On the mechanism of the methyl green-pyronin stain for nucleic acids

Uncovering mechanisms of RT-LAMP colorimetric SARS-CoV-2 detection to improve assay reliability

Improved diagnostics are needed to manage the ongoing COVID-19 pandemic. In this study, we enhanced the color changes and sensitivity of colorimetric SARS-CoV-2 RT-LAMP assays based on triarylmethane dyes. We determined a mechanism for the color changes and obtained sensitivities of 10 RNA copies per microliter.

Cancer microcell initiation and determination

BACKGROUND

Cancer remains one of the leading causes of death worldwide, despite the possibilities to detect early onset of the most common cancer types. The search for the optimal therapy is complicated by the cancer diversity within tumors and the unsynchronized development of cancerous cells. Therefore, it is necessary to characterize cancer cell populations after treatment has been applied, because cancer recurrence is not rare. In our research, we concentrated on small cancer cell subpopulation (microcells) that has a potential to be cancer resistance source. Previously made experiments has shown that these cells in small numbers form in specific circumstances after anticancer treatment.

METHODS

In experiments described in this research, the anticancer agents' paclitaxel and doxorubicin were used to stimulate the induction of microcells in fibroblast, cervix adenocarcinoma, and melanoma cell lines. Mainly for the formation of microcells in melanoma cells. The drug-stimulated cells were then characterized in terms of their formation efficiency, morphology, and metabolic activity.

RESULTS

We observed the development of cancer microcells and green fluorescent protein (GFP) transfection efficiency after stress. In the time-lapse experiment, we observed microcell formation through a renewal process and GFP expression in the microcells. Additionally, the microcells were viable after anticancer treatment, as indicated by the nicotinamide adenine dinucleotide hydrogen phosphate (NADPH) enzyme activity assay results. Taken together, these findings indicate that cancer microcells are viable and capable of resisting the stress induced by anticancer drugs, and these cells are prone to chemical substance uptake from the environment.

CONCLUSION

Microcells are not only common to a specific cancer type, but can be found in any tumor type. This study could help to understand cancer emergence and recurrence. The appearance of microcells in the studied cancer cell population could be an indicator of the individual anticancer therapy effectiveness and patient survival.

Comparative analysis of nucleomorphometric parameters in methyl green-pyronin-stained sections of oral epithelial dysplasia, oral submucous fibrosis and oral squamous cell carcinoma

Context:

The diagnosis and grading of epithelial dysplasia is based on a combination of architectural and cytological changes. A gradual increase in quantitative DNA aberrations has been found to correlate with increasing degree of dysplasia in oral mucous membranes.

Aims:

The aim of this study is to assess nuclear parameters in potentially malignant and malignant lesions of the oral cavity and to assess cytomorphometric changes in the nucleus and nucleolus in oral epithelial dysplasia (OED), oral submucous fibrosis (OSMF), oral squamous cell carcinoma (OSCC) and normal oral mucosa using methyl green-pyronin staining to determine its suitability for detecting potentially malignant lesions and the stage of carcinogenesis.

Methods:

Forty-five archival sections of OED, OSMF and OSCC and 5 cases of normal oral mucosa as the control group were stained according to methyl green-pyronin-staining protocol. Cytomorphometric parameters such as nuclear diameter, nucleolar diameter, number of nucleoli and cytoplasmic RNA were assessed.

Statistical Analysis Used:

The study was subjected to statistical analysis to evaluate the association between morphometric parameters using analysis of variance test, followed by Bonferroni's post hoc analysis.

Results:

A progressive increase in the nuclear parameters as well as cytoplasmic RNA content was observed between normal mucosa through dysplasia and OSMF to OSCC.

Conclusion:

This study serves as an effective diagnostic aid in assessing nuclear parameters in potentially malignant and malignant epithelial lesions affecting oral cavity.

Assaying Cell Cycle Status Using Flow Cytometry

In this unit, two protocols are described for analyzing cell cycle status using flow cytometry. The first is based on the simultaneous analysis of proliferation-specific marker (Ki-67) and cellular DNA content, which discriminate resting/quiescent cell populations (G0 cell) and quantify cell cycle distribution (G1, S, or G2/M), respectively. The second is based on differential staining of DNA and RNA through co-staining of Hoechst 33342 and Pyronin Y, which is also useful to identify G0 cells from G1 cells. Along with these methods for analyzing cell cycle status, two additional methods for cell proliferation assays with recent updates of newly developed fluorophores, which allow multiplex analysis of cell cycle status, cell proliferation, and a gene of interest using flow cytometry, are outlined.

