Tubulin is a major cytoskeleton component that has five distinct forms. alpha and beta Tubulins form heterodimers which multimerize to form a microtubule filament. There are five beta Tubulin isoforms (b1, b2, b3, b4A and b4B) that are expressed in mammalian tissues. b1 and b4 are present throughout the cytosol, b2 is present in the nuclei and nucleoplasm, and b3 is a neuron-specific cytoskeletal protein.