High-pressure Freezing Method Research Articles

High pressure frozen oocytes have improved ultrastructure but reduced cleavage rates compared to conventionally fixed or vitrified oocytes.

Live birth rates are lower for cryopreserved oocytes than for fresh IVF cycles, indicating a need for improved methodologies. The aim of this study was to determine if high pressure freezing (HPF) could improve both ultrastructural preservation and cryopreserved oocyte quality when compared to conventional fixation and vitrification methods. Sheep oocytes and embryos were prepared by HPF or vitrification, with or without cryoprotectants. Frozen oocytes were prepared for transmission electron microscopy or warmed, in vitro fertilised and the recovery and cleavage rates recorded. Blastocyst rates were similar between fresh, HPF and vitrified embryos. HPF oocytes had improved ultrastructure compared to conventional fixation or vitrification, but had poorer survival and cleavage rates compared to vitrified oocytes. Freeze-substitution of cryopreserved oocytes and transmission electron microscopy demonstrated disruption of the oocyte ultrastructure in the presence of cryoprotectants. Superior preservation of ultrastructure was observed in HPF oocytes compared to vitrification or conventional fixation methods. In the presence of CP, both embryos and oocytes could survive HPF and warming but oocytes had reduced development. The HPF method has potential to be developed and lead to improved oocyte and embryo cryopreservation and outcomes for assisted reproduction.

High-Pressure Freezing and Transmission Electron Microscopy to Visualize the Ultrastructure of the C. auris Cell Wall.

Transmission electron microscopy (TEM) is the main technique used to study the ultrastructure of biological samples. Chemical fixation was considered the main method for preserving samples for TEM; however, it is a relatively slow method of fixation and can result in morphological alterations. Cryofixation using high-pressure freezing (HPF) overcomes the limitations of chemical fixation by preserving samples instantly. Here, we describe our HPF methods optimized for visualizing Candida auris at the ultrastructural level.

The in vitro Production Potentialities of Secondary Toxic Metabolites by the Fungal Factory Fusarium verticillioides Is, Fortunately, Largely Underestimated in Fields: Pioneering Study on Fumonisins.

This study presents fungi infrequently viewed as fungal factories for secondary metabolite production resources such as mycotoxins in Ascomycota. Additionally, we demonstrated that biochemical warfare of Fusarium verticillioides factory against animal cells is not only due to mycotoxins such as fumonisins, but acute cytotoxic firing is based on different excreted secondary metabolite series, potentially leading to animal and human diseases. In this study, fumonisins, which can be followed by in situ localization, quantification, or expression of the key gene implicated in their synthesis, are used to understand secondary metabolite production by this fungus. It is known that F. verticillioides produces mycotoxins such as fumonisins on cereals, but until now, there is no evidence demonstrating a method to totally block fumonisin production on feed and food. In this paper, we explained, what was never clearly established before, that fumonisin production depends on two bottlenecks. The fumonisin synthesis and secretion in fungal articles of the mycelium are medium-independent and follow the fungal cell cycle developmental program (ontogenesis). Conversely, the fumonisin excretion into the medium depends on its composition, which also impacts fumonisin biosynthesis level. Using a high-pressure freezing method, we showed that, in non-permissive fumonisin excretion (NPFE) medium, FB1 is sequestered inside extra-vesicles and in the first third of the cell wall next to the plasmalemma, leading to the hypothesis that the fungus develops mechanisms to protect its cytosolic homeostasis against this cytotoxic. In permissive fumonisin excretion (PFE) medium, leading to very high quantities of excreted fumonisins, FB1 localized inside extra-vesicles, crosses the entire cell wall thickness, and then releases into the medium. Our results demonstrated a delayed and lower expression of Fvpks gene in mycelium developed on NPFE medium as compared to PFE medium. Conversely, higher amounts of fumonisins were accumulated in NPFE-grown mycelium than in PFE-grown mycelium. Thus, our results demonstrated for the first time that we have to take into account that the synthesis and secretion inside the article of secondary metabolites depend on the occurrence of cryptic biochemical specialized articles, differentiated in the mycelium. However, those are not morphologically different from other colonial hyphae.

