An in vivo RNAi screen identifies evolutionary conserved Drosophila fat storage regulators
by Jens Baumbach
Date of Examination:2014-04-22
Date of issue:2014-05-12
Advisor:Dr. Ronald P. Kühnlein
Referee:Dr. Ronald P. Kühnlein
Referee:Prof. Dr. Herbert Jäckle
Persistent Address:
http://dx.doi.org/10.53846/goediss-4487
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Abstract
English
One main goal for all organisms, in order to survive under environmental changes, is to maintain energy homeostasis. Energy homeostasis depends mainly on three processes, the energy uptake, energy storage and energy consumption, respectively. An impairment of energy homeostasis or the lipid metabolism can cause body fat accumulation, which could finally lead to obesity. Since the outspread of obesity widely increased over the last years, the need to unveil new regulators of body fat storage rises. In order to identify novel body fat storage regulators, we used the fruit fly Drosophila melanogaster to do a conditional in vivo RNAi knockdown (KD) screen in the fat storage tissue of adult flies. Hereby, lethality due to developmental impairment can be excluded, which allows to screen for novel regulators in adult flies. By this approach, 6796 genes were down-regulated directly in the fat storage tissue of the fly and the body fat levels were determined. By further validations, I was able to identify 77 gene KDs, which resulted in obese or lean flies. Notably, most of the identified genes and processes are conserved up to humans. A Gene Ontology analysis of these genes revealed several processes, including store-operated calcium entry (SOCE), which was so far unrelated to body fat storage control. Interestingly, modulations of SOCE genes, which resulted in decreased intracellular Ca2+ levels (iCa2+) causes obesity in flies. Controversial, modulations that leads to increased iCa2+ resulted in lean flies. In order to reveal the role of SOCE for body fat storage control, I characterized the effects of the central component known as the Stromal interaction molecule (Stim). A Stim KD in the fat storage tissue of mature adult flies resulted in decreased iCa2+ and obese flies, which also showed an increase in fat cell mass, likely driven through hypertrophy and hyperplasia. Further characterization of these flies revealed no effects on the activity or the metabolic rate, indicating that the body fat accumulation is independent from the energy expenditure. On the other hand, Stim KD flies show hyperphagia, which is driven by up-regulation of the orexigenic short neuropeptide F (sNPF) in the central nervous system of the fly. This regulation and the enriched energy intake drives an obesogenic program in the fat storage tissue of Stim KD flies, by up-regulation of the lipogenic mdy/DmDGAT1 and down-regulation of the lipolytic bmm/DmATGL genes. These findings suggest a control of the energy storage, which is driven by SOCE via an inter-organ communication signaling pathway.
Keywords: Drosophila; RNAi; Lipids; Screen; Fat; Stim; calcium