Measuring translocation of fluorescent lipid derivatives across yeast Golgi membranes

Phospholipid asymmetry is a fundamental feature of the plasma membrane of most eukaryotic cells and its regulation is linked to diverse physiological processes such as apoptosis and blood clotting [P. Williamson, R.A. Schlegel, Biochim. Biophys. Acta 1585 (2002) 53-63; R.F. Zwaal, A.J. Schroit, Blood 89 (1997) 1121-1132]. In addition, the phospholipid translocases (flippases) that are thought to establish asymmetry are also implicated in vesicle-mediated protein transport throughout the secretory and endocytic pathways [T.R. Graham, Trends Cell Biol. 14 (2004) 670-677]. However, the biochemical properties of phospholipid translocases in membranes of the Golgi complex and endosomes have received much less attention than translocases in the plasma membrane. We describe here a method for purifying yeast Golgi membranes and assaying an ATP-dependent phospholipid translocase activity in these membranes using fluorescent lipid analogues. This assay detects ATP-dependent translocation of labeled phosphatidylserine across late Golgi membranes, which requires the activity of a P-type ATPase called Drs2p [P. Natarajan, J. Wang, Z. Hua, T.R. Graham, Proc. Natl. Acad. Sci. USA 101 (2004) 10614-10619].

Spherical vs. granular immobilization support selection and performance on an optical flow cell immunosensor based on the fluorescence of Cyanine-5

A spherical porous glass support Trisoperl (TRISO) with four pore diameters (ø 47.8; 55.9; 102.6, and 108.8 nm) was characterized and selected for application in an optical flow cell immunosensor, in comparison with controlled pore glass (CPG). The TRISO support was functionalized with aldehyde and isothiocyanate (-NCS) groups to attach bovine serum albumin and alkaline phosphatase (AP). The TRISO isothiocyanate pore diameter 47.8 nm (TRISO(-NCS) 47.8 nm) showed the better potential to be used in the immunosensor. It immobilized more protein (19.3 mg AP per g support) while presenting an optical performance comparable to the CPG. CPG(-NCS) and TRISO(-NCS) 47.8 nm were tested in the immunosensor model where the saturation of the Goat IgG immobilized in the supports with Monoclonal Anti-Goat IgG conjugated with Cyanine-5 was reached, followed by regeneration with the elution buffer modified PBS pH 2.0. The TRISO(-NCS) 47.8 nm presented lower fluorescence intensity at saturation (around 39 AU) than CPG(-NCS) (150 to 104 AU), but revealed a major advantage related to the uniform arrangement of the spherical particles in the flow cell, generating no significant fluorescence differences between gravity and flow package.

The Application of Fluorescence Lifetime Readouts in High-Throughput Screening

Measurement of fluorescence lifetime is a well-established technique, which has recently been introduced into the portfolio of assay formats used in high-throughput screening (HTS). This investigation establishes appropriate conditions for using lifetime measurements to reduce the impact of compound interference effects during large-scale HTS of corporate screening files. Experimental data on mixtures of standard fluorophores and interfering compounds (from 5 HTS campaigns) have been combined with a theoretical model to identify the minimum data quality required, defined by the photon count in the peak channel, for discrimination of biological activity. Single-component fluorophore lifetimes can be recovered with an error of 1%, with a peak photon count of 102, but the same accuracy with a 2-component decay requires a peak photon count of 103. When a 3rd component is introduced, the minimum peak count increases to 104. The influence of scattered light on lifetime determination was investigated using an emulsion (diameters 25-675 nm). The measured decays of interfering compounds, identified as autofluorescent, show that the vast majority have a very short lifetime that can readily be resolved from the reporter fluorophore, using appropriate data-fitting methods.

