Cryo Samples Research Articles

Near-atomic resolution reconstructions from in situ revitrified cryo samples.

A microsecond time-resolved version of cryo-electron microscopy (cryo-EM) has recently been introduced to enable observation of the fast conformational motions of proteins. The technique involves locally melting a cryo sample with a laser beam to allow the proteins to undergo dynamics in the liquid phase. When the laser is switched off, the sample cools within just a few microseconds and revitrifies, trapping particles in their transient configurations, in which they can subsequently be imaged. Two alternative implementations of the technique have previously been described, using either an optical microscope or performing revitrification experiments in situ. Here, it is shown that it is possible to obtain near-atomic resolution reconstructions from in situ revitrified cryo samples. Moreover, the resulting map is indistinguishable from that obtained from a conventional sample within the spatial resolution. Interestingly, it is observed that revitrification leads to a more homogeneous angular distribution of the particles, suggesting that revitrification may potentially be used to overcome issues of preferred particle orientation.

Microsecond melting and revitrification of cryo samples with a correlative light-electron microscopy approach.

We have recently introduced a novel approach to time-resolved cryo-electron microscopy (cryo-EM) that affords microsecond time resolution. It involves melting a cryo sample with a laser beam to allow dynamics of the embedded particles to occur. Once the laser beam is switched off, the sample revitrifies within just a few microseconds, trapping the particles in their transient configurations, which can subsequently be imaged to obtain a snap shot of the dynamics at this point in time. While we have previously performed such experiments with a modified transmission electron microscope, we here demonstrate a simpler implementation that uses an optical microscope. We believe that this will make our technique more easily accessible and hope that it will encourage other groups to apply microsecond time-resolved cryo-EM to study the fast dynamics of a variety of proteins.

Microsecond melting and revitrification of cryo samples: protein structure and beam-induced motion.

A novel approach to time-resolved cryo-electron microscopy (cryo-EM) has recently been introduced that involves melting a cryo sample with a laser beam to allow protein dynamics to briefly occur in the liquid, before trapping the particles in their transient configurations by rapidly revitrifying the sample. With a time resolution of just a few microseconds, this approach is notably fast enough to study the domain motions that are typically associated with the activity of proteins but which have previously remained inaccessible. Here, crucial details are added to the characterization of the method. It is shown that single-particle reconstructions of apoferritin and Cowpea chlorotic mottle virus from revitrified samples are indistinguishable from those from conventional samples, demonstrating that melting and revitrification leaves the particles intact and that they do not undergo structural changes within the spatial resolution afforded by the instrument. How rapid revitrification affects the properties of the ice is also characterized, showing that revitrified samples exhibit comparable amounts of beam-induced motion. The results pave the way for microsecond time-resolved studies of the conformational dynamics of proteins and open up new avenues to study the vitrification process and to address beam-induced specimen movement.

Microsecond melting and revitrification of cryo samples.

The dynamics of proteins that are associated with their function typically occur on the microsecond timescale, orders of magnitude faster than the time resolution of cryo-electron microscopy. We have recently introduced a novel approach to time-resolved cryo-electron microscopy that affords microsecond time resolution. It involves melting a cryo sample with a heating laser, so as to allow dynamics of the proteins to briefly occur in the liquid phase. When the laser is turned off, the sample rapidly revitrifies, trapping the particles in their transient configurations. Precise control of the temperature evolution of the sample is crucial for such an approach to succeed. Here, we provide a detailed characterization of the heat transfer occurring under laser irradiation as well as the associated phase behavior of the cryo sample. While areas close to the laser focus undergo melting and revitrification, surrounding regions crystallize. In situ observations of these phase changes therefore provide a convenient approach for assessing the temperature reached in each melting and revitrification experiment and for adjusting the heating laser power on the fly.

Investigation of friction performance and surface integrity of cryogenically treated AISI 430 ferritic stainless steel

In this study, the effect of shallow cryogenic treatment on the friction coefficient of AISI 430 ferritic stainless steel was investigated. The friction coefficient experiments were carried out in a ball-on-disc wear tester under 5 N load at 400 rpm. As a result of the tests, the study examined the surface topography of the wear traces, the abrasion profile, microscopic images of the wear traces, and the hardness change of the wear traces. After applying shallow cryogenic treatment, the friction coefficient of the samples was increased by 7.5%. The micro hardness value around the wear traces of the cryogenic (Cryo) samples was 28.4% higher than the value for the commercial samples. The width of the wear trace of the Cryo samples was reduced by 44%. The average roughness value of the wear trace was 33.3% improved in the Cryo sample compared to the commercial sample.

