Analysis of actin assembly by in vitro TIRF microscopy

Since directed movement toward an extracellular chemoattractant requires rapid and continuous reorganization of the actin cytoskeleton to form complex structures such as a protruding lamellipodium, it is of great interest to analyze and understand the individual contribution of proteins specifically involved in this process. Over the last decade, enormous progress has been made toward understanding the versatile molecular mechanisms underlying actin-based cell motility and the regulation of site-specific F-actin assembly and disassembly. In spite of this wealth of knowledge and due to the constant discovery of novel regulatory factors, many questions remain to be answered. In this chapter, we describe a powerful method that allows to study the effects of actin-binding proteins on the assembly of single filaments by in vitro total internal reflection fluorescence (TIRF) microscopy using purified proteins and fluorescently labeled actin.