Chronological appearance of spontaneous and induced apoptosis during preimplantation development of rabbit and mouse embryos

This study was undertaken to obtain specific information on the characteristics of spontaneous and induced apoptosis during preimplantation development of rabbit in vivo and in vitro developed embryos and mouse in vitro embryos. After reaching appropriate developmental stages, embryos were transferred into culture media with or without apoptotic inductor (actinomycin D 500 ng/mL) and cultured for 10 h. The identification of apoptotic cells was based on morphological assessment of nuclei and on detection of specific DNA degradation, phosphatidylserine redistribution and active caspase-3 under fluorescence microscope.Our experiments proved that apoptosis is a frequent physiological event occurring during normal preimplantation development. A high number of untreated rabbit and mouse blastocysts contained at least one apoptotic cell. Rabbit embryos showed a lower incidence of spontaneous apoptosis. Treated blastocysts of both species responded to the presence of apoptotic inductor by significant decrease in the average number of blastomeres and significant increase in the incidence of apoptotic cell death. The occurrence of spontaneous apoptosis during earlier preimplantation development was sporadic and its presence was observed only at stages following embryonic genome activation (at 4-cell stage and later in mouse, at 16-cell and morula stage in rabbit). The susceptibility of embryos at early stages to the apoptotic inductor was much lower. The presence of actinomycin D did not increase the incidence of apoptotic embryos or apoptotic cells. Nevertheless, it slowed down embryo growth and triggered earlier appearance of some apoptotic features (at the 6-cell stage in rabbit). The results show that the occurrence of both spontaneous and induced apoptosis in preimplantation embryos is stage- and species-specific.     

The effect of oxygen on the development of preimplantation mouse embryos in vitro

The optimal oxygen tension for development of preimplantation mouse embryos to the blastocyst stage in vitro was found to be between 2.5% and 5%. One- and two-cell embryos had a more sharply defined range of oxygen tension capable of supporting development than 8-cell and morula stages. At all stages of development, more embryos developed to the blastocyst stage under 5% O2 compared to the numbers of developing under higher oxygen tensions (20% and 40% O2). The blastocysts developing under 20% O2 had fewer blastomeres than those which developed under 5% O2. As the time required for development to the blastocyst stage in vitro increased, there were fewer blastomeres present at the blastocyst stage. These results indicate that the cleaving mouse embryo has an optimal oxygen requirement in vitro of about 5%. At higher oxygen tensions, fewer embryos develop to the blastocyst stage and in those which do develop, there are fewer cell divisions. If a gradient of oxygen tension exists across the blastomeres from the outside of the embryo to its centre, the blastomeres might be using this gradient to obtain imformation about their location within the embryo and respond accordingly. Thus blastomeres on the outside at a higher oxygen tension would divide at a slower rate and form trophectoderm whereas those on the inside at a lower oxygen tension would divide more rapidly and contribute to the inner cell mass.     

Developmental responses of 2-cell embryos to oxygen tension and bovine serum albumin in Wistar rats.

To improve rat embryo culture conditions, responses of Wistar 2-cell embryos from 2 breeders to oxygen tension (5 vs 20%) and bovine serum albumin (BSA) (0 vs 3 mg/ml) were examined using rat 1-cell embryo culture medium (mR1ECM). Supplementation of 3 mg/ml BSA significantly stimulated and accelerated development to the blastocyst and expanded blastocyst stages during 72 and 96 h culture, while reduced oxygen tension stimulated cell division. Fetus development after transfer of blastocysts obtained from 72 h culture under 5% O2 with BSA was significantly higher than those cultured under atmospheric oxygen without BSA. However, the nuclear numbers of in vitro cultured blastocysts and fetus development after embryo transfer were still significantly lower than in vivo developed blastocysts, indicating the current culture condition is still suboptimal.     

