Academic literature on the topic 'Blastocyst hatching process'

Hatching has been suggested to occur as a result of protease-mediated lysis and the blastocoele tension. However, even if rupturing is initiated at multiple sites, interestingly only a single site is used for escape. This implies that there are several mechanisms involved in hatching. In this study, the involvement of actin filaments in mouse embryo hatching was examined. We treated mouse embryos with cytochalasin B for 12 h or 24 h at the morula, middle blastocyst, expanded blastocyst, lobe-formed blastocyst and hatching blastocyst stages, and measured the amount and distribution of actin filaments using a confocal microscope. At morula, middle blastocyst, lobe-formed blastocyst and hatching blastocyst stages embryonic development was completely arrested by cytochalasin B. However, when transferred to cytochalasin-B-free medium, the embryos resumed development and escaped the zona pellucida. In the expanded blastocysts development was almost completely inhibited by cytochalasin B, but rupturing occurred in some embryos. However, development stopped completely at the ruptured stage. Distribution of actin filaments was prominent at rupturing and hatching sites regardless of cytochalasin B treatment. The amount of actin filaments was prominent at hatching embryos compared with other developmental stages of embryos. These actin filaments were distributed intensively between the trophectodermal cells, and formed locomotion patterns. Taken together, these results suggest that not only tension and lytic enzymes are required to rupture, but the activity of actin filaments may have a crucial role in the process of hatching.

For last 20 years, the efficiency of animal cloning has remained extremely low, despite many attempts to improve it. Although nuclear transfer experiments have been almost optimized, artificial holes are inevitably made in the zona pellucida (ZP) during nuclear transfer experiments, such as enucleation of maternal genome or injection of nuclear donor. Hatching from the ZP is a prerequisite for mammalian embryo implantation, and the condition of the ZP has a lot of influence on hatching. The present studies were performed to investigate the effects of artificial holes in the ZP, because of the nuclear transfer procedure, on hatching of clone embryos in pigs. All experiments were done in triplicate. Statistical analysis was performed using SPSS statistical software (SPSS Inc., Chicago, IL, USA). First, we made a slit in the ZP of porcine parthenote that was identical to the artificial holes of nuclear transfer experiment and compared in vitro development of Day 7 embryos with control group with intact ZP. Of slit blastocysts, 89.9% (80/89) were trapped at a slit, which looked like typical figure-eight shape, and did not complete the hatching process until Day 8, though 68.8% (64/93) of control blastocysts completed the hatching at Day 7. Then, to solve these abnormal hatchings caused by a slit in the ZP, we applied partial zona dissection (PZD) to porcine clone embryos and compared the hatching process with that of conventional clone embryos. Contrary to conventional clone blastocysts that were trapped at slit in the ZP (91.4%; 43/47), 89.5% (60/67) of clone blastocysts in PZD group were preferentially hatched through dissected hole at Day 7. These results suggest that trapping of conventional clone blastocyst in a slit of the ZP could be avoided by PZD. Through this study, we demonstrated that a slit in the ZP would hinder a blastocyst from hatching from the ZP and that partial dissection at the ZP could help clone blastocyst to hatch without trapping at a slit in the ZP. This assisted hatching in clone embryos would be useful for the successful hatching of clone blastocysts with a capacity of full-term development, so that the efficiency of animal cloning might be improved.

SummaryThe objective of this study was to evaluate the effect of supplementation of recombinant leukaemia inhibitory factor (LIF) in culture media on blastocyst development, total cell number and blastocyst hatching rates and the reverse transcription-polymerase chain reaction analysis of preimplantation buffalo embryos to determine whether they contain the LIF-encoding mRNA and its beta receptor (LIFRβ) genes in different stages of preimplantation buffalo embryos. Cumulus–oocyte complexes retrieved from slaughterhouse buffalo ovaries were matured in vitro and fertilized using frozen buffalo semen. After 18 h of co-incubation with sperm, the presumptive zygotes were cultured in modified synthetic oviductal fluid without (control) or with rhLIF (100 ng/ml). There was no significant difference in the overall cleavage rate up to morula stage however the development of blastocysts, hatching rate and total cell numbers were significantly higher in the LIF-treated group than control. Transcripts for LIFRβ were detected from immature, in vitro-matured oocytes and in the embryos up to blastocyst stage, while transcripts for the LIF were detected from 8–16-cell stage up to blastocyst, which indicated that embryo-derived LIF can act in an autocrine manner on differentiation process and blastocyst formation. This study indicated that the addition of LIF to the embryo culture medium improved development of blastocysts, functional (hatching) and morphological (number of cells) quality of the blastocysts produced in vitro. The stage-specific expression pattern of LIF and LIFRβ mRNA transcripts in buffalo embryos indicated that LIF might play an important role in the preimplantation development and subsequent implantation of buffalo embryos.

