Monitoring fly feeding behavior and timingby beetle luciferase reporters v2

Abstract

Monitoring Drosophila feeding behavior usually requires laborious procedures and custom-made equipment. This protocol describes how feeding behavior of individual flies carrying a beetle (e.g. firefly) luciferase gene can be conveniently monitored in real-time by measuring bioluminescence in 96-well microplates. Drosophila flies expressing a beetle luciferase gene produce bioluminescence if fed with a food containing luciferin. Bioluminescence in flies appears within a minute and peaks within 2-3 minutes after a food ingestion. When refraining from eating or placed on a luciferin-free food, fly bioluminescence decays with about 0.3-1 hour half-life and essentially returns to the baseline after 4 hours. Naturally, under non-stressed conditions, flies eat sporadically and often make intervals of many hours between eating. This makes beetle luciferase bioluminescence a very convenient system to monitor fly feeding timing and, to a considerable extent, food intake in real time for many days (see the Abstract Figure). In this protocol I describe one of the possible procedures to monitor fly feeding using commonly available plate readers, outline a historical background on recording bioluminescence in live flies to study circadian gene expression, illustrate several examples of feeding behaviors that can be analyzed by this procedure and discuss some potential applications. Bioluminescence signal in live freely moving flies is usually overwhelmingly dominated by fly feeding and movement. This makes firefly luciferase reporters poorly suitable to report changes in gene expression or other intracellular parameters in live flies despite their historically popular application for this purpose. Some approaches to address this problem are also discussed.