Quetol 651: Not just a low viscosity resin.

Quetol 651, a low viscosity epoxy resin, is miscible with alcohols, acetone, and water. It is versatile and can be used as a single epoxide or mixed with other epoxides and anhydrides. The most important characteristic is that the addition of Quetol 651 to a formulation results in a lower viscosity embedding medium and allows for good detection of antigenic activity. Properly formulated and mixed resins containing Quetol 651 have excellent sectioning properties and good beam stability. The decrease in viscosity lends to lower specific gravity of the embedding medium and less interfering electron density between specimen elements resulting in better spatial resolution. New formulations and viscosity data are presented and compared to long used, embedding formulations and the extensive uses of Quetol 651 are reviewed.

Regulation of extracellular matrix organization by BMP signaling in Caenorhabditis elegans.

In mammals, Bone Morphogenetic Protein (BMP) pathway signaling is important for the growth and homeostasis of extracellular matrix, including basement membrane remodeling, scarring, and bone growth. A conserved BMP member in Caenorhabditis elegans, DBL-1, regulates body length in a dose-sensitive manner. Loss of DBL-1 pathway signaling also results in increased anesthetic sensitivity. However, the physiological basis of these pleiotropic phenotypes is largely unknown. We created a DBL-1 over-expressing strain and show that sensitivity to anesthetics is inversely related to the dose of DBL-1. Using pharmacological, genetic analyses, and a novel dye permeability assay for live, microwave-treated animals, we confirm that DBL-1 is required for the barrier function of the cuticle, a specialized extracellular matrix. We show that DBL-1 signaling is required to prevent animals from forming tail-entangled aggregates in liquid. Stripping lipids off the surface of wild-type animals recapitulates this phenotype. Finally, we find that DBL-1 signaling affects ultrastructure of the nematode cuticle in a dose-dependent manner, as surface lipid content and cuticular organization are disrupted in animals with genetically altered DBL-1 levels. We propose that the lipid layer coating the nematode cuticle normally prevents tail entanglement, and that reduction of this layer by loss of DBL-1 signaling promotes aggregation. This work provides a physiological mechanism that unites the DBL-1 signaling pathway roles of not only body size regulation and drug responsiveness, but also the novel Hoechst 33342 staining and aggregation phenotypes, through barrier function, content, and organization of the cuticle.

Comparing the detection of iron-based pottery pigment on a carbon-coated sherd by SEM-EDS and by Micro-XRF-SEM.

The same sherd was analyzed using a scanning electron microscope with energy dispersive spectroscopy (SEM-EDS) and a micro X-ray fluorescence tube attached to a scanning electron microscope (Micro-XRF-SEM) to compare the effectiveness of elemental detection of iron-based pigment. To enhance SEM-EDS mapping, the sherd was carbon coated. The carbon coating was not required to produce Micro-XRF-SEM maps but was applied to maintain an unbiased comparison between the systems. The Micro-XRF-SEM analysis was capable of lower limits of detection than that of the SEM-EDS system, and therefore the Micro-XRF-SEM system could produce elemental maps of elements not easily detected by SEM-EDS mapping systems. Because SEM-EDS and Micro-XRF-SEM have been used for imaging and chemical analysis of biological samples, this comparison of the detection systems should be useful to biologists, especially those involved in bone or tooth (hard tissue) analysis.

Photoinduced membrane damage of E. coli and S. aureus by the photosensitizer-antimicrobial peptide conjugate eosin-(KLAKLAK)2.

BACKGROUND/OBJECTIVES: Upon irradiation with visible light, the photosensitizer-peptide conjugate eosin-(KLAKLAK)2 kills a broad spectrum of bacteria without damaging human cells. Eosin-(KLAKLAK)2 therefore represents an interesting lead compound for the treatment of local infection by photodynamic bacterial inactivation. The mechanisms of cellular killing by eosin-(KLAKLAK)2, however, remain unclear and this lack of knowledge hampers the development of optimized therapeutic agents. Herein, we investigate the localization of eosin-(KLAKLAK)2 in bacteria prior to light treatment and examine the molecular basis for the photodynamic activity of this conjugate. METHODOLOGY/PRINCIPAL FINDINGS: By employing photooxidation of 3,3-diaminobenzidine (DAB), (scanning) transmission electron microscopy ((S)TEM), and energy dispersive X-ray spectroscopy (EDS) methodologies, eosin-(KLAKLAK)2 is visualized at the surface of E. coli and S. aureus prior to photodynamic irradiation. Subsequent irradiation leads to severe membrane damage. Consistent with these observations, eosin-(KLAKLAK)2 binds to liposomes of bacterial lipid composition and causes liposomal leakage upon irradiation. The eosin moiety of the conjugate mediates bacterial killing and lipid bilayer leakage by generating the reactive oxygen species singlet oxygen and superoxide. In contrast, the (KLAKLAK)2 moiety targets the photosensitizer to bacterial lipid bilayers. In addition, while (KLAKLAK)2 does not disrupt intact liposomes, the peptide accelerates the leakage of photo-oxidized liposomes. CONCLUSIONS/SIGNIFICANCE: Together, our results suggest that (KLAKLAK)2 promotes the binding of eosin Y to bacteria cell walls and lipid bilayers. Subsequent light irradiation results in membrane damage from the production of both Type I & II photodynamic products. Membrane damage by oxidation is then further aggravated by the (KLAKLAK)2 moiety and membrane lysis is accelerated by the peptide. These results therefore establish how photosensitizer and peptide act in synergy to achieve bacterial photo-inactivation. Learning how to exploit and optimize this synergy should lead to the development of future bacterial photoinactivation agents that are effective at low concentrations and at low light doses.

