• Clinical and Experimental Reproductive Medicine
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• v.25 no.3
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• pp.287-292
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• 1998

The objective of this study was to confirm whether the vitrification method using EFS35 has detrimental effect for cytoskeleton and chromosome constitution of the mouse oocytes by indirect immunocytochemistry and chromosome analysis. Mouse oocytes were vitrified using EFS35 which consisted of 35% ethylene glycol, 18% ficoll, 0.3 M sucrose and 10% FBS in M2 medium. The results obtained in this experiment were summarized as follows: When the survival rates after being exposed or vitrified in EFS35 were examined, there were not different between two groups (97.7 and 89.3%). Also, when the microtubule morphology and microfilament distribution in vitrified oocytes were examined, normal percentage of two cytoskeleton in vitrified group (95.5 and 100%) was not different from that in control (97.5 and 100%) and exposed group (92.3 and 100%). In addition, the rate of oocytes containing a normal chromosome number in vitrified group (73.5%) after IVF was not different from that in control (79.5%) and exposed group (78.7%). These results indicated that the cytoskeletal morphology and chromosome constitution of mouse oocytes were not affected by cryoprotectant (EFS35) or freezing apd that vitrification methods using EFS35 was suitable for cryopreservation of mouse oocytes.

• Clinical and Experimental Reproductive Medicine
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• v.43 no.1
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• pp.9-14
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• 2016

Objective: Autophagy contributes to the clearance and recycling of macromolecules and organelles in response to stress. We previously reported that vitrified mouse oocytes show acute increases in autophagy during warming. Herein, we investigate the potential role of Atg7 in oocyte vitrification by using an oocyte-specific deletion model of the Atg7 gene, a crucial upstream gene in the autophagic pathway. Methods: Oocyte-specific Atg7 deficient mice were generated by crossing Atg7 floxed mice and Zp3-Cre transgenic mice. The oocytes were vitrified-warmed and then subjected to in vitro fertilization and development. The rates of survival, fertilization, and development were assessed in the Atg7 deficient oocytes in comparison with the wildtype oocytes. Light chain 3 (LC3) immunofluorescence staining was performed to determine whether this method effectively evaluates the autophagy status of oocytes. Results: The survival rate of vitrified-warmed $Atg7^{f/f}$;Zp3-Cre ($Atg7^{d/d}$) metaphase II (MII) oocytes was not significantly different from that of the wildtype ($Atg7^{f/f}$) oocytes. Fertilization and development in the $Atg7^{d/d}$ oocytes were significantly lower than the $Atg7^{f/f}$ oocytes, comparable to the $Atg5^{d/d}$ oocytes previously described. Notably, the developmental rate improved slightly in vitrified-warmed $Atg7^{d/d}$ MII oocytes when compared to fresh $Atg7^{d/d}$ oocytes. LC3 immunofluorescence staining showed that this method can be reliably used to assess autophagic activation in oocytes. Conclusion: We confirmed that the LC3-positive signal is nearly absent in $Atg7^{d/d}$ oocytes. While autophagy is induced during the warming process after vitrification of MII oocytes, the Atg7 gene is not essential for survival of vitrified-warmed oocytes. Thus, induction of autophagy during warming of vitrified MII oocytes seems to be a natural response to manage cold or other cellular stresses.

• Molecules and Cells
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• v.37 no.2
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• pp.126-132
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• 2014

