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- Liu, Yiting, 1986-
(author)
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Morphological and functional effects of insulin signaling and the bHLH transcription factor Dimmed on different neuron types in Drosophila
- 2016
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Doctoral thesis (other academic/artistic)abstract
- In Drosophila, the insulin signaling pathway is at the interface between dietary conditions and control of growth and development, reproduction, stress responses and life span. Eight insulin like peptides (Dilp1-8), an insulin tyrosine kinase receptor (dInR) and its downstream components, as well as a relaxin-like receptor type (Lgr3) form the core of this signaling. Here we showed that the dInR mediates post-mitotic cell growth specifically in about 300 peptidergic neurons expressing the basic helix loop helix (bHLH) transcription factor Dimmed (Paper I). Overexpression of dInR in Dimm positive neurons leads to increased size of cell body, Golgi apparatus and nucleus, whereas dInR knockdown causes an opposite effect. Manipulation of downstream components of insulin signaling induces similar changes in Dimm positive neurons. This mechanism is nutrient dependent. In Paper II, we further investigate the relation between Dimmed and dInR for regulation of cell growth. Coexpressing Dimm and dInR in a range of Dimm negative neurons results in increased cell size in both larval and adult stages. We provide further evidence that dInR regulates cell growth in a Dimm dependent manner and that DILP6 from glia cells is involved in this regulation. In addition, we find that Dimm alone is capable of triggering cell growth in certain neuron types at different developmental stages. Furthermore, ectopic Dimm alone can block apoptosis. Dimm is a known master regulator of peptidergic cell fate. In paper III we find that ectopic expression of Dimm in Dimm negative motor neurons results in transformation the neurons towards a neuroendocrine phenotype. They acquire enlarged axon terminations and boutons, lose both pre- and postsynaptic markers, and display diminished levels of wingless and its receptor dFrizzled. Furthermore they show increased expression of several Dimm targets. Finally, combined ectopic Dimm and dInR expression gives rise to stronger phenotypes. In paper IV we studied another DILP possibly involved in growth regulation, the under-investigated DILP1. We generated Dilp1-Gal4 lines and anti DILP1 antibodies and found that DILP1 is transiently expressed in brain insulin producing cells (IPCs) from pupal stages to newly hatched adult flies. Diapausing virgin female flies display a high expression level of dilp1/DILP1 over at least 9 weeks of adult life. DILP1 expression is also correlated with the persistence of larval/pupal fat body and its expression is regulated by other DILPs and short neuropeptide F (sNPF). Flies mutant in dilp1 display increased food intake, but decreased stress resistance and life span. We found no obvious role of DILP1 in growth regulation.
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- Söderberg, Jeannette, 1983-
(author)
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Neuropeptides and GABA in control of insulin producing cells in Drosophila
- 2011
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Doctoral thesis (other academic/artistic)abstract
- Insulin plays an important role in metabolic regulation as well as in growth, fecundity and stress resistance. In order to understand more about the regulation of insulin-like peptide (DILP) production and release we investigate the impact of neuropeptide (DTK) signaling and classical neurotransmitter (GABA) signaling onto the insulin producing cells of the Drosophila brain. DTK was shown to regulate insulin production through DTK receptors found on the insulin producing cells of the brain. DTK has an impact on carbohydrate and lipid levels as well as effect stress resistance (Paper I). Manipulations of DTK signaling differentially affect Dilp transcript levels. We also showed that GABA regulates the production and release of insulin-like peptides via GABABRs (Paper II). Both these two signaling pathways have an inhibitory action on insulin production and release. The Malpighian (renal) tubules were discovered as a novel site of insulin-like peptide expression and DTK signaling was shown to converge on the insulin pathway also here (Paper III). Stress seems to induce hormonal release of DTK that acts on the renal tubules to regulate DILP 5 signaling. Manipulations of superoxide dismutase (SOD2) in principal cells also affect survival at stress, suggesting that DILP 5 acts locally on tubules, possibly in oxidative stress regulation. Finally, we demonstrated that a cholecystokinin-like (CCK) peptide, DSK, is present in the IPCs and affects meal size regulation and food preference (Paper IV). DSK, like CCK, therefore acts to induce satiety. DSK and Dilp transcripts levels were also found to affect each other, suggesting coordination and possibly a feedback mechanism between the two signaling pathways. In summary, we have studied control of Insulin signaling in Drosophila and have found that the different DILP isoforms have may separate functions and that they are separately regulated by both neuropeptides and classical neurotransmitters.
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