Staining sectioned biological specimens for transmission electron microscopy: conventional and en bloc stains.

Post-staining of ultrathin sections and/or en bloc staining of specimens is necessary for differential contrast and improved resolution of cellular structures. Often specimens are fixed and stained with osmium tetroxide during fixation, but additional contrast is the result of additional heavy metal stains on the sections. The most common post-staining of sections is done on grids by aqueous uranyl acetate followed by lead citrate. When it is apparent that simple, aqueous uranium and lead post-staining is not adequate, other stains are invoked. These procedures can be as simple as en bloc staining with uranyl acetate after primary fixation and osmication. Over the years, several other treatments have been developed for use with the primary fixation or during dehydration. Tannic acid, paraphenylenediamine (PPD), and malachite green can all serve as en bloc stains and can contribute to overall improved visualization of ultrastructural details in biological specimens. Tannic acid and PPD improve membrane preservation, and malachite green is a phospholipid stain. All of these stains are compatible with aqueous fixatives and should be considered when the usual stains are not satisfactory. Marinozzi rings and microwave-assisted post-staining offer alternatives to traditional grid staining. In addition, stain precipitates on grids often can be removed by treatment with 10 % (v/v) acetic acid.

Understanding E. coli internalization in lettuce leaves for optimization of irradiation treatment.

Irradiation penetrates food tissues and effectively reduces the number of food microorganisms in fresh produce, but the efficacy of the process against internalized bacteria is unknown. The objective of this study was to understand the mechanisms of pathogen colonization of plants relative to lettuce leaf structures so that radiation treatment of fresh leafy vegetables can be optimized. Leaves of iceberg, Boston, green leaf, and red leaf lettuces were cut into pieces, submerged in a cocktail mixture of two isolates of Escherichia coli (Rifampicin resistant), and subjected to a vacuum perfusion process to force the bacterial cells into the intercellular spaces in the leaves. Sixty bags containing 20g of lettuce each were tested. The inoculated leaves were gamma irradiated (Lanthanum-140, 0.16kGy/h) at 0.25-1.0-kGy (surface dose values), with increments of 0.25kGy at 15 degrees C. Microbial analysis was performed right after irradiation, including non-irradiated leaf pieces (controls). A dose uniformity ratio (max/min dose) of 2.8 was set to confirm the effect of non-uniform dose distribution. Calculated D(10)-values varied between 48 and 62% based on the dose distribution from the entrance dose. However, despite the subtle differences in composition and structure among the four lettuce varieties, the D(10)-values were not significantly different. Irradiation up to 1.0-kGy resulted in 3-4-log reduction of internalized E. coli on the lettuce leaves. The SEM images suggest that the contamination sites of pathogens in leafy vegetables are mainly localized on crevices and into the stomata. This study shows that irradiation effectively reduces viable E. coli cells internalized in lettuce, and decontamination is not influenced by lettuce variety. Ionizing irradiation effectively reduced the population of internalized pathogen in a dose-dependent manner and could be used as an effective killing step to mitigate the risk of foodborne disease outbreaks.

Biophysical characterization of the iron in mitochondria from Atm1p-depleted Saccharomyces cerevisiae.

