title: PIP3 is involved in neuronal polarization and axon formation.
abstract: Recent experiments in various cell types such as mammalian neutrophils and Dictyostelium discoideum amoebae point to a key role for the lipid product of PI 3-kinase, PIP(3), in determining internal polarity. In neurons, as a consequence of the elongation of one neurite, the axon is specified and the cell acquires its polarity. To test the hypothesis that PI 3-kinase and PIP(3) may play a role in neuronal polarity, and especially in axon specification, we observed localization of PIP(3) visualized by Akt-PH-GFP in developing hippocampal neurons. We found that PIP(3) accumulates in the tip of the growing processes. This accumulation is inhibited by addition of PI 3-kinase inhibitors. Those inhibitors, consistently with a role of PIP(3) in process formation and elongation, delay the transition from stage 1 neurons to stage 3 neurons, and both axon formation and elongation. Moreover, when the immature neurite contacts a bead coated with laminin, a substrate known to induce axon specification, PIP(3) accumulates in its growth cone followed by a rapid elongation of the neurite. In such conditions, the addition of PI 3-kinase inhibitors inhibits both PIP(3) accumulation and future axon elongation. These results suggest that PIP(3) is involved in axon specification, possibly by stimulating neurite outgrowth. In addition, when a second neurite contacted the beads, this neurite rapidly elongates whereas the elongation of the first laminin-contacting neurite stops, consistently with the hypothesis of a negative feedback mechanism from the growing future axon to the other neurites.
authors.affiliation: Department of Cell Pharmacology, Nagoya University, Graduate School of Medicine, Showa, Nagoya, Aichi, Japan.
authors.forename: Céline
authors.initials: C
authors.lastname: Ménager
authors.forename: Nariko
authors.initials: N
authors.lastname: Arimura
authors.forename: Yuko
authors.initials: Y
authors.lastname: Fukata
authors.forename: Kozo
authors.initials: K
authors.lastname: Kaibuchi
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology*; D016764:Cell Polarity / Q000502:physiology*; D002478:Cells, Cultured; D049452:Green Fluorescent Proteins; D006624:Hippocampus / Q000166:cytology; D007797:Laminin / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics; D016501:Neurites / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000235:genetics; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D049452:Green Fluorescent Proteins; D007797:Laminin; D008164:Luminescent Proteins; D019869:Phosphatidylinositol 3-Kinases; D018129:Phosphatidylinositol Phosphates; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011993:Recombinant Fusion Proteins; C060974:phosphatidylinositol 3,4,5-triphosphate; C494920:Akt1 protein, rat