The longterm goal of this investigation is to understand the cell lineage decisions involved in neural crest cell differentiation in situ. We will accomplish this goal by means of a prospective cell lineage analysis performed by microinjecting single neural crest cells with cell autonomous dyes. We will study neural crest cell lineage in two species, chick and frog; the latter is especially useful because of the ease of microsurgical manipulations which allow one to alter a cell's location and, thus, challenge its fate. Preliminary results demonstrate that some individual labelled trunk neural crest cells are multipotent (i.e. can give rise to numerous neural crest derivatives) both at premigratory and migratory stages. The proposed experiments will extend these findings to examine neural crest cells from different regions of the neural axis and at later developmental stages. In addition to experiments in situ, we will examine the role of the environment in influencing cell lineage decisions in vitro. Our approach for analyzing cell lineage utilizes microinjection of a vital dye to mark individual cells and their descendants. Lysinated rhodamine dextran (LRD) is selected for this purpose because it is large, membrane impermeant, and non-degradable by the cell. Because of its large size and charge, LRD can be passed from a cell only to its progeny by cell division. Therefore, this technique offers a means to reliably label individual cells and their descendants within intact organisms or in cell culture in a nondeleterious manner. The proposed experiments will explore: 1. the developmental potential of neural crest cells in situ during late stages of migration and localization. 2. the developmental potential of neural crest cells derived from different axial levels of chick and Xenopus embryos in situ. 3. the effects of transplantation in situ on the phenotypic expression of labelled neural crest cell clones. 4. the effects of the environment on the phenotypic expression of clonally related neural crest cells in vitro. 5. the effects on the lineage of premigratory neural crest cells of altering the local environment in the dorsal neural tube by implanting an additional notochord. The proposed experiments are designed to demonstrate definitively the range of derivatives that can descend from single neural crest cells at various stages of development. By challenging the developmental potential of labelled cells by transplantation, we can test for possible restrictions in cell fate. The results promise to provide new insights into the mechanisms by which cells adopt a phenotype, which is a central question in developmental biology.