Atm1p is an ABC transporter localized in the mitochondrial inner membrane; it functions to export an unknown species into the cytosol and is involved in cellular iron metabolism. Depletion or deletion of Atm1p causes Fe accumulation in mitochondria and a defect in cytosolic Fe/S cluster assembly but reportedly not a defect in mitochondrial Fe/S cluster assembly. In this study the nature of the accumulated Fe was examined using Mossbauer spectroscopy, EPR, electronic absorption spectroscopy, X-ray absorption spectroscopy, and electron microscopy. The Fe that accumulated in aerobically grown cells was in the form of iron(III) phosphate nanoparticles similar to that which accumulates in yeast frataxin Yfh1p-deleted or yeast ferredoxin Yah1p-depleted cells. Relative to WT mitochondria, Fe/S cluster and heme levels in Atm1p-depleted mitochondria from aerobic cells were significantly diminished. Atm1p depletion also caused a buildup of nonheme Fe(II) ions in the mitochondria and an increase in oxidative damage. Atm1p-depleted mitochondria isolated from anaerobically grown cells exhibited WT levels of Fe/S clusters and hemes, and they did not hyperaccumulate Fe. Atm1p-depleted cells lacked Leu1p activity, regardless of whether they were grown aerobically or anaerobically. These results indicate that Atm1p does not participate in mitochondrial Fe/S cluster assembly and that the species exported by Atm1p is required for cytosolic Fe/S cluster assembly. The Fe/S cluster defect and the Fe-accumulation phenotype, resulting from the depletion of Atm1p in aerobic cells (but not in anaerobic cells), may be secondary effects that are observed only when cells are exposed to oxygen during growth. Reactive oxygen species generated under these conditions might degrade iron-sulfur clusters and lower heme levels in the organelle.

Regulation of adult hematopoietic stem cells fate for enhanced tissue-specific repair.

The ability to control the differentiation of adult hematopoietic stem cells (HSCs) would promote development of new cell-based therapies to treat multiple degenerative diseases. Systemic injection of NaIO(3) was used to ablate the retinal pigment epithelial (RPE) layer in C57Bl6 mice and initiate neural retinal degeneration. HSCs infected ex vivo with lentiviral vector expressing the RPE-specific gene RPE65 restored a functional RPE layer, with typical RPE phenotype including coexpression of another RPE-specific marker, CRALBP, and photoreceptor outer segment phagocytosis. Retinal degeneration was prevented and visual function, as measured by electroretinography (ERG), was restored to levels similar to that found in normal animals. None of the controls (no HSCs, HSCs alone and HSCs infected with lentiviral vector expressing LacZ) showed these effects. In vitro gene array studies demonstrated that infection of HSC with RPE65 increased adenylate cyclase mRNA. In vitro exposure of HSCs to a pharmacological agonist of adenylate cyclase also led to in vitro differentiation of HSCs to RPE-like cells expressing pigment granules and the RPE-specific marker, CRALBP. Our data confirm that expression of the cell-specific gene RPE65 promoted fate determination of HSCs toward RPE for targeted tissue repair, and did so in part by activation of adenylate cyclase signaling pathways. Expression by HSCs of single genes unique to a differentiated cell may represent a novel experimental paradigm to influence HSC plasticity, force selective differentiation, and ultimately lead to identification of pharmacological alternatives to viral gene delivery.

Improved protein detection using cold microwave technology.

Protein screening/detection is an essential tool in many laboratories. Owing to the relatively large time investments that are required by standard protocols, the development of methods with higher throughput while maintaining an at least comparable signal-to-noise ratio would be highly beneficial to many researchers. This chapter describes how cold microwave technology can be used to enhance the rate of molecular interactions and provides protocols for dot blots, western blots, and ELISA procedures permitting a completion of all incubation steps (blocking and antibody steps) within 45 min.

Correlative transmission microscopy: cytochemical localization and immunocytochemical localization in studies of oxidative and nitrosative stress.

Microscopy studies of oxidative stress have often consisted of only immunocytochemical localization or only cytochemical localization studies. However, correlative studies on the same sections provide more useful data in interpreting oxidative and nitrosative stress. Cellular sites of superoxide and hydrogen peroxide production can be identified using cerium-based cytochemical localization of NADH oxidase enzymatic activity, while areas of nitrosative stress can be identified by immunocytochemical localization of nitrotyrosine in the same sections of tissue.

EPR and Mössbauer spectroscopy of intact mitochondria isolated from Yah1p-depleted Saccharomyces cerevisiae.

