Quantitative phase imaging of adherent mammalian cells: a comparative study

The Quantitative phase imaging methods have several advantages when it comes to monitoring cultures of adherent mammalian cells. Because of low photo-toxicity and no need for staining, we can follow cells in a minimally invasive way over a long period of time. The ability to measure the optical path difference in a quantitative manner allows the measurement of the cell dry mass, an important metric for studying the growth kinetics of mammalian cells. Here we present and compare cell measurements obtained with three different techniques: digital holographic microscopy, lens-free microscopy and quadriwave lateral sheering interferometry. We report a linear relationship between optical volume density values measured with these different techniques and estimate the precisions of this measurement for the different individual instruments.

Modular organization of cardiac energy metabolism: energy conversion, transfer and feedback regulation

To meet high cellular demands, the energy metabolism of cardiac muscles is organized by precise and coordinated functioning of intracellular energetic units (ICEUs). ICEUs represent structural and functional modules integrating multiple fluxes at sites of ATP generation in mitochondria and ATP utilization by myofibrillar, sarcoplasmic reticulum and sarcolemma ion-pump ATPases. The role of ICEUs is to enhance the efficiency of vectorial intracellular energy transfer and fine tuning of oxidative ATP synthesis maintaining stable metabolite levels to adjust to intracellular energy needs through the dynamic system of compartmentalized phosphoryl transfer networks. One of the key elements in regulation of energy flux distribution and feedback communication is the selective permeability of mitochondrial outer membrane (MOM) which represents a bottleneck in adenine nucleotide and other energy metabolite transfer and microcompartmentalization. Based on the experimental and theoretical (mathematical modelling) arguments, we describe regulation of mitochondrial ATP synthesis within ICEUs allowing heart workload to be linearly correlated with oxygen consumption ensuring conditions of metabolic stability, signal communication and synchronization. Particular attention was paid to the structure-function relationship in the development of ICEU, and the role of mitochondria interaction with cytoskeletal proteins, like tubulin, in the regulation of MOM permeability in response to energy metabolic signals providing regulation of mitochondrial respiration. Emphasis was given to the importance of creatine metabolism for the cardiac energy homoeostasis.

Generalization of the polar representation in time domain fluorescence lifetime imaging microscopy for biological applications: practical implementation

The polar representation or phasor, which provides a fast and visual indication on the number of exponentials present in the intensity decay of the fluorescence lifetime images is increasingly used in time domain fluorescence lifetime imaging microscopy experiments. The calculations of the polar coordinates in time domain fluorescence lifetime imaging microscopy experiments involve several experimental parameters (e.g. instrumental response function, background, angular frequency, number of temporal channels) whose role has not been exhaustively investigated. Here, we study theoretically, computationally and experimentally the influence of each parameter on the polar calculations and suggest parameter optimization for minimizing errors. We identify several sources of mistakes that may occur in the calculations of the polar coordinates and propose adapted corrections to compensate for them. For instance, we demonstrate that the numerical integration method employed for integrals calculations may induce errors when the number of temporal channels is low. We report theoretical generalized expressions to compensate for these deviations and conserve the semicircle integrity, facilitating the comparison between fluorescence lifetime imaging microscopy images acquired with distinct channels number. These theoretical generalized expressions were finally corroborated with both Monte Carlo simulations and experiments.

Quantitative comparison of polar approach versus fitting method in time domain FLIM image analysis

We calculate here analytically the performance of the polar approach (or phasor) in terms of signal-to-noise ratio and F values when performing time-domain Fluorescence Lifetime Imaging Microscopy (FLIM) to determine the minimal number of photons necessary for FLIM measurements (which is directly related to the F value), and compare them to those obtained from a well-known fitting strategy using the Least Square Method (LSM). The importance of the fluorescence background on the lifetime measurement precision is also investigated. We demonstrate here that the LSM does not provide the best estimator of the lifetime parameter for fluorophores exhibiting mono-exponential intensity decays as soon as fluorescence background is superior to 5%. The polar approach enables indeed to determine more precisely the lifetime values for a limited range corresponding to usually encountered fluorescence lifetime values. These theoretical results are corroborated with Monte Carlo simulations. We finally demonstrate experimentally that the polar approach allows distinguishing in living cells two fluorophores undetectable with usual time-domain LSM fitting software.

Brilliant molecular nanocrystals emerging from sol-gel thin films: towards a new generation of fluorescent biochips

To develop highly sensitive biosensors, we made directly available to biological aqueous solutions organic nanocrystals previously grown in the pores of sol-gel films. Through the controlled dissolution of the sol-gel surface, we obtained emerging nanocrystals that remained strongly anchored to the sol-gel coating for good mechanical stability of the final sensing device. We demonstrated that in the presence of a solution of DNA functionalized with a molecular probe, the nanocrystal fluorescence is strongly quenched by Förster resonance energy transfer thus opening the way towards very sensitive fluorescent biosensors through biomolecules grafted onto fluorescent nanocrystals. Finally, this controlled dissolution, involving weak concentrated NaOH solution, is a generic process that can be used for the thinning of any kind of sol-gel layer.

Continuous photobleaching in vesicles and living cells: a measure of diffusion and compartmentation

We present a comprehensive and analytical treatment of continuous photobleaching in a compartment, under single photon excitation. In the very short time regime (t<0.1 ms), the diffusion does not play any role. After a transition (or short time regime), one enters in the long time regime (t>0.1-5 s), for which the diffusion and the photobleaching balance each other. In this long time regime, the diffusion is either fast (i.e., the photobleaching probability of a molecule diffusing through the laser beam is low) so that the photobleaching rate is independent of the diffusion constant and dependent only of the laser power, or the diffusion is slow (i.e., the photobleaching probability is high) and the photobleaching rate is mainly dependent on the diffusion constant. We illustrate our theory by using giant unilamellar vesicles ranging from approximately 10 to 100 microm in diameter, loaded with molecules of various diffusion constants (from 20 to 300 microm2/s) and various photobleaching cross sections, illuminated under laser powers between 3 and 100 microW. We also demonstrated that information about compartmentation can be obtained by this method in living cells expressing enhanced green fluorescent proteins or that were loaded with small FITC-dextrans. Our quantitative approach shows that molecules freely diffusing in a cellular compartment do experience a continuous photobleaching. We provide a generic theoretical framework that should be taken into account when studying, under confocal microscopy, molecular interactions, permeability, etc.

In vivo assessment of tumoral angiogenesis

Vessel size imaging (VSI) for brain tumor characterization was evaluated and the vessel size index measured by MRI (VSIMRI) was correlated with VSI obtained by histology (VSIhisto). Blood volume (BV) and VSI maps were obtained on 12 rats by simultaneous measurements of R2* and R2, before and after the injection of a macromolecular contrast agent, AMI-227. Immunostaining of collagen IV in vessels was performed. An expression was derived for evaluating VSI from stereologic measurements on histology data (VSIhisto). On BV and VSI images obtained from large-size tumors (n = 9), three regions could be distinguished and correlated well with histological sections: a high BV region surrounding the tumor, a necrotic area where BV is very low, and a viable tumor tissue region showing lower BV but higher VSI than the normal rat cortex, with the presence of larger vessels. The quantitative analysis showed a good correlation (Spearman rank's rho = 0.74) between VSIhisto and VSIMRI with a linear regression coefficient of 1.17. The good correlation coefficient supports VSI imaging as a quantitative method for tumor vasculature characterization.

