Quantification of nuclear DNA and intracellular glycogen in a single cell by fluorescent double-staining

Summary It was found that intracellular glycogen is stabilized against acid treatment when it is stored under dry conditions for three months after methanol fixation. This stabilization allowed quantitative double fluorescence staining, for nuclear DNA and intracellular glycogen, in a single cell. A Feulgen nucleal reaction with acriflavine-Schiff's reagent following 5 N HCl hydrolysis at 25°C for 4 min, was followed by a pararosanilin-Schiff PAS reaction for glycogen. This short term hydrolysis was found to be sufficient for the performance of a acriflavine-Schiff's Feulgen nucleal reaction and to provide good preservation of intracellular glycogen. Quantification of nuclear DNA and intracellular glycogen was consecutively carried out with a digital microfluorometer on a single ascites cancer cell of the AH-13 line stained by this method. It was found that there is a positive linear correlation between the amount of DNA and glycogen in this cell line.This work was partly supported by a Grant-in-Aid for Cancer Research from the Ministry of Education, Science and Culture, Japan     

Rapid DNA mapping by fluorescent single molecule detection

DNA mapping is an important analytical tool in genomic sequencing, medical diagnostics and pathogen identification. Here we report an optical DNA mapping strategy based on direct imaging of individual DNA molecules and localization of multiple sequence motifs on the molecules. Individual genomic DNA molecules were labeled with fluorescent dyes at specific sequence motifs by the action of nicking endonuclease followed by the incorporation of dye terminators with DNA polymerase. The labeled DNA molecules were then stretched into linear form on a modified glass surface and imaged using total internal reflection fluorescence (TIRF) microscopy. By determining the positions of the fluorescent labels with respect to the DNA backbone, the distribution of the sequence motif recognized by the nicking endonuclease can be established with good accuracy, in a manner similar to reading a barcode. With this approach, we constructed a specific sequence motif map of lambda-DNA. We further demonstrated the capability of this approach to rapidly type a human adenovirus and several strains of human rhinovirus.     

Quantification of unintegrated HIV-1 DNA at the single cell level in vivo

In the nucleus of HIV-1 infected cells, unintegrated HIV-1 DNA molecules exist in the form of one and two LTR circles and linear molecules with degraded extremities. In tissue culture they are invariably more numerous than the provirus, the relative proportion of integrated to unintegrated forms varies widely from ～1:1 to 1:10 and even over 1:100. In vivo, this ratio is unknown. To determine it, single nuclei from two infected patients with a known provirus copy number were microdissected, HIV DNA was amplified by nested PCR, cloned and individual clones sequenced. Given the extraordinary sequence complexity, we made the assumption that the total number of distinct sequences approximated to real number of amplifiable HIV-1 DNA templates in the nucleus. We found that the number of unintegrated DNA molecules increased linearly with the proviral copy number there being on average 86 unintegrated molecules per provirus.     

Detection of glycogen in a glycogen storage disease by C nuclear magnetic resonance

The livers of gsd/gsd rats homozygous for the glycogen storage disease phosphorylase b kinase deficiency were observed by ¹³C NMR using a surface coil. Clear signals were detected from glycogen. The concentration of glycogen as determined by NMR was 3-times that found in normal strains agreeing well with chemical determinations Starvation did not significantly reduce the glycogen content of the livers with glycogen storage disease whereas it reduced the signal below detectability in normal rats. Difference spectra of starved normal rats from fed gsd/gsd rats gave spectra similar in appearance to that of purified glycogen. Glycogen both in vivo and in vitro is fully visible using ¹³C NMR.     