Yah1p, an [Fe 2S 2]-containing ferredoxin located in the matrix of Saccharomyces cerevisiae mitochondria, functions in the synthesis of Fe/S clusters and heme a prosthetic groups. EPR, Mossbauer spectroscopy, and electron microscopy were used to characterize the Fe that accumulates in Yah1p-depleted isolated intact mitochondria. Gal- YAH1 cells were grown in standard rich media (YPD and YPGal) under O 2 or argon atmospheres. Mitochondria were isolated anaerobically, then prepared in the as-isolated redox state, the dithionite-treated state, and the O 2-treated state. The absence of strong EPR signals from Fe/S clusters when Yah1p was depleted confirms that Yah1p is required in Fe/S cluster assembly. Yah1p-depleted mitochondria, grown with O 2 bubbling through the media, accumulated excess Fe (up to 10 mM) that was present as 2-4 nm diameter ferric nanoparticles, similar to those observed in mitochondria from yfh1Delta cells. These particles yielded a broad isotropic EPR signal centered around g = 2, characteristic of superparamagnetic relaxation. Treatment with dithionite caused Fe (3+) ions of the nanoparticles to become reduced and largely exported from the mitochondria. Fe did not accumulate in mitochondria isolated from cells grown under Ar; a significant portion of the Fe in these organelles was in the high-spin Fe (2+) state. This suggests that the O 2 used during growth of Gal- YAH1 cells is responsible, either directly or indirectly, for Fe accumulation and for oxidizing Fe (2+) --> Fe (3+) prior to aggregation. Models are proposed in which the accumulation of ferric nanoparticles is caused either by the absence of a ligand that prevents such precipitation in wild-type mitochondria or by a more oxidizing environment within the mitochondria of Yah1p-depleted cells exposed to O 2. The efficacy of reducing accumulated Fe along with chelating it should be considered as a strategy for its removal in diseases involving such accumulations.

Poststaining grids for transmission electron microscopy: conventional and alternative protocols.

Poststaining ultrathin sections on grids is an essential process in preparing specimens for examination using transmission electron microscopy. This process commonly consists of staining in aqueous solutions of uranyl acetate followed by lead citrate and can result in good consistent quality staining if certain precautions are taken. This chapter covers conventional and alternative methods for poststaining ultrathin sections, including microwave-assisted procedures and corrective measures when problems are encountered.

Quantification and confocal imaging of protein specific molecularly imprinted polymers.

We have employed FITC--albumin as the protein template molecule in an aqueous phase molecular imprinted polymer (HydroMIP) strategy. For the first time, the use of a fluorescently labeled template is reported, with subsequent characterization of the smart material to show that the HydroMIP possesses a significant molecular memory in comparison to that of the nonimprinted control polymer (HydroNIP). The imaging of the FITC--albumin imprinted HydroMIP using confocal microscopy is described, with the in situ removal of the imprinted protein displayed in terms of observed changes in the fluorescence of the imprinted polymer, both before and after template elution (using a 10% SDS/10% AcOH (w/v) solution). We also report the imaging of a bovine hemoglobin (BHb) imprinted HydroMIP using two-photon confocal microscopy and describe the effects of template elution upon protein autofluorescence. The findings further contribute to the understanding of aqueous phase molecular imprinting protocols and document the use of fluorescence as a useful tool in template labeling/detection and novel imaging strategies.

Bone marrow-derived cells home to and regenerate retinal pigment epithelium after injury.

PURPOSE: To determine whether hematopoietic stem and progenitor cells (HSCs/HPCs) can home to and regenerate the retinal pigment epithelium (RPE) after induced injury. METHODS: Enriched HSCs/HPCs from green fluorescent protein (gfp) transgenic mice were transplanted into irradiated recipient mice to track bone marrow-derived cells. Physical damage was induced by breaching Bruch's membrane and inducing vascular endothelial growth factor A (VEGFa) expression to promote neovascularization. RPE damage was also induced by sodium iodate injection (40 mg/kg) into wild-type or albino C57Bl/6 mice. Cell morphology, gfp expression, the presence of the Y chromosome, and the presence of melanosomes were used to determine whether the injured RPE was being repaired by the donor bone marrow. RESULTS: Injury to the RPE recruits HSC/HPC-derived cells to incorporate into the RPE layer and differentiate into an RPE phenotype. A portion of the HSCs/HPCs adopt RPE morphology, express melanosomes, and integrate into the RPE without cell fusion. CONCLUSIONS: HSCs/HPCs can migrate to the RPE layer after physical or chemical injury and regenerate a portion of the damaged cell layer.

Nitric oxide synthases modulate progenitor and resident endothelial cell behavior in galactosemia.

