To rule out the possibility that the high levels of Sox2 in the cells within the lumenal layer in the CKO organ of Corti is due to developmental delay and confirm that those high Sox2+ cells are indeed hair cells, we harvested cochlea 1–2 days later at E18.5-P0 after tamoxifen administration at E11.5–12.5 and performed immunostaining for Sox2 and Myo7a, a marker specific for differentiating hair cells. This evidence concerns the gene SOX2 and Global developmental delay.