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Gary Ruvkun PhD.
InsR/IGF1R signalling and microRNAs in C. elegans development and longevity My lab investigates neuroendocrine control of C. elegans development, metabolism and longevity, as well as control of temporal pattern formation by heterochronic genes. We use a combination of genetic analysis and the resources of the now complete C. elegans genome sequence to discover genes in these pathways. These genetic screens have accelerated recently with the advent of feeding RNA inhibition genomic libraries that allow each of the 19,000 C. elegans genes to be tested for activity in the pathways we study. This allows instant molecular identification of genetic loci, bypass laborious positional cloning. A C. elegans insulin signaling pathway that is homologous to mammalian insulin signaling regulates metabolism and longevity. Genomic analysis reveals 37 insulin-like genes. The insulin superfamily member most like human insulin acts in the pathway and human insulin can also interact. Longevity is regulated by insulin signaling within the nervous system, suggesting that it is the metabolism within particular neurons that are key to regulation of lifespan. We also study how these neuroendocrine pathways are coupled to sensory inputs. For example, the insulin pathway is coupled to a thermosensory pathway, allowing metabolism to be coupled to temperature. We are now exploring the neural signaling pathways that couple these systems. We are using powerful genetic selections to identify signaling molecules downstream of insulin-like receptors, as well as a novel insulin reception pathway that may act more broadly in animals. Our studies of the C. elegans heterochronic pathway revealed two examples of small RNA duplexes that regulate the temporal axis of development. These 21 nucleotide RNAs base pair to target genes to down-regulate their activities, triggering developmental transitions. We are studying how these RNA duplexes regulate target gene activity, using genetics and biochemistry. We found that the larval stage specific regulatory RNA, let-7, is conserved across the animal kingdom, from flies to chordates to annelids to sea urchins, but not so far in jellyfish or plants or yeast. Remarkably, the zebrafish and Drosophila let-7 homologs are also temporally regulated, suggesting conservation of function. This is the first indication that regulatory RNAs may regulate temporal patterning in other animals species. This year we discovered that the molecular mechanisms by which these small RNAs regulate target genes is mechanistically related to RNA interference. References:
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