Simultaneous detection of EGFP and cell surface markers by fluorescence microscopy in lymphoid tissues.

Enhanced GFP (EGFP) is a powerful tool for the visualization of tagged proteins and transfected cells and is easily detected by fluorescence microscopy or flow cytometry in living cells. However, soluble EGFP molecules can be lost if cell integrity is disrupted by freezing, sectioning, or permeablization. Furthermore, the fluorescence of EGFP is dependent on its conformation. Therefore, fixation protocols that immobilize EGFP may also destroy its usefulness as a fluorescent reporter. Here we determined which methods of preparing murine lymphoid tissues immobilized soluble EGFP protein and retained its fluorescence while simultaneously maintaining the antigenicity of various immunologically important molecules and best preserving the overall morphology of the tissues. We found that EGFP could not be visualized in frozen sections of spleen that had not been fixed before freezing. However, robust EGFP fluorescence could be observed in frozen sections of tissues fixed under various conditions. Fixation was important to immobilize EGFP rather than to maintain conformation, because only minimal EGFP could be detected by immunofluorescence in unfixed frozen sections. Although it had little effect on EGFP fluorescence, the inclusion of sucrose during fixation better preserved the morphology of fixed tissues. These methods also preserved the antigenicity of a wide variety of molecules used to identify cell types in lymphoid tissues.     

Rapid and sensitive detection of enhanced green fluorescent protein expression in paraffin sections by confocal laser scanning microscopy

Various forms of green fluorescent protein (GFP) have become important reporters of gene transfer and expression after transfection or infection of cells in cell culture. Frequently, molecular biological assays (Northern blots, PCR) are applied to detect reporter gene expression in target organs. However, these methods are not suitable for evaluation of tissue- or cell-specific expression which would be of great interest especially in case of using tissue-specific promoters. Therefore, organs of transgenic mice with the enhanced green fluorescent protein (EGFP) gene under control of the cytomegalovirus (CMV) promoter were processed for histology by formaldehyde fixation and embedding in paraffin. Sections were deparaffinized, mounted and evaluated for fluorescence in a confocal laser scanning microscope. This method combines the advantages of direct exploitation of tissue sections without further staining procedures with evaluable tissue-, cell-, and even subcellular-specific distribution patterns of EGFP expression in tissues. Results obtained by direct evaluation of EGFP fluorescence in paraffin sections were confirmed by immunohistochemical staining with anti-EGFP. In the present report, we demonstrate that application of confocal microscopy on routinely processed histological preparations is very suitable for determining gene transfer efficiency and promotor activities.     

Effects of tissue processing techniques in acoustical (1.2 GHz) and light microscopy

Summary In this study the influence of various tissue processing and staining techniques on the acoustical properties of liver tissue was investigated. A qualitative study was performed using ultrasound attenuation as the imaged parameter of a combined optical/acoustical microscope with a 1.2 GHz transducer. Images were made of three sets of adjacent liver sections (6 m in thickness) which were prepared in ten different ways: fixed by alcohol or formalin; stained by hematoxylineosin (HE), toluidine blue (TB) or non-stained; sectioned by a cryostat or by a paraffin microtome. It was concluded that the images obtained from cryostat sections were of much higher quality than those from paraffin sections. Images obtained from sections that were sectioned while embedded in paraffin displayed no detail at all. No consistent effect was noticed with respect to staining by HE or TB. Alcohol fixed sections gave more detailed images than formalin fixed sections. Formalin fixation in combination with cryostat sectioning yielded many cytoplasmic vacuoles.     

