Cytochemistry and electron microscopy. The preservation of cellular ultrastructure and enzymatic activity by aldehyde fixation

Nanoscale intracellular ultrastructures affected by osmotic pressure using small-angle X-ray scattering

Although intracellular ultrastructures have typically been studied using microscopic techniques, it is difficult to observe ultrastructures at the submicron scale of living cells due to spatial resolution (fluorescence microscopy) or high vacuum environment (electron microscopy). We investigate the nanometer scale intracellular ultrastructures of living CHO cells in various osmolality using small-angle X-ray scattering (SAXS), and especially the structures of ribosomes, DNA double helix, and plasma membranes in-cell environment are observed. Ribosomes expand and contract in response to osmotic pressure, and the inter-ribosomal correlation occurs under isotonic and hyperosmolality. The DNA double helix is not dependent on the osmotic pressure. Under high osmotic pressure, the plasma membrane folds into form a multilamellar structure with a periodic length of about 6 nm. We also study the ultrastructural changes caused by formaldehyde fixation, freezing and heating.

The influence of Au-based nanoparticles on some physiological, biochemical and molecular characteristics of wheat plants during low temperature hardening

One of the most significant problems of the 21st century is the anthropogenic strain on the environment. The development of nanotechnology makes it possible to produce a variety of nanomaterials widely used in people's daily lives. However, nanomaterials can accumulate in ecosystems and spread through food chains. The environmental risks of nanoparticle proliferation are unclear. At the same time, certain nanoparticles act as adaptogens, improving plant tolerance to unfavorable stress factors. It is quite realistic to choose such experimental conditions, under which the effect on plant stress tolerance will be obvious and the accumulation of nanoparticles in tissues will be minimal. In this case, the main relevant factors are the type of nanoparticles, their concentration and their way of penetration into plants. We chose to study gold nanoparticles (Au-NPs), widely used in biomedical research. The concentration of Au-NPs was 20 μg/mL, which is considered safe for living organisms. The influence of Au-NPs on some physiological, biochemical and molecular characteristics of wheat plants during low temperature hardening was examined. The study of the photosynthetic apparatus and antioxidant system was the primary focus. The stimulating effect of Au-NPs on cold tolerance of wheat plants was shown. The results expand our knowledge of the processes by which nanoparticles impact plants and the potential applications of nanoparticles as adaptogens in science and agriculture.

Glyoxal acid-free (GAF) histological fixative is a suitable alternative to formalin: results from an open-label comparative non-inferiority study

Formalin, an aqueous solution of formaldehyde, has been the gold standard for fixation of histological samples for over a century. Despite its considerable advantages, growing evidence points to objective toxicity, particularly highlighting its carcinogenicity and mutagenic effects. In 2016, the European Union proposed a ban, but a temporary permission was granted in consideration of its fundamental role in the medical-diagnostic field. In the present study, we tested an innovative fixative, glyoxal acid-free (GAF) (a glyoxal solution deprived of acids), which allows optimal tissue fixation at structural and molecular level combined with the absence of toxicity and carcinogenic activity. An open-label, non-inferiority, multicentric trial was performed comparing fixation of histological specimens with GAF fixative vs standard phosphate-buffered formalin (PBF), evaluating the morphological preservation and the diagnostic value with four binary score questions answered by both the central pathology reviewer and local center reviewers. The mean of total score in the GAF vs PBF fixative groups was 3.7 ± 0.5 vs 3.9 ± 0.3 for the central reviewer and 3.8 ± 0.5 vs 4.0 ± 0.1 for the local pathologist reviewers, respectively. In terms of median value, similar results were observed between the two fixative groups, with a median value of 4.0. Data collected indicate the non-inferiority of GAF as compared to PBF for all organs tested. The present clinical performance study, performed following the international standard for performance evaluation of in vitro diagnostic medical devices, highlights the capability of GAF to ensure both structural preservation and diagnostic value of the preparations.

Unraveling the ultrastructure and dynamics of autophagic vesicles: Insights from advanced imaging techniques

Autophagy, an intracellular self-degradation process, is governed by a complex interplay of signaling pathways and interactions between proteins and organelles. Its fundamental purpose is to efficiently clear and recycle cellular components that are damaged or redundant. Central to this process are autophagic vesicles, specialized structures that encapsulate targeted cellular elements, playing a pivotal role in autophagy. Despite growing interest in the molecular components of autophagic machinery and their regulatory mechanisms, capturing the detailed ultrastructural dynamics of autophagosome formation continues to present significant challenges. However, recent advancements in microscopy, particularly in electron microscopy, have begun to illuminate the dynamic regulatory processes underpinning autophagy. This review endeavors to provide an exhaustive overview of contemporary research on the ultrastructure of autophagic processes. By synthesizing observations from diverse technological methodologies, this review seeks to deepen our understanding of the genesis of autophagic vesicles, their membrane origins, and the dynamic alterations that transpire during the autophagy process. The aim is to bridge gaps in current knowledge and foster a more comprehensive comprehension of this crucial cellular mechanism.

Optimizing protein crosslinking control: Synergistic quenching effects of glycine, histidine, and lysine on glutaraldehyde reactions

Glutaraldehyde (GA) is a protein crosslinker widely used in biochemical and pharmaceutical research because it can rapidly stabilize and immobilize substrates via amine group interactions. However, controlling GA crosslinking is challenging owing to its swift reactivity and the influence of various solution conditions, such as pH and concentrations of the substrate and crosslinker. Although extensive research has focused on GA cross-linking mechanisms, studies on quenching, which is critical for preventing non-specific aggregation during prolonged storage, remain sparse. This study examines the quenching efficiency of a combined amino acid mixture of glycine, histidine, and lysine, which are commonly used as individual quenchers. Our findings, confirmed using sodium dodecyl sulphate-polyacrylamide gel electrophoresis, demonstrate that this amino acid blend offers superior quenching compared to single amino acids, enhancing quenching activity across a wide pH spectrum. These results provide a novel approach for mitigating the high reactivity of GA with implications for improving sample preservation and stabilization in a range of biochemical applications, including microscopy and cell fixation.

SARS-CoV-2 inactivation in laboratory animal tissues with 4% formaldehyde or 5% glutaraldehyde for transfer to biosafety level 1 laboratories

The SARS-CoV-2 pandemic required the immediate need to transfer inactivated tissue from biosafety level (BSL)-3 to BSL-1 areas to enable downstream analytical methods. No validated SARS-CoV-2 inactivation protocols were available for either formaldehyde (FA)-fixed or glutaraldehyde (GA)-fixed tissues. Therefore, representative tissue from ferrets and hamsters was spiked with 2.2 × 106 tissue culture infectious dose 50% per ml (TCID50/ml) SARS-CoV-2 or were obtained from mice experimentally infected with SARS-CoV-2. SARS-CoV-2 inactivation was demonstrated with 4% FA or 5% GA at room temperature for 72 hours by a titer reduction of up to 103.8 TCID50/ml in different animal tissues with a maximum protein content of 100 µg/mg and a thickness of up to 10 mm for FA and 8 mm for GA. Our protocols can be easily adapted for validating the inactivation of other pathogens to allow for the transfer of biological samples from BSL-3 areas to BSL-1 laboratories.

