A role for the polarity complex and PI3 kinase in branch formation within retinotectal arbors of zebrafish.
The developing zebrafish retinotectal arbors make many trial branches with synapses but most are retracted. With NMDA blockers, branches are withdrawn at a higher rate, and a synapse on a branch not only stabilizes that branch, but biases new branches to form nearby. Here, we tested whether new branch formation requires the polarity complex, which is essential for organizing the cytoskeleton in initial axon formation. The complex (PAR3, PAR6, and atypical protein kinase C [aPKC]) is downstream of phosphatidyl-inositol-3-kinase (PI3K), and its aPKC could be activated by retrograde arachidonic acid synaptic signaling. DiO-labeled arbors in zebrafish were imaged on day 3 (before treatment) and 1-2 days after treatment to suppress or inhibit PAR3, PAR6, or PI3K. Intraocular antisense (AS) oligos to PAR3 or PAR6 both severely limited branch addition, which was most evident in arbors with few branches before treatment. As a result of the inability to branch, arbor segments grew longer than in controls. Both PI3K inhibition (LY294002) and AS suppression of PI3Kα and PI3Kδ isoforms likewise limited branch addition but also decreased growth, as the sum of segment lengths was below normal after 2 days. Both the results support the idea that the polarity complex and PI3K participate in arbor branch formation. The PKC inhibitor Go6983 also severely restricted branch addition and growth, as did bisindolyl-maleimide and calphostin C reported previously, consistent with PKCζ, but not PKCµ, participation. These experiments suggest a mechanism whereby activity signaling could affect the branching of retinotectal arbors.
Department of Biological Science and Neuroscience Research Center, University at Albany, State University of New York, Albany, New York, 12222.
John T
JT
Schmidt
Laura
L
Mariconda
Francelina
F
Morillo
Elizabeth
E
Apraku
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D021621:Imaging, Three-Dimensional; D007211:Indoles / Q000494:pharmacology; D007814:Larva; D008301:Maleimides / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism*; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology; D061848:Optical Imaging; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D012160:Retina / Q000502:physiology*; D013477:Superior Colliculi / Q000502:physiology*; D013997:Time Factors; D014795:Visual Pathways / Q000502:physiology*; D015027:Zebrafish
C465664:2-(1-(3-dimethylaminopropyl)-5-methoxyindol-3-yl)-3-(1H-indol-3-yl)maleimide; D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D007211:Indoles; D008301:Maleimides; D008565:Membrane Proteins; D020319:Oligodeoxyribonucleotides, Antisense; C509689:PARD3 protein, human; C499657:PARD6A protein, human; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C
PI3Kinase; axon branching; par complex; protein kinase C; retinotectal