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Fig. 1. The centrosome cycle. At the beginning of G1 phase, cells contain a single centrosome with two perpendicularly aligned, closely associated centrioles. The two centrioles are not identical at this stage. The daughter centriole originates from the previous cell cycle, whereas the mother centriole (centriole with black cap) assembled at least two cell cycles ago. During G1 phase, the tight link (purple bar) between the centrioles is dissolved (centriole disengagement), but centrioles remain connected by a loose fibrous structure. Centriole disengagement is a prerequisite for centrosome duplication. In S phase, the centrosome duplicates simultaneously with DNA replication. Duplication involves the assembly of two new centrioles perpendicular to the existing centrioles. Note that at this point there are three different types of centriole in the cell: two newly formed centrioles, the daughter and the mother centriole. Next, the daughter centriole finally acquires the same molecular characteristics as the mother centriole and the fibrous tether between the mother and daughter centrioles is severed. Due to the tight link (purple bars) between the old centrioles and the newly formed ones, the two centrosomes are now engaged and prevented from further replication. In late G2 phase, the two centrosomes undergo maturation by recruiting additional PCM (grey circle) components to prepare for their role as spindle poles. The centrosomes then separate and move to the opposite side of the nucleus. Here, we show this as simultaneous with nuclear envelope breakdown (NEBD) and mitotic commitment; however, separation can be completed before or after NEBD (see text). Also, the timing and ordering of these events vary between cell types and organisms. After NEBD, the centrosomes start nucleating MT asters that capture chromosomes and form a bipolar spindle structure. The bipolar nature of mitosis ensures that each daughter cell inherits one centrosome. In dark-purple text, we list the experimental systems in which there is evidence for Aurora-A involvement in a particular step of the centrosome cycle (for more details, see Table 1).
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