Intracytoplasmic glutathione concentration and the role of beta-mercaptoethanol in preimplantation development of bovine embryos

In vitro-matured/in vitro-fertilized bovine oocytes were cultured on cumulus cell layers in a serum-free medium (bovine embryo culture medium; BECM) supplemented with 3 mg/ml fatty acid-free BSA. The intracytoplasmic glutathione concentration of embryos was found to change significantly (P < 0.008) during the preimplantation stages, beginning to increase at the 9- to 16-cell stage (20.7 pM/embryo) and reaching the highest (P < 0.03) level at the hatched-blastocyst stage (36.7 pM/embryo). A significantly (P < 0.06) lower concentration of glutathione was obtained at the 2- to 8-cell stage (7.1 pM/embryo) than at any other stage. When inseminated oocytes were cultured in BECM supplemented with different concentrations of beta-mercaptoethanol (2-ME) to promote glutathione synthesis, higher (P < 0.05) percentages of embryos developed to the 9- to 16-cell, morula and blastocyst stages at 96, 144 and 192 h post insemination, following the addition of 6.25 and 12.5 microM than after no supplementation with 2-ME. However, when 16-cell embryos were cultured in BECM supplemented with 6.25 and 12.5 microM of 2-ME, blastocyst formation was not significantly (P > 0.9) increased. When the combined effects of 2-ME and/or cumulus cells were compared in a 2 x 2 factorial design, there was a significant (P < 0.03) effect of 2-ME on the development of oocytes to blastocysts. The presence of cumulus cells significantly (P < 0.001) affected development after the fourth cleavage (morula compaction and blastocyst formation), but there was no significant (P > 0.11) interaction between 2-ME and cumulus cells. In conclusion, intracytoplasmic glutathione concentration of bovine embryos derived from in vitro-culture increases during preimplantation development. The glutathione synthesis promoter 2-ME exerts its embryotropic role on the development before the fourth cleavage, thus yielding an improvement in blastocyst formation.     

模拟微重力环境对昆明小鼠早期胚胎体外发育的影响（简报）

In order to investigate the development of Kunming mouse preimplantation embryos cultured in vitro under simulated microgravtiy, one-cell and 4-cell embryos of Kunming mouse (Fertilization In Situ) were cultured in CZB or KSOM media under simulated microgravity or normal gravity environment respectively. The results showed that under normal gravity, the percentage of passing 2-cell development block embryos was not different in CZB with in KSOM, but the percentage of blastocysts was lower in CZB than that in KSOM significantly. The percentages of passing 2-cell development block embryos and blastocysts in CZB or KSOM were lower under simulated microgravity than those under normal gravity. It is suggested that the frequency of early embryonic lethality is possibly increased by simulated microgravity.     

模拟微重力环境对昆明小鼠早期胚胎体外发育的影响

90年代初,美国航空航天局(NASA)设计研制出一种转壁式生物反应器(Rotating Wall Vessel Bioreactor,RWVB)。采用RWVB进行基地试验时,意外地发现离体细胞在RWVB中呈现高密度聚集,并形成较大的组织样结构。RWVB的核心结构是由两个同心圆柱体构成的旋转培养装置。将细胞与培养液置入内、外圆柱体之间,整个装置绕水平纵轴旋转,使培养物长时间保持悬浮状态。由于在旋转过程中     

