When one thinks of lamellopodia, the image is usually of a neuronal growth cone, but the leading edge of myelin-forming oligodendrocyte processes can be considered to be giant lamellopodia. This week, Kim et al. identify a role for WAVE1 in oligodendrocyte process formation. WASP (Wiskott-Aldrich syndrome proteins) and WAVE (WASP family verprolin homologous) proteins alter actin dynamics and lamellopodia formation by linking small Rho GTPases to Arp2/3, the controller of de novo actin nucleation. The authors report that WAVE1 was expressed by oligodendrocytes and neurons, but a dominant-negative WAVE1 decreased process formation only in oligodendrocyte precursor cells (OPCs). In cultured oligodendrocytes, WAVE1 was concentrated at the edges of processes. In rat optic nerve, WAVE1 expression increased at postnatal day 9, when myelination begins. In WAVE1-deficient mice, the number of nodes of Ranvier was decreased, and the mice had hypomyelination in the corpus callosum and optic nerve, consistent with a defect in myelin formation.
2. The Wnt Receptor Ryk and the Corpus Callosum
Thomas R. Keeble, Michael M. Halford, Clare Seaman, Nigel Kee, Maria Macheda, Richard B. Anderson, Steven A. Stacker, and Helen M. Cooper
For axons seeking to get to the other hemisphere, it is good idea to pack along some Ryk (receptor related to tyrosine kinase) according to work by Keeble et al. this week. Signaling by Wnt ligands directs many developmental processes, each coupled to specific receptor interactions. In general, WntRyk interactions are chemorepulsive, whereas WntFrizzled are chemoattractive. The authors examined Wnt signaling associated with Ryk. In mice lacking Ryk, the corpus callosum was abnormally wide, and loosely fasciculated axons accumulated on eit
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Society for Neuroscience