Damage from ice and potential toxicity of ice-inhibiting cryoprotective agents (CPAs) are key issues in assisted reproduction of humans, domestic and research animals, and endangered species using cryopreserved oocytes and embryos. The nature of ice formed in bovine oocytes (similar in size to oocytes of humans and most other mammals) after rapid cooling and during rapid warming was examined using synchrotron-based time-resolved x-ray diffraction. Using cooling rates, warming rates and CPA concentrations of current practice, oocytes show no ice after cooling but always develop large ice fractions-consistent with crystallization of most free water-during warming, so most ice-related damage must occur during warming. The detailed behavior of ice at warming depended on the nature of ice formed during cooling. Increasing cooling rates allows oocytes soaked as in current practice to remain essentially ice free during both cooling and warming. Much larger convective warming rates are demonstrated and will allow routine ice-free cryopreservation with smaller CPA concentrations. These results clarify the roles of cooling, warming, and CPA concentration in generating ice in oocytes and establish the structure and grain size of ice formed. Ice formation can be eliminated as a factor affecting post-warming oocyte viability and development in many species, improving outcomes and allowing other deleterious effects of the cryopreservation cycle to be independently studied.

BACKGROUND: Vitrification is commonly used for in vitro fertilization and has significant impact on gametes.
OBJECTIVE: To investigate changes in ultrastructure, membrane potential and distribution of mitochondria in mouse oocytes after vitrification.
METHODS: Mouse oocytes were divided into three groups: one group as fresh control, one group for the toxicity test (treated with cryoprotectant but without vitrification), and the other for vitrification.
RESULTS: Most mitochondria in oocytes were damaged after cooling and warming, being rough and fuzzy in appearance, even swollen and broken. The membrane potential of the toxicity test group and the vitrification group was 0.320 +/-0.030 and 0.244 +/- 0.038, respectively, in comparison to the fresh group (0.398 +/- 0.043). The membrane potential of the vitrified oocytes was significantly lower than fresh oocytes and the toxicity test oocytes (P % 0.05), but there was no significant difference between fresh oocytes and the toxicity test oocytes (P > 0.05). Mitochondria in fresh oocytes were denser and strained stronger, with 59.5> distributed homogeneously and 36.4> polarized. The majority of mitochondria in the toxicity-tested oocytes were clustered (69.3>) and only a small portion were distributed homogeneously (19.6>), while mitochondria in vitrified oocytes were clustered (56.3>) and deficient (24.4>), and their fluorescent staining was weak and blurred. There was a significant disruption in mitochondrial function after vitrification.
CONCLUSIONS: Vitrification alters the ultrastructure, membrane potential and distribution of mitochondria in oocytes, most likely caused by toxicity and mechanical injury. Doi.org/10.54680/fr24510110212.

Vitrification is a promising treatment for municipal solid waste incineration fly ash (MSWI-FA); however, high energy consumption due to the high MSWI-FA fusion temperature limits the development and application of this technique. In this study, fine slag ash (FSA) derived from coal gasification and coal gangue ash (CGA) were mixed with MSWI-FA to reduce the ash fusion temperature. The transformation of minerals in ash during thermal treatment was examined via X-ray diffraction and thermodynamic equilibrium calculations. The ash flow behaviour was observed using a thermal platform microscope, and the silicate structure was quantified using Raman spectra. The co-melting mechanisms for the mixed ash were systematically investigated. Results indicate that the flow temperature (FT) of the mixed ash exhibited an initial decrease and subsequent increase as a function of the addition ratio of FSA or CGA. Lowest ash FT of 1215 °C and 1223 °C were recorded for addition of 50% FSA and 50% CGA, respectively; further, these temperatures were lowered by > 285 °C and >277 °C respectively, relative to FT of the MSWI-FA. The transformation of minerals and silicate structure during mixed ash heating was responsible for the variation in the ash fusion temperature. CaO in MSWI-FA tended to react with mullite, quartz and haematite in FSA and CGA, forming minerals such as anorthite, gehlenite, and andradite with relatively low melting points. The addition of FSA or CGA caused changes in the silicate network structure of the mixed ash. In particular, 50% FSA incorporation caused the transformation of Q4 and Q3 to Q2, whereas 50% CGA introduction resulted in the conversion of Q4 and Q2 into Q3 and Q1 + Q0, respectively. The silicate network depolymerised, causing reduction in the ash fusion temperature and increasing the melting rate.

