Basally, the pattern is similar to the one described for clarin-1 and parallels the developmental window when synaptic remodeling takes place at the base of the OHCs during the first post-natal weeks in mouse cochlea. We show, for the first time, that CDH23, PCDH15, VLGR1 and clarin-1 are also expressed by both types of afferent fibers, with very prominent expression in a sub-population of type I afferent neurons. The expression is not restricted to the neuronal terminals but is observed throughout the neuronal Epoxomicin Proteasome inhibitor fibers to the SGN cell bodies. We also observed weak and diffuse immunostaining in the cell bodies and at brighter spots of immunostaining at the base of isolated hair cells from P3 mice. Although this basal immunoreactivity was observed repetitively in the different hair cell preparations, we cannot rule out the possibility that this staining may be due to post-synaptic fibers that remain attached after the isolation procedure. We feel this is unlikely, however, given the clear co-localization of these CHIR-99021 moa proteins with myosin7A in the isolated hair cell preparations. Cochlea cross-sections also show diffuse Usher protein expression in the hair cell bodies that is similar to that observed for other synaptic proteins at early developmental stages. This may reflect the active protein trafficking that is taking place during this maturational process. In mature mouse cochlea the Usher proteins are still present post-synaptically at the base of IHCs and in the contacting type I afferent fibers. This suggests two different roles for the Usher proteins at the synapses, i) an early role that may involve type I afferent synaptic maturation and ii) a later role most likely related to maintenance of the afferent fibers and their synaptic contacts in the adult cochlea. While mature hair cells show absence of basal immunostaining for the Usher proteins, their expression persists at the stereocilia level. In the case of VLGR1, a component of the transient ankle links involved in hair bundle development, we were able to detect strong expression in the apical region of the stereocilia at P30 suggesting an additional and novel role for EAR/EPTP domain-containing VLGR1 isoform in mature stereocilia. The fraction of uncharacterized proteins in the human proteome currently still comprises more than 75% in the UniProt knowledgebase, which is the most comprehensive available protein sequence database. Current techniques to predict the function of uncharacterized proteins rely mainly on their sequence homology to already characterized proteins. More advanced methods use sequence-profile or profile-profile alignments. Although these methods have significantly improved in terms of detection of remote homology, still more than 20% of the human proteome has not been annotated because no characterized homologs could be identified with the necessary statistical significance.