Granular bodies in root primary meristem cells of Zea mays L. var. Cuscoensis K. (Poaceae) that enter young vacuoles by invagination: a novel ribophagy mechanism

Because it has a very large, very rapidly growing primary root, we evaluated giant maize (Zea mays var. Cuscoensis) as a model organism for root research. Granular inclusions are a common feature of cells in many organisms, but they are not common in root meristems. We here report the presence of granules in root tip cells of giant maize. Seeds were germinated at 20 °C in sterile conditions. Four to 5-day-old primary roots were fixed, embedded, and sectioned for light and electron microscopy. Granules (1-2 μm) were observed in small vacuoles in all cell types of the apical meristem zone and mainly in parenchyma cells of the procambium in the primary meristem zone. Some sections were treated with ribonuclease and/or proteinase and then stained with toluidine blue, methyl green pyronin, or Coomassie brilliant blue. The results were used to determine that the granules were composed primarily of RNA and protein. In electron micrographs, consistent with the enzyme experiment results, granules appeared to be dense aggregates of polyribosomes and rough endoplasmic reticulum. They formed first in the cytosol, then invaginated into an adjacent vacuole. The granules are apparently ephemeral and therefore may not have a function other than being subject to autolysis. We speculate that they are part of a previously undescribed ribophagy system that operates during rapid cell growth and differentiation to regulate translation and recycle granule components.

Differential staining of DNA and RNA

Cell cycle analysis by means of differential staining of RNA and DNA permits determination of RNA content, which in turn allows one to discriminate G(0) versus G(1) cells and to detect cell differentiation. This unit presents two protocols for differential staining, one using the metachromatic dye acridine orange (AO) and the other a combination of pyronin Y (PY) and Hoechst 33342. Each method has its advantages and limitations, and the Hoechst-PY method is not applicable to single-laser instruments. A third protocol describes staining of viable cells to identify/sort hematopoietic stem cells, with an alternative that includes simultaneous immunostaining.

Gastrointestinal-tract models and techniques for use in safety pharmacology

The gastrointestinal tract (GI tract), which extracts nutrients, electrolytes, minerals, and water, is prone to injury as a result of oral drug administration. Clinical assessment of the GI tract is often limited to measurements of transit time and observations of vomiting or diarrhoea, despite the existence of methods and techniques capable of assessing specific changes in GI function at the membrane, cell, and whole animal levels. Membrane studies, record the uptake of solutes, and electrolyte transport, assessing the affects of compounds on transepithelial GI transport and flux. Such methods lend themselves to permeability, immunohistochemistry, morphology, and molecular biology techniques. Isolated cells from the GI tract or cultured cell lines provide knowledge of regulation and function at a cellular level, whilst motility patterns, taken in vivo or from biopsies, provide information at a more integrated level. In anesthetised animals, ligated segments of the intestine can be infused with test compounds, providing information about absorptive and secretory processes important for the treatment of diarrhoea. Computer simulations and modelling are used to predict the disposition of a chemical and its metabolite and can, to some extent, replace animal testing, thereby reducing development costs. Indeed, software programs can be used to simulate the dissolution, absorption, distribution, metabolism, and excretion (ADME) properties of potential drugs in the human GI tract. Finally, advances in the field of imaging, combined with endoscopy, have resulted in a wireless capsule, allowing the inspection of the GI tract anatomy and pathology without surgical intervention. It is concluded that the field of safety pharmacology could rapidly, cheaply, and routinely incorporate membrane, isolated tissue, and endoscopy techniques for GI tract testing of drugs.

Methyl green-pyronin Y staining of nucleic acids: studies on the effects of staining time, dye composition and diffusion rates

Since the introduction of the methyl green-pyronin Y procedure as a differential histological stain more than 100 years ago, the method has become a histochemical procedure for differential demonstration of DNA and RNA. Numerous variants of the procedure have been suggested, and a number of hypotheses have been put forward concerning kinetics and binding mechanisms. Using both filter paper models containing DNA, RNA or heparin and histological sections, we have attempted to evaluate the kinetics of staining and the role of staining time for methyl green and pyronin Y by applying the dyes individually, simultaneously and sequentially. The results are presented as color charts approximating the observed staining patterns using a computerized palette. Our results indicate unequivocally that the differential staining is not time-dependent, but that it is dictated by the relative concentrations of methyl green and pyronin Y and by the pH of the staining solution.

Pyronin Y as a fluorescent stain for paraffin sections

Pyronin Y has long been used, in combination with other dyes such as Methyl Green, as a differential stain for nucleic acids in paraffin tissue sections. It also forms fluorescent complexes with double-stranded nucleic acids, especially RNA, enabling semi-quantitative analysis of cellular RNA in flow cytometry. However, the possibility of using pyronin Y as a fluorescent stain for paraffin tissue sections has rarely been investigated. We herein report that in sections stained with Methyl Green-pyronin Y, red blood cells, elastic fibre of blood vessels, zymogen granules of pancreatic acinar cells, surface membrane of heptocytes and kidney tubular cells showed strikingly strong green and/or red fluorescence, while the nuclei of cells appeared non-fluorescent. The use of confocal laser-scanning microscope greatly improved the resolution and selectivity of the fluorescent images. Staining with pyronin Y alone gave similar results in terms of fluorescence properties of the specimens. Pretreatment of paraffin sections with RNase significantly reduced cytoplasmic pyronin Y staining as judged by transmission light microscopy, but it had little effect on the fluorescence intensity of red blood cells, elastic fibres and zymogen granules.

