Gene expression regulating blastocyst formation

Epigenetic Changes in Equine Embryos after Short-Term Storage at Different Temperatures

Simple Summary

In embryos subjected to assisted reproductive techniques, epigenetic modifications may occur that can influence embryonic development and establishment of pregnancy. In horses, the storage temperature during transport of fresh embryos before transfer is a major concern. The aim of this study was, therefore, to determine the effects of two storage temperatures (5 °C and 20 °C) on equine embryos, collected at day seven after ovulation and stored for 24 h, concerning morphological development, expression of candidate genes associated with embryo growth and development, maternal recognition of pregnancy, methylation, apoptosis and gene-specific and global DNA methylation. Temperature during storage did not affect embryo size. There were no changes in pH and lipid peroxidation of the medium irrespective of group. mRNA expression and gene-specific DNA methylation of genes related to growth and development, maternal recognition of pregnancy, DNA methylation and apoptosis in stored embryos (5 °C and 20 °C) were altered when compared to fresh embryos. Therefore, our study demonstrates for the first time the gene-specific and global DNA methylation status of fresh equine embryos collected on days seven and eight after ovulation. Short-term storage, regardless of temperature, may compromise embryo development after transfer.

Abstract

In embryos subjected to assisted reproductive techniques, epigenetic modifications may occur that can influence embryonic development and the establishment of pregnancy. In horses, the storage temperature during transport of fresh embryos before transfer is a major concern. The aim of this study was, therefore, to determine the effects of two storage temperatures (5 °C and 20 °C) on equine embryos, collected at day seven after ovulation and stored for 24 h, on: (i) morphological development; (ii) expression of candidate genes associated with embryo growth and development, maternal recognition of pregnancy, methylation and apoptosis, and (iii) gene-specific and global DNA methylation. Embryos (n = 80) were collected on day seven or day eight after ovulation and assigned to four groups: day seven control (E7F, fresh); day seven, stored for 24 h at 5 °C (E5C); day seven, stored for 24 h at 20 °C (E20C) and day eight control (E8F, fresh 24h time control). The embryos and the storage medium (EquiHold, holding medium, Minitube, Tiefenbach, Germany) from all treatment groups were analyzed for (i) medium temperature, pH, and lipid peroxidation (malondialdehyde; MDA) and (ii) embryo morphology, mRNA expression and DNA methylation (immunohistochemistry and gene-specific DNA methylation). The size of embryos stored at 5 °C was larger (p < 0.01), whereas embryos stored at 20 °C were smaller (p < 0.05) after 24 h. There were no changes in pH and MDA accumulation irrespective of the group. The mRNA expression of specific genes related to growth and development (POU5F1, SOX2, NANOG), maternal recognition of pregnancy (CYP19A1, PTGES2), DNA methylation (DNMT1, DNMT3A, DNMT3B) and apoptosis (BAX) in the E5C and E20C were either up or downregulated (p < 0.05) when compared to controls (E7F and E8F). The immune expression of 5mC and 5hmC was similar among treatment groups. Percentage of methylation in the CpG islands was lower in the specific genes ESR1, NANOG and DNMT1 (p < 0.001) in E20C embryos when compared to E8F (advanced embryo stage). Therefore, our study demonstrates for the first time the gene-specific and global DNA methylation status of fresh equine embryos collected on days seven and eight after ovulation. Although our results suggest some beneficial effects of storage at 20 °C in comparison to 5 °C, the short-term storage, regardless of temperature, modified gene expression and methylation of genes involved in embryo development and may compromise embryo viability and development after transfer.

Cell differentiation events in pre-implantation mouse and bovine embryos

Early mammal embryogenesis starts with oocyte fertilization, giving rise to the zygote. The events that the newly formed zygote surpasses are crucial to the embryo developmental success. Shortly after activation of its genome, cells of the embryo segregate into the inner cell mass (ICM) or the trophectoderm (TE). The first will give rise to the embryo while the latter will become the placenta. This first segregation involves cellular and molecular processes that include cell polarity linked to intracellular pathway activation, which will regulate the transcription of trophectoderm-related genes. Then, cells of the ICM undergo the second event of mammalian cell differentiation, which consists of the separation between epiblast (EPI) and hypoblast or primitive endoderm (PrE). This second segregation involves paracrine signaling, leading to differential expression of key genes that will dictate the fate of the cell. Although these processes are described in detail in the mouse, recent studies suggest that the bovine embryo could also be an interesting model for early development, since there are differences to the mouse and similarities with early human embryogenesis. In this review, we gathered the main data available in the literature upon bovine and mouse early development events, suggesting that both models should be analyzed and studied in a complementary way, to better model early events occurring in human development.

Transcriptome profile and association study revealed STAT3 gene as a potential quality marker of bovine gametes

The present study was aimed to investigate differences in molecular signatures in oocytes derived from Holstein-Friesian heifers with different genetic merit for fertility, euthanized during day 0 or day 12 of the estrous cycle. Moreover, association between single nucleotide polymorphisms (SNPs) of ODC1 and STAT3 genes and bull fertility traits was investigated. The gene expression patterns were analyzed using cDNA array and validated with quantitative real-time polymerase chain reaction (PCR). The result revealed that several genes have shown not only to be regulated by fertility merit but also by the day of oocyte recovery during the estrous cycle. The STAT3 gene was found to be upregulated in oocytes recovered from animals with high fertility merit at both day 0 and day 12. Some other genes like PTTG1, ODC1 and TUBA1C were downregulated at day 0 and upregulated at day 12 in high, compared with low, fertility merit recovered oocytes. In contrast, the transcript abundance of TPM3 was upregulated at day 0 and downregulated at day 12 in high, compared with low, fertility merit recovered oocytes. In addition, ODC1 and STAT3 were found to be associated (P < 0.05) with sperm quality traits as well as flow cytometry parameters. Therefore, the expression of several candidate genes including ODC1 and STAT3 was related to the genetic merit of the cow. In addition polymorphisms in these two genes were found to be associated with bull semen quality.

Contrasting effects of heat shock during in vitro maturation on development of in vitro-fertilized and parthenogenetic bovine embryos

This study investigated the influence of heat shock during in vitro maturation on embryo development following in vitro fertilization (IVF) or parthenogenesis (Part). Immature bovine cumulus-oocyte complexes were exposed to heat shock (41.0°C) during the first 12 hr of in vitro maturation (IVM), followed by 12 hr at 38.5°C. Control group consisted of in vitro maturation for 24 hr at 38.5°C. Oocytes were in vitro-fertilized or activated with ionomycin and cultured in vitro for 192 hr post-in vitro insemination or parthenogenetic activation (hpia). There was an interaction (p < .01) between temperature of IVM and method of oocyte activation (IVF or Part) for cleavage at 48 hpia. Heat shock had a negative impact (p < .01) on cleavage of IVF embryos, whereas no (p > .05) effect was found in the Part embryos. Embryo development towards blastocyst stage at 168 and 192 hpia decreased in both IVF and Part embryos derived from heat-shocked oocytes. Heat shock increased (p < .05) the apoptotic index in Part blastocysts, but no effect (p > .05) was found in IVF counterparts. Heat shock also down-regulated the expression of AQP3 (p < .01) and up-regulated the expression of HSP70.1 (p < .01) in Part blastocysts, whereas it down-regulated the expression of ATP1A1 (p < .05) in IVF blastocysts. In conclusion, the effects of heat shock during IVM on early embryo cleavage and blastocyst apoptosis are influenced by the method of oocyte activation and expression of some genes can be disturbed in embryos derived from heat-shocked oocytes.