A number of extracellular helical protein polymers are crucial for supporting bacterial motility. The bacterial flagellum is a polymeric appendage used to support cellular motility. Historically, structural studies of flagellar and other filaments were limited to those present as or locked into straightened states. Here, we present a robust workflow that produces biologically relevant high-resolution cryo-electron microscopy (cryo-EM) structures of bacterial flagellar filaments. We highlight how a simple purification method, centered around several centrifugation steps, exploits the process of filament ejection in Caulobacter crescentus and results in isolated filaments amenable to transmission electron microscopy (TEM) studies. The quality of the sample is validated by SDS-PAGE and negative stain TEM analysis before a sample is vitrified for cryogenic electron microscopy (cryo-EM) data collection. We provide a detailed protocol for reconstructing either straight or curved flagellar filaments by cryo-EM helical reconstruction methods, followed by an overview of model building and validation. In our hands, this workflow resulted in several flagellar structures below 3 Å resolution, with one data set reaching a global resolution of 2.1 Å. The application of this workflow supports structure-function studies to better understand the molecular interactions that regulate filament architecture in biologically relevant states. Future work will not only examine interactions that regulate bacterial flagellar and other filament organization but also provide a foundation for developing new helical biopolymers for biotech applications. Key features • Rapid high-quality purification of bacterial flagella via simple bacterial culturing, centrifugation, and resuspension methods. • High-throughput cryo-EM data collection of filamentous objects. • Use of cryoSPARC implementations of helical reconstruction algorithms to generate high-resolution 3D structures of bacterial flagella or other helical polymers.

Vitrification has important application in assisted reproductive technology (ART) and this technique has been widely used in the cryopreservation of oocytes and embryos. However, due to susceptibility of epigenetic modifications to environmental changes induced by cryopreservation procedures, there are concerns about the potential epigenetic consequences of oocyte and embryo vitrification. This review comprehensively summarized the effect of cryopreservation-especially the vitrification method in ART-on oocytes and embryos. Various studies have reported changes in different aspects of genomic status which directly affect the quality of fertilized embryos.  The objective of this review is to assess existing literature on the epigenetic modifications that occur in vitrified oocytes and early embryos resulting from oocyte vitrification, including DNA modifications, RNA methylation, histone modification and microRNAs related to ART.

Vitrification is the most promising method for cryopreservation of complex structures such as organs and tissue constructs. However, this method requires multimolar concentrations of cell-permeant cryoprotective agents (CPAs), which can be toxic at such elevated levels. The selection of CPAs for organ vitrification has been limited to a few chemicals; however, there are numerous chemicals with properties similar to commonly used CPAs. In this study, we developed a high-throughput method that significantly increases the speed of cell membrane permeability measurement, enabling ~100 times faster permeability measurement than previous methods. The method also allows assessment of CPA toxicity using the same 96-well plate. We tested five commonly used CPAs and 22 less common ones at both 4 °C and room temperature, with 23 of them passing the screening process based on their favorable toxicity and permeability properties. Considering its advantages such as high throughput measurement of membrane permeability along with simultaneous toxicity assessment, the presented method holds promise as an effective initial screening tool to identify new CPAs for cryopreservation.

Plasma membrane damage in vitrified oocytes is closely linked to mitochondrial dysfunction. However, the mechanism underlying mitochondria-regulated membrane stability is not elucidated. A growing body of evidence indicates that mitochondrial activity plays a pivotal role in cell adaptation. Since mitochondria work at a higher temperature than the constant external temperature of the cell, we hypothesize that suppressing mitochondrial activity would protect oocytes from extreme stimuli during vitrification. Here we show that metformin suppresses mitochondrial activity by reducing mitochondrial temperature. In addition, metformin affects the developmental potential of oocytes and improves the survival rate after vitrification. Transmission electron microscopy results show that mitochondrial abnormalities are markedly reduced in vitrified oocytes pretreated with metformin. Moreover, we find that metformin transiently inhibits mitochondrial activity. Interestingly, metformin pretreatment decreases cell membrane fluidity after vitrification. Furthermore, transcriptome results demonstrate that metformin pretreatment modulates the expression levels of genes involved in fatty acid elongation process, which is further verified by the increased long-chain saturated fatty acid contents in metformin-pretreated vitrified oocytes by lipidomic profile analysis. In summary, our study indicates that metformin alleviates cryoinjuries by reducing membrane fluidity via mitochondrial activity regulation.