Effect of cholesterol on lateral diffusion of fluorescent lipid probes in native hippocampal membranes

Cholesterol is an abundant lipid of mammalian membranes and plays a crucial role in membrane organization, dynamics, function and sorting. The role of cholesterol in membrane organization has been a subject of intense investigation that has largely been carried out in model membrane systems. An extension of these studies in natural membranes, more importantly in neuronal membranes, is important to establish a relationship between disease states and changes in membrane physical properties resulting from an alteration in lipid composition. We have monitored the lateral diffusion of lipid probes, DiIC(18)(3) and FAST DiI which are similar in their intrinsic fluorescence properties but differ in their structure, in native and cholesterol-depleted hippocampal membranes using the fluorescence recovery after photobleaching (FRAP) approach. Our results show that the mobility of these probes is in general higher in hippocampal membranes depleted of cholesterol. Interestingly, the increase in mobility of these probes does not linearly correlate with the extent of cholesterol depletion. These results assume significance in the light of recent reports on the requirement of cholesterol to support the function of the G-protein coupled serotonin(1A) receptor present endogenously in hippocampal membranes.

FISH and Calcofluor staining techniques to detect in situ filamentous fungal biofilms in water

Filamentous fungi are a ubiquitous and diverse group of eukaryotic organisms and may contribute, along with bacteria, yeasts, protozoa and viruses, to the formation of biofilms in water distribution systems. However, fungal involvement in biofilms has not been demonstrated unambiguously. Furthermore, these fungi may be responsible for the production of tastes, odours and mycotoxins in drinking water making their early detection important. The detection of fme these problems a combination of two fluorescent techniques for direct detection was tested: (a) Fluorescence In Situ Hybridization (FISH) employing the universal rRNA probe EUK516, labelled with the red Cy3, followed by (b) staining with Calcofluor White MR2 fluorescent dye which stains fungal cell walls blue. Pure cultures of Penicillium brevicompactum were used to establish the methods followed by separate experiments with real water biofilm samples in PVC-C and cast iron coupons. FISH demonstrated eukaryotic microrganisms after approximately 5 h while the calcofluor method revealed chitinous filamentous structures in less than one hour. When the two methods were combined, additional resolution was obtained from the images of filamentous walls (blue) with intact protoplasm (red). In conclusion, FISH and Calcofluor staining provide rapid, direct and unambiguous information on the involvement of ff in biofilms which form in water.

Measurement of FRET efficiency and ratio of donor to acceptor concentration in living cells

Measurement of fluorescence resonance energy transfer (FRET) efficiency and the relative concentration of donor and acceptor fluorophores in living cells using the three-filter cube approach requires the determination of two constants: 1), the ratio of sensitized acceptor emission to donor fluorescence quenching (G factor) and 2), the ratio of donor/acceptor fluorescence intensity for equimolar concentrations in the absence of FRET (k factor). We have developed a method to determine G and k that utilizes two donor-acceptor fusion proteins with differing FRET efficiencies-the value of which need not be known. We validated the method by measuring the FRET efficiency and concentration ratio of the fluorescent proteins Cerulean and Venus in mammalian cells expressing a series of fusion proteins with varying stoichiometries. The method greatly simplifies quantitative FRET measurement in living cells as it does not require cell fixation, acceptor photobleaching, protein purification, or specialized equipment for determining fluorescence spectra or lifetime.

Nanoparticle imaging of integrins on tumor cells

Nanoparticles 10 to 100 nm in size can deliver large payloads to molecular targets, but undergo slow diffusion and/or slow transport through delivery barriers. To examine the feasibility of nanoparticles targeting a marker expressed in tumor cells, we used the binding of cyclic arginine-glycine-aspartic acid (RGD) nanoparticle targeting integrins on BT-20 tumor as a model system. The goals of this study were: 1) to use nanoparticles to image alpha(V)beta3 integrins expressed in BT-20 tumor cells by fluorescence-based imaging and magnetic resonance imaging, and, 2) to identify factors associated with the ability of nanoparticles to target tumor cell integrins. Three factors were identified: 1) tumor cell integrin expression (the alpha(V)beta3 integrin was expressed in BT-20 cells, but not in 9L cells); 2) nanoparticle pharmacokinetics (the cyclic RGD peptide cross-linked iron oxide had a blood half-life of 180 minutes and was able to escape from the vasculature over its long circulation time); and 3) tumor vascularization (the tumor had a dense capillary bed, with distances of <100 microm between capillaries). These results suggest that nanoparticles could be targeted to the cell surface markers expressed in tumor cells, at least in the case wherein the nanoparticles and the tumor model have characteristics similar to those of the BT-20 tumor employed here.

