Analysis of gene expression in mouse 2-cell embryos using fluorescein differential display: comparison of culture environments

MYC-MAX heterodimerization is essential for the induction of major zygotic genome activation and subsequent preimplantation development

In mouse preimplantation development, zygotic genome activation (ZGA), which synthesizes new transcripts in the embryo, begins in the S phase at the one-cell stage, with major ZGA occurring especially at the late two-cell stage. Myc is a transcription factor expressed in parallel with ZGA, but its direct association with major ZGA has not been clarified. In this study, we found that developmental arrest occurs at the two-cell stage when mouse embryos were treated with antisense oligonucleotides targeting Myc or MYC-specific inhibitors from the one-cell stage. To identify when MYC inhibition affects development, we applied time-limited inhibitor treatment and found that inhibition of MYC at the one-cell, four-cell, and morula stages had no effect on preimplantation development, whereas inhibitor treatment at the two-cell stage arrested development at the two-cell stage. Furthermore, transcriptome analysis revealed that when MYC function was inhibited, genes expressed in the major ZGA phase were suppressed. These results suggest that MYC is essential for the induction of major ZGA and subsequent preimplantation development. Revealing the function of MYC in preimplantation development is expected to contribute to advances in assisted reproductive technology.

H4K20 monomethylation inhibition causes loss of genomic integrity in mouse preimplantation embryos

Maintaining genomic integrity in mammalian early embryos, which are deficient in DNA damage repair, is critical for normal preimplantation and subsequent development. Abnormalities in DNA damage repair in preimplantation embryos can cause not only developmental arrest, but also diseases such as congenital disorders and cancers. Histone H4 lysine 20 monomethylation (H4K20me1) is involved in DNA damage repair and regulation of gene expression. However, little is known about the role of H4K20me1 during mouse preimplantation development. In this study, we revealed that H4K20me1 mediated by SETD8 is involved in maintaining genomic integrity. H4K20me1 was present throughout preimplantation development. In addition, reduction in the level of H4K20me1 by inhibition of SETD8 activity or a dominant-negative mutant of histone H4 resulted in developmental arrest at the S/G2 phase and excessive accumulation of DNA double-strand breaks. Together, our results suggest that H4K20me1, a type of epigenetic modification, is associated with the maintenance of genomic integrity and is essential for preimplantation development. A better understanding of the mechanisms involved in maintaining genome integrity during preimplantation development could contribute to advances in reproductive medicine and technology.

Melatonin Pretreated Blastocysts along with Calcitonin Administration Improved Implantation by Upregulation of Heparin Binding-Epidermal Growth Factor Expression in Murine Endometrium

Objective

Implantation failure is an obstacle in assisted reproduction techniques (ART). Calcitonin is a molecules involved in uterine receptivity and embryo implantation. Melatonin can promote embryo quality and improve implantation. This study examines the effect of pretreatment of blastocysts with melatonin and calcitonin on heparin binding-epidermal growth factor (HB-EGF) expression in murine endometrium.

Materials and Methods

In this experimental study, we collected 2-cell embryos from the oviducts of 1.5 day pregnant NMRI mice. Embryos were cultured to the blastocyst in G^TM medium with or without 10^-9 M melatonin. Pregnant and pseudo-pregnant mice received intraperitoneal (IP) injections of 2 IU calcitonin. After 24 hours, we transferred the cultured blastocysts into the uteri of pseudo-pregnant mice. Two days later, implantation sites were counted and we assessed the levels of HB-EGF mRNA and protein in the uteri of naturally pregnant and pseudo-pregnant mice by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. Statistical analysis was performed with one-way ANOVA followed by the Tukey post hoc test. P<0.05 was considered statistically significant.

Results

Melatonin pretreatment of blastocysts along with calcitonin administration significantly increased HB-EGF mRNA and protein (P<0.001) in the endometrium of pseudo-pregnant mice. Administration of calcitonin in naturally pregnant mice significantly increased HB-EGF mRNA and protein levels (P<0.001). Compared with the control group (2.6 ± 0.5), the average number of implantation sites in the melatonin group (4.6 ± 0.5, P<0.05) and calcitonin group (7 ± 1, P<0.001) significantly increased. There was a significant increase in implantation sites in the combined melatonin and calcitonin group (8.6 ± 0.5, P<0.001). Calcitonin significantly enhanced calcitonin receptor mRNA (P<0.001) and protein (P<0.05) in the uteri of naturally pregnant and pseudo-pregnant mice.

