The centrosome is the main microtubule organizing center (MTOC) in human cells. At the heart of the centrosome are two centrioles, which act as scaffolds upon which the pericentriolar material is assembled. This fibrous material contains factors that nucleate and organize microtubules. Thus, centrosomes play a vital role in microtubule-dependent processes, such as mitosis and intracellular transport. The centrosome replicates in S phase in a semi-conservative manner that maintains one of the parental centrioles in each centrosome. In M phase, the two centrosomes move apart to opposite ends of the cell, where they participate in formation of the bipolar mitotic spindle.
In interphase, the centrosome is located in close proximity to the nuclear membrane, at the center of the network of microtubules in cells. Upon mitosis, the centrosomes move to opposite ends of the cell and form the poles of the mitotic spindle. Centrosomes vary in size as the amount of pericentriolar material varies during the cell cycle and between cell types, making it difficult to define their border. In the subcellular section, a staining of one or two distinct dots at the region where microtubules originates is annotated as centrosome, whereas a more diffuse, sometimes punctate, staining of this area is annotated as centriolar satellites. Several proteins are in fact known to localize to both of these compartments. Moreover, while centrosomes are seen at the centers of the mitotic spindle, centriolar satellites undergo dissolution and are no longer visible upon entry into mitosis. Centriolar satellites start to reappear after completion of cytokinesis.
Read more about the proteome of the centrosome.