Cancer Cell Analyses at the Single Cell-Level Using Electroactive Microwell Array Device

Circulating tumor cells (CTCs), shed from primary tumors and disseminated into peripheral blood, are playing a major role in metastasis. Even after isolation of CTCs from blood, the target cells are mixed with a population of other cell types. Here, we propose a new method for analyses of cell mixture at the single-cell level using a microfluidic device that contains arrayed electroactive microwells. Dielectrophoretic (DEP) force, induced by the electrodes patterned on the bottom surface of the microwells, allows efficient trapping and stable positioning of single cells for high-throughput biochemical analyses. We demonstrated that various on-chip analyses including immunostaining, viability/apoptosis assay and fluorescent in situ hybridization (FISH) at the single-cell level could be conducted just by applying specific reagents for each assay. Our simple method should greatly help discrimination and analysis of rare cancer cells among a population of blood cells.     

Localization of low molecular weight GTP binding proteins to exocytic and endocytic compartments

A set of 11 clones encoding putative GTP binding proteins highly homologous to the yeast YPT1/SEC4 gene products have been isolated from an MDCK cell cDNA library. We localized three of the corresponding proteins in mammalian cells by using affinity-purified antibodies in immunofluorescence and immunoelectron microscopy studies. One, the MDCK homolog of rab2, is associated with a structure having the characteristics of an intermediate compartment between the endoplasmic reticulum and the Golgi apparatus. The second, rab5, is located at the cytoplasmic surface of the plasma membrane and on early endosomes, while the third, rab7, is found on late endosomes. These findings provide evidence that members of the YPT1/SEC4 subfamily of GTP binding proteins are localized to specific exocytic and endocytic subcompartments in mammalian cells.     

Rapid and Serial Quantification of Adhesion Forces of Yeast and Mammalian Cells

Cell adhesion to surfaces represents the basis for niche colonization and survival. Here we establish serial quantification of adhesion forces of different cell types using a single probe. The pace of single-cell force-spectroscopy was accelerated to up to 200 yeast and 20 mammalian cells per probe when replacing the conventional cell trapping cantilever chemistry of atomic force microscopy by underpressure immobilization with fluidic force microscopy (FluidFM). In consequence, statistically relevant data could be recorded in a rapid manner, the spectrum of examinable cells was enlarged, and the cell physiology preserved until approached for force spectroscopy. Adhesion forces of Candida albicans increased from below 4 up to 16 nN at 37°C on hydrophobic surfaces, whereas a Δhgc1-mutant showed forces consistently below 4 nN. Monitoring adhesion of mammalian cells revealed mean adhesion forces of 600 nN of HeLa cells on fibronectin and were one order of magnitude higher than those observed for HEK cells.     

Sensing of silver nanoparticles on/in endothelial cells using atomic force spectroscopy

Endothelial cells, due to their location, are interesting objects for atomic force spectroscopy study. They constitute a barrier between blood and vessel tissues located deeper, and therefore they are the first line of contact with various substances present in blood, eg, drugs or nanoparticles. This work intends to verify whether the mechanical response of immortalized human umbilical vein endothelial cells (EA.hy926), when exposed to silver nanoparticles, as measured using force spectroscopy, could be effectively used as a bio‐indicator of the physiological state of the cells. Silver nanoparticles were characterized with transmission electron microscopy and dynamic light scattering techniques. Tetrazolium salt reduction test was used to determine cell viability after treatment with silver nanoparticles. An elasticity of native cells was examined in the Hanks' buffer whereas fixed cells were softly fixed with formaldehyde. Additional aspect of the work is the comparative force spectroscopy utilizing AFM probes of ball‐shape and conical geometries, in order to understand what changes in cell elasticity, caused by SNPs, were detectable with each probe. As a supplement to elasticity studies, cell morphology observation by atomic force microscopy and detection of silver nanoparticles inside cells using transmission electron microscopy were also performed. Cells exposed to silver nanoparticles at the highest selected concentrations (3.6 μg/mL, 16 μg/mL) are less elastic. It may be associated with the reorganization of the cellular cytoskeleton and the “strengthening” of the cell cortex caused by presence of silver nanoparticles. This observation does not depend on cell fixation. Agglomerates of silver nanoparticles were observed on the cell membrane as well as inside the cells.     