Universal screening methods and applications of ThermoFluor

The genomics revolution has unveiled a wealth of poorly characterized proteins. Scientists are often able to produce milligram quantities of proteins for which function is unknown or hypothetical, based only on very distant sequence homology. Broadly applicable tools for functional characterization are essential to the illumination of these orphan proteins. An additional challenge is the direct detection of inhibitors of protein-protein interactions (and allosteric effectors). Both of these research problems are relevant to, among other things, the challenge of finding and validating new protein targets for drug action. Screening collections of small molecules has long been used in the pharmaceutical industry as 1 method of discovering drug leads. Screening in this context typically involves a function-based assay. Given a sufficient quantity of a protein of interest, significant effort may still be required for functional characterization, assay development, and assay configuration for screening. Increasingly, techniques are being reported that facilitate screening for specific ligands for a protein of unknown function. Such techniques also allow for function-independent screening with better characterized proteins. ThermoFluor, a screening instrument based on monitoring ligand effects on temperature-dependent protein unfolding, can be applied when protein function is unknown. This technology has proven useful in the decryption of an essential bacterial enzyme and in the discovery of a series of inhibitors of a cancer-related, protein-protein interaction. The authors review some of the tools relevant to these research problems in drug discovery, and describe our experiences with 2 different proteins.

Imaging molecular events in single living cells

Fluorescence imaging could be the most powerful technique available for observing spatial and temporal dynamics of biomolecules in living cells, if fluorescent indicators for the relevant biomolecules become available. We have recently developed fluorescent indicators for a variety of second messengers or protein phosphorylations. Using the indicators, we have visualized spatial and temporal dynamics of these molecular events in single living cells. These fluorescent indicators are becoming an indispensable tool for understanding the complex mechanism of signal transduction in living cells.

Gap junctional intercellular communication in bovine corneal endothelial cells

Gap junctions and/or paracrine mediators, such as ATP, mediate intercellular communication (IC) in non-excitable cells. This study investigates the contribution of gap junctions toward IC during propagation of Ca(2+) waves in cultured bovine corneal endothelial cells (BCEC) elicited by applying a point mechanical stimulus to a single cell in a confluent monolayer. Changes in [Ca(2+)](i) were visualized using the fluorescent dye Fluo-4. The area reached by the Ca(2+) wave, called the active area (AA), was determined as a measure of efficacy of IC. RT-PCR and Western blotting showed expression of Cx43, a major form of connexin, in BCEC. In scrape-loading (using lucifer yellow) and fluorescence recovery after photobleaching (FRAP; using carboxyfluorescein) protocols, significant dye transfer of the hydrophilic dyes was evident indicating functional gap junctional IC (GJIC) in BCEC. Gap27 (300 microM), a connexin mimetic peptide that blocks gap junctions formed by Cx43, reduced the fluorescence recovery in FRAP experiments by 19%. Gap27 also reduced the active area of the Ca(2+) wave induced by point mechanical stimulation from 73,689 microm(2) to 26,936 microm(2), implying that GJIC contribution to the spread of the wave is at least approximately 63%. Inhibitors of ATP-mediated paracrine IC (PIC), such as a combination of apyrase VI and apyrase VII (5U/ml each; exogenous ATPases), suramin (200 microM; P2Y antagonist), or Gap26 (300 microM; blocker of Cx43 hemichannels) reduced the active area by 91%, 67%, and 55%, respectively. Therefore, estimating the contribution of GJIC from the residual active area after PIC inhibition appears to suggest that GJIC contributes no more than approximately 9% towards the active area of the Ca(2+) wave. Gap27 did not affect the enhancement in active area induced by ARL-67156 (200 microM, ectonucleotidase inhibitor), ATP release induced by point mechanical stimulation, and zero [Ca(2+)](o)-induced lucifer yellow uptake, indicating that the peptide has no influence on PIC. Exposure to Gap27 in the presence of PIC inhibitors led to a significant further inhibition of the Ca(2+) wave. The finding that the residual active area after inhibition of PIC by apyrases was much smaller than the reduction of the active area by Gap27, provides evidence for interaction between GJIC and PIC. These findings together suggest that functional gap junctions are present in BCEC, that both GJIC and PIC contribute significantly to IC, and that the two pathways interact.

