Optimal tamoxifen concentration and incubation time for nuclear localization of the ATOH1-ER-DSRED fusion protein. The Atoh1-ER-DsRed construct was electroporated into cochlear spheres generated from ROSA26-GFP mice (green) and incubated with graded doses of tamoxifen. Top left: In the absence of tamoxifen, the ATOH1-ER-DSRED fusion protein (red) is expressed diffusely in the cytoplasm of transfected cells. Top right: Addition of 1 nM tamoxifen for 48 hr results in a decrease in diffuse cytosolic DsRed signaling and increase in punctate localization of the ATOH1-ER-DSRED fusion protein after 48 hr, which is suggestive of nuclear localization (DsRed fluorescence=red). The table describes dose and temporal effects of tamoxifen on punctate expression of the fusion protein. The yellow box highlights minimal effective conditions (+, nuclear localization in <90% of cells; −/+, ∼50% nuclear localization; −, >10% nuclear localization). Scale bars=10 μM.