As a tumor suppressor homologue during mitosis, Chk2 is involved in replication checkpoints, DNA repair, and cell cycle arrest, although its functions during mouse oocyte meiosis and early embryo development remain uncertain. We investigated the functions of Chk2 during mouse oocyte maturation and early embryo development. Chk2 exhibited a dynamic localization pattern; Chk2 expression was restricted to germinal vesicles at the germinal vesicle (GV) stage, was associated with centromeres at pro-metaphase I (Pro-MI), and localized to spindle poles at metaphase I (MI). Disrupting Chk2 activity resulted in cell cycle progression defects. First, inhibitor-treated oocytes were arrested at the GV stage and failed to undergo germinal vesicle breakdown (GVBD); this could be rescued after Chk2 inhibition release. Second, Chk2 inhibition after oocyte GVBD caused MI arrest. Third, the first cleavage of early embryo development was disrupted by Chk2 inhibition. Additionally, in inhibitor-treated oocytes, checkpoint protein Bub3 expression was consistently localized at centromeres at the MI stage, which indicated that the spindle assembly checkpoint (SAC) was activated. Moreover, disrupting Chk2 activity in oocytes caused severe chromosome misalignments and spindle disruption. In inhibitor-treated oocytes, centrosome protein ${\gamma}$-tubulin and Polo-like kinase 1 (Plk1) were dissociated from spindle poles. These results indicated that Chk2 regulated cell cycle progression and spindle assembly during mouse oocyte maturation and early embryo development.

• Clinical and Experimental Reproductive Medicine
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• v.28 no.3
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• pp.199-207
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• 2001

Objective: The present study was undertaken to examine the effects of magnesium ion in the culture medium on the development of mouse fertilized oocytes either before or after pronuclear formation, and to investigate whether the effect of magnesium ion is related with the redistributional change of mitochondria. Methods : Fertilized oocytes obtained from the oviducts of mice at 15 hr after hCG injection before pronuclear formation (pre-PN) or 21 hr after hCG injection after pronuclear formation (post-PN) were used. The embryos were cultured for 3 days with basic T6 medium-magnesium free and various concentrations of magnesium ion, 0.0, 0.5, 1.0, 2.0, 4.0 or 8.0 mM, respectively. After culture, the developmental stages of embryos and the number of nuclei were evaluated. To observe the effects of magnesium ion on the mitochondrial distribution, fertilized oocytes were collected at 21 hr after hCG injection and cultured for 6 hr with various concentration of magnesium ion. As a control, fertilized oocytes with pronuclei at 27 hr after hCG injection were used. Results: The concentration of magnesium ion to accelerate the in vitro development of mouse fertilized oocytes appeared to be at 2.0 mM for the pre-PN and the post-PN stage embryos. In the mitochondrial redistribution patterns, the embryos cultured in 2.0 mM concentration of magnesium ion showed the highest percentage (22.6%) of distinct perinuclear clustering pattern comparing to other experimental group. Conclusion: The effect of magnesium ion may be related to the cytoplasmic redistribution of mitochondria. This relationship seems to connect the developmental competence of preimplantation mouse embryos in vitro. These results can suggest that higher concentration of magnesium ion (2.0 mM) than those of conventional culture medium ($0.2{\sim}1.2\;mM$) is more suitable for in vitro culture of preimplantation mouse embryos.

• Journal of Embryo Transfer
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• v.13 no.2
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• pp.89-96
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• 1998

Anti-phospholipid antihodies (aPL) have important roles in various pregnancy complications such as recurrent miscarrige, growth retardation, placental abruption and stillbirth. However, their biological actions on preimplantation development of oocytes are still unclear. In this study, we investigated whether either aPL containing sera or phospholipids could affect in vitro fertilization and development of mouse oocytes. Sera used in this study were collected from three patients and the presence of aPL in the sera was confirmed by enzymatic-linked immunosorbent assay. When mouse oocytes were cultured in a serum-free, Chatot, Ziomek and Bavister (CZB) medium (Experiment 1), addition of aPL-containing sera (10%) to CZB medium did not. significantly (P>0.05) influence sperm penetration of oocytes. However, development to the blastocyst stage was significantly (P<0.05) inhibited by serum addition, and formation of morulae (16-23% vs. 58%) and blastocysts (0-4% vs. 21%) was markedly reduced compared with no addition (Experiment 2). In Experiment 3, pronuclear stage embryos were cultured for 96 h in GZB medium supplemented with 1 $\mu$g /ml phosphatidyl ethanolamine, 1 $\mu$g/ml phosphatidyl inositol or 1 $\mu$g /ml phosphatidyl choline. No increase in embryo development was found after addition of the phospholipids to CZB medium. These results suggest that 1) aPL have an inhibitory role in preimplantation development of mouse embryos, and that 2) the action of aPL may be related to a specific phospholid (s) rather than the tested phospholipids in the present study.

