Cytoskeleton generally refers to the longitudinal and transverse fiber network in the cytoplasm of eukaryotic cells, which is divided into microtubules, microfilaments and intermediate fibers according to the fiber diameter, composition and assembly structure. The cytoskeleton can be observed by electron microscopy, histochemistry, enzyme labeling, immunofluorescence and other methods. Microfilaments (microfilament) are fibers composed of actin. Microfilaments form different subcellular structures in different kinds of cells together with certain binding proteins (e.g., muscle filaments, intestinal epithelial microvillous axons, stress fibers, etc.).

The microfilament staining solution (R250 method) mainly uses Kaumas Brilliant Blue R250 to show stress fibers composed of microfilaments, and Kaumas Brilliant Blue R250 can stain a wide range of proteins and is not specific for staining microfilaments, and under the conditions of this method, due to the instability of microtubule structure, some types of fibers are too fine to be identified under the light microscope, so the fibers that can be seen are mainly stress fibers composed of microfilaments, with a diameter of about 40 nm, and this fiber is particularly well developed in adherent cells cultured in vitro due to the attachment of the cells to the culture substrate and the maintenance of a flat spreading shape.