Second-Harmonic Generation Imaging of Microtubules
Microtubules are a well-studied class of cytoskeleton and serve numerous vital functions for the cell. ey are the mechanical supports for cellular compartments and the roadways for active intracellular transport. A single microtubule consists of 13 parallel protolaments, each a linear chain of the tubulin proteins connected end to end. e protolaments are attracted to each other lengthwise; so, each microtubule is a 25-μm-diameter rod with a hollow core. Tubulin, the basic repeating unit, is a heterodimer of α-and β-tubulins. One end of the tubulin dimer has an accessible, bound guanosine-5′- triphosphate (GTP). is GTP can be hydrolyzed readily so that the end can bond with another tubulin, and therefore, this is the fast-growing end, or the “plus end.” Since tubulins are joined end to end to form protolaments, each microtubule is structurally asymmetric. is polarity is particularly important for active transport because it dictates the travel direction of molecular motors, which carry cargoes from the soma to distal cellular compartments (Hirokawa and Takemura, 2005).