Eric Maréchal

Université Grenoble Alpes, Grenoble, Rhône-Alpes, France

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Publications (117)457.29 Total impact

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    ABSTRACT: Monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) are the major lipid components of photosynthetic membranes and hence the most abundant lipids in the biosphere. They are essential for the assembly and function of the photosynthetic apparatus. In Arabidopsis, the first step of galactolipid synthesis is catalyzed by MGDG synthase 1 (MGD1), which transfers a galactosyl residue from UDP-galactose to diacylglycerol (DAG). MGD1 is a monotopic protein embedded in the inner envelope membrane of chloroplasts. Once produced, MGDG is transferred to the outer envelope membrane, where DGDG synthesis occurs, and to thylakoids. Here we present the crystal structures of MGD1, both unliganded and complexed with UDP. MGD1 has a long and flexible region (~50 amino acids) that is required for DAG binding. The structures reveal critical features of the MGD1 catalytic mechanism and its membrane binding mode, tested on biomimetic Langmuir monolayers, giving insights into chloroplast membrane biogenesis. The structural plasticity of MGD1, ensuring a very rapid capture and utilization of DAG, and its interaction with anionic lipids possibly driving the construction of lipoproteic clusters, are consistent with the role of this enzyme, not only in the expansion of the inner envelope membrane, but also in supplying MGDG to the outer envelope and nascent thylakoid membranes. This article is protected by copyright. All rights reserved.
    No preview · Article · Jan 2016 · The Plant Journal
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    ABSTRACT: Biogenesis of photosynthetic membranes relies on galactoglycerolipids, which are synthesized via pathways that are dispatched over several cell compartments. This membrane biogenesis requires both trafficking of lipid intermediates and a tight homeostatic regulation. In this work, we address the role of ALA10, a P4 type-ATPase, in a process counteracting with monogalactosyldiacylglycerol (MGDG) shortage in Arabidopsis leaves. ALA10 can interact with protein partners, ALIS1 or ALIS5 (ALA-Interacting Subunit 1 or 5), leading to differential endomembrane localizations of the interacting proteins, close to the plasma membrane with ALIS1 or to chloroplasts with ALIS5. ALA10 interacts also with Fatty acid desaturase 2 (FAD2) and modification of ALA10 expression affects phosphatidylcholine (PC) fatty acyl desaturation by disturbing the balance between FAD2 and FAD3 activities. Modulation of ALA10 expression downstream impacts on fatty acyl composition of chloroplast PC. ALA10 expression also enhances leaf growth and improves the MGDG over PC level, possibly through MGDG synthase 1 (MGD1) activation by phosphatidic acid. The positive effect of ALA10 on leaf development is significant in conditions such as upon treatment of plants with Galvestine-1, an inhibitor of MGDG synthases, or when plants are grown at chilling temperature.
    No preview · Article · Dec 2015 · Plant physiology
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    ABSTRACT: In higher plants, fatty acids (FAs) with 18 carbons (18C) represent about 70% of total FAs, the most abundant species being 18:2 and 18:3. These two polyunsaturated FAs (PUFAs) represent about 55% of total FAs in Arabidopsis cell suspension cultures, whereas 18:1 represents about 10%. The level of PUFAs may vary, depending on ill-defined factors. Here, we compared various sets of plant cell cultures and noticed a correlation between the growth rate of a cell population and the level of unsaturation of 18C FAs. These observations suggest that the final level of PUFAs might depend in part on the rate of cell division, and that FAD2 and FAD3 desaturases, which are respectively responsible for the formation of 18:2 and 18:3 on phospholipids, have limiting activities in fast-growing cultures. In plant cell culture, phosphate (Pi) deprivation is known to impair cell division and to trigger lipid remodeling. We observed that Pi starvation had no effect on the expression of FAD genes, and that the level of PUFAs in this situation was also correlated with the growth rate. Thus, the level of PUFAs appears as a hallmark in determining cell maturity and aging.
    Full-text · Article · Oct 2015 · Scientific Reports
  • Lina-Juana Dolch · Eric Maréchal