Photobleaching, Mobility, and Compartmentalisation: Inferences in Fluorescence Correlation Spectroscopy

In living cells the transport and diffusion of molecules is constrained by compartments of various sizes. This paper is an attempt to show that the size of these compartments can in principle be estimated experimentally from Fluorescence Correlation Spectroscopy (FCS) combined with the measurement of the photobleaching rate. In this work, confocal fluorescence microscopy experiments have been carried out on giant unilamellar vesicles, a system that mimics cellular compartmentalisation. We have developed numerical and analytical models to describe the fluorescence decay due to photobleaching in this geometry, which has enabled us to point out two regimes depending on the value of the parameter P(B) = sigma(B)P/D (where sigma(B) is the photobleaching cross section of the dye, D its diffusion constant, and P the laser power (in photon/s)). In particular, when P(B) << 1 (i.e. in the fast diffusion regime), the photobleaching rate is independent of the diffusion constant and scales like sigma(B)P/R2, in agreement with the experimental results. On the other hand, the standard diffusion models used to analyse the FCS data do not take into account the effects of the fluorescence decay on the autocorrelation curve. We show here how to correct the raw data for these drawbacks.

Metabolic consequences of functional complexes of mitochondria, myofibrils and sarcoplasmic reticulum in muscle cells

Regulation of mitochondrial respiration both by endogenous and exogenous ADP in the cells in situ was studied in isolated and permeabilized cardiomyocytes, permeabilized cardiac fibers and 'ghost' fibers (all with a diameter of 10-20 micro m) at different (0-3 micro moll(-1)) free Ca(2+) concentrations in the medium. In all these preparations, the apparent K(m) of mitochondrial respiration for exogenous ADP at free Ca(2+) concentrations of 0-0.1 micro moll(-1) was very high, in the range of 250-350 micro moll(-1), in contrast to isolated mitochondria in vitro (apparent K(m) for ADP is approximately 20 micro moll(-1)). An increase in the free Ca(2+) concentration (up to 3 micro moll(-1), which is within physiological range), resulted in a very significant decrease of the apparent K(m) value to 20-30 micro moll(-1), a decrease of V(max) of respiration in permeabilized intact fibers and a strong contraction of sarcomeres. In ghost cardiac fibers, from which myosin was extracted but mitochondria were intact, neither the high apparent K(m) for ADP (300-350 micro moll(-1)) nor V(max) of respiration changed in the range of free Ca(2+) concentration studied, and no sarcomere contraction was observed. The exogenous-ADP-trapping system (pyruvate kinase + phosphoenolpyruvate) inhibited endogenous-ADP-supported respiration in permeabilized cells by no more than 40%, and this inhibition was reversed by creatine due to activation of mitochondrial creatine kinase. These results are taken to show strong structural associations (functional complexes) among mitochondria, sarcomeres and sarcoplasmic reticulum. Inside these complexes, mitochondrial functional state is controlled by channeling of ADP, mostly via energy- and phosphoryl-transfer networks, and apparently depends on the state of sarcomere structures.

[Magnetic resonance cerebral blood volume maps. Comparison with histologic findings in different types of brain lesions]

Recent developments in magnetic resonance (MR) have made it possible to obtain measurements of the microvasculature within brain lesions. Cerebral blood volume (CBV) maps calculated from dynamic contrast-enhanced MR imaging are particularly sensitive for depicting the microvasculature, and can enable the detection of neovascularization as well as its quantification in relative terms. The purpose of the present work is to compare the results of CBV maps calculated from MR imaging with those from histologic examination of the same region of interest: the biopsy site. Nineteen patients with brain lesions were studied (18 brain tumors and one case of multiple sclerosis). All patients underwent stereotactic biopsy, and calculation of CBV was performed from perfusion MR imaging. Three histopathologic parameters were assessed: the number of vessels (vessel density), the vessel size and the surface area filled by vessels (%). We observed a statistically significant correlation between the vessel density and the CBV, which is consistent with some previous publications. A noninvasive imaging method for characterizing the functional properties, especially hemodynamic activity, of malignant processes seems to be of great benefit to clinical practice.

Cell cycling determines integrin-mediated adhesion in osteoblastic ROS 17/2.8 cells exposed to space-related conditions

Six days of microgravity (Bion10 mission) induced dramatic shape changes in ROS 17/2.8 osteoblasts (7). During the Foton 11 and 12 space flights, we studied the kinetics (0-4 days) of ROS 17/2.8 morphology and adhesion, the relationships between adhesion and cell cycle progression after 4 days in space, and osteoblastic growth and activity after 6 days in space. Quantitative analysis of high-resolution adhesion [focal adhesion area imaged by total interference reflection fluorescent microscopy (TIRFM)] and integrin-dependent adhesion (imaged on confocal microscope by vinculin and phosphotyrosine staining) as well as cell cycle phase classification [Ki-67 staining, S-G2, mitotic cells and G1 (postmitotic cells)] were performed using programs validated in parabolic flight and clinostat. We observed disorganization of the cytoskeleton associated with disassembling of vinculin spots and phosphorylated proteins within focal contacts with no major change in TIRFM adhesion after 2 and 4 days of microgravity. Postmitotic cells, alone, accounted for the differences observed in the whole population. They are characterized by immature peripheral contacts with complete loss of central spots and decreased spreading. Osteocalcin, P1CP and alkaline phosphatase, and proliferation were similar in flight cells and 1 g centrifuge and ground controls after 6 days. In conclusion, microgravity substantially affected osteoblastic integrin-mediated cell adhesion. ROS17/2.8 cells responded differently, whether or not they were cycling by reorganizing adhesion plaque topography or morphology. In ROS 17/2.8, this reorganization did not impair osteoblastic phenotype.

Improvement of FISH mapping resolution on combed DNA molecules by iterative constrained deconvolution: a quantitative study

Image restoration approaches, such as digital deconvolution, are becoming widely used for improving the quality of microscopic images. However, no quantification of the gain in resolution of fluorescence images is available. We show that, after iterative constrained deconvolution, fluorescent cosmid signals appear to be 25% smaller, and 1.2-kb fragment signals on combed molecules faithfully display the expected length.

Pore-forming activity of type III system-secreted proteins leads to oncosis of Pseudomonas aeruginosa-infected macrophages

The Pseudomonas aeruginosa cystic fibrosis isolate CHA induces type III secretion system-dependent but ExoU-independent oncosis of neutrophils and macrophages. Time-lapse microscopy of the infection process revealed the rapid accumulation of motile bacteria around infected cells undergoing the process of oncosis, a phenomenon we termed pack swarming. Characterization of the non-chemotactic CHAcheZ mutant showed that pack swarming is a bacterial chemotactic response to infected macrophages. A non-cytotoxic mutant, lacking the type III-secreted proteins PcrV, PopB and PopD, was able to pack swarm only in the presence of the parental strain CHA or when macrophages were pretreated with the pore-forming toxin streptolysin O. Interaction of P. aeruginosa with red blood cells (RBCs) showed that the contact-dependent haemolysis provoked by CHA requires secretion via the type III system and the PcrV, PopB/PopD proteins. The pore inserted into RBC membrane was estimated from osmoprotection experiments to be between 2.8 and 3.5 nm. CHA-infected macrophages could be protected from cell lysis with PEG3350, indicating that the pore introduced into RBC and macrophage membranes is of similar size. The time course uptake of the vital fluorescent dye, Yo-Pro-1, into infected macrophages confirmed that the formation of transmembrane pores by CHA precedes cellular oncosis. Therefore, CHA-induced macrophage death results from a pore-forming activity that is dependent on the intact pcrGVHpopBD operon.

