Further structures in the jaw apparatus of Limnognathia maerski (Micrognathozoa), with notes on the phylogeny of the Gnathifera

The jaws of Limnognathia maerski, Micrognathozoa, were investigated with light- and scanning electron microscopy. The study yielded several new structures and sclerites, including the ventral part of main jaw, the pharyngeal lamellae, the manus, the dorsal and ventral fibularium teeth, and a reinterpretation of the fibularium compartmentalization. Furthermore, it was shown that several jaw elements are composed of densely packed rods. Comparison with Rotifera and Gnathostomulida suggested that the micrognathozoan main jaw is homologous with the rotifer incus and the gnathostomulid articularium and that the pseudophalangids (the ventral jaws) and their associated sclerites correspond to the rotifer mallei. These results imply that Micrognathozoa is more closely related to Rotifera than to Gnathostomulida.     

Mitochondrial structure revealed by high-resolution scanning electron microscopy

Mitochondrial structure has been examined in three dimensions using high-resolution scanning electron microscopy in cells from rat liver, retina (photoreceptors and retinal pigment epithelium), and kidney (proximal convoluted tubular cells and podocytes). Tissues were prepared by aldehyde-osmium fixation and freeze cleavage using a cryoprotectant, followed by removal of the cytosol by immersion in a dilute osmium tetroxide solution. The microscope used (Hitachi S-570) was equipped with a secondary electron detector located in the column above the specimen, situated within the objective lens. Mitochondria in all tissues examined were found to have only tubular cristae, which in some instances could be seen to span the entire diameter of the organelle. The walls of the tubular cristae, when unfractured, were in contact with the inner mitochondrial membrane; and their lumens were open to the intermembranous space. We hypothesize that in cells of many, perhaps most tissues, mitochondrial cristae are not shelf-like but are, in fact, tubes which span the mitochondrial matrix and are continuous with the inner mitochondrial membrane at both ends.     

External sense organs in freshwater oligochaetes (Annelida, Clitellata) revealed by scanning electron microscopy

Freshwater oligochaetes have at least two kinds of external sense organs: multiciliate organs of short cilia (also present in earthworms) and sense organs with one to three long cilia (unknown in earthworms and possibly acting as rheoreceptors). Ciliate sense organs of freshwater oligochaetes are distributed over their entire body surface, including the clitellum. They are scattered on the prostomium and pigidium and are arranged into a transversal chaetal row and dispersed or forming a few other discrete transversal rows on chaetal segments. Three species display very prominent sense organs (sensory buds in Protuberodrilus tourenqui and papillae in Ophidonais serpentina and Spirosperma velutinus). The number of cilia per organ at the prostomium of freshwater families appears to be fewer than that of terrestrial ones. It is suggested that the total number of cilia at the prostomium of the freshwater species could be related to their habitat, evolving from an epibenthic to an endobenthic way of life.     

Structure of trichomonads as revealed by scanning electron microscopy.

A scanning electron microscope (SEM) study of Hypotrichomonas acosta (Moskowitz), Trichomonas vaginalis Donné, Pentatrichomonas hominis (Davaine), and Tritrichomonas foetus (Riedmüller) provided new information about the structure of the periflagellar canal; emergence of the flagella from the cell body; structure of the undulating membrane; and position, shape, and size of the pelta. Of special interest were the spatial relationships of the attached part of the recurrent flagellum and the accessory filament in Hypotrichomonas and in the members of Trichomonadinae, i.e. Trichomonas and Pentatrichomonas.     

New morphological characters for classifying Phoridae (Diptera) from the structure of the thorax

Forty‐six characters, mostly of the thoracic pleuron, are proposed for the reconstruction of the phylogenetic relationships among the major groups of the family Phoridae. Analysis of these characters, in conjunction with the pre‐existing suite of morphological characters from other body parts, provides a basis for a strongly supported new classification of the Phoridae, in which Sciadocerinae is the sister group of ((Chonocephalus Wandolleck & Cyphocephalus Borgmeier) + (Termitoxeniinae + (Metopininae + Phorinae s.l.))). A new subfamily, Chonocephalinae subfamily nov. , is proposed for Chonocephalus and Cyphocephalus, and a new genus, Hirotophora gen. nov. , is proposed for Chaetopleurophora multiseriata (Aldrich) ( comb. nov. ). © 2015 The Linnean Society of London     

The maxillae of Drosophila melanogaster as revealed by scanning electron microscopy

The scanning electron micrographs show the external morphology of the maxillae of Drosophila melanogaster. Specifically, they illustrate the patterning of the different types of chemo-receptive sensilla on the maxillary palpi making possible a clearer understanding of the structure of the tiny maxillary lobes. It appears that the maxillary lobes act as “cleaning brushes” during the feeding process.     

