An open-source deconvolution software package for 3-D quantitative fluorescence microscopy imaging

Deconvolution techniques have been widely used for restoring the 3-D quantitative information of an unknown specimen observed using a wide-field fluorescence microscope. Deconv, an open-source deconvolution software package, was developed for 3-D quantitative fluorescence microscopy imaging and was released under the GNU Public License. Deconv provides numerical routines for simulation of a 3-D point spread function and deconvolution routines implemented three constrained iterative deconvolution algorithms: one based on a Poisson noise model and two others based on a Gaussian noise model. These algorithms are presented and evaluated using synthetic images and experimentally obtained microscope images, and the use of the library is explained. Deconv allows users to assess the utility of these deconvolution algorithms and to determine which are suited for a particular imaging application. The design of Deconv makes it easy for deconvolution capabilities to be incorporated into existing imaging applications.

Direct Comparison of Biological Effectiveness of Protons and Alpha-particles of the Same LET. II. Mutation Induction at the HPRT Locus in V79 Cells

Mutation induction at the hprt locus has been studied in V79-4 Chinese hamster cells irradiated with mono-energetic protons and alpha-particles with LET of 20.3 and 23 keV microns-1. The mutation frequency increased linearly with the dose for all the four radiation qualities investigated, so that effectiveness for mutation induction could be expressed by the slope of the relevant curve. This effectiveness did not significantly change with the small change in LET of each kind of particle, while sizeable differences were found between particles. Protons were more effective in mutation induction than alpha-particles with the same LET by a factor of about 2. This finding is similar to, although slightly larger than, the factors 1.5-1.8 found for inactivation of the same cells in the same series of experiments.

Direct Comparison of Biological Effectiveness of Protons and Alpha-particles of the Same LET. III. Initial Yield of DNA Double-strand Breaks in V79 Cells

The results reported form part of a series of experiments to substantiate and extend the findings by Belli et al. (1989) that protons are more biologically effective at cell killing than alpha-particles of the same LET. The irradiations were carried out using the Variable Energy Cyclotron (VEC) at the Harwell Laboratories. V79-4 Chinese hamster cells were exposed to alpha-particles and protons with LETs of 20 and 23 keV microns-1 in the dose range 40-150 Gy. X-rays were also used for comparison. Two methods were used for measurement of initial DNA double-strand breaks: sedimentation and DNA precipitation assays. The dose-response relationships were found to be well fitted by straight lines in all cases. With the sedimentation assay a slightly lower yield of dsb was found from protons than from alpha-particles of the same LET. The yield from X-rays was not significantly different from either. The precipitation assay showed similar yields of DNA damage from both particle types but significantly higher yields from X-rays. This may reflect a difference in the type of lesions scored by the two methods. Since the initial amount of dsb does not account for the observed differences in cellular response to radiations of different qualities, it is likely that these are related to the nature of the dsb (affecting reparability) or to the occurrence of other types of molecular damage.

Segregation of genomes in polyploid tumour cells following mitotic catastrophe

Following irradiation p53-function-deficient tumour cells undergo mitotic catastrophe and form endopolyploid cells. A small proportion of these segregates nuclei, and give rise to viable descendants. Here we studied this process in five tumour cell lines. After mitotic failure, tumour cells enter the endocycle and form mono-nucleated or multi-nucleated giant cells (MOGC and MNGC). MNGC arise from arrested anaphases, MOGC, from arrested metaphases. In both cases the individual genomes establish a radial pattern by links to a single microtubule organizing centre. Segregation of genomes is also ordered. MNGC present features of mitosis being resumed from late anaphase. In MOGC the sub-nuclei retain arrangement of stacked metaphase plates and are separated by folds of the nuclear envelope. Mitosis then resumes in sub-nuclei directly from metaphase. The data presented indicate that endopolyploid tumour cells preserve the integrity of individual genomes and can potentially re-initiate mitosis from the point at which it was interrupted.

