a, The OHC electromotility protein prestin is expressed in the OHCs of Ikzf2cello/cello mutants (n = 6 biologically independent samples). In addition, the pattern of prestin expression is not affected by Anc80-eGFP transduction, but is induced in Anc80-Ikzf2-transduced IHCs (n = 3 biologically independent samples per condition). Scale bars, 10 µm. b, Expression of prestin can be seen in Anc80-Ikzf2-transduced IHCs as early as P8 and up to 8 weeks of age, and overlaps with MYC staining (n = 6 biologically independent samples at P8, n = 3 biologically independent samples at 6–8 weeks). Scale bars, 20 µm. c, Scanning electron micrographs of IHC and OHC stereocilia bundles of Anc80-Ikzf2- and Anc80-eGFP-injected mice at P23 showing expected bundle patterning. Images are from the mid-basal region of the cochlear spiral. Scale bars, 1 µm. Number of biologically independent samples (P16–P23): Anc80-Ikzf2-injected cochlea n = 8, Anc80-Ikzf2 contralateral cochlea n = 6, Anc80-eGFP-injected cochlea n = 3. d, Representative traces of the voltage-dependent (nonlinear) component of the membrane capacitance (an electrical signature of electromotility) in the IHCs of Anc80-Ikzf2-injected mouse (red) and its non-injected littermate (grey). Mice were injected with Anc80-Ikzf2 at P2 and recorded at P16. e, Normalized maximal nonlinear capacitance in all recorded IHCs of mice injected with Anc80-Ikzf2 at P2 (red) at different ages after injection and their non-injected littermates (black). Each symbol represents one biologically independent cell, and the total number of cells is indicated in parentheses. Because Anc80-Ikzf2 transduction is not 100% efficient in the apical turn of the cochlea at the time points tested, some IHCs of Anc80-Ikzf2-injected mice do not show prominent nonlinear capacitance, whereas the other IHCs do. In the IHCs with maximal nonlinear capacitance of more than 0.25 pF (due to presumable Ikzf2 expression), the parameters of the Boltzmann fit were as following (mean ± s.e.m.): Q max = 0.10 ± 0.02 pC; V pk = −31 ± 1 mV; z = 0.91 ± 0.02; C lin = 11.7 ± 1.2 pF; ΔC sa = 0.14 ± 0.07 pF (n = 12). For information on the fitting procedure, see Methods.