Expression of members of Wnt and Frizzled gene families in the postnatal rat cochlea

The functioning of the mammalian cochlea is entirely based on its mechanical properties, which are supported by a highly complex tissue architecture resulting from the precise arrangement of sensory hair cells and non-sensory supporting cells. Growing evidence indicates that evolutionary conserved signaling pathways are involved in inner ear development and in the differentiation of its diverse cell types. We investigated whether members of the Wnt and Frizzled gene families, which play key roles in a wide variety of cellular and developmental processes, are expressed in the postnatal rat cochlea. A PCR screening of a rat cochlea cDNA library performed with degenerate primers allowed us to isolate five members of the Wnt gene family (RWnt-2B, -4, -5A, -5B, and -7A) and six members of the Frizzled gene family (Rfz1, Rfz2, Rfz3, Rfz4, Rfz6, Rfz9). In situ hybridization and immunocytochemistry experiments demonstrated that RWnt-4, -5B, -7A have distinct, although partly overlapping, expression patterns in the juvenile rat cochlea. These results suggest that the Wnt-Frizzled signaling pathway could be involved in several aspects of late cochlear differentiation and/or auditory function.