The effects of storage on the retention of enzyme activity in cryostat sections. A quantitative histochemical study on rat liver

Summary The effect of storage of unfixed cryostat sections from rat liver for 4 h, 24 h, 3 days and 7 days at -25°C was studied on the activities of lactate dehydrogenase, glucose-6-phosphate dehydrogenase, xanthine oxidoreductase, glutamate dehydrogenase, succinate dehydrogenase (all demonstrated with tetrazolium salt procedures), glucose-6-phosphatase (cerium-diaminobenzidine method), 5-nucleotidase (lead salt method), dipeptidyl peptidase II, acid phosphatase (both simultaneous azo coupling methods), d-amino acid oxidase (cerium-diaminobenzidine-cobalt-hydrogen peroxide procedure) and catalase (diaminobenzidine method). The effect of drying of the cryostat sections at room temperature for 5 and 60 min was investigated as well. The enzyme activities were quantified by cytophotometric measurements of test and control reactions. The test minus control reaction was taken as a measure for specific enzyme activity. It was found that the activities of all the enzymes investigated, with one exception, were affected neither by storage of the cryostat sections at -25°C for up to 7 days, nor by drying of the sections at room temperature for up to 60 min. The exception was xanthine oxidoreductase, whose activity was reduced by 20% after 5 min drying of sections or after 4 h storage. Therefore, only incubations for xanthine oxidoreductase activity have to be performed immediately after cutting cryostat sections, whereas for the other enzymes a considerable margin appears to exist.     

Fixation requirements for the immunohistochemical reactivity of PCNA antibody PC10 on cryostat sections

Summary In contrast to that in paraffin-embedded tissue, the reactivity of monoclonal PCNA antibody PC10 on cryostat sections requires a special fixation procedure as the target epitope is seemingly not accessible to its antibody. A panel of 18 fixation protocols was investigated. Chilled methanol or acetone, or PLP (paraformaldehyde-lysine-periodate) was found to be unsuitable for skin preparations. A two-step fixation protocol was developed for normal skin and basal cell carcinomas. They were fixed first in 3.4% buffered formaldehyde, followed by fixation in 2:1 v/v ethanol-acetic acid. Following this fixation regime, cryostat sections displayed the same PCNA/PC10 labelling pattern as paraffin sections of formalin-fixed tissue.     

Selective visualization of human dendritic reticulum cells in reactive lymphoid follicles by the immunohistochemical demonstration of the subunit A of factor XIII (F-XIIIa)

Immunohistochemical techniques have been used to localize clotting factor XIII subunit A in human reactive lymphoid follicles. The follicular dendritic reticulum cells (DRCs) were identified by the monoclonal antibodies R4/23 and OKB-7 as well as by their 5'-nucleotidase positivity. Follicular histiocytic reticulum cells (HRCs) were demonstrated by their acid phosphatase and non-specific esterase reactions. Capillaries were selectively visualized by adenosine triphosphatase. The immunohistochemical demonstration of F-XIIIa was preferably carried out in combination with one or two of the above marker techniques, on the same cryostat section. The subunit A of factor XIII is present in follicular DRCs. Their selective immunohistochemical demonstration with antibody against F-XIIIa requires formaldehyde fixation of cryostat sections. Similar fixation, however, is inappropriate for the demonstration of F-XIIIa reactivity of DRCs in paraffin sections. For this purpose, acetic acid-formalin fixation is useful. Follicular HRCs are consistently negative for F-XIIIa, contrary to the F-XIIIa positivity of sinusoidal and interfollicular HRCs. Developmental and functional implications of F-XIIIa reactivity in DRCs and HRCs are suggested.     

Immunocytochemical localization of nerve growth factor: effects of fixation

The fixation dependence of immunocytochemically demonstrable nerve growth factor (NGF) was investigated. Several commonly used fixation methods have been employed, including buffered formaldehyde, Bouin's fluid, and chloroform-methanol, as well as freezing and cryostat sectioning. The immunostaining technique was an immunoenzyme bridge procedure on either paraffin sections or frozen sections. Of those methods tested, fixation for 1 hr in a buffered formaldehyde appeared to provide optimal preservation and localization of immunoreactive material. Using this method, reaction product was localized in granules of the granular tubule cells of the male mouse submandibular gland. Prolonged fixation in buffered formaldehyde resulted in a diffuse background staining and loss of granule immunoreactivity. In frozen sections and in tissues fixed with either Bouin's solution, chloroform-methanol, or buffered paraformaldehyde-glutaraldehyde increased cytoplasmic background staining and loss of granule immunoreactivity were observed. It was concluded that, for the localization of NGF at the light microscopic level, a brief (1 hr) buffered formaldehyde fixation is optimal.     

