Phosphoinositide signaling is essential for successful phagocytosis. Phosphoinositides regulate processes such as actin assembly and the recruitment of molecular motors required for ingestion, as well as fusion events required for the maturation of the phagosome. Phosphoinositides not only serve as substrates for the generation of second messengers, but also function to anchor to the membrane cytosolic proteins that contain phosphoinositide-binding motifs. Conventional methods for the detection of phosphoinositides involve their extraction from the cells and separation by chromatographic procedures. These approaches are laborious and expensive and fail to provide spatio-temporal information, which is critical when analyzing localized and transient phenomena like phagocytosis. In this chapter we describe a method to monitor phosphoinositides dynamically by transfection of fluorescently tagged probes (biosensors) into cultured macrophages. These biosensors are based on the fusion of phosphoinositide-binding protein domains with fluorescent proteins. Some specifications for live cell imaging of such phosphoinositide-specific probes are also provided.
