Genetic and Molecular Mechanisms of Nuclear Receptor Signaling

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The broad, long-term objectives of this project are to determine the genetic and molecular mechanisms by which nuclear receptors control post-embryonic development. The short-term goals are to identify genes involved in nuclear receptor signaling pathways. Genes that are involved in nuclear receptor signaling will be identified in Drosophila melanogaster using both genetic and molecular approaches. A primary genetic screen will identify candidate loci that enhance phenotypes associated with sensitized stocks in which nuclear receptor signaling has been compromised. A secondary screen will identify those candidate loci in which the enhancement correlates with altered expression levels of ecdysone-responsive genes; genes whose expression is dependent upon appropriate nuclear receptor signaling. A subset of chromosomal deficiencies stocks and approximately 100 EP stocks will be tested. EP stocks carry single random insertions of a modified P-element that allows ectopic expression of the gene residing near the P-element. These genetic screens have the potential to identify genes that physically interact with nuclear receptors, genes that are direct targets of nuclear receptors, and genes that are further downstream in nuclear receptor regulated pathways. To complement this genetic approach, a yeast two-hybrid screen will b used to identify proteins that physically interact with the amino-terminal domain of the A-isoform of the ecdysone receptor (EcR-A). Understanding the genetic and molecular mechanisms by which nuclear receptors and their ligands function is significant because nuclear receptor signaling coordinates the development of virtually all organs and tissues in higher eukaryotes. Thus, to fully appreciate and understand developmental mechanisms, it is necessary to understand the role that nuclear receptors play in orchestrating the developmental program. The proposed activities are significant because they have the potential to identify biologically relevant interactions between genes involved in nuclear receptor signaling pathways.