Visualization of cytoskeletal elements by the atomic force microscope

Correlation of cell mechanics with the resistance to malignant transformation in naked mole rat fibroblasts

Naked mole rats (NMRs) demonstrate exceptional longevity and resistance to cancer. Using a biochemical approach, it was previously shown that the treatment of mouse fibroblast cells with RasV12 oncogene and SV40 Large T antigen (viral oncoprotein) led to malignant transformations of cells. In contrast, NMR fibroblasts were resistant to malignant transformations upon this treatment. Here we demonstrate that atomic force microscopy (AFM) can provide information which is in agreement with the above finding, and further, adds unique information about the physical properties of cells that is impossible to obtain by other existing techniques. AFM indentation data were collected from individual cells and subsequently processed through the brush model to obtain information about the mechanics of the cell body (absolute values of the effective Young's moduli). Furthermore, information about the physical properties of the pericellular layer surrounding the cells was obtained. We found a statistically significant decrease in the rigidity of mouse cells after the treatment, whereas there was no significant change found in the rigidity of NMR cells upon the treatment. We also found that the treatment caused a substantial increase in a long part of the pericellular layer in NMR cells only (the long brush was defined as having a size of >10 microns). The mouse cells and smaller brush did not show statistically significant changes upon treatment. The observed change in cell mechanics is in agreement with the frequently observed decrease in cell rigidity during progression towards cancer. The change in the pericellular layer due to the malignant transformation of fibroblast cells has practically not been studied, though it was shown that the removal of part of the pericellular layer of NMR fibroblasts made the cells susceptible to malignant transformation. Although it is plausible to speculate that the observed increase in the long part of the brush layer of NMR cells might help cells to resist malignant transformations, the significance of the observed change in the pericellular layer is yet to be understood. As of now, we can conclude that changes in cell mechanics might be used as an indication of the resistance of NMR cells to malignant transformations.

Correlative 3D microscopy of single cells using super-resolution and scanning ion-conductance microscopy

High-resolution live-cell imaging is necessary to study complex biological phenomena. Modern fluorescence microscopy methods are increasingly combined with complementary, label-free techniques to put the fluorescence information into the cellular context. The most common high-resolution imaging approaches used in combination with fluorescence imaging are electron microscopy and atomic-force microscopy (AFM), originally developed for solid-state material characterization. AFM routinely resolves atomic steps, however on soft biological samples, the forces between the tip and the sample deform the fragile membrane, thereby distorting the otherwise high axial resolution of the technique. Here we present scanning ion-conductance microscopy (SICM) as an alternative approach for topographical imaging of soft biological samples, preserving high axial resolution on cells. SICM is complemented with live-cell compatible super-resolution optical fluctuation imaging (SOFI). To demonstrate the capabilities of our method we show correlative 3D cellular maps with SOFI implementation in both 2D and 3D with self-blinking dyes for two-color high-order SOFI imaging. Finally, we employ correlative SICM/SOFI microscopy for visualizing actin dynamics in live COS-7 cells with subdiffraction-resolution.

Red Blood Cell Stiffness and Adhesion Are Species-Specific Properties Strongly Affected by Temperature and Medium Changes in Single Cell Force Spectroscopy

Besides human red blood cells (RBC), a standard model used in AFM-single cell force spectroscopy (SCFS), little is known about apparent Young's modulus (Ea) or adhesion of animal RBCs displaying distinct cellular features. To close this knowledge gap, we probed chicken, horse, camel, and human fetal RBCs and compared data with human adults serving as a repository for future studies. Additionally, we assessed how measurements are affected under physiological conditions (species-specific temperature in autologous plasma vs. 25 °C in aqueous NaCl solution). In all RBC types, Ea decreased with increasing temperature irrespective of the suspension medium. In mammalian RBCs, adhesion increased with elevated temperatures and scaled with reported membrane sialic acid concentrations. In chicken only adhesion decreased with higher temperature, which we attribute to the lower AE-1 concentration allowing more membrane undulations. Ea decreased further in plasma at every test temperature, and adhesion was completely abolished, pointing to functional cell enlargement by adsorption of plasma components. This halo elevated RBC size by several hundreds of nanometers, blunted the thermal input, and will affect the coupling of RBCs with the flowing plasma. The study evidences the presence of a RBC surface layer and discusses the tremendous effects when RBCs are probed at physiological conditions.