Quantification of unscheduled DNA synthesis by a whole cell counting method

A procedure was developed for the quantification of the autoradiographic assay for unscheduled DNA synthesis. Relative to commonly used practices for grain counting, this procedure provides a more accurate net nuclear grain count by eliminating the subjectivity currently associated with selection of the areas to be counted for the cytoplasmic background count. Briefly, the object area and aperture area modes of an ARTEK 880 colony counter are used to collect values for the total number of silver grains over a particular cell (nuclear and cytoplasmic counts), as well as for the nuclear and cytoplasmic areas. These values are then employed in a short algorithm to determine the net nuclear grain count. This new method provides greater sensitivity for defining weak UDS responses and the data collected readily lends itself to statistical analysis.     

Higher plant cell membrane resistance by a single intracellular electrode method

A single intracellular microelectrode technique has been adapted to measure membrane resistance in a higher plant cell. As a direct result of the convenience of this method, which allows relatively long term recordings on a single cell, it has been found that membrane resistance increases for about 30 minutes after cell impalement in Pisum sativum L. cv. Alaska root cortical cells, although cell potential is established at a constant value in less than 2 minutes. It is proposed that these observations imply a regulating feedback loop between electrogenic pump rates and membrane potential.     

Impact of cell division on intracellular uptake and nuclear targeting with fluorescent SiC‐based nanoparticles

Semiconductor nanoparticles (NPs) became important and wide‐used tool for cell imaging because of their unique remarkable properties. Nevertheless, all previous investigations in this area were done on proliferating cells. For the first time, this work demonstrates strong influence of cell active proliferation/contact inhibition of proliferation on uptake of NPs. In addition, we show that cell division plays key‐role in penetration of silicon carbide based NPs (SiC NPs) inside the cell nucleus. This may very likely concern other types of NPs able to reach the cell nuclei. In particular, observed effect of cell division gives perspectives for future selective cancer treatment with NPs. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Monitoring promoter activity in a single bacterial cell by using green and red fluorescent proteins

We investigated the possibility of monitoring promoter activity with flow cytometry by using green fluorescent protein (GFPmut2) and red fluorescent protein (drFP583) in a single bacterial cell. The drFP583 was used as an intrinsic marker of the bacterial cells, because it was expressed constantly in Escherichia coli MC1061 strain. The GFPmut2 expressed under the control of the Hg(2+) ion inducible mer promoter/operator, was used to study promoter activity. Over 75% of the cells were positive for red and green fluorescence in flow cytometric analysis. The average green fluorescence of the whole population increased from 6.7 to 1700 when the mercury concentration was increased from 0 to 1 x 10(-4) M, while the red fluorescence was unaffected by the mercury concentration. These results show that gfpmut2 and drFP583 could be expressed under different promoters in one bacterial cell and measured independently with a flow cytometer.     

Quantification of serum HBXAP DNA in lung cancer patients by quantitative fluorescent polymerase chain reaction

Hepatitis B virus x associated protein (HBXAP), as a subunit of chromatin remodeling and spacing factor, plays a critical role in cancer development through gene amplification. In this study, we aimed to quantify the levels of serum HBXAP DNA, to analyze and compare its diagnostic value with existing clinical parameters in lung cancer, and to potentially provide a novel tumor marker for lung cancer. Serum HBXAP DNA from 65 lung cancer patients and 20 healthy controls was quantified using real-time fluorescent quantitative polymerase chain reaction (FQ-PCR) analysis. The data were analyzed by statistical software SPSS 13.0. We found that serum HBXAP DNA levels in lung cancer patients were higher compared to healthy controls (u = 219.0, p = 0.001) and were closely associated with TNM stage and lymph node metastasis (p = 0.015 and p = 0.016, respectively). However, serum HBXAP DNA levels were not associated with patient age, gender, smoking status, histological type, or tumor size (p > 0.05). We identified a sensitivity of 61.9 % and a specificity of 93.7 % for the ability of HBXAP DNA levels to detect lung cancer at a cutoff value of 1,557.6 copies/μl. The sensitivity for existing lung-tumor markers, such as squamous cell carcinoma antigen, cytokeratin fragment 21-1, and neuron specific enolase, was increased from 35.7 %, 53.5 %, and 56.0 % to 75.0 %, 86.0 %, and 80.0 %, respectively, by inclusion of serum HBXAP DNA. Taken together, quantification of serum HBXAP DNA by FQ-PCR could potentially serve as a novel complementary tool for the clinical screening and detection of lung cancer.     

