D. Eichert

Bio: D. Eichert is an academic researcher from European Synchrotron Radiation Facility. The author has contributed to research in topics: Microscopy & Cambisol. The author has an hindex of 6, co-authored 10 publications receiving 441 citations.

Apatite-mediated Actin Dynamics in Resorbing Osteoclasts

Abstract: The actin cytoskeleton is essential for osteoclasts main function, bone resorption. Two different organizations of actin have been described in osteoclasts, the podosomes belt corresponding to numerous F-actin columns arranged at the cell periphery, and the sealing zone defined as a unique large band of actin. To compare the role of these two different actin organizations, we imaged osteoclasts on various substrata: glass, dentin, and apatite. Using primary osteoclasts expressing GFP-actin, we found that podosome belts and sealing zones, both very dynamic actin structures, were present in mature osteoclasts; podosome belts were observed only in spread osteoclasts adhering onto glass, whereas sealing zone were seen in apico-basal polarized osteoclasts adherent on mineralized matrix. Dynamic observations of several resorption cycles of osteoclasts seeded on apatite revealed that 1) podosomes do not fuse together to form the sealing zone; 2) osteoclasts alternate successive stationary polarized resorption phases with a sealing zone and migration, nonresorption phases without any specific actin structure; and 3) apatite itself promotes sealing zone formation though c-src and Rho signaling. Finally, our work suggests that apatite-mediated sealing zone formation is dependent on both c-src and Rho whereas apico-basal polarization requires only Rho.

Iron speciation in soils and soil aggregates by synchrotron-based X-ray microspectroscopy (XANES,μ-XANES)

Abstract: Summary Iron speciation in soils is still poorly understood. We have investigated inorganic and organic standard substances, diluted mixtures of common Fe minerals in soils (pyrite, ferrihydrite, goethite), soils in a forested watershed which constitute a toposequence with a hydrological gradient (Dystric Cambisol, Dystric Planosol, Rheic Histosol), and microsites of a dissected soil aggregate by X-ray Absorption Near Edge Spectroscopy (XANES) at the iron K-edge (7112 eV) to identify different Fe(II) and Fe(III) components. We calculated the pre-edge peak centroid energy of all spectra and quantified the contribution of different organic and inorganic Fe-bearing compounds by Linear Combination Fitting (LCF) conducted on the entire spectrum (E = 7085–7240 eV) and on the pre-edge peak. Fe-XANES conducted on organic and inorganic standards and on synthetic mixtures of pyrite, ferrihydrite and goethite showed that by calculating the pre-edge peak centroid energy, the Fe(II)/Fe(III) ratio of different Fe-bearing minerals (Fe sulphides, Fe oxyhydroxides) in mineral mixtures and soils can be quantified with reasonable accuracy. A more accurate quantification of the Fe(II)/Fe(III) ratio was possible with LCF conducted on the entire XANES spectrum. For the soil toposequence, an increased groundwater influence from the Cambisol to the Histosol was reflected in a larger contribution of Fe(II) compounds (Fe(II) silicate, Fe monosulphide, pyrite) and a smaller contribution of Fe(III) oxyhydroxides (ferrihydrite, goethite) to total iron both in the topsoil and the subsoil. In the organic topsoils, organically bonded Fe (33–45% of total Fe) was 100% Fe(III). For different microsites in the dissected aggregate, spatial resolution ofμ-XANES revealed different proportions of Fe(II) and Fe(III) compounds. Fe K-edge XANES andμ-XANES allows an approximate quantification of Fe(II) and Fe(III) and different Fe compounds in soils and (sub)micron regions of soil sections, such as mottles, concretions, and rhizosphere regions, thus opening new perspectives in soil research.

Differentiation between adsorbed and precipitated sulphate in soils and at micro-sites of soil aggregates by sulphur K-edge XANES

Abstract: To investigate the potential of synchrotron-based X-ray Absorption Near-Edge Structure spectroscopy (XANES) at the sulphur (S) K-edge for a discrimination of adsorbed and precipitated sulphate in soils and soil particles, XANES spectra of ionic sulphate compounds and Al/Fe hydroxy sulphate minerals were compared with spectra of SO 4 2- adsorbed to ferrihydrite, goethite, haematite, gibbsite or allophane. Ionic sulphate and hydroxy sulphate precipitates had broader white-lines (WL) at 2482.5 eV (full width at half maximum (FWHM) of edge-normalized spectra, 2.4-4.2 eV; Al hydroxy sulphates, 3.0 eV) than SO 4 2- adsorbed to Al/Fe oxyhydroxides or allophane (FWHM, 1.8-2.4 eV). The ratio of the white-line (WL) height to the height of the post-edge feature at 2499 eV (WL/PEF) was larger for SO 4 2- adsorbed to Al/Fe oxyhydroxides or allophane (8.1-11.9) than for Al/Fe hydroxy sulphates and ionic sulphates (3.9-5.7). The WL/PEF ratio of edge-normalized S K-edge XANES spectra can be used to distinguish adsorbed from precipitated SO 4 2- in soils and also at microsites of soil particles. The contribution of adsorbed and precipitated SO 4 2- to the total SO 4 2- pool can be roughly quantified. Adsorbed ester sulphate may result in overestimation of precipitated SO 4 2- . The spectra of most soils could be fitted by linear combination fitting (LCF), yielding a similar partitioning between adsorbed and precipitated SO 4 2- as an evaluation of the WL/PEF ratio. The SO 4 2- pool of German forest soils on silicate parent material in most cases was strongly dominated by adsorbed SO 4 2- ; however, in three German forest soils subject to elevated atmospheric S deposition, a considerable portion of the SO 4 2- pool was precipitated SO 4 2- , most likely Al hydroxy sulphate. The same is true for Nicaraguan Eutric and Vitric Andosols subject to high volcanogenic S input. In the subsoil of the Vitric Andosol, adsorbed SO 4 2- and Al hydroxy sulphate coexist on a micron scale.

