Alkaline phosphatase activity in bovine oocytes and preimplantation embryos as affected by removal of the zona pellucida and culture medium constituents

The aims of the present study were: (1) to characterize alkaline phosphatase (AP) activity in bovine oocytes and embryos with intact or removed zona pellucida (ZP); and (2) to evaluate the effect of culture medium constituents on AP activity. Alkaline phosphatase activity in non-matured and matured oocytes was most evident nearest the plasma membrane and perivitelline space. In more than 90% of two- to 16-cell embryos, AP activity was observed in the perivitelline space and at blastomere contacts. In blastocysts, AP activity was localized to the trophectoderm. Only after immunodissection was AP activity detected in the inner cell mass. Removal of the ZP by pronase or mechanical means reduced AP activity. Alkaline phosphatase activity was detected in evacuated ZP after mechanical removal. Specific constituents comprising the embryo culture medium altered AP activity. Alkaline phosphatase activity was reduced in eight- to 16-cell embryos and evacuated ZP cultured in CR1aa + 0.4% bovine serum albumin compared with embryos cultured in CR1aa alone or embryos co-cultured on a monolayer of Buffalo rat liver cells in the presence of 10% fetal bovine serum. The presence of AP activity at blastomere contacts and in evacuated ZP limits its usefulness as a marker for the differentiation of embryonic cells comprising the early cleavage-stage embryo.

Successful inactivation of endogenous Oct-3/4 and c-mos genes in mouse preimplantation embryos and oocytes using short interfering RNAs

Understanding oocyte maturation and early development in mammals is very important, especially because these cells serve as a source of materials useful in medical applications, such as ES cells. However, the limited availability of oocytes and embryos hampers the molecular dissection of the very early stage of mammalian development. Recently, the RNA interference technology has been acknowledged to be very effective and useful in diverse groups of cells, including mammalian cells. In this study, we examined whether short interfering RNAs (siRNAs) are applicable to mouse oocytes and preimplantation embryos, by targeting two genes, namely, Oct-3/4 and c-mos. siRNA injections successfully extinguished the production of these target genes. Moreover, the siRNA-injected oocytes and embryos showed phenotypes very similar to those exhibited by Oct-3/4- or Mos-knockout mice in previous studies. Accordingly, we concluded that siRNA is a useful tool in molecular studies on the early development of mouse.

The gamma-subunit of the Na-K-ATPase as a potential regulator of apical and basolateral Na+-pump isozymes during development of bovine pre-attachment embryos

Expression and activity of the Na-K-ATPase within the basolateral membrane domains of the trophectoderm epithelium provide the driving force for accumulation of Na(+) and Cl(-) across the nascent epithelium, mediating fluid movement into the forming blastocoel. Within the trophectoderm of the bovine blastocyst, multiple isozymes of the Na-K-ATPase are expressed. Immunolocalization has demonstrated that the alpha1-isozyme localizes within the basolateral membrane, whereas the alpha 3-isozyme localizes to the apical cell margins. Gene-specific RT-PCR and wholemount indirect immunofluorescence confocal laser scanning microscopy were used to examine expression of the Na-K-ATPase gamma-subunit (a regulatory subunit of the Na-K-ATPase) throughout development of bovine preattachment embryos in vitro. Expression of mRNA transcripts for the gamma-subunit was detected throughout bovine pre-attachment development from the fertilized one-cell embryo to the blastocyst stage. A similar pattern of expression was also observed for gamma-subunit protein, and immunofluorescence was detected within the membranes of embryonic blastomeres at all stages of development. In contrast to the expression patterns observed for the alpha-subunits, gamma-subunit proteins were detected in both the basolateral and apical cell margins of the trophectoderm, and surrounding all cells of the inner cell mass. Co-localization studies demonstrated that gamma-subunit peptides are co-expressed with the alpha1-subunit in the basolateral domains of the trophectoderm. These results indicate a role for the gamma-subunit of the Na-K-ATPase in modulating Na(+)-pump activity in both apical and basolateral margins of the trophectoderm during formation and expansion of the bovine blastocyst, and adds a further level of complexity to Na(+)-pump regulation of cavitation.

