title: AKT signaling mediates IGF-I survival actions on otic neural progenitors.
abstract: BACKGROUND
  Otic neurons and sensory cells derive from common progenitors whose transition into mature cells requires the coordination of cell survival, proliferation and differentiation programmes. Neurotrophic support and survival of post-mitotic otic neurons have been intensively studied, but the bases underlying the regulation of programmed cell death in immature proliferative otic neuroblasts remains poorly understood. The protein kinase AKT acts as a node, playing a critical role in controlling cell survival and cell cycle progression. AKT is activated by trophic factors, including insulin-like growth factor I (IGF-I), through the generation of the lipidic second messenger phosphatidylinositol 3-phosphate by phosphatidylinositol 3-kinase (PI3K). Here we have investigated the role of IGF-dependent activation of the PI3K-AKT pathway in maintenance of otic neuroblasts.
  
  
  RESULTS
  By using a combination of organotypic cultures of chicken (Gallus gallus) otic vesicles and acoustic-vestibular ganglia, Western blotting, immunohistochemistry and in situ hybridization, we show that IGF-I-activation of AKT protects neural progenitors from programmed cell death. IGF-I maintains otic neuroblasts in an undifferentiated and proliferative state, which is characterised by the upregulation of the forkhead box M1 (FoxM1) transcription factor. By contrast, our results indicate that post-mitotic p27(Kip)-positive neurons become IGF-I independent as they extend their neuronal processes. Neurons gradually reduce their expression of the Igf1r, while they increase that of the neurotrophin receptor, TrkC.
  
  
  CONCLUSIONS
  Proliferative otic neuroblasts are dependent on the activation of the PI3K-AKT pathway by IGF-I for survival during the otic neuronal progenitor phase of early inner ear development.
authors.affiliation: Instituto de Investigaciones Biomedicas Alberto Sols, CSIC-UAM, Madrid, Spain.
authors.forename: Maria R
authors.initials: MR
authors.lastname: Aburto
authors.forename: Marta
authors.initials: M
authors.lastname: Magariños
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Leon
authors.forename: Isabel
authors.initials: I
authors.lastname: Varela-Nieto
authors.forename: Hortensia
authors.initials: H
authors.lastname: Sanchez-Calderon
mesh_terms: D000818:Animals; D053148:Caspase 3 / Q000378:metabolism / Q000502:physiology; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002642:Chick Embryo; D007758:Ear, Inner / Q000196:embryology* / Q000294:innervation*; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000235:genetics; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008954:Models, Biological; D058953:Neural Stem Cells / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D051058:Oncogene Protein v-akt / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D013997:Time Factors
chemical_list: D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D051058:Oncogene Protein v-akt; D053148:Caspase 3