Development of the large scale digital cell analysis system

Quantitative analysis of large numbers of cells exposed to various stresses would be facilitated by an automated microscope system designed to monitor up to 1000 microscope fields over time intervals of up to one month. The Large Scale Digital Cell Analysis System (LSDCAS) was designed by the authors to provide such analysis capabilities. This report presents a description of the development of the LSDCAS and its application to the study of cells undergoing radiation-induced mitotic catastrophe. A detailed description of the data acquisition algorithms used and the hardware configuration underlying the system is presented. Quantitative analysis of colony formation of cells exposed to 5 Gy X irradiation is presented. Upon analysis, it was found that the plating efficiency in irradiated populations agreed with that obtained using conventional colony-formation assays, indicating the accuracy of LSDCAS in the determination of cell clonogenicity. An unexpected finding was that fully 50% of the surviving colonies exhibited mitotic catastrophe that persisted throughout colony formation. Ongoing extension of the capabilities of the LSDCAS using image segmentation techniques applied to a variety of cellular endpoints is then briefly described.

Enhancement of radiation-induced mitotic catastrophe by moderate hyperthermia

PURPOSE

To determine if a maximally radiosensitizing but non-toxic moderate hyperthermia treatment enhances radiation-induced mitotic catastrophe.

MATERIALS AND METHODS

HeLa S3 cells were given a non-lethal heat treatment (41.5 degrees C, 4 h) and irradiated with 5 Gy X-irradiation. Alterations in cell-cycle distribution, intracellular cyclin B1 levels, and the yield of mitotic catastrophe were then measured and compared to heat-only and radiation-only groups, as a function of time following treatment.

RESULTS

A greater accumulation of cells in S and G2 phases of the first cell-cycle post-treatment was observed in the combined heat and radiation groups, when compared with that observed following treatment with heat or radiation alone. Similarly, intracellular levels of cyclin B1 and the incidence of mitotic catastrophe were found to be greater in the combined treatment groups.

CONCLUSIONS

This study provides further evidence that delays late in the cell cycle are implicated in increases in intracellular cyclin B1 levels and the subsequent development of mitotic catastrophe. Further, these data suggest a role for mitotic catastrophe occurring as a result of G2/M checkpoint abrogation in the process of thermal radiosensitization.

Mitotic catastrophe induced by exposure of V79 Chinese hamster cells to low-energy protons

PURPOSE

To determine the yield of mitotic catastrophe induced after low energy proton irradiation and to compare this yield with that induced by X-rays.

MATERIALS

Asynchronous Chinese hamster V79 cells were irradiated with 0.5, 1, 2, 5 and 10 Gy proton beams and X-rays. Proton LET of 7.7, 11.0 and 30.5 keV microm(-1), corresponding to energies of 5.01, 3.20 and 0.76 MeV respectively, evaluated at the cell mid-plane, were used for experiments. The occurrence and yield of mitotic catastrophe was measured as the percentage of cells exhibiting fragmented nuclei.

RESULTS

Proton irradiation led to an enhanced induction of mitotic catastrophe in V79 cells. The onset of nuclear fragmentation, a hallmark of mitotic catastrophe, occurred much earlier after cell exposure to proton particles than to X-ray irradiation.

CONCLUSIONS

Mitotic catastrophe is persistent in the subsequent cell generations after proton and X irradiation of V79 cells; but protons are more effective than X-rays for the induction of this phenomenon. These results are discussed in terms of their importance in space exposures and possible acquisition of genomic instability by the progeny of irradiated cells.

RBE-LET relationships for cell inactivation and mutation induced by low energy protons in V79 cells: further results at the LNL facility

PURPOSE

RBE-LET relationships for cell inactivation and hprt mutation in V79 cells have been studied with mono-energetic low-energy proton beams at the radiobiological facility of the INFN-Laboratori Nazionali di Legnaro (LNL), Padova, Italy.

MATERIALS AND METHODS

V79 cells were irradiated in mono-layer on mylar coated stainless steel petri dishes, in air. Inactivation data were obtained at 7.7, 34.6 and 37.8 keV/microm and hprt mutation was studied at 7 7 and 37.8 keV/microm. Additional data were also collected for both the end points with the proton LET already considered in our previous publications, namely 11.0, 20.0 and 30.5 keV/microm.

RESULTS

A maximum in the RBE-LET relationship for cell inactivation was found at around 31 keV/microm, while the RBE for mutation induction increased continuously with LET.