Glycerol-3-phosphate acyltransferase 2 expression modulates cell roughness and membrane permeability: An atomic force microscopy study

In mammalian cells, de novo glycerolipid synthesis begins with the acylation of glycerol-3-phosphate, catalyzed by glycerol-3-phosphate acyltransferases (GPAT). GPAT2 is a mitochondrial isoform primarily expressed in testis under physiological conditions, and overexpressed in several types of cancers and cancer-derived human cell lines where its expression contributes to the tumor phenotype. Using gene silencing and atomic force microscopy, we studied the correlation between GPAT2 expression and cell surface topography, roughness and membrane permeability in MDA-MB-231 cells. In addition, we analyzed the glycerolipid composition by gas-liquid chromatography. GPAT2 expression altered the arachidonic acid content in glycerolipids, and the lack of GPAT2 seems to be partially compensated by the overexpression of another arachidonic-acid-metabolizing enzyme, AGPAT11. GPAT2 expressing cells exhibited a rougher topography and less membrane damage than GPAT2 silenced cells. Pore-like structures were present only in GPAT2 subexpressing cells, correlating with higher membrane damage evidenced by lactate dehydrogenase release. These GPAT2-induced changes are consistent with its proposed function as a tumor-promoting gene, and might be used as a phenotypic differentiation marker. AFM provides the basis for the identification and quantification of those changes, and demonstrates the utility of this technique in the study of cancer cell biology.

Effects of Tumor Necrosis Factor-α on Morphology and Mechanical Properties of HCT116 Human Colon Cancer Cells Investigated by Atomic Force Microscopy

Chronic inflammation orchestrates the tumor microenvironment and is strongly associated with cancer. Tumor necrosis factor-α (TNFα) is involved in tumor invasion and metastasis by inducing epithelial to mesenchymal transition (EMT). This process is defined by the loss of epithelial characteristics and gain of mesenchymal traits. The mechanisms of TNFα-induced EMT in cancer cells have been well studied. However, mechanical properties have not yet been probed. In this work, atomic force microscopy (AFM) was applied to investigate the morphology and mechanical properties of EMT in HCT116 human colon cancer cells. A remarkable morphological change from cobblestone shape to spindle-like morphology was observed. In parallel, AFM images showed that the cellular cytoskeleton was rearranged from a cortical to a stress-fiber pattern. Moreover, cell stiffness measurements indicated that Young's modulus of cells gradually reduced from 1 to 3 days with TNFα-treatment, but it has an apparent increase after 4 days of treatment compared with that for 3 days. Additionally, Young's modulus of the cells treated with TNFα for 4 days is slightly larger than that for 1 or 2 days, but still less than that of the untreated cells. Our work contributes to a better understanding of colorectal cancer metastasis induced by inflammation.

An Unroofing Method to Observe the Cytoskeleton Directly at Molecular Resolution Using Atomic Force Microscopy

An improved unroofing method enabled the cantilever of an atomic force microscope (AFM) to reach directly into a cell to visualize the intracellular cytoskeletal actin filaments, microtubules, clathrin coats, and caveolae in phosphate-buffered saline (PBS) at a higher resolution than conventional electron microscopy. All of the actin filaments clearly exhibited a short periodicity of approximately 5-6 nm, which was derived from globular actins linked to each other to form filaments, as well as a long helical periodicity. The polarity of the actin filaments appeared to be determined by the shape of the periodic striations. Microtubules were identified based on their thickness. Clathrin coats and caveolae were observed on the cytoplasmic surface of cell membranes. The area containing clathrin molecules and their terminal domains was directly visualized. Characteristic ridge structures located at the surface of the caveolae were observed at high resolution, similar to those observed with electron microscopy (EM). Overall, unroofing allowed intracellular AFM imaging in a liquid environment with a level of quality equivalent or superior to that of EM. Thus, AFMs are anticipated to provide cutting-edge findings in cell biology and histology.

