Insights into the Evolution of Chordate Body Plans Through Correlated Developmental Genetic and Fate Mapping Studies of the Early Embryos of Amphioxus

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0078599HollandAmphioxus is a lower chordate that represents the closest living invertebrate relative of the vertebrates. In recent years, gene expression data from relatively late developmental stages of amphioxus have helped to indicate body part homologies between amphioxus and vertebrates. For instance, mapping the expression of neural genes has suggested that amphioxus (and, by extension, the proximate ancestor of the vertebrates) has major brain regions homologous to those of vertebrates. In contrast, relatively little is yet known about gene expression during early development of amphioxus. In the vertebrates, such early acting genes play key roles in setting up signaling centers (organizers), establishing primary body axes, and large-scale patterning of the tissues. This proposal is focused on genes involved in the initial establishment and early regionalization of the amphioxus central nervous system. The ultimate aim is to test the hypothesis that mechanisms for establishing and large-scale patterning of the nervous system were already largely in place in the last common ancestor of amphioxus and the vertebrates. The research comprises two tightly linked approaches. The first is to isolate and study the expression of amphioxus homologs of vertebrate genes known to be important in early nervous system development. The second is to use vital dye tracing to elucidate cell and tissue movements associated with the early morphogenesis of the amphioxus nervous system, including gastrulation, extension of the anterior-posterior axis of the embryo, and establishment of regional identities. Taken together, the expression of key developmental genes in the context of a detailed map of cell and tissue movements will provide insights into the evolution of mechanisms involved in the establishment and regionalization of the central nervous system during the early evolution of the vertebrates.