DRAQ5-based DNA content analysis of hematolymphoid cell subpopulations discriminated by surface antigens and light scatter properties

Flow Cytometry and Cell Cycle Analysis: An Overview

Cell cycle analysis is one of the earliest applications in flow cytometry and continues to be highly used to this day. Since the first reported method of Feulgen-DNA staining, cell cycle analysis has continued to grow and mature. With the recent advances in DNA dyes, understanding of additional cell cycle phase markers, and new technologies, cell cycle analysis continues to be a dynamic field within the flow cytometry community. This chapter will give an overview of the current state of cell cycle analysis by flow cytometry.

Development of a novel flow cytometry-based approach for reticulocytes micronucleus test in rat peripheral blood

The micronucleus test (MNT) is the most widely applied short-term assay to detect clastogens or spindle disruptors. The use of flow cytometry (FCM) has been reported for micronucleated erythrocytes scoring in peripheral blood. The aim of this study was to develop a novel and practical protocol for MNT in rat peripheral blood by FCM, with the method validation. CD71-fluorescein isothiocyanate and DRAQ5 were adopted for the fluorescent staining of proteins and DNA, respectively, to detect micronuclei. To validate the method, groups of male Sprague-Dawley rats (five per group) received two oral gavage doses at 0 and 24 h of six chemicals (four positive mutagens: ethyl methanesulphonate [EMS], cyclophosphamide [CP], colchicine [COL], and ethyl nitrosourea [ENU]; two nongenotoxic chemicals: sodium saccharin and eugenol). Blood samples were collected from the tail vein before and on the five continuous days after treatments; all of which were analyzed for micronuclei presence by both the manual (Giemsa staining) and FCM methods. The FCM-based method consistently demonstrated highly sensitive responses for micronucleus detection at all concentrations and all time points for EMS, CP, COL, and ENU. Sodium saccharin and eugenol could be identified as negative in this protocol. Results obtained with the FCM-based method correlated well with the micronucleus frequencies (r = 0.659-0.952), and the proportion of immature erythrocytes (r = 0.915-0.981) tested by Giemsa staining. The method reported here, with easy operation, low background, and requirement for a regular FCM, could be an efficient system for micronucleus scoring.

Transcriptional Activation of Pericentromeric Satellite Repeats and Disruption of Centromeric Clustering upon Proteasome Inhibition

Heterochromatinisation of pericentromeres, which in mice consist of arrays of major satellite repeats, are important for centromere formation and maintenance of genome stability. The dysregulation of this process has been linked to genomic stress and various cancers. Here we show in mice that the proteasome binds to major satellite repeats and proteasome inhibition by MG132 results in their transcriptional de-repression; this de-repression is independent of cell-cycle perturbation. The transcriptional activation of major satellite repeats upon proteasome inhibition is accompanied by delocalisation of heterochromatin protein 1 alpha (HP1α) from chromocentres, without detectable change in the levels of histone H3K9me3, H3K4me3, H3K36me3 and H3 acetylation on the major satellite repeats. Moreover, inhibition of the proteasome was found to increase the number of chromocentres per cell, reflecting destabilisation of the chromocentre structures. Our findings suggest that the proteasome plays a role in maintaining heterochromatin integrity of pericentromeres.

Label-free cell cycle analysis for high-throughput imaging flow cytometry

Imaging flow cytometry combines the high-throughput capabilities of conventional flow cytometry with single-cell imaging. Here we demonstrate label-free prediction of DNA content and quantification of the mitotic cell cycle phases by applying supervised machine learning to morphological features extracted from brightfield and the typically ignored darkfield images of cells from an imaging flow cytometer. This method facilitates non-destructive monitoring of cells avoiding potentially confounding effects of fluorescent stains while maximizing available fluorescence channels. The method is effective in cell cycle analysis for mammalian cells, both fixed and live, and accurately assesses the impact of a cell cycle mitotic phase blocking agent. As the same method is effective in predicting the DNA content of fission yeast, it is likely to have a broad application to other cell types.

