Preimplantation development and viability of in vitro cultured rabbit embryos derived from in vivo fertilized gene-microinjected eggs: apoptosis and ultrastructure analyses

Real-Time Visualization of Embryonic Apoptosis Using a Near-Infrared Fluorogenic Probe for Embryo Development Evaluation

Developing an accurate and reliable detection technique for early embryonic apoptosis is of great significance for real-time monitoring and evaluation of embryonic development in living systems. Herein, we have rationally designed and synthesized a novel near-infrared (NIR) fluorogenic probe CGK(QSY21)DEVD-Cy5.5 for real-time imaging of embryonic apoptosis. This probe is constructed with a NIR dye Cy5.5, a fluorescence quencher QSY21, and a peptide substrate Asp-Glu-Val-Asp (DEVD) of the caspase-3 enzyme that is a key executor of cell apoptosis. The probe was initially nonfluorescent in aqueous solution but emitted strong NIR fluorescence upon specific cleavage by activated caspase-3 in a concentration-dependent manner. Taking advantage of this unique feature, this fluorogenic probe was for the first time used for real-time imaging of caspase-3 activity in apoptotic embryos. More notably, significant fluorescence enhancement was solely determined from the apoptotic embryos with the treatment of the probe both in vitro and in vivo, highly suggesting that this probe has great potential to monitor the apoptosis of embryos. We thus envision that this probe would provide a very useful means for real-time visualization and accurate evaluation of embryonic development in the future.

Optimizing injection time of GFP plasmid into sheep zygote

Microinjection of exogenous DNA into the cytoplasm of matured oocytes or zygotes is a promising technique to generate transgenic animals. However, the data about the microinjection time and procedure in sheep are limited and have not treated in detail. To obtain more in-depth information, the Sarda sheep oocytes from abattoir-derived ovaries were subjected to IVM and IVF. Then, the GFP plasmid as a reporter gene was injected into the cytoplasm of MII oocytes (n: 95) and zygotes at different post-insemination intervals (6-8 hpi, n: 120; 8-10 hpi, n: 122; 10-12 hpi, n: 110 and 12-14 hpi, n: 96). There were no significant differences in the cleavage rates between the groups. However, blastocyst rate of injected zygotes at all-time intervals was significantly lower than injected MII oocytes and control group (p < 0.05). Interestingly, the proportion of GFP-positive embryos was higher at 8-10 hpi compared with other injected groups (4 % versus 0 %, p  < 0.01). Among these, the proportion of mosaic embryos was high and two of those embryos developed to the blastocyst stage. In conclusion, we settled on the cytoplasmic microinjection of GFP plasmid at 8-10 hpi as an optimized time point for the production of transgenic sheep and subsequent experiments.

Embryotropic effects of vascular endothelial growth factor on porcine embryos produced by in vitro fertilization

Current research suggests that supplementing in vitro culture (IVC) media with vascular endothelial growth factor (VEGF) may have beneficial effects on the development of porcine embryos in vitro. However, the molecular signaling mechanisms underlying this effect are unclear. Therefore, we aimed to investigate the effects of VEGF on molecular signaling events during in vitro embryonic development of porcine embryos. Porcine oocytes matured in vitro were fertilized, and the resultant zygotes were cultured with 5 ng/mL of VEGF supplemented with or without fetal bovine serum from day 4 till day 7. Without VEGF and/or FBS served as the control group. Real-time quantitative PCR was used to detect expression patterns of apoptosis- and oxidative stress-related genes in day 7 blastocysts (BLs). Early-stage apoptosis was detected by annexin-V assays in day 2 and day 7 embryos. We found that the addition of VEGF throughout the culture period with or without FBS supplementation significantly improved embryo survival and development. Supplementation with VEGF in the IVC medium significantly increased early BL formation (p < 0.05), although addition of FBS on day 4 significantly increased hatched BL formation (p < 0.05) regardless of VEGF supplementation. However, supplementation of media with both VEGF and FBS increased the formation of expanded BLs synergistically. The average total cell numbers per BL were significantly (p < 0.05) higher in embryos supplemented with VEGF and FBS than in those supplemented with either VEGF or FBS alone. We also found that accumulation of reactive oxygen species in VEGF-treated embryos was significantly lower (p < 0.05) than that in untreated embryos. The mRNA levels of caspase-3 were significantly lower (p < 0.05), and those of Bcl-2 and Nrf-2 were significantly higher (p < 0.05) in embryos grown in VEGF-supplemented media than in embryos grown in non-supplemented media. Furthermore, on day 2, the numbers of viable embryos (44.06 ± 3.94%) and blastomeres (67.18 ± 3.60%) were significantly higher (p < 0.05), and the numbers of early apoptotic embryos (55.94 ± 3.94) and blastomeres (23.23 ± 4.22) were significantly lower (p < 0.05) in VEGF-treated BLs than in controls. Furthermore, the numbers of early apoptotic cells in BLs on day 7 were also significantly lower (p < 0.05) in VEGF-treated BLs than in controls. Overall, our results indicate that supplementing IVC media with VEGF during in vitro culture of porcine embryos increases their developmental potential.

