Pericentriolar material

Radial arrays are best exemplified by mitotic half-spindles, which have a central MTOC, the centrosome. The centrosome consists of two centrioles (which are homologous with the basal body) surrounded by dense pericentriolar material (Kalt and Schliwa, 1993). In plant cells, the MTOC of the mitotic spindle consists of dense material only without centrioles. The plus ends of microtubules of the mitotic spindle are directed toward the equator of the cell. Some are free, and others attach to kinetochores on chromatids (see Figure 4). 

Kubiak We can only speculate. In different mammals the centrioles appear at different times. We do not know whether pericentriolar material (PCM) foci duplicate like mature centrosomes. Do they preserve any structure We don t know, although we find them amorphous at the electron microscope level. 

The second arises from replication of the centrioles during the S and G2 phases of interphase. During prophase, the two pairs of centrioles move apart from one another and the pericentriolar material surrounding them both can nucleate and stabilize microtubules. These two MTOCs become the spindle poles. 

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