Determination Of Cellular DNA Content Research Articles

Multiparametric Cell Cycle Analysis by Automated Microscopy

Cell cycle analysis using flow cytometry (FC) to measure cellular DNA content is a common procedure in drug mechanism of action studies. Although this technique lends itself readily to cell lines that grow in suspension, adherent cell cultures must be resuspended in a cumbersome and potentially invasive procedure that normally involves trypsinization and mechanical agitation of monolayer cultures. High-content analysis (HCA), an automated microscopy-based technology, is well suited to analysis of monolayer cell cultures but provides intrinsically less accurate determination of cellular DNA content than does FC and thus is not the method of choice for cell cycle analysis. Using Cellomics's ArrayScan reader, the authors have developed a 4-color multiparametric HCA approach for cell cycle analysis of adherent cells based on detection of DNA content (4,6-diamidino-2-phenylindole [DAPI] fluorescence), together with the known cell cycle markers bromo-2-deoxyuridine (BrdU) incorporation, cyclin B1 expression, and histone H3 (Ser28) phosphorylation within a single cell population. Considering all 4 markers together, a reliable and accurate quantification of cell cycle phases was possible, as compared with flow cytometric analysis. Using this assay, specific cell cycle blocks induced by treatment with thymidine, paclitaxel, or nocodazole as test drugs were easily monitored in adherent cultures of U-2 OS osteosarcoma cells.

Simultaneous flow cytometric analysis of two cell surface markers, telomere length, and DNA content.

Various protocols for estimation of telomere length in individual cells by flow cytometry using fluorescence in situ hybridization of fluorescently labeled peptide nucleic acid (PNA) probes (Flow-FISH) have been described. Combined analysis of telomere length and cell phenotype, however, remains difficult because few fluorochromes with suitable emission spectra tolerate the harsh conditions needed for DNA denaturation during hybridization of the telomere-specific PNA probe. We overcame these problems and developed a method for measuring telomere length in cell subsets characterized by the expression of two surface antigens. Alexa Fluor 488 and Alexa Fluor 546 were used for cell surface staining. Antigen-antibody complexes were covalently cross-linked onto the cell membrane before Flow-FISH. Cells were hybridized with a PNA probe conjugated to cyanine 5 (Cy5). Hoechst 33342 (HO342) was added for determination of cellular DNA content. For assay standardization, we added an aliquot of a single batch of 1,301 cells to each sample as an internal control before hybridization with the PNA probe. Samples were prepared in duplicate and analyzed on a standard three-laser BD LSR flow cytometer. For assay validation, the same samples were analyzed in parallel to correlate the percentage of telomere length of the sample versus 1,301 control cells to the mean size of terminal restriction fragments (TRFs) of DNA as determined by Southern gel analysis. The method permitted clear identification of lymphocyte subsets in samples hybridized for Flow-FISH, with subset frequencies comparable to those of untreated samples. At a concentration of 10 nM, the Cy5-labeled telomere-specific PNA probe produced a bright fluorescence signal well separated from background. Addition of HO342 in low concentration did not interfere with Cy5 telomere fluorescence, produced adequate DNA histograms, and permitted clear identification of cell phenotype. The probe concentration of 10 nM also proved optimal for inclusion of 1,301 control cells for assay standardization. Telomere length estimations by the current method correlated highly with TRF calculations by Southern gel hybridization (r(2)= 0.9, P = 0.0003). Application of our protocol to the analysis of human CD8CD28 lymphocyte subsets showed that CD8(+bright)CD28(-) lymphocytes generally exhibit shorter telomeres than CD8(+bright)CD28(+) cells. These data concurred with previous results of telomere shortening in CD8(+)CD28(-) T cells that were obtained by using different techniques. The multiparameter Flow-FISH protocol permitted rapid determination of differences in telomere length in subpopulations characterized by two surface markers without prior cell separation.

Determination of cellular DNA content of Iberian salamanders by flow cytometry

AbstractThe DNA content per diploid nucleus (2 C-value) was determined for the eight species of Iberian salamanders by flow cytometry. All species showed high values, which are characteristic of Caudata. The species with the lowest value was Pleurodeles waltl (48.25 pg DNA/cell) and Salamandra salamandra had the highest values (70.55 pg DNA/cell). There were no statistical differences between sexes in any of the eight species and DNA content was not directly related with phylogeny. The values obtained are often higher than previously published estimates obtained with older and potentially less accurate methodologies. We discuss the possible relationship between cellular DNA content and reproductive biology. Se determinó el contenido en ADN por núcleo diploide (valor 2-C) por citometría de flujo de ocho especies de salamandras ibéricas. Todas las especies mostraron altos valores, lo que es característico de Caudata. La especie con el menor valor fue Pleurodeles waltl (48,25 pg ADN/célula) mientras Salamandra salamandra tuvo las valores más altos (70,55 pg ADN/célula). No se encontraron diferencias estadísticas entre sexos en ninguna de las 8 especies y el contenido en ADN no se relacionó directamente con la filogenia. Los valores obtenidos son, a menudo, más altos que los publicados previamente con técnicas más antigüas, y potencialmente menos precisas. Discutimos las posibles relaciones entre el contenido en ADN celular y la biología reproductiva de cada especie.