Imaging Bunyavirus Infections by Transmission Electron Microscopy: Conventional Sample Preparation vs High-Pressure Freezing and Freeze-Substitution

Transmission electron microscopy significantly contributed to unveil the course of virus entry, replication, morphogenesis, and egress. For these studies, the most widely used approach is imaging ultrathin sections of virus-infected cells embedded in a plastic resin that is transparent to electrons. Before infiltration in a resin, cells must be processed to stabilize their components under the observation conditions in an electron microscope, such as high vacuum and irradiation with electrons. For conventional sample preparation, chemical fixation and dehydration are followed by infiltration in the resin and polymerization to produce a hard block that can be sectioned with an ultramicrotome. Another method that provides a superior preservation of cell components is high-pressure freezing (HPF) followed by freeze substitution (FS) before resin infiltration and polymerization. This chapter describes both procedures with cells infected with Bunyamwera virus (BUNV), a well characterized member of the Bunyavirales, and compares the morphological details of different viral structures imaged in the two types of samples. Advantages, disadvantages, and applications of conventional processing and HPF/FS are also presented and discussed.

Direct observation of the effects of chemical fixation in MNT-1 cells: A SE-ADM and Raman study

Aldehydes fixation was accidentally discovered in the early 20th century and soon became a widely adopted practice in the histological field, due to an excellent staining enhancement in tissues imaging. However, the fixation process itself entails cell proteins denaturation and crosslinking. The possible presence of artifacts, that depends on the specific system under observation, must therefore be considered to avoid data misinterpretation. This contribution takes advantage of scanning electron assisted-dielectric microscopy (SE-ADM) and Raman 2D imaging to reveal the possible presence and the nature of artifacts in unstained, and paraformldehyde, PFA, fixed MNT-1 cells. The high resolution of the innovative SE-ADM technique allowed the identification of globular protein clusters in the cell cytoplasm, formed after protein denaturation and crosslinking. Concurrently, SE-ADM images showed a preferential melanosome adsorption on the cluster's outer surface. The micron-sized aggregates were discernible in Raman 2D images, as the melanosomes signal, extracted through 2D principal component analysis, unequivocally mapped their location and distribution within the cells, appearing randomly distributed in the cytoplasm. Protein clusters were not observed in living MNT-1 cells. In this case, mature melanosomes accumulate preferentially at the cell periphery and are more closely packed than in fixed cells. Our results show that, although PFA does not affect the melanin structure, it disrupts melanosome distribution within the cells. Proteins secondary structure, conversely, is partially lost, as shown by the Raman signals related to α-helix, β-sheets, and specific amino acids that significantly decrease after the PFA treatment.

Glyoxal fixation: An approach to solve immunohistochemical problem in neuroscience research

The gold-standard fixative for immunohistochemistry is 4% formaldehyde; however, it limits antibody access to target molecules that are buried within specialized neuronal components, such as ionotropic receptors at the postsynapse and voltage-gated ion channels at the axon initial segment, often requiring additional antigen-exposing techniques to detect their authentic signals. To solve this problem, we used glyoxal, a two-carbon atom di-aldehyde. We found that glyoxal fixation greatly improved antibody penetration and immunoreactivity, uncovering signals for buried molecules by conventional immunohistochemical procedures at light and electron microscopic levels. It also enhanced immunosignals of most other molecules, which are known to be detectable in formaldehyde-fixed sections. Furthermore, we unearthed several specific primary antibodies that were once judged to be unusable in formaldehyde-fixed tissues, allowing us to successfully localize so far controversial synaptic adhesion molecule Neuroligin 1. Thus, glyoxal is a highly effective fixative for immunostaining, and a side-by-side comparison of glyoxal and formaldehyde fixation is recommended for routine immunostaining in neuroscience research.

Magnify is a universal molecular anchoring strategy for expansion microscopy

Expansion microscopy enables nanoimaging with conventional microscopes by physically and isotropically magnifying preserved biological specimens embedded in a crosslinked water-swellable hydrogel. Current expansion microscopy protocols require prior treatment with reactive anchoring chemicals to link specific labels and biomolecule classes to the gel. We describe a strategy called Magnify, which uses a mechanically sturdy gel that retains nucleic acids, proteins and lipids without the need for a separate anchoring step. Magnify expands biological specimens up to 11 times and facilitates imaging of cells and tissues with effectively around 25-nm resolution using a diffraction-limited objective lens of about 280 nm on conventional optical microscopes or with around 15 nm effective resolution if combined with super-resolution optical fluctuation imaging. We demonstrate Magnify on a broad range of biological specimens, providing insight into nanoscopic subcellular structures, including synaptic proteins from mouse brain, podocyte foot processes in formalin-fixed paraffin-embedded human kidney and defects in cilia and basal bodies in drug-treated human lung organoids.

Nanogold based protein localization enables subcellular visualization of cell junction protein by SBF-SEM

Recent advances in volume electron microscopy (vEM) allow unprecedented visualization of the electron-dense structures of cells, tissues and model organisms at nanometric resolution in three dimensions (3D). Light-based microscopy has been widely used for specific localization of proteins; however, it is restricted by the diffraction limit of light, and lacks the ability to identify underlying structures. Here, we describe a protocol for ultrastructural detection, in three dimensions, of a protein (Connexin 43) expressed in the intercalated disc region of adult murine heart. Our protocol does not rest on the expression of genetically encoded proteins and it overcomes hurdles related to pre-embedding and immunolabeling, such as the penetration of the label and the preservation of the tissue. The pre-embedding volumetric immuno-electron microscopy (pre-embedding vIEM) protocol presented here combines several practical strategies to balance sample fixation with antigen and ultrastructural preservation, and penetration of labeling with blocking of non-specific antigen binding sites. The small 1.4 nm gold along with surrounded silver used as a detection marker buried in the sample also serves as a functional conductive resin that significantly reduces the charging of samples. Our protocol also presents strategies for facilitating the successful cutting of the samples during serial block-face scanning electron microscopy (SBF-SEM) imaging. Our results suggest that the small gold-based pre-embedding vIEM is an ideal labeling method for molecular localization throughout the depth of the sample at subcellular compartments and membrane microdomains.

Gum Acacia attenuates cisplatin toxic effect spermatogenesis dysfunction and infertility in rats

This study aimed to investigate the potential benefits Gum Arabic/Acacia Senegal (GA) in mitigating the harmful effects of cisplatin (CP) on spermatogenesis and testicular health in male adult rats. A total of forty albino rats were used in the study and divided into four groups; control, GA, CP, and Co-treated group, which received both CP and GA concurrently. The results revealed that CP caused a significant increase in oxidative stress and a decrease in antioxidant levels (CAT, SOD, and GSH), which disturbed the testicular machinery. This caused significant histological and ultrastructural damage to the testicular structure, including atrophied seminiferous tubules with severely reduced germinal epithelium. Additionally, CP caused a decrease in reproductive hormones (testosterone and LH), a decline in nucleic proliferation PCNA immunoexpression, and an increase in cytoplasmic apoptotic Caspase-3 protein expression in testicular tissue, when compared to the control and GA groups. Moreover, The CP treatment impaired spermatogenesis and decreased sperm number and motility with abnormal morphology. However, co-administration of GA with CP mitigated the dysfunction in spermatogenesis and reversed testicular damage caused by CP through significantly (P < 0.01) reducing oxidative stress (MDA) and increasing the activities of CAT, SOD, and GSH. Additionally, co-administration of GA elevated the levels of testosterone and luteinizing hormone in blood sera, significantly (P < 0.01) improved the histometric measurements of seminiferous tubules diameter, their epithelial height, Johnsen's score of spermatogenesis, 4-level histological grading scale Cosentino's score, immunohistochemical expression of nucleic PCNA, and cytoplasmic Caspase-3 proteins. Furthermore, TEM examination confirmed the synergistic effect of GA in restoring the germinal epithelial cells ultrastructure, the elongated and transverse sections of spermatozoa in the lumen, and the interstitial tissue. All of these effects resulted in a significant improvement in sperm quality in the Co-treated animals compared with the CP group, as well as, a significant decline in the morphological abnormalities of sperm in Co-treated rats compared to those in the CP group. GA is a valuable agent for ameliorating chemotherapy-related infertility.

