Human birth defects and cancers are caused by misregulation of the Wnt signaling pathway. In early vertebrate embryos, development of the body axis critically requires the activation of the Wnt pathway on one side of the embryo. In the frog Xenopus, a predominant model organism for axis formation, this asymmetric signaling is achieved by the differential localization of maternally derived molecules stored in the egg. These proteins and mRNAs are redistributed toward the future dorsal side by rotational movements of the egg cortex following fertilization, resulting in the activation of Wnt signaling. Interference with this process results in embryos lacking the dorsal tissues of the primary germ layers, including the CNS, notochord and dorsal musculature. The exact mechanism of Wnt activation in axis formation is unclear, but data from maternal loss-of-function studies, including Preliminary Studies for this proposal, have implicated vegetally localized factors. The long-term goal of this research is to understand the role of these localized maternal gene products in embryonic axis formation. Preliminary Studies for this proposal have identified novel localized mRNAs, using microarray analysis of cortex-bound RNAs. Two candidate genes, trim36 and exdl2, which were restricted to the germ plasm, a subregion of the vegetal cortex, were found to have roles in axis formation. These genes encode a Tripartite Motif protein and a novel exonuclease domain-containing protein, respectively. The studies in this proposal will determine the mechanisms underlying the function of these genes in axis formation, via antisense-mediated depletion of their maternal stores and gain-of-function assays. Furthermore, these proposed studies will identify additional axis regulators through a more targeted microarray screen.
The specific aims are 1) to characterize the role of trim36 by determining the extent of its interaction with the Wnt pathway, 2) to identify biochemical functions of trim36 associated with its role in axis formation, 3) to further characterize the role of exdl2 in dorsal specification and, 4) to identify and characterize additional germ plasm-localized genes as candidates for regulating axis formation. The findings of these proposed studies are relevant to, and will benefit public health by enhancing the understanding of basic signaling pathways involved in cell and tissue differentiation, which are conserved in human development. Novel insights would be gained into these mechanisms will be an essential step toward improving the diagnosis, prevention and treatment of human birth defects and genetic diseases. Public Health Relevance: The findings of these proposed studies are relevant to, and will benefit public health by enhancing the understanding of basic signaling pathways involved in cell and tissue differentiation, which are con- served in human development. Novel insights would be gained into these mechanisms will be an essential step toward improving the diagnosis, prevention and treatment of human birth defects and genetic diseases.
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