Centriole | EPFL Graph Search

In cell biology a centriole is a cylindrical organelle composed mainly of a protein called tubulin. Centrioles are found in most eukaryotic cells, but are not present in conifers (Pinophyta), flowering plants (angiosperms) and most fungi, and are only present in the male gametes of charophytes, bryophytes, seedless vascular plants, cycads, and Ginkgo. A bound pair of centrioles, surrounded by a highly ordered mass of dense material, called the pericentriolar material (PCM), makes up a structure called a centrosome. Centrioles are typically made up of nine sets of short microtubule triplets, arranged in a cylinder. Deviations from this structure include crabs and Drosophila melanogaster embryos, with nine doublets, and Caenorhabditis elegans sperm cells and early embryos, with nine singlets. Additional proteins include centrin, cenexin and tektin. The main function of centrioles is to produce cilia during interphase and the aster and the spindle during cell division.

Functional characterization of the SAS-4-related protein CPAP in centrosome biology of human cells

Gregor Kohlmaier

The centrosome is an organelle that resides at the center of most animal cells and comprises two microtubule-based centriole cylinders surrounded by pericentriolar material (PCM). The centrosome plays a fundamental role for nucleating and organizing a radial array of cytoplasmic microtubules during interphase and promoting the assembly of the mitotic spindle during mitosis. In proliferating cells, the centrosome duplicates once per cell cycle, a process that involves notably the formation of one procentriole at the base of each centriole. The procentriole then grows until it reaches the same size of its associated centriole. The formation of supernumerary centrosomes causes severe problems, since this can lead to multipolar spindle formation, chromosome missegregation and genomic instability, which are hallmarks of cancer cells. The mechanisms regulating centrosome duplication are still incompletely understood. We have studied the role of the centrosomal P4.1-associated protein (CPAP) in human cells. We found that this protein is required for efficient growth of cytoplasmic microtubules from centrosomes as well as for centrosome duplication. There, CPAP is required at an early step during procentriole assembly, after the incorporation of HsSAS-6 but before that of Centrin. Importantly, we found also that the overexpression of CPAP leads to abnormal elongation of procentrioles and centrioles, indicating that the levels of CPAP determine centriole length. Excess CPAP levels furthermore lead to the formation of multiple procentrioles along overly elongated centrioles, multipolar spindle formation and cell division errors. Therefore, proper regulation of proteins such as CPAP that set centriole length contributes to ensure genome integrity. Overall, we gained important insights into the functions of CPAP at the centrosome and identified a novel control mechanism of centriole length. This will be relevant for a better understanding of how centrosomes function in the progression of cancer and other diseases.

EPFL2009

Integrative approach to analyze the proximal region of the Trichonympha agilis centriole

Veronika Nemcíková Villímová

The centrosome, the major microtubule organizing center in animal cells, is composed of two orthogonally arranged centrioles and surrounding pericentriolar material. Centrioles are evolutionary conserved organelles characterized by a nine-fold symmetry of microtubules and are built around a cartwheel in their proximal region. The overall architecture at ~ 40 Å resolution of the exceptionally long proximal region of Trichonympha spp. basal body has been uncovered previously using cryo-electron tomography (cryo-ET) followed by subtomogram averaging. The resulting 3D map revealed not only a central cartwheel hub that can accommodate rings of the evolutionarily conserved SAS-6 proteins, but also novel features, whose identity is unknown. In this thesis, we used T. agilis, which is the only Trichonympha sp. with an assembled genome and transcriptomic data, to gain some more insight into the structure, composition and first steps of cartwheel assembly. With the aim of generating a high-resolution 3D model of the T. agilis proximal region, we used cryo-ET and subtomogram averaging to refine the structure of the cartwheel hub and cartwheel inner densities (CID). We uncovered that the CID is polarized, and discovered inter-cartwheel pillars (ICP) between superimposed cartwheel rings. Moreover, we discovered and analysed a new type of the cartwheel of Teranympha mirabilis with a novel type of cartwheel central densities (CCD). We also analyzed the composition of the proximal region of the T. agilis centriole using a proteomic approach. We optimized a density gradient centrifugation protocol for isolation of the T. agilis rostrum, which harbors ~ 1400 centrioles, and performed protein correlation profiling. In this manner, we have identified 47 candidates of the rostrum proteome, including three new T. agilis SAS-6 homologs, which were further characterized. Furthermore, we addressed the oligomerization properties of human and two T. agilis SAS-6 proteins (HsSAS-6, TaSAS-6_1 and TaSAS-6_2) in vitro. We found that HsSAS-6 requires an interaction partner in order to be stabilized and form rings and stacks. In contrast, TaSAS-6_1 did not oligomerize in our setup, and TaSAS-6_2 is able to oligomerize and form different types of oligomers, rings included. In conclusion, the structure and composition of the proximal region of the T. agilis centriole uncovered here are anticipated to be of a general significance for studies of the biogenesis and structure of centrioles.

EPFL2018

Mechanisms of differential centriole inheritance in C. elegans

Lukas von Tobel

Centrosomes are the principal microtubule organizing center (MTOC) of animal cells and comprise a pair of centrioles surrounded by pericentriolar material (PCM). Centriole number must be carefully regulated to ensure bipolar spindle formation and thus faithful chromosome segregation. In the germ line of most metazoan species, centrioles are maintained during spermatogenesis, but eliminated during oogenesis. Such differential behavior ensures that the appropriate number of centrioles is present in the newly fertilized zygote. In this doctoral thesis work, I describe our investigation of centriole elimination during oogenesis in C. elegans and I characterize sas-1, a factor important for maintaining centriole integrity, especially during spermatogenesis, to ensure that two centrioles are present in the zygote. Despite being a fundamental feature of sexual reproduction in metazoans, themechanisms governing centriole elimination during oogenesis are poorly understood. We investigate this question using antibodies directed against centriolar components and serial-section electron microscopy and we establish that centrioles are eliminated during the diplotene stage of the meiotic cell cycle. Moreover, we show that centriole elimination is compromised upon depletion of the helicase CGH-1. We also find that somatic cellsmake a minor contribution to this process, and demonstrate that the germcell karyotype is important for timely centriole elimination. These findings set the stage for a mechanistic dissection of centriole elimination in ametazoan organism. How centriole integrity is ensured after organelle assembly is poorly understood, including in sperm cells, where such integrity is particularly critical. In a genetic screen in C. elegans, sas-1 was identified as a locus important for the maintenance of centrioles in the early embryo. Our analysis reveals that sperm-derived sas-1 mutant centrioles lose their integrity shortly after fertilization, and that a related defect occurs when maternal sas-1 function is absent. We establish that sas-1 encodes a C2 domain containing protein that localizes to centrioles once they are assembled. Futhermore, we demonstrate that SAS-1 can bind and stabilize microtubules when expressed in human cells. We also identify C2CD3, a protein required for proper centriole formation, as a putative mammalian SAS-1 homolog. Together, we uncover an important component required for maintaining centrioles in sperm cells to ensure that two centrioles are present after fertilization and thus guarantee the continuity of the species.

EPFL2014