Quantitative amplification of genomic DNA from histological tissue sections after staining with nuclear dyes and laser capture microdissection

Laser capture microdissection (LCM) allows the selective sampling of tissue from histological sections. A prerequisite for this technique is the availability of histological dyes that do not interfere with downstream analysis of the sampled genetic material. We have examined the effect of four histological nuclear dyes (methyl green, hematoxylin, toluidine blue O, azure B) on TaqMan polymerase chain reaction amplification of beta-actin genomic DNA prepared from fixed and frozen tissue. Tissue sampled from the histological sections by manual dissection was compared with tissue sampled by LCM. As previously reported, when manually dissected tissue sections were analyzed, polymerase chain reaction amplification of DNA after hematoxylin staining was inferior to that after staining with the other dyes. In contrast, when tissue sampled by LCM was examined, DNA recovery after hematoxylin staining was equivalent to the recovery after methyl green staining. We conclude that DNA recovery from LCM-sampled tissue is independent of the histological stain chosen to highlight nuclear detail.

Novel fixation of plant tissue, staining through paraffin with alcian blue and hematoxylin, and improved slide preparation

Onion (Allium cepa) root tips were fixed in a proprietary solution without aldehyde, toxic metals or acetic acid. Fixed specimens were embedded in paraffin, sectioned on a rotary microtome and mounted on detergent-washed slides without adhesive. Slides with ribbon segments affixed were immersed in 0.2% aqueous alcian blue 8GX in screw-capped Coplin jars in a water bath at 50 C for 1 hr. Excess alcian blue was rinsed off under cold running tap water and the slides were immersed in quick-mixed hematoxylin at room temperature for 15 min. Stained slides were deparaffinized, rinsed with isopropanol, air dried, and coverslips were affixed with resin. Thus, the traditional paraffin microtechnique has been modified at all steps from fixation to finishing slides with coverslips.

Simultaneous three-color analysis of the surface phenotype and DNA-RNA quantitation using 7-amino-actinomycin D and pyronin Y

We developed an improved technique that permits simultaneous DNA and RNA quantitation by a flow cytofluorometry using 7-amino-actinomycin D (7AAD) and pyronin Y (PY), respectively. Detailed cell cycle analyses based upon the cellular DNA/RNA levels were performed using cells suspended in a buffer containing 0.004% saponin. This method preserved the light scattering properties of human peripheral blood cells, thus lymphocyte, monocyte and granulocyte populations could be evaluated. In addition, since 7AAD and PY exhibit red (> 650 nm) and orange fluorescence (570 nm) respectively, the green fluorescence channel of the flow cytometer was reserved for surface phenotyping using FITC-conjugated antibodies. The 7AAD/PY method is applicable to the simultaneous three-color analysis of the surface phenotype and DNA-RNA quantitation when combined with FITC-conjugated surface markers in heterogeneous samples. To demonstrate the three-color analysis, PHA-activated human peripheral blood lymphocytes were stained for cell surface markers with monoclonal antibodies. The cells were suspended in buffer containing 0.004% saponin, then stained with 7AAD and PY. The DNA and RNA were analyzed in indivisual CD4+, CD8+ and CD20+ cells, and the characteristic cell cycle status was found. Cell activation was further analyzed using antibodies against interleukin-2 (IL-2) receptors (CD25), transferrin receptors (CD71) or HLA-DR molecules. Transferrin receptors were expressed in late G1 phase (G1B) just before the initiation of DNA synthesis, whereas IL-2 receptors and HLA-DR were expressed very early in the G1 phase (G1T). Since this technique preserves both light scatter properties as well as cell surface proteins, it is ideally suited for detailed cell cycle analyses of heterogeneous samples such as peripheral blood or bone marrow cells.

Influence of inorganic salts on the staining reaction of eosinophil leukocyte granules by anionic dyes

The use of salts as competing agents in staining solutions allows to evaluate to what extent ionic interactions take place between microscopical substrates and cationic or anionic dyes. We have employed this method to study the staining reaction of horse eosinophil leucocyte granules by the anionic dyes nuclear fast red, naphthol yellow S, eosin Y, indigocarmin, acid fuchsin, alizarin red S, orange G, and Evans blue in the presence of NaCl (from 0.015 to 2 mol/l). Different values of "minimal electrolyte concentration" (the least amount of salt which reduces the staining intensity) were found for these dyes. Comparative observations using ammonium sulphate as competing salt showed that it is less effective than NaCl. Staining of eosinophil granules by anionic dyes could be not suppressed at 2 mol/l NaCl, which indicates that in addition to electrostatic forces, other non-ionic interactions are also responsible for some staining reaction of these acidophilic structures.

