Spatiotemporal expression of bmi1 in the developing mouse cochlea

Bmi1 is a member of the Polycomb protein family and has been reported to play important roles in regulating the survival of auditory hair cells. However, the detailed expression profile of Bmi1 during mouse cochlear development has not yet been fully investigated. Here, we used C56BL/6J mice to examine the spatiotemporal expression of Bmi1 in the cochlear duct during embryonic and postnatal development. Bmi1 expression was first observed throughout the nuclei of the otocyst at embryonic day 11 (E11). At E14.5 and E15.5, Bmi1 was expressed in the nuclei of differentiating cochlear epithelia from the apical to the basal turns. At E15.5, Bmi1 also began to be expressed in the spiral ganglion. From E18 to postnatal day 0 (P0), the expression of Bmi1 was located in the nuclei of the cochlear epithelium in all three turns and could be distinctly seen in the outer hair cells, inner hair cells, supporting cells (inner phalangeal cells, Deiters’ cells, pillar cells, and Hensen’s cells), Kölliker’s organ, the striae vascularis, and tympanic border cells. Bmi1 continued to be expressed in spiral ganglion cells from E18 to P0. Our results provide the basic expression pattern of Bmi1 and might be helpful for future investigations of the detailed role of Bmi1 during the development of the cochlea.