Mammalian embryos are surrounded by an acellular shell, the zona pellucida. Hatching out of the zona is crucial for implantation and continued development of the embryo. Clinically, problems in hatching can contribute to failure in assisted reproductive intervention. Although hatching is fundamentally a mechanical process, due to limitations in methodology most studies focus on its biochemical properties. To understand the role of mechanical forces in hatching, we developed a hydrogel deformation-based method and analytical approach for measuring pressure in cyst-like tissues. Using this approach, we found that, in cultured blastocysts, pressure increased linearly, with intermittent falls. Inhibition of Na/K-ATPase led to a dosage-dependent reduction in blastocyst cavity pressure, consistent with its requirement for cavity formation. Reducing blastocyst pressure reduced the probability of hatching, highlighting the importance of mechanical forces in hatching. These measurements allowed us to infer details of microphysiology such as osmolarity, ion and water transport kinetics across the trophectoderm, and zona stiffness, allowing us to model the embryo as a thin-shell pressure vessel. We applied this technique to test whether cryopreservation, a process commonly used in assisted reproductive technology (ART), leads to alteration of the embryo and found that thawed embryos generated significantly lower pressure than fresh embryos, a previously unknown effect of cryopreservation. We show that reduced pressure is linked to delayed hatching. Our approach can be used to optimize in vitro fertilization (IVF) using precise measurement of embryo microphysiology. It is also applicable to other biological systems involving cavity formation, providing an approach for measuring forces in diverse contexts.

The aim of our study was to assess whether the cryotolerance of in vitro-produced embryos could be influenced by the length of in vitro culture and size of blastocoel cavity before vitrification, using the pig as a model. For this purpose we analysed the cryoresistance and apoptosis rate of blastocysts at different stages of development as derived on Day 5 and 6 of in vitro culture. Blastocysts were subsequently vitrified, warmed and cultured for 24 h. Re-expansion rates were recorded at 3 and 24 h and total cell number and apoptotic cells were determined at 24 h. Day-6 blastocysts showed the highest rates of survival after warming, which indicates higher quality compared with Day-5 blastocysts. Higher re-expansion rates were observed for expanded blastocysts and those in the process of hatching when compared with early blastocysts. Total cell number and apoptotic cells were affected by blastocyst stage, vitrification–warming procedures and length of in vitro culture, as expanding and hatching–hatched blastocysts from Day 6 presented higher percentages of apoptotic cells than fresh blastocysts and blastocysts vitrified at Day 5. Our findings suggest that the cryotop vitrification method is useful for the cryopreservation of porcine blastocysts presenting a high degree of expansion, particularly when vitrification is performed after 6 days of in vitro culture. Furthermore, these results show that faster embryo development underlies higher blastocyst cryotolerance and provide evidence that blastocoel cavity expansion before vitrification is a reliable index of in vitro-produced embryo quality and developmental potential.

