ChemInform Abstract Compounds of type (III), (VI) and (IX) may be used in organic synthesis.
Embryonic germ (EG) cells, derived from primordial germ cells in the developing fetus, are similar to embryonic stem (ES) cells in terms of expression pattern of undifferentiated markers and their ability to colonize both the somatic and the germ cell lines following injection into a host blastocyst, which has been proven in mouse. Several studies using porcine EG cells have shown that it is possible to produce somatic chimeras after blastocyst injection. However, not only was the degree of reported chimerism low, but also there has been no report about the fate of injected EG cells in porcine blastocysts. This study was designed to observe the distribution pattern of porcine EG cells in chimeric blastocyst after injection into cleavage-stage porcine embryos. To ascertain development of microinjected porcine embryos with EG cells, 10 to 15 EG cells were injected into cleavage stage of in vitro fertilized embryos and cultured up to blastocyst. Also, porcine EG cells were labeled with DiO (Invitrogen, Carlsbad, CA) on the cell membrane or transfected with green fluorescent protein gene to observe whether the EG cells injected in the host embryo would incorporate into the inner cell mass (ICM) or trophectoderm (TE). Chimeric embryos were produced and allowed to develop into blastocysts to investigate the injected EG cells would come to lie in ICM and/or TE of the blastocyst, by scoring their position. In result, developmental rate was similar in all treatments. In all treatments, EG cells were mainly allocated in both ICM and TE of the chimeric blastocysts. These results suggest that examining the allocation pattern of injected EG cells, maintained pluripotency in vitro, could provide clues of differentiation process in vivo. Furthermore, to enhance the allocation of EG cells into the embryonic lineage, it would be required to optimize the culture condition for EG cells as well as embryos. Further experiment are needed to determine whether the injected EG cells could maintain their properties throughout the environment in the embryonic development in vitro. Table 1. Distribution of the porcine EG cells microinjected into cleavage-stage embryos
X-chromosome inactivation (XCI) is an epigenetically essential process for balancing dosage of X-linked genes between male and female eutherian. Importance of this complex and species-specific event has been highlighted recently in developmental and stem cell biology. However, the process has been confirmed only in restricted species, even though the species-specific studies are needed for comprehensive understanding of XCI in specific species. XCI is regulated by the various genes, many of which are coded on the X chromosome inactivation centre (XIC). Among the XIC-linked genes, especially non-coding RNA (ncRNA) like XIST, which is master gene for XCI, are known to regulate XIC. But the centre is not identified in various species. In this study, we identified XIC in pig and analysed the dosage differences of XIC-linked gene in porcine embryos. At first, the centre was searched in pig. The genomic length of the porcine XIC was similar to human XIC and the order and coding strand of the counterparts in pig XIC were same as the human XIC-linked genes. However, sequence comparison between human XIC-linked gene and its porcine counterpart showed that ncRNA around XIST were less conserved rather than protein-coding genes. This would be caused by rapid evolution of genomic region harboring ncRNA. The expression of XIC-linked genes was compared between male and female porcine embryonic fibroblast (PEF) to confirm that dosage compensation is completed in PEF. Most of the genes were not expressed sex-specifically, but two genes, XIST and an uncharacterized gene, LOC102165544, were expressed female preferentially in PEF. Interestingly, LOC102165544, which had low sequence homology with human JPX, was expressed about 2-fold higher in female PEF. This means that XIST and LOC102165544 are XCI-escaping genes. Among the XIC-linked genes, CHIC1, XIST, LOC102165544, and RLIM were stably expressed in embryonic stage, and XIST and LOC102165544 were up-regulated after morula formation. As XIST accumulation is a requisite for XCI initiation, expression levels of the 4 genes between male and female blastocysts were compared. Interestingly, expression levels of CHIC1 and RLIM were not different in male and female blastocysts. This means their dosage would be already compensated in porcine blastocyst. Additionally, to confirm loci of the 2 genes CHIC1 and RLIM harbor one of the inactive alleles in female blastocyst, the DNA methylation pattern was examined. One of the CHIC1 alleles was inactive but RLIM CpG site was hypo-methylated in female blastocyst. This would indicate that one of the RLIM alleles is transcriptionally inactivated by chromatin modification rather than by DNA methylation of the allele. Regulatory regions of XIST and LOC102165544 were demethylated in blastocyst and this showed XCI was not finished in porcine blastocyst. Conclusively, our results demonstrate the XCI already occurs in porcine blastocyst at least one gene but it is not completed.This work was supported by Next BioGreen21 program (PJ009493), Rural Development Administration, Republic of Korea.