• The Korean Journal of Zoology
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• v.29 no.3
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• pp.181-189
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• 1986

The present study was undertaken to investigate whether the known adenylate cyclase activators, forskolin and cholera toxin, would affect the germinal vesicle breakdown (GVBD) and the production of cAMP in mouse oocytes in vitro. To do this, in vitro oocyte culture method and adenylate cyclase assay were employed. In response to different concentrations of forskolin (20 to 80 $\\mu$g/ml) added to a culture medium, the percentage of GVBD significantly decreased (56 to 31%) in a dose-dependent manner as compared to that of control (63%). This inhibitory phenomenon by forskolin was reversible since the rate of GVBD was returned to the control level when the oocytes were transferred to a control medium following exposure to forskolin (80 $\\mu$g/ml). Treatment of cholera toxin (10 to 1, 000 ng/ml) was, however, ineffective in suppressing GVBD. When forskolin (10 to 80 $\\mu$g/ml) was added to the mouse oocyte extracts, cAMP production significantly increased by 5 to 18 fold, whereas cholera toxin (10 to 1, 000 ng/ml) was no longer effective. In addition, treatment of guanidyl-imidodiphosphate (GppNHp, 100 $\\mu$M), which is an activator of the regulatory unit of adenylate cycleas, with forskolin did not exhibit any changes in cAMP production as compared to that induced by forskolin alone. Neither cholera toxin nor cholera toxin plus GppNHp (100 $\\mu$M) exhibited any differences in mouse oocytes. From the above results, the suppression of GVBD by forskolin may be mediated by a high level of intracellular cAMP in mouse oocytes. It appears that the changes in intracellular cAMP level may an important role in the mouse oocyte maturation.

• Development and Reproduction
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• v.8 no.1
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• pp.27-33
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• 2004

To investigate the mechanism of germ cell death in postnatal stage of mouse, the involvement of apoptotic executioners, caspase-3 and caspase-activated DNase(CAD), and apoptotic initiators, Bax Fas and Fas ligand, in the germ cell death has been studied. Immune-labels of active caspase-3 and CAD were located in TUNEL-positive, apoptotic, oocytes as well as normal oocytes of primary or secondary follicles. CAD immune-labels were also detected in the nucleus of TUNEL-positive oocytes. Most of oocytes showing positive immune-labeling of active caspase-3 or CAD had vacuoles in their cytoplasm, which is the morphological characteristic of oocyte during folliclar atresia. Bax immune-stains were detected in the atretic oocytes which showed the vacuole in their cytoplasm. Positive immune-labels for Fas ligand was localized in TUNEL-positive or atretic oocytes. Presence of immunoreactivity of active caspase-3 and CAD in TUNEL-positive germ cells implicate that active raspase-3 and CAD might play a role in germ cell apoptosis during early development of mouse ovarian follicle. Immunohistochemical localization of Bax and Fas ligand in TUNEL-positive oocytes suggests that these might be the most plausible modulator of oocyte apoptosis.

