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      Insulin signaling and the regulation of insect diapause

      1 , 2

      Frontiers in Physiology

      Frontiers Media S.A.

      diapause, dauer, insulin signaling, FOXO, Culex pipiens

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          Abstract

          A rich chapter in the history of insect endocrinology has focused on hormonal control of diapause, especially the major roles played by juvenile hormones (JHs), ecdysteroids, and the neuropeptides that govern JH and ecdysteroid synthesis. More recently, experiments with adult diapause in Drosophila melanogaster and the mosquito Culex pipiens, and pupal diapause in the flesh fly Sarcophaga crassipalpis provide strong evidence that insulin signaling is also an important component of the regulatory pathway leading to the diapause phenotype. Insects produce many different insulin-like peptides (ILPs), and not all are involved in the diapause response; ILP-1 appears to be the one most closely linked to diapause in C. pipiens. Many steps in the pathway leading from perception of daylength (the primary environmental cue used to program diapause) to generation of the diapause phenotype remain unknown, but the role for insulin signaling in mosquito diapause appears to be upstream of JH, as evidenced by the fact that application of exogenous JH can rescue the effects of knocking down expression of ILP-1 or the Insulin Receptor. Fat accumulation, enhancement of stress tolerance, and other features of the diapause phenotype are likely linked to the insulin pathway through the action of a key transcription factor, FOXO. This review highlights many parallels for the role of insulin signaling as a regulator in insect diapause and dauer formation in the nematode Caenorhabditis elegans.

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          Most cited references 154

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          Tight control of cell-cell communication is essential for the generation of a normally patterned embryo. A critical mediator of key cell-cell signaling events during embryogenesis is the highly conserved Wnt family of secreted proteins. Recent biochemical and genetic analyses have greatly enriched our understanding of how Wnts signal, and the list of canonical Wnt signaling components has exploded. The data reveal that multiple extracellular, cytoplasmic, and nuclear regulators intricately modulate Wnt signaling levels. In addition, receptor-ligand specificity and feedback loops help to determine Wnt signaling outputs. Wnts are required for adult tissue maintenance, and perturbations in Wnt signaling promote both human degenerative diseases and cancer. The next few years are likely to see novel therapeutic reagents aimed at controlling Wnt signaling in order to alleviate these conditions.
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            Genes that act downstream of DAF-16 to influence the lifespan of Caenorhabditis elegans.

            Ageing is a fundamental, unsolved mystery in biology. DAF-16, a FOXO-family transcription factor, influences the rate of ageing of Caenorhabditis elegans in response to insulin/insulin-like growth factor 1 (IGF-I) signalling. Using DNA microarray analysis, we have found that DAF-16 affects expression of a set of genes during early adulthood, the time at which this pathway is known to control ageing. Here we find that many of these genes influence the ageing process. The insulin/IGF-I pathway functions cell non-autonomously to regulate lifespan, and our findings suggest that it signals other cells, at least in part, by feedback regulation of an insulin/IGF-I homologue. Furthermore, our findings suggest that the insulin/IGF-I pathway ultimately exerts its effect on lifespan by upregulating a wide variety of genes, including cellular stress-response, antimicrobial and metabolic genes, and by downregulating specific life-shortening genes.
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                Author and article information

                Journal
                Front Physiol
                Front Physiol
                Front. Physiol.
                Frontiers in Physiology
                Frontiers Media S.A.
                1664-042X
                26 May 2013
                22 July 2013
                2013
                : 4
                Affiliations
                1Department of Biology, Baylor University Waco, TX, USA
                2Departments of Entomology and Evolution, Ecology, and Organismal Biology, Ohio State University Columbus, OH, USA
                Author notes

                Edited by: Xanthe Vafopoulou, York University, Canada

                Reviewed by: Hong Lei, University of Arizona, USA; Michael Strand, University of Georgia, USA

                *Correspondence: Cheolho Sim, Department of Biology, Baylor University, A119, Baylor Science Building, 101 Bagby Avenue, Waco, TX 76798, USA e-mail: cheolho_sim@ 123456baylor.edu;
                David L. Denlinger, Departments of Entomology and Evolution, Ecology, and Organismal Biology, Ohio State University, 300 Aronoff Laboratory, 318 West 12th Avenue, Columbus, OH 43210, USA e-mail: denlinger.1@ 123456osu.edu

                This article was submitted to Frontiers in Invertebrate Physiology, a specialty of Frontiers in Physiology.

                Article
                10.3389/fphys.2013.00189
                3717507
                23885240
                Copyright © 2013 Sim and Denlinger.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.

                Page count
                Figures: 1, Tables: 0, Equations: 0, References: 153, Pages: 10, Words: 9378
                Categories
                Physiology
                Review Article

                Anatomy & Physiology

                diapause, culex pipiens, foxo, insulin signaling, dauer

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