Notch and Wnt signalling interact for proper prosensory and non-sensory domain formation

Abstract

The prosensory domain (PSD) of the developing inner ear develops into the sensory hair cells, supporting cells, and neurons necessary for hearing and balance. Although Notch-Jag1 signalling is known to maintain Sox2 expression in this domain, the mechanisms by which Notch sustains prosensory identity have remained unclear. Here, we show that this function does not require canonical RBPJ{kappa}-dependent transcription. Using chick in ovo electroporation, Notch reporter assays, and conditional mouse mutants, we find that canonical Notch signalling is active during neurogenesis but not within the Sox2-positive PSD. Jag1 loss leads to a gradual loss of Sox2, yet RBPJ{kappa} mutants retain Sox2, indicating a non- canonical Notch pathway. We further reveal that the non-sensory determinant Lmx1a is regulated by Wnt/{beta}-catenin signalling and that manipulating Wnt activity shifts the balance between Lmx1a and Sox2 expression. Finally, we show that NICD can directly interact with {beta}-catenin in the cytoplasm, suggesting that NICD sequesters {beta}-catenin to suppress Wnt activity and stabilise Sox2 in the PSD. Collectively, these findings support a model where prosensory maintenance occurs through non-canonical Notch signalling acting together with Wnt, forming a combined WNTCH regulatory module that coordinates sensory and non-sensory fate specification.