Caspase activity and expression of cell death genes during development of human preimplantation embryos

It has been observed that apoptosis occurs in human blastocysts. In other types of cell, the characteristic morphological changes seen in apoptotic cells are executed by caspases, which are regulated by the BCL-2 family of proteins. This study investigated whether these components of the apoptotic cascade are present throughout human preimplantation development. Developing and arrested two pronucleate embryos at all stages were incubated with a fluorescently tagged caspase inhibitor that binds only to active caspases, fixed, counterstained with 4,6-diamidino-2-phenylindole (DAPI) to assess nuclear morphology and examined using confocal microscopy. Active caspases were detected only after compaction, at the morula and blastocyst stages, and were frequently associated with apoptotic nuclei. Occasional labelling was seen in arrested embryos. Expression of proapoptotic BAX and BAD and anti-apoptotic BCL-2 was examined in single embryos using RT-PCR and immunohistochemistry. BAX and BCL-2 mRNAs were expressed throughout development, whereas BAD mRNA was expressed mainly after compaction. Simultaneous expression of BAX and BCL-2 proteins within individual embryos was confirmed using immunohistochemistry. The onset of caspase activity and BAD expression after compaction correlates with the previously reported appearance of apoptotic nuclei. As in other types of cell, human embryos express common molecular components of the apoptotic cascade, although apoptosis appears to be suppressed before compaction and differentiation.

Caspase activity in preimplantation human embryos is not associated with apoptosis

BACKGROUND

Previous studies on mammalian preimplantation embryos have suggested an association between caspase activation, blastomere fragmentation and apoptosis. However, some reports on human embryos questioned the causal relationship between blastomere fragmentation and apoptosis, and information about the presence and activity of caspases in human embryos is lacking.

METHODS

A fluorochrome-labelled universal caspase inhibitor was used to visualize active caspases in blastomeres and fragments of preimplantation human embryos.

RESULTS

Caspase activity was detected only after fertilization, and was rare in blastomeres but frequent in fragments. The incidence of caspase activity in blastomeres and fragments was stable between the 2-cell and 12-cell stages. Caspase-positive blastomeres were only seen in poor-morphology embryos. The percentage of caspase-positive fragments was increased in embryos with multinucleated blastomeres but was unrelated to embryo morphology. Moreover, caspase-positive fragments detached from healthy blastomeres that were isolated by embryo biopsy and subsequently underwent mitotic division in culture.

CONCLUSIONS

These data suggest that caspases in preimplantation human embryos are involved in developmental processes unrelated to cell death.

Dynamics of Dnmt1 methyltransferase expression and intracellular localization during oogenesis and preimplantation development

The imprinting of mammalian genes depends on the maintenance of DNA methylation patterns during pre- and postimplantation development. Dnmt1o is a variant form of the somatically expressed Dnmt1 cytosine methyltransferase that is synthesized and stored in the oocyte cytoplasm and trafficks to the eight-cell nucleus during preimplantation development, where it maintains DNA methylation patterns on alleles of imprinted genes. Transcripts encoding Dnmt1 are present in preimplantation embryos, suggesting that Dnmt1 protein is also expressed in the preimplantation embryo, and may account for maintenance methylation at preimplantation stages other than the eight-cell embryo. However, using an antibody that detects Dnmt1, but not Dnmt1o, no Dnmt1 protein was detected on immunoblots or by immunocytochemical staining in wildtype preimplantation embryos. Moreover, Dnmt1 protein produced in the oocyte from a modified Dnmt1 allele, Dnmt1(1s/1o), trafficked to nuclei of eight-cell embryos, but not to nuclei of other stages. The highly restricted nuclear localization patterns of oocyte-derived Dnmt1o and Dnmt1 during preimplantation development add further support to the notion that DNA methyltransferases other than Dnmt1 are required for maintaining imprints during preimplantation development.