Dynamic characterization of recombinant Chinese hamster ovary cells containing an inducible c-fos promoter GFP expression system as a biomarker.

An inducible reporter gene system for Chinese Hamster Ovary (CHO-DHFR(-)) cells has been developed and characterized with respect to its dynamic properties. The reporter gene system consists of the human c-fos promoter and variants of the green fluorescence protein (GFP), either EGFP with enhanced fluorescence or its destabilized form d2EGFP. The expression of wild-type EGFP or its destabilized form was studied in CHO-DHFR(-) cells in response to serum addition or deprivation. It was shown that serum-induced c-fos promoter mediated EGFP expression was considerably higher than expression from the human CMV promoter, a strong, constitutive promoter preferentially used for high-level expression in CHO cells. However, EGFP was less suitable for studying expression dynamics than d2EGFP due to the protein's long half-life in mammalian cells. The use of d2EGFP resulted in a significant improvement in the dynamic characteristics of the biomarker, particularly when the recombinant cells were selected for high-level GFP expression by subcloning or fluorescence activated cell/sorting (FACS). GFP expression in different subclones and cell populations sorted by FACS was characterized with respect to its dynamic responses in the presence or absence of serum in the culture medium. Significant differences in the GFP expression dynamics were observed for the isolated cell populations. The experimental results indicate that cells with high-level GFP expression also have a faster dynamic response and are thus, desirable for practical application of the reporter gene system e.g. in toxicity monitoring.     

Novel dual-reporter transgenic rodents enable cell tracking in animal models of stem cell transplantation

In the present study, we have established a novel transgenic mouse and transgenic rats with dual reporters of EGFP and ELuc. In these transgenic (Tg) rodents, both GFP fluorescent and luciferase luminescent signals were ubiquitously detected in the heart, liver, kidney and testis, while only the GFP signal was detected in the brain. This expression system is based on a P2A linked EGFP/ELuc protein allowing both signals to be generated simultaneously. Microscopy experiments, FCM, and luciferase assays showed strong expression in freshly isolated ADSCs from Tg rodents upon transplantation of Tg rat-derived ADSCs into wild-type-mice. The ELuc transgene signal was observed and traced in vivo, and EGFP positive cells could be recovered from ELuc positive tissues in engraftment sites of wild-type mice for multiple analysis. These dual reporter Tg rodents are a useful reconstituted model system of regenerative medicine and are a valuable tool to study stem cells.     

Influence of fixation and buffer treatment on the release of enzymes from the plasma membrane

Summary 1. Pretreatment of frozen cryostat sections with formaldehyde or calcium ions inhibits diffusion of the plasma membrane enzymes 5-nucleotidase, ATP-ase and alkaline phosphatase during incubation. 2. Treatment of fixed sections with different kinds of buffer at 37°C induces diffusion of enzyme activity from the plasma membrane to other sites of the section and into the incubation medium. This buffer influence depends on temperature: at 4°C only a slight diffusion occurs. Addition of phospholipase C, digitonin or taurocholate to the buffer opposes the buffer effect. 3. Pretreatment of frozen cryostat sections with a mixture of equal parts of chloroform and acetone gives a good fixation of the plasma membrane enzymes 5-nucleotidase, ATP-ase, alkaline phosphatase and leucyl--naphthylamidase. During this treatment the different kinds of lipids present in the membrane are extracted equally. After this fixation buffer treatment does not cause a visible diffusion of enzyme activity in the section. Only a slight diffusion (1 till 7 percent) into the buffer solution takes place. 4. The mentioned treatments open up possibilities to get insight into the membrane anchorage of plasma membrane enzymes.     

