The Mouse Tectorins

Abstract

The cDNA and derived amino acid sequences for the two major non-collagenous proteins of the mouse tectorial membrane, ␣-and ␤-tectorin, are presented. The cDNA for ␣-tectorin predicts a protein of 239,034 Da with 33 potential N-glycosylation sites, and that of ␤-tectorin a smaller protein of 36,074 Da with 4 consensus N-glycosylation sites. Southern and Northern blot analysis indicate ␣-and ␤-tectorin are single copy genes only expressed in the inner ear, and in situ hybridization shows they are expressed by cells both in and surrounding the mechanosensory epithelia. Both sequences terminate with a hydrophobic COOH terminus preceded by a potential endoproteinase cleavage site suggesting the tectorins are synthesized as glycosylphosphatidylinositollinked, membrane bound precursors, targeted to the apical surface of the inner ear epithelia by the lipid and proteolytically released into the extracellular compartment. The mouse ␤-tectorin sequence contains a single zona pellucida domain, whereas ␣-tectorin is composed of three distinct modules: an NH 2 -terminal region similar to part of the entactin G1 domain, a large central segment with three full and two partial von Willebrand factor type D repeats, and a carboxyl-terminal region which, like ␤-tectorin, contains a single zona pellucida domain. The central, high molecular mass region of ␣-tectorin containing the von Willebrand factor type D repeats has homology with zonadhesin, a sperm membrane protein that binds to the zona pellucida. These results indicate the two major non-collagenous proteins of the tectorial membrane are similar to components of the sperm-egg adhesion system, and, as such may interact in the same manner.The sensory epithelia of the inner ear contain hair and supporting cells, and the apical surfaces of these epithelia are covered by extracellular matrices which transmit forces to the mechanosensitive stereociliary bundles of the hair cells. In the ampullae of the semi-circular canals, a cupula sits on top of each crista; in the saccule and utricule, the maculae are covered by an otolithic membrane; in the cochlea, a tectorial membrane lies over the surface of the organ of Corti. The structures of these three types of matrices, the cupula, the otolithic membrane, and the tectorial membrane, are complex and not identical, and each may be tailored to provide the optimal stimulus for the type of hair cell present in each organ.The tectorial membrane is the best characterized of these matrices. In the chick it is a dense fibrillogranular matrix (1) composed of two major glycoproteins, ␣-and ␤-tectorin (2, 3). Chick ␣-tectorin is a large (M r ϭ 196,000) disulfide cross-linked complex composed of six polypeptides, the ␣1-to ␣6-tectorins, whereas chick ␤-tectorin is considerably smaller (M r ϭ 43,000) and not covalently associated with ␣-tectorin. The cDNA for chick ␤-tectorin has been recently cloned (3) and analysis of the sequence indicates ␤-tectorin is related to the pancreatic zymogen granule protein GP2, the urinary glycoprotein uromodulin (T...

Structural Characterization of Native Mouse Zona Pellucida Proteins Using Mass Spectrometry

“…The zona domain has been implicated in forming protein polymers not only in the zona pellucida matrix, but between constituents of the extracellular tectorin membrane found in the inner ear (10,47). Genetically altered mice lacking ZP1 form a zona matrix composed of ZP2 and ZP3 (48); mice lacking ZP2 form a thinner, more fragile matrix composed of ZP1 and ZP3 (49); but mice lacking ZP3 do not form a zona pellucida (11,50).…”

Measurement of the mechanical properties of isolated tectorial membrane using atomic force microscopy

“…Considering the above, the TM is likely to play an important role in delivering sound-induced mechanical stimuli to OHC hair bundles, as well as in communicating between OHC and IHC hair bundles. Further support for the important role of the TM in hearing is obtained from recent studies, which have shown that mutations in proteins of the TM cause auditory impairments (5)(6)(7)(8).…”

Zona Pellucida Glycoproteins

“…Mutations in ZPDs, especially in the NTS, can result in severe pathologies, such as infertility, deafness, and cancer. In this context, it was proposed that ZPDs might play a role in polymerization of proteins into fibrils or matrices (25). Indeed, it was found that ZPDs polymerize into fibrils on their own (26) and that the NTS is responsible for polymerization (27).…”