Fibre Orientation in Human Fetal Heart and Ventricular Mechanics : A Small Perturbation Analysis

The study of the topological organisation of myocardial cells is a basic requirement for understanding the mechanical design of the normal and pathological heart. Anatomical observations show that cardiac muscle tissue has a highly specialized architecture. We have made new quantitative measurements of fibre orientation through the heart wall by means of polarized light analysis on some thick sections of human fetal heart embedded in a resin and polymerized. A small perturbation method to find an equilibrium solution in a cylindrical left ventricular (LV) geometry with fibres running on toroidal shells of revolution is used to investigate the mechanical behaviour of three human fetal hearts (FH) of 14, 20 and 33 weeks of gestational age. The results of fibre strains and stresses presented for end-systolic state show significant differences when compared to results of the cylindrical geometry with regular helicoidal fibres running on cylindrical surfaces. Moreover, the toroidal shells of revolution explain shear stresses and strains in the transverse plane which also exist in the adult heart.

Organization of the X and Y chromosomes in human, chimpanzee and mouse pachytene nuclei using molecular cytogenetics and three-dimensional confocal analyses

We used multicolour fluorescence in-situ hybridization on air-dried pachytene nuclei to analyse the structural and functional domains of the sex vesicle (SV) in human, chimpanzee and mouse. The same technology associated with 3-dimensional analysis was then performed on human and mouse pachytene nuclei from cytospin preparations and tissue cryosections. The human and the chimpanzee SVs were very similar, with a consistently small size and a high degree of condensation. The mouse SV was most often seen to be large and poorly condensed, although it did undergo progressive condensation during pachynema. These results suggest that the condensation of the sex chromosomes is not a prerequisite for the formation of the mouse SV, and that a different specific mechanism could be responsible for its formation. We also found that the X and Y chromosomes are organized into two separate and non-entangled chromatin domains in the SV of the three species. In each species, telomeres of the X and Y chromosomes remain clustered in a small area of the SV, even those without a pseudoautosomal region. The possible mechanisms involved in the organization of the sex chromosomes and in SV formation are discussed.

Correlation between silver-stained nucleolar organizer region area and cell cycle time

BACKGROUND

The relationship between the population doubling time and the quantity of silver-stained nucleolar organizer region (AgNOR) interphase proteins was studied in cell culture at three different temperatures used to modulate the cell cycle duration.

METHODS

After MIB 1 and AgNOR combined staining, the quantity of AgNOR proteins was measured in cycling cells by image cytometry.

RESULTS

Among the several parameters calculated, the AgNOR relative area showed a strong correlation with the changes of the population doubling time induced by different temperatures.

CONCLUSIONS

The results support the hypothesis that the cell cycle time and the size of the ribogenesis machinery are coregulated and that measurements of AgNORs can thus be used as a static evaluation of the cell cycle duration in arbitrary units.

Identification of membrane calcium channels essential for cytoplasmic and nuclear calcium elevations induced by vascular endothelial growth factor in human endothelial cells

Vascular endothelial growth factor (VEGF) is mitogenic for endothelial cells and has been shown to induce angiogenesis and endothelial cell migration through stimulation of endothelial tyrosine-kinase receptors. Here, using confocal microscopy and the patch-clamp technique on endothelial cells, membrane permeability to calcium as well as cytoplasmic and nuclear free calcium levels have been investigated in the first stages of tyrosine-kinase receptor activation by VEGF. VEGF (0.5nM) as well as inositol trisphosphate (IP3) induced an activation of membrane calcium-permeable channels exhibiting a similar low conductance in the range of 10 pS. The VEGF-triggered activation of these calcium channels, mediated by IP3 and involving the intracellular calcium stores, results in an increase in both cytoplasmic and nuclear calcium levels in endothelial cells, potentially modulating gene expression. Finally, the effect of Ni2+, a calcium channel blocker, on endothelial cell proliferation has been studied. The results show that inhibition of extracellular calcium influx significantly inhibits VEGF-induced cell proliferation. In the process of cell stimulation by VEGF, and possibly by other growth factors, activation of calcium channels could then be a key step in calcium-regulated gene expression and cell activation. These results suggest that the use of calcium channel blockers could be a novel way of prevention or reversion of VEGF-induced tumoral angiogenesis.

Effects of prolonged exposure to hypoxia on morphological changes of endothelial cells plated on fibrin gel

Since tissue oxygenation has a profound effect on capillary growth, the effect of pO2 on endothelial cell functions was studied. Under normoxic conditions, EA.hy926 endothelial cells and HUVEC plated onto fibrin gels in low-serum culture medium underwent rapid and profound morphological changes within 12 to 48 hours depending on the cell line used. Their characteristic cobblestone organisation was transformed into a network of cord-like or tube-like structures. We showed that when exposed to low oxygen concentrations for 3 days, HUVEC and EA.hy926 have their ability to rearrange reduced to around 50 %. With EA.hy926 this effect was amplified by 79% after 9 days of hypoxia. The altered behaviour of hypoxia-adapted cells was not caused by a loss in their fibrinolytic activity. In fact, the fibrin degradation rate and the generated fibrin fragments appeared identical in normoxia and hypoxia. Confocal microscopy and gel densitometry showed that in normoxia the remaining undegraded fibrin gel underwent a dynamic remodeling whereas in hypoxia it remained undisturbed. It is likely that hypoxia induces modification in the factors that integrate matrix information and cytoskeletal organisation in order to contract fibrin.

Regulated hyperacetylation of core histones during mouse spermatogenesis: involvement of histone deacetylases

Here we report a detailed analysis of waves of histone acetylation that occurs throughout spermatogenesis in mouse. Our data showed that spermatogonia and preleptotene spermatocytes contained acetylated core histones H2A, H2B and H4, whereas no acetylated histones were observed throughout meiosis in leptotene or pachytene spermatocytes. Histones remained unacetylated in most round spermatids. Acetylated forms of H2A and H2B, H3 and H4 reappeared in step 9 to 11 elongating spermatids, and disappeared later in condensing spermatids. The spatial distribution pattern of acetylated H4 within the spermatids nuclei, analyzed in 3D by immunofluorescence combined with confocal microscopy, showed a spatial sequence of events tightly associated with chromatin condensation. In order to gain an insight into mechanisms controlling histone hyperacetylation during spermiogenesis, we treated spermatogenic cells with a histone deacetylase inhibitor, trichostatin A (TSA), which showed a spectacular increase of histone acetylation in round spermatids. This observation suggests that deacetylases are responsible for maintaining a deacetylated state of histones in these cells. TSA treatment could not induce histone acetylation in condensing spermatids, suggesting that acetylated core histones are replaced by transition proteins without being previously deacetylated. Moreover, our data showed a dramatic decrease in histone deacetylases in condensing spermatids. Therefore, the regulation of histone deacetylase activity/concentration appears to play a major role in controling histone hyperacetylation and probably histone replacement during spermiogenesis.