高圧凍結技法を取り入れた広域透過電顕像自動取得システムの開発とその応用

高圧凍結技法を取り入れた広域透過電顕像自動取得システムの開発とその応用

A method for efficient observation of intracellular membranes of monolayer culture cells by quick-freeze and freeze-fracture electron microscopy

We previously developed a method of analyzing the two-dimensional distribution of membrane lipids by combining quick-freezing and freeze-fracture replica labeling (QF-FRL). In principle, this method can be applied to any membrane, but in practice it is not easy to observe cytoplasmic organelles efficiently without ice crystal damage. In this paper, we report a modification of our method that circumvents this problem. In the modified method, cells are cultured on a gold foil scratched with sandpaper and quick-frozen according to a high-pressure freezing method. This technique enables the efficient observation of intracellular structures such as the nucleus, endoplasmic reticulum, Golgi apparatus and mitochondria. Specific labeling of phosphoinositide 4,5-bisphosphate was confirmed in the obtained freeze-fracture replica. The present QF-FRL method is easy to use and should expedite the analysis of intracellular lipid distribution.

Optimal preservation of the shark retina for ultrastructural analysis: An assessment of chemical, microwave, and high‐pressure freezing fixation techniques

Recent advances in microwave chemical fixation (MCF) and/or high pressure freezing (HPF) combined with transmission electron microscopy have resulted in superior ultrastructural detail in a variety of tissue types. To date, selachian tissue has been fixed and processed using only standard chemical fixation (CF) methods, and the resulting ultrastructure has been less than ideal. In this study, we compared the ultrastructure of the fragile retinal tissue from the brown banded bamboo shark, Chiloscyllium punctatum, obtained using CF, MCF, and HPF methods. For all fixation protocols, ultrastructural preservation was improved by keeping the tissue in oxygenated Ringer solution until the time of fixation. Both MCF and HPF produced superior retinal ultrastructure compared to conventional CF. Although HPF occasionally resulted in very high quality ultrastructure, microwave fixation was almost comparable, quicker and far more consistent.

Fast high-pressure freezing of protein crystals in their mother liquor.

High-pressure freezing (HPF) is a method which allows sample vitrification without cryoprotectants. In the present work, protein crystals were cooled to cryogenic temperatures at a pressure of 210 MPa. In contrast to other HPF methods published to date in the field of cryocrystallography, this protocol involves rapid sample cooling using a standard HPF device. The fast cooling rates allow HPF of protein crystals directly in their mother liquor without the need for cryoprotectants or external reagents. HPF was first attempted with hen egg-white lysozyme and cubic insulin crystals, yielding good to excellent diffraction quality. Non-cryoprotected crystals of the membrane protein photosystem II have been successfully cryocooled for the first time. This indicates that the presented HPF method is well suited to the vitrification of challenging systems with large unit cells and weak crystal contacts.

The use of cyanobacteria as filler in nitrocellulose capillaries improves ultrastructural preservation of immature barley pollen upon high pressure freezing

The high pressure freezing (HPF) followed by freeze substitution technique has advantages over chemical fixation in the context of preserving sample ultrastructure. However, when HPF is applied to cultured pollen grains, the large intercellular spaces present lead to a poor level of ultrastructure preservation. We report here that the mixing of cyanobacteria with immature barley pollen grains succeeded in greatly reducing the volume of liquid present between the large pollen grains, and so improved the loading of the sample into a nitrocellulose capillary. The use of yeast or cyanobacteria paste to surround the filled capillaries was beneficial in speeding the transfer of heat during the freezing process. This modification of the HPF method resulted in a greatly improved level of ultrastructure preservation.

High Pressure Freezing (HPF)을 이용한 조류 Ptilota filicina의 미세구조 관찰:HPF 고정법과 화학 고정법의 비교

In preparation of the biological samples for electron microscopy, the chemical fixation by glutaraldehyde, paraformaldehyde, and OsO4 has been generally used for a long time. However, the chemical fixation method has some problems: the infiltration time is a little bit long and the ultrastructure of cell or tissue transforms before complete fixation of sample. So, recently, cryo-fixation is considered more often in biomedical field. In this study, we compared High Pressure Freezing (HPF) method with chemical fixation method using a algal sample (Ptilota filicina J. Agardh), which was difficult to fix using chemical fixation method. In chloroplast, the ultrastructure of thylakoid lamella and phycobilisome can not show clearly by chemical fixation. In this study we could observe the ultrastructure of thylakoid lamella and phycobilisome of chloroplast very clearly using HPF fixation. An improved images of ultrastructures of nucleus, mitochondrion and floridean starch could obtain. These results suggest that HPF method is very useful method in algal specimen for electron microscopy.