Expression of genes for alcohol and aldehyde metabolizing enzymes in mouse oocytes and preimplantation embryos

Alcohols and aldehydes are metabolized primarily by alcohol (ADH) and aldehyde (ALDH) dehydrogenase isozymes. Although significant progress has been made towards understanding the involvement of these isozymes in the oxidation of alcohol and aldehydes in the body, it is not known how these compounds are handled during fertilization and preimplantation embryogenesis. In this study, reverse transcription and the polymerase chain reaction (RT-PCR) was used to determine which ADH and ALDH isozymes are expressed at the oocyte, zygote, morula, and blastocyst stages of preimplantation development in the mouse. Transcripts of beta-actin and vimentin, assayed as controls, were detected at all stages, as well as Class III ADH (Adh-2) and Class 3 ALDH (Ahd-4), involved in the detoxification of formaldehyde and aromatic aldehydes, respectively. In contrast, transcripts for the major ethanol oxidizing isozyme, Class I ADH (Adh-1) was not detected during preimplantation development. Cytosolic retinol dehydrogenase (Adh-3) transcripts were marginally detected in oocytes and zygotes. The mRNA for cytosolic retinal dehydrogenase (Ahd-2), microsomal short-chain retinol dehydrogenases (RoDH Type I), and the mitochondrial low-Km acetaldehyde dehydrogenase (Ahd-5) only appeared as maternal transcripts. Microsomal ALDH (Ahd-3), which is induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), was not expressed until the blastocyst stage. ADH and ALDH enzyme systems may guard mouse preimplantation embryos against the toxic effects of industrial pollutants, such as formaldehyde and TCDD, as well as peroxidatic aldehydes generated during lipid peroxidation. The absence of enzymes to convert ethanol to acetaldehyde, coupled with oocyte expression of the acetaldehyde-degrading enzyme, Ahd-5, may be protective for the early embryo.

Influence of transforming growth factor-alpha on expression of matrix metalloproteinase-2, matrix metalloproteinase-9, and epidermal growth factor receptor gene in the mouse blastocysts

PURPOSE

This study was carried out to investigate the influence of transforming growth factor-alpha (TGF-alpha) on the expression of mRNA for matrix metalloproteinase-2 (MMP-2), MMP-9, and epidermal growth factor receptor (EGFR) in mouse blastocysts and the effect on the production and activation of MMP-2 and MMP- 9 during blastocyst outgrowth.

METHODS

Two-cell mouse embryos were cultured for 96 h in the presence or absence of various concentrations of TGF-alpha. Reverse transcription-polymerase chain reaction (RT-PCR) was used to examine the expression of mRNA for MMP-2, MMP-9, and EGFR in in vitro cultured blastocysts. To investigate the effect on the production and activation of MMP-2 and MMP-9 during blastocyst outgrowth, the conditioned medium collected after 3 and 5 days of embryo culture were assayed for MMP activity by gelatin zymography.

RESULTS

The relative mRNA levels of MMP-2 and MMP-9 in blastocysts treated with TGF-alpha were higher than that of the control in a concentration-dependent manner. The relative mRNA level of EGFR in blastocysts treated with TGF-alpha was higher than that of the control. In conditioned medium collected after 3 days of embryo culture, TGF-alpha induced the gelatinase activities of proMMP-9 in all groups and activated MMP-2 in the 10 and 100 ng/mL TGF-alpha treated groups. In conditioned medium collected after 5 days, TGF-alpha induced the gelatinase activities of proMMP-9 in all groups and activated MMP-9 in the TGF-alpha treated group. TGF-alpha also induced the gelatinase activities of activated MMP-2 in the 1 and 10 ng/mL TGF-alpha treated groups and the control.

CONCLUSIONS

These results suggest that the addition of TGF-alpha to in vitro culture medium is proper to create a favorable environment for preimplantation embryo development and implantation.

Embryonic stem cells and somatic cells differ in mutation frequency and type

Pluripotent embryonic stem (ES) cells have been used to produce genetically modified mice as experimental models of human genetic diseases. Increasingly, human ES cells are being considered for their potential in the treatment of injury and disease. Here we have shown that mutation in murine ES cells, heterozygous at the selectable Aprt locus, differs from that in embryonic somatic cells. The mutation frequency in ES cells is significantly lower than that in mouse embryonic fibroblasts, which is similar to that in adult cells in vivo. The distribution of spontaneous mutagenic events is remarkably different between the two cell types. Although loss of the functional allele is the predominant mutation type in both cases, representing about 80% of all events, mitotic recombination accounted for all loss of heterozygosity events detected in somatic cells. In contrast, mitotic recombination in ES cells appeared to be suppressed and chromosome loss/reduplication, leading to uniparental disomy (UPD), represented more than half of the loss of heterozygosity events. Extended culture of ES cells led to accumulation of cells with adenine phosphoribosyltransferase deficiency and UPD. Because UPD leads to reduction to homozygosity at multiple recessive disease loci, including tumor suppressor loci, in the affected chromosome, the increased risk of tumor formation after stem cell therapy should be viewed with concern.

