Stable Isotope-Labeled Raman Imaging Reveals Dynamic Proteome Localization to Lipid Droplets in Single Fission Yeast Cells

Lipid droplets have been hypothesized to be intimately associated with intracellular proteins. However, there is little direct evidence for both spatiotemporal and functional relations between lipid droplets and proteins provided by molecular-level studies on intact cells. Here, we present in vivo time-lapse Raman imaging, coupled with stable-isotope (C-13) labeling, of single living Schizosaccharomyces pombe cells. Using characteristic Raman bands of proteins and lipids, we dynamically visualized the process by which C-13-glucose in the medium was assimilated into those intracellular components. Our results show that the proteins newly synthesized from incorporated C-13-substrate are localized specifically to lipid droplets as the lipid concentration within the cell increases. We demonstrate that the present method offers a unique platform for proteome visualization without the need for tagging individual proteins with fluorescent probes.