The types of cells contacted by growth cones were examined in chick-quail and vice versa chimeras. Simultaneously, the presence of nonspecific cholinesterase (nChE) was monitored in developing peripheral nerves of these embryos. In all the chimeras studied, the growth cones were in contact with both Schwann cell progenitors and mesenchymal cells of the limb bud. This observation implies that the growth cones may obtained guidance cues directly from the mesenchymal cells of the limb bud. Schwann cell progenitors as well as mesenchymal cells in contact with growth cones were capable to produce nChE molecules. The reaction product indicating nChE activity was localized on the outer surface of the plasma membrane of both types of cells in contact with growth cones. However, mesenchymal cells forming the "primitive perineurium" were devoid of the reaction product on their plasma membrane. We conclude that with exception of classic adhesive molecules the process of axonal guidance can be mediated by nChE molecules.

Department of Neurosurgery Medical Faculty Charles University Prague Czechoslovakia

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Schwann cells are not required for guidance of motor nerves in the hindlimb in Splotch mutant mouse embryos