The Xenopus embryo has long served as a major model for the study of embryonic development because of its numerous advantages, including external development, large size, identifiable blastomeres, and its ability to withstand extensive surgical intervention and culture in vitro. These advantages enable extensive investigation of the earliest embryonic patterning events. In fact, much of our current understanding of early embryonic development derives from experiments performed in the Xenopus embryo.

The earliest events of all animal embryos are controlled by messenger RNAs that are deposited in the egg by the mother. These maternal mRNAs control the embryonic processes that occur prior to the transcription of the embryonic genome. These processes can best be examined in Xenopus because, in these embryos, they occur during an especially long period of time, and because they occur while the embryo is developing externally. These features have enabled Xenopus to produce a detailed cellular and molecular understanding of early patterning events, including a comprehensive view of the role of specific extracellular growth factors, cell surface receptors, and intracellular signaling pathway components. These events include the patterning of the basic body plan, the determination of cell fate, and the early patterning of major organs, including the digestive system, circulatory system and nervous system. In addition, many of the factors originally identified in Xenopus were subsequently shown to control numerous later developmental events, as well as other critical biological processes, and oncogenesis. Finally, Xenopus is a major contributor to our understanding of cell biological and biochemical processes, including chromosome replication; chromatin, cytoskeleton, and nuclear assembly; cell cycle progression; and intracellular signaling. Thus, Xenopus is ideally suited to provide critical breakthroughs in early embryonic patterning and cell fate determination, later development and organogenesis, oncogenesis, and cell biological and biochemical processes.