TectaY1870C/+ mice with alterations in the structure and porosity of the tectorial membrane display large numbers of spontaneous emissions

Spontaneous otoacoustic emissions (SOAEs) are a signature of cochlear amplification, a process associated with outer hair cell (OHC) function and required for the sensitivity and frequency selectivity of cochlear responses. Although normal mice rarely exhibit these signals, those with mutations that influence the structure of the tectorial membrane (TM) show a greater incidence of these phenomena. In this report, we study mouse models with mutations affecting the striated-sheet matrix that forms the body of this accessory structure. In addition to CEACAM16, the matrix is composed of both α- and β-tectorin (TECTA and TECTB respectively) and these latter two noncollagenous proteins are the focus of this study. Of all the mutants tested to date, mice heterozygous (het) for a missense mutation (c.5609A>G, p.Tyr1870Cys) in Tecta (TectaY1870C/+ mice) are prolific emitters with an average of ∼7 SOAEs per cochlea, which is higher than in the very few normal mice with SOAEs where the average is 2-3 per cochlea. A small number of homozygous Tectb−/- mice lacking TECTB are also emitters, but they produce only one SOAE in any given ear. Although both mouse mutants have hearing loss, SOAE frequencies coincide with frequency regions where some degree of amplification is retained. The larger number of SOAEs in TectaY1870C/+ mice appears to correlate with an increase in porosity (1), which controls the spread of excitation of tectorial membrane traveling waves. Sellon and colleagues reported that this change in the material properties of the TM was associated with the larger size of nanoscale pores linked to the Y1870C missense mutation in TECTA. In mice lacking Tectb, where porosity is wild-type like, the number of SOAEs per cochlea is small and only a few of these animals present with this phenomenon. Characterization of traveling-wave properties in other emitting TM mutants will be required to know if the correlation between increased porosity and increased numbers of SOAEs reliably causes the change in phenotype.