Analysis of Lipid Signaling in Drosophila Photoreceptors using Mass Spectrometry

The activation of phospholipase Cβ (PLCβ) is an essential step during sensory transduction in Drosophila photoreceptors. PLCβ activity results in the hydrolysis of the membrane lipid phosphatidylinositol 4,5 bisphosphate [PI(4,5)P₂] leading ultimately to the activation of transient receptor potential (TRP) and TRP like (TRPL) channels. The activity of PLCβ also leads subsequently to the generation of many lipid species several of which have been proposed to play a role in TRP and TRPL activation. In addition, several classes of lipids have been proposed to play key roles in organizing the cell biology of photoreceptors to optimize signaling reactions for optimal sensory transduction. Historically, these discoveries have been driven by the ability to isolate Drosophila mutants for enzymes that control the levels of specific lipids and perform analysis of photoreceptor physiology in these mutants. More recently, powerful mass spectrometry methods for isolation and quantitative analysis of lipids with high sensitivity and specificity have been developed. These are particularly suited for use in Drosophila where lipid analysis is now possible from photoreceptors without the need for radionuclide labeling. In this article, the conceptual and practical considerations in the use of lipid mass spectrometry for the robust, sensitive, and accurate quantitative assessment of various signaling lipids in Drosophila photoreceptors are covered. Along with existing methods in molecular genetics and physiological analysis such lipid is likely to enhance the power of photoreceptors as a model system for discoveries in biology.