title: In vivo Notch reactivation in differentiating cochlear hair cells induces Sox2 and Prox1 expression but does not disrupt hair cell maturation.
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 Atoh1(CreER+) ; Rosa26-NICD(loxp/+) or Atoh1(CreER+) ; Rosa26-NICD(loxp/+) ; RBP-J(loxp/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 Prox1(CreER/+) ; Rosa26-EYFP(loxp/+) and Prox1(CreEGFP/+) ; Rosa26-EYFP(loxp/+) 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.
authors.affiliation: Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Liu
authors.forename: Thomas
authors.initials: T
authors.lastname: Owen
authors.forename: Jie
authors.initials: J
authors.lastname: Fang
authors.forename: R Sathish
authors.initials: RS
authors.lastname: Srinivasan
authors.forename: Jian
authors.initials: J
authors.lastname: Zuo
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D019070:Cell Lineage / Q000502:physiology; D006198:Hair Cells, Auditory / Q000166:cytology* / Q000502:physiology; D018398:Homeodomain Proteins / Q000502:physiology*; D051379:Mice; D051880:Receptors, Notch / Q000502:physiology*; D055748:SOXB1 Transcription Factors / Q000502:physiology*; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000502:physiology*; D000098551:Prospero-Related Homeobox 1 Protein
chemical_list: D018398:Homeodomain Proteins; D051880:Receptors, Notch; D055748:SOXB1 Transcription Factors; C527783:Sox2 protein, mouse; D025521:Tumor Suppressor Proteins; D000098551:Prospero-Related Homeobox 1 Protein