Lab journal club: measuring circulating insulins in flies

In a recent lab journal club we discussed a paper from the lab of Seung Kim:

A genetic strategy to measure circulating Drosophila insulin reveals genes regulating insulin production and secretion. Park S, Alfa RW, Topper SM, Kim GE, Kockel L, Kim SK. (2014) PLoS Genetics, Aug 7;10(8):e1004555.

This paper described a new approach to measure circulating insulins in Drosophila. The authors generated transgenic flies that carry epitope-tagged versions of a drosophila insulin-like peptide (dILP). They then developed an efficient and high- throughput ELISA approach to measure levels of circulating dILP within the hemeolymph of these flies. Using this approach they defined new genes required for controlling dILP release (vs expression). They also showed that changes in circulating dILPs often are not reflected in altered mRNA or protein levels, and that dILP release from neurosecretory cells can be influenced by peripheral insulin signaling.

Measuring circulating dILPs in flies is not straightforward. Many papers have relied on indirect measures (such as dILP mRNA or protein in neurosecretory cells, or assays for downstream insulin/PI3K/FOXO signaling) to infer changes in circulating dILPs. We liked the paper because it provides a powerful new tool to actually measure hemolymph dILP levels. These flies and ELISA assays will help with future studies on the genetic and signaling mechanisms that control insulin function.