Three populations of migrating amphibian embryonic cells utilize different guidance cues

Previous investigations designed to identify the molecule(s) governing the directed migration of the amphibian pronephric duct (PND) revealed a requirement for a glycosyl phosphatidylinositol (GPI)-linked cell surface molecule, possibly the ectoenzyme alkaline phosphatase (AP). Cranial neural crest cells (CNC) grafted to the flank migrate along the same pathways as the PND, suggesting that PND and CNC guidance systems might have a common molecular basis. Both PND and CNC migration pathways display AP. The present experiments demonstrate, however, that GPI-linked molecules on these pathways are not required for migration of either cell type. Because PND cells themselves express AP prominently but CNC cells do not, we asked whether the GPI-linked molecule required for PND migration resides on the PND cells themselves. Treatment of PND cells with phosphatidylinositol-specific phospholipase C, an enzyme that removes GPI-linked proteins, prevents their migration. Transplantation experiments show that although CNC cells are capable of following PND migration pathways, the converse is not the case. Extension of the transplantation experiments to include trunk neural crest (TNC) cells indicates that although CNC cells can follow PND guidance information on the flank, PND, CNC, and TNC cells all normally utilize different molecular cues to guide their migrations in situ.