Imaging flow cytometry enables high-throughput acquisition of fluorescence, brightfield and darkfield images of biological cells. Here, Blasi et al. demonstrate that applying machine learning algorithms on brightfield and darkfield images can detect cellular phenotypes without the need for fluorescent stains, enabling label-free assays.

A novel and easy FxCycle™ violet based flow cytometric method for simultaneous assessment of DNA ploidy and six-color immunophenotyping

Abnormal DNA ploidy is a valuable prognostic factor in many neoplasms, especially in hematological neoplasms like B-cell acute lymphoblastic leukemia (B-ALL) and multiple myeloma (MM). Current methods of flow-cytometric (FC) DNA-ploidy evaluation are either technically difficult or limited to three- to four-color immunophenotyping and hence, challenging to evaluate DNA-ploidy in minute tumor population with background rich of its normal counterpart cells and other hematopoietic cells. We standardized a novel sensitive and easy method of simultaneous evaluation of six- to seven-color immunophenotyping and DNA-ploidy using a dye-FxCycle Violet (FCV). Linearity, resolution, and coefficient of variation (CV) for FCV were studied using chicken erythrocyte nuclei. Ploidy results of FCV were compared with Propidium iodide (PI) in 20 samples and intra-assay variation for FCV was studied. Using this six-color immunophenotyping & FCV-protocol DNA-ploidy was determined in bone-marrow samples from 124 B-ALL & 50 MM patients. Dilution experiment was also conducted to determine the sensitivity in detection of aneuploidy in minute tumor population. FCV revealed high linearity and resolution in 450/50 channel. On comparison with PI, CV of Go/G1-peak with FCV (mean-CV 4.1%) was slightly higher than PI (mean-CV 2.9%) but had complete agreement in ploidy results. Dilution experiment showed that aneuploidy could be accurately detected up to the limit of 0.01% tumor cells. Intra-assay variation was very low with CV of 0.005%. In B-ALL, hypodiploidy was noted in 4%, hyperdiploidy in 24%, near-hyperdiploidy in 13% and remaining 59% were diploid. In MM, hypodiploidy was in 2%, hyperdiploidy in 58%, near-hyperdiploidy in 8% and remaining 30% were diploid. FCV-based DNA-ploidy method is a sensitive and easy method for simultaneous evaluation of six-color immunophenotyping and DNA analysis. It is useful in DNA-ploidy evaluation of minute tumor population in cases like minimal residual disease and MM precursor conditions.

Oxidative stress and mitochondrial dysfunction play a role in myelodysplastic syndrome development, diagnosis, and prognosis: A pilot study

The imbalance between reactive oxygen species (ROS) production and their elimination by antioxidants leads to oxidative stress. Depending on their concentration, ROS can trigger apoptosis or stimulate cell proliferation. We hypothesized that oxidative stress and mitochondrial dysfunction may participate not only in apoptosis detected in some myelodysplastic syndrome (MDS) patients, but also in increasing proliferation in other patients. We investigated the involvement of oxidative stress and mitochondrial dysfunction in MDS pathogenesis, as well as assessed their diagnostic and prognostic values. Intracellular peroxides, superoxide, superoxide/peroxides ratio, reduced glutathione (GSH), and mitochondrial membrane potential (Δψ(mit)) levels were analyzed in bone marrow cells from 27 MDS patients and 12 controls, by flow cytometry. We observed that all bone marrow cell types from MDS patients had increased intracellular peroxide levels and decreased GSH content, compared with control cells. Moreover, oxidative stress levels were MDS subtype- and risk group-dependent. Low-risk patients had the highest ROS levels, which can be related with their high apoptosis; and intermediate-2-risk patients had high Δψ(mit) that may be associated with their proliferative potential. GSH levels were negatively correlated with transfusion dependency, and peroxide levels were positively correlated with serum ferritin level. GSH content proved to be an accurate parameter to discriminate patients from controls. Finally, patients with high ROS or low GSH levels, as well as high superoxide/peroxides ratio had lower overall survival. Our results suggest that oxidative stress and mitochondrial dysfunction are involved in MDS development, and that oxidative stress parameters may constitute novel diagnosis and/or prognosis biomarkers for MDS.

