Insertional Mutagenesis Strategies in Xenopus tropicalis

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Understanding the molecular mechanisms of early vertebrate development remains a central goal in the biological sciences. The use of amphibians as vertebrate developmental model systems dates back over 100 years. The most widely used amphibian in the last 50 years has been the African clawed frog, Xenopus laevis. Biochemical and developmental studies in X. laevis have changed the way we view the early embryonic development of vertebrates. Despite the utility of this model system, genetic studies are not feasible in this species due to a long generation time (approximately 1 year) and tetraploid genome. Recently, a close relative of X. laevis has been proposed as an alternate model animal for genetic analysis. X. tropicalis is diploid, has a short generation time (approximately 4 months) and, in addition, shares the qualities that has made X. laevis a powerful developmental model. My laboratory will use insertional mutagenesis approaches in X. tropicalis to identify genes that play a critical role in early development. While not as efficient as chemical mutagenesis strategies, insertional methods have the important advantage of introducing a stable genetic tag at the site of the mutation. This feature allows comparatively simple cloning of the disrupted gene and the cloning techniques do not rely on genetic maps. We will use transposase- and retroviral-mediated integration systems to introduce heritable genetic changes into the X. tropicalis genome. Our preliminary data demonstrate that these methods work well in the frog. In addition to mutagenesis screens, we will use the transposon system to generate gene and enhancer traps. The biological question that my laboratory will focus on is early development of the hematopoietic system. Little is known about the origin of hematopoietic stem cells (HSCs) in vertebrates. The development of an amphibian genetic model will provide an important tool to study the early events in HSC formation. Mutants and gene traps that affect the production of blood in the developing embryo will be cloned and characterized. The proposed study will provide valuable insight into the biology of hematopoiesis in both normal and disease states.