Deletion of maternal UHRF1 severely reduces mouse oocyte quality and causes developmental defects in preimplantation embryos

The ubiquitin-like, containing PHD and RING finger domains, 1 (UHRF1) protein recognizes DNA methylation and histone modification and plays a critical role in epigenetic regulation. Recently, UHRF1 was shown to have a role in DNA methylation in oocytes and early embryos. Here, we reveal that maternal UHRF1 determines the quality of mouse oocytes. We generated oocyte-specific Uhrf1-knockout mice and found that females were sterile, and few maternal UHRF1-null embryos developed into blastocysts. The UHRF1-null oocytes had an increased incidence of aneuploidy and DNA damage. In addition to defective DNA methylation, histone modification was affected during oogenesis, with UHRF1-null germinal vesicle and metaphase II-stage oocytes exhibiting reduced global histone H3 lysine 9 dimethylation levels and elevated acetylation of histone H4 lysine 12. Taken together, our results suggest that UHRF1 plays an important role in determining oocyte quality and affects epigenetic regulation of oocyte maturation as a maternal protein, which is crucial for embryo developmental potential. Further exploration of the biologic function and underlying mechanisms of maternal UHRF1 will enhance our understanding of the maternal control of the oocyte and early embryonic development.-Cao, Y., Li, M., Liu, F., Ni, X., Wang, S., Zhang, H., Sui, X., Huo, R. Deletion of maternal UHRF1 severely reduces mouse oocyte quality and causes developmental defects in preimplantation embryos.

Effect of co-culture human endothelial progenitor cells with porcine oocytes during maturation and subsequent embryo development of parthenotes in vitro

Human endothelial progenitor cells (EPCs) have been applied to regenerative medicine for their roles in angiogenesis as well as neovascularization, and these angiogenetic functions have beneficial effects on maturation of ovarian follicles. However, little information is available on whether EPCs on culture systems affect oocyte maturation and subsequent embryo development. Therefore, the objective of this study was to investigate the effect of EPC co-culture on porcine oocytes during in vitro maturation (IVM) and subsequent embryo development, and to examine gene expression in cumulus cells, oocytes and blastocysts. The effect of co-culture using EPC on porcine oocyte IVM was investigated. Oocytes were activated using electrical stimulation and embryo developmental competence was estimated. The expression of the genes related to cumulus expansion, oocyte maturation, embryo development, and apoptosis were analyzed. In result, there was a significantly increased maturation rate in EPC group compared with control (p < 0.05). Also, oocytes co-cultured with EPCs exhibited significantly improved blastocyst formation rates (p < 0.05). The expression of mRNAs associated with cumulus expansion and apoptosis in cumulus cells was significantly up-regulated in EPC group. Also, markedly increased levels of GDF9, BMP15, and BCL2 were observed in oocytes from the EPC group. Blastocysts in the co-culture group showed significantly higher SOX2, OCT4, and NANOG levels. In conclusion, co-culturing porcine oocytes with EPCs improves their maturation by regulating genes involved in cumulus cell expansion, oocyte maturation, and apoptosis. Moreover, EPC co-culture during IVM enhanced embryo development as shown by increased blastocyst formation rate and pluripotency-related gene expression.

Effect of crotamine, a cell-penetrating peptide, on blastocyst production and gene expression of in vitro fertilized bovine embryos

The present study investigated the effects of crotamine, a cell-penetrating peptide from rattlesnake venom, at different exposure times and concentrations, on both developmental competence and gene expression (ATP1A1, AQP3, GLUT1 and GLUT3) of in vitro fertilized (IVF) bovine embryos. In Experiment 1, presumptive zygotes were exposed to 0.1 μM crotamine for 6, 12 or 24 h and control groups (vehicle and IVF) were included. In Experiment 2, presumptive zygotes were exposed to 0 (vehicle), 0.1, 1 and 10 μM crotamine for 24 h. Additionally, to visualize crotamine uptake, embryos were exposed to rhodamine B-labelled crotamine and subjected to confocal microscopy. In Experiment 1, no difference (P > 0.05) was observed among different exposure times and control groups for cleavage and blastocyst rates and total cells number per blastocyst. Within each exposure time, mRNA levels were similar (P > 0.05) in embryos cultured with or without crotamine. In Experiment 2, concentrations as high as 10 μM crotamine did not affect (P > 0.05) the blastocyst rate. Crotamine at 0.1 and 10 μM did not alter mRNA levels when compared with the control (P > 0.05). Remarkably, only 1 μM crotamine decreased both ATP1A1 and AQP3 expression levels relative to the control group (P < 0.05). Also, it was possible to visualize the intracellular localization of crotamine. These results indicate that crotamine can translocate intact IVF bovine embryos and its application in the culture medium is possible at concentrations from 0.1–10 μM for 6–24 h.

In vivo and in vitro environmental effects on mammalian oocyte quality

The oocyte is at the center of the equation that results in female fertility. Many factors influence oocyte quality, including external factors such as maternal nutrition, stress, and environmental exposures, as well as ovarian factors such as steroids, intercellular communication, antral follicle count, and follicular fluid composition. These influences are interconnected; changes in the external environment of the female translate into ovarian changes that affect the oocyte. The lengthy period during which the oocyte remains arrested in the ovary provides ample time and opportunity for environmental factors to take their toll. An appropriate environment for growth and maturation of the oocyte, in vivo and in vitro, is critical to ensure optimal oocyte quality, which determines the success of fertilization and preimplantation embryo development, and has long-term implications for implantation, fetal growth, and offspring health.

Localization and expression of peptidylarginine deiminase 4 (PAD4) in mammalian oocytes and preimplantation embryos

Post-translational modifications generally involve the addition or removal of various functional groups to or from the protein residues. However, citrullination, which is catalyzed by the peptidylarginine deiminases (PADs), involves conversion of one kind of amino acid residue into another. One of five isoforms, PAD4 is a nuclear enzyme known to play a role in development, differentiation and apoptosis through gene regulation. To investigate the possible role of PAD4 in mammalian preimplantation embryonic development, we first studied localization and expression of PAD4 and citrullinated proteins in pig and mouse oocytes, and parthenogenetic or in vitro fertilized (IVF) embryos. Immunofluorescence study revealed that PAD4 primarily localizes in the cytoplasm in pig oocytes and parthenogenetic embryos. However, the nuclear translocation of PAD4 was observed in late germinal vesicle (GV) stage oocytes prior to GV breakdown and was localized around the metaphase (M)I and II spindle. Nucleus localized PAD4 was noticed partially again in blastocysts. In mouse IVF embryos, nuclear translocation started from the 2-cell stage and gradually increased up to blastocyst. Western blot studies confirmed that PAD4 was expressed in oocytes, and parthenogenetic embryos of pig. Citrullinated proteins were detected in granular form on the chromatin in GV, MI and MII oocytes and nuclei in all the stages of the embryos studied. It was found that the target of citrullination was histone protein (H3), not B23. Therefore the presence of PAD4 and citrullinated histone H3 in oocytes and embryos suggested a possible role for PAD4 in preimplantation embryonic development.