Quantification by laser scan microscopy of intracellular doxorubicin distribution.

Changes in intracellular drug localization accompany doxorubicin resistance in multidrug resistant tumor cells. The purpose of this study was to develop a method to quantify these changes and so detect different levels of resistance. Tumor cells were incubated with the fluorescent anthracycline doxorubicin (excitation at 480 nm; emission maximum at 560-590 nm) and were quantified using laser scanning microscopy. The fluorescent mode was used to record the intracellular drug distribution, whereas the absorption mode was used to define the nuclear and cytoplasmic boundaries. The cell compartments were delineated interactively on an image processing system and the ratio nuclear fluorescence/cytoplasmic fluorescence (N/C ratio) was determined. N/C ratios were: 1.8 in the Chinese hamster ovarian cell line AUXB1 and 0.1 in its MDR subline CHRC5; 3.8 in the human squamous lung cancer cell line SW-1573 and 1.8 and 0.4 in its MDR sublines SW-1573/2R120 and SW-1573/2R160, respectively; and 3.6 in the human myeloma cell line 8226/S and 2.1 and 1.0 in its MDR sublines 8226/Dox4 and 8226/Dox40, respectively. The doxorubicin distribution was independent of the doxorubicin concentration within a range from 1-32 microM. Furthermore, the progressive mean of the nuclear/cytoplasmic doxorubicin fluorescence ratio showed that a minimal sample size of 30 cells is necessary for reliable results. The results of two independent assessments showed a high reproducibility (r = 0.97). Thus, with the method described in this paper, it is possible to detect relatively low levels of doxorubicin resistance (factor 8).     

Antibody-based nanoprobe for measurement of a fluorescent analyte in a single cell

We report here the application of an antibody-based nanoprobe for in situ measurements of a single cell. The nanoprobe employs antibody-based receptors targeted to a fluorescent analyte, benzopyrene tetrol (BPT), a metabolite of the carcinogen benzo[a]pyrene (BaP) and of the BaP-DNA adduct. Detection of BPT is of great biomedical interest, since this species can serve as a biomarker for monitoring DNA damage due to BaP exposure and for possible precancer diagnosis. The measurements were performed on the rat liver epithelial clone 9 cell line, which was used as the model cell system. Before making measurements, the cells were treated with BPT. Nanoprobes were inserted into individual cells, incubated 5 min to allow antigen-antibody binding, and then removed for fluorescence detection. We determined a concentration of 9.6+/-0.2x10(-11) M for BPT in the individual cells investigated. The results demonstrate the possibility of in situ measurements inside a single cell using an antibody-based nanoprobe.     

Quantification of nuclear DNA and G-C content in marine macroalgae by flow cytometry of isolated nuclei

Summary The amounts of nuclear DNA in ten species of seaweeds belonging to the Rhodophyceae, Phaeophyceae, and Chlorophyceae were determined by flow cytometric analysis of nuclei isolated from protoplasts. Genome size was determined from the fluorescence of the nuclei stained with ethidium bromide. The size of the nuclear genome ranged from 0.13 pg per cell in the 1 C population ofUlva rigida to 3.40 pg per cell in the 2 C population ofSphacelaria sp. GC% analysis was based on staining with either Hoechst 33342 or mithramycin A, two fluorochromes specific for the bases A-T and G-C, respectively. Two models were used for the estimation of the proportion of guanine plus cytosine in the nuclear genome. The first one was based on the linear relationships mithramycin A fluorescence/G-C content and ethidium bromide fluorescence/total DNA content. The second model, based on the curvilinear relationships Hoechst 33342 fluorescence/A-T content and mithramycin A fluorescence/G-C content, resulted in comparatively more homogenous and consistent data and appears more accurate. Comparison with previous reports from other methods for the physical investigation of nuclear genomes shows that flow cytometry of nuclei isolated from protoplasts is an accurate, convenient and robust technique to assay for genome sizes and base pair composition in marine macroalgae.Abbreviations A-T nucleic bases adenine and thymine - CRBC chicken red blood cell - FALS forward-angle light scatter - G-C nucleic bases guanine and cytosine - SEIM sorbitol enzymatic incubation medium - SWIM sea water incubation medium - Tm thermal denaturation temperature of DNA     

