The placement of Metazoan species into correct clades has become of prime concern to the study of evolutionary development, since the most recent phylogeny of Metazoans indicates embryological divergence. Genetic regulatory networks have been extensively described for some species but not for others. This study examines possible divergence of bilaterians at the protostome-deuterostome divide by examining dorsoventral patterning genes. A specific maternally active gene, dorsal/rela, the final element in the maternal pathway, was found to be a driving force behind this divergence and was co-opted from genes already existing in the Metazoan ancestor.

xiii, 135 p. ; ill. (some col.) A print copy of this title is available through the UO Libraries. Search the library catalog for the location and call number. / This thesis explores the origin and evolution of animal germ layers via evolutionary-developmental analyses of the GATA family of transcription factors. GATA factors identified via a conserved dual zinc-finger domain direct early germ layer specification across a wide variety of animals. However, most of these developmental roles are characterized in invertebrate models, whose rapidly evolved sequences make it difficult to reconstruct evolutionary relationships. This study reconstructs the stepwise evolution of metazoan GATA transcription factors, defining homologous developmental roles based upon clear orthology assignments. We identified two GATA transcription factors ( PdGATA123 and PdGATA456 ) from the marine annelid Platynereis dumerilii to aid comparison of protostome and deuterostome GATA factors. Our phylogenetic analyses defined these as protostome orthologs of GATA1/2/3 and GATA4/5/6 vertebrate subfamilies, while the mRNA localization of the Platynereis GATAs showed ectodermal versus endomesodermal germ layer restrictions, similar to their vertebrate orthologs. To define the phylogenetic relationships of more divergent genes in the invertebrate models, we identified GATA homologs from recently sequenced protostome genomes. Molecular phylogenetic analyses, comparisons of intron/exon structure, and conserved synteny confirm all protostome GATA transcription factor genes are members of either the GATA123 or GATA456 class. These data allowed us to identify multiple protostome-specific duplications of GATA456 homologs and reconstruct the origin and relationships of all arthropod GATA genes. To probe GATA transcription factor evolution in deuterostomes, including vertebrates, we identified GATA factors in basal deuterostomes, including the cephalochordate Branchiostoma floridae and the hemichordate Saccoglossus kowalevskii. Phylogenetic analyses of these data independently confirmed that the ancestral deuterostome and chordate--like the bilaterian ancestor--possessed only two GATA transcription factors. This work was facilitated by a bioinformatics platform we are developing to identify gene families from preassembled genomic sequence. We generated anti- PdGATA antibodies to further explore the role of Platynereis GATAs in germ layer formation. We identified multiple presumptive endomesodermal cells in which nuclear localization of PdGATA456 protein first occurs and utilized PdGATA456 protein localization to follow endomesodermal cell populations throughout development. These analyses represent some of the first cellular and molecular analyses of Platynereis germ layer formation. This dissertation includes both my previously published and unpublished co-authored material. / Adviser: Stephan Q. Schneider