Elevated non-esterified fatty acid concentrations during bovine oocyte maturation compromise early embryo physiology

Elevated concentrations of serum non-esterified fatty acids (NEFA), associated with maternal disorders such as obesity and type II diabetes, alter the ovarian follicular micro-environment and have been associated with subfertility arising from reduced oocyte developmental competence. We have asked whether elevated NEFA concentrations during oocyte maturation affect the development and physiology of zygotes formed from such oocytes, using the cow as a model. The zygotes were grown to blastocysts, which were evaluated for their quality in terms of cell number, apoptosis, expression of key genes, amino acid turnover and oxidative metabolism. Oocyte maturation under elevated NEFA concentrations resulted in blastocysts with significantly lower cell number, increased apoptotic cell ratio and altered mRNA abundance of DNMT3A, IGF2R and SLC2A1. In addition, the blastocysts displayed reduced oxygen, pyruvate and glucose consumption, up-regulated lactate consumption and higher amino acid metabolism. These data indicate that exposure of maturing oocytes to elevated NEFA concentrations has a negative impact on fertility not only through a reduction in oocyte developmental capacity but through compromised early embryo quality, viability and metabolism.

Embryo Culture Media, Culture Techniques and Embryo Selection: A Tribute to Wesley Kingston Whitten

This review article gives a brief history of the classical experiments that led to the development of the embryo culture medium and in vitro embryo culture. It proposes that, in view of the outstanding and significant pioneering contributions of Wesley Kingston Whitten to the development of embryo culture medium, he be considered the “Father of Embryo Culture Medium”. Furthermore, it describes the nutritional requirements of early embryos and how these requirements with specific references to carbohydrates, amino acids, phosphates, growth factors, etc, have been utilized to formulate increasingly more complex embryo culture media. This has led to the development of progressively more efficacious embryo culture media including the formulation of completely defined and synthetic protein-free embryo culture medium. The review also describes physical factors, growth factors, insemination methods for the fertilization of oocytes and culture methods affecting embryo growth, development, metabolism, oxygen embryotoxicity and survival. In procedural terms, the review also summarizes the evolution of embryo culture techniques from tube culture to, microdrop culture under oil to co-culture to ultra microdrop culture techniques. It includes techniques of in vitro maturation and for the selection of potentially viable embryos of various developmental stages.

RFD Award Lecture 2009. In vitro maturation of farm animal oocytes: a useful tool for investigating the mechanisms leading to full-term development

Due to logistical and economic reasons, assisted reproduction of domestic animals has been based mostly on the use of oocytes isolated from ovaries collected at the slaughterhouse. In order to propagate valuable or rare genetic material, perform somatic cell nuclear transfer or generate genetically modified animals, it is essential to obtain fully competent oocytes that will allow full-term development of the in vitro-produced embryos. Such a need makes clear the crucial role played by oocyte quality. In fact, it is easy to compromise the oocyte's developmental potential but it is impossible to restore once it has been lost. Almost three decades after the first cow, sheep, goat, horse and pig in vitro-generated offspring were born, a large body of information has accumulated on the mechanisms regulating oocyte competence and on how the latter may be preserved during all the required manipulations. The amount of knowledge is far from complete and many laboratories are actively working to further expand it. In this review we will highlight the aspects of the ongoing research in which we have been actively involved.

Gene expression in the in vitro-produced preimplantation bovine embryos

Recent studies have demonstrated the relevance of a gene expression profile as a clinically important key feature determining embryo quality during the in vitro preimplantation period. Although the oocyte origin can play a crucial role in blastocyst yield, the postfertilization culture period has a profound effect in determining the blastocyst quality with particular regard to the relative abundance of many developmentally and clinically important candidate genes. During the preimplantation period, the embryo undergoes several morphogenetic developmental events including oocyte maturation, minor and major forms of embryonic genome activation and transition of transcription from maternal to embryonic control. The effect of an altered gene expression pattern on the in vitro-produced bovine embryos, particularly when cultured under suboptimal conditions, was reflected by the occurrence of clinically important phenomena like apoptosis and the large offspring syndrome. This review attempts to focus on the morphogenetic embryo development and gene expression profile in the in vitro-produced bovine embryos, with special emphasis on the different parameters that may alter gene expression pattern during the critical period of in vitro culture. The effect of the in vitro system, as reflected by some clinically important phenomena like apoptosis, is also discussed.

Transcript profiles of some developmentally important genes detected in bovine oocytes and in vitro-produced blastocysts using RNA amplification and cDNA microarrays

To study the mRNA transcript profiles of some potential candidate developmental genes during bovine oocyte and blastocyst stages, RNA amplification procedures, cDNA microarray of 82 target genes spotted onto glass slide and real-time polymerase chain reaction (PCR) were used. Messenger RNAs were isolated from in vitro-produced bovine matured oocytes and blastocysts. Using equal amounts of input mRNAs but different cycles of amplifications, cDNAs were produced and served as template for RNA amplification by the in vitro transcriptions. After amplification, the RNA yields transcribed from cDNAs of different cycles were evaluated both by hybridization on the cDNA microarrays and by using real-time PCR techniques. The analyses indicated best results from lower amplification cycle templates with consistent signals at hybridization. Generally, the RNA yield was directly proportional to the amplification cycle but inversely related with signal consistency at repeated hybridizations. Using the protocols established, equal amounts of amplified RNA from matured oocytes and blastocysts were hybridized to the array. Analyses of replicated hybridizations indicated that 35 transcripts were differentially expressed. Most of these were not described in previous bovine embryo studies. Independent analyses of 23 transcripts with real-time PCR and unamplified RNA confirmed the results of 22 genes. Moreover, the functional analyses showed various roles related to development. Hence, it is possible to conclude that the genes identified here are potential candidates for characterizing developmental competence, and that the methods established can be used for large-scale gene expression analysis with more comprehensive arrays.

Nucleolar remodeling in nuclear transfer embryos

Transcription of the ribosomal RNA (rRNA) genes occurs in the nucleolus and results in ribosome biogenesis. The rRNA gene activation and the associated nucleolus formation may be used as a marker for the activation of the embryonic genome in mammalian embryos and, thus serve to evaluate the developmental potential of embryos originating from varied nuclear transfer protocols. In bovine in vivo developed embryos, functional ribosome-synthesizing nucleoli become structurally distinct toward the end of the 4th post-fertilization cell cycle. In embryonic cell nuclear transfer embryos, fully developed nucleoli are not apparent until the 5th cell cycle, whereas in somatic cell nuclear transfer embryos the functional nucleoli emerge already during the 3rd cell cycle. Intergeneric reconstructed embryos produced by the fusion of bovine differentiated somatic cell to a nonactivated ovine cytoplast fail to develop fully functional nucleoli. In bovine in vivo developed embryos, a range of important nucleolar proteins (e.g., topoisomerase I, upstream binding factor and RNA polymerase I, fibrillarin, nucleophosmin and nucleolin) become localized to the nucleolar anlage over several cell cycles. This relocation is completed toward the end of the 4th cell cycle. A substantial proportion of bovine embryos produced by nuclear transfer of embryonic or somatic cells to bovine ooplasts display aberrations in protein localization in one or more blastomers. This information is indicative of underlying aberrations in genomic reprogramming and may help to explain the abnormalities observed in a proportion of fetuses and offspring derive from nuclear transfer embryos.