Use of blastocysts produced in vitro would be an efficient way to generate embryonic stem (ES) cells for the production of transgenic animals and the study of developmental gene regulation. In pigs, the morphology and cell number of in vitro-produced blastocysts are inferior to these parameters in their in vivo counterparts. Therefore, establishment of ES cells from blastocysts produced in vitro might be hindered by poor embryo quality. The objective of this study was to increase the cell number of blastocysts derived by aggregating 4–8-cell stage porcine embryos produced in vitro. Cumulus–oocyte complexes were collected from prepubertal gilt ovaries, and matured in vitro. Embryos at the 4–8-cell stage were produced by culturing embryos for two days after in vitro fertilization (IVF). After removal of the zona pellucida with acid Tyrode’s solution, one (1X), two (2X), and three (3X) 4–8-cell stage embryos were aggregated by co-culturing them in aggregation plates followed by culturing to the blastocyst stage. After 7 days, the developmental ability and the number of cells in aggregated embryos were determined by staining with Hoechst 33342 and propidium iodide. The percentage of blastocysts was higher in both 2X and 3X aggregated embryos compared to that of 1X and that of intact controls (Table 1). The cell number of blastocysts also increased in aggregated embryos compared to that of non-aggregated (1X) embryos and controls. This result suggests that aggregation might improve the quality of in vitro-fertilized porcine blastocysts by increasing cell numbers, thus becoming a useful resource for isolation and establishment of porcine ES cells. Further studies are required to investigate the quality of the aggregated embryos in terms of increasing the pluripotent cell population by staining for Oct-4 and to apply improved aggregation methods in nuclear-transferred (NT) porcine embryos. Table 1. Development, cell number, and ICM ratio of aggregated porcine embryos
In vitro production (IVP) of porcine embryos facilitates research related to biotechnology and biomedicine. Even though many attempts have been made to optimize the IVP of porcine embryos, the outcome is still unsatisfactory compared to other species, such as mouse and cattle. The high incidence of polyspermic fertilization is one of the major causes lowering the overall efficiency of porcine IVF. The common procedure for fertilization in vitro involves the co-culture of both gametes in the medium drop, which increases sperm concentration and incidence of polyspermy. Therefore, the present study was carried out to increase the efficiency of porcine IVF by reducing polyspermy using a modified swim-up method. This method modifies conventional swim-up washing by placing oocytes directly at the time of washing. Porcine oocytes were aspirated from ovaries and matured. Sperm pellet was prepared in the tube and mature oocytes were placed on a cell strainer with 70-μm pore size (Falcon 2350) at the top of the tube. After fertilization, the oocytes were fixed and stained for examination. Also, the developmental potential of fertilized embryos was measured to evaluate for the feasibility of this method. While penetration rates were similar in both methods (86.67±2.36% to 83.33±1.36%), there was a significant reduction of polyspermy in the modified swim-up method (17.50±1.60%) compared to the control (44.1±3.70%) (P<0.05). Subsequent culture showed higher rate of blastocyst formation in the modified swim-up method (20.44±0.99%) than in the control (15.73±3.26%) (P<0.05), even though the difference was not significant. These results suggest that, by controlling the number of spermatozoa reaching the oocytes, porcine oocytes might be protected from polyspermy in vitro. Also, the developmental potential of the fertilized embryos using this method could be improved by increasing the pool of spermatozoa with better quality. Further optimization of the procedure is required to impliment this method in routine porcine IVF.
