isolation-fluorescence-imaging-for-single-particle-reconstruction

Isolation and Fluorescence Imaging for Single-particle Reconstruction of <em>Chlamydomonas</em> Centrioles

Centrioles are large macromolecular assemblies important for the proper execution of fundamental cell biological processes such as cell division, cell ...

University of Geneva

Centrioles are evolutionarily conserved macromolecular structures that are fundamental to form cilia, flagella, and centrosomes. Centrioles are 9-fold symmetrical microtubule-based cylindrical barrels comprising three regions that can be clearly distinguished in the Chlamydomonas reinhardtii organelle: an ∼100-nm-long proximal region harboring a cartwheel; an ∼250-nm-long central core region containing a Y-shaped linker; and an ∼150-nm-long distal region ending at the transitional plate. Despite the discovery of many centriolar components, no protein has been localized specifically to the central core region in Chlamydomonas thus far. Here, combining relative quantitative mass spectrometry and super-resolution microscopy on purified Chlamydomonas centrioles, we identified POB15 and POC16 as two proteins of the central core region, the distribution of which correlates with that of tubulin glutamylation. We demonstrated that POB15 is an inner barrel protein within this region. Moreover, we developed an assay to uncover temporal relationships between centriolar proteins during organelle assembly and thus established that POB15 is recruited after the cartwheel protein CrSAS-6 and before tubulin glutamylation takes place. Furthermore, we discovered that two poc16 mutants exhibit flagellar defects, indicating that POC16 is important for flagellum biogenesis. In addition, we discovered that WDR90, the human homolog of POC16, localizes to a region of human centrioles that we propose is analogous to the central core of Chlamydomonas centrioles. Moreover, we demonstrate that WDR90 is required for ciliogenesis, echoing the findings in Chlamydomonas. Overall, our work provides novel insights into the identity and function of centriolar central core components.

Identification of Chlamydomonas Central Core Centriolar Proteins Reveals a Role for Human WDR90 in Ciliogenesis.

The cartwheel is a striking structure critical for building the centriole, a microtubule-based organelle fundamental for organizing centrosomes, cilia, and flagella. Over the last 50 years, the cartwheel has been described in many systems using electron microscopy, but the molecular nature of its constituent building blocks and their assembly mechanisms have long remained mysterious. Here, we review discoveries that led to the current understanding of cartwheel structure, assembly, and function. We focus on the key role of SAS-6 protein self-organization, both for building the signature ring-like structure with hub and spokes, as well as for their vertical stacking. The resemblance of assembly intermediates in vitro and in vivo leads us to propose a novel registration step in cartwheel biogenesis, whereby stacked SAS-6-containing rings are put in register through interactions with peripheral elements anchored to microtubules. We conclude by evoking some avenues for further uncovering cartwheel and centriole assembly mechanisms.

Article	Year
Identification of Chlamydomonas Central Core Centriolar Proteins Reveals a Role for Human WDR90 in Ciliogenesis. Current biology : CB\| PubMed ID: 28781053	2017
The Rise of the Cartwheel: Seeding the Centriole Organelle. BioEssays : news and reviews in molecular, cellular and developmental biology\| PubMed ID: 29508910	2018

Virginie Hamel

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