Feeling for Filaments: Quantification of the Cortical Actin Web in Live Vascular Endothelium

Contact-mode atomic force microscopy (AFM) has been shown to reveal cortical actin structures. Using live endothelial cells, we visualized cortical actin dynamics simultaneously by AFM and confocal fluorescence microscopy. We present a method that quantifies dynamic changes in the mechanical ultrastructure of the cortical actin web. We argue that the commonly used, so-called error signal imaging in AFM allows a qualitative, but not quantitative, analysis of cortical actin dynamics. The approach we used comprises fast force-curve-based topography imaging and subsequent image processing that enhances local height differences. Dynamic changes in the organization of the cytoskeleton network can be observed and quantified by surface roughness calculations and automated morphometrics. Upon treatment with low concentrations of the actin-destabilizing agent cytochalasin D, the cortical cytoskeleton network is thinned out and the average mesh size increases. In contrast, jasplakinolide, a drug that enhances actin polymerization, consolidates the cytoskeleton network and reduces the average mesh area. In conclusion, cortical actin dynamics can be quantified in live cells. To our knowledge, this opens a new pathway for conducting quantitative structure-function analyses of the endothelial actin web just beneath the apical plasma membrane.

Semi-in situ atomic force microscopy imaging of intracellular neurofilaments under physiological conditions through the 'sandwich' method

Neurofilaments are intermediate filament proteins specific for neurons and characterized by formation of biochemically stable, obligate heteropolymers in vivo While purified or reassembled neurofilaments have been subjected to morphological analyses by electron microscopy and atomic force microscopy, there has been a need for direct imaging of cytoplasmic genuine intermediate filaments with minimal risk of artefactualization. In this study, we applied the modified 'cells on glass sandwich' method to exteriorize intracellular neurofilaments, reducing the risk of causing artefacts through sample preparation. SW13vim(-) cells were double transduced with neurofilament medium polypeptide (NF-M) and alpha-internexin (α-inx). Cultured cells were covered with a cationized coverslip after prestabilization with tannic acid to form a sandwich and then split into two. After confirming that neurofilaments could be deposited on ventral plasma membranes exposed via unroofing, we performed atomic force microscopy imaging semi-in situ in aqueous solution. The observed thin filaments, considered to retain native structures of the neurofilaments, exhibited an approximate periodicity of 50-60 nm along their length. Their structural property appeared to reflect the morphology formed by their constituents, i.e. NF-M and α-inx. The success of semi-in situ atomic force microscopy of exposed bona fide assembled neurofilaments through separating the sandwich suggests that it can be an effective and alternative method for investigating cytoplasmic intermediate filaments under physiological conditions by atomic force microscopy.

Kaempferol targets Krt-14 and induces cytoskeletal mineralization in osteoblasts: A mechanistic approach

Kaempferol (KEM) has been observed to stimulate Krt-14 protein which subsequently contributes to matrix maturation and mineralization in rat primary osteoblast cells. Incorporation of Krt-14 siRNA results in reduced mRNA and protein expression after 48h post transfection and remained low for 9days. At day 9 Krt-14 siRNA significantly reduced mineralization without concomitant change in the cell number. ColI and OCN gene expression was reduced in Krt-14 siRNA-treated osteoblast cells. Soluble osteocalcin and collagen levels were markedly decreased in conditioned medium as well as in acid-salt soluble cell-ECM layer treated with Krt-14 siRNA compared to control siRNA treated cells corroborated at the ultrastructral level by AFM. Further, knockdown of Krt-14 and inhibitors against AMPK and mTOR, repressed the activation of mTOR and mineralization attenuated by KEM confirmed the role of Krt-14 in mineralization. These findings strongly suggest that Krt-14 regulates osteoblast mineralization by organizing osteoblast derived ECM.

Sensing biophysical alterations of human lung epithelial cells (A549) in the context of toxicity effects of diesel exhaust particles

Diesel exhaust particles (DEP) in urban air are associated with numerous respiratory diseases. The role of underlying biomechanics in cytotoxicity of individual lung cells relating to DEP exposure is unclear. In this study, atomic force microscopy (AFM), confocal Raman microspectroscopy (RM), and fluorescence (FL) microscopy were used to monitor alterations of single A549 cells exposed to DEP. Results revealed a significant decrease in membrane surface adhesion force and a significant change in cell elasticity as a function of DEP-cell interaction time, and the dynamic changes in cellular biocomponents which were reflected by changes of characteristic Raman bands: 726 cm(-1) (adenine), 782 cm(-1) (uracil, cytosine, thymine), 788 cm(-1) (O-P-O), 1006 cm(-1) (phenylalanine), and 1320 cm(-1) (guanine) after DEP exposure. These findings suggest that the combination of multi-instruments (e.g., AFM/FL) may offer an exciting platform for investigating the roles of biophysical and biochemical responses to particulate matter-induced cell toxicity.

