Structure and duplication of the centrosome

The centrosome has evolved in multicellular organisms from the basal body/axoneme of the unicellular ancestor (Azimzadeh and Bornens, 2004). It plays a major role in organizing the microtubule cytoskeleton in animal cells. During interphase, the centrosome organizes an astral array of microtubules (MTs) that participate in fundamental cellular functions such as intracellular trafficking, cell motility, cell adhesion and cell polarity. In proliferating cells, the centrosome starts duplicating just before, or at, the onset of S phase and the two newly formed centrosomes participate in the assembly and organization of the mitotic spindle, its orientation with respect to cortical cues, and the late events of cytokinesis. The animal centrosome consists of a pair of centrioles linked together through their proximal regions by a matrix consisting in part of large coiled-coil proteins of the pericentrin family, which anchor other matrix components. The centrioles contain cylindrical arrays of triplet MTs organized with nine-fold radial symmetry and the proximal region is structurally similar to the basal bodies of cilia and flagella. In animals, centrioles retain the ability to act as basal bodies by templating the assembly at their distal end (the plus ends of the centriole MTs) either of a primary cilium or of beating cilia during ciliogenesis in specialized cells. Recent discoveries have revealed that cilia have crucial roles in an increasing number of cellular and developmental processes, establishing a link between dysfunctional cilia and several genetic diseases (for reviews, see Davis et al., 2006; Bisgrove and Yost, 2006; Dawe et al., 2007). In post-mitotic cells, the centrosome contains a mature centriole called the mother centriole and an immature centriole assembled during the previous cell cycle, the daughter centriole, which is about 80 % the length of the mother centriole (Chretien et al., 1997). Mother