DNA topoisomerase II is essential for preimplantation mouse development

Topoisomerase II (topo II) is an essential enzyme that alters DNA topology. This activity is important for a variety of chromosome functions including DNA replication, transcription, recombination, and chromosome condensation and segregation. Previously we localized topo II in mouse gametes and preimplantation embryos using isoform-specific antibodies demonstrating the presence of the enzyme in oocytes and embryos, but not sperm. To probe functions of topo II during preimplantation development, we treated mouse zygotes with 100 nM teniposide, and assessed embryo morphology and DNA replication. Teniposide blocked cleavage in 69% embryos; the remainder cleaved once but had abnormal nuclei. Teniposide-treated embryos were devoid of topo II immunofluorescence. Teniposide also prevented DNA replication, implicating topo II in this process. Embryos treated with a 2 hr pulse of teniposide recovered and developed to the blastocyst stage, indicating 100 nM teniposide did not induce apoptosis. To more specifically analyze topo IIalpha function, we treated zygotes with topo IIalpha-targeted antisense oligodeoxynucleotides. Most zygotes arrested at the 2-cell stage while controls developed into blastocysts indicating topo IIalpha is essential for preimplantation development. The absence of topo IIalpha, but not beta immunofluorescence in antisense-treated embryos confirms the specificity and impact of the treatment. In addition, topo IIalpha is newly synthesized at the 2-cell stage. These results establish an essential function for topo II in mouse preimplantation embryonic development.

Inhibitor profiles of alkaline phosphatases in bovine preattachment embryos and adult tissues

The alkaline phosphatases are a small family of isozymes. Bovine preattachment embryos transcribe mRNA for two tissue-specific alkaline phosphatases (TSAP2 and TSAP3) beginning at the 4- and 8-cell stages. Whereas no mRNA has been detected in oocytes, there is maternally inherited alkaline phosphatase activity. It is not known which isozyme(s) is responsible for the maternal activity or when TSAP2 and TSAP3 form functional protein. No antibodies are available that recognize the relevant bovine alkaline phosphatases. Therefore, sensitivity to heat and chemical inhibition was used to separate the different isozymes. By screening tissues, it was determined that the bovine tissue-nonspecific alkaline phosphatase (TNAP) is inactivated by low temperatures (65C) and low concentrations of levamisole (<1 mM), whereas bovine tissue-specific isozymes require higher temperatures (90C) and levamisole concentrations (>5 mM). Inhibition by L-homoarginine and L-phenylalanine was less informative. Cumulus cells transcribe two isozymes and the pattern of inhibition suggested heterodimer formation. Inhibition of alkaline phosphatase in bovine embryos before the 8-cell stage indicated the presence of only TNAP. At the 16-cell stage the pattern was consistent with TNAP plus TSAP2 or -3 activity, and in morulae and blastocysts the pattern indicated that the maternal TNAP is fully supplanted by TSAP2 or TSAP3.

DNA topoisomerase II distribution in mouse preimplantation embryos

DNA topoisomerase II (topo II) is an essential enzyme that mediates a variety of chromosome activities including DNA replication, transcription, recombination, and chromosome condensation and segregation. Isoform-specific anti-topo II antibodies were used to determine the distribution of topo II alpha and beta in mouse gametes and embryos. Immunoblot analysis with two anti-topo IIalpha antibodies revealed that a 170 kDa topo IIalpha band was present in ovary and testis. Mature sperm exhibited an 89 kDa band only, which may be a degradation product of topo IIalpha. Immunoblots probed with a monoclonal antibody that recognizes both isoforms, showed bands at 170 and 180 kDa, which correspond to topo IIalpha and beta, respectively. An additional 100 kDa band was also present in ovary and testis. Mature sperm did not exhibit staining with this antibody. We also localized topo II in mouse gametes and embryos up to the blastocyst stage using immunofluorescence microscopy. While both isoforms were found in nuclei and nucleoli of germinal vesicle oocytes, topo IIalpha localized to metaphase chromosomes during meiosis, and only to nucleoli during embryonic interphase. Topo IIbeta was absent from chromosomes of metaphase II oocytes, but localized to embryonic interphase nuclei. Both full-length isoforms were absent from sperm, indicating topo II is stored maternally. These results identify topo II as an important component of mouse oocyte and embryonic chromatin, and suggest its involvement in oocyte maturation and preimplantation embryonic development. The different immunofluorescent staining patterns indicate topo IIalpha and beta may serve different roles during the embryonic cell cycle.

