Canonical Notch Signaling Is Not Necessary for Prosensory Induction in the Mouse Cochlea: Insights from a Conditional Mutant of RBPjκ

The mammalian organ of Corti consists of a highly organized array of hair cells and supporting cells that originate from a common population of prosensory progenitors. Proper differentiation of this complex cellular mosaic requires lateral inhibition mediated by Notch signaling. Several studies have implicated Notch signaling in the earlier induction of the prosensory domain that lies along the length of the cochlear duct, and which forms before the onset of hair cell and supporting cell differentiation. To investigate the role of Notch signaling in prosensory domain formation, we conditionally inactivated the transcriptional mediator of canonical Notch signaling, RBPj kappa, throughout the inner ear. Although RBPj kappa mutants have severe vestibular defects and a shortened cochlear duct, markers of the prosensory domain appear at the normal time and location in the cochlea of RBPj kappa mutants. Despite the lack of RBPj kappa, hair cell and supporting cell markers also appear at appropriate times in the cochlea, suggesting that RBPj kappa is dispensable for differentiation of the cochlear sensory epithelium. However, we also observed that differentiating hair cells and supporting cells rapidly die in RBPj kappa mutants, suggesting a requirement of RBPj kappa for cell survival in this tissue. Finally, in contrast to the chick basilar papilla, ectopic activation of Notch signaling did not induce ectopic sensory patches in nonsensory regions of the cochlea. Our results indicate that canonical Notch signaling is not necessary for prosensory specification in the mouse cochlea, suggesting that other signaling pathways may specify this highly derived sensory organ.