    No preview · Article · Sep 2015 · Marine Drugs
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    Full-text · Article · Sep 2015
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    ABSTRACT: Biochemical processes rely on elaborate networks containing thousands of compounds participating in thousands of reaction. Rapid turnover of diverse metabolites and lipids in an organism is an essential part of homeostasis. It affects energy production and storage, two important processes utilized in bioengineering. Conventional approaches to simultaneously quantify a large number of turnover rates in biological systems are currently not feasible. Here we show that pulse-chase analysis followed by laser ablation electrospray ionization mass spectrometry (LAESI-MS) enable the simultaneous and rapid determination of metabolic turnover rates. The incorporation of ion mobility separation (IMS) allowed an additional dimension of analysis, i.e., the detection and identification of isotopologs based on their collision cross sections. We demonstrated these capabilities by determining metabolite, lipid, and peptide turnover in the photosynthetic green algae, Chlamydomonas reinhardtii, in the presence of 15N-labeled ammonium chloride as the main nitrogen source. Following the reversal of isotope patterns in the chase phase by LAESI-IMS-MS revealed the turnover rates and half-lives for biochemical species with a wide range of natural concentrations, e.g., chlorophyll metabolites, lipids, and peptides. For example, the half-lives of lyso-DGTS(16:0) and DGTS(18:3/16:0), t1/2 = 43.6 ± 4.5 h and 47.6 ± 2.2 h, respectively, provided insight into lipid synthesis and degradation in this organism. Within the same experiment, half-lives for chlorophyll a, t1/2 = 24.1 ± 2.2 h, and a 2.8 kDa peptide, t1/2 = 10.4 ± 3.6 h, were also determined.
    Full-text · Article · Aug 2015 · Analytica Chimica Acta
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    ABSTRACT: The metabolome of an organism results from a complex biochemical network of thousands of enzymatic reaction and metabolites. Mass spectrometry (MS) in combination with extraction and separation methods has been successfully applied for the detection, identification, and quantitation of these chemical species. However, these methods are slow and provide limited information on the metabolic fluxes essential for the understanding of disease response to treatment and for mechanism of action studies. Stable isotope pulse-chase analysis can be used to study critical pathways in metabolic networks by monitoring the propagation of isotope tracers using MS.1 Pulse-chase analysis has been used in the clinical laboratory to determine the turnover rates of peptides in diseases such as amyloidosis. In the pulse phase of these experiments, cells assimilate the labeled molecules, whereas in the chase phase unlabeled molecules are reintroduced into the cells. Molecular turnover rates and half-lives of the affected molecules can be calculated by measuring the kinetics of these processes.
    Full-text · Conference Paper · Mar 2015

  • No preview · Article · Mar 2015 · Medecine sciences: M/S
  • Florian Chevalier · Éric Maréchal