Current Progress in Expansion Microscopy: Chemical Strategies and Applications

Expansion microscopy (ExM) is a newly developed super-resolution technique, allowing visualization of biological targets at nanoscale resolution on conventional fluorescence microscopes. Since its introduction in 2015, many efforts have been dedicated to broaden its application range or increase the resolution that can be achieved. As a consequence, recent years have witnessed remarkable advances in ExM. This review summarizes recent progress in ExM, with the focus on the chemical aspects of the method, from chemistries for biomolecule grafting to polymer synthesis and the impact on biological analysis. The combination of ExM with other microscopy techniques, in search of additional resolution improvement, is also discussed. In addition, we compare pre- and postexpansion labeling strategies and discuss the impact of fixation methods on ultrastructure preservation. We conclude this review with a perspective on existing challenges and future directions. We believe that this review will provide a comprehensive understanding of ExM and facilitate its usage and further development.

Near-Native Visualization of SARS-CoV-2 Induced Membrane Remodeling and Virion Morphogenesis

Infection with the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of the COVID-19 pandemic, leads to profound remodeling of cellular membranes, promoting viral replication and virion assembly. A full understanding of this drastic remodeling and the process of virion morphogenesis remains lacking. In this study, we applied room temperature transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) tomography to visualize the SARS-CoV-2 replication factory in Vero cells, and present our results in comparison with published cryo-EM studies. We obtained cryo-EM-like clarity of the ultrastructure by employing high-pressure freezing, freeze substitution (HPF-FS) and embedding, allowing room temperature visualization of double-membrane vesicles (DMVs) in a near-native state. In addition, our data illustrate the consecutive stages of virion morphogenesis and reveal that SARS-CoV-2 ribonucleoprotein assembly and membrane curvature occur simultaneously. Finally, we show the tethering of virions to the plasma membrane in 3D, and that accumulations of virus particles lacking spike protein in large vesicles are most likely not a result of defective virion assembly at their membrane. In conclusion, this study puts forward a room-temperature EM technique providing near-native ultrastructural information about SARS-CoV-2 replication, adding to our understanding of the interaction of this pandemic virus with its host cell.

Priming with gold nanoparticles leads to changes in the photosynthetic apparatus and improves the cold tolerance of wheat

Nanotechnologies provide a great platform for researching nanoparticles effects on living organisms including plants. This work shows the stimulating effect of seed priming with gold nanoparticles (AuNPs) on photosynthetic apparatus of Triticum aestivum seedlings. It was found using inductively coupled plasma-atomic emission and mass spectrometry that AuNPs (the average diameter of 15.3 nm, concentration of 20 μg ml^-1) penetrated into the seeds, but were not found in seedling leaves. Ultrastructural changes in chloroplasts were found using transmission electron microscopy in plants grown from treated seeds: increases in the size of plastids, starch grains, grana in chloroplasts, and the number of thylakoids in grana. The intensity of photosynthesis, the content of chlorophylls, and the portion of unsaturated fatty acids in the composition of total leaf lipids were increased in treated AuNPs plants. This study demonstrates that revealed changes determined the increased tolerance of wheat to low temperature. The adaptive significance of these changes, possible mechanisms of the AuNPs effects on plants and future perspectives of study are discussed. This is the first report showing nanopriming with AuNPs as a new method to study the mechanisms of stress tolerance.

Influence of SARS-CoV-2 inactivation by different chemical reagents on the humoral response evaluated in a murine model

Viral inactivation for antibody induction purposes, among other applications, should ensure biosafety, completely avoiding the risk of infectivity, and preserving viral immunogenicity. β-propiolactone (BPL) is one of the most used reagents for viral inactivation, despite its high toxicity and recent difficulties related to importation, experienced in Brazil during the SARS-CoV-2 pandemic. In this context, the main objectives of this work were to test different inactivation procedures for SARS-CoV-2 and to evaluate the induction of neutralizing antibodies in mice immunized with antigenic preparations obtained after viral treatment with formaldehyde (FDE), glutaraldehyde (GDE), peroxide hydrogen (H₂O₂), as well as with viral proteins extract (VPE), in parallel with BPL. Verification of viral inactivation was performed by subsequent incubations of the inactivated virus in Vero cells, followed by cytopathic effect and lysis plaques observation, as well as by quantification of RNA load using reverse transcription-quantitative real time polymerase chain reaction. Once viral inactivation was confirmed, cell culture supernatants were concentrated and purified. In addition, an aliquot inactivated by BPL was also subjected to viral protein extraction (VPE). The different antigens were prepared using a previously developed microemulsion as adjuvant, and were administered in a four-dose immunization protocol. Antibody production was comparatively evaluated by ELISA and Plaque Reduction Neutralization Tests (PRNT). All immunogens evaluated showed some level of IgG anti-SARS-CoV-2 antibodies in the ELISA assay, with the highest levels presented by the group immunized with FDE-inactivated viral antigen. In the PRNT results, except for VPE-antigen, all other immunogens evaluated induced some level of neutralizing anti-SARS-CoV-2 antibodies, and the FDE-antigen stood out again with the most expressive values. Taken together, the present work shows that FDE can be an efficient and affordable alternative to BPL for the production of inactivated SARS-CoV-2 viral antigen.

One for All, All for One: A Close Look at In-Resin Fluorescence Protocols for CLEM

Sample preparation is the novel bottleneck for high throughput correlative light and electron microscopy (CLEM). Protocols suitable for both imaging methods must therefore balance the requirements of each technique. For fluorescence light microscopy, a structure of interest can be targeted using: 1) staining, which is often structure or tissue specific rather than protein specific, 2) dye-coupled proteins or antibodies, or 3) genetically encoded fluorescent proteins. Each of these three methods has its own advantages. For ultrastructural investigation by electron microscopy (EM) resin embedding remains a significant sample preparation approach, as it stabilizes the sample such that it withstands the vacuum conditions of the EM, and enables long-term storage. Traditionally, samples are treated with heavy metal salts prior to resin embedding, in order to increase imaging contrast for EM. This is particularly important for volume EM (vEM) techniques. Yet, commonly used contrasting agents (e.g., osmium tetroxide, uranyl acetate) tend to impair fluorescence. The discovery that fluorescence can be preserved in resin-embedded specimens after mild heavy metal staining was a game changer for CLEM. These so-called in-resin fluorescence protocols present a significant leap forward for CLEM approaches towards high precision localization of a fluorescent signal in (volume) EM data. Integrated microscopy approaches, combining LM and EM detection into a single instrument certainly require such an “all in one” sample preparation. Preserving, or adding, dedicated fluorescence prior to resin embedding requires a compromise, which often comes at the expense of EM imaging contrast and membrane visibility. Especially vEM can be strongly hampered by a lack of heavy metal contrasting. This review critically reflects upon the fundamental aspects of resin embedding with regard to 1) specimen fixation and the physics and chemistry underlying the preservation of protein structure with respect to fluorescence and antigenicity, 2) optimization of EM contrast for transmission or scanning EM, and 3) the choice of embedding resin. On this basis, various existing workflows employing in-resin fluorescence are described, highlighting their common features, discussing advantages and disadvantages of the respective approach, and finally concluding with promising future developments for in-resin CLEM.

