Schneider, F. Z. | Search bioRxiv

bioRxiv2022

Molecular architecture of the C. elegans centriole

Uncovering organizing principles of organelle assembly is a fundamental pursuit in the life sciences. C. elegans was key in identifying evolutionary conserved components governing assembly of the centriole organelle. However, localizing these components with high precision has been hampered by the minute size of the worm centriole, thus impeding understanding of underlying assembly mechanisms. Here, we used Ultrastructure Expansion coupled with STimulated Emission Depletion microscopy (U-Ex-STED), as well as electron microscopy (EM) and tomography (ET), to decipher the molecular architecture of the worm centriole. Achieving an effective lateral resolution of [~]14 nm, we localize centriolar and PeriCentriolar Material (PCM) components in a comprehensive manner with utmost spatial precision. We uncovered that the procentriole assembles from a location on the centriole margin characterized by SPD-2 and ZYG-1 accumulation. Moreover, we found that SAS-6 and SAS-5 are present in the nascent procentriole, with SAS-4 and microtubules recruited thereafter. We registered U-Ex-STED and EM data using the radial array of microtubules, thus allowing us to map each centriolar and PCM protein to a specific ultrastructural compartment. Importantly, we discovered that SAS-6 and SAS-4 exhibit a radial symmetry that is offset relative to microtubules, leading to a chiral centriole ensemble. Furthermore, we establish that the centriole is surrounded by a region from which ribosomes are excluded and to which SAS-7 localizes. Overall, our work uncovers the molecular architecture of the C. elegans centriole in unprecedented detail and establishes a comprehensive framework for understanding mechanisms of organelle biogenesis and function.

cell biology↗

bioRxiv2022

Atypical and distinct microtubule radial symmetries in the centriole and the axoneme of Lecudina tuzetae.

The centriole is a minute cylindrical organelle present in a wide range of eukaryotic species. Most centrioles have a signature 9-fold radial symmetry of microtubules that is imparted onto the axoneme of the cilia and flagella they template, with 9 centriolar microtubule doublets growing into 9 axonemal microtubule doublets. There are exceptions to the 9-fold symmetrical arrangement of axonemal microtubules, with lower or higher fold symmetries in some species. In the few cases where this has been examined, such alterations in axonemal symmetries are grounded in likewise alterations in centriolar symmetries. Here, we examine the question of microtubule number continuity between centriole and axoneme in flagellated gametes of the gregarine Lecudina tuzetae, which have been reported to exhibit a 6-fold radial symmetry of axonemal microtubules. We used time-lapse differential interference microscopy to identify the stage at which flagellated gametes are present. Thereafter, using electron microscopy and ultrastructure-expansion microscopy coupled to STimulated Emission Depletion (STED) super-resolution imaging, we uncover that a 6- or 5-fold radial symmetry in the axoneme is accompanied by an 8-fold radial symmetry in the centriole. We conclude that there can be plasticity in the transition between centriolar and axonemal microtubules.

cell biology↗