Lipids are a potent source of cellular energy and are metabolized within mitochondria via fatty acid β-oxidation, a process that also requires carnitine. Embryos metabolize lipids during pre-implantation development, but relatively little is known about the effect of fatty acid supplementation for early bovine embryogenesis in culture. The objective of this study was to evaluate the effect of lipid supplementation (via albumin) and l-carnitine (C; 5 mM) during embryo culture in a novel medium with reduced concentrations of nutrients, compared with our standard culture medium (control). Following in vitro maturation and IVF, zygotes were cultured using a serum-free sequential media system (0-72 h step 1; 72-168 h step 2). Concentrations of salts, bicarbonate, and protein [2.5 mg mL−1 fatty acid-free (FAF) or fraction V (FrV) BSA] were the same in all treatments to maintain consistent osmolarity and pH. Nutrients (glucose/fructose, citrate, lactate, pyruvate, amino acids, vitamins, and EDTA) were diluted to 6.25% of control. In addition to the control medium (100%+FAF; n = 587), experimental treatments included 6.25%+FAF+C (essentially lipid free; n = 573) and 6.25%+FrV+C (lipid rich; n = 585). Following in vitro culture (7 reps), hatching blastocysts were stained to determine inner cell mass (ICM; SOX2+) and trophectoderm (TE; CDX2+) cell numbers. Lipid content of single expanded blastocysts was determined using gas chromatography coupled to an ISQ-LT MS/MS (GC-MS). Data (mean ± SEM) were analysed by ANOVA. Embryo cleavage did not differ between treatments. Blastocyst development (per cleaved embryo) was higher (P < 0.05) after culture in lipid rich (38.3 ± 1.5%) compared with control (29.6 ± 2.2%) and lipid free (28.1 ± 3.6%). Blastocyst hatching was reduced (P < 0.05) in lipid free (1.4 ± 0.7%) but not in lipid rich (5.2 ± 1.7) compared with control (9.8 ± 2.1). However, blastocysts developed in lipid rich and lipid free had reduced cell numbers compared with control: TE, 98.7 ± 5.9 and 98.8 ± 9.1 v. 160.3 ± 9.0; ICM, 19.2 ± 2.9 and 25.2 ± 6.1 v. 43.3 ± 4.0; and total cell number, 117.9 ± 7.3 and 124.0 ± 8.7 v. 203.6 ± 10.2, respectively. Analysis by GC-MS identified 40 annotated lipids (i.e. triacylglycerols and phosphatidyl cholines) that were significantly reduced in blastocysts cultured in lipid rich compared with control. In summary, blastocyst development was significantly improved after supplementation of fatty acids and l-carnitine to a medium with reduced nutrient concentrations. The mechanism underlying this phenomenon may be related to increased lipid metabolism in the low nutrient environment. Although more embryos developed in this novel medium, these blastocysts had reduced cell numbers even though blastocyst expansion and hatching were not affected. This reduced nutrient medium may provide an experimental model in which to independently study pathways controlling cell proliferation and blastocyst development. Future studies will investigate whether embryo cell number can be rescued while maintaining improved blastocyst development.

The control of oxidative processes in in vitro production (IVP) systems by the use of additives may be an alternative approach to improve embryo cryotolerance. The aim of this study was to verify the effect of β-mercaptoethanol (βME) on the cryotolerance of bovine IVP embryos. In 7 replications, and following IVM-IVF, presumptive zygotes (n = 3735) were in vitro-cultured in SOF medium supplemented or not with 100 μm βME (IVC treatment), at 38.5°C and high humidity. The initial 24 h of IVC was performed in 5% CO2 in air, with the remaining 6 days of IVC carried out in 5% CO2, 5% O2, and 90% N2. On Day 7, resulting blastocysts and expanded blastocysts were vitrified in glass micropipettes in a solution with 20% ethylene glycol + 20% propylene glycol. After warming, embryos were randomly allocated to 1 of 2 sub-groups for an additional 72 h of IVC to the hatching blastocyst (HBL) stage, in fresh SOF medium supplemented or not with 100 μm βME (PVC treatment), at 38.5°C, high humidity and 5% CO2. Experimental groups were as follows: G1 (βME-free medium during IVC and PVC); G2 (βME only during PVC); G3 (βME only during IVC); and G4 (βME during IVC and PVC). Cleavage (Day 2) and blastocyst (Day 7) rates in the IVC treatment and hatching rates (Days 7 to 9) for the PVC treatment were analyzed by the chi-square test, for P < 0.05. Total cell number (TCN) estimated by fluorescence staining in HBL derived from vitrified and nonvitrified embryos was analyzed by ANOVA. The use of βME during IVC did not affect cleavage rates (βME-free, 1491/1858, 80.2% v. βME, 1522/1877, 81.1%), but negatively affected development to the blastocyst stage (βME-free, 813/1858, 43.8% v. βME, 525/1877, 28.0%). Following vitrification, however, βME supplementation during PVC improved hatching rates (G2, 58.1% and G4, 63.8%) compared with groups without the additive (G1, 36.6% and G3, 42.0%). In addition, the presence of βME either during IVC or PVC, or during both culture periods, increased TCN in HBL from vitrified embryos (Table 1). The use of βME during IVC, irrespective of the presence of βME during the PCV period, caused an increase in TCN in HBL in G3 + G4, with no effects on hatching rates (Table 1b), whereas the addition of βME during PVC, irrespective of the presence of βME during the IVC period, resulted in greater hatching rates and TCN in HBL in G2 + G4 than in G1 + G3 (Table 1). In conclusion, the addition of βME during the IVC period did not affect cleavage, but reduced blastocyst yield. Despite that, βME supplementation during the IVC period appeared to have increased the cryotolerance of the resulting blastocysts, expressed by greater TCN in HBL, whereas βME supplementation during the PVC period also improved embryo survival to the vitrification process, manifested by greater hatching rates and TCN in HBL. Table 1.Effect of βME on the cryotolerance of bovine IVP embryos This study was supported by a grant from CNPq/Brazil.