Chemical fixation creates nanoscale clusters on the cell surface by aggregating membrane proteins

Chemical fixations have been thought to preserve the structures of the cells or tissues. However, given that the fixatives create crosslinks or aggregate proteins, there is a possibility that these fixatives create nanoscale artefacts by aggregation of membrane proteins which move around freely to some extent on the cell surface. Despite this, little research has been conducted about this problem, probably because there has been no method for observing cell surface structures at the nanoscale. In this study, we have developed a method to observe cell surfaces stably and with high resolution using atomic force microscopy and a microporous silicon nitride membrane. We demonstrate that the size of the protrusions on the cell surface is increased after treatment with three commonly used fixatives and show that these protrusions were created by the aggregation of membrane proteins by fixatives. These results call attention when observing fixed cell surfaces at the nanoscale.

Atomic force microscopy imaging shows that cell fixation can lead to unwanted aggregation of membrane proteins.

X-ray Fluorescence Microscopy Methods for Biological Tissues

Synchrotron-based X-ray fluorescence microscopy is a flexible tool for identifying the distribution of trace elements in biological specimens across a broad range of sample sizes. The technique is not particularly limited by sample type and can be performed on ancient fossils, fixed or fresh tissue specimens, and in some cases even live tissue and live cells can be studied. The technique can also be expanded to provide chemical specificity to elemental maps, either at individual points of interest in a map or across a large field of view. While virtually any sample type can be characterized with X-ray fluorescence microscopy, common biological sample preparation methods (often borrowed from other fields, such as histology) can lead to unforeseen pitfalls, resulting in altered element distributions and concentrations. A general overview of sample preparation and data acquisition methods for X-ray fluorescence microscopy is presented, along with outlining the general approach for applying this technique to a new field of investigation for prospective new-users. Considerations for improving data acquisition and quality are reviewed as well as the effects of sample preparation, with a particular focus on soft tissues. The effects of common sample pre-treatment steps as well as the underlying factors that govern which, and to what extent, specific elements are likely to be altered are reviewed along with common artifacts observed in X-ray fluorescence microscopy data.

Pollen Development and Viability in Diploid and Doubled Diploid Citrus Species

Seedlessness is one of the most important agronomic traits in mandarins on the fresh fruit market. Creation of triploid plants is an important breeding strategy for development of new commercial varieties of seedless citrus. To this end, one strategy is to perform sexual hybridizations, with tetraploid genotypes as male parents. However, while seed development has been widely studied in citrus, knowledge of key steps such as microsporogenesis and microgametogenesis, is scarce, especially in polyploids. Therefore, we performed a study on the effect of ploidy level on pollen development by including diploid and tetraploid (double diploid) genotypes with different degrees of pollen performance. A comprehensive study on the pollen ontogeny of diploid and doubled diploid "Sanguinelli" blood orange and "Clemenules" clementine was performed, with focus on pollen grain germination in vitro and in planta, morphology of mature pollen grains by scanning electron microscopy (SEM), cytochemical characterization of carbohydrates by periodic acid-Shiff staining, and specific cell wall components revealed by immunolocalization. During microsporogenesis, the main difference between diploid and doubled diploid genotypes was cell area, which was larger in doubled diploid genotypes. However, after increase in size and vacuolization of microspores, but before mitosis I, doubled diploid "Clemenules" clementine showed drastic differences in shape, cell area, and starch hydrolysis, which resulted in shrinkage of pollen grains. The loss of fertility in doubled diploid "Clemenules" clementine is mainly due to lack of carbohydrate accumulation in pollen during microgametogenesis, especially starch content, which led to pollen grain abortion. All these changes make the pollen of this genotype unviable and very difficult to use as a male parent in sexual hybridization with the objective of recovering large progenies of triploid hybrids.

Crosslinkers for polysaccharides and proteins: Synthesis conditions, mechanisms, and crosslinking efficiency, a review

Polysaccharides and proteins are important macromolecules for developing hydrogels devoted to biomedical applications. Chemical hydrogels offer chemical, mechanical, and dimensional stability than physical hydrogels due to the chemical bonds among the chains mediated by crosslinkers. There are many crosslinkers to synthesize polysaccharides and proteins based on hydrogels. In this review, we revisited the crosslinking reaction mechanisms between synthetic or natural crosslinkers and polysaccharides or proteins. The selected synthetic crosslinkers were glutaraldehyde, carbodiimide, boric acid, sodium trimetaphosphate, N,N'-methylene bisacrylamide, and polycarboxylic acid, whereas the selected natural crosslinkers included transglutaminase, tyrosinase, horseradish peroxidase, laccase, sortase A, genipin, vanillin, tannic acid, and phytic acid. No less important are the reactions involving click chemistry and the macromolecular crosslinkers for polysaccharides and proteins. Literature examples of polysaccharides or proteins crosslinked by the different strategies were presented along with the corresponding highlights. The general mechanism involved in chemical crosslinking mediated by gamma and UV radiation was discussed, with particular attention to materials commonly used in digital light processing. The evaluation of crosslinking efficiency by gravimetric measurements, rheology, and spectroscopic techniques was presented. Finally, we presented the challenges and opportunities to create safe chemical hydrogels for biomedical applications.

Control of Synapse Structure and Function by Actin and Its Regulators

Neurons transmit and receive information at specialized junctions called synapses. Excitatory synapses form at the junction between a presynaptic axon terminal and a postsynaptic dendritic spine. Supporting the shape and function of these junctions is a complex network of actin filaments and its regulators. Advances in microscopic techniques have enabled studies of the organization of actin at synapses and its dynamic regulation. In addition to highlighting recent advances in the field, we will provide a brief historical perspective of the understanding of synaptic actin at the synapse. We will also highlight key neuronal functions regulated by actin, including organization of proteins in the pre- and post- synaptic compartments and endocytosis of ion channels. We review the evidence that synapses contain distinct actin pools that differ in their localization and dynamic behaviors and discuss key functions for these actin pools. Finally, whole exome sequencing of humans with neurodevelopmental and psychiatric disorders has identified synaptic actin regulators as key disease risk genes. We briefly summarize how genetic variants in these genes impact neurotransmission via their impact on synaptic actin.