Rapid detection of haemotropic mycoplasma infection of feline erythrocytes using a novel flow cytometric approach

Background

The haemotropic mycoplasmas Mycoplasma haemofelis and Candidatus Mycoplasma haemominutum cause feline infectious anaemia with infection rates in feline populations reflecting widespread subclinical infection. Clinically significant infections are much rarer but can be life-threatening. Current diagnosis is dependent upon visualising organisms in stained blood smears, PCR or quantitative PCR (qPCR). These procedures are labour-intensive and time-consuming. Furthermore, PCR-based approaches offer limited insight into the disease burden of the infected animal.

Methods

We have developed a novel and rapid flow cytometric system that permits diagnosis of haemotropic mycoplasma infections and quantitation of the percentage of erythrocytes that are parasitized. The method exploits the fact that mature mammalian erythrocytes, the host cell for haemoplasmas, are enucleated and thus lack nucleic acid. DRAQ5 is a synthetic anthrocycline dye which rapidly crosses cell membranes and binds to nucleic acids. The presence of exogenous bacterial DNA in mammalian erythrocytes can, therefore, be detected by DRAQ5 uptake and flow cytometric detection of DRAQ5 fluorescence.

Results

Here, we show that this system can detect epi-erythrocytic infection of companion felines by haemotropic mycoplasma. Due to their differences in size, and hence the quantity of DNA, the two major feline hemoplasmas M. haemofelis and Candidatus M. haemominutum can be distinguished according to DRAQ5 fluorescence. We have also shown the usefulness of DRAQ5 uptake in monitoring a cat infected with M. haemofelis sequentially during treatment with doxycycline.

Conclusions

The technique described is the first report of a flow cytometric method for detecting haemotropic mycoplasmas in any species and could be applied to widespread screening of animal populations to assess infection by these epi-erythrocytic parasites.

Red/far-red fluorescing DNA-specific anthraquinones for nucl:cyto segmentation and viability reporting in cell-based assays

The advent and wide use of image-based, high-content screening assay formats demands reliable solutions for cellular compartment segmentation to track critical events-for example, those reported by GFP fusions within cell cycle control pathways, signaling pathways, protein translocations, and those associated with drug-induced toxicity such as mitochondrial membrane depolarization, plasma membrane permeabilization, and reactive oxygen species. To meet this need, a series of nuclear/cytoplasmic discriminating probes has been developed: the supravital dyes DRAQ5™ and CyTRAK Orange™ and most recently the viability dye DRAQ7™. These are all spectrally compatible with GFP reporters offering new solutions in imaging and cytometry. As red/far-red emitting dyes, they provide convenient fluorescent emission signatures which are spectrally separated from the majority of commonly used reporter proteins (e.g., eGFP, YFP, mRFP), and a wide range of fluorescent tags such as Alexafluor 488, fluorescein, and Cy2 and fluorescent functional probes used to report cell health status or demark organellar structures. In addition, they are not excited by UV wavelengths thus avoiding complications of the frequently seen pharmacophore UV-autofluorescence in drug discovery. Conversely, their preferential red excitation reduces interference by biological sample autofluorescence. High water solubility and high-affinity DNA-binding properties provide a convenient means of stoichiometrically labeling cell nuclei in live cells without the aid of DMSO and can equally be used for fixed cells. Powerfully, they permit the simultaneous and differential labeling of both nuclear and cytoplasmic compartments in live and fixed cells to clearly render the precise location of cell boundaries which may be beneficial for quantitative expression measurements, cell-cell interactions, and most recently compound in vitro toxicology testing. In one case, DRAQ7™, the core structure has been chemically derivatized to render it intact-cell-membrane impermeant. This far-red viability dye can be more widely combined with other fluorescent reporters to reveal temporally separated events and shows negligible cytotoxicity as determined by sensitive bioassays.