Grapevine (Vitis vinifera L.) crops are continuously exposed to biotic and abiotic stresses, which can cause genetic and epigenetic alterations. To determine the possible effects of grapevine cryopreservation on the regulation of DNA demethylase genes, this work studied the expression of DNA demethylase genes in cryopreserved and post-cryopreserved grapevine tissues. V. vinifera DNA demethylases were characterized by in silico analysis, and gene expression quantification was conducted by RT‒qPCR. Three DNA demethylase sequences were found: VIT_13s0074g00450 (VvDMT), VIT_08s0007g03920 (VvROS1), and VIT_06s0061g01270 (VvDML3). Phylogenetic analysis revealed that the sequences from V. vinifera and A. thaliana had a common ancestry. In the promoters of responsive elements to transcription factors such as AP-2, Myb, bZIP, TBP, and GATA, the conserved domains RRM DME and Perm CXXC were detected. These responsive elements play roles in the response to abiotic stress and the regulation of cell growth. These data helped us characterize the V. vinifera DNA demethylase genes. Gene expression analysis indicated that plant vitrification solution 2 (PVS2) treatment does not alter the expression of DNA demethylase genes. The expression levels of VvDMT and VvROS1 increased in response to cryopreservation by vitrification. Furthermore, in post-cryopreservation, VvROS1 was highly induced, and VvDML3 was repressed in all the treatment groups. Gene expression differences between different treatments and tissues may play roles in controlling methylation patterns during gene regulation in tissues stressed by cryopreservation procedures and in the post-cryopreservation period during plant growth and development.

Cellular electron cryo-tomography (cryoET) produces high-resolution three-dimensional images of subcellular structures in a near-native frozen-hydrated state. These three-dimensional images are obtained by recording a series of two-dimensional tilt images on a transmission electron cryo-microscope that are subsequently back-projected to form a tomogram. Key to a successful experiment is however a high-quality sample. This chapter outlines a basic workflow for the preparation of cellular cryoET samples. It covers the preparation of infected cells on electron cryo-microscopy grids and the vitrification by plunge-freezing and clipping of grids into AutoGrid rims. It also provides a general overview of the workflow for thinning the vitrified cells by focused ion beam (FIB) milling. Although this book is dedicated to Rift Valley fever virus research, the present protocol may also be applied to any other research subject where high-resolution structural insight into intracellular processes is desired.

UNASSIGNED: Vitrification is a recently introduced yet widely applied assisted reproduction technique. So far, the effects of the chemicals and devices in vitrification on sperm motility and DNA integrity are still unclear.
UNASSIGNED: This study aimed to examine sperm quality, as determined by semen analysis and sperm DNA integrity when vitrified with or without cryoprotectant agents (CPAs) using pulled-glass capillaries.
UNASSIGNED: Between February and June 2020, 50 infertile men from the Hue Center for Reproductive Endocrinology and Infertility, Hue University of Medicine and Pharmacy, Vietnam, were enrolled. Sperm samples, prepared using the swim-up technique, were divided into 2 groups: vitrification with CPAs (group 1) and without CPAs (group 2). Vitrified sperm samples were preserved in 10 µL pulled-glass capillaries. Motility, sperm membrane integrity, and the DNA fragmentation index were tested.
UNASSIGNED: Sperm motility in vitrified media with CPAs (54.4 ± 11%) was statistically higher than in media without CPAs (51.14 ± 10.6%, p < 0.05). CPAs did not affect sperm membrane integrity or large halo ratio (71.34 ± 8.47 vs. 70.38 ± 8.11 and 50.84 ± 18.92 vs. 51.98 ± 19.44, respectively). Group 2 exhibited a lower DNA fragmentation index than group 1 after vitrification (14.2 ± 8.47 vs. 12.60 ± 9.03, p = 0.021).
UNASSIGNED: Using a pulled-glass capillary for sperm vitrification, the presence of CPAs in the vitrification medium resulted in higher progressive motility and lower DNA fragmentation index than the medium without CPAs.