The cells of the neural crest migrate throughout the embryo to generate a remarkably diverse array of differentiated derivatives, including the entire peripheral nervous system. The extraordinary developmental repertoire of this apparently homogeneous precursor population is likely to require both developmental restrictions imposed by lineage, and choices among alternative fates determined by environmental interactions. The neural crest thus provides a unique biological context in which to investigate the molecular basis of the contributions of lineage and environment to developmental fate. In turn, by focusing on the expression of specific genes, we may better define lineal restriction and multipotentiality and their roles in the biology of this system. In this proposal, I describe strategies for the isolation of genes expressed specifically in neural crest cells and/or their derivatives and their use as developmental markers. We have developed procedures for the direct isolation of cDNA clones which define various crest-derived phenotypes, by differential screening of appropriate cDNA libraries. When combined with the ability to establish clonal lines from neural crest precursors, these markers may define the developmental fates which arise from different neural crest lineages and the role of environmental factors in determining the expression of these fates. In our initial experiments, we isolated several genes expressed in sympathetic neurons but not in adrenal chromaffin cells, two derivatives thought to arise from a multipotential sympathoadrenal precursor. Using these probes and established cell culture systems, we will proceed with experiments aimed at understanding how environmental factors control the expression of genes whose products define alternative phenotypes. By introducing cloned copies of these genes into various crest-derived cell types, we can examine the ways in which cell lineage determines the ability of precursors to express specific genes in response to environmental signals, and study the biochemical mechanisms underlying phenotypic plasticity. Finally, the possibility will be investigated that alterations in the chromatin structure of these genes may be used to mark latent multipotentiality and plasticity in the sympathoadrenal lineage. Ultimately, studies of these genes may permit one to create perturbations in specific cell types within the intact embryo, and examine their developmental consequences.