Extended Data Fig. 1: Expression of Tbx2 mRNA in cochlea.
From: Tbx2 is a master regulator of inner versus outer hair cell differentiation
(a,d) In situ hybridizations in sections of neonatal (P0 and P1) cochleae from control mice (Insm1F/F) reveal Tbx2 expression in most cells lining the scala media including IHCs, Inner Phalangeal Cells (IPhC), Inner Border Cells (IBC), Greater Epithelial Ridge (GER), interdental cells of the Spiral Limbus (SL), Reissner’s Membrane (RM), some cells of the Stria Vascularis (SV), Spiral Prominence (SP), and Claudius’ Cells (CCs); but little or no expression (above background levels) of Tbx2 in OHCs or other cells of the outer compartment, namely Hensen’s Cells (HeCs), Deiters’ Cells (DCs), and Outer and Inner Pillar cells (OPC and IPC). (b,c,e) In situ hybridizations in sections of developing Insm1 mutant cochleae (Atoh1Cre/+; Insm1F/F in b and c; TgPax2Cre/+; Insm1F/F in e) reveal that Tbx2 is expressed in about half of the OHCs, presumably those transdifferentiating into IHCs. In controls, none of the OHCs (0/117 from N=4 Insm1F/F mice at E16.5, P0 and P1) expressed Tbx2, whereas in Insm1 mutants, in which nearly half of the OHCs transdifferentiate into IHCs (46.0±5.6%)2, an equivalent fraction of hair cells in the position of the OHCs expressed Tbx2 (46.6%; 62/133 cells from N=4 TgPax2Cre/+; Insm1F/F or Atoh1Cre/+; Insm1F/F mice at E16.5, P0 and P1). (f-h) Double in situ hybridizations in sections of neonatal (P0) cochleae for detection of Tbx2 (magenta) and Vglut3 (blue), the earliest marker of functional, mature IHCs. (f) In Insm1F/F controls, only IHCs express high levels of Vglut3 (a few dots label OHCs, perhaps representing a much lower level of expression). (g,h) In TgPax2Cre/+; Insm1F/F cochleae, only OHCs misexpressing Tbx2 (50/114 at P0, 14/30 at P2 and 9/21 at P4) also misexpressed high levels (those characteristic of IHCs) of Vglut3, whereas none of the OHCs misexpressed either gene alone (at IHC-like levels). Hence, early expression of Tbx2 in OHCs lacking INSM1 appears to correlate perfectly with their transdifferentiating into IHCs. Images shown are examples of results obtained in three separate tissue samples (n=3 biologically independent samples). Scale bar of 20 µm in (a) applies to all other panels.