Three-dimensional cartography of the pattern of the myofibres in the second trimester fetal human heart

The aim of the present study was to describe the fibre architecture of the fetal heart at mid gestation, and to clarify some persistent controversies concerning the architecture of the myofibres in the right ventricular wall and the muscular ventricular septum. We used quantitative polarized light microscopy to obtain information about the orientation of myocardial cells in the ventricular mass. These cells, joined into a network by anastomoses, have at any point in the ventricular mass a principal direction--the fibre direction. We have quantitated this information in the form of maps of the azimuth and elevation angles, in 18 midgestation fetal hearts. Our findings show that the fibre architecture of the heart can be conceptualised as myocardial fibres running like geodesics on a nested set of warped "pretzels". This model is an extension to the whole ventricular mass of Krehl's Triebwerk, and Streeter's model which was restricted to the left ventricle. A "pretzel" itself can be considered as two doughnuts joined side-by-side, with the tunnel at the center of each doughnut corresponding to the ventricular cavity. Over and above the excellence of the fit between the data and the geodesic representation, three strong arguments support this model. First, it is the only existing model that explains the observed rolling over of fibres around the atrioventricular valvar orifices. Second, it explains the trajectory of the fibres from the epicardium to the endocardium at the basal parts of both ventricles and at the apical part of the left ventricle. Third, the predicted topological singularities of the model are systematically observed in each of the 18 hearts studied.

A reassessment of the factors affecting microtubule assembly and disassembly in vitro

Current models of microtubule assembly from pure tubulin involve a nucleation phase followed by microtubule elongation at a constant polymer number. Both the rate of microtubule nucleation and elongation are thought to be tightly influenced by the free GTP-tubulin concentration, in a law of mass action-dependent manner. However, these basic hypotheses have remained largely untested due to a lack of data reporting actual measurements of the microtubule length and number concentration during microtubule assembly.Here, we performed simultaneous measurements of the polymeric tubulin concentration, of the free GTP-tubulin concentration, and of the microtubule length and number concentration in both polymerizing and depolymerizing conditions. In agreement with previous work we find that the microtubule nucleation rate is strongly dependent on the initial GTP-tubulin concentration. But we find that microtubule nucleation persists during microtubule elongation. At any given initial tubulin-GTP concentration, the microtubule nucleation rate remains constant during polymer assembly, despite the wide variation in free GTP-tubulin concentration. We also find a remarkable constancy of the rate of microtubule elongation during assembly. Apparently, the rate of microtubule elongation is intrinsic to the polymers, insensitive to large variations of the free GTP-tubulin concentration. Finally we observe that when, following assembly, microtubules depolymerize below the free GTP-tubulin critical concentration, the rate-limiting factor for disassembly is the frequency of microtubule catastrophe. At all time-points during disassembly, the microtubule catastrophe frequency is independent of the free GTP-tubulin concentration but, as the microtubule nucleation rate, is strongly dependent on the initial free GTP-tubulin concentration. We conclude that the dynamics of both microtubule assembly and disassembly depend largely on factors other than the free GTP-tubulin concentration. We propose that intrinsic structural factors and endogenous regulators, whose concentration varies with the initial conditions, are also major determinants of these dynamics.

Genome organization in the human sperm nucleus studied by FISH and confocal microscopy

The sperm nucleus has a unique chromatin structure where the DNA is highly condensed and associated with specific proteins, the protamines. It is a nondividing cell which is also transcriptionally inactive. After fusion with an oocyte, the sperm nucleus undergoes decondensation and, in the same time, starts replication and transcription. It has been suggested that somatic chromosomes during interphase are organized in territories which display a cell type and cell cycle specific distribution. The purpose of this work was to investigate whether chromosomes would also have a specific distribution in the sperm nucleus, which could be related to its inactive state, and have implications on the early stages of fertilization. In the present study, centromeric and telomeric sequences were detected by fluorescent techniques performed on human decondensed spermatozoa. Chromosome painting probes were used to detect the chromosome X and chromosome 13 on interphase sperm nuclei. The fluorescent signals were captured in 3D with a confocal microscope. For each of these chromatin structures, the volume, position, and distribution of the signals were analyzed in samples of 30 nuclei with the help of image analysis software. The centromeres appeared grouped in several foci that were randomly distributed within the sperm nucleus. The telomeres gave an approximately haploid number of small signals, evenly distributed throughout the nucleus. The chromosomes X and 13 occupied 4.7% and 3. 7% of the total nuclear volume, respectively. Interestingly, the X chromosome territory showed a preferential position in the anterior half of the volume of the nucleus, whereas chromosome 13 had a random position. This work shows a particular distribution of chromosome territories in the human sperm nucleus that could be related to mechanisms implicated in its specific functions. The analysis of more chromosomes and chromosomal structures, including the Y chromosome, would help to understand the structure of the human sperm chromatin, and its fundamental and clinical implications.

PS-100 and NF 70-200 double immunolabeling for human digital skin meissner corpuscle 3D imaging

For detailed study of complex structures such as corpuscular mechanoreceptors, confocal microscopy can be used with multiple immunolabeling that identifies specifically different subcomponents. In addition, anatomic interpretation is enhanced by three-dimensional reconstruction. Confocal laser micrographs, reconstructed from serial images 1 microm thick of human skin Meissner corpuscles simultaneously immunostained for neurofilaments (NF 70-200) and protein S-100 (PS-100), clearly reveal the complex 3D relationship between Schwann-related lamellar cells immunoreactive for PS-100 and the nerve fibers marked by NF 70-200. The nerve fiber, after branching into the corpuscle, divides into several ramifications, presenting discoidal expansions and flattened fringed sections. The mean nerve diameter was 4 microm +/- 1 (2-5 microm) and the mean size of the discoidal expansions was 15 microm +/- 1 (7-30 microm). Corpuscle size varied from 30-140 +/- 1 microm in length and from 20-60 +/- 1 microm in diameter. This study confirms the presence of neural discoidal areas in Meissner's corpuscles, which are probably involved to some extent with the transduction process. Despite the accuracy of immunolabeling and imaging, an extracorpuscular neural network was never observed in the vicinity of corpuscles, thus giving doubt as to their existence. (J Histochem Cytochem 48:295-302, 2000)

Nonrandom distribution of metaphase AgNOR staining patterns on human acrocentric chromosomes

The metaphase nucleolar organizer regions (NORs) contain ribosomal genes associated with proteins such as upstream binding factor (UBF) and RNA polymerase I (RPI). These genes are clustered in 10 loci of the human acrocentric chromosomes (13, 14, 15, 21, and 22). Some NOR-associated proteins, termed AgNOR proteins, can be specifically stained by silver. In this study we took advantage of technical advances in digital imaging, image restoration techniques, and factorial correspondence analysis (FCA) to study the different AgNOR staining patterns of metaphase chromosomes in human lymphocytes. Three predominant patterns could be distinguished: pair (47%), stick-like (28%), and unstained (18%) structures. By studying the frequency of occurrence of each pattern on different chromosomes, two groups could be defined. Chromosomes 13, 14, and 21 carried predominantly pair or stick-like AgNOR structures, whereas chromosomes 15 and 22 mainly carried pair AgNOR structures or remained unstained. We suggest that the different AgNOR shapes reflect both the number of ribosomal genes carried by each chromosome and the differential recruitment of active ribosomal genes in each NOR cluster. This is the first study showing a nonrandom distribution of AgNOR shape among acrocentric chromosomes.