A combined light and scanning electron microscopy study

The uppermost Eocene Florissant Formation, Rocky Mountains, Colorado, has yielded numerous insect, vertebrate and plant fossils. Three previous comprehensive palynological studies investigated sections of lacustrine deposits of the Florissant Formation and documented the response of plant communities to volcanic eruptive phases but overall found little change in plant composition throughout the investigated sections. These studies reported up to 150 pollen and spore phenotypes. In the present paper, we used a taxonomic approach to the investigation of dispersed pollen and spores of the Florissant Formation. Sediment samples from the shale units containing macrofossils were investigated using light microscopy (LM) and scanning electron microscopy (SEM). The general picture of the palynoflora is in agreement with previous studies. However, the combined LM and SEM investigation provides important complementary information to previous LM studies. While a fairly large amount of previous pollen determinations could be confirmed, the purported taxonomic affinities of several pollen phenotypes need to be revised. For example, pollen referred to as Podocarpus or Podocarpidites sp. belongs to the Pinaceae Cathaya, Malus/Pyrus actually belongs to Dryadoideae, pollen of the form genus Boehlensipollis referred to as Proteaceae/Sapindaceae/Elaeagnaceae or Cardiospermum belongs to Sapindaceae but not to Cardiospermum, and pollen of Persicarioipollis sp. B with previously assumed affinities to Polygonaceae actually belongs to Thymelaeaceae. Pandaniidites and one type of Malvacipollis cannot be linked with Pandanaceae and Malvaceae. A few taxa are new records for Florissant (Ebenaceae: Diospyros; Mernispermaceae; Trochodendraceae: Tetracentron). In general, SEM investigations complement the LM palynological studies and improve the identification of dispersed pollen and spores and enable integration of data from dispersed fossil pollen into a wide range of comparative morphological, taxonomic, evolutionary, biogeographic and phylogenetic studies.     

External morphogenesis of the tardigrade Hypsibius dujardini as revealed by scanning electron microscopy

Tardigrada, commonly called water bears, is a taxon of microscopic panarthropods with five‐segmented bodies and four pairs of walking legs. Although tardigrades have been known to science for several centuries, questions remain regarding many aspects of their biology, such as embryogenesis. Herein, we used scanning electron microscopy to document the external changes that occur during embryonic development in the tardigrade Hypsibius dujardini (Eutardigrada, Parachela, Hypsibiidae). Our results show an accelerated development of external features, with approximately 30 hrs separating the point at which external structures first become recognizable and a fully formed embryo. All segments appear to arise simultaneously between ∼20 and 25 hrs of development, and no differences in the degree of development could be detected between the limb buds at any stage. Claws emerge shortly after the limb buds and are morphologically similar to those of adults. The origin of the claws is concurrent with that of the sclerotized parts of the mouth, suggesting that all cuticular structures arise simultaneously at ∼30 hrs. The mouth arises as an invagination in the terminal region of the head at ∼25 hrs, closes later in development, and opens again shortly before hatching. The anlagen of the peribuccal lobes arise as one dorsal and one ventral row, each consisting of three lobes, and later form a ring in the late embryo, whereas there is no indication of a labrum anlage at any point during development. Furthermore, we describe limited postembryonic development in the form of cuticular pores that are absent in juveniles but present in adults. This study represents the first scanning electron micrographs of tardigrade embryos, demonstrating the utility of this technique for studying embryogenesis in tardigrades. This work further adds an external morphological perspective to the developmental data already available for H. dujardini , facilitating future comparisons to related panarthropod taxa. J. Morphol. 278:563–573, 2017. © 2017 Wiley Periodicals, Inc.     

Comparative scanning electron microscopy of Gasterophilus third instars

Comparison of cuticular features, including spine distribution and shape, structure of the maxillae and mandibles, the cephalic sensillae and the terminal abdominal segments of third instar Gasterophilus haemorrhoidalis, Gasterophilus inermis, Gasterophilus intestinalis, Gasterophilus meridionalis, Gasterophilus nasalis and Gasterophilus pecorum was conducted using scanning electron microscopy. One or more features distinguished among the species, with the exception of G. haemorrhoidalis and G. intestinalis, which shared all morphological characteristics. The features presented in this study complement and extend those presented in Zumpt's compendium. The function of some features described by Zumpt (e.g. the 'warts' on the rim of the respiratory chamber) is clarified and the presence of previously described sensory structures in the grooves on the maxillae of G. intestinalis is called into question.     

Origins of prehistoric flints: The neocortex memory revealed by scanning electron microscopy

Flint has been widely used during prehistoric times and the question of determining the origin of specific pieces is recurrent in archaeological discussions. We have run a scanning electron microscope examination of the surfaces of both natural flints from geological deposits and flaked artefacts excavated from prehistoric sites in the Massif Central (France). These samples exhibit mineralogical textures resulting from genomorphic and phenomorphic processes, dispersed alteration in the form of erosion as well as the dissolution and migration of more or less mobile elements. Rocks used to manufacture artefacts at Sainte-Anne 1 (Haute-Loire, France) and Payre (Ardèche, France) show various kinds of alteration related to the range of phases of transport and deposition to which they were subjected, beginning with their first exposure in a geological context and following through to the post-depositional phase, (i.e., following abandonment as artefacts in an archaeological site). Later phenomena do not however completely obliterate stigma imprinted prior to their prehistoric collection, because the main late-phase change that occurs on flat surfaces prior to their collection is preserved in the hollows of remnant natural surfaces on archaeological tools. With the scanning electron microscope, five distinct morphologies representative of different environments have been characterised by establishing associations between the different forms and by plotting their regional distribution.     