Ultrastructural analysis of the behavior of the dimorphic fungus Microbotryum violaceum in fungus-induced anthers of female Silene latifolia flowers

The development of male organs is induced in female flowers of the dioecious plant Silene latifolia by infection with the fungus Microbotryum violaceum. Stamens in a healthy female flower grow only to stage 6, whereas those in an infected female flower develop to the mature stage (stage 12), at which the stamens are filled with fungal teliospores instead of pollen grains. To investigate these host-parasite interactions, young floral buds and fungus-induced anthers of infected female flowers were examined by electron microscopy following fixation by a high-pressure freezing method. Using this approach, we found that parasitic hyphae of this fungus contain several extracellular vesicles and have a consistent appearance up to stage 8. At that stage, parasitic hyphae are observed adjacent to dying sporogenous cells in the infected female anther. At stage 9, an increased number of dead and dying sporogenous cells is observed, among which the sporogenous hyphae of the fungus develop and form initial teliospores. Several types of electron-dense material are present in proximity to some fungi at this stage. The initial teliospores contain two types of vacuoles, and the fungus cell wall contains abundant carbohydrate, as revealed by silver protein staining. The sporogenous cell is probably sensitive to infection by the fungus, resulting in disruption. In addition, the fungus accelerates cell death in the anther and utilizes constituents of the dead host cell to form the mature teliospore.

"In vivo cryotechnique" for paradigm shift to "living morphology" of animal organs

The morphological study has been one of the major approaches in medical and biological fields. For the last century, the conventional chemical fixation and alcohol dehydration were commonly used as an easy preparation method, but it was frequently pointed out that they usually yield many structural artifacts during their preparation processes. Although both conventional quick-freezing and high-pressure freezing methods, by which animal tissues are resected and frozen for physical fixation,can reduce such structural artifacts, the tissues have to be removed from living animal organs for the freezing. Therefore, such specimens are inevitably exposed to noxious stresses of anoxia and ischemia, exhibiting only dead morphological states of animal tissues without blood circulation. To the contrary, our "in vivo cryotechnique", by which all cells and tissues in animal bodies are cryofixed in vivo, can prevent such artifacts of resected specimens. By means of the cryotechnique, it is now possible to reveal the in vivo morphology of cells and tissues in living animal organs. Actually, it has been already applied to several animal organs, such as kidney, liver, intestine, cerebellum, eye ball, blood vessel, and joint cartilage, and brought new morphological findings, reflecting their physiological significance, which had been difficult to demonstrate by the conventional preparation methods. Moreover, its application to immunohistochemistry has also revealed more precise immunolocalizations of dynamically changing molecules in living animal organs, easily translocated by ischemic stresses and anoxia caused during the tissue resection. The "in vivo cryotechnique" allows us to perform novel morphological investigations of "living" morphological states, and develops new medical and biological fields with "living morphology" during this 21st century. Biomedical Reviews 2004; 15: 1-19.

Electron microscopy of pathogenic yeasts Cryptococcus neoformans and Exophiala dermatitidis by high-pressure freezing.

A high-pressure freezing method was used to observe the ultrastructure of pathogenic yeasts, Cryptococcus neoformans and Exophiala dermatitidis, after freeze-substitution and ultrathin sectioning. The method well preserved the cell structure in its natural state, since the capsule, cell wall, plasma membrane, nucleus, outer and inner nuclear membranes, nuclear pores, nucleolus, mitochondria, mitochondrial membrane and cristae, vacuoles, endoplasmic reticulum, Golgi apparatus, spindle pole body, ribosomes, lipid droplets, microtubules, actin filaments, and glycogen granules were clearly visible. The method was shown to freeze cells as deep as 0.1 mm by sectioning the sample perpendicular to specimen surface. The quality of the cell image was similar to that obtained by a rapid freezing method when compared using the same materials. Thus, high-pressure freezing would be useful for making serial ultrathin sections for three-dimensional analysis of cells, which should give basic information of structure and function of pathogenic yeast cells necessary for finding an effective therapy for mycoses.

Cytochemical investigation of gastric gland component cells with high-pressure freezing followed by freeze-substitution and hydrophilic resin embedding.