Atomic force microscopy of living cells: advances and future outlooks

The advances of the method of atomic force microscopy for investigating the animal cells and an analysis of its development have been reviewed, with much attention being given to studies of living cells. The features and problems of the method have been considered, and a number of special methods based on the use of atomic force microscopy have been analyzed. The problems of choosing the geometry of probes for studies of animal cells, determination of cell adhesion on substrate, mapping of the cell surface using chemically modified cantilevers, and the distribution of molecular components inside the cell with the use of micro- and nanosurgical approaches have been discussed. The problems of combining the atomic force microscopy with optical and laser scanning confocal microscopy have been considered. Possible applications of the method in biotechnology and medicine are discussed.     

Differential distribution of factors involved in pre-mRNA processing in the yeast cell nucleus.

The yeast cell nucleus has previously been shown to be divided into two regions by a variety of microscopic approaches. We used antibodies specific for the 2,2,7-trimethylguanosine cap structure of small nuclear ribonucleic acids (snRNAs) and for a protein component of small nuclear ribonucleoprotein particles to identify the distribution of small nuclear ribonucleoprotein particles within the yeast cell nucleus. These studies were performed with the fission yeast Schizosaccharomyces pombe and the budding yeast Saccharomyces cerevisiae. By using immunofluorescence microscopy and immunoelectron microscopy, most of the abundant snRNAs were localized to the portion of the nucleus which has heretofore been referred to as the nucleolus. This distribution of snRNAs is different from that found in mammalian cells and suggests that the nucleolar portion of the yeast nucleus contains functional domains in addition to those associated with RNA polymerase I activity.     

Detection and measurement of a single blood cell surface antigen by thermal lens microscopy

A highly sensitive method for detection of antigens on the surface of a single blood cell using thermal lens microscopy is described. Colloidal gold, coated with antibody, was used to stain membrane antigens of leukocytes. Human leukocyte antigens on the lymphocytes and mononuclear leukocytes were observed by new thermal lens microscopy, which involves spectrometry using a laser-induced thermal-lens effect. Antigens of HLA-A, -B, and -C loci on the lymphocytes were identified and quantitated using a single cell. The image of HLA-A, -B, and -C antigen distribution on a mononuclear leukocyte was obtained. Our laser microscope, newly devised for measuring convex surface cells, is a powerful analytical tool for detecting and quantitating localized antigens in a single cell and/or cell-surface-associated molecules.     

Biochemical characterization of the mammalian stress proteins and identification of two stress proteins as glucose- and Ca2+-ionophore-regulated proteins

Biochemical properties of the heat shock or stress proteins of mammalian cells have been investigated using two-dimensional gel electrophoresis and immunological techniques. Of the major mammalian stress proteins (Mr = 72,000, 73,000, and 90,000) and minor stress proteins (Mr = 80,000, 100,000, and 110,000), the 80- and 90-kDa proteins were found to be phosphoproteins in all cell types examined. The 100-kDa protein was found to incorporate phosphate in only some cell types examined. In studies of the metabolic incorporation of mannose into the stress proteins, only the 100-kDa protein was found to be a glycoprotein. Two of the stress proteins, the 80- and 100-kDa species, were found to be identical with the proteins induced in cells grown in the absence of glucose (i.e. the "glucose-regulated proteins"). These same two proteins also were induced in cells treated with the calcium ionophore A23187. To begin examining the intracellular location of these multiregulated proteins, immunofluorescence microscopy studies were carried out using a monoclonal antibody against the 100-kDa stress protein. The antigen was localized primarily with the Golgi apparatus and less prominently with the plasma membrane and nucleus. Heat shock treatment resulted in an increased number of the cells exhibiting a nuclear location of 100 kDa.     