EMT, the cytoskeleton, and cancer cell invasion

Abstract: The metastatic process, i.e. the dissemination of cancer cells throughout the body to seed secondary tumors at distant sites, requires cancer cells to leave the primary tumor and to acquire migratory and invasive capabilities. In a process of epithelial-mesenchymal transition (EMT), besides changing their adhesive repertoire, cancer cells employ developmental processes to gain migratory and invasive properties that involve a dramatic reorganization of the actin cytoskeleton and the concomitant formation of membrane protrusions required for invasive growth. The molecular processes underlying such cellular changes are still only poorly understood, and the various migratory organelles, including lamellipodia, filopodia, invadopodia and podosomes, still require a better functional and molecular characterization. Notably, direct experimental evidence linking the formation of migratory membrane protrusions and the process of EMT and tumor metastasis is still lacking. In this review, we have summarized recent novel insights into the molecular processes and players underlying EMT on one side and the formation of invasive membrane protrusions on the other side.

Biology of Bone Tissue: Structure, Function, and Factors That Influence Bone Cells

Abstract: Bone tissue is continuously remodeled through the concerted actions of bone cells, which include bone resorption by osteoclasts and bone formation by osteoblasts, whereas osteocytes act as mechanosensors and orchestrators of the bone remodeling process. This process is under the control of local (e.g., growth factors and cytokines) and systemic (e.g., calcitonin and estrogens) factors that all together contribute for bone homeostasis. An imbalance between bone resorption and formation can result in bone diseases including osteoporosis. Recently, it has been recognized that, during bone remodeling, there are an intricate communication among bone cells. For instance, the coupling from bone resorption to bone formation is achieved by interaction between osteoclasts and osteoblasts. Moreover, osteocytes produce factors that influence osteoblast and osteoclast activities, whereas osteocyte apoptosis is followed by osteoclastic bone resorption. The increasing knowledge about the structure and functions of bone cells contributed to a better understanding of bone biology. It has been suggested that there is a complex communication between bone cells and other organs, indicating the dynamic nature of bone tissue. In this review, we discuss the current data about the structure and functions of bone cells and the factors that influence bone remodeling.

Multi-step pericellular proteolysis controls the transition from individual to collective cancer cell invasion

Abstract: Invasive cell migration through tissue barriers requires pericellular remodelling of extracellular matrix (ECM) executed by cell-surface proteases, particularly membrane-type-1 matrix metalloproteinase (MT1-MMP/MMP-14). Using time-resolved multimodal microscopy, we show how invasive HT-1080 fibrosarcoma and MDA-MB-231 breast cancer cells coordinate mechanotransduction and fibrillar collagen remodelling by segregating the anterior force-generating leading edge containing beta1 integrin, MT1-MMP and F-actin from a posterior proteolytic zone executing fibre breakdown. During forward movement, sterically impeding fibres are selectively realigned into microtracks of single-cell calibre. Microtracks become expanded by multiple following cells by means of the large-scale degradation of lateral ECM interfaces, ultimately prompting transition towards collective invasion similar to that in vivo. Both ECM track widening and transition to multicellular invasion are dependent on MT1-MMP-mediated collagenolysis, shown by broad-spectrum protease inhibition and RNA interference. Thus, invasive migration and proteolytic ECM remodelling are interdependent processes that control tissue micropatterning and macropatterning and, consequently, individual and collective cell migration.

The renaissance of iron-based Fischer-Tropsch synthesis: on the multifaceted catalyst deactivation behaviour.

Abstract: Iron-based Fischer–Tropsch catalysts, which are applied in the conversion of CO and H2 into longer hydrocarbon chains, are historically amongst the most intensively studied systems in heterogeneous catalysis. Despite this, fundamental understanding of the complex and dynamic chemistry of the iron–carbon–oxygen system and its implications for the rapid deactivation of the iron-based catalysts is still a developing field. Fischer–Tropsch catalysis is characterized by its multidisciplinary nature and therefore deals with a wide variety of fundamental chemical and physical problems. This critical review will summarize the current state of knowledge of the underlying mechanisms for the activation and eventual deactivation of iron-based Fischer–Tropsch catalysts and suggest systematic approaches for relating chemical identity to performance in next generation iron-based catalyst systems (210 references).