Ethanol effects on electrophysiological properties of astrocytes in striatal brain slices

Ethanol (EtOH) is known to alter neuronal physiology, but much less is known about the actions of this drug on glial function. To this end, we examined acute effects of ethanol on resting and voltage-activated membrane currents in striatal astrocytes using rat brain slices. Ten minutes exposure to 50mM EtOH reduced slope conductance by 20%, increased input resistance by 25% and decreased capacitance by 38% but did not affect resting membrane potential. Current generated by a hyperpolarizing pulse was inhibited in a concentration dependent manner in passive astrocytes, while no significant EtOH effect was observed in complex astrocytes or neurons. The EtOH effect was blocked when intracellular KCl was replaced with CsCl, but not during chelation of intracellular calcium with BAPTA. During blockage of gap junction coupling with high intracellular CaCl(2) or extracellular carbenoxolone the EtOH effect persisted but was reduced. Interestingly, EtOH effects were largely irreversible when gap junctions were open, but were fully reversible when gap junctions were closed. Ethanol also reduced the spread to other cells of Lucifer Yellow dye from individual glia filled via the patch pipette. These data suggest that EtOH inhibits a calcium-insensitive potassium channel, most likely a passive potassium channel, but also affects gap junction coupling in a way that is sustained after ethanol withdrawal. Astrocytes play a critical role in brain potassium homeostasis, and therefore EtOH effects on astrocytic function could influence neuronal activity.

Analysis of mitochondria isolated from single cells

Bulk studies are not suitable to describe and study cell-to-cell variation, which is of high importance in biological processes such as embryogenesis, tissue differentiation, and disease. Previously, capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) was used to measure the properties of organelles isolated from millions of cells. As such, these bulk measurements reported average properties for the organelles of cell populations. Similar measurements for organelles released from single cells would be highly relevant to describe the subcellular variations among cells. Toward this goal, here we introduce an approach to analyze the mitochondria released from single mammalian cells. Osteosarcoma 143B cells are labeled with either the fluorescent mitochondrion-specific 10-N-nonyl acridine orange (NAO) or via expression of the fluorescent protein DsRed2. Subsequently, a single cell is introduced into the CE-LIF capillary where the organelles are released by a combined treatment of digitonin and trypsin. After this treatment, an electric field is applied and the released organelles electromigrate toward the LIF detector. From an electropherogram, the number of detected events per cell, their individual electrophoretic mobilities, and their individual fluorescence intensities are calculated. The results obtained from DsRed2 labeling, which is retained in intact mitochondria, and NAO labeling, which labels all mitochondria, are the basis for discussion of the strengths and limitations of this single-cell approach.

Classification of hepatitis B virus genotypes by the PCR-Invader method with genotype-specific probes

Hepatitis B virus is a worldwide public health problem. A simple and effective test to identify viral genotypes would greatly aid efforts to understand and control the spread of this disease. A serial invasive signal amplification reaction assay (PCR-Invader assay) was developed for distinguishing the known eight genotypes (A-H) and four subgenotypes (Aa, Ae, Ba, Bj) of hepatitis B virus (HBV). The preS/S and core regions were amplified by multiplex PCR and delivered to 12 wells containing genotype-specific Invader probes. By observing the fluorescence patterns in the wells, HBV sub/genotypes can be assigned. A total of 505 serum samples containing HBV/HBsAg in Japan was examined by PCR-Invader and compared the results with those from ELISA assays with monoclonal antibodies against epitopes on gene products of the preS2 region and with a genotype-specific probe assay (GSPA) based on the preS1 region. Genotypes determined by the PCR-Invader agreed with those of the ELISA method in 98.2% of cases and with the GSPA method in 97.1% of cases. Co-infection with two distinct genotypes was correctly identified by the PCR-Invader in four serum samples, as determined by GSPA. Thus, the PCR-Invader assay is a useful tool for detecting the 10 known HBV sub/genotypes.

Cell-matrix contact prevents recognition and damage of endothelial cells in states of heightened immunity

BACKGROUND

Autoimmunity may exacerbate vascular disease, particularly in the form of anti-endothelial cell (EC) antibodies. The increased morbidity of cardiovascular diseases in concert with diabetes mellitus, hypertension, and other systemic illnesses may reflect the increase presence and potency of these antibodies. Matrix-embedded ECs act as powerful regulators of vascular repair accompanied by significant reduction in expected systemic and local inflammation. We compared the immune response against free and matrix-embedded ECs in naïve mice and mice with heightened EC immune reactivity.