Expression of 3 beta-hydroxysteroid dehydrogenase in early bovine embryo development

We analyzed the presence of 3 beta-Hydroxysteroid Dehydrogenase/Delta(5-->4)-isomerase enzyme (3 beta-HSD) activity, a key enzyme of the steroid metabolic pathway, the mRNA of this enzyme, and the steroid metabolism in in vitro produced bovine embryos. 3 beta-HSD activity was detected in in vitro matured oocytes (74.4 +/- 1.4%), 1-cell (72.9 +/- 6.1%), 2-cell (61.8 +/- 7.4%), 8-cell (50 +/- 5%), morulae (50.8 +/- 2.6%), blastocysts (94.4 +/- 3%), and hatched blastocysts (100 +/- 0%) meanwhile the 4-cell stage showed a significant reduction (16.7 +/- 4.7%). When total embryonic RNA of different stages was subjected to RT-PCR assays, the mRNA of 3 beta-HSD was found to be present in all developmental stages of in vitro produced bovine embryos, from the oocyte to the blastocyst, with a marked decrease at the 4-cell stage. To determine whether the temporal pattern of enzyme activity was dependent on the maternal to zygotic transition, embryos were incubated in the presence of a transcription inhibitor, alpha-amanitin. The reappearance of the enzyme activity after the 4-cell stage was blocked in alpha-amanitin treated embryos, indicating the requirement of embryonic transcription. On the other hand, the embryonic steroid metabolism was tested by incubating blastocyst with tritiated pregnenolone. Analysis of the metabolites by TLC indicated the production of a compound with a mobility identical to progesterone. These results described the expression of the 3 beta-HSD and the activity of this metabolic enzyme in bovine oocytes and preimplantation embryos, suggesting that steroids may act as autocrine effectors on preimplantation embryo development.

Localization of nitric oxide synthase activity in unfertilized oocytes and fertilized embryos during preimplantation development in mice

Changes in the activities of nitric oxide synthase (NOS) during embryonic development, and the distribution of endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) isoforms were examined in unfertilized mouse oocytes at the second meiotic metaphase (MII) stage and in fertilized mouse embryos during preimplantation development. In addition, the effects of NOS inhibitors on mouse preimplantation development in vitro were investigated. The activities of NOS in MII oocytes and fertilized embryos during the preimplantation period were determined by NADPH-diaphorase staining. Although NOS activity was detected in unfertilized MII oocytes, the intensity of staining was much weaker than that of fertilized embryos at the one-cell stage. There was a decrease in NOS activity in embryos from the four-cell to the eight-cell stage; however, NOS activity increased again in embryos at the morula stage, particularly in the inner cell population. In the expanded blastocysts, staining was confined to the inner cell mass. Immuno-cytochemical staining showed that eNOS and iNOS were expressed in the cytoplasm of oocytes and embryos during the preimplantation period, and eNOS was also distributed in the nuclei of the embryos. When one-cell embryos were treated with 1 mmol N(omega)-nitro-L-arginine methyl ester (L-NAME) l(-1), their development in vitro was arrested at the two-cell stage. This inhibition of development was overcome by the addition of 1 mmol L-arginine l(-1) to the medium. These observations indicate that nitric oxide plays an important role as a diffusible regulator of cell proliferation and differentiation, especially at the developmental transition from the two-cell to the four-cell stage during preimplantation development of mice.

Transforming growth factor-alpha promotes mouse blastocyst outgrowth and secretion of matrix metalloproteinases

OBJECTIVE

To study the effect of transforming growth factor-alpha (TGF-alpha) on early stage of embryo implantation.

METHODS

Mouse blastocysts were cultured in vitro in medium containing various concentrations of TGF-alpha. Blastocyst implantation capacity was evaluated by calculating the percentage of embryos with attachment or outgrowth. Matrix metalloproteinases (MMPs) secretion of blastocysts was observed using gelatin zymography.

