does not connect anisotropy changes to molecular matrix organization
   • Single-lab measurement
5. 2021 Medium

   Delimited the functional reach of the TECTB-dependent TM, showing it is dispensable for MET channel maturation and resting bundle position but required for Ca2+ regulation near stereocilia during sustained stimulation.

   Evidence Tecta/Tectb double-knockout mouse with patch-clamp MET recordings, cochlear microphonics, and distortion product otoacoustic emissions

   PMID:33559882

   Open questions at the time

   • Ca2+ regulation role is inferred indirectly from OAE adaptation failure
   • Cannot isolate TECTB-specific from TECTA-specific contributions in the double knockout
6. 2024 Medium

   Defined a maturation step for TECTB, showing hepsin protease activity is required for its proteolytic processing and incorporation into the TM.

   Evidence Hepsin knockout mice rescued with wild-type vs. protease-dead hepsin, with TECTB/TECTA immunostaining and TM morphology

   PMID:39437584

   Open questions at the time

   • Direct cleavage of TECTB by hepsin not demonstrated biochemically
   • Cleavage site and processed product unidentified
7. 2025 Medium

   Tied TECTB to human disease and assigned a structural role to its ZP-domain cysteines, showing a cysteine-disrupting variant causes dominant hearing loss and noise susceptibility.

   Evidence Multigenerational family genetics with co-segregation plus Tectb-C225Y knock-in mouse with ABR, TM histology, and noise-exposure testing (preprint)

   PMID:40832383

   Open questions at the time

   • Preprint, not yet peer-reviewed
   • Molecular consequence of the cysteine substitution on disulfide bonding/folding not directly resolved

• The biochemical details of TECTB assembly remain open: how its ZP domain mediates polymerization, the precise hepsin cleavage event, and the structural organization of the TECTA/TECTB/CEACAM16 matrix are not directly defined.
• No reconstituted structure of the TECTB-containing matrix
• Hepsin cleavage site on TECTB unmapped
• ZP-domain polymerization mechanism uncharacterized