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Abstract
Regulation of meal size and assessing the nutritional value of food are two important aspects of feeding behavior. The mechanisms that regulate these two aspects have not been fully elucidated in Drosophila. Diminished signaling with insulin-like peptides Drosophila insulin-like peptides (DILPs) affects food intake in flies, but it is not clear what signal(s) mediates satiety. Here we investigate the role of DILPs and drosulfakinins (DSKs), cholecystokinin-like peptides, as satiety signals in Drosophila. We show that DSKs and DILPs are co-expressed in insulin-producing cells (IPCs) of the brain. Next we analyzed the effects of diminishing DSKs or DILPs employing the Gal4-UAS system by (1) diminishing DSK-levels without directly affecting DILP levels by targeted Dsk-RNAi, either in all DSK-producing cells (DPCs) or only in the IPCs or (2) expressing a hyperpolarizing potassium channel to inactivate either all the DPCs or only the IPCs, affecting release of both peptides. The transgenic flies were assayed for feeding and food choice, resistance to starvation, and for levels of Dilp and Dsk transcripts in brains of fed and starved animals. Diminishment of DSK in the IPCs alone is sufficient to cause defective regulation of food intake and food choice, indicating that DSK functions as a hormonal satiety signal in Drosophila. Quantification of Dsk and Dilp transcript levels reveals that knockdown of either peptide type affects the transcript levels of the other, suggesting a possible feedback regulation between the two signaling pathways. In summary, DSK and DILPs released from the IPCs regulate feeding, food choice and metabolic homeostasis in Drosophila in a coordinated fashion.
Highlights
Caloric intake is tightly regulated in animals to ensure energy stores sufficient for daily activity, and, at least in mammals, the nutrient consumption is controlled to maintain body weight near constancy over extended periods (Woods et al, 2000; Murphy and Bloom, 2006; Murphy et al, 2006; Woods and D’Alessio, 2008; Al-Anzi et al, 2010)
Since we found DSK immunoreactivity and D. melanogaster sulfakinin gene (Dsk)-Gal4 expression in several cells among the median secretory cells, probably including the insulin-producing cells (IPCs), we applied DILP2 antiserum to adult brains for identification
We confirmed that the Dsk-GFP-expressing median secretory cells are Drosophila insulin-like peptides (DILPs) immunopositive (Figures 1B1–B3) and we showed that most of the Dilp2-Gal4-expressing IPCs react with antiserum to DSK (Figures 1C1–C3)
Summary
Caloric intake is tightly regulated in animals to ensure energy stores sufficient for daily activity, and, at least in mammals, the nutrient consumption is controlled to maintain body weight near constancy over extended periods (Woods et al, 2000; Murphy and Bloom, 2006; Murphy et al, 2006; Woods and D’Alessio, 2008; Al-Anzi et al, 2010). Far there is evidence for several peptides acting at different levels in regulation of feeding in insects: leucokinins (Al-Anzi et al, 2010), neuropeptide F (NPF; Wu et al, 2003, 2005a), short neuropeptide F (sNPF; Lee et al, 2004, 2008), insulin-like peptides (Broughton et al, 2010; Cognigni et al, 2011), Hugin derived peptides (Melcher and Pankratz, 2005), sulfakinins (Wei et al, 2000; Maestro et al, 2001; Wu et al, 2003; Downer et al, 2007; Meyering-Vos and Muller, 2007), allatostatins (Aguilar et al, 2003; Hergarden et al, 2012), and sex peptide (Carvalho et al, 2006) It is, not yet clear how these peptide signals are coordinated to control the initiation, maintenance, and termination of feeding (see Audsley and Weaver, 2009; Nässel and Winther, 2010). We investigate the coordinated roles in feeding in Drosophila of the CCK-like Drosophila sulfakinins (drosulfakinins, DSKs), and Drosophila insulin-like peptides (DILPs)
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