• Clinical and Experimental Reproductive Medicine
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• v.29 no.3
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• pp.201-207
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• 2002

Objective: To observe the capability of fertilization and embryo development including blastocyst formation of the oocytes in simple media after thawing of the cryopreserved cumulus-free mouse oocytes by vitrification method. Methods: Oocytes were collected from 5 to 6 weeks old ICR female mice, and were denuded from the cumulus cells by 0.1% hyaluronidase. Recovered mature oocytes in study group were cryopreserved by vitrification method using EM grid for $5{\sim}7$ days. In brief, oocytes were exposed in dPBS containing 1.5 M EG and 5.5 M EG+1 M sucrose for 2.5 minutes and 20 seconds each, and then executed vitrification by plunging in LN2 after loading on EM grid. Thawing treated by exposure of 1, 0.5, 0.25 and 0.125 M sucrose solution for 2.5 minutes each in order and used for experiments. Spermatozoa aspirated form the epididymis of 12 weeks old ICR male mice were used for insemination after capacitation. T6 media containing 0.4% BSA were used for fertilization and development. Results: Survival and fertilization rates after thawing were 76.9% and 79.6% respectively. Fertilization rate was lower (p<0.005) than that of control group (92.9%). There was no difference in embryo developmental rates from 2-cell to morula, however, the blastocyst formation rate and mean cell numbers of blastocysts in study group (63.3%, $58.9{\pm}9.2$) were lower compared with those of control group (76.1%, $63.5{\pm}8.9$). Conclusion: Vitrification is an effective method for mouse mature oocyte cryopreservation with high survival and fertilization rate after thawing. And in simple media, fertilization rates and embryo development of frozen-thawed mouse oocytes are satisfactory.

• The Korean Journal of Zoology
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• v.33 no.1
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• pp.45-52
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• 1990

In order to determine whether maturation inhibiting activity(MIA) in the cytoplasm of growing follicular oocytes would suppress the cleavage of the embryonal cells, the growing oocytes were fused with the 2 or 4 cell blastomeres and then examined for the nuclear phase of the fused giant cells 24 hr after culture. A significant number of the giant cells(60%) composed of growing mouse oocyte and 2 cell mouse blastomere(1/2) in interphase has contained 2 nuclei 24 hr after culture and most of the giant cells (90%) composed of the growing oocyte and 4 cell blastomere(1/4) also contained 2 nuclei after culture. The unfused blastomeres or the isolated blastomeres cultured without fusion treatment cleaved one cell cycle under the same culture condition. In contrast, the nucleus of the growing oocytes was disintegrated and the chromosome condensed when fused with 2 cell blastomere in mitosis. The growing rat oocytes also suppressed the nuclear disintegration of the mouse embryonal cells during culture. The data presented here showed that MIA in the growing mammalian oocyte inhibited the cleavage of the embryonal cells in interphase stage, but not in milosis stage.

• Reproductive and Developmental Biology
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• v.35 no.4
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• pp.499-502
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• 2011

Aurora A kinase is a mitotic serine/threonine kinase whose proposed functions include the maturation of centrosomes, G2/M transition, alignment of chromosomes at metaphase, and cytokinesis. In this study, we investigated the effect of MLN8237, an aurora A kinase inhibitor, on the postovulatory aging of oocytes based on the frequency of oocyte fragmentation, cdk1 kinase activity, and cyclin B degradation. The fragmentation of ovulated oocytes during prolonged culture was inhibited by treatment with MLN8237 in a concentration-dependent manner. The frequency of fragmented oocytes was significantly lower in oocytes treated with 2 ${\mu}M$ MLN8237 (13%) than in control oocytes (64%) after two days of culture. Most of the control (non-fragmented) oocytes (91%) were activated after two days of culture. In comparison, only 22% of the MLN8237-treated oocytes were activated; the rest of the oocytes (78%) were still in metaphase with an abnormal spindle and dispersed chromosomes. Next, cdk1 activity and the level of cyclin B were examined. The level of cyclin B and cdk1 activity in MLN8237-treated oocytes were nearly equal to those in control oocytes. Our results indicate that MLN8237 inhibited the fragmentation of ovulated oocytes during prolonged culture, although it blocked the spontaneous decrease in activity of cdk1 and degradation of cyclin B. This mechanism of inhibition is different from that in oocytes treated with nocodazole, which have high levels of cdk1 activity and cyclin B.