Conditional deletion of Atoh1 using Pax2-Cre results in viable mice without differentiated cochlear hair cells that have lost most of the organ of Corti

► Conditional knockout (CKO) of Atoh1 using Pax2-Cre eliminates most Atoh1 in the ear. ► Atoh1 CKO is viable but lacks differentiated hair cells in most sensory epithelia. ► Atoh1 CKO loses most precursor cells in the organ of Corti (OC) through apoptosis. ► Some cells in the OC survive and stain positive for Myo7a and Tubulin. ► The OC is mostly replaced by a flat epithelium expressing Fgf10, Gata3 and Bmp4.