Rapid and reversible relocalization of heat shock factor 1 within seconds to nuclear stress granules

Heat shock factor 1 (HSF1) is essential for the stress-induced expression of heat shock genes. On exposure to heat shock, HSF1 localizes within seconds to discrete nuclear granules. On recovery from heat shock, HSF1 rapidly dissipates from these stress granules to a diffuse nucleoplasmic distribution, typical of unstressed cells. Subsequent reexposure to heat shock results in the rapid relocalization of HSF1 to the same stress granules with identical kinetics. Although the appearance of HSF1 stress granules corresponds to the hyperphosphorylated, trimeric DNA-binding state of HSF1 and correlates temporally with the inducible transcription of heat shock genes, they are also present in heat-shocked mitotic cells that are devoid of transcription. This finding suggests a role for HSF1 stress granules as a nuclear compartment for the temporal regulation and spatial organization of HSF1 activity and reveals new features of the dynamics of nuclear organization.

Quantitative assessment of the alteration of chromatin during the course of FISH procedures. Fluorescent in situ hybridization

BACKGROUND

DNA denaturation, required for fluorescent in situ hybridization (FISH) experiments, is likely to induce chromatin alterations. Only few attempts have been made to quantify the extent of these perturbations. We propose a quality-control approach based on image analysis to monitor the effect of a procedure commonly used in FISH experiments.

METHODS

Using DAPI as a probe, the same nuclei were successively imaged with a CCD camera after fixation, after permeabilization, and after thermal denaturation and hybridization with a centromeric probe. The modifications of the staining pattern were analyzed. Volumes of the FISH signals were measured using confocal imaging.

RESULTS

DAPI staining combined with image analysis proved to be a sensitive tool to visualize the effects of different treatments used in FISH experiments. Permeabilization of nuclei after fixation has only limited impact on the chromatin. On the contrary, the denaturation procedure modifies the staining of DNA by DAPI, as well as the underlying chromatin structure as assessed by the increase of FISH signal volume with denaturation time. The protocol that involves a pre-fixation permeabilization step results in a more severe loss of chromatin structure.

CONCLUSIONS

Our results clearly show that analysis of alterations of DAPI staining patterns is a useful monitoring tool to control and standardize hybridization procedures.

Merkel complexes of human digital skin: three-dimensional imaging with confocal laser microscopy and double immunofluorescence

Three-dimensional (3-D) reconstruction of images provided by confocal scanning laser microscopy (CSLM) is a powerful tool in a morpho-functional approach to cutaneous innervation studies. To investigate mechanoreceptors in the hand, a study of Merkel complexes was performed in human finger. A double fluorescent-conjugated immunolabeling with antibodies against neurofilament (NF 200) and cytokeratin (CK 20) on floating, thick cutaneous samples (80 to 100 microm), was used. After acquisition of serial optical planes by CSLM, reconstruction was performed with 3-D reconstruction software tools. Merkel cells were clearly labeled with CK 20, whereas nerve components were only NF 200 reactive. The cells, localized on the basal lamina of the epidermis, were usually arranged in clusters of five to eight cells. Each cell was connected to a nerve process ramification originating from a unique fiber. Quantitative data, compiled from a sample of 25 Merkel complexes, gave a mean cell diameter of 13 +/- 1 microm and a mean nerve fiber size of 3 +/- 1 microm. Surface measurements were done on a single reconstructed cluster with a mean and standard error which only refers to the optical 3-D resolution. It gives a surface of 12 +/- 1 microm2 for the contact zone between cell and nerve fiber and a cluster area of about 500 microm2. The great precision of reconstructed images provides a detailed analysis of spatial relationships between abutting nerve fibers and Merkel cells. Data interpretation is improved with complementary ultrastructural and physiological studies results, and this allows an accurate investigation of cutaneous sensory endings.

Disomy rates for chromosomes 14 and 21 studied by fluorescent in-situ hybridization in spermatozoa from three men over 60 years of age

In order to further investigate the paternal-age effect on meiotic non-disjunction rates for the chromosomes 14 and 21, we examined spermatozoa from three men aged > 60, using multicolour fluorescent in-situ hybridization (FISH). More than 10,000 sperm cells were analysed for each of the three subjects (A, B and C), by simultaneously hybridizing two YAC probes specific for chromosomes 14 and 21 respectively using two-colour FISH. The results show that the disomy 21 rates observed in the spermatozoa of two out of the three men aged > 60 years were higher (1.02 and 1.17% respectively) than the rates observed in eight control adults aged < 30 years (mean frequency 0.48%) analysed under similar conditions. These results suggest that there may be a small effect of age on male non-disjunction rates for chromosome 21. However, before any firm conclusions could be drawn, a much bigger sample of older men would have to be compared with a paired control population using the same FISH experimental approach.

Nuclear and cytoplasmic free calcium level changes induced by elastin peptides in human endothelial cells

The extracellular matrix protein "elastin" is the major component of elastic fibers present in the arterial wall. Physiological degradation of elastic fibers, enhanced in vascular pathologies, leads to the presence of circulating elastin peptides (EP). EP have been demonstrated to influence cell migration and proliferation. EP also induce, at circulating pathophysiological concentrations (and not below), an endothelium- and NO- dependent vasorelaxation mediated by the 67-kDa subunit of the elastin-laminin receptor. Here, by using the techniques of patch-clamp, spectrofluorimetry and confocal microscopy, we demonstrate that circulating concentrations of EP activate low specificity calcium channels on human umbilical venous endothelial cells, resulting in increase in cytoplasmic and nuclear free calcium concentrations. This action is independent of phosphoinositide metabolism. Furthermore, these effects are inhibited by lactose, an antagonist of the elastin-laminin receptor, and by cytochalasin D, an actin microfilament depolymerizer. These observations suggest that EP-induced signal transduction is mediated by the elastin-laminin receptor via coupling of cytoskeletal actin microfilaments to membrane channels and to the nucleus. Because vascular remodeling and carcinogenesis are accompanied by extracellular matrix modifications involving elastin, the processes here described could play a role in the elastin-laminin receptor-mediated cellular migration, differentiation, proliferation, as in atherogenesis, and metastasis formation.