Analytical capabilities of the ImageStream cytometer

Imaging cytometry has recently become an important achievement in development of flow cytometric technologies. The ImageStream cytometer combines the vast features of classical flow cytometry including an impartial analysis of great number of cells in short period of time which results in strong statistical data output, with essential features of fluorescence microscopy such us collecting of real multiparameter images of analyzed objects. In this chapter, we would like to introduce an overview of imaging cytometry platform and emphasize the potential advantages of using this system for several experimental purposes. Moreover, both well established as well as potential applications of imaging cytometry will be described. Eventually, we would like to illustrate the unique use of ImageStream cytometer for identification and characterization of subpopulations of stem/ progenitor cells present in different biological specimens.

Neuronal DNA content variation (DCV) with regional and individual differences in the human brain

It is widely assumed that the human brain contains genetically identical cells through which postgenomic mechanisms contribute to its enormous diversity and complexity. The relatively recent identification of neural cells throughout the neuraxis showing somatically generated mosaic aneuploidy indicates that the vertebrate brain can be genomically heterogeneous (Rehen et al. [2001] Proc. Natl. Acad. Sci. U. S. A. 98:13361-13366; Rehen et al. [2005] J. Neurosci. 25:2176-2180; Yurov et al. [2007] PLoS ONE:e558; Westra et al. [2008] J. Comp. Neurol. 507:1944-1951). The extent of human neural aneuploidy is currently unknown because of technically limited sample sizes, but is reported to be small (Iourov et al. [2006] Int. Rev. Cytol. 249:143-191). During efforts to interrogate larger cell populations by using DNA content analyses, a surprising result was obtained: human frontal cortex brain cells were found to display "DNA content variation (DCV)" characterized by an increased range of DNA content both in cell populations and within single cells. On average, DNA content increased by approximately 250 megabases, often representing a substantial fraction of cells within a given sample. DCV within individual human brains showed regional variation, with increased prevalence in the frontal cortex and less variation in the cerebellum. Further, DCV varied between individual brains. These results identify DCV as a new feature of the human brain, encompassing and further extending genomic alterations produced by aneuploidy, which may contribute to neural diversity in normal and pathophysiological states, altered functions of normal and disease-linked genes, and differences among individuals.

Conventional apoptosis assays using propidium iodide generate a significant number of false positives that prevent accurate assessment of cell death

The advent of flow cytometry-based applications has significantly impacted the study of cellular apoptosis. Propidium iodide (PI) is a commonly used viability stain in these studies. Unfortunately, we find that conventional Annexin V/PI protocols lead to a significant number of false positive events (up to 40%), which are associated with PI staining of RNA within the cytoplasmic compartment. Both primary cells and cell lines are affected, with large cells (nuclear: cytoplasmic ratios <0.5) showing the highest occurrence. This distribution spans a wide range of animal models including mice, swine, avian, and teleost fish and potentially affects up to 1016 out of 1019 of peer-reviewed papers published in this area since 1995. We show that the primary ramifications from these findings relate to cells experiencing changes in RNA content. Virally infected cells, for example, are qualified as undergoing apoptosis in response to infection based on conventional staining protocols; in fact, these cells are alive and actively producing viral RNA that can serve to produce additional infectious viral particles. Based on our observations we propose a modified protocol, show that it overcomes previous drawbacks for this technique, and that it will allow for more accurate assessment of cell death across various platforms.

The use of DRAQ5 to monitor intracellular DNA in Escherichia coli by flow cytometry

Flow cytometry provides a rapid and high-content multiparameter analysis of individual microorganisms within a population. In the past years, several fluorescent stains were developed in order to monitor DNA content distribution and cell-cycle phases, mainly in eukaryotic cells. Recently, due to its low detection limits, several of these fluorescent stains were also applied to prokaryotic cells. In this study, the ability of a novel far-red fluorescent stain DRAQ5 in assessing intracellular DNA content distribution in Escherichia coli DH5alpha was evaluated. The results showed that a DRAQ5-labelled live E. coli suspension can be obtained by incubation of 1 x 10(6) cells/mL with 5 microM DRAQ5 in PBS buffer supplemented with EDTA (pH = 7.4) during 30 min at 37 degrees C. Flow cytometric analysis of fixed E. coli cells revealed that ethanol should be used in detriment of glutaraldehyde for DRAQ5 labelling. After the analysis of RNase and DNase digested samples, DRAQ5 was proven to be a specific DNA labelling stain. The present study demonstrates that the use of DRAQ5 as a DNA-labelling stain provides an easy assessment of intracellular DNA content and cell-cycle phases in gram-negative bacteria such as E. coli.

