The mitotic spindle is a transient microtubule-based structure that is present during mitosis and that mediates accurate separation of replicated sister chromatids to the daughter cells. Upon entry into mitosis, the interphase network of microtubules disassembles, and the duplicated centrosomes move to opposite ends of the cell. This is achieved with the help of astral microtubules connected to motor proteins at the plasma membrane. The mitotic spindle also includes interpolar microtubules that radiate towards the center of the spindle, and kinetochore microtubules that connect to kinetochores of the condensed sister chromatids. Careful regulation of microtubule polymerization and depolymerization, and the action of motor proteins, successively mediates bipolar attachment of sister chromatids to opposite spindle poles, alignment of sister chromatids at the equatorial plane, and finally separation of sister chromatids to each of the daughter cells.
The mitotic spindle can be seen as an intricate structure of microtubules radiating from each of the centrosomes at opposite ends of a mitotic cell. At this stage, the chromatin of the cell is condensed, as visible by intense DAPI staining. The size and exact shape of the mitotic spindle changes during mitotic progression, clearly reflecting the different stages of mitosis.
Read more about the proteome of the mitotic spindle as a substructure of microtubules.