Labeling lysosomes in live cells with fluorescent dyes for imaging

INTRODUCTIONThe eukaryotic cell has evolved to compartmentalize its functions and transport various metabolites among cellular compartments. Therefore, in cell biology, the study of organization and structure/function relationships is of great importance. Lysosomes are membranous sacs--diverse in shape and size--containing more than 40 different acid hydrolases. The enzymes operate optimally at the acidic pH (~5) within the lysosome to break down various substances. It is thought that the highly glycosylated nature of the proteins of the Golgi membrane helps to protect them from degradation. A number of the fluorescent approaches to visualizing lysosomes make use of their acidic pH. Commonly used probes include neutral red, N-(3-[2,4-dinitrophenyl amino] propyl)-N-(3-aminopropyl)methylamine (DAMP), and acridine orange (a DNA stain). This protocol describes the labeling of lysosomes in live cells with neutral red.