Atomic force microscopy of animal cells: Advances and prospects

We review the advances of the method of atomic force microscopy (AFM) for investigating the animal cells and analyze its development, paying much attention to studies of living cells. We consider the specific features and tasks of AFM, and a number of special AFM-based techniques. We discuss the choice of probe geometry for studies of animal cells, determination of cell adhesion on substrate, mapping of the cell surface using chemically modified cantilevers, and analysis of the distribution of molecular components inside the cell with the use of micro- and nanosurgical approaches, as well as combining AFM with optical and laser scanning confocal microscopy, and the possible applications of AFM in biotechnology and medicine.     

Murine mCLCA5 is expressed in granular layer keratinocytes of stratified epithelia

CLCA proteins represent a large family of proteins widely expressed in mammalian tissues with a unique expression pattern for each family member analyzed so far. However, their functions in normal and diseased tissues are poorly understood. Here, we present the cellular expression pattern of mCLCA5 in murine tissues using immunohistochemistry, confocal laser scanning microscopy and immune electron microscopy with specific antibodies and RT-qPCR following laser-capture microdissection. The mCLCA5 protein was localized to granular layer keratinocytes of virtually all stratified squamous epithelia of the body. Biochemical protein characterizations revealed that the amino-terminal cleavage product is fully secreted by the cell, while the carboxy-terminal cleavage product remains associated with the cell. The results imply that mCLCA5 may play a role in maturation and keratinization of squamous epithelial cells.     

Baculovirus entry into human hepatoma cells

Autographa californica multiple nucleopolyhedrovirus (AcMNPV), a prototype member of the Baculoviridae family, has gained increasing interest as a potential vector candidate for mammalian gene delivery applications. AcMNPV is known to enter both dividing and nondividing mammalian cell lines in vitro, but the mode and kinetics of entry as well as the intracellular transport of the virus in mammalian cells is poorly understood. The general objective of this study was to characterize the entry steps of AcMNPV- and green fluorescent protein-displaying recombinant baculoviruses in human hepatoma cells. The viruses were found to bind and transduce the cell line efficiently, and electron microscopy studies revealed that virions were located on the cell surface in pits with an electron-dense coating resembling clathrin. In addition, virus particles were found in larger noncoated plasma membrane invaginations and in intracellular vesicles resembling macropinosomes. In double-labeling experiments, virus particles were detected by confocal microscopy in early endosomes at 30 min and in late endosomes starting at 45 min posttransduction. Viruses were also seen in structures specific for early endosomal as well as late endosomal/lysosomal markers by nanogold preembedding immunoelectron microscopy. No indication of viral entry into recycling endosomes or the Golgi complex was observed by confocal microscopy. In conclusion, these results suggest that AcMNPV enters mammalian cells via clathrin-mediated endocytosis and possibly via macropinocytosis. Thus, the data presented here should enable future design of baculovirus vectors suitable for more specific and enhanced delivery of genetic material into mammalian cells.     

Cpn60 is exclusively localized into mitochondria of rat liver and embryonic Drosophila cells

Several reports have claimed that the mitochondrial chaperonin cpn60, or a close homolog, is also present in some other subcellular compartments of the eukaryotic cell. Immunoelectron microscopy studies, using a polyclonal serum against cpn60, revealed that the protein is exclusively localized within the mitochondria of rat liver and embryonic Drosophila cells (SL2). Furthermore, no cpn60 immunoreactive material could be found within the nucleus of SL2 cells subjected to a 1 h 37°C heat-shock treatment. In contrast to these findings, immunoelectron microscopy studies, using a cpn60 monoclonal antibody, revealed mitochondrial and extramitochondrial (plasma membrane, nucleus) immunoreactive material in rat liver cells. Surprisingly, the monoclonal antibody also reacted with fixed proteins of the mature red blood cell. The monoclonal antibody, as well as cpn60 polyclonal sera, only recognize mitochondrial cpn60 in Western blots of liver proteins. Furthermore, none of the cpn60 antibodies used in this study recognized blotted proteins from rat red blood cells. Therefore, we suggest that the reported extramitochondrial localization of cpn60 in metazoan cells may be due to cross-reactivity of some of cpn60 antibodies with conformational epitopes also present in distantly related cpn60 protein homologs that are preserved during fixation procedures of the cells. © 1995 Wiley-Liss, Inc.     

