Otospheres derived from neonatal mouse cochleae retain the progenitor cell phenotype after ex vivo expansions

► Otospheres are generated from the cochlear epithelia of neonatal mice. ► Otospheres after ex vivo expansions retained the stemness characteristics. ► Otospheres after ex vivo expansions differentiated into hair-cell phenotypes. ► The activity for self-renewal in otospheres was weakened by ex vivo expansions. ► Otospheres after ex vivo expansions are useful for studying hair cell regeneration.