Identification of non-proliferating cells in melanoma B16 tumour

The G1 period. Two cycles of chromatin conformational changes monitored by single cell dye intercalation

In previous papers the existence of two cycles of chromosome condensation-decondensation per cell cycle was suggested based on experiments involving nuclear morphometry measurements of Feulgen-stained nuclei. This conclusion can be criticized since its assumption of a relationship between nuclear morphology and chromatin structure is derived from indirect evidence. In this paper, we report simultaneous measurements of nuclear area and nuclear fluorescence intensity on individual cells stained with the intercalating dye, acridine orange (AO). Using cells in various stages of G1 and synchronized by two different methods, our results demonstrate a linear correlation between nuclear area and fluorescence intensity. They also indicate two cycles of chromatin condensation-decondensation during the G1 period, as assayed by the number of chromatin primary, intercalating AO binding sites. Finally, they show that the first of these cycles involves a transition in early G1 from a very small condensed nucleus (immediately after telephase) to a relatively large, dispersed nucleus that occurs abruptly.

Biophysical identification and sorting of high metastatic variants from B16 melanoma tumor

Chromatin structure, in terms of higher order nuclear-DNA condensation (scanning cytometry) and in terms of acridine orange primary binding sites (flow cytometry), is analyzed and shown to be significantly different between high (B16-F10) and low (B16-F1) metastatic variants of B16 melanoma. Furthermore, double staining of B16-F10 and B16-F1 with ethidium bromide (chromatin) and fluorescamine (membranes) provides the identification of a homogeneous subpopulation of cells with enhanced metastatic potential based on differential fluorescamine uptake. Fluorescamine uptake and poststaining viability is shown to be dependent upon the dye/cell ratio at which staining occurs. Utilizing a sterile cell sorting technique, a subpopulation of B16-F10 with increased fluorescamine uptake representing 30% of the total "intact cell" population was isolated by means of a fluorescence activated cell sorter and replated in vitro. This subpopulation when assayed in vivo produced significantly more pulmonary metastases than its parent cell line. Scanning cytometry of the Feulgen stained sorted subpopulation reveals that the cells possess a unique nuclear morphometry characterized by a 2C-3C DNA content and a large nuclear area (disperse chromatin). Finally, when we assay simultaneously for nuclear-DNA organization and cell membrane organization a progressive uncoupling between nuclear and cell morphometry is apparent if B16-F10 (versus B16-F1).

Normal versus abnormal cell proliferation. A unitary and analytical overview

The most recent findings on the molecular and cellular characterization of normal and abnormal cell proliferation are summarized. They include molecular spectroscopy, nucleic acid conformation, protein modifications, premature chromosome condensation, nucleoli changes, nuclear and cell morphometry, image analysis, flow microfluorimetry, and time-lapse cinematography. Biophysical and biochemical evidence in favor or against two cycles of chromatin condensation, followed by two abrupt random decondensations, per cell cycle are presented. Other biphasic changes at the molecular and cellular levels that favor the existence of two random transitions, or restriction points, per cell cycle are discussed. A comprehensive unitary model of the cell cycle is then outlined; this model is able to explain most findings on continuously dividing cells and on quiescent cells induced to proliferate. Within this analytical framework the physical-chemical and biological properties are given, in either normal or tumor cells, for the various types of "noncycling" cells that are here viewed as necessary steps in mammalian cell growth rather than separates states. The implications of the coupling of higher-order chromatin structure with cell geometry and growth, high in fibroblast-like cells but low in transformed cells, are also discussed. Molecular mechanisms likely responsible for the chromatin conformational changes occurring at the G0 leads to G1, G1 leads to S, G2 leads to M transitions are finally discussed in terms of polyelectrolyte theory.

The quinternary chromatin-DNA structure. Three-dimensional reconstruction and functional significance

Nuclear DNA-space images from Feulgen-stained HeLa cells synchronized at 1, 3, 5, 8, 12, 15, and 18 h following mitosis are digitized and their densitometric-geometric patterns are analyzed by means of a Quantimet 720-D image analyzer on line with a PDP11/40 computer. Frequency distributions of picture point optical densities for the phases and subphases as seen in nuclear images show that DNA packing changes are evident by means of ordinary optical microscopy. Radii of gyration of the images, and optical density profiles and distributions for several squashes of similar cells reveal that in particular instances chromatin DNA is distributed mostly towards the periphery, and usually with high circular isotropy. Cross power spectra of individual scan lines suggest that existence of higher order "quinternary" periodic structure for chromatin that modulates during the cell cycle. Three-dimensional reconstruction 2- micrometer sections of intact, Feulgen-stained mammalian tumor tissue show stainable material only toward the nuclear perimeter and not in the center (compatible with the evidence that initial thymidine incorporation in HeLa cells is generally at the nuclear border). Densitometric properties of reconstructed interphase chromatin-DNA bodies are highly coupled with similar properties of the whole nucleus, showing that a more condensed nucleus is always accompanied by a more condensed interphase chromatin DNA. The effect of micrococcal nuclease digestion on the digitized nuclear images is also presented. All the above data are then discussed in terms of a quinternary chromatin-DNA structure and its modulation during the cell cycle.

