In vivo notch reactivation in differentiating cochlear hair cells induces sox2 and prox1 expression but does not disrupt hair cell maturation

Authors

  • Zhiyong Liu,

    1. Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee
    2. Integrated Program in Biomedical Sciences, University of Tennessee Health Science Center, Memphis, Tennessee
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  • Thomas Owen,

    1. Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee
    2. University of Bath, Bath, United Kingdom
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  • Jie Fang,

    1. Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee
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  • R. Sathish Srinivasan,

    1. Department of Genetics and Tumor Cell Biology, St. Jude Children's Research Hospital, Memphis, Tennessee
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  • Jian Zuo

    Corresponding author
    1. Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee
    • Department of Developmental Neurobiology, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105

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Abstract

Background: Notch signaling is active in mouse cochlear prosensory progenitors but declines in differentiating sensory hair cells (HCs). Overactivation of the Notch1 intracellular domain (NICD) in progenitors blocks HC fate commitment and/or differentiation. However, it is not known whether reactivation of NICD in differentiating HCs also interrupts their developmental program and reactivates its downstream targets. Results: By analyzing Atoh1CreER+; Rosa26-NICDloxp/+ or Atoh1CreER+; Rosa26-NICDloxp/+; RBP-Jloxp/loxp mice, we demonstrated that ectopic NICD in differentiating HCs caused reactivation of Sox2 and Prox1 in an RBP-J-dependent manner. Interestingly, Prox1 reactivation was exclusive to outer HCs (OHCs). In addition, lineage tracing analysis of Prox1CreER/+; Rosa26-EYFPloxp/+ and Prox1CreEGFP/+; Rosa26-EYFPloxp/+ mice showed that nearly all HCs experiencing Prox1 expression were OHCs. Surprisingly, these HCs still matured normally with expression of prestin, wild-type-like morphology, and uptake of FM4-64FX dye at adult ages. Conclusions: Our results suggest that the developmental program of cochlear differentiating HCs is refractory to Notch reactivation and that Notch is an upstream regulator of Sox2 and Prox1 in cochlear development. In addition, our results support that Sox2 and Prox1 should not be the main blockers for terminal differentiation of HCs newly regenerated from postnatal cochlear SCs that still maintain Sox2 and Prox1 expression. Developmental Dynamics 241:684–696, 2012. © 2012 Wiley Periodicals, Inc.

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