Temperature response of the neuronal cytoskeleton mapped via atomic force and fluorescence microscopy

Neuronal cells change their growth properties in response to external physical stimuli such as variations in external temperature, stiffness of the growth substrate, or topographical guidance cues. Detailed knowledge of the mechanisms that control these biomechanical responses is necessary for understanding the basic principles that underlie neuronal growth and regeneration. Here, we present elasticity maps of living cortical neurons (embryonic rat) as a function of temperature, and correlate these maps to the locations of internal structural components of the cytoskeleton. Neurons display a significant increase in the average elastic modulus upon a decrease in ambient temperature from 37 to 25 °C. We demonstrate that the dominant mechanism by which the elasticity of the neurons changes in response to temperature is the stiffening of the actin components of the cytoskeleton induced by myosin II. We also report a reversible shift in the location and composition of the high-stiffness areas of the neuron cytoskeleton with temperature. At 37 °C the areas of the cell displaying high elastic modulus overlap with the tubulin-dense regions, while at 25 °C these high-stiffness areas correspond to the actin-dense regions of the cytoskeleton. These results demonstrate the importance of considering temperature effects when investigating cytoskeletal dynamics in cells.

Atomic force microscopy observation of lipopolysaccharide-induced cardiomyocyte cytoskeleton reorganization

We applied atomic force microscopy (AFM) to observe lipopolysaccharide (LPS)-induced intracellular cytoskeleton reorganization in primary cardiomyocytes from neonatal mouse. The nonionic detergent Triton X-100 was used to remove the membrane, soluble proteins, and organelles from the cell. The remaining cytoskeleton can then be directly visualized by AFM. Using three-dimensional technique of AFM, we were able to quantify the changes of cytoskeleton by the "density" and total "volume" of the cytoskeleton fibers. Compared to the control group, the density of cytoskeleton was remarkably decreased and the volume of cytoskeleton was significantly increased after LPS treatment, which suggests that LPS may induce the cytoskeleton reorganization and change the cardiomyocyte morphology.

Curcumin disturbed cell-cycle distribution of HepG2 cells via cytoskeletal arrangement

Due to its extensive antitumor activity, curcumin has been focused on by more researchers. But, its antiproliferative mechanisms are still unknown. Here we studied the antiproliferative activity of curcumin in human liver cancer HepG2 cells. In order to analyze the cytotoxic activity and anticancer mechanisms of curcumin, we carried out cytotoxicity tests using 3-[4,5-dimethyl-2-thiazolyl]-2,5 diphenyltetrazolium bromide (MTT) assay. The HepG2 cell cycle distribution and the expression of tubulin were detected by flow cytometry. Alterations in morphological and cytoskeletal properties of HepG2 cells were investigated using atomic force microscopy (AFM). Simultaneously, the effects of curcumin on the growth and proliferation of HepG2 cells were also assayed by MTT method. Cells were incubated with different doses of curcumin (0-80 μmol/l) for 24 h, the cell viability decreased from 91.10 ± 3.2% to 10.84 ± 4.0%, and the 50% inhibiting concentration (IC50 ) was 23.15 ± 0.37 μmol/l. Moreover, flow cytometry quantitatively detected that curcumin treatment resulted in a dose-dependent accumulation of HepG2 cells in G2/M phase with concomitant losses from G0/G1 phase, so curcumin caused cell-cycle arrest at G2/M phase. Furthermore, we discovered that curcumin was able to upregulate the expression of tubulin in HepG2 cells. In addition, AFM analysis including cell-membrane structure and cytoskeleton networks is helpful to explain the relationship between the changes of cells and external pharmacologic stimulation.