Effects of thioredoxin on the preimplantation development of bovine embryos

Thioredoxin (TRX) is an ubiquitous protein disulfide reductase, which is known to be involved in the implantation development of mouse embryos. In the present study, recombinant human TRX was used to evaluate its effect on the promotion of preimplantation development of bovine embryos derived from in vitro maturation and fertilization. Supplementation of the medium 24h post insemination with TRX significantly (P<0.05) enhanced the frequency of development to the blastocyst stage in 5% O(2) concentration. The optimal concentration was 0.5 microg/ml (P<0.05, compared with 0, 0.1 and 1.0 microg/ml). This effect of TRX was evident only when added around the time of the first cleavage stage (24 h post insemination); no promotion was found with treatment at 6h (one-cell) or 44 h (six- to eight-cell) after insemination. Moreover, it is of interest that even with the best combination of the dose and timing of TRX treatment (0.5 microg/ml, at 24 h post insemination), no promotion of development was observed when embryos were cultured under 20% O(2). However, a preincubation of TRX in the culture medium under 20% oxygen for 24h did not diminish the promoting effect in the subsequent TRX treatment under optimal conditions, thus suggesting that the possible oxidation of TRX alone may not be the reason for the disappearance of the effect under a high oxygen concentration. These results indicate that TRX does improve the development of bovine embryos in vitro, though unlike the general reducing reagents such as beta-mercaptoethanol or cysteamine, TRX may have to exert its effect at specific times and in more physiologic oxygen environments.     

Open-pulled straw vitrification differentiates cryotolerance of in vitro cultured rabbit embryos at the eight-cell stage

The objective was to determine cryotolerance of in vitro cultured rabbit embryos to the open-pulled straw (OPS) method. Overall, 844 rabbit embryos at pronuclear, 2- to 4-cell, 8-cell, and morula/blastocyst stages were vitrified, and ≥ 1 mo later, were sequentially warmed, rehydrated, and subjected to continuous culture (n = 691) or embryo transfer (ET, n = 153). Embryos vitrified at the 8-cell stage or beyond had greater survival, expanded blastocyst and hatched blastocyst rates in vitro, and better term development than those vitrified at earlier stages. The 8-cell group had 70.1% expanded blastocysts, 63.7% hatched blastocysts, and 25.7% term development, as compared to 1.5-17.7%, 1.5-4.3% and 2.8-3.7% in the pronuclear, 2-cell and 4-cell embryos, respectively (P < 0.05). The expanded and hatched blastocyst rates in vitrified morula/blastocyst post-warming were higher than that in the 8-cell group; however, their term development after ET was similar (8-cell vs morula/blastocyst: 25.7 vs 19.4%, P > 0.05). Development after ET was comparable between vitrified-warmed embryos and fresh controls at 8-cell and morula/blastocyst stages (19.4-25.7 vs 13.7-26.6%, P > 0.05). For embryos at pronuclear or 2- to 4-cell stages, however, term rates were lower in the vitrified-warmed (2.8-3.7%) than in fresh controls (28.6-35.6%, P < 0.05). Therefore, cultured rabbit embryos at various developmental stages had differential crytolerance. Under the present experimental conditions, the 8-cell stage appeared to be the critical point for acquiring cryotolerance. We inferred that for this OPS cryopreservation protocol, rabbit embryos should be vitrified no earlier than the 8-cell stage, and stage-specific protocols may be needed to maximize embryo survival after vitrification and re-warming.     

Chronological appearance of spontaneous and induced apoptosis during preimplantation development of rabbit and mouse embryos

This study was undertaken to obtain specific information on the characteristics of spontaneous and induced apoptosis during preimplantation development of rabbit in vivo and in vitro developed embryos and mouse in vitro embryos. After reaching appropriate developmental stages, embryos were transferred into culture media with or without apoptotic inductor (actinomycin D 500 ng/mL) and cultured for 10 h. The identification of apoptotic cells was based on morphological assessment of nuclei and on detection of specific DNA degradation, phosphatidylserine redistribution and active caspase-3 under fluorescence microscope. Our experiments proved that apoptosis is a frequent physiological event occurring during normal preimplantation development. A high number of untreated rabbit and mouse blastocysts contained at least one apoptotic cell. Rabbit embryos showed a lower incidence of spontaneous apoptosis. Treated blastocysts of both species responded to the presence of apoptotic inductor by significant decrease in the average number of blastomeres and significant increase in the incidence of apoptotic cell death. The occurrence of spontaneous apoptosis during earlier preimplantation development was sporadic and its presence was observed only at stages following embryonic genome activation (at 4-cell stage and later in mouse, at 16-cell and morula stage in rabbit). The susceptibility of embryos at early stages to the apoptotic inductor was much lower. The presence of actinomycin D did not increase the incidence of apoptotic embryos or apoptotic cells. Nevertheless, it slowed down embryo growth and triggered earlier appearance of some apoptotic features (at the 6-cell stage in rabbit). The results show that the occurrence of both spontaneous and induced apoptosis in preimplantation embryos is stage- and species-specific.     

