Growth conelike sensorimotor structures are characteristic features of postmigratory, premyelinating oligodendrocytes

During development, postmigratory, premyelinating oligodendrocytes extend processes that navigate through the central nervous system (CNS) environment, where they recognize a number of extracellular cues, including axonal segments to be myelinated. Ultimately this recognition event leads to the formation of the CNS myelin sheath. However, the morphological structures and molecular mechanisms that control such oligodendroglial pathfinding are poorly understood. Here we show that postmigratory, premyelinating oligodendrocyte processes possess at their distal tips expansions that ultrastructurally resemble growth cones of postmigratory neurons and that we will refer to as OLG-growth cones. OLG-growth cones are highly motile and capable of mediating process outgrowth, retraction, and branching. In addition, they express regulators of cytoskeletal organization, GAP43 and cofilin, that are known to mediate neuronal growth cone navigation. In a choice situation, processes of postmigratory, premyelinating oligodendrocytes and their OLG-growth cones have the ability to selectively avoid a nonpermissive substrate, that is, collagen IV Thus, our findings provide, for the first time, a detailed characterization of sensorimotor structures present at the tips of postmigratory, premyelinating oligodendrocyte processes. Furthermore, the data presented here suggest that, although the cellular mechanisms involved in growth cone steering may be similar for postmigratory neuronal and oligodendroglial cells, extracellular cues may be interpreted in a cell-type-specific fashion. (C) 2005 Wiley-Liss, Inc.