Reversible (G0) and nonreadily reversible (Q) noncycling cells in human peripheral blood. Immunological, structural, and biological characterization

PHA-stimulated human lymphocytes (normal-resting-proliferating) at 0, 24, 48, 72, and 144 h were studied with Acridine Orange (AO) staining. By viable cell sorting, by subsequent subculturing, and by the use of biochemical, biophysical, and immunological assays, not only have the G0 resting and G1 (cycling) cell cycle phases been objectively characterized, but a separate subpopulation of quiescent cells that are functionally viable and deeply committed to nonproliferation, the Q cells, has been identified. Multiparameter cytofluorimetric analysis, methyl14C-thymidine incorporation, automated image analysis, and mitogen stimulation studies have shown that the "Q" cell, compared to the "G0" resting but easily recruitable cell, exhibits quite lower red and green AO emission, possesses 2c to 4c DNA content (rather than only 2c), has a higher average optical density, and is either nonrecruitable or recruitable-with-difficulty in PHA-stimulated lymphocyte cultures.

FPi analysis. II. Use of the method to monitor the in vivo kinetics of cell populations perturbed by hydroxyurea

In a previous report, we described a new method called FPi analysis to analyze time sequences of DNA histograms taken from a perturbed population of cells. In this paper we utilize the method to analyze the in vivo kinetic response of bone marrow and of lung metastases of the B16 tumor to various chemotherapeutic agents. We show that the technique allows useful kinetic data to be obtained with minimal processing of the raw histograms, thus allowing fast analysis of the data. We also show that, in order to monitor the kinetic response of living tissues, it is essential to collect multiparameter distributions; to monitor only the one dimensional fluorescence histogram can give rise to misleading results. Using these multiparameter histograms, we are also able to monitor the growth fraction of the lung metastases during treatment, allowing discrimination between cell synchrony and cell recruitment from the resting compartment.

Coupling of nuclear morphometry to cell geometry and growth in human fibroblasts

The nuclear morphology of WI-38 cells plated on increasing thicknesses of the polymer, poly-2-hydroxyethylmethacrylate, was studied. Changes in nuclear morphometry were found to parallel changes in cellular morphometry: namely a transition to a more rounded and compact conformation, with increasing thicknesses of the polymer. Such changes in nuclear morphometry were opposite to those already observed after stimulation of proliferation by serum addition and similar to those observed with increasing confluency. These results suggest that coupling between cell and nuclear geometry may represent a mechanism for the control of proliferation by cell shape in nontransformed cells.

Morphometric analysis of B2cAMP induced reverse transformation in synchronized CHO cells

Synchronized tranformed and reverse-transformed (by 10(-3) M B2cAMP) CHO-K1 cells, growing adherent to plastic, are characterized by means of geometric and densitometric parameters at the level of both the entire cell and of the nuclei at various time intervals after selective miotic detachment. Transformed and reverse-transformed cells triple-stained with Feulgen, Napthol Yellow S, and periodic acid-Schiff appeared very similar in terms of integrated optical density (IOD), related to either polysaccharides, protein, or DNA amount. On the other hand, a shift from a polygonal to a spindle-shaped morphology is a accompanied by a significant decrease in both form factor and average optical density (AOD) of intact cell and nuclei, which are the most conspicuous measured changes caused by B2cAMP, in addition to a lengthening of the cell cycle duration. In both control and treated cells, important and parallel cell-cycle-dependent modulations of geometric and densitometric parameters are also observed, for both the cytoplasmic (i.e., cell morphometry) and DNA space (i e., nuclear morphometry). Specifically, the modulation in nulear morphometry during G1, S, G2, and M phases confirms previous findings on synchronized HeLa cells. The optical density threshold-dependence of geometric parameters shows that, while becoming fusiform, the cytoplasm of reverse-transformed cells had a particularly low optical density precisely in the polar area. Utilization of such an approach in the development of an objective morphological classification of all cell lines grown as monolayers "in vitro" is also discussed.

Size dependence of cell cycle parameters for lung metastases from B16 melanoma

Data presented show that the cell cycle time of the lung metastases from a B16 melanoma tumor growing in the foot pad of C57 BL/6J mice increases as the size of the metastases increases. This increased cell phase durations of the small metastases being closer to those of the primary tumor. The growth fractions of the primary tumor and of the lung metastases of different sizes are analyzed.