Nanoscale differences in the shape and size of X and Y chromosome-bearing bovine sperm heads assessed by atomic force microscopy

Sperm dimensions and the question of whether X and Y chromosome-bearing sperm differ in size or shape has been of great interest, especially for the development of alternative methods to sort or classify sperm cells. The aim of the present study was to evaluate possible differences in the shape and size of the sperm head between X and Y chromosome-bearing sperm by atomic force microscopy (AFM). One ejaculate per bull (n = 4) was used. Each ejaculate was separated into four fractions: non-sexed (NS), sexed for X-sperm (SX), sexed for Y-sperm (SY) and a pooling of SX and SY samples (SXY). Using AFM, 400 sperm heads per group were measured. Twenty three structural features were assessed including one-, two- and three-dimensional parameters and shape descriptors. These measurements determine the micro- to nanoscale features of X- and Y-bearing chromosomes in sperm cells. No differences were observed for any individual variables between SX and SY groups. Next, a simultaneous evaluation of all features using statistical discriminant analysis was performed to determine if it was possible to distinguish to which group belong each individual cells. This analysis clearly showed, a distinct separation of NS, SXY, SX and SY groups. The recognition of this structural possibility to distinguish between X and Y sperm cell might improve the understanding of sperm cells biology. These results indicated that the associations of several structural measurements of the sperm cell head are promising candidates for development of a new method of sperm sexing.

Cancer cell detection based on the interaction between an anticancer drug and cell membrane components

Simple and general cancer cell detection methods are required in point-of-care diagnostics. Herein, the interaction between an anticancer drug, daunomycin, and cancer cell membrane components has been studied using an aptamer probe immobilized on a conducting polymer-gold nanoparticle composite film through electrochemical and fluorescence methods and applied to the quantitative detection of cancer cells. The developed method differentiates between cancerous and noncancerous cells effectively.

Atomic force microscopy demonstration of cytoskeleton instability in mouse erythrocytes with dematin-headpiece and β-adducin deficiency

The pattern of disassembly of the cytoskeletal network of murine erythrocytes with deficiency of either dematin-headpiece or β-adducin or both proteins were investigated using atomic force microscopy. A heterogeneous complex structure with fine filament features and coarse features was observed in the cytoskeleton of wild type mouse erythrocytes, whereas a significant amount of rearrangement and aggregation occurred in the mutants, particularly in the cells carrying double gene mutations. These results are consistent with the cellular and biochemical phenotype of the mutant cell membranes as being more fragile due to weakened vertical connections with the plasma membrane.

Extracellular ultrathin fibers sensitive to intracellular reactive oxygen species: formation of intercellular membrane bridges

Membrane bridges are key cellular structures involved in intercellular communication; however, dynamics for their formation are not well understood. We demonstrated the formation and regulation of novel extracellular ultrathin fibers in NIH3T3 cells using confocal and atomic force microscopy. At adjacent regions of neighboring cells, phorbol 12-myristate 13-acetate (PMA) and glucose oxidase induced ultrathin fiber formation, which was prevented by Trolox, a reactive oxygen species (ROS) scavenger. The height of ROS-sensitive ultrathin fibers ranged from 2 to 4 nm. PMA-induced formation of ultrathin fibers was inhibited by cytochalasin D, but not by Taxol or colchicine, indicating that ultrathin fibers mainly comprise microfilaments. PMA-induced ultrathin fibers underwent dynamic structural changes, resulting in formation of intercellular membrane bridges. Thus, these fibers are formed by a mechanism(s) involving ROS and involved in formation of intercellular membrane bridges. Furthermore, ultrastructural imaging of ultrathin fibers may contribute to understanding the diverse mechanisms of cell-to-cell communication and the intercellular transfer of biomolecules, including proteins and cell organelles.

Towards nano-physiology of insects with atomic force microscopy

Little study of insects with modern nanotechnology tools has been done so far. Here we use one of such tool, atomic force microscopy (AFM) to study surface oscillations of the ladybird beetles (Hippodamia convergens) measured in different parts of the insect at picometer level. This allows us to record a much broader spectral range of possible surface vibrations (up to several kHz) than the previously studied oscillations due to breathing, heartbeat cycles, coelopulses, etc. (up to 5-10Hz). Here we demonstrate three different ways with which one can identify the origins of the observed peaks - by physical positioning the probe near a specific organ, and by using biological or chemical stimuli. We report on identification of high frequency peaks associated with H. convergens heart, spiracular closer muscles, and oscillations associated with muscles activated while drinking. The method, being a relatively non-invasive technique providing a new type of information, may be useful in developing "nanophysiology" of insects.

Atomic force microscopy characterization of corneocytes: effect of moisturizer on their topology, rigidity, and friction

BACKGROUND/PURPOSE

Atomic force microscopy (AFM) is a novel technique for skin characterization.

