Analysis of cranial neural crest cell migration and early fates in postimplantation rat chimaeras

Rat embryos were grown in vitro during the period of cranial neural crest cell migration. In order to study the pathways and positional fates of cells from different regions of the neural crest, labelled premigratory crest cells from donor embryos were microinjected orthotopically into host embryos of the same developmental stage except for area 1 (forebrain) grafts which were, for technical reasons, injected into area 2. After various periods of time in whole embryo culture, the embryos were examined by immunohistochemical staining in order to determine the new positions of the labelled cells, and a map of their migration pathways was constructed. The observed patterns of migration were consistent with predictions from morphological studies in mammals and with extrapolations from transplantation studies in birds. However, crest cell migratory behaviour in rat and chick embryos was not identical; possible reasons for this are discussed.