Microtubule organizing center

The microtubule-organizing center (MTOC) is located close to the nucleus and consists of the two centrioles together with the pericentriolar matrix around it. This matrix is responsible for the minus end formation of the microtubule filaments

Centrosome

The centrosome is the starting point of microtubule growth. It consists of a centrosome matrix enclosing two centrioles. The major role of the centrosome is to regulate the intracellular organization of the microtubules, which is essential for cell division. After replication of the DNA, the (duplicated) centrosomes move to opposite sides of the nucleus to form the two poles of the mitotic spindle that separates the chromosomes. In motile cells, one of the centrioles serves as the basal body of cilia and flagella during all cell cycle stages except mitosis.

Immunofluorescent staining

The MTOC always overlaps with the center of the microtubules, making it easy to find. Antibodies that very specifically stain the two centrioles as well as a single spot staining at the origin of microtubules are annotated as centrosome.

If the staining is larger and less distinct but still overlapping with the center of the microtubules, it is annotated as MTOC. MTOC stainings can show both vesicle-like and granular characteristics. Unlike the centrosome the staining of MTOC varies more between different cell lines making them more difficult to identify than centrosomes.

Read more about the proteome of the MTOC.