Most eukaryotic cells exhibit three different varieties of cytoskeletal filaments, each of which functions in a characteristic manner. The long, hollow filaments known as microtubules are primarily responsible for regulating the transport of molecules between intracellular compartments and governing the positioning of organelles bound by membranes. A microtubule exhibits an outer diameter of approximately 25 nanometers and is significantly more rigid than an actin filament. In a typical animal cell, microtubules are nucleated around a small region of cytoplasm bordering the nucleus of the cell called a microtubule-organizing center (MTOC), or centrosome. From the MTOC, the filaments extend out in an astral-like configuration, with their minus ends embedded in the centrosome and their plus ends situated towards the periphery of the cell. A specialized variety of tubulin (gamma-tubulin) apparently plays a key role in the organization of microtubules, forming ring-shaped complexes with proteins that are widely supposed to act as templates for the nucleation of microtubules that have grown to contain the 13 protafilaments characteristic of the structures.

The digital image presented above features a cell culture of Indian Muntjac fibroblasts that was immunofluorescently labeled with primary anti-tubulin mouse monoclonal antibodies followed by goat anti-mouse Fab fragments conjugated to the cyanine dye, Cy2. In addition, the culture was counterstained for DNA with DAPI, and for the cytoskeletal filamentous actin network with Alexa Fluor 568 conjugated to phalloidin. 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.