Figure 3.

The PCM assembly cycle in embryonic systems. (a) During interphase, a thin layer of PCM surrounds the centrioles. In the cytoplasm are unincorporated PCM proteins, and there are species-specific differences in their assembly state. In C. elegans, the unincorporated core PCM components are separate entities, whereas in Drosophila, the core PCM proteins may already be pre-assembled into small complexes of defined stoichiometry. (b) As the cell progresses into mitosis, polo kinase phosphorylates the key scaffolding proteins, thereby inducing their incorporation around the established inner PCM layer. This new addition of protein causes the PCM to expand dramatically. As the mitotic PCM expands, Aurora A kinase phosphorylation promotes the deposition of protein complexes that aid in nucleating and stabilizing MTs (blue lines). The steady-state size of the PCM is determined by the total amount of a limiting component and the rates of phosphorylation and de-phosphorylation reactions. (c) Once mitosis is complete, MT-mediated cortical forces rupture the PCM, and protein phosphatases remove polo kinase-derived phosphorylations from the scaffold proteins. These two activities promote rapid disassembly of the mitotic PCM. (Illustration courtesy of Julia Eichhorn.)