Filopodia are enriched in a cell cohesion molecule of Mr 80,000 and participate in cell-cell contact formation in Dictyostelium discoideum

During the early phase of Dictyostelium discoideum development, cells undergo chemotactic migration to form tight aggregates. A developmentally regulated surface glycoprotein of Mr 80,000 (gp80) has been implicated in mediating the EDTA-resistant type of cell cohesion at this stage. We have used a monoclonal antibody directed against gp80 to study the topographical distribution of gp80 on the cell surface. Indirect immunofluorescence studies showed that gp80 was primarily localized on the cell surface, with a higher concentration at contact areas. Immunoelectron microscopy was carried out by indirect labeling using protein A-gold, and a nonrandom distribution of gp80 was revealed. In addition to contact regions, gold particles were found preferentially localized on filopodia. Quantitative analysis using transmission electron microscopy (TEM) showed that approximately 60% more gold particles were localized in contact regions in comparison with the noncontact regions, and the filopodial surfaces had a twofold higher gold density. Both TEM and scanning electron microscopy showed that contact areas were enriched in filopodial structures. Filopodia often appeared to adhere to either smooth surfaces or similar filopodial structures of an adjacent cell. These observations suggest that the formation of stable cell-cell contacts involves at least four sequential steps in which filopodia and gp80 probably play an important role in the initial stages of recognition and cohesion among cells.     

Morphology of the blood cells from three species of wobbegong sharks (Orectolobus species) on the east coast of New South Wales

This study is the first study to describe blood cell morphology, using light microscopy, for three species of wild‐caught wobbegong shark. Blood cell morphology was similar to that described previously in fish. Wobbegong sharks possess erythrocytes, at least three different morphological types of thrombocytes, lymphocytes, eosinophils, neutrophils, granuloblasts and monocytes. No basophils were observed in this study. Similarities and differences in morphological appearance of wobbegong shark blood cells compared to Chondrichthyes, teleosts and mammalian blood cells are discussed. Zoo Biol 0:1–10, 2005. © 2005 Wiley‐Liss, Inc.     

Assay for characterizing the recovery of vertebrate cells for adhesion measurements by single-cell force spectroscopy

Single-cell force spectroscopy (SCFS) is becoming a widely used method to quantify the adhesion of a living cell to a substrate, another cell or tissue. The high sensitivity of SCFS permits determining the contributions of individual cell adhesion molecules (CAMs) to the adhesion force of an entire cell. However, to prepare adherent cells for SCFS, they must first be detached from tissue-culture flasks or plates. EDTA and trypsin are often applied for this purpose. Because cellular properties can be affected by this treatment, cells need to recover before being further characterized by SCFS. Here we introduce atomic force microscopy (AFM)-based SCFS to measure the mechanical and adhesive properties of HeLa cells and mouse embryonic kidney fibroblasts while they are recovering after detachment from tissue-culture. We find that mechanical and adhesive properties of both cell lines recover quickly (<10 min) after detachment using EDTA, while trypsin-detached fibroblasts require >60 min to fully recover. Our assay introduced to characterize the recovery of mammalian cells after detachment can in future be used to estimate the recovery behavior of other adherent cell types.     

Nanoanalytics for medicine

The applications of atomic force microscopy and the methods based on atomic force microscopy that can be useful in medical nanoanalytics have been reviewed. The main fields of possible application of scanning probe microscopy in medicine have been outlined. Among these are studying the resistance of bacterial cells to modern antibiotics and drugs, morphological analysis of blood components, trichology, nanotoxicology, DNA sequencing, and biocompatibility of medicinal materials. Examples of application of atomic force microscopy for studies in these fields have been considered, and prospects for its use in medicine have been demonstrated.     

