Phenolic Determination in Proembryogenic Cell Complexes of Buckwheat Morphogenic Cell Culture with Osmium Tetroxide, Toluidine Blue O Dye, and Iron Chloride

The study of the localization of secondary metabolites in both plants and the cell cultures on the intravital sections is hampered by the difficulty of obtaining thin, correctly oriented sections. Techniques for fixing tissues in resins allow these difficulties to be overcome. Properly selected tissue fixation techniques allow using different dyes to identify the compound of interest. In addition, some components of tissue fixation can act as fixatives and as a dye for identifying secondary metabolites. For example, osmium tetroxide, which fixes lipids in tissues, stains phenolic compounds black. This paper describes methods for the detection of phenolic compounds in morphogenic callus culture of buckwheat using osmium tetroxide, Toluidine Blue O dye, and ferric chloride as dyes in epoxy resin-embedded cell culture with double fixation of the material and when material fixed in Karnovsky's fixative.

Application of immuno- and affinity labeling with fluorescent dyes to in-resin CLEM of Epon-embedded cells

In-resin CLEM (Correlative Light and Electron Microscopy) of Epon-embedded cells involves correlating fluorescence microscopy with electron microscopy in the same Epon-embedded ultrathin section. This method offers the advantage of high positional accuracy compared to standard CLEM. However, it requires the expression of recombinant proteins. In order to detect the localization of endogenous target(s) and their localized ultrastructures of Epon-embedded samples using in-resin CLEM, we investigated whether immunological and affinity-labeling using fluorescent dyes applied to in-resin CLEM of Epon-embedded cells. The orange fluorescent (λ_em ∼550 nm) and far-red (λ_em ∼650 nm) fluorescent dyes examined maintained a sufficient level of fluorescent intensity after staining with osmium tetroxide and subsequent dehydration treatment with ethanol. Immunological in-resin CLEM of mitochondria and the Golgi apparatus was achieved using anti-TOM20, anti-GM130 antibodies, and fluorescent dyes. Two-color in-resin CLEM revealed that wheat germ agglutinin-puncta showed the ultrastructures of multivesicular body-like structures. Finally, taking the advantage of high positional accuracy, volume in-resin CLEM of mitochondria in the semi-thin section (2 μm thick) of Epon-embedded cells was performed by focused ion beam scanning electron microscopy. These results suggested that the application of immunological reaction and affinity-labeling with fluorescent dyes to in-resin CLEM of Epon-embedded cells is suitable for analyzing the localization of endogenous targets and their ultrastructures by scanning and transmission electron microscopy.

Staining Methods for Normal and Regenerative Myelin in the Nervous System

Histochemical and fluorescence-based techniques enable the specific identification of myelin by bright-field or fluorescence microscopy. In this chapter, we describe four histological methods for the evaluation of myelin on peripheral nerve tissue sections. The first method combines the Luxol fast blue (LFB) technique with a modified Picrosirius staining contrasted with Harris hematoxylin, called MCOLL. This method simultaneously stains myelin, collagen fibers, and cell nuclei, thus giving an integrated overview of the histology, collagen network, and myelin content of the tissue in paraffin-embedded or cryosectioned samples. Secondly, we describe the osmium tetroxide method, which provides a permanent positive reaction for myelin as well as other lipids present in the tissue. The third method is the immunofluorescence-based detection of myelin proteins that allows to combine information about their expression status with other proteins of interest. Finally, the FluoroMyelin™ stains enable a fast detection of the myelin content that can be easily implemented in immunofluorescence staining panels for cryosectioned tissues. Together, this chapter provides a variety of methods to accurately identify myelin in different experimental approaches.

Osmium-Resistant Fluorescent Proteins and In-Resin Correlative Light-Electron Microscopy of Epon-Embedded Mammalian Cultured Cells

Postfixation with osmium tetroxide and Epon embedding are essential for the preservation and visualization of subcellular ultrastructures via electron microscopy. These chemical treatments diminish the fluorescent intensity of most fluorescent proteins in cells, creating a problem for the in-resin correlative light-electron microscopy (CLEM) of Epon-embedded mammalian cultured cells. We found that two green and two far-red fluorescent proteins retain their fluorescence after chemical fixation with glutaraldehyde, osmium tetroxide-staining, dehydration, and polymerization of Epon resins. Consequently, we could observe the fluorescence of fluorescent proteins in ultrathin sections of Epon-embedded cells via fluorescence microscopy, investigate ultrastructures of the cells in the same sections via electron microscopy, and correlate the fluorescent image with the electron microscopic image without chemical or physical distortion of the cells. In other words, referred as "in-resin CLEM" of Epon-embedded samples. This technique also improves the Z-axis resolution of fluorescent images. In this chapter, we introduce the detailed protocol for in-resin CLEM of Epon-embedded mammalian cultured cells using these fluorescent proteins.

