Fig. 1: Tbx2/TBX2 expression is progressively confined to IHCs and ISCs during cochlear development.

a Scheme showing the basal (1) and the apical (4) turn of the mature cochlea, a cross section through the cochlea, and a magnification of the basal turn with the cellular organization in and around the organ of Corti (OoC): with Deiters’ cells (DCs) and OHCs in the outer compartment (OC, shades of green), inner phalangeal cells (IPhCs), inner border cells (IBCs) and IHCs in the inner compartment (IC, shades of yellow) separated by pillar cells (PCs) that form the tunnel of Corti. Laterally, the OoC is flanked by cells of the outer sulcus, and medially by cells of the inner sulcus. GER greater epithelial ridge (primordium of the inner sulcus), L lateral, LER lesser epithelial ridge (primordium of the outer sulcus), M medial. b–d Expression of Tbx2 mRNA and TBX2 protein on sections of the developing cochlea of wildtype embryos. b RNA in situ hybridization analysis of Tbx2 expression in the prosensory epithelium of the cochlea at E12.5 and E13.5 as well as in the developing OoC between E14.5 and E18.5. Dotted circles mark the nucleus of the three OHCs and of one IHC in the OoC at E18.5. c, d Co-immunofluorescence analysis of expression of TBX2 with markers for differentiation (SOX2: pro-sensory cells/supporting cells; MYO7A: hair cells) and compartmentalization (CDH2: inner; CDH1: outer) from E12.5 to E18.5 (c) and with markers for all hair cells (MYO7A), IHCs (SLC17A8, CALB2), OHCs (BCL11B, SLC26A5, KCNQ4), DCs and PCs (PROX1) at E18.5 and P21 (d). n = 3 for each assay at each stage. Scale bars: 30 µm. e Scheme of TBX2 expression (red nuclei) in the OoC at E18.5. The color code is the same as in a.