G-MOPS™ (Vitrolife, Sweden AB, Göteborg, Sweden) was used as a carrier for the cryoprotectants. Additionally, the effects of oocyte freezing via the Cryotop method with the mixture of CPAs, as well as the effects of docetaxel on the survival, morphology, and gene expression of mouse oocytes, were examined. Hence, the objective of the present study was to determine the expression of some mitochondrial genes, including Tfam and Cox1. To the best of our knowledge, gene expression has not been completely investigated in mammalian vitrified oocytes. There are currently inadequate data on the effects of freezing/thawing on the cytoplasmic maturation of oocytes and the expression regulation of mitochondrial genes. 19 Novin and others 20 showed that Cox1 could be considered an indirect indicator of mtDNA activity and quantity. 18 Cytochrome c oxidase subunit 1 (Cox1) is one of the three genomic components of the mitochondrial respiratory chain. Tfam, a nuclear-encoded high-mobility group box protein, acts as the regulator of mtDNA promoters. 17 Mitochondrial transcription factor A (Tfam) regulates mtDNA transcription and replication in several tissues. A previous study showed the direct effect of gene-specific transcription factors on gene transcription in mitochondria. 16 The cytoplasmic maturation and developmental competence of oocytes are related to mitochondrial distribution. In other words, the function of mitochondria is interconnected with mtDNA. Mitochondria have their own genetic material, known as mitochondrial DNA (mtDNA). 14 High concentrations of CPAs might induce osmotic stress consequently, establishing stability between high concentrations of CPAs and low toxicity can reduce this negative effect. Furthermore, EG permeability can be facilitated by DMSO. 13 EG has a low molecular weight, high permeation ability, and low toxicity, making it suitable for use in the vitrification of human oocytes and embryos. A previous study reported that a mixture of DMSO and EG in identical quantities was the most efficient method. Sucrose is the most common non-permeable CPAs and is used in oocyte vitrification. There are many different types of permeable cryoprotectants used for vitrification, including ethylene glycol (EG), 1,2-propanediol, and dimethyl sulfoxide (DMSO). Thus, damage to cytoskeleton fibers can be reduced by docetaxel during vitrification, and the viability of oocytes might improve after vitrification/warming. Docetaxel, an anti-cancer drug, inhibits the depolymerization of microtubules, which stabilizes them by binding them with the b-subunit of tubulin in microtubules. Spindle fiber stabilization plays a critical role in the successful vitrification of oocytes. 9- 11 Therefore, the results can be improved by changing the vitrification condition. Since mammalian oocytes are large in size, they are more prone to damage by changes in the temperature and concentration of CPAs. 8 The level of oocyte viability after vitrification is dependent on the CPA concentration, time of exposure to the CPA, temperature of the equilibration solution, speed of vitrification (all steps), and cell size. These factors may destroy microfilaments and organelles, harden zonae pellucidae, and damage chromosomes. 6, 7 It is the exceptional advantage of vitrification among the cryopreservation methods.Ī variety of factors during vitrification might affect oocytes, including the toxicity of highly concentrated CPAs, cold shock, and osmotic stress. This method is a physical process through which a high concentrated cryoprotectant agent (CPA) prevents the formation of ice crystals. 5 Vitrification is the main approach to the cryopreservation of human oocytes and embryos. 1 The cryopreservation of oocytes and embryos is an opportunity to increase the efficiency of IVF cycles in several species, including mice, 2 rabbits, 3 bovines, 4 and humans. Moreover, cryopreservation is an established method to preserve fertility in women who are at risk of cancer and autoimmune diseases. Gamete cryopreservation is an integral part of assisted reproductive technology and includes in vitro fertilization (IVF), which is wildly used in clinical practice.
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