The small GTPase Rac is involved in clustering of hippocampal neurons and fasciculation of their neurites.
In hippocampal neurons cultured from brains of newborn rats, the glutamate receptor agonist N-methyl-D-aspartate induced the clustering of neuronal perikarya and the fasciculation of neurites. In addition, N-methyl-D-aspartate activated the small GTPase Rac1. Other stimuli of Rac activity, such as the Rho kinase inhibitors Y-27632, H-1152, and H89, as well as the cytotoxic necrotizing factor-1 from Escherichia coli, also caused neuronal clustering and neurite bundling. In neurons transiently transfected with dominant negative Rac1N17 neither N-methyl-D-aspartate nor Y-27632 induced clustering and fasciculation. In addition, the PI3-kinase inhibitors wortmannin and LY-294002 prevented these effects, as did a dominant negative form of p110PI3-Kgamma. Time-lapse microscopy showed that lethal toxin from Clostridium sordellii, which inhibits Rac, and wortmannin blocked the neuronal migration induced by Y-27632. In contrast, only lethal toxin reversed the clustering and fasciculation induced by pre-treatment with Y-27632. This effect of the toxin may be due to inactivation of Ras, since FTI-277, which prevents the farnesylation of Ras and thereby inactivates the GTPase, also dissolved the preformed clusters. We suggest that active Rac and a PI3-kinase synergistically induce neuronal migration, whereas a Ras isoform is responsible for the lasting attachment of neurons necessary for clustering and neurite fasciculation.
Leemhuis
J
J
Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Zentrum für Neurowissenschaften, Albert-Ludwigs-Universität, Albertstrasse 23, 79104 Freiburg, Germany.
Mayer
U
U
Barth
H
H
Schmidt
G
G
Meyer
D K
DK
D000577:Amides / Q000494:pharmacology; D000818:Animals; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D020558:GTP Phosphohydrolases / Q000187:drug effects / Q000502:physiology*; D006624:Hippocampus / Q000187:drug effects*; D016202:N-Methylaspartate / Q000494:pharmacology*; D016501:Neurites / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014162:Transfection; D020830:rac1 GTP-Binding Protein / Q000187:drug effects / Q000502:physiology*
D000577:Amides; D004791:Enzyme Inhibitors; D018690:Excitatory Amino Acid Agonists; D011725:Pyridines; C108830:Y 27632; D016202:N-Methylaspartate; D019869:Phosphatidylinositol 3-Kinases; D020558:GTP Phosphohydrolases; D020830:rac1 GTP-Binding Protein