    No preview · Article · Mar 2015
  • Florian Chevalier · Éric Maréchal
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    ABSTRACT: In eukaryotic cells, phosphatidic acid (PA) and diacylglycerol (DAG), are at the origin of all membrane glycerolipids. Their interconversion is achieved by dephosphorylation of PA and phosphorylation of DAG: they form therefore a metabolic hub. PA and DAG are also known to be versatile signaling molecules. Two independent pharmacological screenings conducted on plant and human targets, led to the discovery of a new family of compounds acting on enzymes binding to either PA or DAG, in biological contexts that seemed initially independent. On the one hand, in plants, monogalactosyldiacylglycerol synthases (MGDG synthases or MGD) are responsible for the synthesis of MGDG, which is the most profuse lipid of photosynthetic membranes, and thus essential for metabolism and development. MGD use DAG as substrate. On the other hand, in mammals, phospholipases D (PLD), that produce PA, are involved in a variety of signaling cascades that control a broad spectrum of cellular functions, and play a role in the development of cancers. The two independent pharmacological screenings described in this review aimed to identify inhibitory molecules of either MGD of the plant model Arabidopsis, or human PLD. In both cases, the obtained molecules are piperidinyl-benzimidazolone derivatives, thereby allowing to propose this family of molecules as a novel source of inspiration for the search of compounds interfering with glycerolipid metabolism, that could be useful for other biological and therapeutics contexts. © 2015 médecine/sciences – Inserm.
    No preview · Article · Mar 2015 · Medecine sciences: M/S
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    Lina-Juana Dolch · Eric Maréchal
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    ABSTRACT: The diatom Phaeodactylum is rich in very long chain polyunsaturated fatty acids (PUFAs). Fatty acid (FA) synthesis, elongation, and desaturation have been studied in depth in plants including Arabidopsis, but for secondary endosymbionts the full picture remains unclear. FAs are synthesized up to a chain length of 18 carbons inside chloroplasts, where they can be incorporated into glycerolipids. They are also exported to the ER for phospho- and betaine lipid syntheses. Elongation of FAs up to 22 carbons occurs in the ER. PUFAs can be reimported into plastids to serve as precursors for glycerolipids. In both organelles, FA desaturases are present, introducing double bonds between carbon atoms and giving rise to a variety of molecular species. In addition to the four desaturases characterized in Phaeodactylum (FAD2, FAD6, PtD5, PtD6), we identified eight putative desaturase genes. Combining subcellular localization predictions and comparisons with desaturases from other organisms like Arabidopsis, we propose a scheme at the whole cell level, including features that are likely specific to secondary endosymbionts.
    Full-text · Article · Mar 2015 · Marine Drugs
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    ABSTRACT: Oleaginous photosynthetic organisms such as microalgae are promising sources for biofuel production through the generation of carbon-neutral sustainable energy. However, the metabolic mechanisms driving high-rate lipid production in these oleaginous organisms remain unclear, thus impeding efforts to improve productivity through genetic modifications. We analyzed the genome and transcriptome of the oleaginous diatom Fistulifera solaris JPCC DA0580. Next-generation sequencing technology provided evidence of an allodiploid genome structure, suggesting unorthodox molecular evolutionary and genetic regulatory systems for reinforcing metabolic efficiencies. Although major metabolic pathways were shared with nonoleaginous diatoms, transcriptome analysis revealed unique expression patterns, such as concomitant upregulation of fatty acid/triacylglycerol biosynthesis and fatty acid degradation (β-oxidation) in concert with ATP production. This peculiar pattern of gene expression may account for the simultaneous growth and oil accumulation phenotype and may inspire novel biofuel production technology based on this oleaginous microalga. © 2015 American Society of Plant Biologists. All rights reserved.
    No preview · Article · Jan 2015 · The Plant Cell
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    ABSTRACT: ] The pollen tube, a fast tip-growing cell, is an excellent model to study membrane and cell wall biosynthesis. Here, we describe a simple protocol using an easy to use device to perform immunofluorescence labelling of pollen tube membrane and cell wall. The use of the NucleoSpin column to perform all the steps of the immunolabelling procedure results in obtaining more intact pollen tubes.
    Full-text · Article · Jan 2015
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    ABSTRACT: Diatoms constitute a major phylum of phytoplankton biodiversity in ocean and fresh water ecosystems. They are known to respond to some chemical variations of the environment by the accumulation of triacylglycerol, but the relative changes occurring in membrane glycerolipids has not yet been studied. Our goal was first to define a reference for the glycerolipidome of the marine model diatom Phaeodacylum tricornutum, a necessary prerequisite to characterize and dissect the lipid metabolic routes that are orchestrated and regulated to build up each subcellular membrane compartment. By combining multiple analytical techniques, we determined the glycerolipid profile of Phaeodactylum grown with various levels of nitrogen or phosphorus supplies. In different Phaeodactylum accessions collected worldwide, a deprivation of either nutrient triggered an accumulation of triacylglycerol, but with different time scales and magnitudes. We investigated in depth the effect of nutrient starvation on the Pt1 strain (culture collection CCAP 1055/3). Nitrogen deprivation was the more severe stress, triggering thylakoid senescence and growth arrest. By contrast, phosphorus deprivation induced a stepwise adaptive response. The timescale of the glycerolipidome changes and the comparison with large scale transcriptome studies were consistent with an exhaustion of unknown primary P-storage molecules (possibly polyphosphate) and a transcriptional control of some genes coding for specific lipid synthesis enzymes. We propose that phospholipids are secondary P-storage molecules broken down upon P deprivation, while non-phosphorus lipids are synthesized consistently with a phosphatidylglycerol-to-sulfolipid and a phosphatidycholine-to-betaine lipid replacement followed by a late accumulation of triacylglycerol. Copyright © 2014, American Society of Plant Biologists.
    Full-text · Article · Dec 2014 · Plant physiology