Measurement of green fluorescent protein concentration in single cells by image analysis

The gene encoding the green fluorescent protein (GFP) has been widely used in studies of gene expression. The GFP can be detected nondestructively in living cells or tissues by the green fluorescence of the protein under blue light. Solutions of enhanced GFP (EGFP) of known concentration were filled in glass capillaries and used to calibrate a method for quantitative determination of EGFP or GFP-S65T in plant cells. Images captured by a digital camera were analyzed to determine the linear range for measurement of EGFP expression. The value of the method was illustrated by analysis of the relative levels of GFP expression under control of different promoters in aleurone cells of barley.     

A new method for flat-embedding large native cryostat sections for targeting small preneoplastic lesions in comparative ultrastructural and ultracytochemical investigations

 Ultrastructural studies of rare and small cellular lesions in pathologically altered tissue are difficult to perform by applying conventional electron microscopic preparation. The search for lesions, often consisting of only a few cells in randomly obtained small specimen blocks, is time consuming and often without success. The methodological requirements for comparative enzyme cytochemical and morphological studies, i.e., preservation of both enzyme activity and ultrastructure, are divergent. By processing large native cryostat sections for electron microscopy, small preneoplastic focal lesions were successfully targeted in liver and kidney. Glucose-6-phosphatase, alkaline phosphatase, acid phosphatase, catalase, and cytochrome c oxidase activities were distinctly localized to endoplasmic reticulum, canalicular membrane, lysosomes, peroxisomes, and mitochondria, respectively, in the morphologically altered cells. Fixation of serial cryostat sections and enzyme reactions were both carried out through a semipermeable membrane except those for cytochrome c oxidase, which was demonstrated after fixation through the membrane by floating the section in incubation medium containing cytochrome c. Thereafter, the sections were flat embedded and polymerized between epoxy resin disks and aluminum dishes fitting exactly together. The objects of interest were identified in the light microscope, cut out, and reembedded in reversed gelatine capsules. By using this technique an ultrastructural preservation was achieved similar to that seen after immersion fixation. The enzyme activities were clearly localized without diffusion of the reaction product or unspecific deposits. The procedure permits precise targeting and complex studies of rare and small lesions, and opens new perspectives for the use of cryo-preserved tissue. Accepted: 10 March 1998     

Influence of fixation and buffer treatment on the release of enzymes from the plasma membrane.

1. Pretreatment of frozon cryostat sections with formaldehyde or calcium ions inhibits diffusion of the plasma membrane enzymes 5' nucleotidase, ATP-ase and alkaline phosphatase during incubation. 2. Treatment of fixed sections with different kinds of buffer at 37 degrees C induces diffusion of enzyme activity from the plasma membrane to other sites of the section and into the incubation medium. This buffer influence depends on temperature: at 4 degrees C only a slight diffusion occurs. Addition of phospholipase C, digitonin or taurocholate to the buffer opposes the buffer effect. 3. Pretreatment of frozen cryostat sections with a mixture of equal parts of chloroform and acetone give a good fixation of the plasma membrane enzymes 5'-nucleotidase, ATP-ase, alkaline phosphate and leucyl-beta-naphthylamidase. During this treatment the different kinds of lipids present in the membrane are ex-racted equally. After this fixation buffer treatment does not cause a visible diffusion of enzyme activity in the section. Only a slight diffusion (1 till 7 percent) into the buffer solution takes place. 4. The mentioned treatments open up possibilities to get insight into the membrane anchorage of plasma membrane enzymes.     

Techniques for Studying Adipocytes

Various fixatives as well as tissue and slide handling procedures have been evaluated in attempts to demonstrate adipocytes histochemically while maintaining cell and tissue integrity. The optimal procedure for analysis of immature adipose depots consists of the following steps: 1) fresh, unfixed tissues are frozen rapidly in isopentane quenched in a liquid nitrogen bath; 2) cryostat sections are cut, removed from the knife with a room temperature slide, and then air dried for 5-10 minutes; 3) slides can be stained directly with picro-Ponceau or toluidine blue procedures or with oil red O following fixation for 30 minutes in cold (4 C) 10% formalin-CaCl₂ (1.25%). For analysis of mature rat adipose depots steps 2 and 3 are modified as follows: 2) cryostat sections are removed from the knife with a cold slide (-20 C) and dried for 30 minutes at 4 C; 3) the mounted sections are stained with oil red O following fixation for 30 minutes in cold (4 C) 10% formalin-HgCl₂ (2.5%). When procedures described above for immature adipose depots are combined with esterase fining, adipocyte cytoplasm is clearly demonstrated. These procedures allow the routine use of fresh frozen, unfixed cryostat sections in studies of adipose cellularity.     

