Pioneering work in the genetically tractable organism, C. elegans, has shown that single gene mutations potently extend life span. Phylogenetically conserved endocrine systems figure prominently, revealing that aging is hormonally regulated. Notably, reduction of Insulin/IGF signaling doubles worm life span, with similar influences in flies and mice. More recently, nuclear hormone receptors (NHR), transcription factors regulated by fat soluble hormones, have emerged as regulators of development and aging in worms and flies. Our long-term goal is to understand how such endocrine systems govern these processes. In C. elegans, the NHR, DAF-12, retards reproductive development and aging. NHR and Insulin/IGF signaling somehow work together during development, and have complex interactions for life span. DAF-12's molecular identity suggests regulation by lipophilic hormones, but such hormones remain unidentified. Accordingly, our previous work identified DAF-9, a cytochrome P450 (CYP450) related to steroidogenic hydroxylases, as a proximal regulator of DAF-12, suggesting a sterol hormone controls development and aging. However, the extent of the lipophilic hormone pathway and the relationship with insulin/IGF signaling are largely unknown. The goals of this proposal are to: 1) molecularly dissect the DAF-12 lipophilic hormone pathway, 2) understand how the pathway is linked to insulin/IGF signaling, and 3) test hormonal hypotheses of development and aging. Our preliminary RNAi screens identified 4 new genes putatively involved in hormone metabolism. We propose to characterize these genes and identify more. For the genes in hand, we will generate mutant alleles, determine larval developmental and adult aging phenotypes, and associated traits of stress resistance. We will also elucidate the cellular localization to pinpoint endocrine cells, and test regulation by insulin/IGF signaling in vivo. Finally, we will order the genes within pathways by genetic epistasis and synergy, as well as by using phenotypic rescue by lipid extracts. Further genetic screens will focus on novel genes involved in hormone metabolism, sterol transport, and transcriptional activation. Our work comprises the first broad studies of lipophilic hormone signals and their regulation of nuclear receptor biology in a key model system for aging. Such studies should illuminate endocrine networks in humans that control development, lipid metabolism and aging, and their dysregulation in diabetes, obesity, and cardiovascular disease. ? ?
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