Structural bases of cellular processes

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Structural bases of cellular processes

Group leader: Sergio Marco

Assistant group leader: Anne-Marie Tassin

We are mainly focused in the comprehension of the mechanisms for cell signal integration at the centrosome-microtubules system level. For this purpose, we study between different centrosomal proteins and their functional consequences and the structural interactions on the cell cycle and on cilia organisation. We approach these questions by molecular biology and biochemischal methods as well as by cryo-electron tomography. Thus, we have recently described the procentriole assembly process. Furthermore, we develop 2D and 3D chemical mapping by secondary ions mass spectrometry and energy filter transmission electron tomography. This requires sensitivity and resolution improvementas well as specific data-processing tools developments. Up to date, 53 publications and book chapters in cell biology and bio-informatics journals have been published form January 2006 and industrial collaborations (Jeol, Digisens, Sanofi-Pasteur) has been established resulting in the commercialization of a graphic card based accelerated software for tomographic reconstructions presently distributed by Digisens (http://www.digisens.fr/fr/soft/2-Digi_ECT.html).

Procentriole structure: Visualization of the initial procentriole structures by cryo-electron tomography. (a), Central structure of the cartwheel (boxed) and connecting stalk (arrow). (b), Magnified view of the boxed region in (a) (projection of 23 images). (c), The connecting stalk (box in left panel) is observed in the absence of a procentriole. (d), Magnified view of the boxed region in (c). Scale bars, 100 nm (a, c) and 20 nm (b, d). (Adapted from Guichard et al., EMBO J. 2010)

Model of human procentriole assembly: a, The first step of procentriole assembly involves the formation of a stalk at the proximal end of the mature centriole (b). c, The cartwheel assembles from this stalk and organises the procentriolar wall, where some A-microtubules start growing from the γ-TuRCs. d, Enlargment of the procentriole shown in (c). e, Before completion of the nine A-microtubule round, some B-microtubules start growing from the wall of A microtubules. f, B-microtubules grow bidirectionally, and C-microtubules start growing from the wall of the B-microtubules. g, C-microtubules grow bidirectionally until the B- and C-microtubules reach the proximal end of the A-microtubule. h, Growth continues at the distal end until completion of the microtubule triplet blades.

Key publications

Year of publication: 2010

Desulfovibrio magneticus RS-1 contains an iron- and phosphorus-rich organelle distinct from its bullet-shaped magnetosomes
Byrne M. E., Ball D. A., Guerquin-Kern J.-L., Rouiller I., Wu T.-D., Downing K. H., Vali H. & Komeili A.
P Natl Acad Sci USA (2010), 107, 12263-12268
DOI: 10.1073/pnas.1001290107
Intracellular magnetite crystal formation by magnetotactic bacteria has emerged as a powerful model for investigating the cellular and molecular mechanisms of biomineralization, a process common to all branches of life. Although magnetotactic bacteria are phylogenetically diverse and their crystals morphologically diverse, studies to date have focused on a few, closely related species with similar crystal habits. Here, we investigate the process of magnetite biomineralization in Desulfovibrio magneticus sp.
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Procentriole assembly revealed by cryo-electron tomography
Guichard P., Chrétien D., Marco S. & Tassin A.-M.
The EMBO Journal (2010), 29, 1565-1572
DOI: 10.1038/emboj.2010.45
Centrosomes are cellular organelles that have a major role in the spatial organisation of the microtubule network. The centrosome is comprised of two centrioles that duplicate only once during the cell cycle, generating a procentriole from each mature centriole. Despite the essential roles of centrosomes, the detailed structural mechanisms involved in centriole duplication remain largely unknown. Here, we describe human procentriole assembly using cryo-electron tomography.
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Year of publication: 2009

Marker-free image registration of electron tomography tilt-series
Sorzano C. O., Messaoudi C., Eibauer M., Bilbao-Castro J. R., Hegerl R., Nickell S., Marco S. & Carazo J. M.
BMC Bioinformatics (2009), 10, 124-135
DOI: 10.1186/1471-2105-10-124
Background

Tilt series are commonly used in electron tomography as a means of collecting three-dimensional information from two-dimensional projections. A common problem encountered is the projection alignment prior to 3D reconstruction. Current alignment techniques usually employ gold particles or image derived markers to correctly align the images. When these markers are not present, correlation between adjacent views is used to align them.
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Year of publication: 2007

TomoJ: tomography software for 3D reconstruction in transmission electron microscopy
Messaoudi C., Boudier T., Sorzano C. O. S. & Marco S.
BMC Bioinformatics (2007), 8, 288-297
DOI: 10.1186/1471-2105-8-288
Background

Transmission electron tomography is an increasingly common three-dimensional electron microscopy approach that can provide new insights into the structure of subcellular components. Transmission electron tomography fills the gap between high resolution structural methods (X-ray diffraction or nuclear magnetic resonance) and optical microscopy. We developed new software for transmission electron tomography, TomoJ. TomoJ is a plug-in for the now standard image analysis and processing software for optical microscopy, ImageJ.
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Imagerie intégrative : de la molécule à l'organisme

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