Techniques for studying adipocytes

Various fixatives as well as tissue and slide handling procedures have been evaluated in attempts to demonstrate adipocytes histochemically while maintaining cell and tissue integrity. The optimal procedure for analysis of immature adipose depots consists of the following steps: 1) fresh, unfixed tissues are rapidly in isopentane quenched in a liquid nitrogen bath; 2) cryostat sections are cut, removed from the knife with a room temperature slide, and then air dried for 5-10 minutes; 3) slides can be stained directly with picro-Ponceau or toluidine blue procedures or with oil red O following fixation for 30 minutes in cold (4 C) 10% formalin-CaCl2 (1.25%). For analysis of mature rat adipose depots steps 2 and 3 are modified as follows: 2) cryostat sections are removed from the knife with a cold slide (-20 C) and dried for 30 minutes at 4 C; 3) the mounted sections are stained with oil red O following fixation for 30 minutes in cold (4 C) 10% formalin-HgCl2 (2.5%). When procedures described above for immature adipose depots are combined with esterase staining, adipocyte cytoplasm is clearly demonstrated. These procedures allow the routine use of fresh frozen, unfixed cryostat sections in studies of adipose cellularity.     

Ultrastructural localization of xanthine oxidase activity in the digestive tract of the rat

Summary Precise localization of xanthine oxidase activity might elucidate physiological functions of the enzyme, which have not been established so far. Because xanthine oxidase is sensitive to chemical (aldehyde) fixation, we have localized its activity in unfixed cryostat sections of rat duodenum, oesophagus and tongue mounted on a semipermeable membrane. Previous studies had shown that this procedure enables the exact localization of activities of peroxisomal oxidases with maintenance of acceptable ultrastructure. Moreover, leakage and/or diffusion of enzyme molecules was prevented with this method. The incubation medium to detect xanthine oxidase activity contained hypoxanthine as substrate and cerium ions as capturing agent for hydrogen peroxide. After incubation, reaction product in the sections was either visualized for light microscopy or sections were fixed immediately and processed for electron microscopy. At the ultrastructural level, crystalline reaction product specifically formed by xanthine oxidase activity was found to be present in the cytoplasmic matrix of enterocytes and goblet cells and in mucus of duodenum. Moderate activity was found in the cytoplasm of apical cell layers of epithelia of oesophagus and tongue, with highest activity in the cornified layer. Moreover, large amounts of reaction product were found to surround bacteria present between cell remnants of the cornified layer of the oesophagus. Many bacteria surrounded by the enzyme showed signs of destruction and/or cell death. The intracellular localization of xanthine oxidase activity in the cytoplasm of epithelial cells as well as the extracellular localization suggest that the enzyme plays a role in the lumen of the digestive tract, for instance in the defence against microorganisms.     

Effects of tissue processing techniques in acoustical (1.2 GHz) and light microscopy.

In this study the influence of various tissue processing and staining techniques on the acoustical properties of liver tissue was investigated. A qualitative study was performed using ultrasound attenuation as the imaged parameter of a combined optical/acoustical microscope with a 1.2 GHz transducer. Images were made of three sets of adjacent liver sections (6 microns in thickness) which were prepared in ten different ways: fixed by alcohol or formalin; stained by hematoxylin-eosin (HE), toluidine blue (TB) or non-stained; sectioned by a cryostat or by a paraffin microtome. It was concluded that the images obtained from cryostat sections were of much higher quality than those from paraffin sections. Images obtained from sections that were sectioned while embedded in paraffin displayed no detail at all. No consistent effect was noticed with respect to staining by HE or TB. Alcohol fixed sections gave more detailed images than formalin fixed sections. Formalin fixation in combination with cryostat sectioning yielded many cytoplasmic vacuoles.     

