The colonization of limb buds by neural crest cells was studied in quail-chick chimeras and in chick embryos using HNK-1 and DiI staining and the LD-DOPA reaction. Two populations of neural crest cells were found to colonize the limb bud. They migrate successively and use different routes of migration. The first population migrates within the limb bud subectodermally at stages before the limb is innervated. In the wing bud the migration route is localized postaxially and in the leg bud preaxially. Two cell types were identified differentiating from this first population: melanoblasts and Merkel cells. The second population of crest cells invades the limb bud at a later stage. These cells follow the routes of ingrowing nerves and migrate along a dorsal and a ventral path which correspond to the position of nerves for extensor and flexor muscles. Crest cells were found here also in the absence of nerves. Schwann cells and terminal glial cells develop from this second population of neural crest cells.

Institute of Anatomy Charles University Prague Czechoslovakia