OBJECTIVES

To develop AFM tests for characterization of the outermost epidermis layer, corneocytes. As an example, the effect of moisturizer on the corneocyte properties is studied.

METHODS AND MATERIALS

Topology, rigidity, and friction (between individual corneocytes and AFM probe) of the top layer of corneocytes were measured by means of Veeco DM3100 AFM. Quench moisturizing cream was applied daily on the forearm of five volunteers for a period of 9 days. The skin flakes were collected before and after the treatment using Cuderm tape strips. No additional treatment of flakes was performed before the measurements.

RESULTS

A protocol for the AFM study of corneocytes is developed. After the treatment, we observed overall smoothening of the corneocyte surface, an increase of friction, and a decrease of rigidity (the Young modulus).

CONCLUSION

AFM can be used as a very sensitive tool for early detection of changes in corneocytes.

Molecular imaging of membrane proteins and microfilaments using atomic force microscopy

Atomic force microscopy (AFM) is an emerging technique for a variety of uses involving the analysis of cells. AFM is widely applied to obtain information about both cellular structural and subcellular events. In particular, a variety of investigations into membrane proteins and microfilaments were performed with AFM. Here, we introduce applications of AFM to molecular imaging of membrane proteins, and various approaches for observation and identification of intracellular microfilaments at the molecular level. These approaches can contribute to many applications of AFM in cell imaging.

Tumor suppressor protein SMAR1 modulates the roughness of cell surface: combined AFM and SEM study

Background

Imaging tools such as scanning electron microscope (SEM) and atomic force microscope (AFM) can be used to produce high-resolution topographic images of biomedical specimens and hence are well suited for imaging alterations in cell morphology. We have studied the correlation of SMAR1 expression with cell surface smoothness in cell lines as well as in different grades of human breast cancer and mouse tumor sections.

Methods

We validated knockdown and overexpression of SMAR1 using RT-PCR as well as Western blotting in human embryonic kidney (HEK) 293, human breast cancer (MCF-7) and mouse melanoma (B16F1) cell lines. The samples were then processed for cell surface roughness studies using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The same samples were used for microarray analysis as well. Tumors sections from control and SMAR1 treated mice as well as tissues sections from different grades of human breast cancer on poly L-lysine coated slides were used for AFM and SEM studies.

Results

Tumor sections from mice injected with melanoma cells showed pronounced surface roughness. In contrast, tumor sections obtained from nude mice that were first injected with melanoma cells followed by repeated injections of SMAR1-P44 peptide, exhibited relatively smoother surface profile. Interestingly, human breast cancer tissue sections that showed reduced SMAR1 expression exhibited increased surface roughness compared to the adjacent normal breast tissue. Our AFM data establishes that treatment of cells with SMAR1-P44 results into increase in cytoskeletal volume that is supported by comparative gene expression data showing an increase in the expression of specific cytoskeletal proteins compared to the control cells. Altogether, these findings indicate that tumor suppressor function of SMAR1 might be exhibited through smoothening of cell surface by regulating expression of cell surface proteins.

Conclusion

Tumor suppressor protein SMAR1 might be used as a phenotypic differentiation marker between cancerous and non-cancerous cells.

Atomic force microscopy detects differences in the surface brush of normal and cancerous cells

The atomic force microscope is broadly used to study the morphology of cells, but it can also probe the mechanics of cells. It is now known that cancerous cells may have different mechanical properties to those of normal cells, but the reasons for these differences are poorly understood. Here, we report quantitatively the differences between normal and cancerous human cervical epithelial cells by considering the brush layer on the cell surface. These brush layers, which consist mainly of microvilli, microridges and cilia, are important for interactions with the environment. Deformation force curves obtained from cells in vitro were processed according to the 'brush on soft cell model'. We found that normal cells have brushes of one length, whereas cancerous cells have mostly two brush lengths of significantly different densities. The observed differences suggest that brush layers should be taken into account when characterizing the cell surface by mechanical means.