Effect of composition and method of preparation of 2-hydroxyethyl methacrylate/gelatin hydrogels on biological in vitro (cell line) and in vivo (zebrafish) properties

We have studied the effect of compositions and methods of preparation on the physico-chemical and biocompatible behavior of the hydrogel matrices. Hydrogel matrices are synthesized by free radical polymerization of 2-hydroxyethyl methacrylate net and with gelatin. Highly porous hydrogel structures were obtained by porogenation, and by cryogenic treatment followed by freeze-drying. All samples were characterized for structural, morphological, absorption, degradation and in vitro (healthy human fibroblast cell line) and in vivo (zebrafish Danio rerio) biocompatible properties. The obtained results show that cryo samples, especially with gelatin show better, favorable absorption, morphological and biocompatible properties in comparison with PHEMA samples, which makes these materials highly attractive for biomedical uses.

The effect of pathogen inactivation on cryoprecipitate: a functional and quantitative evaluation.

As a pooled donor blood product, cryoprecipitate (cryo) carries risks of pathogen transmission. Pathogen inactivation (PI) improves the safety of cryoprecipitate, but its effects on haemostatic properties remain unclear. This study investigated protein expression in samples of pathogen inactivated cryoprecipitate (PI-cryo) using non-targeted quantitative proteomics and in vitro haemostatic capacity of PI-cryo. Whole blood (WB)- and apheresis (APH)-derived plasma was subject to PI with INTERCEPT® Blood System (Cerus Corporation, Concord, CA, USA) and cryo was prepared from treated plasma. Protein levels in PI-cryo and paired controls were quantified using liquid chromatography-tandem mass spectrometry. Functional haemostatic properties of PI-cryo were assessed using a microparticle (MP) prothrombinase assay, thrombin generation assay, and an in vitro coagulopathy model subjected to thromboelastometry. Over 300 proteins were quantified across paired PI-cryo and controls. PI did not alter the expression of coagulation factors, but levels of platelet-derived proteins and platelet-derived MPs were markedly lower in the WB PI-cryo group. Compared to controls, WB (but not APH) cryo samples demonstrated significantly lower MP prothrombinase activity, prolonged clotting time, and lower clot firmness on thromboelastometry after PI. However, PI did not affect overall thrombin generation variables in either group. Data from this study suggest that PI via INTERCEPT® Blood System does not significantly impact the coagulation factor content or function of cryo but reduces the higher MP content in WB-derived cryo. PI-cryo products may confer benefits in reducing pathogen transmission without affecting haemostatic function, but further in vivo assessment is warranted.

A fast cross-validation method for alignment of electron tomography images based on Beer-Lambert law.

In electron tomography, accurate alignment of tilt series is an essential step in attaining high-resolution 3D reconstructions. Nevertheless, quantitative assessment of alignment quality has remained a challenging issue, even though many alignment methods have been reported. Here, we report a fast and accurate method, tomoAlignEval, based on the Beer-Lambert law, for the evaluation of alignment quality. Our method is able to globally estimate the alignment accuracy by measuring the goodness of log-linear relationship of the beam intensity attenuations at different tilt angles. Extensive tests with experimental data demonstrated its robust performance with stained and cryo samples. Our method is not only significantly faster but also more sensitive than measurements of tomogram resolution using Fourier shell correlation method (FSCe/o). From these tests, we also conclude that while current alignment methods are sufficiently accurate for stained samples, inaccurate alignments remain a major limitation for high resolution cryo-electron tomography.

In-Focus Electrostatic Zach Phase Plate Imaging for Transmission Electron Microscopy with Tunable Phase Contrast of Frozen Hydrated Biological Samples

Transmission electron microscopy (TEM) images of beam sensitive weak-phase objects such as biological cryo samples usually show a very low signal-to-noise ratio. These samples have almost no amplitude contrast and instead structural information is mainly encoded in the phase contrast. To increase the sample contrast in the image, especially for low spatial frequencies, the use of phase plates for close to focus phase contrast enhancement in TEM has long been discussed. Electrostatic phase plates are favorable in particular, as their tunable potential will allow an optimal phase shift adjustment and higher resolution than film phase plates as they avoid additional scattering events in matter. Here we show the first realization of close to focus phase contrast images of actin filament cryo samples acquired using an electrostatic Zach phase plate. Both positive and negative phase contrast is shown, which is obtained by applying appropriate potentials to the phase plate. The dependence of phase contrast improvement on sample orientation with respect to the phase plate is demonstrated and single-sideband artifacts are discussed. Additionally, possibilities to reduce contamination and charging effects of the phase plate are shown.