Alkaline phosphatase activity in the brain of the American cockroach Periplaneta americana L

Summary The supra- and suboesophageal ganglia of the American cockroach contain material which catalyses the alkaline hydrolysis (pH 9.5) of 5-bromo-4-chloro-3-indolyl phosphate in the presence of Nitro blue tetrazolium. Histochemical studies on unfixed cryostat sections indicate that this type of alkaline phosphatase is restricted to discrete regions in the cockroach brain. Highest enzyme activity is encountered in the mushroom bodies, central body, antennal glomeruli and specific parts of some distinct neural connections including the optic nerve, antennal nerve, circumoesophageal connectives and nerves leaving the suboesophageal ganglion. Tissue fixation by use of formaldehyde-type fixatives, as well as routine paraffin-embedding, completely destroy all histochemically detectable enzyme activity.Native polyacrylamide gradient electrophoresis suggests that the alkaline phosphatase activity is present as multiple isozymic forms, which show up in the 120–130 kD range of standard proteins. Enzyme activity becomes undetectable after fixation (trichloroacetic acid, formaldehyde containing fixatives) of electrophoretically separated native proteins, as well as after electrophoresis in denaturing conditions (SDS and -mercapto-ethanol, boiling). However, the enzyme activity remains virtually unaffected after storage of the sample for prolonged periods at –20 to –80°C.     

Comparative study of procedures for histological detection of lectin binding by use of Griffonia simplicifolia agglutinin I and gastrointestinal mucosa of the rat

Summary The histological localisation of -D-galactopyranosyl residues in glycoconjugates of rat stomach and duodenal mucosae was studied by use of Griffonia simplicifolia agglutinin I, i.e. the isolectin mixture (A+B) and the isolectin B₄ (B₄). Cryostat sections which were either unfixed or acetone fixed and paraffin sections from both ethanolacetic acid and formaldehyde fixed tissue blocks were compared. Cellular details were better preserved in paraffin than in cryostat sections. Reactivity of cells binding GS I was less sensitive after formaldehyde than after ethanol-acetic acid fixation inasmuch as higher concentrations of lectins were needed. This drawback could be overcome by trypsinisation of the sections. The binding pattern of GS I (A+B) corresponded with that of GS I (B₄) in either cryostat or paraffin sections. GS I was detected in the cytoplasm of parietal cells and in Brunner's gland cells. In duodenal crypts and villi, lectin was bound to supranuclear regions in the cytoplasm of columnar and goblet cells. The staining efficiency of fluorescein (FITC), horseradish peroxidase (HRP) and colloidal gold particle (CGP) labels in both direct and indirect lectin stainings was compared. Under all experimental conditions, indirect methods required lower concentrations of lectins than direct ones; indirect procedures increased sensitivity about 5–10 fold. CGP labels were always of highest sensitivity when gold particles were further developed by a silver precipitation method. HRP was not as efficient in lectin localisation as CGP, but cytochemical staining was more convenient in routine work. Direct FITC labellings proved to be of lowest sensitivity.     

大鼠纹状体内移植神经干细胞的迁移分化行为

本文分离培养胎鼠脑室下带区(SVZ)神经干细胞,经含绿色荧光蛋白基因(GFP)的2型重组腺相关病毒感染,获得具有GFP标记的神经干细胞。标记后的细胞移植到成年SD大鼠纹状体内。分别在移植后45天、90天、120天时,取移植大鼠全脑进行矢状连续冰冻切片观察。结果显示,在各时间段,移植位点始终能检测到标记细胞,但有相当数量的细胞远离移植位点向周围迁移。移植后45天,细胞迁移出现明显的方向性、迁移细胞成链式排列。移植后120天,明显观察到两条迁移路线:一条沿弧形路线向背后侧迁移到达胼胝体下缘;另一条向腹后侧迁移到达黑质,并有细胞绕过或穿过黑质到达大脑底端。免疫组织化学分析显示,迁移细胞呈现β-tubulinⅢ阳性。