Cell Cycle: Order in the Pericentriolar Material

RESEARCH HIGHLIGHTS

Nature Reviews Molecular Cell Biology | AOP, published online 25 October 2012; doi:10.1038/nrm3471

CELL CYCLE Order in the pericentriolar material The centrosome is the main micro- domains with distinct molecular Spindle-defective protein 2 (SPD2). tubule-organizing centre in animal composition: an inner layer that is Centriolar Polo-like kinase 1 (PLK1) cells and has many crucial functions, juxtaposed to the centriole wall; and lies at the head of the hierarchy, including the assembly of the mitotic an outer layer that extends further whereas CNN is required for SPD2 spindle and establishing the axis of away from the centrioles. to localize to the PCM and together cell division. It comprises a pair By combining 3D-SIM with vol- they recruit γ-tubulin. of barrel-shaped centrioles that ume averaging, Mennella et al. At each cell cycle, centrioles dupli- are surrounded by pericentriolar were able to map the position of cate, and all four studies examined material (PCM). Although the PCM pericentrin-like protein (PLP) how the localization of the PCM and is normally described as an electron- domains with nanometre precision, centriolar components relates to the dense amorphous protein cloud, four showing that PLP forms elongated assembly of nascent daughter centri- studies now reveal that it is in fact structures oriented radial to the oles (which appear perpendicular to highly organized. centriole wall, with the C terminus the mother centrioles). Interestingly, Lawo et al. and Sonnen et al. positioned towards the centriole. they observed that PCNT and PLP visualized the localization of PCM Stochastic optical reconstruction around the mother centrioles form components in human cells using microscopy (STROM), which pro- a gap at the site where the daughter three-dimensional structured illumi- vides higher resolution than SIM, centriole emerges. Furthermore, nation microscopy (3D-SIM). They further revealed that PLP has a quasi- Sonnen et al. also report that centriolar observed that, with the exception of ninefold symmetry and thus extends PLK4 constitutes an early marker for pericentrin (PCNT), PCM proteins the centriole symmetry into the PCM this site of nascent centriole formation. are organized in a layered manner matrix. Crucially, RNAi experiments These four studies show that and form cylinders that surround the showed that, like PCNT in human the PCM has a conserved ordered mother centriole during interphase. cells, these PLP fibrils function as a structure in which proteins occupy PCNT, which is one of many pro- scaffold for the 3D assembly of the distinct domains, and also suggest teins implicated in the recruitment outer PCM. that these locations have functional and/‌or attachment of γ-tubulin ring The PCM assembles in the implications for the assembly and complexes (that mediate microtubule vicinity of centrioles during mitosis maturation of the centrosome. nucleation), was found to adopt an and expands during centrosome Importantly, they highlight the power elongated conformation spanning the maturation, so Sonnen et al. and of new microscopy methods, paving width of the PCM, with the carboxyl Fu and Glover asked whether protein the way for future investigations. terminus positioned near the centri- localization in the PCM changes at Kim Baumann ole and the amino terminus extend- mitotic entry. Interestingly, Sonnen ORIGINAL RESEARCH PAPERS Lawo, S. et al. ing out to the periphery. Importantly, et al. observed that, instead of the Subdiffraction imaging of centrosomes reveals Lawo et al. found that the organiza- layered organization seen in inter- higher-order organizational features of tion of the PCM was disrupted when phase, during mitosis PCM proteins pericentriolar material. Nature Cell Biol. 21 Oct 2012 (doi:10.1038/ncb2591) | Sonnen, K. F. et al. cells were depleted of PCNT, which form networks with interspersed 3D-structured illumination microscoscopy suggests that this protein functions as γ-tubulin. Moreover, both groups provides novel insight into architecture of human a scaffold for PCM assembly. show how centriolar proteins con- centrosome. Biol. Open 17 Aug 2012(doi:10.1042/ bio.20122337) | Mennella, V. et al. Subdiffraction- Similarly, Mennella et al. and tribute to the expansion of the PCM. resolution fluorescence microscopy reveals a Fu and Glover used 3D-SIM to For example, they observed that domain of the centrosome critical for pericentriolar material organization. Nature Cell quantitatively map the architecture of Centrosomin (CNN) and γ-tubulin Biol. 21 Oct 2012 (doi:10.1038/ncb2597) | Fu, J. & the PCM in Drosophila melanogaster are first recruited to an inner PCM Glover, D. M. Structured illumination of the cells. They found that the PCM is layer prior to expanding into the interface between centriole and peri-centriolar material. Open Biol. 2, 120104 (2012) organized into two main structural outer part of the PCM together with NPG

NATURE REVIEWS | MOLECULAR CELL BIOLOGY VOLUME 13 | DECEMBER 2012