A technique for fluorescence microscopy in semithin sections

We describe here a procedure to improve contrast and resolution in fluorescence microscopy of sectioned tissues. Tissue fragments were fixed in ethanol-glacial acetic acid, embedded in diethylene glycol distearate, and semithin sectioned. This method maintains tissue antigenicity while preserving the structure of cells and tissues. The thinness of the sections eliminates scattered and emitted light from tissue structures outside the plane of focus. The procedure is simple and quick, and works excellently with fluorescein-conjugated lectins and antibodies.     

A Rapid Rosin-Celloidin-Paraffin method for Embedding Tissues

Pieces of tissue of various sizes or tissue fragments are dehydrated in 95% alcohol, cleared, washed with ether and infiltrated with a solution containing parloidin 9.6 g., camphor 3.0 g., absolute alcohol 200.0 ml., ether 200.0 ml., rosin 45.0 g. and castor oil 10 drops. After evaporation to the desired consistency, the mass is hardened with chloroform vapor, trimmed, passed through 3 changes of xylene to remove the rosin, embedded in paraffin, sectioned serially, stretched and stained as for paraffin methods. Methods of defatting tissues and detailed procedure for embedding fragments of bone marrow by this method are given.     

Mature Cereal Grain Endosperm: Rapid Glass Knife Sectioning for Examination of Proteins

A simple, rapid procedure was developed by which the quality of endosperm protein in cereal grains could be evaluated by microscopic observation of the subcellular protein structure. Kernels with vitreous endosperm were sectioned without pretreatment at 3-4 μ with a glass knife. Floury endosperm tissues were fixed in 10% glutaraldehyde, pH 7.4, for 16 hr at 5 C, and boiled to gelatinize the starch. After drying, this tissue was sectioned as for vitreous endosperm. Sections were mounted on gelatin-coated slides and destarched with a-amylase. To identify sites of prolamine, alcohol-soluble protein was extracted for 1 hr at about 70 C with 80% ethanol. The subcellular proteins were stained with either iodine vapor or various organic dyes. Proteins were differentiated by a combination of staining and mounting in selected high refractive index liquids.     

Imaging Cleared Intact Biological Systems at a Cellular Level by 3DISCO

Tissue clearing and subsequent imaging of transparent organs is a powerful method to analyze fluorescently labeled cells and molecules in 3D, in intact organs. Unlike traditional histological methods, where the tissue of interest is sectioned for fluorescent imaging, 3D imaging of cleared tissue allows examination of labeled cells and molecules in the entire specimen. To this end, optically opaque tissues should be rendered transparent by matching the refractory indices throughout the tissue. Subsequently, the tissue can be imaged at once using laser-scanning microscopes to obtain a complete high-resolution 3D image of the specimen. A growing list of tissue clearing protocols including 3DISCO, CLARITY, Sca/e, ClearT2, and SeeDB provide new ways for researchers to image their tissue of interest as a whole. Among them, 3DISCO is a highly reproducible and straightforward method, which can clear different types of tissues and can be utilized with various microscopy techniques. This protocol describes this straightforward procedure and presents its various applications. It also discusses the limitations and possible difficulties and how to overcome them.     

Molecule-level imaging of Pax6 mRNA distribution in mouse embryonic neocortex by molecular interaction force microscopy

Detection of the cellular and tissue distributions of RNA species is critical in our understanding of the regulatory mechanisms underlying cellular and tissue differentiation. Here, we show that an atomic force microscope tip modified with 27-acid dendron, a cone shaped molecule with 27 monomeric units forming its base, can be successfully used to map the spatial distribution of mouse Pax6 mRNA on sectioned tissues of the mouse embryonic neocortex. Scanning of the sectioned tissue with a 30-mer DNA probe attached to the apex of the dendron resulted in detection of the target mRNA on the tissue section, permitting mapping of the mRNA distribution at nanometer resolution. The unprecedented sensitivity and resolution of this process should be applicable to identification of molecular level distribution of various RNAs in a cell.     