Gastric gland component cells were electron-microscopically and immunoelectronmicroscopically examined with high-pressure freezing followed by freeze substitution and a low-temperature embedding resin method and compared to that of the conventional chemical-fixation method. The rat gastric gland was high-pressure frozen, freeze-substituted with acetone-containing osmium or acrolein, and embedded in Epon 812 or Lowicryl K4M, respectively. Using the high-pressure freezing method, the vitreous freezing range reached the depth of 150 microns from the surface. The ultrathin sections from both procedures embedding in Epon 812 and Lowicryl K4M were doubly stained with uranyl acetate and lead acetate, and histochemically or immunohistochemically stained, respectively. In comparison to the conventional chemical fixation method, excellent results were obtained with respect to ultrastructural preservation. The stainings performed in this experiment included periodic acid-thiocarbohydrazide-silver proteinate staining, cationic colloidal cold at pH 2.5 staining, Helix pomatia lectin-staining, anti-alpha or -beta subunit antibodies of H+K(+)-ATPase immunostaining and pepsinogen immunostaining. The staining intensity of those was stronger than that of the conventional immersion-chemical fixation method. In addition to these results, the labels also showed good specific localization. In this paper, we provide a description of the high-pressure freezing followed by freeze substitution and low-temperature embedding resin method compared to the conventional chemical-fixation method. Our results suggest that this method is a suitable tool for ultrastructural and histochemical/immunohistochemical studies at high resolution.

Fine structure of the extracellular sheath and cell walls inOphiostoma novo-ulmigrowing on various substrates

The presence of microfilamentous-like structures of tubular appearance (MFS) in cell walls and extracellular sheath material (ES) in a number of isolates of Ophiostoma novo-ulmi Brasier grown on various substrates and following various treatments is reported. Standard fixation or high-pressure freezing methods were used, and cytochemical tests were carried out to detect fungal and host wall components and, in some cases, fungal DNA. In some cases, serial 0.2-μm-thick sections were examined at 120 kV and tilted to obtain stereoscopic images. Whether the fungal cell walls were thick and composed of an outer opaque and inner more electron-lucent layers, or thin and barely perceptible, MFS were observed to extend from the cell cytoplasm as parallel structures across the walls into the surrounding medium, including host cell components in infected elm tissues. MFS were associated (in samples from inoculated trees) with cleavage and desquamation of fungal walls. ES and MFS did not label for cellulose or chitin, but generally labelled slightly for β-(1-3)-glucan and mannose, and strongly for galactose. Only the lucent, inner fungal wall layer labelled for chitin and cellulose. DNA labelling was confined to nuclei and mitochondria in fungal cells from cultures on agar medium; in cells from cultures on millipore membranes, it was pronounced over imprecisely delimited cell regions. The possible ontogeny of MFS components and their importance are discussed. Key words: chitin, Dutch elm disease, fungal fimbriae, fungal walls, gold-complexed probes, microfilamentous structures (MFS).

Immunolocalization of glyceraldehyde-3-phosphate dehydrogenase inArabidopsis thaliana

NAD-dependent glyceraldehyde-3-phosphate dehydrogenase (NAD-dependent GAPDH) was purified to homogeneity and injected into a rabbit to induce a polyclonal antibody. The antibody was judged to be of high specificity and high affinity. This antibody was used to probe sections ofArabidopsis leaf, stem or roots which were fixed using either paraformaldehyde or a high-pressure freezing method. Our results show that the NAD-dependent GAPDH localizes in the nucleus as well as in the cytosol. In phloem tissue, the NAD-dependent GAPDH was found in companion cells but not in the sieve element.

Elemental distribution in trace metal-treated Pisolithus tinctorius prepared by propane jet and high pressure freezing methods

Localization of trace metals on or within mycorrhizal (M) fungi may serve a protective function for roots of forest trees growing in soils containing high concentrations of metals such as Pb and Al. The presence of both Pb and Al have been demonstrated in the M fungus Pisolithus tinctorius after preparation by propane jet (PJ) freezing and freeze substitution. High pressure freezing (HPF) is an alternative method of cryopreparation that has demonstrated excellent ultrastructural preservation in studies of developing ascospores. The purpose of this study was to compare ultrastructural preservation and trace metal localization in P. tinctorius using PJ freezing and HPF methods.

Comparative ultrastructure of conventionally fixed and high-pressure frozen chloroplasts of Vitis vinifera

Chemical fixation of biological samples for transmission electron microscopy is still the most widely used method because of the availability of low cost chemicals and universal knowledge of the fixation protocol. Microscopists are very familiar with images of the chemically fixed cell with its irregular membranes, flattened Golgi cisternae, elongated mitochondria and football-shaped chloroplasts. But the advent of high quality ultra-rapid freezing techniques in the past decade or so has greatly increased our knowledge of cellular ultrastructure and altered our perception of biological material preserved in a “lifelike” state. While many of the best freezing techniques achieve a depth of well frozen tissue to only 10-40μm, the high pressure freezing method (HPM) yields well preserved tissue samples to approximately 600μm. Although the HPM is becoming more popular, it is still a relatively novel technique.