title: Phosphatidylinositol-3-kinase-atypical protein kinase C signaling is required for Wnt attraction and anterior-posterior axon guidance.
abstract: Wnt proteins are conserved axon guidance cues that control growth cone navigation. However, the intracellular signaling mechanisms that mediate growth cone turning in response to Wnts are unknown. We previously showed that Wnt-Frizzled signaling directs spinal cord commissural axons to turn anteriorly after midline crossing through an attractive mechanism. Here we show that atypical protein kinase C (aPKC), is required for Wnt-mediated attraction of commissural axons and proper anterior-posterior (A-P) pathfinding. A PKCzeta pseudosubstrate, a specific blocker of aPKC activity, and expression of a kinase-defective PKCzeta mutant in commissural neurons resulted in A-P randomization in "open-book" explants. Upstream of PKCzeta, heterotrimeric G-proteins and phosphatidylinositol-3-kinases (PI3Ks), are also required for A-P guidance, because pertussis toxin, wortmannin, and expression of a p110gamma kinase-defective construct all resulted in A-P randomization. Overexpression of p110gamma, the catalytic subunit of PI3Kgamma, caused precocious anterior turning of commissural axons before midline crossing in open-book explants and caused dissociated precrossing commissural axons, which are normally insensitive to Wnt attraction, to turn toward Wnt4-expressing cells. Therefore, we propose that atypical PKC signaling is required for Wnt-mediated A-P axon guidance and that PI3K can act as a switch to activate Wnt responsiveness during midline crossing.
authors: Committee on Developmental Biology, The University of Chicago, Chicago, Illinois 60637, USA.
authors: Alex M
authors: AM
authors: Wolf
authors: Anna I
authors: AI
authors: Lyuksyutova
authors: Ali G
authors: AG
authors: Fenstermaker
authors: Beth
authors: B
authors: Shafer
authors: Charles G
authors: CG
authors: Lo
authors: Yimin
authors: Y
authors: Zou
mesh_terms: D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology*; D019556:COS Cells; D002522:Chlorocebus aethiops; D018274:Electroporation / Q000379:methods; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000378:metabolism; D051379:Mice; D009154:Mutation / Q000502:physiology; D009474:Neurons / Q000166:cytology*; D009924:Organ Culture Techniques; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D011493:Protein Kinase C / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology*; D013116:Spinal Cord / Q000166:cytology / Q000196:embryology*; D014162:Transfection; D051153:Wnt Proteins / Q000378:metabolism* / Q000494:pharmacology; D060528:Wnt4 Protein; D000099221:Protein Kinase C zeta
chemical_list: D004791:Enzyme Inhibitors; D049452:Green Fluorescent Proteins; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D051153:Wnt Proteins; D060528:Wnt4 Protein; D000099221:Protein Kinase C zeta; C555582:Wnt4 protein, mouse; C485184:enhanced green fluorescent protein