Standardization of biological dyes and stains: pitfalls and possibilities

The present paper gives a review of the actual state of standardization of biological dyes and stains. In a first part general information is given on practical problems encountered by the routine user of dyes with special emphasis on dye contamination. Some theoretical aspects of standardization are discussed. The second part of the paper gives more detailed information on commercial batches of hematoxylin-eosin-, Giemsa- and Papanicolaou-stains and on their standardization. Special problems arising with the application of image analysis techniques are briefly mentioned. User-oriented specifications for the standardization of dyes, stains and staining procedures are given. Fluorescent dyes and dyes used in chromogenic reagents such as the Feulgen-Schiff reaction are not included in this review.

Interactions of pyronin Y(G) with nucleic acids

Spectral properties of pyronin Y(PY) alone or in complexes with natural and synthetic nucleic acids of various base compositions have been studied in aqueous solution containing 10 or 150 mM NaCl and 5 mM Hepes at pH 7.0. The dimerization constant (KD = 6.27 X 10(3), M-1) and the absorption spectra of the dye in monomeric and dimeric form were established. The complexes of PY with single-stranded (ss) nucleic acids show a hypsochromic shift in absorption, and their fluorescence is quenched by over 90% compared to free dye. In contrast, complexes with double-stranded (ds) RNA or DNA (binding by intercalation) exhibit a bathochromic shift in their absorption (excitation) spectrum, and their fluorescence is correlated with the base composition of the binding site. Namely, guanine quenches fluorescence of PY by up to 90%, whereas A, C, I, T, and U bases exert a rather minor effect on the fluorescence quantum yield of the dye. The intrinsic association constant of the dye to ds RNA (Ki = 6.96 X 10(4), M-1) and to ds DNA (Ki = 1.74 X 10(4), M-1) was measured in 150 mM NaCl; the binding site size was 2-3 base pair for both polymers. Implications of these findings for qualitative and quantitative cytochemistry of nucleic acids are discussed.

Application of pyronin Y(G) in cytochemistry of nucleic acids

Chinese hamster ovary (CHO) cells or isolated nuclei were stained with pyronin Y(PY) and analyzed by absorption or fluorescence microscopy, as well as by flow cytometry. Specificity of the staining reaction was assayed by testing sensitivity of the stainable material to RNase or DNase. The colored complexes detected by light absorption in fixed cells stained with PY are nonfluorescent and are most likely the products of condensation of single-stranded (ss) RNA by PY; the poly(rA) and poly(rA,rG) are the most sensitive to condensation. The products of PY interaction with double-stranded (ds) nucleic acids are fluorescent and can be detected in cells by cytofluorometry. PY used alone stains both DNA and RNA, and the staining capabilities of these nucleic acids vary depending upon the PY concentration at equilibrium; at a concentration above 330 microM, the RNA stainability decreases, perhaps due to its denaturation and condensation caused by the dye. In the presence of Hoechst 33342, PY can specifically stain RNA in fixed cells or isolated cell nuclei. Because only complexes of PY with ds RNA are fluorescent, this dye can be used as a probe of RNA conformation, e.g., to monitor denaturation of RNA in situ. The RNA stainability of mitotic cells is about 25% lower than that of cells in G2 phase, which indicates that during mitosis proportionately less cellular RNA is in the ds conformation. The advantages and limitations of the two cytochemical methods for DNA/RNA detection, one based on the use of Hoechst 33342 and PY, and another employing the metachromatic properties of acridine orange, are compared.

Quantitation of dye binding by cell monolayers in a microtiter system

A semi-automated system has been developed for the quantitation of dye binding to cultured eukaryotic cells. It is based on staining precisely controlled numbers of cells seeded into microtiter trays. Cell-bound stain is then released using an appropriate solvent and quantitated in situ by measuring absorbance in a single beam ELISA reader with an interactive microcomputer link. In order to illustrate potential applications of this approach, the time course of dye-monolayer association and influence of cell number and stain concentration on staining has been examined for four dyes, Crystal Violet, Naphthol Yellow S, Ethyl Green and Pyronin Y. In addition, the effect of sequential and simultaneous staining was examined for Ethyl Green and Pyronin Y. The results provide evidence for the overall reliability of this approach as well as revealing several interesting features in the individual procedures examined. The combination of microtiter technology and computer link make the system particularly well suited to the efficient investigation of the permutations involved in optimizing conditions for a given staining procedure, as well as analysis of the thermodynamics of dye substrate interaction. Overall, the approach is viewed as an intermediate between artificial gel systems and microdensitometry.