Measurement of intracellular magnesium in a vascular smooth muscle cell line using a fluorescent probe

Until recently, direct measurement of intracellular free magnesium has been complex and difficult. However, fluorescent probes are now available, based on the same principle as well-established probes for free calcium. Using one such probe, mag-fura-2, we have estimated basal intracellular magnesium concentrations in the A7r5 rat vascular smooth muscle cell line. This level was unaffected by numerous pharmacological manipulations, including agonist stimulation and depolarisation. The possible implications of these findings are discussed.     

Determination of the glycogen content in single neutrophil leukocytes using a micromodel of leukocyte glycogen.

The kinetics of the periodic acid oxidation as part of the periodic acid-Schiff reaction was studied by combined microinterferometry and microspectrophotometry in micromodel systems of liver glycogen and leukocyte glycogen as well as in neutrophil leukocytes. The initial formation of Schiff-positive chromogens was more rapid in neutrophil leukocytes than in liver or leukocyte glycogen. The chromogen formation was, however, practically complete within 60 min in both neutrophil leukocytes and leukocyte glycogen, but this did not appear to be the case in liver glycogen. Differences in the rate of chromogen formation may depend on various factors such as differences in the source and treatment of the glycogen. The complete periodic acid-Schiff reaction appears to be a measure of the glycogen amount in neutrophil leukocytes and the microdroplet system of leukocyte glycogen is considered to be an appropriate model for the estimation of the glycogen amount in single neutrophil leukocytes. A mean value of 13.3 10-12 g glycogen per normal human neutrophil was found.     

Green fluorescent protein as a noninvasive intracellular pH indicator.

It was found that the absorbance and fluorescence of green fluorescent protein (GFP) mutants are strongly pH dependent in aqueous solutions and intracellular compartments in living cells. pH titrations of purified recombinant GFP mutants indicated >10-fold reversible changes in absorbance and fluorescence with pKa values of 6.0 (GFP-F64L/S65T), 5.9 (S65T), 6.1 (Y66H), and 4.8 (T203I) with apparent Hill coefficients of 0.7 for Y66H and approximately 1 for the other proteins. For GFP-S65T in aqueous solution in the pH range 5-8, the fluorescence spectral shape, lifetime (2.8 ns), and circular dichroic spectra were pH independent, and fluorescence responded reversibly to a pH change in <1 ms. At lower pH, the fluorescence response was slowed and not completely reversed. These findings suggest that GFP pH sensitivity involves simple protonation events at a pH of >5, but both protonation and conformational changes at lower pH. To evaluate GFP as an intracellular pH indicator, CHO and LLC-PK1 cells were transfected with cDNAs that targeted GFP-F64L/S65T to cytoplasm, mitochondria, Golgi, and endoplasmic reticulum. Calibration procedures were developed to determine the pH dependence of intracellular GFP fluorescence utilizing ionophore combinations (nigericin and CCCP) or digitonin. The pH sensitivity of GFP-F64L/S65T in cytoplasm and organelles was similar to that of purified GFP-F64L/S65T in saline. NH4Cl pulse experiments indicated that intracellular GFP fluorescence responds very rapidly to a pH change. Applications of intracellular GFP were demonstrated, including cytoplasmic and organellar pH measurement, pH regulation, and response of mitochondrial pH to protonophores. The results establish the application of GFP as a targetable, noninvasive indicator of intracellular pH.