Ultra- and micro-structural changes of respiratory tracts in SARS-CoV-2 infected Syrian hamsters

The severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) pandemic is causing a global crisis. It is still unresolved. Although many therapies and vaccines are being studied, they are still in their infancy. As this pandemic continues, rapid and accurate research for the development of therapies and vaccines is needed. Therefore, it is necessary to understand characteristics of diseases caused by SARS-CoV-2 through animal models. Syrian hamsters are known to be susceptible to SARS-CoV-2. They were intranasally inoculated with SARS-CoV-2. At 2, 4, 8, 12, and 16 days post-infection (dpi), these hamsters were euthanized, and tissues were collected for ultrastructural and microstructural examinations. Microscopic lesions were prominent in the upper and lower respiratory tracts from 2 and 4 dpi groups, respectively. The respiratory epithelium in the trachea, bronchiole, and alveolar showed pathological changes. Inflammatory cells including neutrophils, lymphocytes, macrophages, and eosinophils were infiltrated in/around tracheal lamina propria, pulmonary vessels, alveoli, and bronchiole. In pulmonary lesions, alveolar wall was thickened with infiltrated inflammatory cells, mainly neutrophils and macrophages. In the trachea, epithelial damages started from 2 dpi and recovered from 8 dpi, consistent with microscopic results, High levels of SARS-CoV-2 nucleoprotein were detected at 2 dpi and 4 dpi. In the lung, lesions were most severe at 8 dpi. Meanwhile, high levels of SARS-CoV-2 were detected at 4 dpi. Electron microscopic examinations revealed cellular changes in the trachea epithelium and alveolar epithelium such as vacuolation, sparse micro-organelle, and poor cellular margin. In the trachea epithelium, the number of cytoplasmic organelles was diminished, and small vesicles were prominent from 2 dpi. Some of these electron-lucent vesicles were filled with virion particles. From 8 dpi, the trachea epithelium started to recover. Because of shrunken nucleus and swollen cytoplasm, the N/C ratio of type 2 pneumocyte decreased at 8 and 12 dpi. From 8 dpi, lamellar bodies on type 2 pneumocyte cytoplasm were increasingly observed. Their number then decreased from 16 dpi. However, there was no significant change in type 1 pneumocyte. Viral vesicles were only observed in the cytoplasm of type 2 pneumocyte. In conclusion, ultra- and micro-structural changes presented in this study may provide useful information for SARS-CoV-2 studies in various fields.

Comparative Histological, Histochemical and Ultrastructure Studies on the Exocrine Pancreas of Japanese Quail (Coturnix coturnix japonica) and Cattle Egret (Bubulcus ibis)

The current study targeted to compare between the pancreas (exocrine part) of Japanese quail and Cattle egret. The pancreas was investigated in eight apparent healthy mature female Japanese quail and eight Cattle egret. Histological, histochemical, and ultrastructure studies were carried out. In both birds, the pancreas is located on the right side of the abdomen between the ascending and descending loops of the duodenum. The pancreas of the Japanese quail composed of dorsal, ventral, third, and splenic lobes, while in Cattle egret the pancreas is not lobulated. The Exocrine portion consists of serous acini and intercalated duct, intralobular duct, interlobular duct, and main duct. The duct system was similar in both birds with minor differences. The intralobular duct in the Cattle egret is characterized by the presence of serous glands within its wall. Under electron microscopy, the acinar cells were of two types, electron-dense, and electron-lucent acinar cells. Histochemically, the interlobular duct of the Cattle egret positively reacted to alcian blue (pH1) and aldehyde fuchsin stains but the interlobular duct of the Japanese quail was negatively reacted.

The unusual cytoarchitecture of “vitelline follicles” in freshwater blood flukes of the genus Sanguinicola (Digenea, Aporocotylidae)