Proteoglycan histochemistry--a valuable tool for connective tissue biochemists

The histochemistry of connective tissue proteoglycans (PGs) poses two major requirements, 1. for the specific demonstration of a given PG and, 2. at the ultrastructural level, for the examination of the shape of the PG, and its interactions with other molecules and tissue elements. Techniques for the localisation and identification of PGs are discussed, according to the principles behind their application. The strengths and weaknesses of antibody stains are compared with those of mini-molecular reagents, based on resolution, sensitivity, stoichiometry and tissue penetration. The concept of specificity is analysed in this context. The polyanionic characteristics of PGs are exploited to allow very sensitive detection and localisation by cationic probes, both macro- and mini-molecular. Complex formation by heavy metal cations, basic dyestuffs and polycations with PGs is a simple ion-exchange process (basophilia), which can be manipulated to give considerable specificity, e.g. using the critical electrolyte concentration (CEC) concept. The fundamental physical chemical unity of the phenomena of basophilia, CEC and biochemical fractionations of tissue polyanions by anion-exchange is discussed. This unity allows direct quantitative and qualitative comparisons to be made between histochemical and biochemical results at all levels from the tissue sample to the single molecule of PG in situ. The great value of the partnership between microscopy and analytical biochemistry is emphasised. The expanded solution domain of PGs collapses during formation and processing of the 'stained' complex, obscuring molecular detail and possibly resulting in translocation of the PG. Approaches aimed at restoring the initial situation, and their application to electron microscopy of PGs in tissues are outlined. Complexes of PG with ambient polycations may form, either as artefacts during processing or as an integral part of in vivo ultrastructure. Uptake of stain may be partly or totally blocked, in consequence. Ways of investigating, avoiding, or making use of this phenomenon are described. Application of integrated approaches to the study of PG--collagen and PG--elastin interactions in tissues are discussed. Specific interactions and stoichiometric relationship, particularly of dermatan sulphate proteoglycans with type I collagen have been observed, in skin, tendon, and other non-calcifying tissue, but not in bone.

Increased accessibility of bases in DNA upon binding of acridine orange

Acridine orange (AO) forms 1:1 complexes with dsDNA which are insoluble in aqueous media, exhibit red luminescence, have minimal green luminescence and resemble complexes of AO with ss nucleic acids. During formation and/or dissociation of these complexes, accessibility of DNA bases to two conformational probes, formaldehyde and diethyl pyrocarbonate is increased, suggesting that the base pairing is destroyed and DNA at least partially denatured. Adriamycin and Ellipticine, but not Ethidium Bromide exert similar destabilizing effects. The results confirm our earlier predictions based on thermodynamic calculations that the double helix undergoes destabilization upon binding an intercalator characterized by high cooperativity in interaction with ss nucleic acids. Thus, the highly cooperative ligand binding to ss sections during the "breathing" of the polymer may progressively destabilize the adjacent ds structure.

Cuprolinic Blue: a specific dye for single-stranded RNA in the presence of magnesium chloride. I. Fundamental aspects

Qualitative and quantitative aspects of the cationic dye Cuprolinic Blue were investigated with model films of polyacrylamide gel in which RNA, DNA and other biological polyanionic compounds had been incorporated. In the presence of 1 M MgCl2, Curpolinic Blue was found to bind specifically to single-stranded RNA, leaving native DNA, proteins, (acid) polysaccharides and phospholipids completely unstained. Under these conditions, Cuprolinic Blue is complexed by non-electrostatic bonds with non-stacke purine bases, mainly adenine. Optimal conditions for dye binding and differentiation have been defined. Both the Cuprolinic Blue-MgCl2 staining of single-stranded RNA and the Cuprolinic Blue staining of RNA and DNA in the absence of MgCl2 were found to obey the Lambert-Beer law. The advantages and possible applications of Cuprolinic Blue are compared with well-known (indirect) histochemical RNA staining procedures.

Flow cytometric analysis of RNA content in different cell populations using pyronin Y and methyl green

Pyronin Y (PY) was used, in flow cytometric (FCM) systems, to estimate the RNA content per cell in formalin fixed EL4 leukosis tumor cells, enzyme dispersed R3327-G rat prostatic adenocarcinoma cells, mouse spleen cells stimulated with concanavalin A, and human peripheral blood lymphocytes stimulated with phytohemagglutinin. Preincubation of the cells with methyl green (MG) blocked PY binding to DNA such that the intracellular fluorescence from MG-PY was due primarily to its binding to RNA. Treatment of the cells with ribonuclease resulted in a 3- to 5-fold reduction in the fluorescence intensity of intracellular MG-PY. Mitogen stimulation of either mouse or human lymphocytes resulted in an increase in DNA (propidium iodide fluorescence) and RNA (MG-PY fluorescence) content per cell over resting levels. Further, the changes in stimulated human lymphocyte DNA and RNA contents following 24, 48, and 72 hr of cell culture were monitored. The results showed that RNA levels were significantly increased prior to that of DNA. Also, the effects of different cell cycle phase specific blocking agents on lymphocyte cell cycle traverse were investigated. We found that: a) actinomycin D inhibited the increases in cellular RNA and DNA; b) hydroxyurea inhibited the increases in cellular RNA were only slightly reduced; c) tritiated thymidine caused an accumulation of cells having high DNA and RNA contents; and d) Colcemid promoted an accumulation of cells having high DNA contents while causing a reduction of cells having high RNA contents. These results were nearly identical to reports by other investigators using the metachromatic dye acridine orange to quantitate RNA per cell. Thus, the MG-PY technique described is indicated to provide a stable and accurate measure of RNA content per cell.

