The Anthelmintic Quassinoids Ailanthone and Bruceine a Induce Infertility in the Model Organism Caenorhabditis elegans by an Apoptosis-like Mechanism Induced in Gonadal and Spermathecal Tissues

In continuation of the search for new anthelmintic natural products, the study at hand investigated the nematicidal effects of the two naturally occurring quassinoids ailanthone and bruceine A against the reproductive system of the model nematode Caenorhabditis elegans to pinpoint their anthelmintic mode of action by the application of various microscopic techniques. Differential Interference Contrast (DIC) and the epifluorescence microscopy experiments used in the presented study indicated the genotoxic effects of the tested quassinoids (c _ailanthone = 50 µM, c _{bruceine A} = 100 µM) against the nuclei of the investigated gonadal and spermathecal tissues, leaving other morphological key features such as enterocytes or body wall muscle cells unimpaired. In order to gain nanoscopic insight into the morphology of the gonads as well as the considerably smaller spermathecae of C. elegans, an innovative protocol of polyethylene glycol embedding, ultra-sectioning, acridine orange staining, tissue identification by epifluorescence, and subsequent AFM-based ultrastructural data acquisition was applied. This sequence allowed the facile and fast assessment of the impact of quassinoid treatment not only on the gonadal but also on the considerably smaller spermathecal tissues of C. elegans. These first-time ultrastructural investigations on C. elegans gonads and spermathecae by AFM led to the identification of specific quassinoid-induced alterations to the nuclei of the reproductive tissues (e.g., highly condensed chromatin, impaired nuclear membrane morphology, as well as altered nucleolus morphology), altogether implying an apoptosis-like effect of ailanthone and bruceine A on the reproductive tissues of C. elegans.     

Ultramicrotomy reveals crystallographic information on a sectioned surface of a metallic block specimen

Ultramicrotomy is widely regarded as a thin section preparation method for transmission electron microscopy (TEM) investigations. It is shown that ultramicrotomy can also provide a simple path for microstructure analysis and assessment of mechanical properties for a sectioned block-face. Furthermore, electron backscatter diffraction (EBSD) analysis can be applied directly on ultramicrotomed surfaces without any additional polishing or etching. EBSD analysis relates the inherent cutting artefacts to the crystallographic orientations of the grains, hence delivering a rough assessment of their deformation resistance. TEM investigations revealed that crystallographic-related cutting artefacts, which exhibit a wave-like pattern, are the result of the dislocation pile-ups close to the knife–specimen interface. This technique is considered suitable to be coupled with EBSD for three-dimensional microstructure reconstructions when used for serial sectioning of large volumes.     

Use of thin sectioning (nanoskiving) to fabricate nanostructures for electronic and optical applications

This Review discusses nanoskiving--a simple and inexpensive method of nanofabrication, which minimizes requirements for access to cleanrooms and associated facilities, and which makes it possible to fabricate nanostructures from materials, and of geometries, to which more familiar methods of nanofabrication are not applicable. Nanoskiving requires three steps: 1) deposition of a metallic, semiconducting, ceramic, or polymeric thin film onto an epoxy substrate; 2) embedding this film in epoxy, to form an epoxy block, with the film as an inclusion; and 3) sectioning the epoxy block into slabs with an ultramicrotome. These slabs, which can be 30 nm-10 μm thick, contain nanostructures whose lateral dimensions are equal to the thicknesses of the embedded thin films. Electronic applications of structures produced by this method include nanoelectrodes for electrochemistry, chemoresistive nanowires, and heterostructures of organic semiconductors. Optical applications include surface plasmon resonators, plasmonic waveguides, and frequency-selective surfaces.     

Methods for Characterizing the 3-D Morphology of Polymer Composites

3-dimensional visualization of polymer morphology is of increasing interest in the polymer community because it provides a deeper insight into the arrangement of the phases in heterophasic polymeric materials, for example in composites. Depending on the size of the fillers, an adequate method offering a good compromise between suitable resolution and observable volume must be selected. Different polypropylene composites filled with long glass fibres, mica and talcum particles were investigated. Four methods were applied to account for the different filler sizes. For composites containing fillers larger than several micrometers, i.e. glass fibres and mica particles, X-ray tomography offers a very good combination of visibility and volume. Serial sectioning by polishing in combination with light optical microscopy can be an alternative if no X-ray equipment is available. This combined method has the disadvantage, however, that the imaged volume is smaller and involves more effort, which makes it unsuitable for routine observations. The much smaller talcum particles with thicknesses down to 200 nm were investigated by coupling focused ion beam (FIB) milling and scanning electron microscopy (SEM) and by insitu ultramicrotomy in the SEM. Both methods led to good and comparable results.