This is the first study assessing the cytoarchitecture of the vitellarium of members of the freshwater, teleost-infecting lineage of blood-flukes (Aporocotylidae). The vitelline cytoarchitecture of two innominate species of Sanguinicola from freshwater fishes in Russia showed that vitelline cells at different stages of maturation are widely distributed throughout much of the body and are mixed with other cell types. The latter feature indicates that use of the term “follicular vitellarium” is inappropriate for species of this genus. An additional characteristic of the vitelline cells in these Sanguinicola spp. is their ability to form long, pseudopodia-like extensions of the peripheral cytoplasm that contact neighbouring vitelline cells and sarcoplasmic extensions, forming both heterologous and homologous intercellular junctions. Within the vitelline duct lumen, the cytoplasm of mature vitelline cells is filled with regular clusters (0.5–1.0 μm in diameter), comprising 10–30 vitelline globules, which have heterogeneous contents and electron-lucent lipid droplets (1.1–1.7 μm in diameter), but no apparent modifications of vitelline globules occur within the vitelline duct. The flattened, ciliated, epithelial lining of the common vitelline duct contains intra-epithelial nuclei, its luminal surface bears shallow lamellae and adjacent cells are adjoined by apical septate junctions. All of these observations, when compared to the marine Aporocotyle simplex, likely represent additional characteristics supporting the divergent evolutionary lineages of marine and freshwater aporocotylids.

Ultrastructural Features of an Abundant and Ubiquitous Marine Ciliate, Uronychia binucleata (Protista, Ciliophora, Euplotida)

The ciliate genus Uronychia is a marine group with extremely differentiated cortical and ciliary structures. These structures define its unique evolutionary position in the whole subclass Euplotia. However, to date, few data about the ultrastructure of this genus and related taxa is available. In the present work, a dominant species, Uronychia binucleata, was investigated using scanning electron microscopy and transmission electron microscopy. The findings are as follows: (i) this species lacks the typical alveolar plate in its cortex, whereas the abundant electron-lucent vesicular structures occurred densely; (ii) the subpellicular microtubules form a triad configuration in the dorsal side, while appearing in a single configuration in the ventral side; (iii) the cortical granules are extrusomes, which represent a kind of mucocyst instead of ampules; (iv) two kinetosomes in different rows of one cirrus are linked by the single longitudinal connection; (v) the undulating membrane is highly developed and their insides and outsides are partially covered by the cortical flap; (vi) the single-membrane-bound pharyngeal disks interposed with microtubular sheets, and are distributed in three distinct zones. This first detailed report about the ultrastructural features of the genus Uronychia will be a key to improve the diagnosis and systematics of this widely distributed and ecologically important genus and its family Uronychiidae.

Putative morphology of Neoehrlichia mikurensis in salivary glands of Ixodes ricinus

Neoehrlichia mikurensis is an emerging tick-borne intracellular pathogen causing neoehrlichiosis. Its putative morphology was described in mammalian, but not in tick cells. In this study, we aim to show the presumptive morphology of N. mikurensis in salivary glands of engorged females of Ixodes ricinus. To accomplish this, we collected I. ricinus ticks in a locality with a high N. mikurensis prevalence, allowed them to feed in the artificial in vitro feeding system, dissected salivary glands and screened them by PCR for N. mikurensis and related bacteria. Ultrathin sections of salivary glands positive for N. mikurensis but negative for other pathogens were prepared and examined by transmission electron microscopy. We observed two individual organisms strongly resembling N. mikurensis in mammalian cells as described previously. Both bacteria were of ovoid shape between 0.5–0.8 μm surrounded by the inner cytoplasmic and the rippled outer membrane separated by an irregular electron-lucent periplasmic space. Detection of N. mikurensis in salivary glands of I. ricinus suggests that this bacterium uses the “salivary pathway of transmission” to infect mammals.

How Does Protein Zero Assemble Compact Myelin?

Myelin protein zero (P0), a type I transmembrane protein, is the most abundant protein in peripheral nervous system (PNS) myelin—the lipid-rich, periodic structure of membrane pairs that concentrically encloses long axonal segments. Schwann cells, the myelinating glia of the PNS, express P0 throughout their development until the formation of mature myelin. In the intramyelinic compartment, the immunoglobulin-like domain of P0 bridges apposing membranes via homophilic adhesion, forming, as revealed by electron microscopy, the electron-dense, double “intraperiod line” that is split by a narrow, electron-lucent space corresponding to the extracellular space between membrane pairs. The C-terminal tail of P0 adheres apposing membranes together in the narrow cytoplasmic compartment of compact myelin, much like myelin basic protein (MBP). In mouse models, the absence of P0, unlike that of MBP or P2, severely disturbs myelination. Therefore, P0 is the executive molecule of PNS myelin maturation. How and when P0 is trafficked and modified to enable myelin compaction, and how mutations that give rise to incurable peripheral neuropathies alter the function of P0, are currently open questions. The potential mechanisms of P0 function in myelination are discussed, providing a foundation for the understanding of mature myelin development and how it derails in peripheral neuropathies.