METHODS AND RESULTS

Mice were presensitized to EC with repeated (days 0, 21, 35) subcutaneous injections of saline-suspended porcine EC (PAE) (5 x 10(5) cells). Controls received saline injections. On day 42, mice received 5 x 10(5) matrix-embedded or free PAEs. Circulating PAE-specific antibodies and effector T-cells were analyzed via flow cytometry, and xenoreactive lymphocytes via ELISPOT, 90 days after implantation. PAE-specific antibody-titers, frequency of CD4+-effector cells, and xenoreactive splenocytes were 2- to 4-fold lower (P<0.0001) when naïve mice were injected with matrix-embedded instead of saline-suspended PAEs. Though basal levels of circulating antibodies were significantly elevated after serial PAE injections (2210+/-341 mean fluorescence intensity, day 42) and almost doubled again 90 days after injection of a fourth set of free PAEs, antibody levels declined by half in recipients of matrix-embedded PAEs at day 42 (P<0.0001). Levels of CD4+-effector cells and xenoreactive splenocytes showed similar results.

CONCLUSIONS

Implantation of free PAE elicits a significant immune response in naïve mice and even more pronounced in mice with predeveloped anti-endothelial immunity. Matrix-embedding protects xenogeneic ECs against immune reaction in naïve mice and to a similar extent in mice with heightened immune reactivity. Matrix-embedded EC might offer a promising approach for treatment of advanced cardiovascular disease.

Fluorescence energy transfer probes based on the guanine quadruplex formation for the fluorometric detection of potassium ion

Dual-labeled oligonucleotide derivative, FAT-0, carrying 6-carboxyfluorescein (FAM) and 6-carboxy-tetramethylrhodamine (TAMRA) labels at 5'- and 3'-termini of thrombin-binding aptamer (TBA) sequence 5'-GGTTGGTGTGGTTGG-3' and its derivatives, FAT-n (n=3, 5, and 7) were designed and synthesized. FAT-n derivatives contained a T(m)A spacer (m=2, 4, and 6, respectively) at 5'-end of TBA sequence. The probes were developed to estimate the spacer effect on FRET efficiency and to identify the best probe for sensing of K(+). Circular dichroism (CD), UV-vis absorption, and fluorescence studies revealed that all FAT-n probes could form the intramolecular tetraplex structures after binding K(+). Association constants of particular K(+)/FAT-n complexes were determined using different experimental approaches. Suitability of particular probes for sensitive monitoring of K(+) in intra- and extracellular conditions was examined and discussed. Calibration graphs of fluorescence ratio were linear in the K(+) concentration range of 2-10 mM for extracellular conditions showing sensitivity of 1.2% mM(-1) K(+) and for intracellular conditions in the range of 100-200 mM with sensitivity of 0.49% mM(-1) K(+).

Dendrimer-like DNA-based fluorescence nanobarcodes

A major challenge in clinical diagnostics and environmental analysis is the difficulty in rapid and sensitive detection of multiple target molecules simultaneously (i.e., multiplexed detections). Our group has designed and synthesized a dendrimer-like DNA (DL-DNA) that is multivalent and anisotropic; using this unique DNA structure, we have developed a fluorescence-tagged nanobarcode system for multiplex detection. This nanobarcode system allows the rapid and sensitive detection of multiple pathogens simultaneously using the ratios of two different fluorescent dyes, green and red, with which different DL-DNAs are labeled. The key step of our nanobarcode model lies in the monodisperse preparation of DL-DNA. Two methods, solution phase and solid phase, are presented here. With slight modifications, this platform technology can also be extended to the multiplexed detection of RNA and proteins. This protocol can be completed in 2-5 d.