Evaluation of cyclooxygenase 2 derived endogenous prostacyclin in mouse preimplantation embryo development in vitro

Cyclooxygenase (COX) plays an important role in prostaglandin (PG) synthesis and has two isoforms, COX1 and COX2. PGI synthase (PGIS) catalyzes the isomeization of PGH(2) to prostacyclin (PGI(2)). It is reported that COX2 derived PGI2(2) plays a critical role in blastocyst implantation and decidualization and PGI2 mediates its function via PPARdelta receptor. It is also known that cyclooxygenase derived prostaglandins play an important role in mouse blastocyst hatching in vitro. In this study we hypothesized that COX2 derived PGI2 plays an important role in preimplantation embryonic development by increasing the cell number. To examine this hypothesis, 8-cell stage mouse embryos were cultured in the presence of selective inhibitors of COX1 (SC560), COX2 (NS398) and PGIS (U51605) respectively. COX2 and PGIS inhibitor significantly reduced the blastocyst development and presence of PGI2 analogue along with these inhibitors restored the blastocyst development by increasing the total number of embryonic cells. Our immunohistochemical analysis showed that COX1 is expressed at 2-cell, 8-cell, compaction and blastocyst stage whereas COX2 expression starts from eight cell stage embryos. PGIS and PPARdelta expression starts at 2-cell stage of development. Our results suggest that PGI(2) may affect blastomeres number via the so called hypothesis of PPARdelta nuclear receptor in autocrine manner.     

The roles of parathyroid hormone-like hormone during mouse preimplantation embryonic development

Parathyroid hormone-like hormone (PTHLH) was first identified as a parathyroid hormone (PTH)-like factor responsible for humoral hypercalcemia in malignancies in the 1980s. Previous studies demonstrated that PTHLH is expressed in multiple tissues and is an important regulator of cellular and organ growth, development, migration, differentiation, and survival. However, there is a lack of data on the expression and function of PTHLH during preimplantation embryonic development. In this study, we investigated the expression characteristics and functions of PTHLH during mouse preimplantation embryonic development. The results show that Pthlh is expressed in mouse oocytes and preimplantation embryos at all developmental stages, with the highest expression at the MII stage of the oocytes and the lowest expression at the blastocyst stage of the preimplantation embryos. The siRNA-mediated depletion of Pthlh at the MII stage oocytes or the 1-cell stage embryos significantly decreased the blastocyst formation rate, while this effect could be corrected by culturing the Pthlh depleted embryos in the medium containing PTHLH protein. Moreover, expression of the pluripotency-related genes Nanog and Pou5f1 was significantly reduced in Pthlh-depleted embryos at the morula stage. Additionally, histone acetylation patterns were altered by Pthlh depletion. These results suggest that PTHLH plays important roles during mouse preimplantation embryonic development.     

