DN-erbB4 is expressed in the cochlea of GFAP-DN-erbB4 mice. A, RT-PCR of total RNA from temporal bone of 30-d-old wild-type and transgenic mice with DN-erbB4- and GAPDH-specific primers. B, Anti-flag Western blot of temporal bone extracts of 30-d-old wild-type and transgenic mice. C, In situ hybridization for DN-erbB4 in the cochlea of 15-d-old homozygous (left panel) and wild-type (right panel) mice. The lack of signal in the wild type shows that erbB4 is not expressed in the cochlea. D, Immunostaining for DN-erbB4 in the P17 cochlea. A section through the cochlea of homozygous (left) and wild-type (right) mice stained with an antibody against the extracellular domain of the human erbB4. The arrowheads point to the IHC and OHC supporting cells, which express DN-erbB4. Nonspecific labeling of the osseous spiral lamina was found in both genotypes. Scale bars: C, 50 μm; D, 30 μm.