Vitrification of in vitro matured ovine oocytes affects in vitro pre-implantation development and mRNA abundance

The impact of vitrification procedures on in vitro matured (IVM) ovine oocytes mRNA content and ability to undergo successful fertilization, cleavage and embronic development was assessed. Vitrified-warmed (n = 113) and control (n = 140) IVM oocytes were in vitro fertilized and cultured up to blastocyst stage under standard conditions. Vitrified oocytes showed lower cleavage rate (47% vs. 75%, P < 0.001) and development to blastocyst stage (17% vs. 57%, P < 0.001) than controls. In addition, the timings of the first cleavage and blastocysts production were significantly delayed in the vitrified-warmed group (P < 0.001 in both cases). In parallel, we analyzed by reverse transcriptase real-time PCR the relative abundance of beta-actin, H2A.Z histone, Poli A Polimerase (PAP), Heat Shock Protein 90 beta (HSP90 beta), P34(cdc2), Cyclin b, Na/K-ATPase and Type I cadherin (E-Cad) transcripts in single IVM controls (n = 24) and vitrified-warmed oocytes (n = 40). Results were normalized against the exogenous rabbit alpha-globin mRNA standard and the beta-actin housekeeping gene and similarly described a lower abundance of most mRNAs in oocytes subjected to vitrification procedures. When normalized against the exogenous standard mRNA, all transcripts except for beta-actin and H2A.Z showed a significantly different abundance in the two classes of oocytes. The same results were obtained after normalization against the internal standard, except for HSP90 beta and E-Cad transcripts, whose lower abundance in vitrified-warmed oocytes resulted prominent, but not significant (P = 0.083 and P = 0.068, respectively). The oocyte lower transcripts abundance following vitrification might be an early indicator of poor quality in good correlation with the developmental data to blastocyst stage.

Gene Expression of Cox5a, 5b, or 6b1 and Their Roles in Preimplantation Mouse Embryos1

To investigate the role of nuclear encoded genes in mitochondrial function during oocyte maturation and early embryogenesis we examined the expression pattern and function of the cytochrome oxidase (Cox) subunits, Cox5a, 5b, and 6b1 during oocyte maturation and early embryo development. Transcription of Cox5a, 5b, or 6b1 was observed in oocytes and during early development; their expression levels were abundant in mature oocytes (MII) and zygotes (1C), and lowest at the 2-cell stage (2C), gradually increasing from 4-cell to blastocyst stage. Immunocytochemical studies revealed that COX5A, 5B, or 6B1 proteins were expressed in all blastomeres of the blastocyst. Silencing of mRNA expression by RNA interference (siRNA) did not inhibit oocyte maturation or developmental events up to the morula and blastocyst stages, but disrupted mitochondrial distribution. Significantly higher apoptosis and lower cell numbers were observed in siRNA-treated blastocysts. Real time RT-PCR revealed that silencing of Cox5a, 5b, or 6b1 did not alter mRNA levels of Bcl-xL (Bcl2l1), but increased transcription levels of proapoptotic genes, Bax and caspase 3 (Casp3). Furthermore, mRNA and protein levels of E-cadherin (CDH1) were decreased in siRNA microinjected blastocysts. These results suggest that gene expression of the Cox subunits, Cox5a, 5b, and 6b1 is not required for embryo developmental events up to the blastocyst stage. The loss of these genes leads to mitochondrial dysfunction that results in apoptosis of the blastocyst stage embryos.

Analysis of Development-Related Gene Expression in Cloned Bovine Blastocysts with Different Developmental Potential

The high incidence of abnormalities in cloned calves is a most serious problem for bovine somatic cell nuclear transfer (NT) technology. Because there is little information on the differences in mRNA expression in cloned blastocysts with donor cells of different sex and origin, we compared development-related gene expression in two types of cloned bovine blastocysts with different potentials to develop into normal calves, a female adult cumulus cell line (high potential to develop into live calves) and a male fibroblast cell line (low potential to develop into live calves) to examine the correlation between the normality of cloned calves and blastocyst mRNA expression patterns. We analyzed 12 genes involved in apoptosis, growth factor signaling, metabolism, and DNA methylation in blastocysts originating from two types of donor cells and in vitro-fertilized blastocysts using quantitative real-time polymerase chain reaction. Expression of the pro-apoptotic Bax gene and anti-apoptotic Bcl-2 and Glut-1 genes in fibroblast-derived blastocysts was significantly higher than in cumulus cell-derived and in vitro-fertilized blastocysts. The high Bcl-2 and Glut-1 gene expression suggests that some embryonic cells with damaged DNA in fibroblast-derived blastocysts are not removed, and their descendants later manifest abnormal placenta or fetus formation. Transfer of pre-selected cloned blastocysts into recipients is required, however, to determine whether the expression pattern of these apoptosis-related genes reflects differences in the potential to develop into normal calves.

Targeted suppression of E-cadherin gene expression in bovine preimplantation embryo by RNA interference technology using double-stranded RNA

RNA interference (RNAi) has become acknowledged as an effective and useful tool to study gene function in diverse groups of cells. We aimed to suppress the expression of the E-cadherin gene during in vitro development of bovine preimplantation embryos using RNAi approach. In this experiment the effect of microinjection of E-cadherin and Oct-4 (as control) double-stranded (ds) RNA on the mRNA and protein expression level of the target E-cadherin gene was investigated. For this, a 496 bp long bovine E-cadherin and 341 bp long Oct-4 dsRNA sample were prepared using in vitro transcription. In vitro produced bovine zygotes were categorized into four treatment groups including those injected with E-cadherin dsRNA, Oct-4 dsRNA, RNase-free water, and uninjected controls. While the injection of E-cadherin dsRNA resulted in the reduction of E-cadherin mRNA and protein levels at the morula and blastocyst stage, the transcript and protein product remained unaffected in the Oct-4 dsRNA, water injected and uninjected control groups. The relative abundance of E-cadherin mRNA in the E-cadherin dsRNA injected morula stage embryos was reduced by 80% compared to the control group (P < 0.05). The Western blot analysis also showed a significant decrease in the E-cadherin protein (119 kDa) in E-cadherin dsRNA injected embryos compared to the other three groups. Microinjection of E-cadherin dsRNA has resulted only 22% blastocyst rate compared to 38%-40% in water injected and uninjected controls. In conclusion, our results indicated the suppression of E-cadherin mRNA and protein has resulted in lower blastocyst rate and the RNAi technology is a promising approach to study the function of genes in early bovine embryogenesis.

Relations between relative mRNA abundance and developmental competence of ovine oocytes

The present study was conducted to investigate the relation between in vitro developmental competence and the expression of a panel of developmentally important genes in germinal vesicle (GV) stage oocytes. One-month-old prepubertal and adult sheep oocytes were used as models of low and high quality gametes, respectively. Cumulus-oocyte complexes (COCs) derived from lambs and ewes were in vitro matured and fertilized, and their cleavage rate at 22, 26, and 32 hr post fertilization and the blastocyst yield were observed to assess their developmental potential. In parallel, the relative abundance (RA) of 11 genes was analyzed by semi-quantitative Reverse Transcription Polymerase Chain Reaction (RT-PCR) assay in the two groups of oocytes. We observed similar maturation and fertilization rates in the two groups, but a significant lower rate of cleaved prepubertal oocytes (P < 0.05), a general delay in the timing of their first division (P < 0.01), and a lower blastocysts production (P < 0.05). The analysis of gene expression evidenced no difference in the RA of four transcripts [superoxide dismutase (SOD), ubiquitin, beta-actin, cyclin B] in the two classes of oocytes, but a statistically lower RA of seven messenger RNAs (mRNA) [Na(+)K(+)ATPase, p34(cdc2), Glucose-transporter I (Glut-1), Activin, Zona Occludens Protein 2 (PanZO2), Poli(A)Polymerase (PAP), E-Cadherin (E-Cad)] in the prepubertal oocytes compared to the adult ones. The present data show for the first time in the ovine species that the lower developmental competence is associated with deficiencies in the mRNAs storage during the oocyte growth.

