Investigation of the Lipid Metabolism during Drosophila Larva Development by Coherent Anti-Stokes Raman Scattering (CARS) Microscopy

Abstract

Drosophila melanogaster is one of the most valuable model organisms in studying genetics and developmental biology. The Drosophila fat body stores lipids that act as an energy source for the developing animal during its larval stages. Studies on lipid metabolism of the fat body allow us to better understand human energy metabolism and related illnesses.Coherent anti-Stokes Raman Scattering (CARS) microscopy is a nonlinear optical (NLO) technique which gives three-dimensional imaging based on chemically-selective vibrational scattering signals without any labeling agent. It has been widely used in the imaging of lipids in biological samples due to the strong CARS signal from carbon-hydrogen (C-H) bonds. Here we used CARS microscopy to image the distribution of the fat body in Drosophila larva in vivo with minimal invasion. Combined with two-photon excitation (TPE) and second harmonic generation (SHG), we could also obtain images of internal organs from autofluorescence and collagen/muscular tissues from SHG simultaneously in the same NLO platform. This study allowed us to visualize the three-dimensional structures of the Drosophila larva under the most natural living condition which cannot be achieved by conventional biochemical staining and labeling system. We further investigated the development of the fat body during different larval stages and under various conditions through long-term in vivo observations.To our knowledge, this is the first demonstration on in vivo imaging of unstained/label-free Drosophila fat body to get new insights into the lipid metabolism during Drosophila larva development by using multimodal NLO microscopy.