Characterization of the gut peptidome and the function of brain-gut peptides with regard to food intake and metabolism in Drosophila melanogaster and the agricultural pest Delia radicum

Regulatory peptides, which comprise neuropeptides and peptide hormones, are cell-cell signaling molecules that control a variety of biological processes in insects and other metazoans. The insect midgut, like the mammalian digestive system, contains numerous peptide-producing endocrine cells, and th...

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1. Verfasser: Reiher, Wencke
Beteiligte: Wegener, Christian (Prof. Dr.) (BetreuerIn (Doktorarbeit))
Format: Dissertation
Sprache:Englisch
Veröffentlicht: Philipps-Universität Marburg 2013
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Zusammenfassung:Regulatory peptides, which comprise neuropeptides and peptide hormones, are cell-cell signaling molecules that control a variety of biological processes in insects and other metazoans. The insect midgut, like the mammalian digestive system, contains numerous peptide-producing endocrine cells, and the diversity of insect enteroendocrine peptides gives a hint at their relevance for metabolism, energy balance and feeding behavior. In the first study, we characterized the midgut peptidome of adult and larval Drosophila melanogaster by extraction of peptides from midgut tissue and subsequent LC-MS/MS analysis of peptide structures. By this means we identified 24 peptides originating from 9 different peptide precursors. All gut peptides were found in identical form within the CNS and thus represent brain-gut peptides. Processing of Drosophila neuropeptide hormones was previously shown to require the subtilisin-like proprotein convertase 2 (dPC2, AMON). Our results suggest a general need of AMON for gut peptide production as well. In the second study, we could expand the knowledge on peptide structures of relevant insects. We investigated the peptidome of the cabbage maggot (i.e., the larva of the cabbage root fly Delia radicum), which causes substantial agricultural damage by feeding on plant roots. By mass spectrometric analysis of CNS, neurohemal organ and gut tissue, we could characterize 38 peptides belonging to diverse insect peptide families. Moreover, we identified a new peptide with sequence similarity to the eclosion hormone precursor of several Drosophila species. Immunocytochemical characterization of peptide-producing neurons and enteroendocrine cells in cabbage maggots showed that peptide distribution was largely similar to Drosophila larvae. The observed similarities in the peptidergic systems of both species suggest that Drosophila can serve as a genetically accessible pest species model in terms of peptidergic regulation of, e.g., metabolism. In the future, our results could be of use for the development of a targeted, peptide-based management of cabbage root flies. In the third study, we analyzed the role of allatostatin A (AstA), a peptide family commonly occurring in insects (and other arthropods). Previous studies had already demonstrated a role for AstA in metabolic regulation and nutritional homeostasis of Drosophila. We addressed the question whether specific effects were connected to the activity of certain subsets of the numerous AstA-producing cells found in adult fruit flies. AstA neurons are located in different regions of the CNS. The thorax also contains a few peripheral AstA neurons. The hindgut and the posteriormost portion of the midgut are innervated by central AstA neurons. In addition, a large number of enteroendocrine AstA cells are scattered across the epithelium of the posterior midgut. Thermogenetic activation of certain AstA cells significantly reduced food intake of flies, and also considerably diminished their locomotor activity. The combination of our results with findings of a previous study suggested that two pairs of AstA-producing posterior lateral protocerebrum neurons function to promote satiety, while enteroendocrine AstA cells seem to regulate locomotor activity. In addition, our findings indicated that AstA cells might directly and indirectly influence defecation behavior, while no effect on water and ion homeostasis could be observed. Furthermore, we tested the effect of synthetic AstA peptides on isolated midguts in vitro and observed a dose-dependent inhibition of midgut motility. Downregulation of AstA receptor mRNA in the gut musculature via RNAi showed that the DAR-2 receptor mediates the myoinhibitory effect of AstA peptides. Altogether, by influencing satiety, locomotion, gut peristalsis and possibly also defecation, AstA cells appear to affect different levels of metabolism and different tissues, seemingly promoting several interrelated processes connected to food intake.
DOI:10.17192/z2014.0062