Quality of preimplantation embryos recovered in vivo from dairy cows in relation to their body condition

This study examined the impact of cow body condition on the quality of bovine preimplantation embryos. The embryos (n = 107) were flushed from dairy cows and classified according to a five-point scale body condition score (BCS2 n = 17; BCS3 n = 31; BCS4 n = 11) on the 7th day after insemination and then analyzed for development, dead cell index (DCI), cell number and actin cytoskeleton quality. The highest embryo recovery rate (P < 0.05) was recorded in the BCS3 group and the lowest in the BCS4 group. More transferable (morula, blastocyst) embryos were obtained from the BCS4 cows (79%), compared with the BCS2 (64%) or BCS3 (63%) animals. However, cell numbers were higher in the BCS2 and BCS3 groups (P < 0.05) compared with the BCS4 embryos. Conversely, the DCI was lowest in the BCS2 (3.88%; P < 0.05) and highest in the BCS4 (6.56%) embryos. The proportion of embryos with the best actin quality (grade I) was higher in the BCS2 and BCS3 cows compared with the BCS4 group. Almost 25% of all embryos showed fragmented morphology and a higher DCI (5.65%) than normal morulas (1.76%). More fragmented embryos were revealed in the BCS2 (28.6%) and BCS4 (31.25%) groups, and less (19.15%) in the BCS3 group. The cell numbers in such embryos were lower in the BCS4 (22.57) than in the BCS2 (46.25) or BCS3 (42.4) groups. In conclusion, the body condition of dairy cows affects the quality of preimplantation embryos. A BCS over 3.0 resulted in a higher incidence of poor (fragmented) embryos.

Efficient Generation of Myostatin Knock-Out Sheep Using CRISPR/Cas9 Technology and Microinjection into Zygotes

While CRISPR/Cas9 technology has proven to be a valuable system to generate gene-targeted modified animals in several species, this tool has been scarcely reported in farm animals. Myostatin is encoded by MSTN gene involved in the inhibition of muscle differentiation and growth. We determined the efficiency of the CRISPR/Cas9 system to edit MSTN in sheep and generate knock-out (KO) animals with the aim to promote muscle development and body growth. We generated CRISPR/Cas9 mRNAs specific for ovine MSTN and microinjected them into the cytoplasm of ovine zygotes. When embryo development of CRISPR/Cas9 microinjected zygotes (n = 216) was compared with buffer injected embryos (n = 183) and non microinjected embryos (n = 173), cleavage rate was lower for both microinjected groups (P<0.05) and neither was affected by CRISPR/Cas9 content in the injected medium. Embryo development to blastocyst was not affected by microinjection and was similar among the experimental groups. From 20 embryos analyzed by Sanger sequencing, ten were mutant (heterozygous or mosaic; 50% efficiency). To obtain live MSTN KO lambs, 53 blastocysts produced after zygote CRISPR/Cas9 microinjection were transferred to 29 recipient females resulting in 65.5% (19/29) of pregnant ewes and 41.5% (22/53) of newborns. From 22 born lambs analyzed by T7EI and Sanger sequencing, ten showed indel mutations at MSTN gene. Eight showed mutations in both alleles and five of them were homozygous for indels generating out-of frame mutations that resulted in premature stop codons. Western blot analysis of homozygous KO founders confirmed the absence of myostatin, showing heavier body weight than wild type counterparts. In conclusion, our results demonstrate that CRISPR/Cas9 system was a very efficient tool to generate gene KO sheep. This technology is quick and easy to perform and less expensive than previous techniques, and can be applied to obtain genetically modified animal models of interest for biomedicine and livestock.