A comparison of non-radioactive methods for assessing viability in ex vivo cultured cancellous bone: technical note

Biocompatibility studies are carried out either in two dimensional monolayer culture or in animal studies. Bone organ cultures are therefore required in order to reduce the number of animal studies performed, while at the same time ensuring a more natural environment than that provided by monolayer culture of isolated cells. Due to the three dimensional nature of bone explants, assays that determine the distribution of viable cells are required, however dense mineralised bone is not easily penetrated by soluble factors. We sought to compare a number of non-radioactive viability methods in order to assess their suitability for use with cancellous bone. Fluorescent live/dead staining, MTT activity and lactate dehydrogenase detection were all investigated on either whole bone explants (9.5 mm in diameter, 5 mm high) or on sections of explants. All these assays are routinely used in 2 dimensional cell culture systems, yet each required modifications to be suitable for use with cancellous bone. Factors such as penetration of reagent, incubation time, assay temperature and ease of determining viable cells were all compared. It was demonstrated that penetration of the reagents into whole cores was a major problem which easily led to artefacts that could be overcome by preparing 250 mum unfixed sections. Fluorescent live/dead staining had extra complications caused by the autofluorescence of the bone generating a high signal to noise ratio, making assessment of osteocyte viability impossible. MTT staining was difficult to interpret due to the punctate nature of the stain. We found that lactate dehydrogenase staining of 250 mum thick unfixed sections led to excellent viability determination of osteocytes within the mineralised matrix. It also maintained marrow structure and enabled marrow viability to be assessed as a factor of volume occupied by viable marrow. Decreasing the viscosity of the LDH assay solution used in published methods led to a greatly improved penetration into the calcified matrix. Quantification of thick sections is aided by using the autofluorescence of the bone to highlight the darkly stained osteocytes against the fluorescing bone.

Glucose utilization by the retinal pigment epithelium: Evidence for rapid uptake and storage in glycogen, followed by glycogen utilization

Glucose utilization and glycogen metabolism by human retinal pigment epithelium (RPE) cultures with high transepithelial resistance maintained on porous Millicell polycarbonate filters, were quantified by fluorophore-assisted carbohydrate electrophoresis (FACE). Glucose uptake was more efficient at the apical surface of the RPE. The utilization of glucose when restricted to either the apical or basal medium was also evaluated. Under both conditions, glucose was quickly transported to the opposite compartment and rapidly utilized. However, glucose from the apical compartment was depleted to a greater extent than from the basal compartment. The de novo synthesis and accumulation of glycogen accompanied glucose utilization. This was paralleled by a concomitant increase in lysosomal glycogen degradation measured as an increase in cell-associated maltodextrins. The highest levels of glucose in glycogen and maltodextrins occurred at 24 h, declining to basal levels at 72 h. Glucose transporter expression in the RPE cultures was evaluated with the reverse transcriptase-polymerase chain reaction. Glucose transporter-1 (GLUT 1) was the isoform expressed in these cells. GLUT 1 localization was determined by immunocytochemistry. GLUT 1 localizes to the apical and basolateral border of the RPE. The intensity of fluorescence was higher on the apical border. The rapid depletion of medium glucose suggests that RPE culture studies should replenish medium glucose more frequently than every 72 h to maintain physiologically relevant glucose concentrations. These studies are the first to demonstrate glucose, glycogen and maltodextrin metabolism by RPE cells, and their detection and quantitation by FACE.

Krypton laser photocoagulation induces retinal vascular remodeling rather than choroidal neovascularization