The tubulin code in platelet biogenesis

Blood platelets are small non-nucleated cellular fragments that prevent and stop hemorrhages. They are produced in the bone marrow by megakaryocytes through megakaryopoiesis. This intricate process involves profound microtubule rearrangements culminating in the formation of a unique circular sub-membranous microtubule array, the marginal band, which supports the typical disc-shaped morphology of platelets. Mechanistically, these processes are thought to be controlled by a specific tubulin code. In this review, we summarize the current knowledge on the key isotypes, notably β1-, α4A- and α8-tubulin, and putative post-translational modifications, involved in platelet and marginal band formation. Additionally, we provide a provisional list of microtubule-associated proteins (MAPs) involved in these processes and a survey of tubulin variants identified in patients presenting defective platelet production. A comprehensive characterization of the platelet tubulin code and the identification of essential MAPs may be expected in the near future to shed new light on a very specialized microtubule assembly process with applications in platelet diseases and transfusion.

Bacterial safety study of the production process of hemoglobin-based oxygen carriers

Hemoglobin microparticles (HbMP) produced with a three-step procedure, including coprecipitation of hemoglobin with manganese carbonate, protein cross-linking, and dissolution of the carbonate template were shown to be suitable for application as artificial oxygen carriers. First preclinical safety investigations delivered promising results. Bacterial safety plays a decisive role during the production of HbMP. Therefore, the bioburden and endotoxin content of the starting materials (especially hemoglobin) and the final particle suspension are intensively tested. However, some bacteria may not be detected by standard tests due to low concentration. The aim of this study was to investigate how these bacteria would behave in the fabrication process. Biocidal effects are known for glutaraldehyde and for ethylenediaminetetraacetic acid, chemicals that are used in the fabrication process of HbMP. It was shown that both chemicals prevent bacterial growth at the concentrations used during HbMP fabrication. In addition, the particle production was carried out with hemoglobin solutions spiked with Escherichia coli or Staphylococcus epidermidis. No living bacteria could be detected in the final particle suspensions. Therefore, we conclude that the HbMP fabrication procedure is safe in respect of bacterial contamination.

High-Pressure Freezing and Transmission Electron Microscopy to Visualize the Ultrastructure of the C. auris Cell Wall

Transmission electron microscopy (TEM) is the main technique used to study the ultrastructure of biological samples. Chemical fixation was considered the main method for preserving samples for TEM; however, it is a relatively slow method of fixation and can result in morphological alterations. Cryofixation using high-pressure freezing (HPF) overcomes the limitations of chemical fixation by preserving samples instantly. Here, we describe our HPF methods optimized for visualizing Candida auris at the ultrastructural level.

Imaging Cytoskeleton Components by Electron Microscopy

The cytoskeleton is a complex of detergent-insoluble components of the cytoplasm playing critical roles in cell motility, shape generation, and mechanical properties of a cell. Fibrillar polymers-actin filaments, microtubules, and intermediate filaments-are major constituents of the cytoskeleton, which constantly change their organization during cellular activities. The actin cytoskeleton is especially polymorphic, as actin filaments can form multiple higher-order assemblies performing different functions. Structural information about cytoskeleton organization is critical for understanding its functions and mechanisms underlying various forms of cellular activity. Because of the nanometer-scale thickness of cytoskeletal fibers, electron microscopy (EM) is a key tool to determine the structure of the cytoskeleton.This article describes application of rotary shadowing (or platinum replica ) EM (PREM) for visualization of the cytoskeleton . The procedure is applicable to thin cultured cells growing on glass coverslips and consists of detergent extraction (or mechanical "unroofing") of cells to expose their cytoskeleton , chemical fixation to provide stability, ethanol dehydration and critical point drying to preserve three-dimensionality, rotary shadowing with platinum to create contrast, and carbon coating to stabilize replicas. This technique provides easily interpretable three-dimensional images, in which individual cytoskeletal fibers are clearly resolved and individual proteins can be identified by immunogold labeling. More importantly, PREM is easily compatible with live cell imaging, so that one can correlate the dynamics of a cell or its components, e.g., expressed fluorescent proteins, with high-resolution structural organization of the cytoskeleton in the same cell.

Field-Emission Scanning Electron Microscope as a Tool for Large-Area and Large-Volume Ultrastructural Studies

Simple Summary

Ultrastructural studies of cells and tissues are usually performed using transmission electron microscopy (TEM), which enables imaging at the highest possible resolution. The weak point of TEM is the limited ability to analyze the ultrastructure of large areas and volumes of biological samples. This limitation can be overcome by using modern field-emission scanning electron microscopy (FE-SEM) with high-sensitivity detection, which enables the creation of TEM-like images from the flat surfaces of resin-embedded biological specimens. Several FE-SEM-based techniques for two- and three-dimensional ultrastructural studies of cells, tissues, organs, and organisms have been developed in the 21st century. These techniques have created a new era in structural biology and have changed the role of the scanning electron microscope (SEM) in biological and medical laboratories. Since the premiere of the first commercially available SEM in 1965, these instruments were used almost exclusively to obtain topographical information over a large range of magnifications. Currently, FE-SEM offers many attractive possibilities in the studies of cell and tissue ultrastructure, and they are presented in this review.

Abstract

The development of field-emission scanning electron microscopes for high-resolution imaging at very low acceleration voltages and equipped with highly sensitive detectors of backscattered electrons (BSE) has enabled transmission electron microscopy (TEM)-like imaging of the cut surfaces of tissue blocks, which are impermeable to the electron beam, or tissue sections mounted on the solid substrates. This has resulted in the development of methods that simplify and accelerate ultrastructural studies of large areas and volumes of biological samples. This article provides an overview of these methods, including their advantages and disadvantages. The imaging of large sample areas can be performed using two methods based on the detection of transmitted electrons or BSE. Effective imaging using BSE requires special fixation and en bloc contrasting of samples. BSE imaging has resulted in the development of volume imaging techniques, including array tomography (AT) and serial block-face imaging (SBF-SEM). In AT, serial ultrathin sections are collected manually on a solid substrate such as a glass and silicon wafer or automatically on a tape using a special ultramicrotome. The imaging of serial sections is used to obtain three-dimensional (3D) information. SBF-SEM is based on removing the top layer of a resin-embedded sample using an ultramicrotome inside the SEM specimen chamber and then imaging the exposed surface with a BSE detector. The steps of cutting and imaging the resin block are repeated hundreds or thousands of times to obtain a z-stack for 3D analyses.

Shape-shifting thermoreversible diblock copolymer nano-objects via RAFT aqueous dispersion polymerization of 4-hydroxybutyl acrylate

2-Hydroxypropyl methacrylate (HPMA) is a useful model monomer for understanding aqueous dispersion polymerization. 4-Hydroxybutyl acrylate (HBA) is an isomer of HPMA: it has appreciably higher aqueous solubility so its homopolymer is more weakly hydrophobic. Moreover, PHBA possesses a significantly lower glass transition temperature than PHPMA, which ensures greater chain mobility. The reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of HBA using a poly(ethylene glycol) (PEG113) precursor at 30 °C produces PEG113-PHBA200-700 diblock copolymer nano-objects. Using glutaraldehyde to crosslink the PHBA chains allows TEM studies, which reveal the formation of spheres, worms or vesicles under appropriate conditions. Interestingly, the partially hydrated highly mobile PHBA block enabled linear PEG113-PHBA x spheres, worms or vesicles to be reconstituted from freeze-dried powders on addition of water at 20 °C. Moreover, variable temperature 1H NMR studies indicated that the apparent degree of hydration of the PHBA block increases from 5% to 80% on heating from 0 °C to 60 °C indicating uniform plasticization. In contrast, the PHPMA x chains within PEG113-PHPMA x nano-objects become dehydrated on raising the temperature: this qualitative difference is highly counter-intuitive given that PHBA and PHPMA are isomers. The greater (partial) hydration of the PHBA block at higher temperature drives the morphological evolution of PEG113-PHBA260 spheres to form worms or vesicles, as judged by oscillatory rheology, dynamic light scattering, small-angle X-ray scattering and TEM studies. Finally, a variable temperature phase diagram is constructed for 15% w/w aqueous dispersions of eight PEG113-PHBA200-700 diblock copolymers. Notably, PEG113-PHBA350 can switch reversibly from spheres to worms to vesicles to lamellae during a thermal cycle.

