Where are the limits of the centrosome?

The centrosome is a key component of the cell is involved in the processes of cell division, cell motility, intracellular transport, organization of the microtubules (MT) network and the production of cilia and flagella. The peculiarity of this organelle is that its boundaries are not clearly defined, the centrioles at the center of the centrosome are surrounded by electron dense pericentriolar material, the size and protein composition of this centrosome component experiences significant transformation during the cell cycle. It has been shown in this study that within the centrosome different proteins occupy different areas corresponding to: MT nucleation region (defined as gamma-tubulin-stained area), regulatory region (defined as kinase pEg2-stained area) and motor proteins region (kinesin-like motor XlEg5-stained area). The boundary of pEg2 is near 1.3 times greater while XlEg5 is 3.0 times greater than that of gamma-tubulin. Thus, the size of the centrosome, determined according to the structural electron microscopy (EM) analysis (about 1 µm) corresponds to the regulatory proteins area, but the actual functional centrosome size defined at the motor proteins region, is more than twice the size.