Ultrastructure of rabbit embryos exposed to hyperthermia and anti-Hsp 70

The aim of the study was to determine the effect of short-term hyperthermia and Hsp70 blockage on ultrastructural changes in cell organelles and nucleoli of rabbit preimplantation embryos. The embryos were cultured either at 37.5°C (control, C) or 41.5°C (hyperthermia, HT) during 6 h. The antibody against Hsp70 was added into the culture medium (4 μg/ml) of morula stage embryos from C and HT groups. After termination of the culture, the embryos were processed for transmission electron microscopy. The embryos exposed to hyperthermia showed increased volume of lipid droplets, considerable occurrence of cellular debris in the perivitelline space and slight changes in the occurrence of microvilli on the surface of trophoblastic cells. In the embryos exposed to anti-Hsp 70 at 37.5°C, there were considerable changes in mitochondria morphology, decreased volume of dense bodies in the cytoplasm and considerable changes in the occurrence of microvilli on the surface of trophoblastic cells. In the group of embryos exposed simultaneously to hyperthermia and anti-Hsp 70, mitochondria were also expanded and swollen; the volume of flocculent vesicles and lipid droplets was increased and the volume of dense bodies in the cytoplasm was diminished. General organization of the cytoplasm in groups with anti-Hsp70 was characterized by cell organelle segregation. Averaged size of the nucleolar area was significantly increased in the embryos exposed to hyperthermia, whereas in the group exposed to the anti-Hsp70 without hyperthermia it was significantly diminished. Hyperthermia also caused disintegration of compact status of the nucleoli. In presence of anti-Hsp 70, the structural changes, described within the nucleoli during hyperthermia, were not observed. In conclusion, these results document ultrastructural changes in cell organelles of rabbit preimplantation embryo caused by hyperthermia, and also changes in the nucleolar structures, at which presence of Hsp-70 inhibit these changes.

Quality of rabbit vitrified/thawed transgenic embryos

The aim of our study was to investigate the influence of vitrification on developmental rate and quality (total number of cells, number of blastomeres in inner cell mass (ICM) area, apoptotic index and embryo diameter) of transgenic (carrying an endogenous–hFVIII or exogenous–enhanced green fluorescent protein (EGFP) gene) rabbit embryos. EGFP-positive rabbit embryos were produced under in vitro conditions by the microinjection of foreign genes into the pronucleus of fertilized eggs. The transgenic rabbit embryos with the hFVIII gene were produced by mating homozygous transgenic rabbits and flushing at the single-cell stage. Developmental rate of vitrified/thawed transgenic embryos that reached hatching blastocyst stage (68.00% and 69.00%) and differed significantly (p < 0.001) from those in control embryos (100.00%). Significant difference (p < 0.05) was found in total cell counts between control (117.00 ± 36.00) and vitrified (141.00 ± 34.80) hFVIII-positive embryos. The higher proportion of ICM cells (32.00%) and greatest embryo diameter (130.85 ± 10.90) were found in the control group compared with the transgenic. Ratio of apoptotic cells was significantly higher (p < 0.01) in the control group (2.50%) and vitrified EGFP-positive embryos (2.90%) compared with the vitrified, hFVIII-positive group of embryos (0.70%). Our results demonstrate that neither gene microinjection itself, nor exogenous (EGFP) and endogenous (hFVIII) gene expression interferes with developmental rate and quality of rabbit embryos. However, a combination of microinjection and vitrification significantly decreases (p < 0.001) the survival rate of rabbit embryos.