RESULTS

There was no significant difference in the percentage of attachment between control and TGF-alpha treated groups, but the percentage of outgrowth of TGF-alpha treated groups was significantly higher than that of the control group after 24 h culturing. Gelatin zymography showed that blastocysts cultured in TGF-alpha treated groups started secreting MMPs earlier than those in the control group.

CONCLUSION

TGF-alpha is involved in regulating the mouse embryo implantation process by promoting blastocyst outgrowth and secreting matrix matalloproteinases.

Inhibiting 3-phosphoglycerate kinase by EDTA stimulates the development of the cleavage stage mouse embryo

Addition of EDTA to the medium significantly enhances mouse embryo development in culture. Embryos cultured in the absence of EDTA exhibit abnormal increases in glycolytic activity that result in reduced development. Culture with EDTA was able to prevent this increase in glycolysis and, therefore, maintain developmental competence. EDTA was shown to inhibit the activity of the glycolytic enzyme, 3-phosphoglycerate kinase. Additionally, the effect of EDTA on maintaining high rates of embryo development in culture could be mimicked by the addition of Cibacron blue, an inhibitor of 3-phosphoglycerate kinase. The inhibition of 3-phosphoglycerate kinase by EDTA could be overcome by the addition of exogenous magnesium, indicating that the effect of EDTA was to reduce the availability of this co-factor to the glycolytic kinases. Embryos cultured with EDTA had significantly lower levels of intracellular magnesium compared to embryos cultured without EDTA. Therefore, the effect of EDTA appears to be as a chelator of divalent cations such as magnesium, that are required for normal activity of kinases such as 3-phosphoglycerate kinase.

Characterization of telomerase activity in the human oocyte and preimplantation embryo

Telomerase, a ribonucleoprotein, has been described as an essential component of highly proliferative cells as it stabilizes the telomeres and avoids cellular senescence. The objective of this study was to modify the polymerase chain reaction-based telomeric repeat amplification protocol to detect telomerase activity in the single cell and to characterize the activity expressed in the human oocyte through to the blastocyst stage embryo. A comparative evaluation of telomerase activity and developmental stage was conducted using discarded or donated human oocytes and embryos. Telomerase activity was detected in all developmental stages evaluated from immature oocytes through to blastocyst stage embryos. Immature oocytes and blastocysts had similar levels of telomerase activity; however, both groups had significantly (P < 0.05) higher activity than zygote through to pre-morula stage embryos. Seventy-five thawed zygotes were cultured to day 3, biopsied by removing 1-2 cells, and the biopsied embryos were cultured to blastocyst stage. There was no difference (P < 0.05) in telomerase activity between cells biopsied from embryos that reached the blastocyst stage and cells from those that arrested in growth. This study has shown that human oocytes through to blastocyst stage embryos express telomerase activity, but that the level of telomerase activity in biopsied blastomeres, of the day 3 cleavage stage embryo, is not predictive of embryonic growth potential.

A novel murine tryptase involved in blastocyst hatching and outgrowth

Before implantation the blastocyst is maintained within a proteinaceous coat, the zona pellucida, which prevents polyspermy and ectopic pregnancy. An extracellular trypsin-like activity, which is necessary for hatching from the zona pellucida in vitro, is localized to the abembryonic pole of the blastocyst. Upon hatching, the extracellular matrix-degrading proteinases urokinase plasminogen activator (uPA) and matrix metalloproteinase 9 (MMP-9) are thought to promote blastocyst invasion. However, gene disruption experiments have demonstrated that uPA and MMP-9 are dispensable and, thus, that other key enzymes are involved in implantation. In this study, a novel implantation serine proteinase (ISP1) gene, which is distantly related to haematopoietic tryptases and represents a novel branch of the S1 proteinase family, was cloned. ISP1 is expressed throughout morulae and blastocysts during hatching and outgrowth. Abrogation of ISP1 mRNA accumulation using antisense oligodeoxynucleotides disrupts blastocyst hatching and outgrowth in vitro. The results of this study indicate that the ISP1 gene probably encodes the long sought after 'hatching enzyme' that is localized to the abembryonic pole during hatching in vitro. ISP1 is the earliest embryo-specific proteinase to be expressed in implantation and may play a critical role in connecting embryo hatching to the establishment of implantation competence at the abembryonic pole of the blastocyst.