CONCLUSIONS

The proton RBE-LET relationship for cell inactivation is shifted to lower LET values compared with that for heavier ions. For mutation induction, protons of LET equal to 7.7keV/microm gave an RBE value comparable with that obtained by helium ions of about 20 keV/microm. Mutagenicity and lethality caused by protons at low doses in the LET range 7.7-31 keV/microm were proportional, while the data at 37.8 keV/microm suggest that this may not hold at higher LET values.

Delayed DNA damage associated with mitotic catastrophe following X-irradiation of HeLa S3 cells

Partial loss of the radiation G2/M checkpoint is thought to be an early event in cell immortalization. One of the attributes of immortalized cell lines is an increase in susceptibility to induction of genomic instability by clastogenic agents. Recently we have shown that in irradiated HeLa cells cell cycle delays in late S and G2 lead to overaccumulation of cyclin B1 and that enhanced intracellular levels of this positive regulator of the cell cycle is correlated with cyclin-dependent kinase activation, spontaneous premature chromosome condensation and subsequent mitotic catastrophe occurring following irradiation. Previous studies have shown that spontaneous premature chromosome condensation and mitotic catastrophe are independent of apoptosis. This report shows that 40 h following X-irradiation of HeLa S3 cells, and subsequent to mitotic catastrophe, DNA strand breaks appear which are chemically distinct from those initially produced by ionizing radiation. This delayed damage is recognized by terminal transferase and thus involves generation of free 3'-OH ends. Pulse field gel electrophoresis analysis of DNA size distributions shows that DNA fragments of approximately 40 kbp and smaller are produced. As strand breaks produced as a direct result of irradiation are generally repaired within a few hours after exposure to X-rays at the doses used, these results describe a novel mechanism for generation of DNA damage occurring a day or more following irradiation. These results may be pertinent to the understanding of mechanisms underlying the delayed lethal effects of irradiation and may provide an initiating mechanism for radiation-induced genomic instability.

Spontaneous premature chromosome condensation and mitotic catastrophe following irradiation of HeLa S3 cells

PURPOSE

To study the mechanisms underlying the loss of G2/M checkpoint control which leads to mitotic catastrophe in human tumour cells following exposure to ionizing radiation.

MATERIALS AND METHODS

Asynchronous HeLa S3 cells were irradiated with doses of 5, 10 and 20 Gy X-rays. Cell-cycle progression and cyclin B1 levels were measured using bivariate flow-cytometric techniques as a function of time after irradiation. As indicators of mitotic catastrophe, the appearance of spontaneous premature chromosome condensation (SPCC) and cells presenting nuclear fragmentation were analysed using microscopy. Cyclin B1-dependent kinase activity was determined in immunoprecipitates and analysed using gel electrophoresis.

RESULTS

After X-irradiation of HeLa cells, delays in late S and G2 phases of the cell cycle were followed by SPCC and nuclear fragmentation, both indicative of mitotic catastrophe. The kinetics of appearance of cells that had apparently undergone mitotic catastrophe (i.e. the fraction of cells exhibiting nuclear fragmentation) was independent of the dose-dependent radiation-induced division delay, while the extent of fragmentation (expressed as the number of nuclear fragments per fragmented cell) did increase with dose. Also observed was a 5-fold elevation of cyclin B1 levels in late S/G2 cells, which correlated temporally with the observed delays late in the cell cycle. Following the appearance of elevated cyclin levels, cyclin B1-associated histone H1 kinase activity showed similar increases; these increases in kinase activity occurred prior to increases in the fraction of cells exhibiting nuclear fragmentation.

CONCLUSIONS

In human cells, cyclin B1 gene expression occurs in late S and G2 phases, and thus the increase observed in this protein may be due to the increased time spent by cells in these phases as a result of cell-cycle delays caused by the radiation exposure. It is possible that, under these conditions, over accumulation of cyclin B1 dilutes the mitosis-inhibitory action of the weel or other inhibitory pathways. Thus, this study presents a possible mechanism for G2/M checkpoint abrogation following ionizing radiation which may depend solely on effects associated with perturbed cell-cycle progression.

