Applications of Scanning Electron Microscopy Using Secondary and Backscattered Electron Signals in Neural Structure

Three-dimensional analysis of the intracellular architecture by scanning electron microscopy

The two-dimensional observation of ultrathin sections from resin-embedded specimens provides an insufficient understanding of the three-dimensional (3D) morphological information of membranous organelles. The osmium maceration method, developed by Professor Tanaka's group >40 years ago, is the only technique that allows direct observation of the 3D ultrastructure of membrane systems using scanning electron microscopy (SEM), without the need for any reconstruction process. With this method, the soluble cytoplasmic proteins are removed from the freeze-cracked surface of cells while preserving the integrity of membranous organelles, achieved by immersing tissues in a diluted osmium solution for several days. By employing the maceration method, researchers using SEM have revealed the 3D ultrastructure of organelles such as the Golgi apparatus, mitochondria and endoplasmic reticulum in various cell types. Recently, we have developed new SEM techniques based on the maceration method to explore further possibilities of this method. These include: (i) a rapid osmium maceration method that reduces the reaction duration of the procedure, (ii) a combination method that combines agarose embedding with osmium maceration to elucidate the 3D ultrastructure of organelles in free and cultured cells and (iii) a correlative immunofluorescence and SEM technique that combines cryosectioning with the osmium maceration method, enabling the correlation of the immunocytochemical localization of molecules with the 3D ultrastructure of organelles. In this paper, we review the novel osmium maceration methods described earlier and discuss their potential and future directions in the field of biology and biomedical research.

Antifungal activity of eumelanin-inspired indoylenepheyleneethynylene against Cryptococcus neoformans

Cryptococcus neoformans is an opportunistic fungal pathogen that causes meningitis in >152,000 immunocompromised individuals annually, leading to 112,000 yearly deaths. The four classes of existing antifungal agents target plasma membrane sterols (ergosterol), nucleic acid synthesis, and cell wall synthesis. Existing drugs are not highly effective against Cryptococcus, and antifungal drug resistance is an increasing problem. A novel antimicrobial compound, a eumelanin-inspired indoylenepheyleneethynylene, EIPE-1, was synthesized and has antimicrobial activity against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MSRA), but not towards Gram-negative organisms. Based on EIPE-1's antibacterial activity, we hypothesized that EIPE-1 could have antifungal activity. For these studies, we tested EIPE-1 against C. neoformans strain H99 and 6 additional cryptococcal clinical isolates. We examined antifungal activity, cytotoxicity, effects on fungal gene expression, and mechanism of action of EIPE-1. Results showed that EIPE-1 has fungicidal effects on seven cryptococcal strains with MICs ranging from 1.56 to 3.125 μg/mL depending on the strain, and it is non-toxic to mammalian cells. We conducted scanning and transmission electron microscopy on the exposed cells to examine structural changes to the organism following EIPE-1 treatment. Cells exposed displayed structural changes to their cell wall and membranes, with internal contents leaking out of the cells. To understand the effect of EIPE-1 on fungal gene expression, RNA sequencing was conducted. Results showed that EIPE-1 affects several processes involved stress response, ergosterol biosynthesis, capsule biosynthesis, and cell wall attachment and remodeling. Therefore, our studies demonstrate that EIPE-1 has antifungal activity against C. neoformans, which affects both cellular structure and gene expression of multiple fungal pathways involved in cell membrane stability and viability.

Research-based Analytical Procedures to Evaluate Diabetic Biomarkers and Related Parameters: In Vitro and In Vivo Methods

BACKGROUND

The degenerative tendency of diabetes leads to micro- and macrovascular complications due to abnormal levels of biochemicals, particularly in patients with poor diabetic control. Diabetes is supposed to be treated by reducing blood glucose levels, scavenging free radicals, and maintaining other relevant parameters close to normal ranges. In preclinical studies, numerous in vivo trials on animals as well as in vitro tests are used to assess the antidiabetic and antioxidant effects of the test substances. Since a substance that performs poorly in vitro won't perform better in vivo, the outcomes of in vitro studies can be utilized as a direct indicator of in vivo activities.

OBJECTIVE

The objective of the present study is to provide research scholars with a comprehensive overview of laboratory methods and procedures for a few selected diabetic biomarkers and related parameters.

METHOD

The search was conducted on scientific database portals such as ScienceDirect, PubMed, Google Scholar, BASE, DOAJ, etc. Conclusion: The development of new biomarkers is greatly facilitated by modern technology such as cell culture research, lipidomics study, microRNA biomarkers, machine learning techniques, and improved electron microscopies. These biomarkers do, however, have some usage restrictions. There is a critical need to find more accurate and sensitive biomarkers. With a few modifications, these biomarkers can be used with or even replace conventional markers of diabetes.