The purpose of this study is to analyze the retina and choroid response following krypton laser photocoagulation. Ninety-two C57BL6/Sev129 and 32 C57BL/6J, 5-6-week-old mice received one single krypton (630 nm) laser lesion: 50 microm, 0.05 s, 400 mW. On the following day, every day thereafter for 1 week and every 2-3 days for the following 3 weeks, serial sections throughout the lesion were systematically collected and studied. Immunohistology using specific markers or antibodies for glial fibrillary acidic protein (GFAP) (astrocytes, glia and Muller's cells), von Willebrand (vW) (vascular endothelial cells), TUNEL (cells undergoing caspase dependent apoptosis), PCNA (proliferating cell nuclear antigen) p36, CD4 and F4/80 (infiltrating inflammatory and T cells), DAPI (cell nuclei) and routine histology were carried out. Laser confocal microscopy was also performed on flat mounts. Temporal and spatial observations of the created photocoagulation lesions demonstrate that, after a few hours, activated glial cells within the retinal path of the laser beam express GFAP. After 48 h, GFAP-positive staining was also detected within the choroid lesion center. "Movement" of this GFAP-positive expression towards the lasered choroid was preceded by a well-demarcated and localized apoptosis of the retina outer nuclear layer cells within the laser beam path. Later, death of retinal outer nuclear cells and layer thinning at this site was followed by evagination of the inner nuclear retinal layer. Funneling of the entire inner nuclear and the thinned outer nuclear layers into the choroid lesion center was accompanied by "dragging" of the retinal capillaries. Thus, from days 10 to 14 after krypton laser photocoagulation onward, well-formed blood capillaries (of retinal origin) were observed within the lesion. Only a few of the vW-positive capillary endothelial cells stained also for PCNA p36. In the choroid, dilatation of the vascular bed occurred at the vicinity of the photocoagulation site and around it. Confocal microscopy demonstrates that the vessels throughout the path lesion are located within the neuroretina while in the choroid (after separation of the neural retina) only GFAP-positive but no lectin-positive cells can be seen. The involvement of infiltrating inflammatory cells in these remodeling and healing processes remained minimal throughout the study period. During the 4 weeks following krypton laser photocoagulation in the mouse eye, processes of wound healing and remodeling appear to be driven by cells (and vessels) originating from the retina.

The Neglected Pt−N(sulfonamido) Bond in Pt Chemistry. New Fluorophore-Containing Pt(II) Complexes Useful for Assessing Pt(II) Interactions with Biomolecules

Treatment of cis-Pt(Me2SO)2Cl2 with DNSH-tren afforded [Pt(DNSH-tren)Cl]Cl and with DNSH-dienH, under increasingly more basic conditions, led to Pt(DNSH-dienH)Cl(2), Pt(DNSH-dien)Cl, and Pt(DNS-dien). (DNSH = 5-(dimethylamino)naphthalene-1-sulfonyl, linked via a sulfonamide group to tris(2-aminoethyl)amine (DNSH-tren) and diethylenetriamine (DNSH-dienH); the H's in DNSH-dienH designate protons sometimes lost upon Pt binding, i.e., sulfonamide NH for the dienH moiety and H8 for the DNSH moiety). Respectively, the three neutral DNSH-dienH-derived complexes are difunctional, monofunctional, and nonfunctional and exhibit decreasing fluorescence in this order as the dansyl group distance to Pt decreases. 2D NMR data establish that Pt(DNS-dien) has a Pt-C8 bond and a Pt-N(sulfonamido) bond. Pt(DNSH-dien)Cl and [Pt(DNSH-tren)Cl]Cl bind to N7 of 6-oxopurines (e.g., 5'-GMP, 3'-IMP, and 9-ethylguanine) and sulfur of methionine (met). Competition and challenge reactions for Pt(II) with met and 5'-GMP typically reveal that met binding is favored kinetically but that 5'-GMP binding is favored thermodynamically. This common type of behavior was found for [Pt(DNSH-tren)Cl]Cl. In contrast, Pt(DNSH-dien)Cl had reduced kinetic selectivity for met. This unusual behavior undoubtedly arises as a consequence of the bound Pt-N(sulfonamido) group, which donates strongly to Pt (as indicated by relatively upfield dien NH signals) and which places the bulky DNSH moiety close to the monofunctional reaction site. The decrease in the relatively upfield shifts of the DNSH group signals indicates that this group stacks with the purine. This stacking could explain the unprecedented, relatively low reactivity of a Pt complex bearing a dien-type ligand toward met vs 5'-GMP.

Development and validation of a platelet calcium flux assay using a fluorescent imaging plate reader

Calcium signaling in platelets is an important physiological response to various aggregation stimuli. Loading platelets with various fluorescent dyes and measuring the change in calcium concentration using a spectrofluorometer has been the traditional approach to studying calcium signaling. This method suffers from the need for large platelet samples and a decrease in total fluorescence signal with time due to photobleaching. Therefore, it is rarely used to measure the quantitative effect of an agonist or antagonist on calcium signaling. Adaptation of these measurements to a fluorescent imaging plate reader (FLIPR) format allows the sample size to be reduced by 5- to 10-fold, and the microplate format allows a significant increase in throughput. Addition of the agonists to all wells simultaneously serves to normalize the total response. This article describes the first use of a FLIPR to study the calcium flux in human platelets. The IC(50) values showed a linear correlation with the K(i) for receptor binding in washed platelets. The generality of the methodology was shown by measuring EC(50) values for agonists and IC(50) values for antagonists of the platelet G protein-coupled receptor P2Y(1) and for the ion channel P2X(1).