Telomerase activity in early bovine embryos derived from parthenogenetic activation and nuclear transfer

This study examined the telomerase activity in preimplantation bovine embryos derived from either parthenogenetic activation or nuclear transfer. Telomeres are the DNA-protein structures located at the ends of eukaryotic chromosomes. Telomerase is the ribonuclear enzyme that helps to restore telomere length by synthesizing telomeric DNA repeat (5'-TTAGGG-3') from its own RNA template. Without telomerase activity, telomeres shorten with each cell division through conventional DNA replication. In most mammalian species, telomerase activity is present in germ cells but not in somatic cells. Previously, we reported the dynamics of telomerase activity in bovine in vitro fertilized (IVF) embryos. In the present study, we examined the telomerase activity in bovine embryos derived either from parthenogenetic activation or somatic cell nuclear transfer (i.e., cloning). Embryos from both sources were harvested at different stages, from zygote to blastocyst. Telomerase activity in embryos derived from parthenogenetic activation and nuclear transfer showed a dynamic profile similar to that of those derived from IVF. Telomerase activity was detected in embryos at all stages examined, with the highest level in the blastocyst stage, regardless of the method of embryo production.

Oxidative stress and protection against reactive oxygen species in the pre-implantation embryo and its surroundings

Oxidative stress is involved in the aetiology of defective embryo development. Reactive oxygen species (ROS) may originate from embryo metabolism and/or embryo surroundings. Embryo metabolism generates ROS via several enzymatic mechanisms. The relative contribution of each source seems different depending on the species, the stage of development, and the culture conditions. Several exogenous factors and culture conditions can enhance the production of ROS by embryos. ROS can alter most types of cellular molecules, and also induce development block and retardation. Multiple mechanisms of embryo protection against ROS exist, and these have complementary actions. External protection, present in follicular and tubal fluids, mainly comprises non-enzymatic antioxidants such as hypotaurine, taurine and ascorbic acid. Internal protection mainly comprises antioxidant enzymes: superoxide dismutase, glutathione peroxidase and gamma-glutamylcysteine synthetase. Transcripts encoding for these enzymes are present in the oocyte, embryo and oviduct. It may be important that these transcripts are stored during oocyte maturation in order to allow the embryo to acquire the aptitude to develop. It is now common to add antioxidant compounds to culture media. Nevertheless, maintaining the pro-oxidant-antioxidant equilibrium in embryos through such supplementation is a complex problem. Further studies are necessary to limit oxidative stress during embryo culture.

Identification of caspase-3 and caspase-activated deoxyribonuclease in rat blastocysts and their implication in the induction of chromatin degradation (but not nuclear fragmentation) by high glucose

Previous investigations have shown that maternal diabetes impairs rodent embryo development during the earliest phase of gestation. Exposure to high concentrations of glucose before implantation results in a decrease in the number of cells per embryo and in a concomitant increase in two nuclear markers of apoptosis, chromatin degradation and nuclear fragmentation. In the present study, we show that two intracellular effectors of apoptosis, caspase-3 and caspase-activated deoxyribonuclease (CAD), are involved in the embryotoxicity of high glucose. Using reverse transcription-polymerase chain reaction and immunocytochemistry, we first demonstrated that these two effectors were expressed in rat blastocysts. The two effectors were detected in all the cells of the blastocysts and the immuno-signals were excluded from the nuclei. Rat blastocysts were incubated for 24 h in either 6 mM or 28 mM glucose in the presence or absence of specific inhibitors (DEVD-CHO [10 microM] against caspase-3 and aurin [1 microM] against CAD). After incubation, blastocysts were examined for the proportion of nuclei showing signs of chromatin degradation or nuclear fragmentation. Addition of DEVD-CHO or aurin was found to inhibit the increase in chromatin degradation induced by high glucose. None of these two inhibitors prevented the increase in nuclear fragmentation triggered by excess glucose. Our data indicate that chromatin degradation and nuclear fragmentation are two nuclear damages that are induced separately by high glucose in rat blastocysts. Chromatin degradation is apparently mediated by the activation of caspase-3 and CAD.

