The extracellular membranes of the inner ear are essential constituents to
maintain sensory functions, the cupula for sensing torsional movements of the
head, the otoconial membrane for sensing linear movements and accelerations
like gravity, and the tectorial membrane in the cochlea for hearing. So far a
number of structural proteins have been described, but for the gelatinous
cupula precise data are missing. Here, we describe for the first time a major
proteinogenic component of the cupula structure with an apparent molecular
mass of 45 kDa from salmon. Analyses of respective peptides revealed highly
conserved amino-acid sequences with identity to zona pellucida-like domain
proteins. Immunohistochemistry studies localized the protein in the ampulla of
the inner ear from salmon and according to its anatomical appearance we
identified this glycoprotein as Cupulin. Future research on structure and
function of zona pellucida-like domain proteins will enhance our knowledge of
inner ear diseases, like sudden loss of vestibular function and other
disturbances