Arbuscular mycorrhizal symbioses alleviating salt stress in maize is associated with a decline in root-to-leaf gradient of Na+/K+ ratio

BACKGROUND

Inoculation of arbuscular mycorrhizal (AM) fungi has the potential to alleviate salt stress in host plants through the mitigation of ionic imbalance. However, inoculation effects vary, and the underlying mechanisms remain unclear. Two maize genotypes (JD52, salt-tolerant with large root system, and FSY1, salt-sensitive with small root system) inoculated with or without AM fungus Funneliformis mosseae were grown in pots containing soil amended with 0 or 100 mM NaCl (incrementally added 32 days after sowing, DAS) in a greenhouse. Plants were assessed 59 DAS for plant growth, tissue Na⁺ and K⁺ contents, the expression of plant transporter genes responsible for Na⁺ and/or K⁺ uptake, translocation or compartmentation, and chloroplast ultrastructure alterations.

RESULTS

Under 100 mM NaCl, AM plants of both genotypes grew better with denser root systems than non-AM plants. Relative to non-AM plants, the accumulation of Na⁺ and K⁺ was decreased in AM plant shoots but increased in AM roots with a decrease in the shoot: root Na⁺ ratio particularly in FSY1, accompanied by differential regulation of ion transporter genes (i.e., ZmSOS1, ZmHKT1, and ZmNHX). This induced a relatively higher Na⁺ efflux (recirculating) rate than K⁺ in AM shoots while the converse outcoming (higher Na⁺ influx rate than K⁺) in AM roots. The higher K⁺: Na⁺ ratio in AM shoots contributed to the maintenance of structural and functional integrity of chloroplasts in mesophyll cells.

CONCLUSION

AM symbiosis improved maize salt tolerance by accelerating Na⁺ shoot-to-root translocation rate and mediating Na⁺/K⁺ distribution between shoots and roots.

Processing hair follicles for transmission electron microscopy

Transmission electron microscopy (TEM) has greatly advanced our knowledge of hair growth and follicle morphogenesis, but complex preparations such as fixation, dehydration and embedding compromise ultrastructure. While recent developments with cryofixation have been shown to preserve the ultrastructure of biological materials close to native state, they do have limitations. This review will focus on each stage of the TEM sample preparation process and their effects on the structural integrity of follicles.

Morphological variability in the mucosal attachment site of Trichuris muris revealed by X-ray microcomputed tomography

Parasitic infections can be challenging to study because two dimensional light and electron microscopy are often limited in visualising complex and inaccessible attachment sites. Exemplifying this, Trichuris spp. inhabit a tunnel of epithelial cells within the host caecum and colon. A significant global burden of this infection persists, partly because available anthelminthics lack efficacy, although the mechanisms underlying this remain unknown. Consequently, there is a need to pioneer new approaches to better characterize the parasite niche within the host and investigate how variation in its morphology and integrity may contribute to resistance to therapeutic intervention. To address these aims, we exploited three-dimensional X-ray micro-computed tomography (microCT) to image the mouse whipworm, Trichuris muris, in caeca of wild-type C57BL/6 and SCID mice ex vivo. Using osmium tetroxide staining to effectively enhance the contrast of worms, we found that a subset exhibited preferential positioning towards the bases of the intestinal crypts. Moreover, in one rare event, we demonstrated whipworm traversal of the lamina propria. This morphological variability contradicts widely accepted conclusions from conventional microscopy of the parasite niche, showing Trichuris in close contact with the host proliferative and immune compartments that may facilitate immunomodulation. Furthermore, by using a skeletonization-based approach we demonstrate considerable variation in tunnel length and integrity. The qualitative and quantitative observations provide a new morphological point of reference for future in vitro study of host-Trichuris interactions, and highlight the potential of microCT to characterise enigmatic host-parasite interactions more accurately.

An optimized fixation method containing glyoxal and paraformaldehyde for imaging nuclear bodies

The mammalian cell nucleus contains different types of membrane-less nuclear bodies (NBs) consisting of proteins and RNAs. Microscopic imaging has been widely applied to study the organization and structure of NBs. However, current fixation methods are not optimized for such imaging: When a fixation method is chosen to maximize the quality of the RNA fluorescence in situ hybridization (FISH), it often limits the labeling efficiency of proteins or affects the ultrastructure of NBs. Here, we report that addition of glyoxal (GO) into the classical paraformaldehyde (PFA) fixation step not only improves FISH signals for RNAs in NBs via augmented permeability of the fixed nucleus and enhanced accessibility of probes, but also largely preserves protein fluorescent signals during fixation and immunostaining. We also show that GO/PFA fixation enables the covisualization of different types of nuclear bodies with minimal impact on their ultrastructures under super-resolution microscopy.

The Combination of Paraformaldehyde and Glutaraldehyde Is a Potential Fixative for Mitochondria

Mitochondria are highly dynamic organelles, constantly undergoing shape changes, which are controlled by mitochondrial movement, fusion, and fission. Mitochondria play a pivotal role in various cellular processes under physiological and pathological conditions, including metabolism, superoxide generation, calcium homeostasis, and apoptosis. Abnormal mitochondrial morphology and mitochondrial protein expression are always closely related to the health status of cells. Analysis of mitochondrial morphology and mitochondrial protein expression in situ is widely used to reflect the abnormality of cell function in the chemical fixed sample. Paraformaldehyde (PFA), the most commonly used fixative in cellular immunostaining, still has disadvantages, including loss of antigenicity and disruption of morphology during fixation. We tested the effect of ethanol (ETHO), PFA, and glutaraldehyde (GA) fixation on cellular mitochondria. The results showed that 3% PFA and 1.5% GA (PFA-GA) combination reserved mitochondrial morphology better than them alone in situ in cells. Mitochondrial network and protein antigenicity were well maintained, indicated by preserved MitoTracker and mitochondrial immunostaining after PFA-GA fixation. Our results suggest that the PFA-GA combination is a valuable fixative for the study of mitochondria in situ.

