Analysis of Drosophila Lipids by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometric Imaging

Abstract

Drosophila melanogaster is a major model organism for numerous lipid-related diseases. While comprehensive lipidomic profiles have been generated for D. melanogaster, little information is available on the localization of individual lipid classes and species. Here, we show the use of matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI) to profile lipids in D. melanogaster tissue sections. The preparation of intact cryosections from whole insects presents a challenge due to the brittle hydrophobic cuticle surrounding the body and heterogeneous tissue types beneath the cuticle. However, the introduction of a novel sucrose infiltration step and gelatin as an embedding media greatly improved the quality of tissue sections. We generated MS image profiles of six major lipid classes: phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, phosphatidylserine, and triacylglycerides. In addition, signals corresponding to two male-specific sex pheromones were detected in the ejaculatory bulb, a specialized site of pheromone production. MSI performed with 35 μm lateral resolution provided high sensitivity detection of at least 92 different lipid species, based on exact mass. In contrast, MSI with 10 μm lateral resolution enabled the detection of 36 lipid species but allowed lipid profiling of individual organs. The ability to localize lipid classes in intact sections from whole Drosophila provides a powerful tool for characterizing the effects of diet, age, stress, and environment on lipid production and distribution.

Drosophilaas a model to study obesity and metabolic disease

“…Moreover, advances in analytical technology increasingly compensate for the disadvantage of the fly being a small model organism. Some examples of these analytical technologies are direct analysis in real time mass spectrometry in whole flies (Chiang et al, 2016), tissue-and hemolymph-specific mass spectrometry analyses (Chintapalli et al, 2013;Musselman et al, 2016), in situ lipid profiling in Drosophila sections using matrix-assisted laser desorption/ ionization mass spectrometry imaging for comprehensive lipid composition analysis of individual fly organs (Niehoff et al, 2014), and the use of optical coherence tomography for non-invasive monitoring of Drosophila heart function (Men et al, 2016a).…”

Nanopipettes: probes for local sample analysis

“…41 Earlier reports have described analysis of the chemical composition of individual third instar larva 43,44 and adult flies. 32 To study hemolymph from earlier stages (compared to third instar larvae) with a lower hemolymph volume (∼70–100 nL, hemolymph volume of first instar larva estimated from size), a more appropriate tool for extraction of hemolymph is required. The method described here is appropriate for sampling and analysis of small volumes from first instar larvae.…”

“…A 20 mg mL –1 DHB in 50% methanol–water was used for A. cepa cytoplasm analysis and mouse brain tissue section analysis was performed with 70 mg mL –1 DHB in 50% methanol–water. A 8 mg mL –1 dithranol matrix in 2 : 1 chloroform/methanol 32 was used for D. melanogaster hemolymph analysis.…”

Tracing the fate and transport of secondary plant metabolites in a laboratory mesocosm experiment by employing mass spectrometric imaging

“…A few studies about the MALDI MSI analysis of insects, such as beetles [13], flies [14–16], and honeybees [17], can be found in the literature; however, locusts have only been imaged employing desorption electrospray ionization (DESI) to show the distribution of the pharmaceutical compound terfenadine and its metabolites [18]. …”