We used knockout animals of either inducible nitric oxide synthase (iNOS(/)) or endothelial NOS (eNOS(/)) to characterize the role of NOS in galactosemia, a model of diabetic retinopathy. NADH oxidase and nitrotyrosine were used as biomarkers of oxidative stress and vascular dysfunction. These animals were engrafted with hematopoietic stem cells (HSC) expressing green fluorescence protein (gfp(+)) to characterize the contribution of HSC and endothelial progenitor cells to neovascularization. Increased NADH oxidase activity and superoxide generation occurred in all galactose-fed mice. eNOS(/) mice demonstrated increased iNOS immunoreactivity in their retinal vasculature. Nitrotyrosine levels were low at baseline in the wild-type (WT) mice, eNOS(/) and iNOS(/) mice, and the galactose-fed iNOS mice and increased following galactose feeding in eNOS(/) and WT. Galactose-fed WT.gfp and iNOS(/).gfp chimeric animals had areas of perfused new vessels composed of gfp(+) cells. In contrast, galactose-fed eNOS(/).gfp mice produced copious, unbranched, nonperfused tubes. Thus, nitric oxide modulates HSC behavior and vascular phenotype in the retina. Although there is increased NADH oxidase and superoxide in galactosemic mice of all isoforms, iNOS is the source of nitric oxide responsible for peroxynitrite and nitrotyrosine formation that leads to the pathology observed in galactosemic mice.

Time course of NADH oxidase, inducible nitric oxide synthase and peroxynitrite in diabetic retinopathy in the BBZ/WOR rat.

This study investigated the time course of NADH oxidase, a source of superoxide in the vascular endothelium, inducible nitric oxide synthase (iNOS), and peroxynitrite (ONOO(-)) in the BBZ/Wor rat, a spontaneous model of noninsulin dependent diabetes (NIDDM). Colloidal gold-labeled immunocytochemical studies of iNOS and nitrotyrosine, a marker for OONO(-), were done on sections of retinas from male BBZ/Wor rats in which NADH oxidase was localized by cerium derived cytochemistry at three time points: pre-diabetes (prior to the onset of hyperglycemia); new onset diabetes (2-6 days after onset of hyperglycemia); and chronic diabetes (4-18 months after onset of hyperglycemia). Control retinas were from age matched non-diabetic BB(DR)/Wor rats. The percentage of blood vessels positive for NADH oxidase increased significantly (P = 0.05) in new onset (64.2 +/- 6.5%) and chronic diabetes (83.2 +/- 11.4%), as compared to pre-diabetes (25.8 +/- 5.6%) and nondiabetic controls (33.6 +/- 15.9%). The percentage of blood vessels positive for iNOS immunoreactivity was significantly higher in new onset diabetic retinas (69.6 +/- 5.88%, P = 0.0001; 8.9 +/- 3.29 colloidal gold particles (cgp) /50 microm(2)) than in chronic diabetic retinas (49.9 +/- 9.75%; 7.9 +/- 5.12 cgp) and both were significantly higher (P = 0.0001) than in prediabetic (3.7 +/- 0.81%; 0.4 +/- 0.56 cgp) and nondiabetic control retinas (8.7 +/- 4.66%; 1.2 +/- 1.40 cgp). In new onset diabetes, levels of nitrotyrosine immunoreactivity (60.8 +/- 16.91 cgp) were significantly higher (P = 0.0001) than those in chronic diabetes (29.5 +/- 4.31 cgp); both were significantly higher (P = 0.0001) than those in prediabetic (8.2 +/- 1.70 cgp) and nondiabetic retinas (9.0 +/- 1.87 cgp). There was no cumulative increase in nitrotyrosine in the chronic diabetic retinas as a function of time. In rats with diabetes there was disruption of the inner blood-retinal barrier. These results suggest that iNOS and ONOO(-) may contribute to retinal damage in diabetes from the onset of hyperglycemia in NIDDM.

Lipid hydroperoxide stimulates subretinal choroidal neovascularization in the rabbit.

The authors sought to evaluate the effect of linoleic acid hydroperoxide (18:2/LHP) in promoting choroidal neovascularization (CNV). Albino male rabbits received a subretinal injection of various amounts of LHP (ranging from 5 to 200 microg) dissolved in 50 microl of sodium borate buffer. Control eyes received the buffer only. Eyes were examined up to 4 weeks later with indirect ophthalmoscopy, fundus photography and fluorescein angiography. Animals were killed on days 3, 7, 14 or 28, and eyes examined by light and transmission electron microscopy. In eyes injected with LHP of 150-200 microg, exposed areas turned white as observed ophthalmoscopically and showed both severe retinal and choroidal atrophy histologically. Neither fluorescein leakage nor CNV was found in these eyes or in controls. In 33 eyes injected with LHP of 100 microg or less, prominent fluorescein leakage was seen in three (9%) and less prominent focal leakage in five (15%). In 11 (46%) of the 24 eyes injected with 12.5-50 microg LHP, CNV was found histologically. Subretinal injection of LHP is capable of inducing CNV.