Expression of a constitutively active insulin receptor in Drosulfakinin (Dsk) neurons regulates metabolism and sleep in Drosophila

The ability of organisms to sense their nutritional environment and adjust their behavior accordingly is critical for survival. Insulin-like peptides (ilps) play major roles in controlling behavior and metabolism; however, the tissues and cells that insulin acts on to regulate these processes are not fully understood. In the fruit fly, Drosophila melanogaster, insulin signaling has been shown to function in the fat body to regulate lipid storage, but whether ilps act on the fly brain to regulate nutrient storage is not known. In this study, we manipulate insulin signaling in defined populations of neurons in Drosophila and measure glycogen and triglyceride storage. Expressing a constitutively active form of the insulin receptor (dInR) in the insulin-producing cells had no effect on glycogen or triglyceride levels. However, activating insulin signaling in the Drosulfakinin (Dsk)-producing neurons led to triglyceride accumulation and increased food consumption. The expression of ilp2, ilp3 and ilp5 was increased in flies with activated insulin signaling in the Dsk neurons, which along with the feeding phenotype, may cause the triglyceride storage phenotypes observed in these flies. In addition, expressing a constitutively active dInR in Dsk neurons resulted in decreased sleep in the fed state and less starvation-induced sleep suppression suggesting a role for insulin signaling in regulating nutrient-responsive behaviors. Together, these data support a role for insulin signaling in the Dsk-producing neurons for regulating behavior and maintaining metabolic homeostasis.