SummarySex selection through sperm sorting offers advantages in regards selection pressure in high-producing livestock. However, the sex-sorting process results in sperm membrane and DNA damage that ultimately decrease fertility. We hypothesized that given the role of protamines in DNA packaging, protamine deficiency could account, at least partially, for the DNA damage observed following sperm sex sorting. To test this, we compared protamine status between unsexed and sexed spermatozoa from two bulls using the fluorochrome chromomycin A3 (CMA3) and flow cytometry. Then, we assessed embryo development following in vitro fertilization (IVF) using the same sperm treatments. Overall, sperm protamination was not different between sexed and unsexed semen. However, one of the two bulls displayed higher rates of protamine deficiency for both unsexed and sexed semen (P < 0.05). Moreover, unsexed semen from this bull yielded lower blastocyst (P < 0.05) and blastocyst hatching rates than unsexed sperm from the other bull. CMA3-positive staining was negatively correlated with cleavage (R2 85.1, P = 0.003) and blastocyst hatching (R2 87.6, P = 0.006) rates in unsexed semen. In conclusion, while the sex-sorting process had no effect on sperm protamine content, we observed a bull effect for sperm protamination, which correlated to embryo development rates following IVF.

The investigation of the transcription factors involved in the regulation of pluripotency in pre-implantation embryos of cattle provides important information regarding the early embryonic development and derivation of embryonic stem cells. The present experiment aimed to compare the level of expression of SOX 2 and Stat3, pluripotency markers, in bovine blastocysts (D7) and hatched blastocysts (D10), because it is known that around hatching, the inner cell mass (ICM) differentiates into hypoblast and epiblast. Cumulus–oocyte complexes were matured in TCM 199 for 24 h and fertilized with frozen–thawed sperm. Presumptive zygotes were cultured in SOFaaci for 7 days (group 1) and for 10 days (group 2). All embryos were washed 3 times in PBS, pooled, and frozen at –80°C until RNA extraction. For quantification of SOX2 and Stat3 mRNA levels, total RNA was isolated from pools of 7 embryos per replicate (n = 3) and for each examined developmental stage using RNeasy Micro Kit (Qiagen). The reverse transcriptase Superscript III (Invitrogen) was used for the synthesis of cDNA (cDNA), and the qPCR was performed with the Gotaq qPCR Master Mix (Promega, Madison, WI, USA). As negative control, cDNA was replaced by nuclease-free water in the qPCR reaction. Quantification of expression was determined by the relative standard curve method and normalized to the housekeeping gene YWHAZ. Standard curves for SOX2, Stat 3, and YWHAZ were derived from 10-fold serial dilutions of bovine DNA and gave correlation coefficients greater than 0.99 and efficiencies greater than 94%. The data from 3 replicates were analysed by ANOVA, and it was found that the level of SOX2 abundance is 9.8-fold higher in D7 blastocyst cells compared with D10 blastocyst cells, and the level of Stat 3 transcription is 1.5-fold higher in blastocyst cells than in hatched blastocysts. The expression of pluripotency markers SOX2 and Stat3 was significantly higher in embryos with 7 days of development because at this stage the MCI had not yet begun the process of differentiation. Support of FAPESP is acknowledged.

