What bones are to bodies, the cytoskeleton is to cells. The cytoskeleton maintains cellular structure, builds appendages like flagella and, together with motor proteins, powers cellular movement, transport, and division. Microtubules are a critical component of the cytoskeleton, vital for cell division and, because of that, an excellent target for chemotherapy drugs.
Microtubules can spontaneously self-organize, transforming from many singular components into one large cellular structure capable of performing specific tasks. Think Transformers. How they do that, however, has remained unclear.