Potassium permanganate is an excellent alternative to osmium tetroxide in freeze-substitution

High-pressure freezing followed by freeze-substitution is a valuable method for ultrastructural analyses of resin-embedded biological samples. The visualization of lipid membranes is one of the most critical aspects of any ultrastructural study and can be especially challenging in high-pressure frozen specimens. Historically, osmium tetroxide has been the preferred fixative and staining agent for lipid-containing structures in freeze-substitution solutions. However, osmium tetroxide is not only a rare and expensive material, but also volatile and toxic. Here, we introduce the use of a combination of potassium permanganate, uranyl acetate, and water in acetone as complementing reagents during the freeze-substitution process. This mix imparts an intense en bloc stain to cellular ultrastructure and membranes, which makes poststaining superfluous and is well suited for block-face imaging. Thus, potassium permanganate can effectively replace osmium tetroxide in the freeze-substitution solution without sacrificing the quality of ultrastructural preservation.

Preparation of blood samples for electron microscopy: The standard protocol

Electron microscopy is a powerful tool to study biological samples at higher magnification. The higher magnifications achieved by the electron microscopes are helpful to the researchers to study surface morphology as well as cellular morphology of the samples. The blood sample surface morphology can be visualized at higher magnification by scanning electron microscope (SEM). For the examination of the blood cells at the cellular level, transmission electron microscopes (TEM) are used. In this article, we have described the step-by-step standard protocol for the preparation of blood samples for electron microscopy. The prepared blood samples can be visualized under SEM and TEM. The obtained electron micrographs of blood cells can be used for differential diagnosis of various diseases at the cellular level.

Detection of endogenous lipids in chicken feathers distinct from preen gland constituents

Bird feather lipids are usually attributed to the oily secretion product of the uropygial (preen) gland. We have observed, however, that feathers exhibit a strong reaction with osmium tetroxide (OsO4), even after treatment with detergents. This leads us to postulate the existence of endogenous feather lipids distinct from preen gland lipids. In order to substantiate our hypothesis, we investigated down feathers from a 1-day-old chicken as their uropgygial gland is not functionally active. The results confirmed the osmiophilic reaction, which was concentrated in the center of barbs and strongly reduced after lipid extraction. In these lipid extracts, we identified using thin layer chromatography, cholesterol, various ceramides, glycolipids, phospholipids, and fatty acids, which closely resembled the lipid composition of the water barrier in the chicken-cornified epidermal envelope. This composition is clearly distinct from chicken uropygeal gland secretion (UGS) known to consist of fatty alcohols as part of aliphatic monoester waxes and of free, predominantly saturated, fatty acids. A filter assay showed a strong reactivity between OsO4 and the fatty acids C18:1 and C18:2 and with feather lipid extracts, but not with UGS. These observations were confirmed by gas chromatography detecting unsaturated fatty acids including C18:1 and C18:2 as well as cholesterol exclusively in chicken feathers. Our results indicate that (1) endogenous lipids are detectable in chicken feathers and distinct from UGS and (2) in analogy to the morphogenesis of the cornified envelope of chicken feather lipids that may have derived from cellular feather-precursors, apparently enduring the specific cell death during developmental feather cornification.

Insights into base-free OsO4-catalyzed aminohydroxylations employing chiral ligands

Attempts to perform the OsO4-catalyzed enantioselective base-free aminohydroxylation of β,β-disubstituted enoates are described. Low yields and racemic products were obtained in the presence of standard chiral ligands, suggesting the occurrence of a "Second Cycle" process due to slow hydrolysis of the amino alcohol product from the Os metal center. Support for this hypothesis was provided by the slightly improved enantioselectivity (60:40 er) obtained with an amino alcohol ligand. Based on density functional theory calculations, it is proposed that the lack of significant enantioselectivity is due to a low-energy (3 + 2) oxo/imido cycloaddition transition state without the chiral ligand in the Second Cycle that outcompetes protonolysis in the First Cycle.

Use of osmium tetroxide staining with microcomputerized tomography to visualize and quantify bone marrow adipose tissue in vivo

Adipocytes reside in discrete, well-defined depots throughout the body. In addition to mature adipocytes, white adipose tissue depots are composed of many cell types, including macrophages, endothelial cells, fibroblasts, and stromal cells, which together are referred to as the stromal vascular fraction (SVF). The SVF also contains adipocyte progenitors that give rise to mature adipocytes in those depots. Marrow adipose tissue (MAT) or marrow fat has long been known to be present in bone marrow (BM) but its origin, development, and function remain largely unknown. Clinically, increased MAT is associated with age, metabolic diseases, drug treatment, and marrow recovery in children receiving radiation and chemotherapy. In contrast to the other depots, MAT is unevenly distributed in the BM of long bones. Conventional quantitation relies on sectioning of the bone to overcome issues with distribution but is time-consuming, resource intensive, inconsistent between laboratories and may be unreliable as it may miss changes in MAT volume. Thus, the inability to quantitate MAT in a rapid, systematic, and reproducible manner has hampered a full understanding of its development and function. In this chapter, we describe a new technique that couples histochemical staining of lipid using osmium tetroxide with microcomputerized tomography to visualize and quantitate MAT within the medullary canal in three dimensions. Imaging of osmium staining provides a high-resolution map of existing and developing MAT in the BM. Because this method is simple, reproducible, and quantitative, we expect it will become a useful tool for the precise characterization of MAT.