Advanced Microscopy for Liver and Gut Ultrastructural Pathology in Patients with MVID and PFIC Caused by MYO5B Mutations

Mutations in the actin motor protein myosinVb (myo5b) cause aberrant apical cargo transport and the congenital enteropathy microvillus inclusion disease (MVID). Recently, missense mutations in myo5b were also associated with progressive familial intrahepatic cholestasis (MYO5B-PFIC). Here, we thoroughly characterized the ultrastructural and immuno-cytochemical phenotype of hepatocytes and duodenal enterocytes from a unique case of an adult MYO5B-PFIC patient who showed constant hepatopathy but only periodic enteric symptoms. Selected data from two other patients supported the findings. Advanced methods such as cryo-fixation, freeze-substitution, immuno-gold labeling, electron tomography and immuno-fluorescence microscopy complemented the standard procedures. Liver biopsies showed mislocalization of Rab11 and bile canalicular membrane proteins. Rab11-positive vesicles clustered around bile canaliculi and resembled subapical clusters of aberrant recycling endosomes in enterocytes from MVID patients. The adult patient studied in detail showed a severe, MVID-specific enterocyte phenotype, despite only a mild clinical intestinal presentation. This included mislocalization of numerous proteins essential for apical cargo transport and morphological alterations. We characterized the heterogeneous population of large catabolic organelles regarding their complex ultrastructure and differential distribution of autophagic and lysosomal marker proteins. Finally, we generated duodenal organoids/enteroids from biopsies that recapitulated all MVID hallmarks, demonstrating the potential of this disease model for personalized medicine.

Ovary Signals for Pollen Tube Guidance in Chalazogamous Mangifera indica L

Most flowering plants show porogamy in which the pollen tubes reach the egg apparatus through the micropyle. However, several species show chalazogamy, an unusual pollen tube growth, in which the pollen tubes reach the embryo sac through the chalaza. While ovary signals for pollen tube growth and guidance have been extensively studied in porogamous species, few studies have addressed the process in chalazogamous species such as mango (Mangifera indica L.), one of the five most important fruit crops worldwide in terms of production. In this study, we characterize pollen-pistil interaction in mango, paying special attention to three key players known to be involved in the directional pollen tube growth of porogamous species such as starch, arabinogalactan proteins (AGPs), and γ-aminobutyric acid (GABA). Starch grains were observed in the style and in the ponticulus at anthesis, but their number decreased 1 day after anthesis. AGPs, revealed by JIM8 and JIM13 antibodies, were homogenously observed in the style and ovary, but were more conspicuous in the nucellus around the egg apparatus. GABA, revealed by anti-GABA antibodies, was specifically observed in the transmitting tissue, including the ponticulus. Moreover, GABA was shown to stimulate in vitro mango pollen tube elongation. The results support the heterotrophic growth of mango pollen tubes in the style at the expense of starch, similarly to the observations in porogamous species. However, unlike porogamous species, the micropyle of mango does not show high levels of GABA and starch, although they were observed in the ponticulus and could play a role in supporting the unusual pollen tube growth in chalazogamous species.

In vitro Characterization of Insulin-Producing β-Cell Spheroids

Over the years, immortalized rodent β-cell lines such as RIN, HIT, MIN, βTC, and INS-1 have been used to investigate pancreatic β-cell physiology using conventional two-dimensional (2D) culture techniques. However, physical and physiological limitations inherent to 2D cell culture necessitates confirmatory follow up studies using sentient animals. Three-dimensional (3D) culture models are gaining popularity for their recapitulation of key features of in vivo organ physiology, and thus could pose as potential surrogates for animal experiments. In this study, we aimed to develop and characterize a rat insulinoma INS-1 3D spheroid model to compare with 2D monolayers of the same cell line. Ultrastructural verification was done by transmission electron microscopy and toluidine blue staining, which showed that both 2D monolayers and 3D spheroids contained highly granulated cells with ultrastructural features synonymous with mature pancreatic β-cells, with increased prominence of these features observed in 3D spheroids. Viability, as assessed by cellular ATP quantification, size profiling and glucose utilization, showed that our spheroids remained viable for the experimental period of 30 days, compared to the limiting 5-day passage period of INS-1 monolayers. In fact, increasing ATP content together with spheroid size was observed over time, without adverse changes in glucose utilization. Additionally, β-cell function, assessed by determining insulin and amylin secretion, showed that the 3D spheroids retained glucose sensing and insulin secretory capability, that was more acute when compared to 2D monolayer cultures. Thus, we were able to successfully demonstrate that our in vitro INS-1 β-cell 3D spheroid model exhibits in vivo tissue-like structural features with extended viability and lifespan. This offers enhanced predictive capacity of the model in the study of metabolic disease, β-cell pathophysiology and the potential treatment thereof.

Comparative effect of osmium tetroxide and ruthenium tetroxide on Lacazia loboi ultrastructure

Lobomycosis is a skin infection produced by the fungus Lacazia loboi, which mainly affects some indigenous and afro-descendant populations in Tropical America. We previously reported the comparative effect of osmium tetroxide (OsO₄ ) and ruthenium tetroxide (RuO₄ ) in the electron microscopy (EM) of other related microorganisms. The objective of this study is to compare the effect of postfixation with OsO₄ and RuO₄ in the ultrastructure of L. loboi yeasts. Skin biopsies on patients diagnosed with lobomycosis were fixed in glutaraldehyde at 3% and postfixed in the following solutions: (a) 1% OsO₄ , (b) 0.2% RuO₄ , and (c) OsO₄ at 1% followed by RuO₄ at 0.2%. They were then processed using the conventional method for EM. Unlike OsO_4, the treatment with RuO₄ revealed different shades of gray and electron dense bands in the cell wall and other cell components of L. loboi. The most notable finding was the presence of radial filamentous structures around the yeast, which made the image look like the sun. Postfixation with RuO₄ revealed ultrastructural details that had not been previously reported for L loboi. The combined use of OsO₄ and RuO₄ in EM of microorganisms with cell walls can be useful to evaluate the effect of microbicide substances.

Biochemical synthesis of palladium nanoparticles: The influence of chemical fixatives used in electron microscopy on nanoparticle formation and catalytic performance

Palladium nanoparticles (PdNPs) can catalyse a range of reductive chemical reactions transforming both organic and inorganic environmental pollutants. PdNPs that ranged from <2 to 2-40 nm were synthesized using chemical methods, and bacterial biomass with/without chemical fixatives. PdNP formation was enhanced by adsorption of Pd(II) to bacterial biomass, followed by fixation with formate or glutaraldehyde. TEM-SAED analyses confirmed that the cell associated PdNPs were polycrystalline with a face-centered cubic structure. Chemically formed PdNPs possessed a higher Pd(0):Pd(II) ratio and produced structurally similar nanoparticles as the biotic systems. These PdNPs were employed to catalyze two, reductive chemical reactions, transforming 4-nitrophenol (4-NP) and hexavalent chromium [Cr(VI)], into 4-aminophenol and Cr(IV), respectively. In the reduction of 4-NP, the catalytic performance was directly proportional to PdNP surface area, i.e., the smallest PdNPs in formate-PdCH34 cells had the fastest rate of reaction. The mass of Pd(0) as PdNPs was the main contributor to Cr(VI) reduction; the chemically synthesized PdNPs showed the highest removal efficiency with 96% at 20 min. The use of glutaraldehyde enhanced the reduction of Pd(II) and promoted PdNPs formation, i.e., creating an artefact of fixation; however, this treatment also enhanced the catalytic performance of these PdNPs.