A point mutation in GPI-attachment signal peptide accelerates the development of prion disease

A missense variant from methionine to arginine at codon 232 (M232R) of the prion protein gene accounts for ~ 15% of Japanese patients with genetic prion diseases. However, pathogenic roles of the M232R substitution for the induction of prion disease have remained elusive because family history is usually absent in patients with M232R. In addition, the clinicopathologic phenotypes of patients with M232R are indistinguishable from those of sporadic Creutzfeldt-Jakob disease patients. Furthermore, the M232R substitution is located in the glycosylphosphatidylinositol (GPI)-attachment signal peptide that is cleaved off during the maturation of prion proteins. Therefore, there has been an argument that the M232R substitution might be an uncommon polymorphism rather than a pathogenic mutation. To unveil the role of the M232R substitution in the GPI-attachment signal peptide of prion protein in the pathogenesis of prion disease, here we generated a mouse model expressing human prion proteins with M232R and investigated the susceptibility to prion disease. The M232R substitution accelerates the development of prion disease in a prion strain-dependent manner, without affecting prion strain-specific histopathologic and biochemical features. The M232R substitution did not alter the attachment of GPI nor GPI-attachment site. Instead, the substitution altered endoplasmic reticulum translocation pathway of prion proteins by reducing the hydrophobicity of the GPI-attachment signal peptide, resulting in the reduction of N-linked glycosylation and GPI glycosylation of prion proteins. To the best of our knowledge, this is the first time to show a direct relationship between a point mutation in the GPI-attachment signal peptide and the development of disease.

Air- and Moisture Robust Surface Modification for Ni-Rich Layered Cathode Materials for Li-Ion Batteries

The mainstream of high-energy cathode development is focused on increasing the Ni-ratio in layered structured cathode materials. The increment of the Ni portion in the layered cathode material escalates not only the deliverable capacity but also the structural degradation. High-Ni layered cathodes are highly vulnerable to exposure to air that contains CO₂ and H₂ O, forming problematic residual lithium compounds at the surface. In this work, a novel air- and moisture robust surface modification is reported for LiNi_0.8 Co_0.1 Mn_0.1 O₂ (NCM811) via the sol-gel coating method that selectively coats the internal surface area of the polycrystalline morphology secondary particles. Bare-, Li₂ SnO₃ -coated and LiCoO₂ -coated NCM811 are exposed to different ambient environments (air, hot-air, and moisture-air) to systematically investigate the correlation between the internal/external coating morphology and performance degradations. The LiCoO₂ -coated NCM811s exhibit high-capacity retention after exposure to all environments, due to the internal surface coating that prevents the penetration of harmful compounds into the polycrystalline NCM811. On the other hand, the Li₂ SnO₃ -coated NCM811s exposed to the ambient environments show gradual capacity fading, implying the occurrence of internal degradation. This paper highlights the impact of the internal degradation of polycrystalline NCM811 after environmental exposure and the correct coating mechanisms required to successfully prevent it.

Recent technological advances in correlative light and electron microscopy for the comprehensive analysis of neural circuits

Light microscopy (LM) covers a relatively wide area and is suitable for observing the entire neuronal network. However, resolution of LM is insufficient to identify synapses and determine whether neighboring neurons are connected via synapses. In contrast, the resolution of electron microscopy (EM) is sufficiently high to detect synapses and is useful for identifying neuronal connectivity; however, serial images cannot easily show the entire morphology of neurons, as EM covers a relatively narrow region. Thus, covering a large area requires a large dataset. Furthermore, the three-dimensional (3D) reconstruction of neurons by EM requires considerable time and effort, and the segmentation of neurons is laborious. Correlative light and electron microscopy (CLEM) is an approach for correlating images obtained via LM and EM. Because LM and EM are complementary in terms of compensating for their shortcomings, CLEM is a powerful technique for the comprehensive analysis of neural circuits. This review provides an overview of recent advances in CLEM tools and methods, particularly the fluorescent probes available for CLEM and near-infrared branding technique to match LM and EM images. We also discuss the challenges and limitations associated with contemporary CLEM technologies.

Magnetic Sector Secondary Ion Mass Spectrometry on FIB-SEM Instruments for Nanoscale Chemical Imaging

The structural, morphological, and chemical characterization of samples is of utmost importance for a large number of scientific fields. Furthermore, this characterization very often needs to be performed in three dimensions and at length scales down to the nanometer. Therefore, there is a stringent necessity to develop appropriate instrumentational solutions to fulfill these needs. Here we report on the deployment of magnetic sector secondary ion mass spectrometry (SIMS) on a type of instrument widely used for such nanoscale investigations, namely, focused ion beam (FIB)–scanning electron microscopy (SEM) instruments. First, we present the layout of the FIB-SEM-SIMS instrument and address its performance by using specific test samples. The achieved performance can be summarized as follows: an overall secondary ion beam transmission above 40%, a mass resolving power (M/ΔM) of more than 400, a detectable mass range from 1 to 400 amu, a lateral resolution in two-dimensional (2D) chemical imaging mode of 15 nm, and a depth resolution of ∼4 nm at 3.0 keV of beam landing energy. Second, we show results (depth profiling, 2D imaging, three-dimensional imaging) obtained in a wide range of areas, such as battery research, photovoltaics, multilayered samples, and life science applications. We hereby highlight the system’s versatile capability of conducting high-performance correlative studies in the fields of materials science and life sciences.