The African clawed frog, Xenopus laevis, has long been used as a model system for the study of developmental biology questions, such as how does one cell give rise to many cells with different fates? What are the complex interactions between groups of cells in the embryo which allow establishment of body axes, patterning and specification of body tissues, and organ formation?

In this dissertation, mechanisms and molecular pathways of mesoderm induction and patterning in Xenopus are investigated. Mesoderm is the germ layer of the embryo that forms the heart, blood, blood vessels, notochord, muscle and pronephros (kidney), as well as other tissues. Chapter I provides an overview of Xenopus development and germ layer formation, with an emphasis on mesoderm induction and patterning and the molecular pathways that mediate hematopoeisis (blood development). Chapter II reviews mechanisms of mesoderm patterning that are independent of the Spemann organizer and examines the factors involved in the specification of blood from ventral mesoderm. Chapter III describes experiments evaluating the regulation of the ADMP2 gene, a novel TGF-β molecule in Xenopus involved in blood and heart development.

Finally, Chapter IV provides a summary and general conclusions as well as a prospectus for future work.