Insulin-like growth factor-I as a survival factor for the bovine preimplantation embryo exposed to heat shock

Insulin-like growth factor-I (IGF-I) is a survival factor for preimplantation mammalian embryos exposed to stress. One stress that compromises preimplantation embryonic development is elevated temperature (i.e., heat shock). Using bovine embryos produced in vitro as a model, it was hypothesized that IGF-I would protect preimplantation embryos by reducing the effects of heat shock on total cell number, the proportion of blastomeres that undergo apoptosis, and the percentage of embryos developing to the blastocyst stage. In experiment 1, embryos were cultured with or without IGF-I; on Day 5 after insemination, embryos >or=16 cells were cultured at 38.5 degrees C for 24 h or were subjected to 41 degrees C for 9 h followed by 38.5 degrees C for 15 h. Heat shock reduced the total cell number at 24 h after initiation of heat shock and increased the percentage of blastomeres that were apoptotic. Effects of heat shock were less for IGF-I-treated embryos. Experiment 2 was conducted similarly except that embryos were allowed to develop to Day 8 after insemination. The percentage reduction in blastocyst development for heat-shocked embryos compared with those maintained at 38.5 degrees C was less for embryos cultured with IGF-I than for control embryos. Heat shock reduced the total cell number in blastocysts and increased the percentage of blastomeres that were apoptotic, whereas IGF-I-treated embryos had increased total cell number and a reduced percentage of apoptosis. Taken together, these results demonstrate that IGF-I can serve as a survival factor for preimplantation bovine embryos exposed to heat shock by reducing the effects of heat shock on development and apoptosis.     

The absence of direct effects of prostaglandin F2α on preimplantation mouse embryos in vitro

Preimplantation mouse embryos were cultured in vitro in concentrations of PGF_2α ranging from 5 nanograms/ml to 100 micrograms/ml. Embryos were cultured at the 2-cell stage, 4-cell stage, 8-cell stage and the morula stage and observed for normal development to the blastocyst stage. There was no significant difference (P < .1) between the number of blastocysts attained in the control group and those in the experimental groups. After reaching the blastocyst stage, the embryos were transferred to the uteri of pseudopregnant recipient females. Again, there was no significant difference (P < .3) between controls and PGF_2α treated embryos in the number developing to term. These data suggest that exposure to PGF_2α does not result in teratogenic effects or early death in preimplantation embryos.     

Promotion of Human Early Embryonic Development and Blastocyst Outgrowth In Vitro Using Autocrine/Paracrine Growth Factors

Studies using animal models demonstrated the importance of autocrine/paracrine factors secreted by preimplantation embryos and reproductive tracts for embryonic development and implantation. Although in vitro fertilization-embryo transfer (IVF-ET) is an established procedure, there is no evidence that present culture conditions are optimal for human early embryonic development. In this study, key polypeptide ligands known to be important for early embryonic development in animal models were tested for their ability to improve human early embryo development and blastocyst outgrowth in vitro. We confirmed the expression of key ligand/receptor pairs in cleavage embryos derived from discarded human tri-pronuclear zygotes and in human endometrium. Combined treatment with key embryonic growth factors (brain-derived neurotrophic factor, colony-stimulating factor, epidermal growth factor, granulocyte macrophage colony-stimulating factor, insulin-like growth factor-1, glial cell-line derived neurotrophic factor, and artemin) in serum-free media promoted >2.5-fold the development of tri-pronuclear zygotes to blastocysts. For normally fertilized embryos, day 3 surplus embryos cultured individually with the key growth factors showed >3-fold increases in the development of 6–8 cell stage embryos to blastocysts and >7-fold increase in the proportion of high quality blastocysts based on Gardner’s criteria. Growth factor treatment also led to a 2-fold promotion of blastocyst outgrowth in vitro when day 7 surplus hatching blastocysts were used. When failed-to-be-fertilized oocytes were used to perform somatic cell nuclear transfer (SCNT) using fibroblasts as donor karyoplasts, inclusion of growth factors increased the progression of reconstructed SCNT embryos to >4-cell stage embryos. Growth factor supplementation of serum-free cultures could promote optimal early embryonic development and implantation in IVF-ET and SCNT procedures. This approach is valuable for infertility treatment and future derivation of patient-specific embryonic stem cells.     