Purity of commercial non-certified European samples of Pyronin Y

The purity of six European non-certified samples of Pyronin Y was compared with that of two American samples certified by the Biological Stain Commission. The methods used were spectrophotometry and a Methyl Green-Pyronin staining test (both as applied by the Biological Stain Commission), thin layer chromatography, mass spectrometry, determination of pH, and content of some electrolytes. It was found that none of the European batches of Pyronin Y passed the complete test as prescribed by the Biological Stain Commission. Their dye content was uniformly low (between 5 and 19%). Furthermore, thin layer chromatography and mass spectrometry revealed that two of the dye samples contained no Pyronin Y or only traces. It is concluded that assessment of an unknown sample of a dye labelled Pyronin Y should be initiated with thin layer chromatography. The pH and content of electrolytes in an aqueous solution of the dye should also be determined in order to obtain reproducible staining results. Finally, the value of the work performed by the Biological Stain Commission is underlined, although more sophisticated methods are necessary for testing the purity of dyestuffs.

Staining of interphase nuclei and mitotic figures in cultured cells with alcian blue 8GX

Cultured endothelial cells derived from bovine calf pulmonary artery were subjected to a variety of fixatives and stained with 1% Alcian blue 8GX at pH 2.59 to 3.26. Within this range of pH, interphase nuclei and especially mitotic figures were (a) strongly stained in cells fixed with 10% formalin (phosphate buffered or unbuffered) or 2.5% buffered glutaraldehyde, (b) weakly stained or unstained in cells fixed in formaldehyde containing divalent cations, and (c) unstained in cells fixed in acetic acid-containing fluids. However, optimal nuclear staining with Alcian blue under the conditions of this study was judged to be achieved after fixation with neutral phosphate buffered 10% formalin. Endothelial cell cytoplasm exhibited a similar fixative-dependent staining. At pH 2.59 the cytoplasm of interphase cells fixed in formaldehyde (containing no divalent cations) or glutaraldehyde remained unstained; however, at higher pH cytoplasmic staining did occur and it increased as pH increased. In contrast, when these latter fixatives were employed the cytoplasm of mitotic cells stained at all pH levels tested. In cultured endothelial cells after appropriate fixation, 1% Alcian blue 8GX (pH 2.59) was found to possess the ability to stain nuclei with a selectivity and intensity that compared favorably to those of the Feulgen reaction of Heidenhain iron hematoxylin but without the latters' length and complexity. Therefore, this procedure may provide a rapid, simple, and selective method for visualizing interphase nuclei or mitotic figures, or both in the majority of cultured cells.

The effect of different fixatives on chromatin: cytochemical and ultrastructural approaches

This study explores the effects of two types of fixative on chromatin. The first type (acrolein, glutaraldehyde) engenders a high degree of ultrastructural preservation. The other type are fixatives that are widely used in cytochemistry and cytogenetics (acetic acid, 3:1 by vol. methanol-acetic acid, methanol alone, formaldehyde). Lymphocytes of adult rats so-fixed in vitro were prepared for electron microscopy or microdensitometric evaluations of smears. Assessments were made of variations in their total protein, nuclear basic protein and DNA contents. DNA was determined both as Feulgen-positive material and by its binding of intercalating dyes (Methyl Green, specific for double-stranded polynucleotides). Our results showed that some fixatives break up the chromatin organization by acting on particular components of chromatin fibres. They can thus be considered to be destructive agents in situ. In addition, a revaluation of some aldehyde fixatives is proposed for both ultrastructural and cytochemical research.