Morphology and structure of lipoproteins revealed by an optimized negative-staining protocol of electron microscopy

Plasma lipoprotein levels are predictors of risk for coronary artery disease. Lipoprotein structure-function relationships provide important clues that help identify the role of lipoproteins in cardiovascular disease. The compositional and conformational heterogeneity of lipoproteins are major barriers to the identification of their structures, as discovered using traditional approaches. Although electron microscopy (EM) is an alternative approach, conventional negative staining (NS) produces rouleau artifacts. In a previous study of apolipoprotein (apo)E4-containing reconstituted HDL (rHDL) particles, we optimized the NS method in a way that eliminated rouleaux. Here we report that phosphotungstic acid at high buffer salt concentrations plays a key role in rouleau formation. We also validate our protocol for analyzing the major plasma lipoprotein classes HDL, LDL, IDL, and VLDL, as well as homogeneously prepared apoA-I-containing rHDL. High-contrast EM images revealed morphology and detailed structures of lipoproteins, especially apoA-I-containing rHDL, that are amenable to three-dimensional reconstruction by single-particle analysis and electron tomography.     

Collagen pretzels revealed by electron microscopy

Collagen XV is a million-dalton protein with a structural role in skeletal muscle and capillaries. As with all collagens, studies of its function are hindered by the absence of good structural data: collagens are triple-helical, non-crystallizable, multidomain proteins with extensive post-translational modification that are refractory to analysis by high-resolution structural techniques. For collagen XV, this situation is compounded by the fact that it is also a proteoglycan. In this issue of the Biochemical Journal, Myers and her colleagues use rotary shadowing electron microscopy to obtain images of purified collagen XV molecules that are sufficiently detailed to show the three-lobed structure of the N-terminus and individual glycosaminoglycan side chains. Individual molecules appear as knotted strands resembling a pretzel (a pastry snack folded in a unique figure-of-eight), which contrasts with our conventional image of collagen molecules as semi-rigid rods. Importantly, collagen XV multimerizes into cruciform structures in which simpler forms have two to four molecules per complex. Immunoelectron microscopy revealed knotted collagen XV complexes bridging collagen fibrils adjacent to basement membrane. These accomplishments are made all the more impressive by the fact that collagen XV was purified from human umbilical cord, in which the protein is represented at only (1-2)x10(-4)% of dry weight!     

Aspects of the three-dimensional intracellular organization of mesocarp cells as revealed by scanning electron microscopy

Summary The osmium-ligand binding technique and scanning electron microscopy have been applied to the study of the three-dimensional organization of mesocarp cells of a mature avocado fruit. Using this approach the mitochondria of the cells appear as elongated, branching structures and the endoplasmic reticulum consists of a complex of tubular strands, vesiculated strands and lamellar sheets. Associations of the endoplasmic reticulum with other organelles are also apparent. It is suggested that this approach provides a valuable means to assess the structural transitions in cell organization that occur during development or with functional changes.     

The surface topography of a monogenean, Diclidophora merlangi revealed by scanning electron microscopy

The body surface of adult Diclidophora merlangi is characterized by an annular array of irregularly-shaped ridges, with the intervening troughs of tegument invested with microvilli. The microvilli measure approximately 0.5 micrometer in length and 0.06 micrometer in diameter and at maximum density (10.8/micrometer 2) increase the body surface area by a factor of two. On the anterio-dorsal surface of each peduncle the ridge-like structures consolidate as a distinct area of ornamentaltion some 100 micrometer in diameter. A frontal pit opens just inside the mouth and is thought to provide the outlet for the buccal gland secretions. The tegument surrounding the gonopore and paired excretory pores is unmodified in morphology. Presumed sensory endings are of at least two types: (1) uniciliated structures, projecting from a pit or supported by a collar of tegument, and distributed either singly over the general body surface and in the buccal cavity, or in groups around the mouth; and (2) large numbers of non-ciliated papillae localized on the opisthaptor. A number of these papillae occur on a wart-like outgrowth of tegument positioned on the ventral surface of each peduncle and have obvious significance in contact communications.     

The structure of Escherichia coli signal recognition particle revealed by scanning transmission electron microscopy

Structural studies on various domains of the ribonucleoprotein signal recognition particle (SRP) have not converged on a single complete structure of bacterial SRP consistent with the biochemistry of the particle. We obtained a three-dimensional structure for Escherichia coli SRP by cryoscanning transmission electron microscopy and mapped the internal RNA by electron spectroscopic imaging. Crystallographic data were fit into the SRP reconstruction, and although the resulting model differed from previous models, they could be rationalized by movement through an interdomain linker of Ffh, the protein component of SRP. Fluorescence resonance energy transfer experiments determined interdomain distances that were consistent with our model of SRP. Docking our model onto the bacterial ribosome suggests a mechanism for signal recognition involving interdomain movement of Ffh into and out of the nascent chain exit site and suggests how SRP could interact and/or compete with the ribosome-bound chaperone, trigger factor, for a nascent chain during translation.