  • No preview · Article · Dec 2014
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    Preview · Article · Dec 2014 · Medecine sciences: M/S
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    ABSTRACT: Inorganic phosphate (Pi) is present in most soils at sub-optimal concentrations, strongly limiting plant development. Plants have the ability to sense and adapt to the surrounding ionic environment, and several genes involved in the response to Pi starvation have been identified. However, a global understanding of the regulatory mechanisms involved in this process is still elusive. Here, we have initiated a "chemical genetics" approach and isolated compounds that inhibit the response to Pi starvation in Arabidopsis thaliana. Molecules were screened for their ability to inhibit the expression of a Pi starvation marker gene (the high-affinity Pi transporter PHT1;4). A drug family named Phosphatin (Phosphate starvation inhibitor: PTN) was thus identified, whose members act as partial suppressors of Pi starvation responses. PTN addition also reduced various traits of Pi starvation such as phospholipid/glycolipid conversion, and the accumulation of starch and anthocyanins. A transcriptomic assay revealed a broad impact of PTN on the expression of many genes regulated by low Pi availability. Despite the reduced amount of Pi transporters and resulting reduced Pi uptake capacity, no reduction of Pi content was observed. In addition, PTN improved plant growth; this reveals that the developmental restrictions induced by Pi starvation are not a consequence of metabolic limitation, but also result from genetic regulation. This highlights the existence of signal transduction pathway(s) that limit plant development under the Pi starvation condition.
    Preview · Article · Sep 2014 · Plant physiology
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    ABSTRACT: The metabolic profiling of various microalga species and their genetic variants, grown under varied environmental conditions, has become critical to accelerate the exploration of phytoplankton biodiversity and biology. The accumulation of valuable metabolites, such as glycerolipids, is also sought in microalgae for biotechnological applications ranging from food, feed, medicine, cosmetics to bioenergy and green chemistry. In this report we describe the direct analysis of metabolites and glycerolipids in small cell populations of the green alga Chlamydomonas reinhardtii, using laser ablation electrospray ionization (LAESI) mass spectrometry (MS) coupled with ion mobility separation (IMS). These microorganisms are capable of redirecting energy storage pathways from starch to neutral lipids depending on environmental conditions and nutrient availability. Metabolite and lipid production was monitored in wild type (WT), and genetically modified C. reinhardtii strains with an impaired starch pathway. Lipids, such as triacylglycerols (TAG) and diacylglyceryl-N,N,N-trimethylhomoserine (DGTS) were monitored over time under altered light conditions. More than 200 ions related to metabolites, e.g., arginine, cysteine, serine, palmitate, chlorophyll a, chlorophyll b, etc., were detected. The lipid profiles at different light intensities for strains with impaired starch pathway (Sta1 and Sta6) contained 26 glycerolipids, such as DGTS, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), as well as 33 TAG species. Results were obtained over a 72-hour time period in high and low light conditions for the WT species and the two mutants. Our results indicate that LAESI-IMS-MS can be utilized for the rapid analysis of increased TAG production at elevated light intensities. Compared to WT, the Sta6 strain showed 2.5-times higher lipid production at 72 hours under high light conditions. The results demonstrate our ability to rapidly observe numerous changes in metabolite and lipid levels in microalgae populations. These capabilities are expected to facilitate the exploration of genetically altered microalgae strains for biofuel production.
    Full-text · Article · Sep 2014 · The Analyst
  • Eric Maréchal · Olivier Bastien