Saponaria officinalis karyology and karyotype by means of image analyzer and atomic force microscopy

The aim of this work was to offer a contribution to the characterization of taxonomic entity of Saponaria officinalis (2n = 28; an herbaceous perennial species; saporin, a type 1 Ribosome Inactivating Protein, is present in leaves and seeds) by a cytogenetic and karyomorphological approach. We investigated the karyotype's morphometry correlated with Stebbin's symmetric index; the same information has been used for computing the indices resemblance between chromosomes (REC), symmetric indices (SYI), and total form (TF%) which allow the comparison between species and evaluation of karyological evolution. Fluorescence intensities of the stained nuclei were measured by a flow cytometer and, for the first time, values for nuclear DNA content were estimated by comparing nuclei fluorescence intensities of the test population with those of appropriate internal DNA standards. Our study is also aimed to introduce chromosomal volumes, which were determined by atomic force microscopy (AFM), as novel karyomorphological parameter which could allow for chromosome discrimination especially when tiny ones are present.

Water-soluble organo-silica hybrid nanowires

There has been growing interest in the past decade in one-dimensional (1D) nanostructures, such as nanowires, nanotubes or nanorods, owing to their size-dependent optical and electronic properties and their potential application as building blocks, interconnects and functional components for assembling nanodevices. Significant progress has been made; however, the strict control of the distinctive geometry at extremely small size for 1D structures remains a great challenge in this field. The anisotropic nature of cylindrical polymer brushes has been applied to template 1D nanostructured materials, such as metal, semiconductor or magnetic nanowires. Here, by constructing the cylindrical polymer brushes themselves with a precursor-containing monomer, we successfully synthesized hybrid nanowires with a silsesquioxane core and a shell made up from oligo(ethylene glycol) methacrylate units, which are soluble in water and many organic solvents. The length and diameter of these rigid wires are tunable by the degrees of polymerization of both the backbone and the side chain. They show lyotropic liquid-crystalline behaviour and can be pyrolysed to silica nanowires. This approach provides a route to the controlled fabrication of inorganic or hybrid silica nanostructures by living polymerization techniques.

Ultrastructure of Trypanosoma cruzi revisited by atomic force microscopy

Most advances in atomic force microscopy (AFM) have been accomplished in recent years. Previous attempts to use AFM to analyze the organization of pathogenic protozoa did not significantly contribute with new structural information. In this work, we introduce a new perspective to the study of the ultrastructure of the epimastigote form of Trypanosoma cruzi by AFM. Images were compared with those obtained using field emission scanning electron microscopy of critical point dried cells and transmission electron microscopy of negative stained detergent-extracted and air-dried cells. AFM images of epimastigote forms showed a flagellum furrow separating the axoneme from the paraflagellar rod (PFR) present from the emergence of the flagellar pocket to the tip of the flagellum. At high magnification, a row of periodically organized structures, which probably correspond to the link between the axoneme, the PFR and the flagellar membrane were seen along the furrow. In the origin of the flagellum, two basal bodies were identified. Beyond the basal bodies, small periodically arranged protrusions, positioned at 400 nm from the flagellar basis were seen. This structure was formed by nine substructures distributed around the flagellar circumference and may correspond to the flagellar necklace. Altogether, our results demonstrate the importance of the application of AFM in the structural characterization of the surface components and cytoskeleton on protozoan parasites.

Verification of cell viability at progressively higher scanning forces using a hybrid atomic force and fluorescence microscope

The prudent use of the atomic force microscope as a supra-vital live cell imaging tool requires that cell viability must be determined before and after scanning. Complementary optical techniques in conjunction with the fluorescent dyes rhodamine-123 and ethidium homodimer have been used within this study to determine cell viability after increasing loads are applied in contact mode. Guideline force ranges for five commonly cultured cell lines, human squamous carcinoma (A431), fibroblast, HeLa, Potorous tridactylis (PtK2) and rat intestinal epithelial (RIE) cells are given.

Changes induced by hyperosmotic mannitol in cerebral endothelial cells: an atomic force microscopic study

Understanding the reaction of living cells in response to different extracellular stimuli, such as hyperosmotic stress, is of primordial importance. Mannitol, a cell-impermeable non-toxic alcohol, has been used successfully for reversible opening of the blood-brain barrier in hyperosmotic concentrations. In this study we analyzed the effect of hyperosmotic mannitol on the shape and surface structure of living cerebral endothelial cells by atomic force microscope imaging technique. Addition of clinically relevant concentrations of mannitol to the culture medium of the confluent cells induced a decrease of about 40% in the observed height of the cells. This change was consistent both at the nuclear and peripheral region of the cells. After mannitol treatment even a close examination of the contact surface between the cells did not reveal gap between them. We could observe the appearance of surface protrusions of about 100 nm. By force measurements the elasticity of the cells were estimated. While the Young's modulus of the control cells appeared to be 8.04 +/- 0.12 kPa, for the mannitol-treated cells it decreased to an estimated value of 0.93 +/- 0.04 kPa which points to large structural changes inside the cell.