Conditional gene modification in mouse liver using hydrodynamic delivery of plasmid DNA encoding Cre recombinase

The success of Cre-mediated conditional gene targeting in liver of mice has until now depended on the generation of Cre recombinase transgenic mice or on viral-mediated transduction. Here, we sought to establish the feasibility of using hydrodynamic gene delivery of Cre recombinase into liver, using a ROSA26 EGFP mouse. The expression of EGFP and beta-galactosidase was exclusively detected in the liver of mice treated with hydrodynamic gene delivery of Cre recombinase, as assessed with fluorescence microscopy and X-Gal staining, respectively; Southern blotting also showed that Cre mediated recombination occurred specifically in the liver and not in other organs. The Cre mediated recombination reached about 61% of hepatocytes of mouse after repeated injection, as analyzed by flow cytometry. These results demonstrate that Cre recombinase can be transferred to the liver of mice through a simple hydrodynamic gene-delivery approach and can mediate efficient recombination in hepatocytes. Thus, hydrodynamic gene delivery of the Cre recombinase provides a valuable approach for Cre-loxP-mediated conditional gene modification in the liver of mice.

Involvement of the Rho/Rac family member RhoG in caveolar endocytosis

We show here that the GTPase RhoG is involved in caveolar trafficking. Wild-type RhoG moves sequentially to the plasma membrane, intracellular vesicles, and the Golgi apparatus along markers of this endocytic pathway. Such translocation is associated with changes in RhoG GDP/GTP levels and is highly dependent on lipid raft integrity and on the function of the GTPase dynamin2. In addition, the constitutively active RhoG(Q61L) mutant is preferentially located in endocytic vesicles that can be decorated with markers of the caveola-derived endocytic pathway. RhoG(Q61L), but not the analogous Rac1 mutant protein, affects caveola internalization and the subsequent delivery of endocytic vesicles to the Golgi apparatus. The expression of RhoG/Rac1 chimeric proteins and RhoG(Q61L) effector mutants in cells induces alterations in the internalization of caveolae and severe changes in vesicle structure, respectively. However, the knockdown of endogenous rhoG transcripts using small interfering RNAs does not affect significantly the trafficking of caveola-derived vesicles, suggesting that RhoG function is dispensable for this endocytic process or, alternatively, that its function is compensated by other molecules. Taken together, these observations assign a novel function to RhoG and suggest that caveolar trafficking, as previously shown for other endocytic routes, is modulated by GTPases of the Ras superfamily.

Rapid evaluation of the efficacy of microbial cell removal from fabrics

The efficacy of microbial cell removal (EMR) from fabrics is a practically important indicator for the evaluation of cleansers and detergents. EMR is expressed quantitatively by the relative number of viable cells remaining on a fabric swatch after the treatment with these reagents. In order to count the viable cells on the swatch directly and rapidly, we have developed a unique microscopic imaging system with an ultra-deep focusing range. Standard swatches of cotton fabric were inoculated with microorganisms such as Pseudomonas fluorescence, Staphylococcus aureus, or Candida albicans. After the incubation on an agar medium, each swatch was treated with a fluorescent glucose, 2-[N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl) amino]-2-deoxyglucose, to stain only viable cells. The images of every cell distributed within the surface layer with no greater than 130 microm thickness could be integrated into one image. Thus visualized cells could be counted automatically by a novel imaging program. Using a pair of cotton swatches (0.5 x 1.0 cm(2)) inoculated with C. albicans, EMR was evaluated quantitatively. Before washing, the total number of viable cells found on the observation area (3.8 x 10(-4 )cm(2)) was 288 cells. After washing with a test detergent, no cell (<1) was detected. For this case, EMR was given by the formula: log(288/<1)=greater than 2.5. The imaging and cell count of a test fabric could be performed within 1 h.