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    ABSTRACT: In Angiosperms, the biosynthesis of galactolipids involves enzymes localized in the inner envelope membrane (IEM) of chloroplasts, including a phosphatidic acid phosphatase (PAP), dephosphorylating phosphatidic acid (PA) into diacylglycerol (DAG), and MGD1, transferring a galactose onto DAG thus generating monogalactosyldiacylglycerol (MGDG). It has been shown that PA and DAG could be synthesized in the plastid via the so-called 'prokaryotic' pathway or imported from the endoplasmic reticulum via the 'eukaryotic' pathway. In vitro studies support the existence of (1) a negative regulation of the plastid PAP by DAG and (2) an activation of MGD1 by PA. We developed a mathematical model of the IEM galactolipid biosynthesis pathway to understand the properties of the system ruled by the presence of these two regulatory motifs. We demonstrated that the design of the system implies that PA should accumulate to levels that are not observed experimentally, regardless of its prokaryotic or eukaryotic origin. PA should therefore be used for other syntheses, such as that of phosphatidylglycerol. Whereas a massive influx of eukaryotic PA appears unlikely, an influx of eukaryotic DAG in the IEM is supported by simulations. The model also implies that DAG cannot transiently accumulate and that PA mainly acts as a signal switching the whole system on. Eventually, this analysis highlights the fact that the PAP enzyme could easily become dispensable and that the design of the system, with the two regulatory motifs, could precede the loss of the PAP gene or activity in this pathway, a phenomenon that occurred independently in most clades of Angiosperms.
    No preview · Article · Jul 2014 · Journal of Theoretical Biology
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    ABSTRACT: The microalga Chlamydomonas reinhardtii has been extensively studied for its relevance in biofuel production. This fully sequenced model organism has applications in focused areas such as photosynthesis, metabolism, cell cycle, motility, and genetics.1 To improve the understanding of lipid biosynthesis and its implications for using Chlamydomonas as a biofuel source, factors such as environmental conditions and selection of strains with particular genotypes need to be further investigated. Depending on nutrient availability and environmental conditions C. reinhardtii has the ability to store energy as starch or as neutral lipids, e.g., triacylglycerols (TAG). Here we demonstrate the use of a robust ambient analytical tool, laser ablation electrospray ionization (LAESI) mass spectrometry (MS) with ion mobility separation (IMS), to better understand metabolic changes and adaptations at the biochemical pathway level under varied stress conditions. C. reinhardtii mutants with an impaired starch pathway were investigated for the production of neutral storage lipids under altered light conditions. Starch synthesis is inhibited by disrupting the central enzyme of ADP-glucose pyrophosphorylase (AGPase-SS) that is responsible for the formation of glucosyl nucleotides from glucose-1-phosphate with ATP in the starch pathway. This enzyme is activated by 3-phosphoglyceric acid (3-PGA). The Sta1 mutant has a disrupted large catalytic subunit of AGPase-SS, and as a consequence it exhibits a reduced activation by 3-PGA. This allows the mutant to retain less than ~10% of its normal starch production.2 The Sta6 mutant has a disrupted small catalytic subunit of AGPase-SS and as a result only retains ~1% of the normal starch levels.3 Conventional lipid analysis of microalgae consists of extensive extraction protocols and/or derivatization, resulting in lengthy runs and the loss of some structural information. To reduce the complexity of the sample, a separation step that distinguishes the different classes of compounds and isobaric species is required. LAESI-MS is an ambient ionization technique that has been employed to detect metabolites, lipids, and peptides from diverse biological samples. This technique utilizes the natural water content of cells and tissues to facilitate laser energy deposition by