Block Staining of Botanical Materials

Plant materials, including coleus stem tips, Psilotum stems and onion root tips, were stained in iron-mordanted celestine blue and safranin (Gray and Pickle 1956) prior to embedding and sectioning. Mitotic figures as well as general morphological and anatomical features are adequately stained by this procedure. The plant materials, subdivided so that the largest dimension is about 8-10 mm, are stained for 12-48 hr. The time is dependent upon the tissue and dilution of the stain used. Excess stain is washed out and the tissues are dehydrated, embedded, sectioned and mounted on slides in the usual manner. Following removal of the wax by xylene the sections may be counterstained, or a cover slip may be added immediately.     

Modified Whipf's Polychrome: A Connective Tissue Stain with Special Application for Demonstrating Leishmania

A polychrome stain procedure was developed to demonstrate amastigotes of the protozoan parasite Leishmania braziliensis as well as cytoplasmic and other tissue components in cutaneous lesions of infected animals. The procedure is as follows: stain nuclei for 10 minutes with an iron hematoxylin containing 0.5% hematoxylin and 0.75% ferric ammonium sulfate dissolved in 1:1 0.6 N H₂SO₄:95% ethanol; rinse 4 minutes in distilled water. Cytoplasmic staining is achieved by exposing tissues for 10 minutes to a solution containing 0.25% Biebrich scarlet, 0.45% orange G, 0.5% phosphomolybdic acid and 0.5% phosphotungstic acid in 1% aqueous acetic acid. These first two solutions are modified from Whipf's polychrome stain. Sections are differentiated for 10 seconds in 50% ethanol, rinsed in water, stained 3 minutes in 0.1% aniline blue WS in saturated aqueous picric acid, rinsed in water and differentiated for 1 minute in absolute ethanol containing 0.05% acetic acid. Mordanting overnight in 6% picric acid in 95% ethanol produced optimal results.

This procedure was applied to sectioned material from experimental animals with various protozoa. Trypanosoma cruzi, Besnoitia Jellisoni, Toxoplasma gondii and especially Leishmania braziliensis were well demonstrated. Combining cytoplasmic dyes and phosphomolybdic-phosphotungstic acids into one solution afforded differential staining of tissues by Biebrich scarlet and orange G; connective tissues were stained by this solution. Substantially improved definition of connective tissues resulted after counterstaining. This procedure differs from the Massou sequence in which connective tissues are first stained by cytoplasmic dyes along with other tissues and then destained prior to specific counter-staining. in comparing dyes structurally related to Biebrich scarlet, it was found that Crocein scarlet MOO, but not Poncenu S, was an acceptable substitute. Sirius supra blue GL and Sirius red FSBA were not useful as replacements for aniline blue WS in this procedure.     

Melanoma growth stimulatory activity: isolation from human melanoma tumors and characterization of tissue distribution

Melanoma growth stimulatory activity (MGSA) is an acid and heat stable, auto-stimulatory growth factor which was first isolated from culture medium conditioned by the Hs294T human melanoma cell line. In this report, we describe the purification of MGSA from acid ethanol extracts of Hs294T tumors grown in nude mice using a series of Bio-Gel P30, reverse phase-high performance liquid chromatography and heparin-sepharose steps. This modified procedure provides a 10-fold improved yield of MGSA over previously published procedures. Purified MGSA-stimulated melanoma cell growth in both 3H-thymidine and cell number assays over a concentration range of 0.06 to 6 ng/ml. The MGSA bioactivity was primarily associated with fractions which exhibited molecular weights of 16 and 13-14 Kd based upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Purified platelet-derived growth factor (PDGF), insulin-like growth factor (IGF-1), transforming growth factor-beta (TGF beta), and epidermal growth factor (EGF) in combination with TGF beta did not stimulate 3H-thymidine incorporation in Hs294T cells under the conditions used for MGSA bioassay. Monoclonal antibody to MGSA was used to screen melanoma and benign nevus cultures as well as fixed sectioned tissue for MGSA. The majority of the melanoma cultures were MGSA positive, while most nevus cultures were MGSA negative. However, when fixed sectioned tissue was screened for MGSA immunoreactivity, melanoma tissue was MGSA positive and three-fourths of the benign nevi were MGSA positive. In addition, epidermal keratinocytes and several tissues exhibiting proliferative disorders contained immunoreactive MGSA. These data suggest that MGSA may be a normal regulator of growth and that the microenvironment of the cell may regulate both production of MGSA and response to MGSA.     