Study of regulation of mitochondrial respiration in vivo. An analysis of influence of ADP diffusion and possible role of cytoskeleton

The purpose of this work was to investigate the mechanism of regulation of mitochondrial respiration in vivo in different muscles of normal rat and mice, and in transgenic mice deficient in desmin. Skinned fiber technique was used to study the mitochondrial respiration in the cells in vivo in the heart, soleus and white gastrocnemius skeletal muscles of these animals. Also, cardiomyocytes were isolated from the normal rat heart, permeabilized by saponin and the "ghost" (phantom) cardiomyocytes were produced by extraction of myosin with 800 mM KCl. Use of confocal immunofluorescent microscopy and anti-desmin antibodies showed good preservation of mitochondria and cytoskeletal system in these phantom cells. Kinetics of respiration regulation by ADP was also studied in these cells in detail before and after binding of anti-desmine antibodies with intermediate filaments. In skinned cardiac or soleus skeletal muscle fibers but not in fibers from fast twitch skeletal muscle the kinetics of mitochondrial respiration regulation by ADP was characterized by very high apparent Km (low affinity) equal to 300-400 microM, exceeding that for isolated mitochondria by factor of 25. In skinned fibers from m. soleus, partial inhibition of respiration by NaN3 did not decrease the apparent Km for ADP significantly, this excluding the possible explanation of low apparent affinity of mitochondria to ADP in these cells by its rapid consumption due to high oxidative activity and by intracellular diffusion problems. However, short treatment of fibers with trypsin decreased this constant value to 40-70 microM, confirming the earlier proposition that mitochondrial sensitivity to ADP in vivo is controlled by some cytoplasmic protein. Phantom cardiomyocytes which contain mostly mitochondria and cytoskeleton and retain the normal shape, showed also high apparent Km values for ADP. Therefore, they are probably the most suitable system for studies of cellular factors which control mitochondrial function in the cells in vivo. In these phantom cells anti-desmin antibodies did not change the kinetics of respiration regulation by ADP. However, in skinned fibers from the heart and m. soleus of transgenic desmin-deficient mice some changes in kinetics of respiration regulation by ADP were observed: in these fibers two populations of mitochondria were observed, one with usually high apparent Km for ADP and the second one with very low apparent Km for ADP. Morphological observations by electron microscopy confirmed the existence of two distinct cellular populations in the muscle cells of desmin-deficient mice. The results conform to the conclusion that the reason for observed high apparent Km for ADP in regulation of oxidative phosphorylation in heart and slow twitch skeletal muscle cells in vivo is low permeability of mitochondrial outer membrane porins but not diffusion problems of ADP into and inside the cells. Most probably, in these cells there is a protein associated with cytoskeleton, which controls the permeability of the outer mitochondrial porin pores (VDAC) for ADP. Desmin itself does not display this type of control of mitochondrial porin pores, but its absence results in appearance of cells with disorganised structure and of altered mitochondrial population probably lacking this unknown VDAC controlling protein. Thus, there may be functional connection between mitochondria, cellular structural organisation and cytoskeleton in the cells in vivo due to the existence of still unidentified protein factor(s).

In vitro angiogenesis is modulated by the mechanical properties of fibrin gels and is related to alpha(v)beta3 integrin localization

This study deals with the role of the mechanical properties of matrices in in vitro angiogenesis. The ability of rigid fibrinogen matrices with fibrin gels to promote capillarylike structures was compared. The role of the mechanical properties of the fibrin gels was assessed by varying concentration of the fibrin gels. When the concentration of fibrin gels was decreased from 2 mg/ml to 0.5 mg/ml, the capillarylike network increased. On rigid fibrinogen matrices, capillarylike structures were not formed. The extent of the capillarylike network formed on fibrin gels having the lowest concentration depended on the number of cells seeded. The dynamic analysis of capillarylike network formation permitted a direct visualization of a progressive stretching of the 0.5 mg/ml fibrin gels. This stretching was not observed when fibrin concentration increases. This analysis shows that 10 h after seeding, a prearrangement of cells into ringlike structures was observed. These ringlike structures grew in size. Between 16 and 24 h after seeding, the capillarylike structures were formed at the junction of two ringlike structures. Analysis of the alpha(v)beta3 integrin localization demonstrates that cell adhesion to fibrinogen is mediated through the alpha(v)beta3 integrin localized into adhesion plaques. Conversely, cell adhesion to fibrin shows a diffuse and dot-contact distribution. We suggest that the balance of the stresses between the tractions exerted by the cells and the resistance of the fibrin gels triggers an angiogenic signal into the intracellular compartment. This signal could be associated with modification in the alpha(v)beta3 integrin distribution.

Effects of intermittent or continuous gravitational stresses on cell-matrix adhesion: quantitative analysis of focal contacts in osteoblastic ROS 17/2.8 cells

The relationship between cell morphology and cell metabolism and the role of mechanical load in bone remodeling is well known. Mechanical stimulation induces changes in the shape of osteoblasts, probably mediated by reorganization of focal contacts. We studied the influence of gravity (Gz) variations occurring during parabolic flight on osteoblast focal adhesion of ROS 17/2.8 osteosarcoma cells subjected to 15 or 30 parabolic flights. Significant flight-induced shape changes consisted of decreased cell area associated with focal contact plaque reorganization. Identical durations of continuous mechanical stress induced by centrifugation (2 Gz) or clinorotation (Gz randomization) had no major effect on cell focal adhesion. ROS 17/2.8 G2/M synchronization by treatment with nocodazole inhibited the flight-induced decrease in adhesion parameters. We concluded that ROS 17/2.8 cells are sensitive to Gz switches and that their adaptation is at least dependent on microtubule function.

Basic FGF enhances calcium permeable channel openings in adult rat cardiac myocytes: implication in the bFGF-induced increase of free Ca2+ content

Basic fibroblast growth factor (bFGF) has been implicated in the changes in gene expression that, under pathological conditions such as ischemia or volume overload, lead to adult cardiomyocyte hypertrophy. In many tissues, one of the first events following cell activation by growth factors is an enhancement of the intracellular free calcium concentration, generated by fluxes from internal storage compartments and through channels of the plasma membrane. The present study was undertaken to determine whether cardiac myocytes isolated from adult rat ventricles express Ca2+-permeable channels activated by bFGF. Using the cell-attached mode of the patch-clamp technique, we observed that bFGF (from 0.1-10 nM) induced an increase of fast burst openings, mediated by Ca2+-permeable channels with low conductance (15 pS) and voltage-independence. Inside-out patch-clamp experiments revealed that inositol 1,4,5-trisphosphate (5 microM) enhanced the opening of Ca2+-permeable channels with similar properties as the bFGF-induced channels, indicating that IP3 may be a second messenger of this process. Confocal fluorescence imaging of intracellular free calcium provided direct evidence that bFGF induced an increase of cytoplasmic and nucleoplasmic free Ca2+ concentrations which were generated, in part, by Ca2+ influx through the plasma membrane. In conclusion, this study supports the presence, in the plasma membrane of adult cardiac myocytes, of messenger-activated calcium channels which could play key roles in the calcium-dependent pathways that are activated in response to growth factors.