Metabolic regulation of in-vitro-produced bovine embryos. I. Effects of metabolic regulators at different glucose concentrations with embryos produced by semen from different bulls

The toxic and/or beneficial effects of four metabolic regulators on embryo development were evaluated. In-vitro-produced compact morulae were cultured for 3 days in a chemically defined medium + bovine serum albumin (BSA; CDM-2) plus regulators (4991 total embryos). Phenazine ethosulfate (PES), phloretin (PL), pyrroline-5-carboxylate (P5C), and sodium azide (NaN3) were evaluated at four doses each in factorial combinations with four concentrations of glucose: 0, 0.5, 2, and 8 mm. Phenazine ethosulfate at 0.9 μm resulted in poorer development than lower or no PES. Phloretin was, in general, detrimental for embryo development, but most markedly at the highest dose (270 µm). Pyrroline-5-carboxylate had little effect on post-compaction embryos at the doses studied, 9 to 81 μm. Sodium azide at the concentrations used (3, 9, and 27 μm) had little effect on embryo development compared with controls. Concentrations of glucose had little effect on development of embryos. A fifth metabolic regulator, 2,4-dinitrophenol (DNP), was studied at various doses at pre-morula or morula-blastocyst stages cultured in 2 mm glucose. Embryos (2189 total) cultured in 90 µm DNP developed more slowly and were darker than embryos cultured at lower doses. Embryos cultured in 30 µm DNP had a higher blastocyst rate (48.3%) than controls (34.9%). In the last experiment using G1.2/G2.2 media, DNP (30 μm) resulted in a marked decrease in embryonic development when embryos were exposed at the zygote to 8- to 16-cell stages but had little effect when morulae were exposed for 2 days. The dose–response information for these metabolic regulators is crucial for designing future experiments.

Gene expression profiles of vitrified in vivo derived 8-cell stage mouse embryos detected by high density oligonucleotide microarrays

Very little is known about the effect of vitrification on gene functions after warming. The goals of our study were to compare the gene expression patterns, and identify those most affected. For this, 8-cell stage embryos were collected from ICR mice and vitrified with solid surface vitrification technique, while maintaining equal numbers of embryos as control. Total RNAs were extracted and two rounds of amplification were employed. Finally three micrograms of contrasting RNA samples were hybridized on the Agilent Mouse 22 K oligonucleotide slides and the results were analyzed with subsequent verification by independent real-time PCR analyses. The two rounds of amplification with 5 ng tRNA input have yielded 15-16 microg of cRNA. The analyses of repeated hybridizations showed 20,183 genes/ESTs as common signatures, and unsupervised analysis identified 628 differentially expressed (P < 0.01) genes. However, with at least 1.5-fold change considerations, 183 genes were differentially expressed (P < 0.01) out of which 107 were upregulated. The independent analysis with real-time PCR and unamplified samples fully confirmed the results of microarray, indicating the linearity of amplification. Furthermore, this novel gene expression study for vitrified embryos identified many new candidate genes with overrepresentation in some important biological processes. Thus, it is possible to conclude that the expression pattern reflected a broad spectrum of consequences of vitrification on embryos, with most effects on metabolism, regulatory role and stress response genes and allowed the identification of new candidate marker genes for cryosurvival.

Expression of retinoid X receptor transcripts and their significance for developmental competence in in vitro-produced pre-implantation-stage bovine embryos

Retinoid X receptors are frequently implicated in their role in embryonic development. However, there is no report regarding their expression in embryos with different qualities. In this study, expression pattern and levels of retinoid X receptor transcripts in different qualities and stages of in vitro-produced pre-implantation bovine embryos were examined using real-time polymerase chain reaction (PCR) techniques. Four independent cDNA pools per sample were prepared from mRNAs isolated from different developmental-stage embryos, after classifying them to be of good and bad quality. Primers were also designed to amplify products with PCR. Based on analysis, except retinoid X receptor gamma (RXRG) transcripts, the remaining two types (alpha and beta forms) were expressed in all samples with significantly higher (p < or = 0.05) levels until the eight-cell stage compared with the stages thereafter. However, the transcript levels for bad-quality embryos were consistently lower in all cases in comparison with good-quality embryos. RXRG was identified in 39% of the samples, but all in the pre-embryonic genome activation development stage. Therefore, strong expression patterns of these transcripts in earlier stages indicates their possible role during the maternal phase of embryo development, and the variations of copy number in embryos with different qualities substantiates their possible candidacy as potential quality markers. Moreover, identifying the transcript variations in different qualities and expression of RXRG at these stages is a novel input to the pre-implantation-stage knowledge.

Identification of differentially expressed genes in murine embryos at the blastocyst stage using annealing control primer system

The identification of embryo-specific genes would provide insights into early embryonic development. However, the current methods employed to identify the genes that are expressed at a specific developmental stage are labor intensive and suffer from high rates of false positives. Here we employed a new and accurate reverse transcription-polymerase chain reaction (RT-PCR) method that involves annealing control primers (ACPs) to identify the genes that are specifically or prominently expressed in mouse blastocysts compared to 4-cell stage embryos. Using 120 ACPs, we identified and sequenced 74 of these differentially expressed genes (DEGs). Basic Local Alignment Search Tool (BLAST) searches revealed that 53 were known genes, 9 encoded ribosomal proteins, and 12 were unknown genes. Of the known genes, 14 were selected and further characterized using real-time quantitative PCR to assess their stage-specific expression in mouse embryos. This analysis suggests that the ACP system is a very good method for the identification of stage-specific genes in small numbers of mouse embryos. Further analysis of the differentially expressed blastocyst genes we have identified will provide insights into the molecular basis of preimplantation development.

Deletion of the Na/K-ATPase alpha1-subunit gene (Atp1a1) does not prevent cavitation of the preimplantation mouse embryo

Increases in Na/K-ATPase activity occur concurrently with the onset of cavitation and are associated with increases in Na(+)-pump subunit mRNA and protein expression. We have hypothesized that the alpha1-isozyme of the Na/K-ATPase is required to mediate blastocyst formation. We have tested this hypothesis by characterizing preimplantation development in mice with a targeted disruption of the Na/K-ATPase alpha1-subunit (Atp1a1) using embryos acquired from matings between Atp1a1 heterozygous mice. Mouse embryos homozygous for a null mutation in the Na/K-ATPase alpha1-subunit gene are able to undergo compaction and cavitation. These findings demonstrate that trophectoderm transport mechanisms are maintained in the absence of the predominant isozyme of the Na(+)-pump that has previously been localized to the basolateral membranes of mammalian trophectoderm cells. The presence of multiple isoforms of Na/K-ATPase alpha- and beta-subunits at the time of cavitation suggests that there may be a degree of genetic redundancy amongst isoforms of the catalytic alpha-subunit that allows blastocyst formation to progress in the absence of the alpha1-subunit.

