Centrosome

From Freepedia

The centrosome is the main microtubule organizing center (MTOC) of the cell. It is composed of two orthogonally arranged centrioles surrounded by an amorphous mass of pericentriolar material (PCM). Centrosomes are associated with the nuclear membrane during interphase of the cell cycle, but they become detached from the membrane during cell division. The centrosome nucleates and organizes microtubules. It also plays a central role in mitosis, and in making cilia and flagella.

Higher eukaryotic cells possess a centrosome. Yeast cells have a spindle pole body (SPB) which is equivalent to metazoan centrosomes. The spindle pole body differs from the centrosome in many ways, the major difference is the lack of centrioles. Plant cells have centrosomes, which do not contain centrioles.

The centrosome must replicate once and only once per cell cycle so that each daughter cell can inherit one centrosome. Aberrant numbers of centrosomes in a cell have been associated with cancer. The centrosome replicates during the S phase of the cell cycle. During the prophase of mitosis, the centrosomes migrate to opposite poles of the cell. Mitotic spindle forms between the two centrosomes.

Interestingly, centrosomes are not required for the progression of mitosis. When the centrosomes are irradiated by laser, mitosis proceed normally with a spindle of normal morphology. However, acentrosomal cells lack radial arrays of astral microtubules. They are also defective in spindle positioning and cytokinesis. The function of centrosome in this context seemed to ensure the fidelity of cell division, rather than directing it.

In addition, centrosomes can function independent of its MTOC activity, demonstrated by the cell cycle arrest exhibited by cells with centrosome irradiation. It is also shown that centrosome can determine the cell polarity of nematode zygotes independent of microtubules.