title: Initiation of neuronal differentiation requires PI3-kinase/TOR signalling in the vertebrate neural tube.
abstract: Regulated neuron production within the vertebrate nervous system relies on input from multiple signalling pathways. Work in the Drosophila retina has demonstrated that PI3-kinase and downstream TOR signalling regulate the timing of photoreceptor differentiation; however, the function of such signals during vertebrate neurogenesis is not well understood. Here we show that mutant mice lacking PKB activity downstream of PDK1, the master kinase of the PI3-kinase pathway, exhibit deficient neuron production. We further demonstrate expression of PI3-kinase signalling components and active PKB and TOR signalling in the chick spinal cord, an early site of neurogenesis. Neuron production was also attenuated in the chick neural tube following exposure to small molecule inhibitors of PI3-kinase (LY294002) or TOR (Rapamycin) activity. Furthermore, Rapamycin repressed expression of early neuronal differentiation genes, such as Ngn2, but did not inhibit expression of Sox1B genes characteristic of proliferating neural progenitors. In addition, some cells expressing an early neuronal marker were mis-localised at the ventricular surface in the presence of Rapamycin and remained aberrantly within the cell cycle. These findings suggest that TOR signalling is necessary to initiate neuronal differentiation and that it may facilitate coordination of cell cycle and differentiation programmes. In contrast, stimulating PI3-kinase signalling did not increase neuron production, suggesting that such activity is simply permissive for vertebrate neurogenesis.
authors.affiliation: Neural Development Group, Division of Cell & Developmental Biology, College of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, Scotland, UK.
authors.forename: Katherine J
authors.initials: KJ
authors.lastname: Fishwick
authors.forename: Roman A
authors.initials: RA
authors.lastname: Li
authors.forename: Pamela
authors.initials: P
authors.lastname: Halley
authors.forename: Peiyi
authors.initials: P
authors.lastname: Deng
authors.forename: Kate G
authors.initials: KG
authors.lastname: Storey
mesh_terms: D000818:Animals; D002453:Cell Cycle; D002454:Cell Differentiation / Q000235:genetics; D002642:Chick Embryo; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D051379:Mice; D008817:Mice, Mutant Strains; D054259:Neural Tube / Q000166:cytology* / Q000378:metabolism; D055495:Neurogenesis; D009474:Neurons / Q000166:cytology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C546843:mTOR protein, mouse