Embryotrophic factor-3 from human oviductal cells enhances proliferation, suppresses apoptosis and stimulates the expression of the β1 subunit of sodium–potassium ATPase in mouse embryos

BACKGROUND

Embrytrophic factor-3 (ETF-3) from human oviductal cells enhanced the development of mouse preimplantation embryos. This report studied the embryotrophic mechanisms of the molecule.

METHODS AND RESULTS

Mouse embryos were incubated with ETF-3 for 24 h at different stages of development. ETF-3 treatment between 96 and 120 h post-HCG increased the cell count of blastocysts, whilst treatment between 72 and 96 h post-HCG enhanced the expansion and hatching of the blastocysts. ETF-3 increased the cell number of the embryos by suppressing apoptosis and increasing proliferation as determined by TUNEL and bromodeoxyuridine uptake assays, respectively. Real-time quantitative PCR showed that the in vivo developed and ETF-3-treated blastocysts had a significantly higher mRNA copy number of Na/K-ATPase-beta1, but not of hepsin, than that of blastocysts cultured in medium alone. The former gene was associated with cavitation of blastocysts while the latter was related to hatching of blastocyst. The beneficial effect of ETF-3 on blastocyst hatching was also seen when ETF-3-supplemented commercially available sequential culture medium for human embryo culture was used to culture mouse embryos.

CONCLUSIONS

ETF-3 improves embryo development by enhancing proliferation, suppressing apoptosis and stimulating expression of genes related to blastocyst cavitation. Supplementating human embryo culture medium with ETF-3 may improve the success rate in clinical assisted reproduction.

Gene expression and in vitro development of inter-species nuclear transfer embryos

This study examined the chromatin morphology, in vitro development, and expression of selected genes in cloned embryos produced by transfer of mouse embryonic fibroblasts (MEF) into the bovine ooplasm. After 6 hr of activation, inter-species nuclear transfer (NT) embryos (MEF-NT) had one (70%) or two pronuclei (20%), respectively. After 72 hr of culture in vitro, 62.6% of the MEF-NTs were arrested at the 8-cell stage, 31.2% reached the 2- to 4-cell stage, and only 6.2% had more than eight blastomeres, but none of these developed to the blastocyst stage. Whereas, 20% of NT embryos derived from bovine embryonic fibroblast fused with bovine ooplasm (BEF-NT) reached the blastocyst stage. Donor MEF nuclei expressing an Enhanced Green Fluorescent Protein (EGFP) transgene resulted in 1- to 8-cell stage MEF-NT that expressed EGFP. The expression of selected genes was examined in 8-cell MEF-NTs, 8-cell mouse embryos, enucleated bovine oocytes, and MEFs using RT-PCR. The mRNA for heat shock protein 70.1 (Hsp 70.1) gene was detected in MEF-NTs and MEF, but not in mouse embryos. The hydroxy-phosphoribosyl transferase (HPRT) mRNA was found in normal mouse embryos and MEF but not in MEF-NTs. Expression of Oct-4 and embryonic alkaline phospatase (eAP) genes was only detected in normal mouse embryos and not in the inter-species NT embryos. Abnormal gene expression profiles were associated with an arrest in the development at the 8-cell stage, but MEF-NT embryos appeared to have progressed through gross chromatin remodeling, typical of intra-species NT embryos. Therefore, molecular reprogramming rather than chromatin remodeling may be a better indicator of nuclear reprogramming in inter-species NT embryos.

Expression of Nucleolar-Related Proteins in Porcine Preimplantation Embryos Produced In Vivo and In Vitro1

The expression of nucleolar-related proteins was studied as an indirect marker of the ribosomal RNA (rRNA) gene activation in porcine embryos up to the blastocyst stage produced in vivo and in vitro. A group of the in vivo-developed embryos were cultured with alpha-amanitin to block the de novo embryonic mRNA transcription. Localization of proteins involved in the rRNA transcription (upstream binding factor [UBF], topoisomerase I, RNA polymerase I [RNA Pol I], and the RNA Pol I-associated factor PAF53) and processing (fibrillarin, nucleophosmin, and nucleolin) was assessed by immunocytochemistry and confocal laser-scanning microscopy, and mRNA expression was determined by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). These findings were correlated with ultrastructural data and autoradiography following 20-min [3H]uridine incubation. Additionally, expression of the pocket proteins pRb and p130, which are involved in cell-cycle regulation, was assessed by semiquantitative RT-PCR up to the blastocyst stage. Toward the end of third cell cycle, the nuclei in non-alpha-amanitin-treated, in vivo-produced embryos displayed different stages of transformation of the nuclear precursor bodies (NPBs) into fibrillogranular nucleoli associated with autoradiographic labeling. However, on culture with alpha-amanitin, NPBs were not transformed into a fibrillogranular nucleolus during this cell cycle, demonstrating that embryonic nucleogenesis requires de novo mRNA transcription. Moreover, immunolocalization of RNA Pol I, but not of UBF, and the mRNA expression of PAF53 and UBF were significantly reduced or absent after culture with alpha-amanitin, indicating that RNA Pol I, PAF53, and presumably, UBF are derived from de novo embryonic transcription. Embryonic genomic activation was delayed in porcine embryos produced in vitro compared to the in vivo-derived counterparts with respect to mRNAs encoding PAF53 and UBF. Moreover, differences existed in the mRNA expression patterns of pRb between in vivo- and in vitro-developed embryos. These findings show, to our knowledge for the first time, a nucleolus-related gene expression in the preimplantation porcine embryo, and they highlight the differences in quality between in vivo and in vitro-produced embryos.

Bovine oocyte cytoplasm supports nuclear remodeling but not reprogramming of murine fibroblast cells

Nuclear transfer (NT) is used to elucidate fundamental biological issues such as reversibility of cell differentiation and interactions between the cytoplasm and nucleus. To obtain an insight into interactions between the somatic cell nucleus and oocyte cytoplasm, nuclear remodeling and gene expression were compared in bovine oocytes that had received nuclei from bovine and mouse fibroblast cells. While the embryos that received nuclei from bovine fibroblast cells developed into blastocysts, those that received nuclei from mouse fibroblasts did not develop beyond the 8-cell stage. Similar nuclear remodeling procedures were observed in oocytes reconstructed with mouse and bovine fibroblast cells. Foreign centrosomes during NT were introduced into embryos reconstructed with both fibroblast cell types. A number of housekeeping mouse genes (hsp70, bax, and glt-1) were abnormally expressed in embryos that had received nuclei from mouse fibroblast cells. However, development-related genes, such as Oct-4 and E-cad, were not expressed. The results collectively suggest that the bovine oocyte cytoplasm supports nuclear remodeling, but not reprogramming of mouse fibroblast cells.

Integrating new technologies with embryology and animal production

The present review describes a range of selected farm animal embryo technologies used in embryological research and applied in animal breeding and production. Some of the techniques are driven by the breeder’s wish to obtain animals with higher breeding values, whereas others are primarily driven by the curiosity of researchers. The interaction between basic research and practical application in these areas is still a characteristic feature for people who contribute to the International Embryo Transfer Society (IETS) and has been an advantage for both researchers and breeders. One example of such an interaction is that detailed structural analyses have described quality differences between embryos of various origins and, following embryo transfer, the pregnancy results have confirmed the correlation between morphology and viability. Another example is that polymerase chain reaction technology has allowed detection of Y-specific sequences in male embryos and has become a tool in animal production today. Data from domestic animal genome sequencing will provide a great deal of new information. A major challenge for the years to come will be using this information in a physiologically meaningful context and to continue the efforts to convert the laboratory experience into use in practise. Finally, it is important to obtain societal acceptance for a wider application of many of the technologies, such as in vitro embryo production and cloning.

