Dynamic changes in mitochondrial distribution in human oocytes during meiotic maturation.

PURPOSE: The change of mitochondrial distribution in human oocytes during meiotic maturation was assessed using 223 human oocytes donated from patients undergoing fertility treatment between June 2013 and February 2016. METHODS: Live cell images of fluorescence-labelled mitochondria in human oocytes were analysed to investigate dynamic changes in mitochondrial distribution during meiotic maturation using a confocal microscope combined with an incubator in the presence or absence of colchicine and cytochalasin B, inhibitors for tubulin and actin filament, respectively. Subcellular distribution of mitochondria in human oocytes was also assessed at various stages using a transmission electron microscope (TEM). RESULTS: Live cell imaging analysis revealed that the mitochondria-occupied cytoplasmic area decreased from 83 to 77 % of the total cytoplasmic area around 6 h before germinal vesicle breakdown (GVBD) and that mitochondria accumulated preferentially close to the perinuclear region. Then, the mitochondria-distributed area rapidly increased to 85 % of total cytoplasm at the time of GVBD. On the other hand, there was no significant change in mitochondrial distribution before and after polar body extrusion. Such changes in mitochondrial localization were affected differently by colchicine and cytochalasin B. Most of mitochondria in the cytoplasm formed cluster-like aggregates before GVBD while they distributed homogeneously after GVBD. CONCLUSIONS: Most mitochondria localized predominantly in the non-cortical region of the cytoplasm of GV stage-oocytes, while the mitochondria-occupied area decreased transiently before GVBD and increased rapidly to occupy the entire area of the cytoplasm at GVBD by some cytoskeleton-dependent mechanism.

Good thermally conducting material supports follicle morphologies of porcine ovaries cryopreserved with ultrarapid vitrification.

Effects of supporting materials during vitrification procedure on the morphologies of preantral follicles of pig ovaries were assessed. Ovarian cortical sections of prepubertal pigs were randomly allocated to 5 groups. The sections were vitrified ultrarapidly with 5 different vitrification devices. The sections were put on 4 fine needles (Cryosupport), on a thin copper plate, or on a carbon graphite sheet or were sandwiched between copper plates or between carbon graphite sheets before cooling. The cooling and warming rates with the graphite sheets were significantly higher than those with the copper plates (P<0.05). A total of 3,064 follicles were analyzed following HE staining after vitrification with 5 different devices. The morphologies follicles vitrified on the Cryosupport or on the graphite sheet were well preserved compared with those vitrified on the copper plate or between copper plates (P<0.01). The morphologies of follicles vitrified between copper plates were mostly damaged (P<0.05). Taken together, good thermally conducting material supports follicle morphologies of ovaries cryopreserved with ultrarapid vitrification.

Growth retardation in human blastocysts increases the incidence of abnormal spindles and decreases implantation potential after vitrification.

STUDY QUESTION: Does the human embryo growth rate affect the outcome of vitrified-warmed blastocyst transfer? SUMMARY ANSWER: Following vitrification, the incidence of abnormal spindle morphology was increased and the implantation competence was decreased in growth-retarded embryos compared with normally developing embryos. WHAT IS KNOWN ALREADY: Various types of spindle abnormality occur in human cleavage- and blastocyst-stage embryos. However, the incidence of abnormal spindle morphology in growth-retarded blastocysts is not known. Furthermore, there is conflicting data about the implantation potential of such blastocysts. STUDY DESIGN, SIZE, DURATION: This was a retrospective cohort study including 878 single vitrified-warmed blastocyst transfers between 9 January 2010 and 10 July 2012, and an experimental study using 121 vitrified-warmed blastocysts donated to research. A comparison on the implantation potential and spindle shape of vitrified-warmed blastocysts was made between normally developing and growth-retarded blastocysts. PARTICIPANTS/MATERIALS, SETTING, METHODS: In the clinical study, we compared the implantation rates of vitrified-warmed embryos that developed to the blastocyst stage on Day 5 after insemination (normally developing embryos) with those that required culture to Day 6 (growth-retarded embryo). In the experimental study, donated vitrified-warmed blastocysts were immunostained with an anti-α-tubulin antibody to visualize microtubules, an anti-γ-tubulin antibody to image centrosomes and Hoechst 33342 or 4,6-diamidino-2-phenylindole to visualize DNA. Confocal image analysis captured a z-series stack of 0.5-µm-thick optical sections encompassing the entire blastocyst. Only spindles with fusiform poles and with chromosomes aligned at the equator were classified as normal. MAIN RESULTS AND THE ROLE OF CHANCE: The implantation rate of growth-retarded embryos (47%, n = 270) was significantly lower (P < 0.05) than that of normally developing embryos (57%, n = 608). A total of 533 spindles were analyzed in Day 5 and 6 vitrified-warmed blastocysts. The incidence of abnormal spindles in the growth-retarded embryos (47%, n = 274) was significantly higher (P < 0.01) than in the normally developing embryos (30%, n = 259). LIMITATIONS, REASONS FOR CAUTION: Further studies are required to clarify the link between an increase in abnormal spindle formation and a decrease in embryonic implantation potential. WIDER IMPLICATIONS OF THE FINDINGS: This study provided new insights into the possible implications of abnormalities in spindle formation in growth-retarded human blastocysts.

