Checking out the centrosome.

Centrosomes consist of a pair of barrel-shaped microtubule assemblies called centrioles, surrounded by a pericentriolar matrix. The only well-characterized functions of centrosomes is to recognize both interphase microtubule arrays responsible for cell polarity and the mitotic spindle, which mediates the strictly bipolar separations of chromosomes. In addition to these established functions it has been speculated that centrosomes might be involved in several different cell cycle regulatory events like entry into mitosis, cytokinesis, G(1)/S transition and monitoring of DNA damage. These assumptions are mainly based on a rapidly growing list of centrosome-associated regulatory proteins such as p53, Brca1, Chk1, Chk2, TopBP1, Aurora-A, Plk1, cyclin B1, and Cdk1. However, only very few direct links between their localization to the centrosome and specific cellular functions have been unraveled until recently. This review will focus on recent advances in the understanding of the role of centrosomes as integrators of positive and negative pathways for mitotic entry.