Timing of blastocyst expansion affects spatial messenger RNA expression patterns of genes in bovine blastocysts produced in vitro

Blastocyst formation and expansion are dependent on the differentiation and function of a proper transport of nutrients through the trophectoderm (TE) enclosing the inner cell mass (ICM). Coincident with compaction and cavitation, glucose becomes the preferred energy substrate of the early embryo. These hallmarks in early development require well-orchestrated gene expression patterns specifically with regard to timing and localization. The present study investigated the relative abundance (RA) of gene transcripts in the two lineages of in vitro-produced expanded bovine blastocysts in relation to timing of development, i.e., blastocyst expansion and localization of specific mRNAs. Expanded blastocysts from either Day 7 or Day 8 or isolated ICMs derived thereof were analyzed with the aid of a semiquantitative reverse transcriptase-polymerase chain reaction assay for gene transcripts, which are thought to play a pivotal role in blastocyst expansion, i.e., Na/K-ATPase alpha1 subunit (Na/K), E-cadherin (E-cad), zonula occludens protein-1 (ZO-1), desmocollin II (Dc II), plakophilin (Plako), trophoblastic function (interferon tau [IFtau]), and glucose transport (glucose transporter-1, -3, -4 [Glut-1, -3, -4]). Total cell number, ICM cell number, or ICM/total cells ratio were similar in Day 7 and Day 8 expanded blastocysts. Significant differences were determined in the RA for Na/K, E-cad, Dc II, Plako, and ZO-1 transcripts between TE cells of expanded blastocysts derived from either Day 7 or Day 8. The RA of Dc II, Glut-1, and Glut-4 was significantly decreased in the ICM compared with the TE at Day 7. Similarly, the RA of Na/K, Dc II, Glut-1, and Glut-4 at Day 8 of development was significantly decreased in the ICM compared with the TE. Interestingly, no differences were observed when comparing ICMs originating from blastocysts expanded at either Day 7 or Day 8. Plako and IFtau transcripts were not detected in isolated ICMs, indicating that expression of these mRNAs is restricted to the TE. In contrast, similar expression patterns within the ICM and TE were determined for Na/K, E-cad, ZO-1, and Glut-3 mRNA. Dc II, Glut-1, and Glut-4 were more abundant in the TE than in ICM. Results show that expression of developmentally important genes is related to the two cell lineages in the early embryo and emphasize the critical role of a well controlled spatial gene expression pattern for regular preimplantation development.

Gene expression patterns in bovine in vitro-produced and nuclear transfer-derived embryos and their implications for early development

Bovine in vitro-produced (IVP) and nuclear transfer (NT)-derived embryos differ from their in vivo-developed counterparts in a number of characteristics. A preeminent observation is the occurrence of the large offspring syndrome, which is correlated with considerable embryonic fetal and postnatal losses. We summarize here results from our studies in which we compared gene expression patterns from IVP and NT-derived embryos with those from their IVP counterparts. Numerous aberrations were found in IVP and NT-derived embryos, including a complete lack of expression, an induced expression, or a significant up- or downregulation of a specific gene. These alterations may affect a number of physiological functions and are considered as a kind of stress response of the embryos to deficient environmental conditions. We hypothesize that the alterations are caused by epigenetic modifications, primarily by changes in the methylation patterns. Unravelling these epigenetic modifications is promising to reveal the underlying mechanisms of the large offspring syndrome.

Effects of in vivo prematuration and in vivo final maturation on developmental capacity and quality of pre-implantation embryos

In current in vitro production (IVP) systems, oocytes lack in vivo dominant and preovulatory follicular development, which may compromise pregnancy and viability of calves born. When an oocyte sets off in vivo on the road toward fertilization, it contains numerous transcripts and proteins necessary to survive the first few cell cycles of embryonic development. It is not yet known during which period of development the oocyte builds up the store, possibly primarily during the major growth phase of the oocyte, which is completed at the time a follicle reaches the size of 3 mm. Here, we investigated to what extent the later phases of follicular development, such as prematuration in the dominant follicle before the LH surge and ensuing final maturation in the preovulatory follicle, contribute to oocyte competence and development into viable biastocysts. Recent studies on in vivo vs in vitro oocyte maturation employed oocytes from an identical preovulatory development by applying ovum pick-up (OPU) twice (before and 24 h after the LH surge) in each cow treated for superovulation with a controlled LH surge. The embryo recovery rates at Day 7 of IVC after IVF were similar: 44% (97/219) for in vivo- vs 41% (87/213) for in vitro-matured oocytes, which shows that the natural environment during final maturation is not essential for the mere in vitro development of the prematured oocyte beyond the 8- to 16-cell stage. However, in vivo maturation appeared to contribute to the oocyte's quality in a more subtle way, as indicated by a significant increase in the proportion of expanded blastocysts and a more physiological degree of chromosome aberrations of the embryos. In blastocysts derived from in vivo-matured oocytes, 21% of the embryos were mixoploid vs 50% from in vitro-matured oocytes, concomitant with a higher number of cells (96 vs 54 per normal blastocyst). The expression pattern of a set of six developmentally important genes was, however, not significantly altered in blastocysts derived from in vivo-matured oocytes. Certain deviations were observed compared with the levels of entirely in vivo-developed control blastocysts, which suggests that the beneficial effects of in vivo maturation are possibly exerted at initial stages of embryonic development. Prematuration in vivo, occurring in a dominant follicle developing from about 8 mm into the preovulatory follicle, is accompanied by changes in protein synthesis of the cumulus oocyte complex (COC). Presumably, the differentially expressed proteins are involved in equipping the oocyte with further developmental competence. Although we have unraveled some important biochemical and cellular biological features of the oocyte, further research on in vivo processes is essential to improve in vitro embryo production in practice.

Nucleolar proteins and ultrastructure in preimplantation porcine embryos developed in vivo

Ribosomal RNA genes are transcribed in the nucleolus. The formation of this organelle after fertilization is essential for embryonic protein synthesis and viability. We have examined nucleolus formation in in vivo-derived porcine embryos by light microscopical autoradiography following 20 min of (3)H-uridine incubation, transmission electron microscopy (TEM), and immunocytochemical localization by confocal laser scanning microscopy of key nucleolar proteins involved in rRNA transcription (nucleolin, upstream binding factor, topoisomerase I, and RNA polymerase I) and processing (fibrillarin, nucleophosmin). During the first two postfertilization cell cycles, TEM revealed fibrillar spheres as the most prominent intranuclear entity of the blastomeres. Fibrillogranular nucleoli were established during the third cell cycle. Initially, fibrillar centers, a dense fibrillar component, and a granular component were formed on the surface of the fibrillar spheres. At the same time, autoradiographic labeling over the nucleoplasm and in particular the nucleoli was detected for the first time. The nucleolar proteins were, in general, not immunocytochemically localized to the presumptive nucleolar compartment until late during the third or early during the fourth cell cycle.

