Figure 9.

Centrosome disjunction and C-Nap1 displacement may be distinct events. The schematic model illustrates centrosome disjunction (A) and C-Nap1 displacement (B) as independent events that take place upon onset of mitosis. Disjunction of centrosomes, i.e., loss of cohesion between mother and daughter centrioles, is triggered by activation of Nek2A kinase. This itself is the result of a loss of the antagonistic activity of PP1, perhaps through phosphorylation of PP1 or binding of Inhibitor-2. The substrates of Nek2 involved in centrosome cohesion are likely to include C-Nap1 (blue sphere), although phosphorylation by Nek2 alone may not be sufficient to completely displace C-Nap1 from the centrosome. Nek2 may also have other substrates within the intercentriolar linkage. Likewise, full C-Nap1 displacement may require additional phosphorylation by other mitotic kinases.