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Un flagelle est un organite qui par ses mouvements permet la mobilité d'une cellule. Une même cellule peut en posséder plusieurs. Au plan fonctionnel, on peut considérer les flagelles comme des prolongements du cytoplasme. Ils sont capables de mouvements périodiques induisant le déplacement de la cellule dans un milieu liquide, ou du milieu liquide autour de la cellule. On trouve des flagelles chez les procaryotes (archées et bactéries) comme chez les eucaryotes, mais fondés sur des principes génétiques, architecturaux et fonctionnels très différents.

Chez les procaryotes, les flagelles sont des structures semi-rigides ancrées dans la membrane plasmique et dont l'embase est constituée par un moteur moléculaire qui assure sa rotation. Les flagelles des bactéries et des archées se ressemblent en apparence mais diffèrent profondément, si bien qu'on pense aujourd'hui qu'ils résultent d'une convergence évolutive plutôt que d'une homologie.
Chez les eucaryotes, les flagelles sont mus p

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Eukaryota

Les eucaryotes (Eukaryota) sont un domaine regroupant tous les organismes, unicellulaires ou multicellulaires, qui se caractérisent par la présence d'un noyau et généralement d'organites spécialisés

Bactérie

Le terme bactérie est un nom vernaculaire qui désigne certains organismes vivants microscopiques et procaryotes présents dans tous les milieux. Le plus souvent unicellulaires, elles sont parfois plu

Protista

Les protistes, sont des microorganismes eucaryotes à organisation cellulaire dite simple, unicellulaire le plus souvent, multicellulaire parfois mais sans tissus spécialisés. Ce sont des Eucaryote

Mechanism of DegU-dependent activation of flagellar gene transcription in Listeria monocytogenes

Diane Baer

Flagellar motility is an important process for bacterial survival. It allows bacteria to move to aquire nutrients or to retreat from unfavorable environments. In the Gram-positive bacterium Listeria monocytogenes, flagellar motility is a temperature-dependent process, being restricted to temperatures below 37°C. This regulation is mediated by the activities of the DegU response regulator, the MogR transcriptional repressor and GmaR, the MogR antirepressor. Transcriptional regulation of the fliN-gmaR promoter is central to flagellar motility regulation as pfliN-gmaR is transcriptionally activated by DegU and is also MogR repressed. However, the mechanism by which DegU mediates transcriptional activation of the fliN-gmaR promoter is not well understood. In this study, we further investigated the mechanisms controlling transcription initiating at the fliN-gmaR promoter by performing two comprehensive transposon mutagenesis screens to identify any additional factors involved in the activation and repression of pfliN-gmaR. The mutagenesis screen performed at 30°C to identify factors involved in pfliN-gmaR transcriptional activation led to the identification of a novel factor. We demonstrated that Lmo0866, a protein from the DEAD-box protein family, is required for transcriptional activation of pfliN-gmaR and therefore flagellar motility. Moreover, we identified CodY as being involved in the repression of pfliN-gmaR at 37°C.

2010

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Flagellar membranes are rich in raft-forming phospholipids

Adrian Schmid

The observation that the membranes of flagella are enriched in sterols and sphingolipids has led to the hypothesis that flagella might be enriched in raft-forming lipids. However, a detailed lipidomic analysis of flagellar membranes is not available. Novel protocols to detach and isolate intact flagella from Trypanosoma brucei procyclic forms in combination with reverse-phase liquid chromatography high-resolution tandem mass spectrometry allowed us to determine the phospholipid composition of flagellar membranes relative to whole cells. Our analyses revealed that phosphatidylethanolamine, phosphatidylserine, ceramide and the sphingolipids inositol phosphorylceramide and sphingomyelin are enriched in flagella relative to whole cells. In contrast, phosphatidylcholine and phosphatidylinositol are strongly depleted in flagella. Within individual glycerophospholipid classes, we observed a preference for ether-type over diacyl-type molecular species in membranes of flagella. Our study provides direct evidence for a preferential presence of raft-forming phospholipids in flagellar membranes of T. brucei.

Company Of Biologists Ltd2015

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Mutations in the polyglutamylase geneTTLL5, expressed in photoreceptor cells and spermatozoa, are associated with cone-rod degeneration and reduced male fertility

Hereditary retinal degenerations encompass a group of genetic diseases characterized by extreme clinical variability. Following next-generation sequencing and autozygome-based screening of patients presenting with a peculiar, recessive form of cone-dominated retinopathy, we identified five homozygous variants [p.(Asp594fs), p.(Gln117*), p.(Met712fs), p.(Ile756Phe), and p.(Glu543Lys)] in the polyglutamylase-encoding gene TTLL5, in eight patients from six families. The two male patients carrying truncating TTLL5 variants also displayed a substantial reduction in sperm motility and infertility, whereas those carrying missense changes were fertile. Defects in this polyglutamylase in humans have recently been associated with cone photoreceptor dystrophy, while mouse models carrying truncating mutations in the same gene also display reduced fertility in male animals. We examined the expression levels of TTLL5 in various human tissues and determined that this gene has multiple viable isoforms, being highly expressed in testis and retina. In addition, antibodies against TTLL5 stained the basal body of photoreceptor cells in rat and the centrosome of the spermatozoon flagellum in humans, suggesting a common mechanism of action in these two cell types. Taken together, our data indicate that mutations in TTLL5 delineate a novel, allele-specific syndrome causing defects in two as yet pathogenically unrelated functions, reproduction and vision.

Oxford University Press2016

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PHYS-301: Biophysics : physics of the cell

In this course we will study the cell (minimum unit of life) and its components. We will study several key cellular features: Membranes, genomes, channels and receptors. We will apply the laws of physics to develop models to make quantitative and predictive statements.

BIO-464: Scientific project design in cell and developmental biology

Students are lead to understand selected concepts in cell and developmental biology, primarily through the analysis of scientific literature, and then to apply these concepts to the design and execution of a group project in the Gönczy or Oates laboratory.

BIO-244: Physics of the cell

Living organisms evolve in a physical world: their cells respond to mechanics, electricity and light. In this course, we will describe the behavior and function of cells using physical principles.