In-situ integrity control of frozen-hydrated, vitreous lamellas prepared by the cryo-focused ion beam-scanning electron microscope

Recently a number of new approaches have been presented with the intention to produce electron beam transparent cryo-sections (lamellas in FIB-SEM terminology) from hydrated vitreously frozen cryo samples with a Focused Ion Beam (FIB) system, suitable for cryo-Transmission Electron Microscopy (cryo-TEM). As the workflow is still challenging and time consuming, it is important to be able to determine the integrity and suitability (cells vs. no cells; vitreous vs. crystalline) of the lamellas. Here we present an in situ method that tests both conditions by using the cryo-Scanning Electron Microscope (cryo-SEM) in transmission mode (TSEM; Transmission Scanning Electron Microscope) once the FIB-made lamella is ready. Cryo-TSEM imaging of unstained cells yields strong contrast, enabling direct imaging of material present in the lamellas. In addition, orientation contrast is shown to be suitable for distinguishing crystalline lamellas from vitreous lamellas. Tilting the stage a few degrees results in changes of contrast between ice grains as a function of the tilt angle, whereas the contrast of areas with vitreous ice remains unchanged as a function of the tilt angle. This orientation contrast has subsequently been validated by cryo-Electron BackScattered Diffraction (EBSD) in transmission mode. Integration of the presented method is discussed and the role it can play in future developments for a new and innovative all-in-one cryo-FIB–SEM life sciences instrument.

Abstract 2177: Long-term storage in TRIzol has little effect on microarray-based gene expression profiling in primary myeloma or acute myeloid leukemia cells

Abstract We used paired samples to address whether long-term storage of cells in TRIzol has a significant effect on microarray-based gene expression profiling (GEP). The TRIzol reagent is widely used for the preservation and isolation of RNA, but there is suspicion that prolonged storage of tissues prior to RNA isolation, even at −80 C., can cause chemical modification (depurination) of RNA. This could result in early termination during reverse transcription (RT) of mRNA molecules, potentially affecting GEP more strongly for transcripts with probes located farther from the 3’ end. The Myeloma and Leukemia Tissue Banks at M. D. Anderson Cancer Center routinely collect and store primary tumor samples for research under informed consent. From these banks we selected primary tumor samples of multiple myeloma (MM; CD138+) and acute myeloid leukemia (AML; Ficoll-purified, CD3- and CD19-depleted), for which paired aliquots had been stored frozen in TRIzol (“Tri”) or cryopreservation medium (RPMI + 20% FCS + 10% DMSO, “Cryo”) since the time of initial isolation (range, 2-9 years). Cryo aliquots were quickly thawed, washed, and placed in TRIzol, then total RNA was isolated from all aliquots as per the TRIzol manufacturer's instructions. RNA quality was assessed with a Bioanalyzer 2100 (Agilent); the RNA integrity number (RIN) was > 9 for 12/12 AML Tri, 6/12 AML Cryo, 6/6 MM Tri, and 3/6 MM Cryo samples. RNA from 12 sample pairs (6 AML, 6 MM, all with RIN > 7) was further purified with Qiagen RNAeasy columns, and the Illumina® TotalPrep RNA Amplification Kit (Ambion) was used to generate amplified, biotinylated cRNA after RT by the Eberwine procedure. Bioanalyzer-generated histograms of cRNA were similar for all sample aliquots, suggesting no early termination of RT due to TRIzol. GEP was performed with cRNA on Illumina HT-12 BeadArrays. Analysis of “probe-level” data with GenomeStudio software (Illumina), after median normalization, showed excellent concordance between sample Tri/Cryo pairs for all but probes with low intensities (<50). For the 48795 probes on the arrays, no more than 320 gave DiffScores < −13 or > 13 for any sample pair, and most pairs had <50 probes that differed. After exclusion of low-intensity values, hierarchical clustering associated all Tri aliquots with their corresponding Cryo aliquot. We conclude that long-term TRIzol storage has little effect on microarray-based GEP, and preserves RNA quality better than does cryopreservation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2177.

PTPIP51 mRNA and protein expression in tissue microarrays and promoter methylation of benign prostate hyperplasia and prostate carcinoma

Protein tyrosine phosphatase interacting protein 51 (PTPIP51) shows a tissue-specific expression pattern and is associated with cellular differentiation and apoptosis in several mammalian tissues. Overexpression of the full-length protein enhances apoptosis. It is also expressed in various carcinomas. In this study the expression of PTPIP51 and its in vitro interaction partners was investigated in human benign prostate hyperplasia (BPH) and in prostate carcinoma (PCa). Tissue microarrays of human BPH and PCa were analyzed by immunohistochemistry. For polymerase chain reaction (PCR), cryo samples of BPH and PCa were used. Bisulfite DNA treatment, followed by sequencing of PCR products was performed in order to analyze CpGs methylation within the promoter region of the PTPIP51 gene. PTPIP51 mRNA and protein expression was detected in prostatic epithelia of BPH and in tumor cells of PCa, respectively, and within smooth muscle cells of the stromal compartment. A stronger expression was present in nerve fibers, particularly in PCa, in immune cells and in smooth muscle and endothelial cells of vessels of BPH and PCa. On mRNA levels, a slightly elevated expression of PTPIP51 was observed in the PCa group as tested by real-time quantitative PCR analyses. Methylation experiments revealed that at least 70% of methylated CpGs in the CpG island of the PTPIP51 gene promoter region were identified in BPH samples. In contrast, a loss of methylation has been found in the PCa group. The promoter methylation status of PTPIP51 seems to influence the expression of PTPIP51, which was seen as elevated in the PCa.