A Rapid Bulk Nissl Method

A simplified and time-saving Nissl method is described in which the fresh nervous tissue is placed directly into: dioxane, 65-70 ml.; water, 15 ml.; 95% alcohol, 20-15 ml.; and toluidine blue, 1 g. This solution fixes, stains, partially clears, and dehydrates in one procedure. The material is then sectioned according to a dry-ice method and mounted on the slide either with or without the use of the rapid albumen procedure. Thus it is possible to terminate an experiment one day and have the tissue ready for microscopic observation on the next.     

Antigenic localities in the tissues of Paragonimus westermani by developmental stages using immunogold labeling method]

In order to observe the antigenic localization in the tissues of Paragonimus westermani of developmental stages, immunogold labeling method was applied using serum of the cats which were infected with isolated metacercariae from Cambaroides similis. The sectioned worm tissues from each developmental stage were embedded in Lowicryl HM 20 medium, stained with infected serum IgG and protein A gold complex (particle size: 12 nm) and observed by electron microscopy. In the young adult worm tissue of 4 weeks after infection with metacercariae, the gold particles were specifically concentrated on the tegumental syncytium and cytoplasm of the tegumental cells as well as the secretory granules in the parenchymal tissue. The antigenic materials in the adult worm tissue were specifically concentrated on the secretory granules in the parenchymal tissue, the cytoplasm between granules in the vitelline gland and the epithelial lamella in the lumen of the caecum.     

Curdled Milk for Supporting Tissues in Celloidin Embedding

To make a material for supporting tissues during celloidin embedding, milk curd is hardened in ordinary strong alcohol, cut into suitable shapes, dehydrated, extracted with ether, and preserved indefinitely in 1:1 alcohol-ether. The material, which consists of the precipitated proteins of milk, is embedded and sectioned with the tissue. It presents no detectable opposition to the passage of the microtome-knife.     

Antigenic localities in the tissues of the young adult worm of Paragonimus westermani using immunogold labeling method

In order to observe the antigenic localization in the tissues of the young adult Paragonimus westermani, immunogold labeling method was applied using serum immunoglobulins(IgG) of the dog which infected with isolated metacercariae from Cambaroides similis. The sectioned worm tissue was embedded in Lowicryl HM 20 medium and stained with infected serum IgG and protein A gold complex (particle size; 12 nm). It was observed by electron microscopy at each tissues of the worm. The gold particles were not observed on the basal lamina of the tegument, interstitial matrix of the parenchyma, the muscle tissue and mitochondria of the tegument. The gold particles were specifically labeled in the secretory granules in the vitelline cells. They were predominantly labeling on the epithelial lamela and lumen of caecum. The above finding showed that antigenic materials in young adult worm tissue were specifically concentrated on the tegumental syncytium as well as cytoplasm of tegumental cells.     

Immunohistochemical localization of irisin in mole rats (Spalax leucodon)

Irisin was first identified in skeletal muscle cells. It is an exercise protein that is secreted into the circulation; it causes conversion of white adipose tissue to brown adipose tissue. We investigated irisin immunoreactivity in mole rat (Spalax leucodon) tissues. We examined cerebellum, pituitary, heart, liver, pancreas, spleen, uterus, kidney and striated muscle in female adult mole rats. Tissues were processed, embedded in paraffin, sectioned at 5 μm and stained immunohistochemically for irisin. Irisin immunostaining was detected in the cytoplasm of stained cells; the cytoplasm of Purkinje cells was unstained. We found that irisin may be synthesized in many tissues. The function of locally synthesized irisin currently is unknown.     

