Actin is a highly conserved protein heavily associated with the contractile properties of cells. The important substance is found in almost all cells, but is most pronounced in muscle cells. Two primary types of actin are generally recognized: F-actin and G-actin. A polymeric form, F-actin is actually a chain of multiple actin molecules bound together into long, thin filaments, whereas G-actin exists in a monomeric, globular form, 375 amino acids long. F-actin is the main constituent of microfilaments, which are found predominantly in the cytoskeleton, where they function in contraction, cytoplasmic streaming, and alterations in cellular shape.

The human cortical neuron culture (HCN-1A) featured in the digital image above was immunofluorescently labeled with anti-tubulin mouse monoclonal primary antibodies followed by goat anti-mouse Fab fragments conjugated to Cy2. In addition, the culture was stained for the cytoskeletal F-actin network with Alexa Fluor 568 conjugated to phalloidin, and for DNA in the cell nucleus with Hoechst 33258. Images were recorded in grayscale with a QImaging Retiga Fast-EXi camera system coupled to an Olympus BX-51 microscope equipped with bandpass emission fluorescence filter optical blocks provided by Omega Optical. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.