Simple rule for calculating normal erythrocyte sedimentation rate.

Abstract

Cochlear hair cells (HCs) are mechanosensory receptors that transduce sound into electrical signals. HC damage in nonmammalian vertebrates induces surrounding supporting cells (SCs) to divide, transdifferentiate and replace lost HCs; however, such spontaneous HC regeneration does not occur in the mammalian cochlea. Here, we acutely ablate the retinoblastoma protein (Rb), a crucial cell cycle regulator, in two subtypes of postmitotic SCs (pillar and Deiters9 cells) using an inducible Cre line, <i>Prox1-CreER^T2</i>. Inactivation of Rb in these SCs results in cell cycle reentry of both pillar and Deiters9 cells, and completion of cell division with an increase in cell number of pillar cells. Interestingly, nuclei of <i>Rb</i>^−/− mitotic pillar and Deiters9 cells migrate toward the HC layer and divide near the epithelial surface in a manner similar to the SCs in the regenerating avian auditory epithelium. In contrast to postmitotic <i>Rb</i>^−/− HCs which abort cell division, postmitotic <i>Rb</i>^−/− pillar cells can proliferate, maintain their SC fate and survive for more than a week. However, no newly formed HCs are detected and SC death followed by HC loss occurs. Our studies accomplish a crucial step toward functional HC regeneration in the mammalian cochlea <i>in vivo</i>, demonstrating the critical role of Rb in maintaining quiescence of postmitotic pillar and Deiters9 cells and highlighting the heterogeneity between these two cell types. Therefore, the combination of transient Rb inactivation and further manipulation of transcription factors (i.e., Atoh1 activation) in SCs may represent an effective therapeutic avenue for HC regeneration in the mammalian cochlea.