DNA double strand break production and rejoining in V79 cells irradiated with light ions

Low energy protons and other densely ionizing light ions are known to have RBE>1 for cellular end points relevant for stochastic and deterministic effects. The occurrence of a close relationship between them and induction of DNA dsb is still a matter of debate. We studied the production of DNA dsb in V79 cells irradiated with low energy protons having LET values ranging from 11 to 31 keV/micrometer, i.e. in the energy range characteristic of the Bragg peak, using the sedimentation technique. We found that the initial yield of dsb is quite insensitive to proton LET and not significantly higher than that observed with X-rays, in agreement with recent data on V79 cells irradiated with alpha particles of various LET up to 120 keV/micrometer. By contrast, RBE for cell inactivation and for mutation induction rises with the proton LET. In experiments aimed at evaluating the rejoining of dsb after proton irradiation we found that the amount of dsb left unrepaired after 120 min incubation is higher for protons than for sparsely ionizing radiation. These results indicate that dsb are not homogeneous with respect to repair and give support to the hypothesis that increasing LET leads to an increase in the complexity of DNA lesions with a consequent decrease in their repairability.

DNA double-strand breaks induced by low energy protons in V79 cells

The initial production of DNA double-strand breaks (dsb) was determined in V79 Chinese hamster cells irradiated with proton beams of 3.24, 1.50 and 0.88 MeV, corresponding to values of unrestricted LET evaluated at the cell midplane of 10.9, 20.0 and 30.5 keV/micron, respectively. X-rays were used for comparison. Dsb were measured with the low speed sedimentation technique in neutral sucrose gradients. The initial yield of dsb rose linearly with the dose and did not significantly depend on the proton LET, in contrast with the results obtained in previous studies for cell inactivation and mutation induction. Also, no significant differences for dsb induction were found between protons and X-rays. Two possible explanations, not necessarily mutually exclusive, are proposed: (1) dsb are not the only lesions involved in cellular effects; and (2) the initial number of dsb is not the only important parameter since a fundamental role is played by the degree of clustering, i.e. the association of dsb with other dsb or other types of damage.

Inactivation and mutation induction in V79 cells by low energy protons: re-evaluation of the results at the LNL facility

During the upgrading of the radiobiological facility at the Laboratori Nazionali di Legnaro (LNL) we found that uncorrected values of the proton energy were used in the past. This circumstance prompted us to perform the re-evaluation of the physical parameters for all the proton beams used in our previous radiobiological investigations (Belli et al. 1987) and, subsequently, the re-evaluation of all our previous dose-response curves for inactivation and mutation induction (Belli et al. 1989, 1991). This re-evaluation leads to significant changes in the dose-response curves and in the RBE-LET relationships only at the two lowest energies (highest LET) used. These two points are not reliable for the identification of a peak in RBE-LET relationship for cell inactivation. In spite of that, the extent of the changes is not such as to modify the general conclusion previously drawn, pointing out that there is a LET range where protons are more effective than alpha-particles.

Mutation induction and RBE-LET relationship of low-energy protons in V79 cells

The mutation induction at the HGPRT locus has been studied in V79-753B Chinese hamster cells irradiated with proton beams with energies of 3.36, 1.70 and 1.16 MeV, corresponding to average LET values of 10.6, 17.8 and 23.9 keV/microns, respectively. The mutation curve obtained with 200 kV X-rays was used for comparison. The mutation frequency induced by all the proton beams is considerably higher than that induced at the same dose by X-rays and it is linearly related to the dose. Moreover, the proton effectiveness increases with the LET. The RBEs (evaluated as the initial slope ratios) are 5.0 +/- 0.8, 5.4 +/- 0.8 and 7.7 +/- 1.2 for protons with average LETs of 10.6, 17.8 and 23.9 keV/microns, respectively. These values are higher than those reported in the literature for other ions of comparable LET. This finding parallels what we have already found for cell inactivation (for which RBEs of 3.0, 4.6 and 7.3 were obtained at the same LETs), and indicates that for mutation induction, also, the RBE-LET relationship may depend on the type of radiation.