A Comprehensive Review of the Covalent Immobilization of Biomolecules onto Electrospun Nanofibers

Biomolecule immobilization has attracted the attention of various fields such as fine chemistry and biomedicine for their use in several applications such as wastewater, immunosensors, biofuels, et cetera. The performance of immobilized biomolecules depends on the substrate and the immobilization method utilized. Electrospun nanofibers act as an excellent substrate for immobilization due to their large surface area to volume ratio and interconnectivity. While biomolecules can be immobilized using adsorption and encapsulation, covalent immobilization offers a way to permanently fix the material to the fiber surface resulting in high efficiency, good specificity, and excellent stability. This review aims to highlight the various covalent immobilization techniques being utilized and their benefits and drawbacks. These methods typically fall into two categories: (1) direct immobilization and (2) use of crosslinkers. Direct immobilization techniques are usually simple and utilize the strong electrophilic functional groups on the nanofiber. While crosslinkers are used as an intermediary between the nanofiber substrate and the biomolecule, with some crosslinkers being present in the final product and others simply facilitating the reactions. We aim to provide an explanation of each immobilization technique, biomolecules commonly paired with said technique and the benefit of immobilization over the free biomolecule.

A perfect confluence of physiology and morphology: discovery of the transverse tubular system and inward spread of activation in skeletal muscle

By early 1954, there existed a plausible model of muscle contraction called the sliding filament model. In addition, the nature of muscle excitation was understood. Surprisingly, the link between the membrane excitation and contraction was entirely unknown. This dilemma has been called the time-distance paradox. The path to discovery of the missing link between excitation and contraction was a rocky one involving the simultaneous but independent development of physiological and morphological studies. From the viewpoint of physiology, significant events included the most thrilling moment of a scientific life, confirmation of a hypothesis that was wrong, a major surprise and shock, a result not expected from evolutionary relationships, and disappointment and confusion before clarity. From the viewpoint of morphology, there was the exciting beginning and rapid development of biological electron microscopy, heroic experiments, the importance of sample preparative procedures, and discovery of clues from the old light microscopic literature. However, it was the confluence of physiology and morphology that brought clarity and a major advance in understanding, leading to the discovery of the transverse tubular system and inward spread of activation in skeletal muscle.

The Progress of the Anticancer Agents Related to the Microtubules Target

Anticancer drugs based on the microtubules target are potent mitotic spindle poison agents, which interact directly with the microtubules, and were classified as microtubule-stabilizing agents and microtubule-destabilizing agents. Researchers have worked tremendously towards the improvements of anticancer drugs, in terms of improving the efficacy, solubility and reducing the side effects, which brought about advancement in chemotherapy. In this review, we focused on describing the discovery, structures and functions of the microtubules as well as the progress of anticancer agents related to the microtubules, which will provide adequate references for researchers.

A Novel Microchip Technique for Quickly Identifying Nanogranules in an Aqueous Solution by Transmission Electron Microscopy: Imaging of Platelet Granules

Ultrastructural observation of biological specimens or nanogranules usually requires the use of electron microscopy. Electron microscopy takes a lot of time, requires many steps, and uses many chemicals, which may affect the native state of biological specimens. A novel microchip (K-kit) was used as a specimen kit for in situ imaging of human platelet granules in an aqueous solution using a transmission electron microscope. This microchip enabled us to observe the native human platelet granules very quickly and easily. The protocols included blood collection, platelet purification, platelet granule isolation, sample loading into this microchip, and then observation by a transmission electron microscope. In addition, these granules could still remain in aqueous solution, and only a very small amount of the sample was required for observation and analysis. We used this microchip to identify the native platelet granules by negative staining. Furthermore, we used this microchip to perform immunoelectron microscopy and successfully label α-granules of platelets with the anti-P-selectin antibody. These results demonstrate that the novel microchip can provide researchers with faster and better choices when using a transmission electron microscope to examine nanogranules of biological specimens in aqueous conditions.

Three-dimensional organization of the cytoskeleton: A cryo-electron tomography perspective

Traditionally, structures of cytoskeletal components have been studied ex situ, that is, with biochemically purified materials. There are compelling reasons to develop approaches to study them in situ in their native functional context. In recent years, cryo-electron tomography emerged as a powerful method for visualizing the molecular organization of unperturbed cellular landscapes with the potential to attain near-atomic resolution. Here, we review recent works on the cytoskeleton using cryo-electron tomography, demonstrating the power of in situ studies. We also highlight the potential of this method in addressing important questions pertinent to the field of cytoskeletal biomechanics.

Response of young Nerium oleander plants to long-term non-ionizing radiation

Although exposure to low frequency electromagnetic radiation is harmful to plants, LF-EM irradiated Nerium oleander seedlings exhibited enhanced development and growth, probably taking advantage of defined structural leaf deformations. Currently, evidence supports the undesirable, often destructive impact of low frequency electromagnetic (LF-EM) radiation on plants. The response of plants to LF-EM radiation often entails induction in the biosynthesis of secondary metabolites, a subject matter that is well documented. Nerium oleander is a Mediterranean plant species, which evolved remarkable resistance to various environmental stress conditions. In the current investigation, cultivated N. oleander plants, following their long-term exposure to LF-EM radiation, exhibited major structural modifications as the flattening of crypts, the elimination of trichomes and the reduction of the layers of the epidermal cells. These changes co-existed with an oxidative stress response manifested by a significant increase in reactive oxygen species at both the roots and the above ground parts, a decline in the absorbance of light by photosynthetic pigments and the substantially increased biosynthesis of L-Dopa decarboxylase (DDC), an enzyme catalyzing the production of secondary metabolites that alleviate stress. The exposed plants exhibited greater primary plant productivity, despite a manifested photosynthetic pigment limitation and the severe oxidative stress. This unique response of N. oleander to severe abiotic stress conditions may be owed to the advantage offered by a structural change consistent to an easier diffusion of CO₂ within the leaves. A major plant response to an emerging "pollutant" was documented.

Isolation of a Chinook Salmon Bafinivirus (CSBV) in Imported Goldfish Carassius auratus L. in the United Kingdom and Evaluation of Its Virulence in Resident Fish Species

This is the first record of a fish nidovirus isolated from a consignment of goldfish at the United Kingdom (UK) border. The full-length viral genome was 25,985 nt, sharing a 97.9% nucleotide identity with the Chinook salmon bafinivirus (CSBV) NIDO with two deletions of 537 and 480 nt on the ORF Ia protein. To assess the potential impact on UK fish species, Atlantic salmon, common carp and goldfish were exposed to the virus via an intraperitoneal (IP) injection and bath challenge. Moribundity was recorded in only 8% of IP-injected goldfish. A high viral load, ≈10⁷ of the CSBV PpIa gene, was measured in the kidney of moribund goldfish. Mild histopathological changes were observed in the kidneys of challenged carps. Ultrastructural observations in renal tubule epithelial cells of goldfish showed cylindrical tubes (≈15 nm in diameter) and tubular structures budding spherical virions (≈200 nm in diameter) with external spike-like structures. Negative staining showed both circular and bacilliform virions. Seroconversion was measured in common carp and goldfish but not in Atlantic salmon. This study reinforces the potential risk of novel and emerging pathogens being introduced to recipient countries via the international ornamental fish trade and the importance of regular full health screens at the border inspection posts to reduce this risk.