Abstract
ABSTRACTCentrosomes are 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 (PP2ASUR-6), 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. Purified PP2ASUR-6 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 force-driven fragmentation of the PCM scaffold.
Highlights
Centrosomes are micron-scale, membrane-less organelles that nucleate microtubule arrays
Confirming previous analysis (Decker et al, 2011; Woodruff et al, 2015), pericentriolar material (PCM) localized around centrioles shortly after fertilization, grew in size as the embryo progressed toward mitosis (Movie 1)
Quantification of PCM disassembly using semi-automated tracking and segmentation revealed that PCM mass peaks ∼275 s after nuclear envelope breakdown (NEBD), corresponding to anaphase
Summary
Centrosomes are micron-scale, membrane-less organelles that nucleate microtubule arrays. They are crucial for assembling and positioning the mitotic spindle, establishing membrane polarity, and asymmetric cell division. Centrosomes comprise a pair of nanometer-scale centrioles that organize a micron-scale mass of protein called pericentriolar material (PCM). PCM is required for proper centriole duplication (Dammermann et al, 2004; Loncarek et al, 2008) and determines the activity of centrosomes by serving as a concentration compartment for proteins that nucleate microtubules (Conduit et al, 2015; Woodruff et al, 2014). Post-mitotic cells often lose their PCM and centrioles altogether, suggesting a tight coupling of centrosome assembly status to cellular differentiation.
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