Heparin-binding EGF-like growth factor (HB-EGF) is a newly discovered member of the EGF family of growth factors. HB-EGF can bind to two loci on cell surfaces, heparan sulphate proteoglycans and EGF-receptor (EGF-R), and either one or both of these interactions could play a role in cell-cell interactions. In the rodent, increased endometrial vascular permeability at the site of blastocyst apposition is considered to be an earliest discernible prerequisite event in the process of implantation and this event coincides with the initial attachment reaction between the blastocyst trophectoderm and uterine luminal epithelium. This investigation demonstrates that the HB-EGF gene is expressed in the mouse uterine luminal epithelium surrounding the blastocyst 6–7 hours before the attachment reaction that occurs at 2200–2300 hours on day 4 of pregnancy. It was further demonstrated that this gene is not expressed in the luminal epithelium at the site of the blastocyst apposition during the progesterone-maintained delayed implantation, but is readily induced in the luminal epithelium surrounding an activated blastocyst after termination of the delay by an estrogen injection. In vitro studies showed that HB-EGF induced blastocyst EGF-R autophosphorylation, and promoted blastocyst growth, zona-hatching and trophoblast outgrowth. These results suggest possible interactions between the uterine HB-EGF and blastocyst EGF-R very early in the process of implantation, earlier than any other embryo-uterine interactions defined to date at the molecular level.

The detailed investigation on the embryo-endometrial cytokine expression, in both mouse and hamster, was carried out during the peri-hatching development and it is described in chapter 2. We hypothesize that, for a successful implantation, a balance of embryonic expression and function of pro-inflammatory and anti-inflammatory cytokines are necessary to maintain proper homeostasis of cytokine expression, compatible with peri- hatching embryonic development and hatching, eventually enabling the establishment of early pregnancy. Our cytokine expression studies along with various other reports have successfully established that a number of implantation-associated cytokines are expressed during peri- hatching development and therefore, could be critical for blastocyst to become implantation- competent. One of the cytokines, IL-1β was found to be strongly expressed during the peri- hatching development. The human clinical reports have established that IL-1β is as a potential embryonic biomarker for successful implantation. Besides, there are controversial reports probing its significance in implantation process (Chapter 1, section 3.2.3). Much of the functional data on the critical requirement of IL-1β and their signaling system during the peri-implantation development comes from gene-knockout studies involving the cytokine and their cognate receptor (Chapter 1, Table IV). Due to the redundancy and cross-talk, the IL-1β knock- out mouse does not exhibit profound implantation failure and the least known is the hatching phenotype. In view of the above, the functional involvement of strategically identified pro- inflammatory cytokine, IL-1β along with its natural antagonist and anti- inflammatory cytokine i.e., IL-1ra were investigated in hatching process of both the hamster (Chapter 3) and the mouse (Chapter 4), for comparison. Previous reports on hamster and mouse have established the participation of species- specific proteases associated with blalstocyst hatching. Of relevance, here, is the observation that both IL-1β and IL-1ra are known, in non-embryonic context, to modulate generally proteases (Chapter 1, section 3.2.5). These reports are significant in the context of hatching and therefore, the expression and functional correlation of IL- 1β and hatching promoting proteases during peri- hatching blastocyst development in the hamster and mouse were examined in this study (Chapters 3 and 4). Besides, the involvement of species-specific proteases in the hatching process is examined further at the structural level. In this computational study, the interaction of proteases with individual ZP protein(s) of the hamster and the mouse were analyzed. We studied the sequential and structural variations potentially responsible for the differential susceptibility of zona protein of the mouse and hamster towards different proteases examined (Chapter 5). The defined objectives and implications of the proposed study are depicted in Fig 1. This study is significant in our understanding of cytokines-mediated cellular and molecular regulation of blastocyst hatching phenomenon. The new and improved formulation of culture systems with a possible cytokine supplements could be exploited for sustained in vitro potentially viable development of blastocysts through hatching. The data on the cytokine (IL-1β) expression and function, described here, could be potentially a quality/viable embryo biomarker (i) as a tool to improve efficacy of peri-hatching blastocyst development and importantly, (ii) in the human, it could be exploited for improving the pregnancy outcome of the IVF-ET program in the ART clinic setting.