Somatic cell nuclear transfer (SCNT) has been successfully used to produce live cloned offspring in various mammals. However, some studies had reported that cloned embryos by SCNT had many problems in reprogramming or epigenetic modification, such as DNA methylation. DNA methylation is an essential process in epigenetic modification for development, and aberrant methylation in cloned embryos gives rise to abortion, high birth weight, and perinatal death. In this study, embryonic germ (EG) cells were used as donor cells for nuclear transfer. EG cells may have less reprogramming or demethylation than SCNT because these are already in erased status. However, little is known about methylation state or developmental capacity of the EG cell as a donor. The objective of this study was to analyze the methylation pattern of pre-implantation embryos cloned from porcine EG cells. Two regions, PRE-1 and microsatellite (MS), were analyzed for methylation patterns of cloned embryos from porcine EG cells and compared with the pattern of mature oocytes and in vitro-fertilized (IVF) embryos as a control. Cumulus–oocyte complexes were collected from prepubertal gilt ovaries and matured in vitro for 44 h, followed by use for IVF and NT with porcine EG cells. The porcine EG cells were prepared from 28-day-old fetuses after mating; genital ridges were isolated from fetuses, and then transferred into a culture medium on a feeder layer. The number of embryos for analysis was 300 for matured oocytes, 50–80 for 4–8 cell embryos, 30–40 for morulae, and 20–30 for blastocysts. The genomic DNA was isolated from the embryos and treated with bisulfite solution. PCR was performed for the amplification of PRE-1 and MS regions. The PCR products were sequenced by using an automatic DNA sequencer. The methylation rates of the PRE-1 and MS regions in IVF embryos showed that the demethylation process had occurred during the pre-implantation stage, which is a typical phenomenon of in vivo counterparts (Kang et al. 2001 J. Biol. Chem. 276, 39 980). However, compared to IVF embryos, embryos derived from NT using EG cells showed differences at the morula (PRE-1) and blastocyst (MS) stage. These results indicate that porcine EG cells also have problems in reprogramming during NT. For detailed and reliable results, the methylation pattern analysis of the imprinting region, for example, H19 in maternal allele and Igf2 in paternal allele, must be examined. Table 1.Methylation of PRE-1 and MS regions in embryos derived from IVF and NT using porcine EG cells
In somatic cell nuclear transfer, serum starvation is a widely used method to synchronize donor cells at the quiescent stage (Go) of the cell cycle. However, it has been shown that serum starvation during culture of mammalian cells could induce cell death via apoptosis by removing growth factors and increasing intracellular stress. Therefore, apoptosis caused by serum starvation in somatic cells could induce damages to nuclear DNA contributing to a lower efficiency of nuclear transfer. This study was performed to characterize apoptosis during serum starvation of bovine embryonic fibroblasts (BEFs) and to determine the effects of BEFs treated with apoptosis inhibitors on the development of bovine embryos after nuclear transfer. BEFs, collected from a fetus with a 3–4-cm crown-rump length, were cultured for 7 days in starvation medium consisting of Dulbecco's modified Eagle's medium containing 0.5% fetal bovine serum to induce quiescence. Cells were also placed in starvation medium containing the apoptosis inhibitors, β2-macroglobulin (broad-range protease inhibitor: MAC; 1.4 pM) and glutathione (GSH: reactive oxygen species scavenger; 2.0 mM). Apoptosis of serum starved BEFs with or without apoptosis inhibitors were analyzed morphologically with light and electron microscope, and biochemically using a TUNEL assay. Somatic cell nuclear transfer was performed by our standard procedure as follows. Bovine oocytes were matured in vitro and enucleated after 22 h. Nuclear donor cells were collected randomly before injection. The reconstructed embryos were placed into the fusion chamber in a solution containing 0.28 M mannitol and aligned manually. A double pulse of 1.8 kV/cm for 15 μs was used to fuse the cells and activate the embryos simultaneously. The fused embryos were cultured for 4 min in 5 μÂM ionomycin and 4 h in 2 mM 6-DMAP. Then, embryos were moved to culture media and cultured in 5% CO2 and 39°C in 100% humidity. Development of NT embryos was recorded at 120 h post NT (morulae) and 168 h (blastocysts) with experiments being repeated three times. Serum starved BEFs showed typical morphology of apoptotic cells such as chromatin condensation and membrane blebbing. Also, when stained for DNA fragmentation by TUNEL assay, 22.6% ofBEFs showed apoptosis, in contrast to 0.1% in actively growing cells. However, when BEFs were cultured with MAC and GSH, the proportions of apoptotic BEFs were greatly reduced, 6.0% and 2.1%, respectively. After nuclear transfer with BEFs, embryos reconstructed with BEF treated with apoptosis inhibitors showed significant improvement in in vitro development compared to the controls (Table 1). In conclusion, while there are a number of factors affecting the nuclear transfer procedure, damage to the donor nuclei by serum starvation is likely to reduce the efficiency of the procedure; the addition of apoptosis inhibitors could reduce this unnecessary damage to donor nuclei and result in improvement in the development of nuclear transferred embryos. Further experiments are needed to assess the effect of apoptosis inhibitors on improvement of overall nuclear transfer efficiency. Table 1. Development of bovine embryos nuclear transferred with embryonic fibroblasts treated with or without apoptosis inhibitors
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