Flow cytometric analysis of estrogen, progesterone receptor expression and DNA content in formalin-fixed, paraffin-embedded human breast tumors

Flow cytometric analysis of estrogen (ER) and progesterone (PgR) receptor expression in archival human breast tumors is relatively difficult. We have used enzyme digestion and microwave antigen retrieval procedures for multiparametric flow cytometric analysis of ER and PgR expression and DNA content in nuclei isolated from formalin-fixed/paraffin-embedded primary breast tumors. Deparaffinized rehydrated tissue sections treated with pepsin were subjected to microwave irradiation for unmasking of ER and PgR antigenic sites. Biotinylated ER antibody and streptavidin-fluorescein isothiocyanate (FITC) were used for ER labeling and PgR antibody with phycoerythrin labeled goat anti-mouse antibody was used for PgR labeling. Counter staining with propidium iodide-RNase was used for determination of cellular DNA content. Our results show that enzyme digestion and microwave treatment of formalin-fixed, paraffin-embedded breast tumors can be successfully used for the multiparametric analysis of nuclear hormone receptor expression and DNA content by flow cytometry.

The study of endocrine tumors by flow and image cytometry.

Both DNA flow and image cytometry are methods that can be used for the quantitative determination of cellular DNA content. Objective, quantitative analysis of cellular morphology can also be obtained using image cytometry. Data thus generated have been shown to be of diagnostic and prognostic use in the study of many solid tumors and would be of particular value in the evaluation of endocrine tumors that show a poor correlation between their histology and biological behavior. The main application of these techniques to endocrine tumors has been in the analysis of thyroid nodules, although a limited number of studies of parathyroid, pituitary, adrenal, and pancreatic neuroendocrine tumors and tumors of the dispersed neuroendocrine system have been reported. Review of these studies shows that in the endocrine organs DNA and morphometric measurements have a very limited role in the diagnosis of individual cases, but are important as prognostic variables. The high incidence of abnormal DNA content in histologically benign lesions of the endocrine glands has important biological implications. Further investigation of this phenomenon may help to elucidate the process of endocrine tumorigenesis.

Comparison of image analysis and flow cytometric determination of cellular DNA content.

A good correlation (r = 0.94) was obtained between the DNA indices (DI) using flow cytometry and image analysis of nuclei cytospins extracted from paraffin wax embedded tumour sections. Some of the limitations and problems associated with image analysis which came to light included an unacceptably high coefficient of variation (CV) and a "left-shift" in the DI in most DNA histograms obtained when using image analysis of 5 microns sections. In contrast, the DNA histograms generated using image analysis of cytospun nuclei from paraffin wax blocks were of good quality and similar to those obtained using flow cytometry. Variability in Feulgen staining was common and an important source of error despite rigorous control of the staining technique. This could be overcome by using internal controls such as fibroblasts rather than external controls (rat hepatocytes) to determine the diploid DI with image analysis. A thorough understanding and appreciation of the methodological problems associated with image analysis and flow cytometric determination of DNA content is required before these methods find widespread clinical application.

Squamous papillary neoplasia of the adult upper aerodigestive tract.

Selected papillary squamous tumors of the upper aerodigestive tract (UADT) mucosa in adult patients do not have well-defined histologic criteria and the clinical behavior is poorly understood. To better characterize this spectrum of neoplasms, UADT papillary neoplasms were evaluated by routine histology, determination of cellular DNA content using Feulgen-stained tissue sections, and the typing of human papillomavirus (HPV) by in situ hybridization. Solitary papillomas were studied in two patients; there was no recurrence in either case, both had normal DNA content, and one was typed as HPV-6 while the other was typed as HPV-11. Seven adult patients with recurrent papillomatosis and at least one biopsy with dysplasia/atypia were identified (mean age at diagnosis, 13.3 years; mean age at last contact, 42.7 years). Six of seven patients had abnormal DNA cellular content in foci of epithelial atypia. In all biopsies evaluated, the papillomas of the seven patients were consistently typed as either HPV-6 or HPV-11. Six patients with malignant papillary neoplasms also had abnormal DNA cellular content, but none revealed evidence of HPV type 6, 11, 16, or 18 by in situ hybridization of tissue sections. In many of the recurrent papillomas, the degree of epithelial atypia encountered was pronounced and was commonly misdiagnosed as carcinoma in situ or papillary carcinoma. The aneuploid DNA content of these foci of atypia reflected the abnormal cellular appearance and partially explained the overdiagnosis of malignancy. However, none of the seven patients were treated for malignant disease and none progressed to invasive carcinoma, with an average follow-up period of almost 30 years. We conclude that histologic and cytologic atypia in HPV-containing papillomatosis may be appreciable. The aneuploid DNA content may represent premalignant conditions and the patient may be at an increased risk for the subsequent development of squamous cancer. However, none of the seven patients with recurrent papillomatosis developed any evidence of malignancy. In addition, none of the patients with papillary carcinomas had previous recurrent papillomatosis.