Glycol Methacrylate in Light Microscopy a Routine Method for Embedding and Sectioning Animal Tissues

Glycol methacrylate (GMA), a water and ethanol miscible plastic, was introduced to histology as an embedding medium for electron microscopy. This medium may be made soft enough for cutting thick sections for routine light microscopy by altering its composition. A procedure for the infiltration, polymerization, and sectioning of animal tissues in GMA for light microscopy is presented which is no more complex than paraffin techniques and which has a number of advantages: (I) The GMA medium is compatible with both aqueous fixatives (formaldehyde, glutaraldehyde, Bouin's, and Zenker's) and non-aqueous fixatixes (Carnoy's, Newcomer's, ethanol, and acetone). (2) Undue solvent extraction of the tissue is avoided because adequate dehydration occurs during infiltration of the embedding medium. Separate dehydration and clearing of the tissue prior to embedding is eliminated. (3) When polymerized, the supporting matrix is firm enough that hard and soft tissues adjacent to one another may be sectioned without distortion. (4) Thermal artifact is reduced to a minimum during polymerization because the temperature of the tissue may be maintained at 0-4 C from fixation through ultraviolet light polymerization of the embedding medium. (5) Shrinkage during polymerization of the embedding medium is minimized by prepolymerization of the medium before use. (6) Sections may be easily cut using conventional steel knives and rotary microtomes at a thickness of 0.5 to 3.0 microns, thus improving resolution compared with routinely thicker paraffin sections. (7) The polymerized GMA medium is porous enough so that staining, auto radiography, and other histological procedure are done without removal of the embedding medium from the sections. A list of these stains and related procedures are included. (8) Enzyme digestion of ultra thin sections of tissue embedded in GMA is common in electron microscopic cyto chemistry. me same digestion techniques appear compatible with the thicker seaions used in light microscopy.     

Demonstration of Cholinesterase in Teeth

Human teeth have been studied by treatment with copper thio-choline, the method developed by Koelle for demonstrating activity of both specific and nonspecific cholinesterases. Freshly extracted teeth were collected and immediately sectioned on a cutting machine designed for calcified tissues. One series of teeth was sectioned sufficiently thin for microscopic study. Another series of teeth was bisected to expose the pulp chambers to the reagents. These teeth were divided into 5 experimental groups. The first group was treated with 10^-6M di-isopropylfluorophosphate (DFP) for 30 min at 37°C and then incubated with acetylthiocholine (AThCh) for 16 to 20 hr at 37°C in order to reveal the sites of activity of the specific enzyme, AChEase. The second group was incubated in a substrate of butyrylthiocholine (BuThCh) for 12 to 16 hr at 37°C to indicate the sites of the nonspecific ChEase. The third group was incubated in AThCh for 16 to 20 hr at 37°C without previous treatment by an inhibitor in order to reveal the presence and location of both the specific and nonspecific ChEase. The fourth and fifth groups were utilized as controls. Group 4 tissues were incubated without a substrate while those of group 5 were treated with DFP and then incubated with BuThCh. The specimens then were treated with ammonium sulfide to outline the sites of ChEase activity. The thin sections were mounted directly but the series of halved teeth were decalcified, embedded in paraffin, sectioned and then mounted. By these methods the presence and location of both specific and nonspecific ChEase activity were observed in human teeth. Concentration of specific ChEase was observed along the coronal aspect of the pulp chamber and along the course of the pulpal nerves. The nonspecific ChEase was observed throughout the pulpal tissue and appeared to be concentrated along the nerves and blood vessels. Neither series of control tissues exhibited any staining in the pulp tissue.     

Chemical Stabilization of Golgi Silver Chromate Impregnations

Blocks of neural tissue were processed by a modified Golgi-Kopsch procedure and by the rapid Golgi method. Following the impregnation, the blocks were embedded in celloidin, sectioned at 100μm, and collected in 70% alcohol. The sections were then processed as follows: 1) rinsed in distilled water; 2) substituted with 0.4M sodium bromide for five minutes; 3) reduced in Kodak D-19 developer; and 4) treated in 0.5M sodium thiosulfate. The silver chromate deposits within the impregnated cells are converted successively to silver bromide and to reduced silver by this procedure. Sections so treated resist decomposition of the Golgi impregnation, and they may be counterstained with conventional aqueous cresyl violet to demonstrate the cytoarchitecture of the Golgi-impregnated tissue.     

Chemical stabilization of Golgi silver chromate impregnations.

Blocks of neural tissue were processed by a modified Golgi-Kopsch procedure and by the rapid Golgi method. Following the impregnation, the blocks were embedded in celloidin, sectioned at 100 micrometer, and collected in 70% alcohol. The sections were then processed as follows: 1) rinsed in distilled water; 2) substituted with 0.4M sodium bromide for five minutes; 3) reduced in Kodak D-19 developer; and 4) treated in 0.5M sodium thiosulfate. The silver chromate deposits within the impregnated cells are converted successively to silver bromide and to reduced silver by this procedure. Sections so treated resist decomposition of the Golgi impregnation, and they may be counterstained with conventional aqueous cresyl violet to demonstrate the cytoarchitecture of the Golgi-impregnated tissue.     