Quantitation of cell-matrix adhesion using confocal image analysis of focal contact associated proteins and interference reflection microscopy

We have developed an approach for the quantitation of vinculin, a focal contact associated protein, based on a multimodal confocal microscopy and image analysis. Vinculin spot distribution was imaged in confocal fluorescence microscopy and the corresponding focal contacts were imaged in confocal interference reflection microscopy. These images were analyzed with a SAMBA image cytometer. The image analysis program provided 12 morphometric features describing cellular area, shape, and proportions of vinculin spots as well as six topographical features describing the distribution of vinculin and the relative overlap of vinculin and focal contacts. This approach was applied to the study of rat osteosarcoma cells submitted to mechanical stresses: successions of 2g and 0g accelerations during a series of parabolic flights. The measured features were assessed by means of correlation analysis and stepwise discriminant analysis. After correlation analysis, only ten parameters were retained. Quantitation of cell morphological parameters indicated that cell area was significantly affected by gravitational stresses as well as vinculin distribution. Cell area was reduced by 50% and vinculin spots were restricted to cell periphery. Cell adhesion measured by IRM decreased significantly in the first part of the flight and remained stable at the end of the flight. These results suggest that cell-matrix adhesion is affected by gravitational stresses. Image analysis provides useful tools to investigate focal adhesion re-organization under different physiological stimuli.

Meiotic behaviour of sex chromosomes investigated by three-colour FISH on 35,142 sperm nuclei from two 47,XYY males

Meiotic segregation of sex chromosomes from two fertile 47,XYY men was analysed by a three-colour fluorescence in situ hybridisation procedure. This method allows the identification of hyperhaploidies (spermatozoa with 24 chromosomes) and diploidies (spermatozoa with 46 chromosomes), and their meiotic origin (meiosis I or II). Alpha-satellite probes specific for chromosomes X, Y and 1 were observed simultaneously in 35,142 sperm nuclei. For both 47,XYY men (24,315 sperm nuclei analysed from one male and 10,827 from the other one) the sex ratio differs from the expected 1:1 ratio (P < 0.001). The rates of disomic Y, diploid YY and diploid XY spermatozoa were increased for both 47,XYY men compared with control sperm (142,050 sperm nuclei analysed from five control men), whereas the rates of hyperhaploidy XY, disomy X and disomy 1 were not significantly different from those of control sperm. These results support the hypothesis that the extra Y chromosome is lost before meiosis with a proliferative advantage of the resulting 46,XY germ cells. Our observations also suggest that a few primary spermatocytes with two Y chromosomes are able to progress through meiosis and to produce Y-bearing sperm cells. A theoretical pairing of the three gonosomes in primary spermatocytes with an extra sex chromosome, compatible with active spermatogenesis, is proposed.

A mouse chromosome-specific YAC probe collection for in situ hybridization

To facilitate the identification of mouse metaphase chromosomes by fluorescence in situ hybridization (FISH), a complete collection of mouse chromosome-specific markers has been established. Yeast artificial chromosome libraries were screened by polymerase chain reaction using primers for known loci. DNAs from positive clones were then tested by FISH. One probe per chromosome was selected on the basis of high specificity (nonchimerism) and strong fluorescence.

Desmoplakin expression and organization at human umbilical vein endothelial cell-to-cell junctions

Desmoplakin is an intracellular component of desmosomes which plays a role in the anchorage of intermediate filaments to these structures. We report here that, despite the absence of desmosomes, cultured endothelial cells from human umbilical vein express desmoplakin I and II both at mRNA and protein level. Desmoplakin I/II are found only in the detergent insoluble fraction suggesting that most of the protein is linked to the cytoskeleton. Desmoplakin I/II could be detected by western blot only in long confluent cells even if desmoplakin mRNA levels are unchanged by cell confluency. This suggests that desmoplakin might be stabilized at protein level by its association with junctional components. Immunofluorescence confocal microscopy showed that desmoplakin codistributes with VE-cadherin and plakoglobin along the lateral cell membrane. In contrast, desmoplakin localization was distinct from that of PECAM, an endothelial specific junctional protein localized outside adherence junctions. Endothelial cells do not have keratins but they express vimentin. In confluent cells vimentin forms peripheral filaments which attach to the cell membrane in areas at desmoplakin localization. These data suggest that desmoplakin may participate in the molecular organization of interendothelial junctions by interacting with VE-cadherin and promoting vimentin anchorage. This new type of intercellular junction seems to correspond to the “complexus adhaerentes' described in vivo in lymphatic endothelium.

Quantitative analysis of three-dimensional distribution of AgNOR proteins during interphase in leukemic cells

Acidic proteins of the nucleolar organizer regions, selectively stained by silver (AgNOR-proteins), were investigated during interphase in leukemia cells with a confocal scanning laser microscope (CSLM). Simultaneous confocal fluorescence (for specific labeling of DNA, using propidium iodide) and transmitted light microscopy combined with digital deconvolution (for the location of the AgNOR proteins in nonconfocal mode) were used. The distribution of the AgNOR proteins measured by 3D microscopy was described by their number, the volume occupation of the nucleus by the AgNOR aggregates, the distance between each AgNOR, the distance of each AgNOR to the nucleolar border, and their anisotropy. The results of the 3D analysis were compared to those obtained by conventional 2D analysis, cytogenetical analysis of metaphase nucleolar organiser regions (NORs), and cell duplication rate. The descriptive power of these 3D parameters were assessed for nine leukemic cell lines. The measurements of the 3D spatial distribution of AgNORs was a better discriminant parameter than the morphological parameters (i.e., number and volume). The 3D expression of AgNORs is also a reliable parameter for assessing proliferative activity of leukemic cells and seems to be in relation with the differentiation stage of these leukemic cells.

Increased incidence of hyperhaploid 24,XY spermatozoa detected by three-colour FISH in a 46,XY/47,XXY male

Meiotic segregation of gonosomes from a 46,XY/47,XXY male was analysed by a three-colour fluorescence in situ hybridisation (FISH) procedure. This method allows the identification of hyperhaploid spermatozoa (with 24 chromosomes), diploid spermatozoa (with 46 chromosomes) and their meiotic origin (meiosis I or II). Alpha satellite DNA probes specific for chromosomes X, Y and 1 were observed on 27,097 sperm nuclei. The proportions of X- and Y-bearing sperm were estimated to 52.78% and 43.88%, respectively. Disomy (24,XX, 24,YY, 24,X or Y,+1) and diploidy (46,XX, 46,YY, 46,XY) frequencies were close to those obtained from control sperm, whereas the frequency of hyperhaploid 24,XY spermatozoa (2.09%) was significantly increased compared with controls (0.36%). These results support the hypothesis that a few 47,XXY germ cells would be able to complete meiosis and to produce mature spermatozoa.

Metaphase and interphase mapping by FISH: improvement of chromosome banding and signal resolution in interphase nuclei by means of iterative deconvolution

FISH images obtained with conventional epifluorescence microscopes are always blurred by glare and out of focus light emissions. In order to restore high contrast images, a procedure based on a modelling of the optical system in the microscope was developed and used for the processing of images acquired with a cooled CCD camera mounted on a fluorescence microscope. This procedure was tested on images of both mouse and human chromosomes stained with DAP1 and on images of interphase nuclei hybridized with pairs of cosmid probes. This method improves the definition and the sharpness of the DAPI G-banding and thus facilitates and speeds up the identification of chromosomes. When performed on images of interphase cell nuclei, this procedure allows the discrimination of fluorescent signals which appear partially overlapping on raw images. This significant improvement of spatial resolution is of particular interest for ordering sets of probes on DNA fibers.