High-resolution image analysis.

In many departments of cytology, cytogenetics, hematology, and pathology, research projects using high-resolution computerized microscopy are now being mounted for computation of morphometric measurements on various structural components, as well as for determination of cellular DNA content. The majority of these measurements are made in a partially automated, computer-assisted mode, wherein there is strong interaction between the user and the computerized microscope. At the same time, full automation has been accomplished for both sample preparation and sample examination for clinical determination of the white blood cell differential count. At the time of writing, approximately 1,000 robot differential counting microscopes are in the field, analyzing images of human white blood cells, red blood cells, and platelets at the overall rate of about 100,000 slides per day. This mammoth through-put represents a major accomplishment in the application of machine vision to automated microscopy for hematology. In other areas of automated high-resolution microscopy, such as cytology and cytogenetics, no commercial instruments are available (although a few metaphase-finding machines are available and other new machines have been announced during the past year). This is a disappointing product, considering the nearly half century of research effort in these areas. This paper provides examples of the state of the art in automation of cell analysis for blood smears, cervical smears, and chromosome preparations. Also treated are new developments in multi-resolution automated microscopy, where images are now being generated and analyzed by a single machine over a range of 64:1 magnification and from 10,000 X 20,000 to 500 X 500 in total picture elements (pixels). Examples of images of human lymph node and liver tissue are presented. Semi-automated systems are not treated, although there is mention of recent research in the automation of tissue analysis.

Phytohemagglutinin Response in Systemic Lupus Erythematosus

THE PHYTOHEMAGGLUTININ (PHA) RESPONSE OF LYMPHOCYTES FROM UNTREATED PATIENTS WITH SYSTEMIC LUPUS ERYTHEMATOSUS (SLE) WAS STUDIED USING HIGHLY PURIFIED SUBPOPULATIONS OF CELLS INVOLVED IN THE TRANSFORMATION RESPONSE: T lymphocytes, B lymphocytes, and monocytes. Cell transformation was quantitated using both tritiated thymidine ([(3)H]-TdR) incorporation into DNA and cytofluorographic determination of cellular DNA content. Dose-response curves using six concentrations of PHA and five concentrations of cells over 0-5 days revealed a decrease in [(3)H]TdR by stimulated lymphocytes from some SLE patients. This decrease in [(3)H]TdR was paralleled by a decreased percentage of cells in S, G(2), and M phases of the cell cycle. However, abnormal response occurred entirely in those SLE patients who were hypocomplementemic. The etiology of the impaired response was further examined. Lymphocyte receptors for concanavalin A were studied using cytofluorography of lymphocytes stained with fluorescein-conjugated concanavalin A. The frequency distribution of concanavalin A receptors was similar in the normocomplementemic and hypocomplementemic lupus patients and in normals. The latex phagocytic activity of lupus macrophages was similar to normals when allogeneic normal plasma was used in the culture medium. Phagocytic activity became abnormal in the presence of SLE plasma. However, there was no difference in the [(3)H]TdR response or the percentage of cells in S, G(2), and M phases when T lymphocytes from the hypocomplementemic patients were stimulated on either autologous or normal allogeneic monocyte monolayers. Likewise, normal lymphocytes incorporated similar amounts of [(3)H]TdR and had similar percentages of cells in S, G(2), and M phases whether their T lymphocytes were stimulated on autologous or SLE monocyte monolayers. Highly purified subpopulations of B and T lymphocytes were obtained by density sedimentation or Fenwal Leuko-Pak passage of lymphocyte populations. The response to PHA by lymphocytes from the hypocomplementemic lupus patients could be seen to involve at least two abnormalities. One, in reference to normal lymphocytes, SLE T lymphocytes plus monocytes had an impaired response; two, SLE B lymphocytes plus SLE T lymphocytes plus SLE monocytes had an impaired response. Two patients in the hypocomplementemic group were treated with steroids. 5 days after steroid treatment was initiated, the percentage of cells in S, G(2), and M phases and the [(3)H]TdR response of PHA-stimulated lymphocytes returned to normal. The normalization of the [(3)H]TdR response was explained both by a return of purified T cells plus monocytes, purified B cells plus monocytes, and whole lymphocyte populations to normal responsiveness. These studies suggest that a steroid-correctable defect exists in T and B lymphocytes in SLE.