Pediatric T-cell post-transplant lymphoproliferative disorder after solid organ transplantation

Post-transplant lymphoproliferative disorder (PTLD) is the most common treatment related malignancy that occurs after solid organ transplantation (SOT). PTLD has extended from its initial description as an Epstein-Barr virus (EBV)-driven B-cell proliferation to include EBV-negative and non B-lineage cases. T-cell PTLD (T-PTLD) is rare in both adults and children. We report two cases of pediatric T-PTLD after SOT (liver and lungs) and review cases reported in the literature. Both patients had a bimodal response to therapy with initial eradication of bulky nodal disease with regimens typically used to treat leukemia, but persistence of low-level clonal T-cells in marrow, CSF and lung in one case.

DRAQ5: improved flow cytometric DNA content analysis and minimal residual disease detection in childhood malignancies

BACKGROUND

The majority of flow cytometric DNA content analyses are performed on whole peripheral blood, bone marrow or tumor samples containing significant numbers of non-malignant cells which hamper specific DNA content analysis. Simultaneous analysis of DNA content and immunophenotype greatly improves the specificity of DNA-ploidy measurements. Therefore, a three-color flow cytometric assay using DRAQ5 was developed and validated.

METHODS

The results of DNA content analysis using DRAQ5 and propidium iodide were compared using peripheral blood samples of 15 healthy volunteers. The reproducibility of the multiparameter DRAQ5 assay was assayed in 10 analytical runs and the sensitivity was evaluated with addition experiments.

RESULT

Using DRAQ5, slightly wider CVs of the G0/G1 peak were obtained (average CV=3.29%). When DRAQ5 staining and immunophenotyping were combined, the within- and between-run imprecision was 1.98% and 1.67%, respectively and the DNA content of 25 DNA-hyperdiploid tumor cells (DNA-index=1.16) per 4.10(4) mononuclear cells (0.06%) could be determined.

CONCLUSIONS

The multiparameter DRAQ5 assay has a superior sensitivity and specificity compared to the propidium iodide based method. Since at least 25 DNA-hyperdiploid cells per 10(4) DNA-diploid mononuclear cells could be detected, multiparameter DRAQ5 DNA content analysis could be used to study minimal residual disease.

Maturation and enucleation of primitive erythroblasts during mouse embryogenesis is accompanied by changes in cell-surface antigen expression

Primitive erythroblasts (EryPs) are the first hematopoietic cell type to form during mammalian embryogenesis and emerge within the blood islands of the yolk sac. Large, nucleated EryPs begin to circulate around midgestation, when connections between yolk sac and embryonic vasculature mature. Two to 3 days later, small cells of the definitive erythroid lineage (EryD) begin to differentiate within the fetal liver and rapidly outnumber EryPs in the circulation. The development and maturation of EryPs remain poorly defined. Our analysis of embryonic blood at different stages reveals a stepwise developmental progression within the EryP lineage from E9.5 to E12.5. Thereafter, EryDs are also present in the bloodstream, and the 2 lineages are not easily distinguished. We have generated a transgenic mouse line in which the human epsilon-globin gene promoter drives expression of green fluorescent protein exclusively within the EryP lineage. Here, we have used this line to characterize changes in cell morphology and surface-marker expression as EryPs mature and to track EryP numbers and enucleation throughout gestation. This study identifies previously unrecognized synchronous developmental stages leading to the maturation of EryPs in the mouse embryo. Unexpectedly, we find that EryPs are a stable cell population that persists through the end of gestation.