Mapping of the orientation of myocardial cells by means of polarized light and confocal scanning laser microscopy

The study of the topological organisation of myocardial cells is a basic requirement for the understanding of the mechanical design of the normal and pathological heart. We developed a technique based on multiparametric image analysis of transmitted polarized light to generate maps of the azimuth and the elevation angles of the myocardial cells. The properties of birefringence of the myocardium embedded in methylmetacrylate were measured in papillary muscles with monitored 3D orientation. This birefringence is positive uniaxial with a 0 degree extinction angle when the axis of the fiber is parallel to the axis of the polarizer or the analyzer. Thick sections were studied between crossed polars, and four images of each section were digitized for an angle of the polarizer with the section varying from 0-67.5 degrees in steps of 22.5 degrees. The amounts of transmitted light for each setup of the polarizer were combined in order to extract the values of the azimuth angle (modulo 90 degrees) and the elevation angle of the myocardial cells, according to the Johannsen equation. The respective maps of these angles were calculated and then assessed with confocal scanning laser microscopy. This method provides an efficient and accurate tool for the study of the histological architecture of the fetal and neonatal heart.

Application of confocal laser microscopy and three-dimensional Voronoi diagrams for volume and surface estimates of interphase chromosomes

This study demonstrates the use of Voronoi tessellation procedures to obtain quantitative morphological data for chromosome territories in the cell nucleus. As a model system, chromosomes 7 and X were visualized in human female amniotic fluid cell nuclei by chromosomal in situ suppression hybridization with chromosome-specific composite probes. Light optical serial sections of 18 nuclei were obtained with a confocal scanning laser fluorescence microscope. A three-dimensional (3-D) tessellation of the image volumes defined by the stack of serial sections was then performed. For this purpose a Voronoi diagram, which consists of convex polyhedra structured in a graph environment, was built for each nucleus. The chromosome territories were extracted by applying the Delaunay graph, the dual of the Voronoi diagram, which describes the neighbourhood in the Voronoi diagram. The chromosome territories were then described by three morphological parameters, i.e. volume, surface area and a roundness factor (shape factor). The complete evaluation of a nucleus, including the calculation of the Voronoi diagram, 3-D visualization of extracted territories using computer graphic methods and parameterization was carried out on a Silicon Graphics workstation and was generally completed within 5 min. The geometric information obtained by this procedure revealed that both X- and 7-chromosome territories were similar in volume. Roundness factors indicated a pronounced variability in interphase shape for both pairs of chromosomes. Surface estimates showed a significant difference between the two X-territories but not between chromosome 7-territories.

Improvements in visualisation and localisation of human papillomavirus DNA in CaSki cells by fluorescence in situ hybridization, laser scanning confocal microscopy and three-dimensional image reconstruction

The visual interpretation and localisation of specific DNA sequences in three dimensions in cell nuclei was investigated by fluorescence in situ hybridization (FISH) and laser scanning confocal microscopy (LSCM) using CaSki cells containing 600 copies per cell of human papillomavirus (HPV) DNA type 16 integrated in cellular DNA. Biotinylated DNA probes were used and DNA-DNA hybrids were revealed by a three-step reaction involving a rabbit anti-biotin antibody, a biotinylated goat anti-rabbit antibody and a streptavidin-fluorescein isothiocyanate complex. The DNA from cell nuclei was counterstained with propidium iodide. With standard fluorescence microscopy, some dense fluorescent spots were seen in the cell nuclei. Similarly, with LSCM, some hybridization spots were observed in the cell nuclei but they were at different levels of the nuclei as shown by successive nuclear sections taken along the z axis. The visualisation of multiple hybridization spots confirmed the presence of multiple integration sites of HPV 16 DNA in CaSki cells. Association of LSCM with three-dimensional reconstructions lead to spatial images of hybridization spots obtained by stacking (x,y) images from consecutive confocal planes. Rotation of the reconstructed cell nuclei around the y axis makes it possible to distinguish closely adjacent spots. The combination of these techniques improves the detection of hybridization spots and may be of interest to further determine whether the HPV DNA is episomal or integrated in infected cells.

Method for the study of the three-dimensional orientation of the nuclei of myocardial cells in fetal human heart by means of confocal scanning laser microscopy

A series of three-dimensional image analysis tools are used to measure the three-dimensional orientation of nuclei of myocardial cells. Confocal scanning laser microscopy makes it possible to acquire series of sections up to 100 microns inside thick tissue sections. A mean orientation vector of unit length is calculated for each segmented nucleus. The global orientation statistics are obtained by calculating the vectorial sum of the nuclear unit vectors. The final orientation is expressed by a mean azimuth angle, an elevation angle and a measure of the angular homogeneity. The method is illustrated for two different regions of the myocardium (interventricular septum and papillary muscle) of a normal human fetal heart. This quantitative method will be used to assess and calibrate the information provided by polarized light microscopy.

Internalization of the alpha 5 beta 1 integrin does not depend on "NPXY" signals

The alpha 5 beta 1 integrin is a constitutively internalized fibronectin receptor. It contains in the cytoplasmic tail of its beta 1 subunit two NPXY sequences which have been proposed to mediate internalization. Indeed a NPXY motif constitutes the internalization signal for the Low Density Lipoprotein (LDL) and insulin receptors. To learn more about the putative role of the two NPXY sequences in internalization of the alpha 5 beta 1 receptor, we have made and expressed mutants of the human beta 1 subunit in Chinese Hamster Ovary (CHO) cells, in which the two tyrosines of the NPXY motifs were replaced by serine residues. A cytoplasmic variant beta 1B which does not contain any NPXY sequence was also analyzed. Our results indicate that the NPXY mutants and the cytoplasmic variant are still internalized. Thus in the alpha 5 beta 1 receptor, the highly conserved NPXY sequences do not function as internalization motifs.

Adhesion of CHO cells to fibronectin is mediated by functionally and structurally distinct adhesion plaques

We have investigated the dynamics between free fibronectin receptors and clusters of them organized into adhesion plaques on CHO cells using the ability of these free integrins to be endocytosed and recycled to the plasma membrane. Indirect inhibition of the endocytic cycle by monensin resulted in the subsequent internalization of free receptors, which we followed by indirect immunostaining and confocal microscopy. Consequently, all the adhesive structures that were in equilibrium with free integrins became progressively disorganized. The cellular morphological changes were analyzed and correlated with the distribution of cell-substratum contacts viewed by confocal images obtained after immunostaining with antibodies raised against the fibronectin receptor, talin, vinculin and actin. After cell adhesion to fibronectin, blockage of the endocytic cycle induced disruption of the adhesion plaques that were mainly localized at the cell periphery, and disappearance of the stress fibers. However, the cells remained firmly attached to the substratum through focal contacts localized in the central part of the cell. These central focal contacts, but not the peripheral adhesion plaques, could form when the vesicular traffic was blocked prior to adhesion and they allowed the cells to attach and flatten onto the substratum. Whereas both adhesive structures contained the same receptors linked to talin and vinculin, the central adhesive structures were attached to a short stretch of actin but never permitted the organization of stress fibers.