Structural colours in diverse Mesozoic insects

Structural colours, nature's most pure and intense colours, originate when light is scattered via nanoscale modulations of the refractive index. Original colours in fossils illuminate the ecological interactions among extinct organisms and functional evolution of colours. Here, we report multiple examples of vivid metallic colours in diverse insects from mid-Cretaceous amber. Scanning and transmission electron microscopy revealed a smooth outer surface and five alternating electron-dense and electron-lucent layers in the epicuticle of a fossil wasp, suggesting that multilayer reflectors, the most common biophotonic nanostructure in animals and even plants, are responsible for the exceptional preservation of colour in amber fossils. Based on theoretical modelling of the reflectance spectra, a reflective peak of wavelength of 514 nm was calculated, corresponding to the bluish-green colour observed under white light. The green to blue structural colours in fossil wasps, beetles and a fly most likely functioned as camouflage, although other functions such as thermoregulation cannot be ruled out. This discovery not only provides critical evidence of evolution of structural colours in arthropods, but also sheds light on the preservation potential of nanostructures of ancient animals through geological time.

Pigmented Ependymoma of the Fourth Ventricle—A Curious Entity: Report of a Rare Case With Review of Literature

A 16-year-old boy presented with a tumor located in fourth ventricle, which showed histological features of an ependymoma replete with perivascular pseudorosettes and true ependymal rosettes. Interestingly, many of the tumor cells exhibited abundant cytoplasm stuffed with a grayish brown pigment. Histochemical stains showed the pigment to be acid fast and periodic acid–Schiff positive and negative for Masson-Fontana melanin stain. Additionally, the pigment displayed brilliant autofluorescence under ultraviolet light of a fluorescent microscope. Ultrastructure examination of the pigment revealed a non–membrane-bound biphasic structure with an electron-dense core and electron-lucent periphery. Only few similar case reports mention such pigmented ependymomas to contain a mixture of neuromelanin and lipofuscin while others mention it to be melanin itself. Our workup suggests the pigment to represent lipofuscin or its derivative. Generally known to be a pigment of wear and tear, the significance of finding it in a tumor with such abundance remains to be understood and explored.

Illustration of the Effects of Five Fungi on Acacia saligna Wood Organic Acids and Ultrastructure Alterations in Wood Cell Walls by HPLC and TEM Examinations

In the present study, Acacia saligna (Labill.) H.L.Wendl. wood blocks with dimensions of 0.5 × 1 × 2 cm were inoculated with five molds (Aspergillus niger, A. flavus, Alternaria tenuissima, Fusarium culmorum, and Trichoderma harzianum) and the changes in the organic acids (oxalic, citric, tartaric, succinic, glutaric, acetic, propionic, and butyric) of powdered wood were analyzed by HPLC. The effects of the five inoculated fungi on the alterations to the wood cell wall ultrastructures were examined by TEM. The wood became more acidic as it was inoculated with the studied fungi. From the HPLC analysis, the oxalic acid (293.34 µg/g o.d.) in the A. saligna, A. tenuissima (167.33 µg/g o.d.), and T. harzianum (245.01 µg/g o.d.) wood decreased, but it increased in the A. flavus (362.08 µg/g o.d.), A. niger (1202.53 µg/g o.d.), and F. culmorum (431.85 µg/g o.d.) inoculated wood. Citric acid was observed in the wood inoculated with A. flavus (110 µg/g o.d) and A. niger (2499.63 µg/g o.d). Tartaric (1150.98 µg/g o.d), acetic (2.04 µg/g o.d), and propionic (1.79 µg/g o.d) acids were found in the wood inoculated with A. niger. Butyric acid was found in small amounts. A loss of wood substances appeared as the electron-lucent increased in the middle lamella and the layers of the secondary wall. Within the secondary cell wall regions, checks and splits were also noted, which resulted from the effects of the acids on the carbohydrates, according to the fungus type and the acids. In conclusion, increasing the amount of organic acids in the wood samples through inoculation with fungi results in more degradations in the wood, especially in the wood inoculated with A. niger.