A genetic strategy to measure insulin signaling regulation and physiology in Drosophila

Abstract

Insulin regulation is a hallmark of health, and impaired insulin signaling promotes metabolic diseases like diabetes mellitus. However, current assays for measuring insulin signaling in all animals remain semi-quantitative and lack the sensitivity, tissue-specificity or temporal resolution needed to quantify in vivo physiological signaling dynamics. Insulin signal transduction is remarkably conserved across metazoans, including insulin-dependent phosphorylation and regulation of Akt/Protein kinase B. Here, we generated transgenic fruit flies permitting tissue-specific expression of an immunoepitope-labelled Akt (AktHF). We developed enzyme-linked immunosorption assays (ELISA) to quantify picomolar levels of phosphorylated (pAktHF) and total AktHF in single flies, revealing dynamic tissue-specific physiological regulation of pAktHF in response to fasting and re-feeding, exogenous insulin, or targeted genetic suppression of established insulin signaling regulators. Genetic screening revealed Pp1-87B as an unrecognized regulator of Akt and insulin signaling. Tools and concepts here provide opportunities to discover tissue-specific regulators of in vivo insulin signaling responses. Author SummaryInsulin is an essential hormone that controls metabolism in all animals, by regulating energy use and growth of target tissues. Impaired insulin signaling ("resistance") in humans underlies development of type 2 diabetes, a pandemic disease causing significant morbidity and mortality. The genetic risk for insulin resistance is complex, and studies of diabetes are limited by a lack of tools to measure insulin resistance in a sensitive, quantitative, and tissue-specific way. Here, we describe a new technique to measure the strength of insulin signaling in fruit flies. By combining fruit fly genetics with antibody-based assays, we can quantify phosphorylated Akt, an evolutionarily conserved target of insulin signaling, in specific tissues of the adult fly. We show this technique can detect changes in insulin signaling after fasting and refeeding, addition of exogenous insulin, or genetic disruption of the insulin signaling pathway. We used this method to discover a new regulator of insulin signaling, a phosphatase enzyme encoded by Pp1-87B. This exciting new tool should advance our ability to study and discover additional regulators of insulin signaling and resistance.