Microfluorometric investigations of chromatin structure. I. Evaluation of nine DNA-specific fluorochromes as probes of chromatin organization

The ability of the highly condensed chromatin of small thymocyte nuclei and the more loosely organized chromatin of hepatocyte nuclei to interact with nine DNA-specific fluorochromes was assessed by microfluorometry. Although the results obtained with five of the fluorochromes - mithramycin, 7-aminoactinomycin D, Hoechst 33258, DAPI, and propidium iodide - were found to be virtually unaffected by differences in the degree of condensation of the chromatin, the values obtained with the remaining fluorochromes - proflavine, quinacrine mustard, berberine sulfate, and pyronin Y - appeared to be affected significantly by organizational differences of the chromatin. All of the latter "structural probes," except quinacrine mustard, produced fluorescence values which were higher in the 2c nuclei of hepatocytes than in the nuclei of small thymocytes. Quinacrine mustard yielded higher values in thymocyte nuclei; and in the hepatocyte polyploid series (2, 4, and 8c), it did not produce the expected multiples of the 2c value. Pretreatment of the two types of nuclei with RNase affected their total fluorescence in unpredictable ways. While RNase extraction lessened the differences between thymocyte and 2c hepatocyte nuclei stained with propidium iodide, Hoechst 33258, proflavine, and berberine sulfate, it increased the differences between nuclei stained with mithramycin, quinacrine mustard, pyronin Y, and 7-aminoactinomycin D. The ability of RNA-depleted chromatin to interact with various types of fluorochromes might be a useful parameter in subsequent studies of chromatin organization.

Staining myelin, elastic fibers and nuclei with iron hematoxylin

Two iron hematoxylin staining procedures were developed. Both use stable stock solutions and can be prepared volumetrically. The nuclear stain is progressive but differentiation is required for myelin sheath and elastic tissue staining. Histochemical procedures demonstrated that acid, hydroxyl, and aldehyde groups play no role in the staining but amine groups are essential. With both types of stains neither electrostatic bonding nor hydrogen bonding is essential but the nature of the union between tissue and the iron hematoxylin complex was not determined.

Chromatin fluorescence by pyronin staining

Human, chicken and mouse cells from different tissues show a bright red-orange fluorescence of the chromatin after staining with pyronin Y. The possibility that intercalation of the dye into double helical nucleic acids accounts for this fluorescence pattern is briefly discussed.

Displacement

Displacement is a noncommital term for the reactions that occur when slides previously stained in phloxine or rose Bengal are immersed for varying lengths of time in a solution of another dye in ethyl Cellosolve. In most histotechnic texts Lendrum's (1947) phloxine-tartrazine is given as the stain for acidophilic inclusion bodies. However the lack between the phloxine and tartrazine has been a serious limitation. A number of dyes were tried as possible substitutes for the tartrazine. A rose Bengal-Bismark brown Y procedure was developed which stains similarly to Lendrum's phloxine-tartrazine and which does have the needed contrast. After staining for 10 min in 1% aqueous rose Bengal and rinsing in isopropyl alcohol slides are placed for 20, 30, 40 and 50 min in 0.05% Bismark brown Y in ethyl Cellosolve. In various tissues and structures the rose Bengal is sequentially displaced by the Bismark brown Y. Thus collagen loses the red stain after 30 min while acedophilic structures like sperm heads and Paneth cell granules retain the red stain after 50 min in the displacement solution. The results are strikingly similar to staining with alkaline Biebrich scarlet.

Differences in the number of nucleolus organizers in Chironomus tepperi shown by in situ hybridization

Two stocks of Chironomus tepperi could be isolated. One stock, N(IV)+, contains nucleolus organizers in chromosome I and IV, whereas the other one, N(IV)-, shows only one nucleolus in chromosome I. It is demonstrated by in situ hybridization with radioactive rRNA that the absence of the nucleolus in chromosome IV of stock N(IV)- is not related to an inactivation of the nucleolar DNA, as might have been suggested, but is due to the lack of ribosomal cistrons.

Methods of denaturation and renaturation of DNA in interphasic chromatin: cytochemical quantitative analysis by Methyl Green staining

Almost diploid nuclei (as judged from the microdensitometric evaluation of the Feulgen positive material) of granular and Purkinje cells of the rat cerebellar cortex, were submitted to in situ DNA denaturation and renaturation experiments. We assessed the double-strandedness of DNA, by Methyl Green staining according to Scott (1967). Under these conditions a stoichiometric ratio between bound dye and DNA exists, suitable for quantitative microdensitometric measurements. Our data show that DNA in the interphasic chromatin is never completely denatured after the treatments we used. Furthermore, the renaturation takes place in a different way in the two cell types. Owing to the unlike chromatin packing of granular and Purkinje nuclei, we suggest that nuclear proteins must interfere differently on the in situ denaturation and renaturation processes.

Methyl green-pyronin with hematoxylin and orange G for the identification of inflammatory cells in tissue sections

Methyl green-pyronin is a notoriously difficult stain to reproduce. Although very useful in detecting cells containing substantial amounts of RNA, it is of limited use in broader problems of cell identification. By careful standardization of the proportions of methyl green to pyronin and combination of these stains with hematoxylin to enhance nuclear contrast and with orange G to improve connective tissue staining, it was possible to produce a consistently reliable staining preparation in which it is possible to identify all the component cells of a mixed inflammatory infiltrate in routine paraffin sections.