Effects of decreased pH on membrane structural organization of Escherichia coli grown in different fatty acid-supplemented media: a 31P NMR study

Total membranes from Escherichia coli cells grown in different fatty acid-supplemented media have been examined by 31P NMR at different pH values. The isolated inner and outer membranes were also studied and compared to the liposomes formed with the corresponding extracted lipids. While the liposomes show structures that are correlated with lipid composition, degree of fatty acid unsaturation, and pH, the membrane structure is mainly bilayer. The presence of two bilayer phases characterized by different chemical shift anisotropy values (delta nu csa) is detectable at neutral pH; a perturbation of the bilayer phase characterized by the smallest delta nu csa is produced by low pH. Moreover, an isotropic peak is always present in the membrane NMR spectra: its attribution to cardiolipin molecules is discussed on the basis of digestion experiments with phospholipase C.

Studies of structural modifications induced by gamma-irradiation in distearoylphosphatidylcholine liposomes

An investigation of the structural and thermodynamical modifications induced by gamma-irradiation in model membranes is reported. Differential scanning calorimetry and X-ray diffraction were used to study the different phases and associated transitions of distearoylphosphatidylcholine multilamellar liposomes after 60Co gamma-irradiation. Changes were observed in the shape of the calorimetric peaks and in the corresponding phase transition temperatures. In particular a shoulder was observed at about 20 kGy. The three phases characteristic of lecithins with identical acyl chains were detected also for the highest radiation dose. The formation of lysolecithin and stearic acid upon phospholipid degradation was observed. The lysolecithin concentration increases as a function of irradiation dose, until a saturation value is reached at 40 kGy. These results correlate quite well with those obtained for interlayer and interchain distances and for the width of the main phase transition calorimetric peak. At the highest dose (approximately equal to 80 kGy) cross-linked adjacent radicals and other molecular species are also formed. Appreciable differences, and some similarities, in the behaviour of DSPC and DPPC liposomes under gamma-irradiation were observed.

Effects of gamma-irradiation on the erythrocyte membrane: ESR, NMR and biochemical studies

The effects of gamma-irradiation on resealed erythrocyte ghosts have been examined with different techniques. Phospholipid analysis reveals peroxidative damage on the polyunsaturated chains of phosphatidylethanolamine. Gel electrophoresis and ESR measurements indicate modifications of the cytoskeletal proteins. 31P Nuclear magnetic resonance data show bilayer modifications that can be interpreted as changes in lipid-protein interactions. The overall picture from the present results favours interaction between lipids and proteins in the inner monolayer of the membrane.

X-ray diffractometry and calorimetry studies of structural modifications induced by gamma-irradiation in phosphatidylcholine multilamellar liposomes

Experimental results are reported on structural and thermodynamic modifications induced by gamma-irradiation in model membranes. Differential scanning calorimetry (DSC) and X-ray diffraction were used to study the different phases and associated transitions of dipalmitoylphosphatidylcholine after 60Co gamma-irradiation. Changes were observed in the shape of calorimetric peaks and in the corresponding enthalpy. The repetition distance of the layers increases while the distances related to the aliphatic chains decrease as a function of gamma-irradiation time. Moreover, an increase in the hexagonal symmetry with increasing dose was detected. No disappearance of a pre-transition was detected even at high doses.

1H- and 2H-n.m.r. studies of water in gamma-irradiated phosphatidylcholine multilamellar liposomes

1H- and 2H-n.m.r. studies of gamma-irradiation-induced variations in the dynamic structure and proportional amounts of free, trapped and bound water species in multilamellar liposomes are reported and discussed. Bound water is shown to increase with dose and to be present in two different structural states. A dose-dependent decrease in the 1H-n.m.r. relaxation times of bound water following gamma-irradiation is reported. Variations are suggested as being due to large scale changes at the bilayer surface.

Gamma-irradiation effects on phosphatidylcholine multilayer liposomes: calorimetric, NMR, and spectrofluorimetric studies

Chemical and structural modifications in multilayer liposomes of synthetic phosphatidylcholine induced by gamma irradiation are investigated with different techniques. Fluorescence anisotropy of the DPH probe and differential scanning calorimetry reveal a broadening of the main lipid transition and the disappearance of pretransition. Fluorescence anisotropy is shown to be higher in the irradiated sample and particularly so at low temperatures. NMR and TLC results show that lysolecithin and palmitic acid are formed with a consequent change in bilayer organization. The possibility that these modifications may account for the permeability variations observed in irradiated natural membranes is discussed.