Nanoanalytics for medicine

The applications of atomic force microscopy and the methods based on atomic force microscopy that can be useful in medical nanoanalytics have been reviewed. The main fields of possible application of scanning probe microscopy in medicine have been outlined. Among these are studying the resistance of bacterial cells to modern antibiotics and drugs, morphological analysis of blood components, trichology, nanotoxicology, DNA sequencing, and biocompatibility of medicinal materials. Examples of application of atomic force microscopy for studies in these fields have been considered, and prospects for its use in medicine have been demonstrated.     

Potential Hydrodynamic Cytoplasmic Transfer between Mammalian Cells: Cell-Projection Pumping

We earlier reported cytoplasmic fluorescence exchange between cultured human fibroblasts (Fibs) and malignant cells (MCs). Others report similar transfer via either tunneling nanotubes (TNTs) or shed membrane vesicles, and this changes the phenotype of recipient cells. Our time-lapse microscopy showed most exchange was from Fibs into MCs, with less in the reverse direction. Although TNTs were seen, we were surprised transfer was not via TNTs but was instead via fine and often branching cell projections that defied direct visual resolution because of their size and rapid movement. Their structure was revealed nonetheless by their organellar cargo and the grooves they formed indenting MCs, which was consistent with holotomography. Discrete, rapid, and highly localized transfer events evidenced against a role for shed vesicles. Transfer coincided with rapid retraction of the cell projections, suggesting a hydrodynamic mechanism. Increased hydrodynamic pressure in retracting cell projections normally returns cytoplasm to the cell body. We hypothesize “cell-projection pumping” (CPP), in which cytoplasm in retracting cell projections partially equilibrates into adjacent recipient cells via microfusions that form temporary intercellular cytoplasmic continuities. We tested plausibility for CPP by combined mathematical modeling, comparison of predictions from the model with experimental results, and then computer simulations based on experimental data. The mathematical model predicted preferential CPP into cells with lower cell stiffness, expected from equilibration of pressure toward least resistance. Predictions from the model were satisfied when Fibs were cocultured with MCs and fluorescence exchange was related to cell stiffness by atomic force microscopy. When transfer into 5000 simulated recipient MCs or Fibs was studied in computer simulations, inputting experimental cell stiffness and donor cell fluorescence values generated transfers to simulated recipient cells similar to those seen by experiment. We propose CPP as a potentially novel mechanism in mammalian intercellular cytoplasmic transfer and communication.     

Ultrastructural localization of epithelial mucin core proteins in colorectal tissues.

Mucins are high molecular weight glycoproteins with a variety of postulated biological functions, including physicochemical protection from toxins and mutagens, adhesion modulation, signal transduction, and regulation of cell growth. Mucins are widely and differentially expressed in the gastrointestinal tract. To date, studies of cellular expression have relied on light microscopy using in situ hybridization and immunohistochemistry. Although informative, it has been difficult with these techniques to ascertain exactly which cell types are producing a given mucin. We studied expression of MUC1, MUC2, and MUC4 apomucins in a series of normal colon biopsies using a combination of immunoelectron microscopy and light microscopy. MUC1 mucin was localized to both goblet and columnar cells, where it was seen in secretory vesicles, microvilli, and in cytoplasmic remnants in goblet cell thecae. MUC2 expression was restricted to goblet cells, in which reactivity was concentrated in the rough endoplasmic reticulum (RER). MUC4 expression was seen in both columnar and goblet cells, localized to the RER. The inability to detect MUC2 and MUC4 apomucins in the Golgi complex and the mature mucous gel probably represents masking of peptide epitopes following O-glycosylation. This study has helped clarify lineage-specific mucin synthesis in the normal colon.