Collaborative Research: Developmental, Molecular and Evolutionary Analysis of Chaetognaths: A Deuterostome-Like Ecdysozoan

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0236479HalanychThe chaetognaths, or "arrow worms", are one of the most abundant marine invertebrates found in all the world's seas. The phylogenetic position of this ubiquitous group of animals is currently unknown. Until recently, chaetognaths were considered to be basal deuterostomes based on developmental features such as their radial cleavage program, classic enterocoeley, posterior position of the blastopore, and tripartite adult body plan. New molecular evidence, including Hox gene data presented in this proposal, has suggested that chaetognaths are not deuterostomes but basal protostomes closely allied with ecdysozoans such as arthropods and nematodes. In fact, chaetognaths are now thought to be one of the most pivotal and understudied groups of metazoan animals for gaining insight into the evolution of protostome body plans. Only a handful of cellular and molecular investigations of chaetognath development have ever been made, however. Drs. Martindale and Halanych's proposal describes a comprehensive and multidisciplinary set of approaches designed to characterize how chaetognath embryos "work". Using both modern developmental (intracellular cell lineage labeling and laser cell deletion experiments) and molecular (cloning, in situ hybridization) techniques, Martindale and Halanych will collect vital information on the normal development of these interesting animals, and be able to and examine the conservation of genetic regulatory mechanisms in the Metazoa. In addition, techniques of gene discovery (EST screening) will provide valuable new information on the ancestral mechanisms of body plan evolution. These data will not only be important to determine the phylogenetic position of chaetognaths, but to also provide molecular and developmental insight in to the evolution of the ecdysozoan clade, and the "evolveability" of developmental programs. Chaetognaths could be the most informative and tractable basal invertebrate system available that will allow an understanding of the evolution of the nematode and arthropod clades, the two most genetically heavily studied group of animals on earth.