A closed system supports the developmental competence of human embryos after vitrification : Closed vitrification of human embryos.

PURPOSE: Closed-system vitrification may enable the risk of contamination to be minimised. We performed three studies to compare the developmental competence of human embryos vitrified using either a closed vitrification system (CVS; Rapid-i®) or an open vitrification system (OVS; Cryo-top®). METHODS: The first study was performed in vitro using 66 zygotes previously vitrified at pronuclear stage. These were warmed and randomised 1:1 to revitrification using either the OVS or the CVS. After re-warming, embryo development and blastocyst cell number were assessed. For the second study, also performed in vitro, 60 vitrified-warmed blastocysts were randomised 1:1:1 into three groups (OVS or CVS revitrification, or no revitrification). The proportion of dead cells was assessed by staining. The third study was performed in vivo, using 263 high-grade blastocysts randomly assigned to vitrification using either the CVS (n = 100) or the OVS (n = 163). After warming, single blastocyst transfer was performed. RESULTS: There were no differences between the CVS and the OVS in survival rate (100 % vs. 97 %), blastulation rate (96 h: 50 % vs. 50 %; 120 h: 68 % vs. 56 %), proportion of good blastocysts (96 h: 32 % vs. 22 %, 120 h: 47 % vs. 41 %), or mean number of cells (137 vs. 138). The proportion of dead cells in blastocysts re-vitrified by CVS (31 %) was similar to that for OVS (38 %) and non-revitrification (32 %). In vivo, the implantation rate for blastocysts vitrified using the CVS (54 %) was similar to that with the OVS (53 %). CONCLUSION: Our studies consistently indicate that human embryos may be vitrified using a CVS without impairment of developmental competence.

Developmental assessment of human vitrified-warmed blastocysts based on oxygen consumption.

BACKGROUND: In this study, we aimed to develop a model for embryo selection based on oxygen consumption following cryopreservation, the relationship between the developmental competence of blastocysts and their oxygen consumption was assessed. METHODS: Oxygen consumption of vitrified-warmed human blastocysts was measured at 0, 1.5, 3, 4.5, 6, 7.5, 9 and 24 h after warming using scanning electrochemical microscopy. On the basis of their developmental stage at 24 h, blastocysts were classified into four groups (hatched, hatching, arrested and degenerated). Moreover, cytochrome c oxidase (CCO) activity in vitrified-warmed blastocysts was assessed at 0 and 24 h. RESULTS: The oxygen consumption rate of blastocysts just after warming was significantly lower than that of non-vitrified blastocysts (P< 0.05). The oxygen consumption rate of blastocysts was significantly higher in the hatched group than in the arrested and the degenerated groups after 1.5 h (P< 0.05) and than in the hatching group (P< 0.05) at 7.5 and 9 h. Moreover, CCO activity was absent in vitrified-warmed blastocysts at 0 h, but was detected at 24 h. CONCLUSIONS: The respiratory rate of vitrified blastocysts after warming was significantly lower than non-cryopreserved blastocysts. Oxygen consumption of blastocysts with high developmental potential was restored earlier than that of blastocysts with low developmental potential. The results of this study suggest that it is possible to select vitrified-warmed blastocysts with high developmental potential based on their respiratory activity.