Expression of activated MAP kinase in Xenopus laevis embryos: evaluating the roles of FGF and other signaling pathways in early induction and patterning

FGF signaling has been implicated in germ layer formation and axial determination. An antibody specific for the activated form of mitogen-activated protein kinase (MAPK) was used to monitor FGF signaling in vivo during early Xenopus development. Activation of MAPK in young embryos is abolished by injection of a dominant negative FGF receptor (XFD) RNA, suggesting that MAPK is activated primarily by FGF in this context. A transition from cytoplasmic to nuclear localization of activated MAPK occurs in morula/blastula stage embryo animal and marginal zones coinciding with the proposed onset of mesodermal competence. Activated MAPK delineates the region of the dorsal marginal zone before blastopore formation and persists in this region during gastrulation, indicating an early role for FGF signaling in dorsal mesoderm. Activated MAPK was also found in posterior neural tissue from late gastrulation onward. Inhibition of FGF signaling does not block posterior neural gene expression (HoxB9) or activation of MAPK; however, inhibition of FGF signaling does cause a statistically significant decrease in the level of activated MAPK. These results point toward the involvement of other receptor tyrosine kinase signaling pathways in posterior neural patterning.

Regulation of gamma-glutamate-cysteine ligase expression by oxidative stress in the mouse preimplantation embryo

The present study examined expression of gamma-glutamate-cysteine ligase (GLCL; also known as gamma-glutamylcysteine synthetase), the rate-limiting enzyme for de novo synthesis of glutathione, in the preimplantation mouse embryo. Previous studies indicated that the cleavage stage embryo is unable to synthesize glutathione de novo. It is hypothesized that GLCL mRNA and protein are not normally expressed in the cleavage stage embryo, but either glutathione depletion or oxidation may induce their expression. In untreated embryos, RT-PCR and Western blotting revealed GLCL heavy subunit (GLCL-H) mRNA and protein only at the blastocyst stage of development. Furthermore, while diethyl maleate (DEM) exposure to deplete cellular glutathione did not induce expression of GLCL-H, exposure to tertiary-butyl hydroperoxide (tBH), an oxidizing agent, resulted in significant upregulation of GLCL-H expression in two-cell embryos. Neither treatment affected expression in blastocysts. Finally, HPLC analysis confirmed that tBH-treated embryos experienced oxidative stress, as indicated by an increase in the ratio of oxidized to reduced glutathione. This oxidative stress induced de novo glutathione synthesis in the cleavage stage embryo, as demonstrated by the subsequent recovery of reduced glutathione levels following DEM-induced depletion. In the absence of tBH treatment, however, cleavage stage embryos could not recover GSH after DEM-mediated depletion. This study demonstrates that the preimplantation embryo has the capacity to upregulate glutathione synthesis in response to oxidative stress but not GSH depletion. These results suggest that, while the preimplantation embryo is well adapted to dealing with oxidative stress, it may be poorly protected from GSH-depleting toxicants.

Catalytic differences between porcine blastocyst and placental aromatase isozymes

Two isozymes of porcine aromatase, the placental and the blastocyst forms, were expressed in CHO cells using the mammalian cell transfection method. Using an 'in-cell' assay (a 3H-water release method), catalytic parameters of the porcine placental aromatase were found to be very similar to those of the human enzyme; however, the activity of the blastocyst isozyme was found to be one-thirtieth that of the placental isozyme. Product isolation assay (using testosterone as the substrate) revealed that the major steroid products were 17beta-estradiol and 19-nortestosterone. The product ratio of estradiol/19-nortestosterone was found to be 94 : 6 for the porcine placental form, 6 : 94 for the porcine blastocyst form, and 92 : 8 for the human wild-type aromatase. Therefore, the porcine blastocyst aromatase isozyme catalyzes mainly androgen 19-desmethylation rather than aromatization. In addition, inhibition profile analyses on the placental and blastocyst isozymes were performed using three steroidal inhibitors [4-hydroxyandro-stenedione (4-OHA), 7alpha-(4'-amino)phenylthio-1, 4-androstandiene-3,17-dione (7alpha-APTADD), and bridge (2, 19-methyleneoxy) androstene-3,17-dione (MDL 101,003)], and four nonsteroidal inhibitors [aminoglutethimide (AG), CGS 20267, ICI D1033, and vorozole (R83842)]. While the two isozymes of porcine aromatase share 93% amino-acid sequence identity, our results indicate that the two porcine aromatase isozymes have distinct responses to various aromatase inhibitors.