A TECHNIQUE FOR ULTRACRYOTOMY OF CELL SUSPENSIONS AND TISSUES

Ultracryotomy of fixed tissue has been investigated for a number of years but, so far, success has been limited for several reasons. The simple technique herein reported allows the ultracryotomy not only of a variety of tissues but also of single cells in suspension, with a preservation and visualization of ultrastructural detail at least equivalent to that obtained with conventional embedding procedures. In this technique, sucrose is infused into glutaraldehyde-fixed tissue pieces before freezing for the purpose of controlling the sectioning consistency. By choosing the proper combinations of sucrose concentration and sectioning temperature, a wide variety of tissues can be smoothly sectioned. Isolated cells, suspended in a sucrose solution, are sectioned by sectioning the frozen droplet of the suspension. A small liquid droplet of a saturated or near-saturated sucrose solution, suspended on the tip of an eyelash probe, is used to transfer frozen sections from the knife edge onto a grid substrate or a water surface. Upon melting of the sections on the surface of the sucrose droplet, they are spread flat and smooth due to surface tension. When the section of a suspension of single cells melts, individual sections of cells remain confined to the small area of the droplet surface. These devices make it possible to cut wide dry sections, and to avoid flotation on dimethyl sulfoxide solutions. With appropriate staining procedures, well-preserved ultrastructural detail can be observed. The technique is illustrated with a number of tissue preparations and with suspensions of erythrocytes and bacterial cells.     

Rapid plastic embedding is compatible with colorimetric detection following whole mount in situ hybridization in plant specimens

In performing in situ hybridizations, nonisotopic nucleic acid labeling coupled with colorimetric detection offers a safer, easier and more rapid alternative to using radioactively labeled nucleic acid probes and microscopic autoradiography. Whole mount in situ hybridization is also advantageous, because many samples can be processed identically and the reduced handling of specimens greatly reduces the risk of exposing tissues to RNase(s). The thickness of whole mount specimens, however, often prevents accurate determination of sites of expression within specific tissues. Although post-hybridization embedding and sectioning is a solution to this problem, the precipitate formed following the common colorimetric detection procedure is soluble in the organic solvents used for dehydration prior to embedding. We have developed a dehydration and embedding procedure that takes advantage of the compatibility of L.R. White^® resin containing 10% (v/v) polyethylene glycol 400, and heat polymerized. The addition of the plasticizer allows L.R. White^® embedded tissues to be sectioned at 10 μm providing excellent signal contrast.     

The structure of the endoplasmic reticulum revealed by osmium tetroxide-potassium ferricyanide staining

Postfixation of plant tissues with a mixture of osmium tetroxide and potassium ferricyanide (OsFeCN) yields a selective staining of the endoplasmic reticulum (ER) and nuclear envelope (NE). The other cytoplasmic organelles and inclusions are evident, but by comparison with the NE-ER they are weakly contrasted. Demarcation of the NE-ER results from the enhanced deposition of an electron-opaque reaction product on the inner leaflet of the membrane that extends into the cisternal space. The procedure thus renders the NE-ER readily apparent even when the elements are sectioned parallel to their surface and makes it possible to easily visualize their cellular pattern. Ultrastructural studies reveal with clarity tubular reticula and fenestrated lamellae that are extensively interconnected into one continuous membrane system. Problems with the OsFeCN procedure include the inability of the reagent to stain the NE-ER in all cells of a tissue, the occasional staining of non-ER such as dictyosomal cisternae and plastids, and the failure to selectively stain the NE-ER in protoplasts or single wall-less cells. Results obtained with OsFeCN are compared with other ER fixatives and stains including potassium permanganate and zinc iodide-osmium tetroxide. Despite its problems, under optimal circumstances OsFeCN is judged to be superior to other stain-fixatives for selectively contrasting the NE-ER compartment and is recommended generally for ultrastructural investigations.