Quality of transgenic rabbit embryos with different EGFP gene constructs

The aim of this study was to compare the quality of rabbit transgenic embryos obtained upon microinjection of gene constructs containing different promoters and green fluorescent proteins (CMVIE–EGFP, PGK–EGFP and CMVIE–hrGFP). Developmental rate, total cell number in hatching blastocyst stage, number of apoptotic cells, diameter of embryos, transgene integration and transgenic mosaicism were investigated.

The rate of rabbit embryos microinjected with the different gene constructs developed up to morula stage was significantly lower (p < 0.05) than that of intact (non-microinjected) rabbit embryos (66–74vs. 98%). The highest efficiency of transgene integration (15%) was found when the CMVIE–EGFP (DrdI) gene construct was used, however a significantly higher transgenic mosaicism (60%) was found in rabbit embryos using this gene. The lowest cell number was counted in rabbit transgenic embryos with CMVIE–rhGFP linearized by ScaI (115.0 ± 8.20), the highest cell number (134.0 ± 35.00) was detected in rabbit transgenic embryos carrying PGK–EGFP (Not I) gene. The highest number of apoptotic cells (2.6 ± 0.33) was recorded in rabbit transgenic embryos with the integrated CMVIE–EGFP (ClaI) transgene.

Based on these results a more suitable gene marker for rabbit transgenic embryos production and selection is the CMVIE–EGFP (ClaI) gene construct. Prior to using microinjected embryos (for embryo transfer, vitrification or ESC isolation) it is necessary to pre-select microinjected embryos with evident transgenic mosaicism.

Ultrastructural changes in goat interspecies and intraspecies reconstructed early embryos

The low efficiency of somatic cell nuclear transfer may be related to the ultrastructural deviations of reconstructed embryos. The present study investigated ultrastructural differences between in vivo-produced and cloned goat embryos, including intra- and interspecies embryos. Goat ear fibroblast cells were used as donors, while the enucleated bovine and goat oocytes matured in vitro as recipients. Goat–goat (GG), goat–cattle (GC) and goat in vivo-produced embryos at the 2-cell, 4-cell, 8-cell and 16-cell stages were compared using transmission electron microscopy. These results showed that the three types of embryos had a similar tendency for mitochondrial change. Nevertheless, changes in GG embryos were more similar to changes in in vivo-produced embryos than were GC embryos, which had more extreme mitochondrial deviation. The results indicate the effects of the cytoplast on mitochondria development. The zona pellucida (ZP) in all three types of embryos became thinner and ZP pores in both GC and GG embryos showed an increased rate of development, especially for GC embryos, while in vivo-produced embryos had smooth ZP. The Golgi apparatus (Gi) and rough endoplasmic reticulum (RER) of the two reconstructed embryos became apparent at the 8-cell stage, as was found for in vivo embryos. The results showed that the excretion of reconstructed embryos was activated on time. Lipid droplets (LD) of GC and GG embryos became bigger, and congregated. In in vivo-produced embryos LD changed little in volume and dispersed gradually from the 4-cell period. The nucleolus of GC and GG embryos changed from electron dense to a fibrillo-granular meshwork at the 16-cell stage, showing that nucleus function in the reconstructed embryos was activated. The broken nuclear envelope and multiple nucleoli in one blastomere illuminated that the nucleus function of reconstructed embryos was partly changed. In addition, at a later stage in GC embryos the nuclear envelope displayed infoldings and the chromatin was concentrated, implying that the blastomeres had an obvious trend towards apoptosis. The gap junctions of the three types of embryos changed differently and GG and GC embryos had bigger perivitelline and intercellular spaces than did in vivo-produced embryos. These results are indicative of normal intercellular communication at an early stage, but this became weaker in later stages in reconstructed embryos. In conclusion, inter- and intraspecies reconstructed embryos have a similar pattern of developmental change to that of in vivo-produced embryos for ZP, rough ER, Gi and nucleolus, but differ for mitochondria, LD, vesicles, nucleus and gap junction development. In particular, the interspecies cloned embryos showed more severe destruction. These ultrastructural deviations might contribute to the compromised developmental potential of reconstructed embryos.

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.