Tubulin is a major cytoskeleton component that has five distinct forms. a and beta Tubulins form heterodimers which multimerize to form a microtubule filament. There are five beta Tubulin isoforms (beta1, beta2, beta3, beta4A and beta4B) that are expressed in mammalian tissues. beta1 and beta4 are present throughout the cytosol, beta2 is present in the nuclei and nucleoplasm, and beta3 is a neuron-specific cytoskeletal protein.