Phosphatase PP2A and microtubule pulling forces disassemble centrosomes during mitotic exit

Abstract

Centrosomes are major microtubule-nucleating organelles that facilitate chromosome segregation and cell division in metazoans. Centrosomes comprise centrioles that organize a micron-scale mass of protein called pericentriolar material (PCM) from which microtubules nucleate. During each cell cycle, PCM accumulates around centrioles through phosphorylation-mediated assembly of PCM scaffold proteins. During mitotic exit, PCM swiftly disassembles by an unknown mechanism. Here, we used Caenorhabditis elegans embryos to determine the mechanism and importance of PCM disassembly in dividing cells. We found that the phosphatase PP2A and its regulatory subunit SUR-6 (PP2A ), together with cortically directed microtubule pulling forces, actively disassemble PCM. In embryos depleted of these activities, ~25% of PCM persisted from one cell cycle into the next, resulting in cytokinetic furrow ingression errors, excessive centrosome accumulation, and embryonic death. Purified PP2A could dephosphorylate the major PCM scaffold protein SPD-5 in vitro. Our data suggest that PCM disassembly occurs through a combination of dephosphorylation of PCM components and catastrophic rupture of the PCM scaffold.

Differential Requirements for Centrioles in Mitotic Centrosome Growth and Maintenance

“…Correcting for fluorescence recovery after photobleaching (see STAR Methods) revealed that PCM signal was stable for the remainder of mitosis in both controls and centriole ablation conditions (Figure 4E). Differences between centrosomes with and without centrioles only became apparent after anaphase onset (Figure 4E), a stage at which the PCM matrix begins to disassemble in response to reversal of mitotic phosphorylation of the PCM scaffold and cortical pulling forces exerted on astral microtubules (Enos et al, 2018;Severson and Bowerman, 2003). Here, PCM disassembly was clearly accelerated compared to controls.…”

Phosphorylation of Plant Microtubule-Associated Proteins During Cell Division

“…They were characterized in both monocots ( Wright et al., 2009 ) and dicots ( Camilleri et al., 2002 ). Moreover, their animal homologs were found to be essential for regulating microtubule structures in both meiosis and mitosis ( Tang et al., 2016 ; Enos et al., 2017 ; Varadkar et al., 2017 ). In plants, PP2A controls organization and dynamics of both cortical and mitotic microtubules ( Figure 1 ; Camilleri et al., 2002 ; Yoon et al., 2018 ).…”

An Acentriolar Centrosome At The C. elegans Ciliary Base

“…In vivo, this process is directed to occur around centrioles with centriolelocalized SPD-2 recruiting both PLK-1 and its activator Aurora A/AIR-1 [2]. Laser ablation experiments have shown that centrioles are essential for mitotic PCM growth, although existing PCM polymer can be maintained by PLK-1 acting within the PCM to counter the destabilizing effect of phosphatases such as PP2A [2,14]. Centrioles are further essential for PCM structural integrity, potentially by acting as anchoring sites for tethering proteins such as PCMD-1, a putative ortholog of pericentrin [2,7].…”

“…Unlike other microtubule-organizing centers in the adult worm the acentriolar centrosome in ciliated neurons derives from a canonical, centriole-organized centrosome present at the initiation of ciliogenesis in the late-stage embryo [6]. A potential explanation for the persistence of PCM is that there is no counteracting phosphatase driving PCM polymer disassembly, as there is during mitosis [2,14]. The PCM at the ciliary base could then simply be a remnant left over from the terminal cell division, surviving the loss of its core organizing structure, the centriole, and the kinase that drove its assembly, PLK-1.…”