Thin-layer chromatography of some cationic dyes commonly used in histology

A number of cationic dyes commonly used in histology may be conveniently and effectively analysed using the thin-layer chromatographic system of Marshall and Lewis. Commercial samples of Acridine Orange, Crystal Violet, Janus Green B,Methyl Violet, Neutral Red, Pyronin B, Pyronin Y(G), Safranin, Victoria Blue B and Victoria Blue 4R have been analysed with this system. All have been found to be complex mixtures of coloured components. Chromatographic data on these components are presented.

Banding of human chromosomes with basic fuchsin

In this paper a technique is described for the banding of human metaphase chromosomes with basic fuchsin. The main characteristics of the G-banding pattern obtained with this cationic triphenylmethane dye are: the secondary constriction regions of chromosomes Nos. 1 and 16 are strongly stained, especially in the latter one; the heterochromatic area of chromosome No. 9, usually negative with most other G-banding techniques, is clearly visible as an intensely stained band adjacent to the centromere; the chromosomal outline is often very distinct, facilitating the study of the telomeres; a number of chromosomal regions with bright Q fluorescence such as the polymorphic regions of the chromosomes Nos. 3, 4, and Y also stain strongly with basic fuchsin. The basic fuchsin technique combines therefore properties of G-, C-, and Q-banding methods and seems very suitable for use in e.g., family and linkage studies. Several triphenylmethanes closely related to basic fuchsin produce similar banding patterns. The band-producing ability is, however, diminished in those dyes which contain methylated amino groups. If the methyl groups are attached to the carbon atoms at the 3-positions in the phenyl rings, band formation seems unaffected. The way in which basic fuchsin and chromatin may interact as well as the possible mechanism(s) of band formation with this dye are discussed.

A comparison of two methods of preparing cells or nuclei for high-resolution microspectrophotometry

Suspensions of isolated mouse thymus cells were subjected to two preparative methods: either they were dropped through several mm of 9:1 v/v ethanol-acetic acid fixative, allowed to stand for 1hr and then processed for staining; or they were fixed, passed through a graded ethanol series to 70% ethanol, centrifuged on to slides in a modified Shandon cytocentrifuge and then carried wet into the staining procedure. All preparations were stained by the Feulgen reaction and evaluated by high-resolution microspectrophotometry. While the two preparative procedures yielded similar results, there appeared to be less variability in the data obtained from the centrifuged cell populations.

A comparison of four quantitative cytochemical methods directed toward demonstration of DNA

Populations of nuclei isolated from mouse brain tissue were stained by the following cytochemical methods considered stoichiometric for DNA: (1) the Feulgen reaction; (2) gallocyanin-chromalum after RNase; (3) pH 4.0 methylene blue after RNase; and (4) methyl green used in the presence of 2M magnesium chloride. Replicate preparations to be stained with gallocyanin-chromalum, methylene blue, and methyl green were acetylated prior to staining. All of these groups were examined by high-resolution scanning microspectrophotometry. The results indicated that of the methods examined, the Feulgen reaction, gallocyanin-chromalum used without prior acetylation, and methylene blue used with prior acetylation were the most useful in revealing differences attributable to variability in chromatin organization. The greatest variability in total extinction measurements was observed in acetylated, methylene blue-stained nuclei, while the least variability was observed in nuclei stained with methyl green in the presence of 2 M magnesium chloride. Acetylation produced different effects on dye-binding in different groups. It greatly increased binding in nuclei stained with methylene blue; it reduced binding in the methyl green-2 M magnesium chloride series.

Studies on the Methyl Green-DNA complex and its dissociation by drugs

Spectrophotometric results indicated that Methyl Green bound stably to native calf thymus DNA and to poly[d(A-T)] but to a lesser extent to phiX 174 DNA, tRNAs, and poly(dG-dC), a copolymer that exists preferentially in the A conformation. Exposing the Methyl Green-DNA complex to graded concentrations of ethyl alcohol liberated part of the dye slowly by a zero-order reaction; higher alcohol concentrations which cause the B leads to A transition of DNA released the bulk of Methyl Green. The viscosity of the Methyl Green-DNA complex was significantly lower than that of the uncomplexed DNA. The dye was progressively liberated from DNA by 1.5 x 10(-1) M NaCl and by much lower concentrations of Mg2+; in its stoichiometric complex with DNA, it increased Tm by approximately 12 degrees C. A series of DNA-complexing drugs displaced Methyl Green from DNA at exponential rates and to end points which were correlated. End points of displacement correlated with the abilities of drugs to unwind supercoiled DNA, to labilize ribosomes to heat, and to eliminate a kanamycin resistance determinant from an R factor carried by Salmonella typhimurium. Additional correlations between Methyl Green displacement and biochemical-biological activities of displacing drugs are cited. In conjunction with these findings, our results suggest that Methyl Green displacement analysis is a useful biochemical screen for the detection or development of biologically active compounds which bind to DNA.