Fig. 2.
Induction of ectopic hair cells after in vivo overexpression of β-catenin. (A) In the cochlea, Atoh1 is expressed in hair cells, and both hair cells and supporting cells are postmitotic. No BrdU incorporation was observed in the wild-type organ of Corti. (B) In β-catenin–overexpressing littermates at P5, ectopic Atoh1 expression was induced in the pillar cell region (brackets) between inner and outer hair cells upon activation of Cre at P1 in compound mutants of Sox2-Cre-ER/β-cateninflox(exon3)/Atoh1-nGFP mice. BrdU incorporation was also seen in the pillar cell region. (C) Ectopic Atoh1 expression was observed in β-cateninΔΔexon3 mutant cells. (D) Constitutive activation of β-catenin resulted in Atoh1 expression (arrowheads) in pillar cells, some of which were positive for BrdU (arrow). Atoh1-expressing cells were not found in ectopic positions in wild-type littermates. (E) Quantification of ectopic Atoh1- and Atoh1/BrdU-positive cells in the pillar cell region in β-catenin mutants and wild-type littermates. n = 3 animals/group. Bars are SEM. (F) Myosin VIIa was used to detect hair cells in the organ of Corti, and EdU incorporation was seen outside the area of the hair cells. (F′) An x–z scan of F was performed at the position indicated by the white line. (G) In Sox2-Cre-ER/β-cateninΔ(exon3) mice, extra hair cells were seen in the pillar cell region based on myosin VIIa staining, and some of the cells had incorporated EdU. (G′) An x–z scan of G at the white line showed an ectopic myosin VIIa/EdU-positive cell (arrow). (H) Lineage tag in supporting cells (red) was seen in the myosin VIIa-expressing hair cells (asterisks). (H′) In an x–z scan of H at the white line, a lineage-tagged hair cell (arrow) appeared in the pillar cell region. Myosin VIIa-expressing hair cells are outlined. (Scale bar, 20 μm.)