Genetic reprogramming of lactate dehydrogenase, citrate synthase, and phosphofructokinase mRNA in bovine nuclear transfer embryos produced using bovine fibroblast cell nuclei

Adult animal cloning has progressed to allow the production of offspring cloned from adult cells, however many cloned calves die prenatally or shortly after birth. This study examined the expression of three important metabolic enzymes, lactate dehydrogenase (LDH), citrate synthase, and phosphofructokinase (PFK), to determine if their detection in nuclear transfer (NT) embryos mimics that determined for in vitro produced embryos. A day 40 nuclear transfer produced fetus derived from an adult cell line was collected and fetal fibroblast cultures were established and maintained. Reconstructed NT embryos were then produced from this cell line, and RT-PCR was used to evaluate mRNA reprogramming. All three mRNAs encoding these enzymes were detected in the regenerated fetal fibroblast cell line. Detection patterns were first determined for IVF produced embryos (1-cell, 2-cell, 6-8 cell, morula, and blastocyst stages) to compare with their detection in NT embryos. PFK has three subunits: PFK-L, PFK-M, and PFK-P. PFK-L and PFK-P were not detected in bovine oocytes. PFK subunits were not detected in 6-8 cell embryos but were detected in blastocysts. Results from NT embryo RT-PCR demonstrated that PFK was not detected in 8-cell NT embryos but was detected in NT blastocysts indicating that proper nuclear reprogramming had occurred. Citrate synthase was detected in oocytes and throughout development to the blastocyst stage in both bovine IVF and NT embryos. LDH-A and LDH-B were detected in bovine oocytes and in all stages of IVF and NT embryos examined up to the blastocyst stage. A third subunit, LDH-C was not detected at the blastocyst stage in IVF or NT embryos but was detected in all earlier stages and in mature oocytes. In addition, LDH-C mRNA was detected in gonad isolated from the NT and an in vivo produced control fetus. These results indicate that the three metabolic enzymes maintain normal expression patterns and therefore must be properly reprogrammed following nuclear transfer.

In vitro culture and embryo metabolism of cattle and sheep embryos - a decade of achievement

At the beginning of the 1990s, co-culture of cattle and sheep embryos was the most favoured method to support embryo development, but the use of this system has hampered progress in raising the efficiency of embryo production. Furthermore, little was known of the requirements of embryos and the biochemistry of early embryo development. As the decade progressed, energy metabolism studies improved our understanding of the energy substrate requirements for embryo development. Furthermore, an appreciation of the reproductive tract environment increased. This resulted in more "defined" systems, which have evolved further in the development of "sequential" media systems, where components change in accordance to the needs of the embryo. Nevertheless, wholly defined systems, such as the replacement of albumin with PVA, are less able to support similar levels of development as protein-containing medium, and the resulting embryos are metabolically compromised. This highlights the nutritive role of albumin. One area in which much work has been conducted, but yet no unifying theory has emerged, is that of the interactive roles of growth factors (including autocrine/paracrine), cytokines and extra-cellular matrix molecules in the development of a viable embryo. A new concept is that of regulation of energy metabolism. Compounds such as ethylenediamine tetraacetic acid (EDTA), NaN(3) and 2,4-dinitrophenol have been shown to increase embryo development and quality of resulting embryos. This demonstrates that the process of ATP production is a key regulator of in vitro embryo development.

Activation of ribosomal RNA genes in preimplantation cattle and swine embryos

Transcription of ribosomal RNA (rRNA) genes occurs in the nucleolus resulting in ribosome synthesis. In cattle and swine embryos, functional ribosome-synthesizing nucleoli become structurally recognizable towards the end of the fourth and third post-fertilization cell cycle, respectively. In cattle, a range of important nucleolar proteins become localized to the nucleolar anlage over several cell cycles and this localization is apparently completed towards the end of the fourth cell cycle. In swine, the localization of these proteins to the anlage is more synchronous and occurs towards the end of the third cell cycle and is apparently completed at the onset of the fourth. The rRNA gene activation and the associated nucleolus formation may be used as a marker for the activation of the embryonic genome in mammalian embryos and, thus, serve to evaluate the developmental potential of embryos originating from different embryo technological procedures. By this approach, we have demonstrated that in vitro produced porcine embryos display a lack of localization of nucleolar proteins to the nucleolar anlage as compared with in vivo developed counterparts. Similarly, bovine embryos produced by nuclear transfer from morulae display such deviations as compared with in vitro produced counterparts. Collectively, this information may help to explain the appearance of abnormalities seen in a certain proportion of offspring derived from in vitro produced embryos and after cloning.

Assessment by differential display-RT-PCR of mRNA transcript transitions and alpha-amanitin sensitivity during bovine preattachment development

The objectives of this study were to compare patterns of mRNA expression, investigate the onset of transcription, and isolate stage-specific and alpha-amanitin-sensitive mRNAs during early bovine development by differential-display-reverse transcription-polymerase chain reaction (DD-RT-PCR). Embryos representing a preattachment developmental series from the 1-cell to the expanded/hatched blastocyst stage were cultured in synthetic oviduct fluid medium + citrate and amino acids (cSOFMaa) with and without alpha-amanitin (100 microg/mL) for 4 and 12 hr. mRNA profiles were displayed by DD-RT-PCR using 5' primers A and N. Total conserved cDNA banding patterns varied according to embryo stage with cDNA band numbers declining during early cleavage stages compared to oocyte values and then increasing in total number from the 6-8-cell stage through to the blastocyst stage. A cDNA banding pattern was established at the 8-16-cell stage that was largely unchanged through to the blastocyst stage. These findings with respect to cDNA banding patterns were conserved between oligo primer sets and experimental replicates. alpha-Amanitin sensitivity was first detected at the 2-5-cell stage but became predominant following the 6-8-cell stage of development to eventually affect the appearance of up to 40% of all cDNA bands by the blastocyst stage. A 12 hr alpha-amanitin treatment was required to effectively block (3)H-uridine incorporation into mRNA in blastocyst stage embryos. Several stage-specific and alpha-amanitin-sensitive cDNAs were isolated and they will be a focus for future studies. In conclusion, DD-RT-PCR is an effective tool for contrasting gene expression patterns and isolating uncharacterized mRNA transcripts during bovine early development. Mol. Reprod. Dev. 55:152-163, 2000.

Environment of oocyte and embryo determines health of IVP offspring

In vitro embryo production (IVP) enhances the number of offspring from a single female and offers the possibility of accelerated genetic progress in animal husbandry. However, it also leads to a low but unacceptable percentage of anomalies in the offspring. The aim of this paper is to introduce the three speakers at this afternoon session who will speak about the demands of culture conditions and the endometrial environment to support normal embryonic development without effects on the embryonic genome. It will be argued that the in vitro conditions should mimic precisely the oviductal contributions to homeostatic mechanisms within the embryo. The further normal development can be guaranteed at synchrony in development of both endometrium and embryo. If that is not the case one can expect disturbances of gene expression, in particular of imprinted genes. However, it cannot be excluded that some processes might have started already in the cytoplasm of the oocyte. Since the oocyte was not planned to be a separate subject in this symposium, this introduction is also aimed to ask attention for the selection of cumulus-oocyte-complexes (COCs) and the conditions around oocyte maturation in vitro. The optimal quality of both the oocyte and maturation medium are prerequisites for an undisturbed cytoplasmic maturation. It has been argued that the exclusion of COCs from atretic follicles, the abjuration of the use of serum and high O2 tension in the gas phase might help to reduce the proportion anomalies in the offspring after synchronous transfers. In human IVF, in vivo matured oocytes are used with no great problems. But before IVP, including oocyte maturation in vitro (IVM) and a longer lasting embryo culture (IVC), will be introduced into the human assisted reproduction, it is important to think about the ins and outs of the potential causes for deviations.