Microtubule organizing center

 Staining of centrosome in human cell line U-2 OS (HPA037682)
Scale bar represents 10µm

Microtubule organizing center

The microtubule organizing center (MTOC) nucleates the polymerization of tubulin into microtubules, thereby enabling their organization into ordered arrays and playing an essential role in defining polarity of the cell. The centrosome, basal bodies and spindle pole bodies are different forms of MTOCs.


The centrosome is the main MTOC of the human cell consisting of two centrioles surrounded by a pericentriolar matrix. The centrioles acts as scaffolds upon which the pericentriolar material is assembled, and this in turn contains factors that nucleate and organize microtubules. Prior to cell division, the two centrioles move apart and replicates to form two complete centrosomes at opposite ends of the cell, where they direct formation of the bipolar mitotic spindle.

Immunofluorescent staining

It is difficult to define the MTOC and centrosomes, as it lacks a clear boundary towards the cytosol as well as the amount of pericentriolar material varies during the cell cycle. In G1 phase of the cell cycle, the centrosome lies at the center of the microtubules and is located close to the nuclear membrane. An antibody that very specifically stains the two centrioles or a small single spot at the origin of microtubules is annotated as centrosome, whereas antibodies giving larger and more diffuse staining of this area are annotated as MTOC. MTOC staining can vary in size and appearance between cell lines and single cells.

Read more about the proteome of the centrosome.