Vitrification of murine mature metaphase II oocytes perturbs DNA methylation reprogramming during preimplantation embryo development

Accurate reprogramming of DNA methylation occurring in preimplantation embryos is critical for normal development of both fetus and placenta. Environmental stresses imposed on oocytes usually cause the abnormal DNA methylation reprogramming of early embryos. However, whether oocyte vitrification alters the reprogramming of DNA methylation (5 mC) and its derivatives in mouse preimplantation embryo development remains largely unknown. Here, we found that the rate of cleavage and blastocyst formation of embryos produced by IVF of vitrified matured oocytes was significantly lower than that in control counterparts, but the quality of blastocysts was not impaired by oocyte vitrification. Additionally, although vitrification neither altered the dynamic changes of 5-hydroxymethylcytosine (5hmC) and 5-formylcytosine (5 fC) before 4-cell stage nor affected the levels of 5 mC and 5-carboxylcytosine (5caC) throughout the preimplantation development, vitrification significantly reduced the levels of 5hmC and 5 fC from 8-cell stage onwards. Correspondingly, vitrification did not alter the expression patterns of Tet3 in preimplantation embryos but apparently reduced the expression levels of Tet1 in 4-cell and 8-cell embryos and increased the expression levels of Tet2 at morula stage. Taken together, these results demonstrate that oocyte vitrification perturbs DNA methylation reprogramming in mouse preimplantation embryo development.     

Offspring from Mouse Embryos Developed Using a Simple Incubator-Free Culture System with a Deoxidizing Agent

To culture preimplantation embryos in vitro, water-jacketed CO₂ incubators are used widely for maintaining an optimal culture environment in terms of gas phase, temperature and humidity. We investigated the possibility of mouse embryo culture in a plastic bag kept at 37°C. Zygotes derived from in vitro fertilization or collected from naturally mated B6D2F1 female mice were put in a drop of medium on a plastic culture dish and then placed in a commercially available plastic bag. When these were placed in an oven under air at 37°C for 96 h, the rate of blastocyst development and the cell numbers of embryos decreased. However, when the concentration of O₂ was reduced to 5% using a deoxidizing agent and a small oxygen meter, most zygotes developed into blastocysts. These blastocysts were judged normal according to their cell number, Oct3/4 and Cdx2 gene expression levels, the apoptosis rate and the potential for full-term development after embryo transfer to pseudopregnant recipients. Furthermore, using this system, normal offspring were obtained simply by keeping the bag on a warming plate. This culture method was applied successfully to both hybrid and inbred strains. In addition, because the developing embryos could be observed through the transparent wall of the bag, it was possible to capture time-lapse images of live embryos until the blastocyst stage without needing an expensive microscope-based incubation chamber. These results suggest that mouse zygotes are more resilient to their environment than generally believed. This method might prove useful in economical culture systems or for the international shipment of embryos.     

Dynamics of zonula occludens-2 expression during preimplantation embryonic development in the hamster

The objective was to study the expression of zonula occludens-2, a tight junction protein, during preimplantation hamster embryonic development, to predict its possible localization, source, and roles in trophectoderm differentiation and blastocyst formation in this species. Comparison of zonula occludens-2 expression pattern between the hamster and mouse preimplantation embryos from the zygote up to the blastocyst stage was also an objective of this study. Zonula occludens-2 localization was noted in nuclei of blastomeres in all stages of hamster and mouse embryonic development. Compared to mice, where zonula occludens-2 was first localized in the interblastomere membrane at the morula stage, hamster embryos had membranous zonula occludens-2 localization from the 2-cell stage onwards. Based on combined results of immunolocalization study in parthenogenic embryos and ovarian and epididymal sections, and quantitative PCR done in oocytes and all developmental stages of preimplantation embryos, perhaps there was a carry-over of zonula occludens-2 proteins or mRNA from the dam to the embryo. Based on these findings, we inferred that maternally derived zonula occludens-2 was involved in nuclear functions, as well as differentiation of blastomeres and blastocoel formation during preimplantation embryonic development in the hamster.