Tubulin is a protein that comprises the basic structural subunits of microtubules, the cytoskeletal filaments associated with the positioning of membrane-bound organelles and intracellular transport. Each tubulin subunit is, in fact, a heterodimer composed of alpha-tubulin and beta-tubulin components linked to one another by noncovalent bonds. The two globular proteins, which only occur in this network, each exhibits a binding site for a single guanosine triphosphate (GTP) molecule. The GTP molecule bound to the alpha-tubulin monomer may be regarded as a fundamental component of the tubulin heterodimer complex because it is physically unable to be exchanged or hydrolyzed, instead remaining constantly confined at the dimer interface. The nucleotide bound to the beta-tubulin monomer, however, is exchangeable and may be hydrolyzed to produce guanosine diphosphate (GDP), an event that significantly impacts the dynamics of the microtubular network.

In order to visualize the microtubules present in the rat kidney mesangial cells illustrated in the digital image above, a RMC culture was immunofluorescently labeled with anti-tubulin mouse monoclonal primary antibodies followed by goat anti-mouse Fab fragments conjugated to Alexa Fluor 568. In addition, the cells were labeled for the cytoskeletal filamentous actin network with Alexa Fluor 350 conjugated to phalloidin, and for cell nuclei with the classic nucleic acid stain, SYTOX Green. 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.