Atomic force microscopy imaging of actin cortical cytoskeleton of Xenopus laevis oocyte

In this study we report an atomic force microscopy (AFM) investigation of the actin cortical cytoskeleton of Xenopus laevis oocytes. Samples consisted of inside-out orientated plasma membrane patches of X. laevis oocytes with overhanging cytoplasmic material. They were spread on a freshly cleaved mica surface, subsequently treated with Triton X-100 detergent and chemically fixed. The presence of actin fibres in oocyte patches was proved by fluorescence microscopy imaging. Contact mode AFM imaging was performed in air in constant force conditions. Reproducible high-resolution AFM images of a filamentous structure were obtained. The filamentous structure was identified as an actin cortical cytoskeleton, investigating its disaggregation induced by cytochalasin D treatment. The thinnest fibres showed a height of 7 nm in accordance with the diameter of a single actin microfilament. The results suggest that AFM imaging can be used for the high-resolution study of the actin cortical cytoskeleton of the X. laevis oocyte and its modifications mediated by the action of drugs and toxins.

Recovery of elasticity of aged human epithelial cells in vitro

We recently found a considerable increase in rigidity of human epithelial cells during aging in vitro. This is important because the loss in elasticity of epithelial tissues with aging contributes to many human diseases. We also found that cultured cells had three distinct regions of rigidity and that the increase in rigidity correlated with an increase in density of cytoskeletal fibers. However, it was not clear which type of fiber was important. Atomic force microscopy and immunofluorescence microscopy were used in this study to characterize aging human epithelial cells in vitro, both before and after treatment with cytochalasin B. We found that the fibers associated with increased rigidity were mostly F-actin microfilaments. Furthermore, using cytochalasin B, a chemical that inhibits polymerization of F-actin, we restored the rigidity of old cells to the young level in all three areas of rigidity simultaneously. These results clarify how the cell mechanics changes during aging in vitro, and they may be relevant for treatment of age-related loss of elasticity in epithelial tissues.

Atomic force microscopy and confocal laser scanning microscopy on the cytoskeleton of permeabilised and embedded cells

We describe a technical method of cell permeabilisation and embedding to study the organisation and distribution of intracellular proteins with aid of atomic force microscopy and confocal laser scanning microscopy in identical areas. While confocal laser scanning microscopy is useful for the identification of certain proteins subsequent labelling with markers or antibodies, atomic force microscopy allows the observation of macromolecular structures in fixed and living cells. To demonstrate the field of application of this preparatory technique, cells were permeabilised, fixed, and the actin cytoskeleton was stained with phalloidin-rhodamine. Confocal laser scanning microscopy was used to show the organisation of these microfilaments, e.g. geodesic dome structures. Thereafter, cells were embedded in Durcupan water-soluble resin, followed by UV-polymerisation of resin at 4 degrees C. This procedure allowed intracellular visualisation of the cell nucleus or cytoskeletal elements by atomic force microscopy, for instance to analyse the globular organisation of actin filaments. Therefore, this method offers a great potential to combine both microscopy techniques in order to understand and interpret intracellular protein relations, for example, the biochemical and morphological interaction of the cytoskeleton.

Developments in Using Scanning Probe Microscopy To Study Molecules on Surfaces — From Thin Films and Single-Molecule Conductivity to Drug–Living Cell Interactions

Scanning probe microscopy (SPM) techniques, including atomic force microscopy (AFM) and scanning tunnelling microscopy (STM), have revolutionized our understanding of molecule–surface interactions. The high resolution and versatility of SPM techniques have helped elucidate the morphology of adsorbed surfactant layers, facilitated the study of electronically conductive single molecules and biomolecules connected to metal substrates, and allowed direct observation of real-time processes such as in situ DNA hybridization and drug–cell interactions. These examples illustrate the power that SPM possesses to study (bio)molecules on surfaces and will be discussed in depth in this review.