the strong absorption of water at 2.94 μm wavelength and to produce an ablation plume. The plume is then ionized by an electrospray and sampled by a high-performance Q- TOF mass spectrometer (Synapt G2 S, Waters Co.). A typical LAESI mass spectrum of Chlamydomonas contains approximately ~250 detected ions but it does not differentiate between structural isomers and isobaric species. Combination of LAESI-MS with IMS has been shown to produce a 3 fold increase in molecular coverage.4 The resulting enhanced data includes m/z ratios, drift times (DT) related to the collision cross section of the ion, and peak intensities. To reduce spectral interferences from the medium and to prevent osmotic shock the cells are deposited in a silica membrane spin tube and the supernatant is separated from the cells by centrifuging at 2,000×g for 1 min. The laser pulses are directly coupled into the remaining pellet of microalgae on the filter.  Initially the wild type (WT) C. reinhardtii was studied under low and high light conditions, with photosynthetically active radiation (PAR) 0 and 150 μmolm-2sec-1, respectively. After a 72 h period, the cells were harvested and LAESI-IMS-MS was performed. In the lipid region of the spectra, normalized for the most abundant diacylglyceryl-N,N,N-trimethylhomoserine (DGTS) ion, DGTS(34:3), enhanced production of monogalactosyldiacylglycerols (MGDG), digalactosyldiacylglycerols (DGDG) and TAG lipids was observed under high light conditions. The Sta1 and Sta6 mutants were investigated for lipid production in altered light conditions ranging from 0 to 200 μmolm-2sec-1 over a 72 h time period. When compared to the WT cells, significant levels of TAG and DGDG were observed in both mutants throughout the 72 h time period. Using LAESI-MS without IMS ~10 TAG lipid species were detected. The introduction of IMS improved the molecular coverage of TAG lipids to ~50 species in the DT range of 189 to 204 ms (see Figure 1a). When compared to WT, the Sta1 mutant showed stronger ion signal for TAG lipids within 800 < m/z < 880 at 72 h under high light condition. Conversely, the Sta6 mutant presented the strongest ion signal for TAG lipids at 72 h in low light illumination. Under opposite lighting conditions, the two Sta mutants exhibited similar TAG lipid profiles. To reduce spectral interferences and differentiate close to isobaric species, for example TAG(54:7) and the 13C peak of chlorophyll a, both at nominal m/z 894, two DT ranges were inspected. In the LAESI-IMS-MS spectrum, the DT range integrated between 201 and 207 ms revealed the TAG(54:7) species at m/z 894.7571, whereas the DT range integrated between 181 and 188 ms showed the 13C isotope peak of chlorophyll a at m/z 894.5512 (see Figure 1b). These results demonstrate our ability to observe numerous changes in lipid levels in WT and genetically modified microalgae populations affected by light exposure. We found that impaired starch pathways C. reinhardtii result in energy storage redirected to neutral lipids. These capabilities are expected to accelerate the research on the utility of genetically altered microalgae strains for biofuel production.
    Full-text · Conference Paper · Jul 2014

Publication Stats

2k Citations
457.29 Total Impact Points

Institutions

  • 2015
    • Université Grenoble Alpes
      Grenoble, Rhône-Alpes, France
  • 2008-2015
    • University of Grenoble
      Grenoble, Rhône-Alpes, France
  • 2014
    • Cea Leti
      Grenoble, Rhône-Alpes, France
  • 2010-2014
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2003-2014
    • Atomic Energy and Alternative Energies Commission
      • Cell and Plant Physiology (PCV)
      Gif, Île-de-France, France
  • 2011-2013
    • French National Institute for Agricultural Research
      Lutetia Parisorum, Île-de-France, France
  • 1994-2012
    • University Joseph Fourier - Grenoble 1
      • Laboratoire de Physiologie Cellulaire Végétale
      Grenoble, Rhône-Alpes, France
  • 2002
    • Philipps University of Marburg
      Marburg, Hesse, Germany
  • 1999
    • Institut de Génétique et de Biologie Moléculaire et Cellulaire
      Strasburg, Alsace, France