Fgf8mcm genetic labeling selectively labels Type-I hair cells contacted by calyxes. (A) Following tamoxifen induction at E11.5, tdTomato-positive hair cells are surrounded by βIII-tubulin rich calyces (arrows) when evaluated at P14, consistent with Type-I hair cell identity. (B) Following tamoxifen induction at E17.5, tdTomato-positive hair cells are surrounded by βIII-tubulin rich calyces (arrows) when evaluated at P14. (C) Following tamoxifen induction at P2, tdTomato-positive hair cells are similarly contacted by calyces (arrows) at P14. A′, B′, C′ show βIII-tubulin channel; A″, B″, C″ show tdTomato channel. (D) The frequency of calyx formation about tdTomato-positive hair cells following tamoxifen induction at different developmental stages. Data are mean±s.d. Scale bars: 10 µm.