hPOC5 is a centrin-binding protein required for assembly of full-length centrioles

Centrin has been shown to be involved in centrosome biogenesis in a variety of eukaryotes. In this study, we characterize hPOC5, a conserved centrin-binding protein that contains Sfi1p-like repeats. hPOC5 is localized, like centrin, in the distal portion of human centrioles. hPOC5 recruitment to procentrioles occurs during G2/M, a process that continues up to the full maturation of the centriole during the next cell cycle and is correlated with hyperphosphorylation of the protein. In the absence of hPOC5, RPE1 cells arrest in G1 phase, whereas HeLa cells show an extended S phase followed by cell death. We show that hPOC5 is not required for the initiation of procentriole assembly but is essential for building the distal half of centrioles. Interestingly, the hPOC5 family reveals an evolutionary divergence between vertebrates and organisms like Drosophila melanogaster or Caenorhabditis elegans, in which the loss of hPOC5 may correlate with the conspicuous differences in centriolar structure

Tracing the origins of centrioles, cilia, and flagella

Centrioles/basal bodies (CBBs) are microtubule-based cylindrical organelles that nucleate the formation of centrosomes, cilia, and flagella. CBBs, cilia, and flagella are ancestral structures; they are present in all major eukaryotic groups. Despite the conservation of their core structure, there is variability in their architecture, function, and biogenesis. Recent genomic and functional studies have provided insight into the evolution of the structure and function of these organelles

Multiciliated Cells in Animals.

International audienceMany animal cells assemble single cilia involved in motile and/or sensory functions. In contrast, multiciliated cells (MCCs) assemble up to 300 motile cilia that beat in a coordinate fashion to generate a directional fluid flow. In the human airways, the brain, and the oviduct, MCCs allow mucus clearance, cerebrospinal fluid circulation, and egg transportation, respectively. Impairment of MCC function leads to chronic respiratory infections and increased risks of hydrocephalus and female infertility. MCC differentiation during development or repair involves the activation of a regulatory cascade triggered by the inhibition of Notch activity in MCC progenitors. The downstream events include the simultaneous assembly of a large number of basal bodies (BBs)-from which cilia are nucleated-in the cytoplasm of the differentiating MCCs, their migration and docking at the plasma membrane associated to an important remodeling of the actin cytoskeleton, and the assembly and polarization of motile cilia. The direction of ciliary beating is coordinated both within cells and at the tissue level by a combination of planar polarity cues affecting BB position and hydrodynamic forces that are both generated and sensed by the cilia. Herein, we review the mechanisms controlling the specification and differentiation of MCCs and BB assembly and organization at the apical surface, as well as ciliary assembly and coordination in MCCs

Basal bodies across eukaryotes series: basal bodies in the freshwater planarian Schmidtea mediterranea.

International audienceThe freshwater planarian Schmidtea mediterranea has recently emerged as a valuable model system to study basal bodies (BBs) and cilia. Planarians are free-living flatworms that use cilia beating at the surface of their ventral epidermis for gliding along substrates. The ventral epidermis is composed of multiciliated cells (MCCs) that are similar to the MCCs in the respiratory airways, the brain ventricles, and the oviducts in vertebrates. In the planarian epidermis, each cell assembles approximately eighty cilia that beat in a coordinate fashion across the tissue. The BBs that nucleate these cilia all assemble de novo during terminal differentiation of MCCs. The genome of the planarian S. mediterranea has been sequenced and efficient methods for targeting gene expression by RNA interference are available. Defects induced by perturbing the expression of BB proteins can be detected simply by analyzing the locomotion of planarians. BBs are present in large numbers and in predictable orientation, which greatly facilitates analyses by immunofluorescence and electron microscopy. The great ease in targeting gene expression and analyzing associated defects allowed to identify a set of proteins required for BB assembly and function in planarian MCCs. Future technological developments, including methods for transgenic expression in planarians and in related species, will achieve turning free-living flatworms into powerful model systems to study MCCs and the associated human pathologies

Etude de mutants d'"Arabidopsis thaliana" affectés dans l'organisation du cytosquelette

La morphogenèse cellulaire, phénomène crucial pour le développement des végétaux, dépend étroitement du cytosquelette chez ces organismes, et en particulier des structures microtubulaires. L'étude de mutants d'Arabidopsis thaliana affectés dans ces structures permet non seulement d'identifier les mécanismes moléculaires qui président à leur mise en place, mais aussi de comprendre la manière dont elles contrôlent la morphogenèse de la cellule et, par conséquent, de la plante. Nous avons étudié les mutants tonneau (tonl et ton2), qui présentent d'importantes altérations morphologiques attribuées à des anomalies dans l'organisation de deux structures microtubulaires typiques des végétaux : la bande de préprophase, et les microtubules corticaux d'interphase. La mutation tonl affecte deux gènes similaires qui codent des protéines de 30 kDa, très conservées chez les plantes, dont nous avons montré qu'elles sont associées au cytosquelette microtubulaire d'interphase...Cell morphogenesis is crucial to plant development and depends on the cytoskeleton, especially the microtubule arrays. Study of Arabidopsis thaliana mutants with altered microtubule arrays not only allows to identify the molecular mechanisms governing their organization, but also provides further understanding of how these arrays control cell morphogenesis, and thus plant morphogenesis. We have studied the tonneau mutants (ton1 and ton2), which exhibit profound morphological alterations resulting from defective organization of two plant-specific microtubule arrays: the preprophase band and the interphase cortical array. The ton1 mutation disrupts two similar genes encoding 30 kDa proteins that are highly conserved among higher plants and associate to the interphase microtubular cytoskeleton. The gene affected by the ton2 mutation codes for a putative regulatory subunit of a type-2A protein phosphatase...ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Générer une symétrie bilatérale à partir de composants asymétriques

International audienc

The planarian Schmidtea mediterranea as a model for studying motile cilia and multiciliated cells.

International audienceIn the past few years, the freshwater planarian Schmidtea mediterranea has emerged as a powerful model system to study the assembly and function of cilia. S. mediterranea is a free-living flatworm that uses the beating of cilia on its ventral epidermis for locomotion. The ventral epidermis is composed of a single layer of multiciliated cells highly similar to the multiciliated cells that line the airway, the brain ventricles, and the oviducts in humans. The genome of S. mediterranea has been sequenced and efficient methods for targeting gene expression by RNA interference (RNAi) are available. Locomotion defects induced by perturbing the expression of ciliary genes can be often detected by simple visual screening, and more subtle defects can be detected by measuring locomotion speed. Cilia are present in large numbers and are directly accessible, which facilitates analyses by immunofluorescence and electron microscopy. Here we describe a set of methods for maintaining planarians in the lab. These include gene knockout by RNAi, cilia visualization by immunofluorescence, transmission electron microscopy, and live imaging