Conclusion

Melatonin pretreated blastocysts along with calcitonin increased HB-EGF expression in the uteri of pseudo- pregnant mice. Calcitonin administration upregulated HB-EGF in uteri of naturally pregnant mice.

Polydatin improves the developmental competence of bovine embryos in vitro via induction of sirtuin 1 (Sirt1)

The aim of the present study was to investigate the beneficial effect of polydatin (PD), the glycoside form of resveratrol, on embryo development in vitro. Oocytes were aspirated from ovaries of Korean Hanwoo cows and cultured until Day 8 in a humidified atmosphere of 5% CO2 in air at 38.5°C. Protein and gene expression levels were determined through confocal microscopy and reverse transcription–polymerase chain reaction respectively, whereas the number of total and apoptotic cells in Day 8 blastocysts was determined using Hoechst 33342 staining and terminal deoxyribonucleotidyl transferase-mediated dUTP–digoxigenin nick end-labelling. Of the different concentrations of PD (0.5, 1.0 and 2.0 µM) added to the IVM medium, only 1.0 µM PD significantly improved blastocyst development. Immunofluorescence analysis confirmed that protein levels of sirtuin 1 (Sirt1) increased significantly (P < 0.05) after PD treatment, whereas levels of reactive oxygen species (ROS) were significantly (P < 0.05) decreased, as evidenced by reductions in 8-oxoguanine immunoreactivity. Similarly, protein levels of nuclear factor (NF)-κB and cyclo-oxygenase (COX)-2  were significantly (P < 0.05) lower in the PD-treated group than in the control group. Treatment with 1.0 µM PD reduced gene expression of BCL2-associated X protein, inducible nitric oxide synthase, COX2 and Nfkb, but increased the expression of Sirt1, supporting the immunofluorescence data. PD possesses antioxidant activity and is useful for embryo development in vitro. We conclude that supplementation of IVM medium with PD improves embryo developmental competence via Sirt1.

CHD1 acts via the Hmgpi pathway to regulate mouse early embryogenesis

The protein CHD1 is a member of the family of ATPase-dependent chromatin remodeling factors. CHD1, which recognizes trimethylated histone H3 lysine 4, has been implicated in transcriptional activation in organisms ranging from yeast to humans. It is required for pre-mRNA maturation, maintenance of mouse embryonic stem cell pluripotency and rapid growth of the mouse epiblast. However, the function(s) of CHD1 in mouse preimplantation embryos has not yet been examined. Here, we show that loss of CHD1 function led to embryonic lethality after implantation. In mouse embryos in which Chd1 was targeted by siRNA microinjection, the expression of the key regulators of cell fate specification Pou5f1 (also known as Oct4), Nanog and Cdx2 was dramatically decreased, starting at mid-preimplantation gene activation (MGA). Moreover, expression of Hmgpi and Klf5, which regulate Pou5f1, Nanog and Cdx2, was also significantly suppressed at zygotic gene activation (ZGA). Suppression of Hmgpi expression in Chd1-knockdown embryos continued until the blastocyst stage, whereas suppression of Klf5 expression was relieved by the morula stage. Next, we rescued HMGPI expression via Hmgpi mRNA microinjection in Chd1-knockdown embryos. Consequently, Pou5f1, Nanog and Cdx2 expression was restored at MGA and live offspring were recovered. These findings indicate that CHD1 plays important roles in mouse early embryogenesis via activation of Hmgpi at ZGA.

A hyperactive piggyBac transposon system is an easy-to-implement method for introducing foreign genes into mouse preimplantation embryos

Transgenic mice are important tools for genetic analysis. A current prominent method for producing transgenic mice involves pronuclear microinjection into 1-cell embryos. However, the total transgenic efficiency obtained using this method is less than 10%. Here, we demonstrate that highly efficient transgenesis in mice can be achieved by cytoplasmic microinjection using a hyperactive piggyBac system. In embryos in which hyPBase mRNA and pPB-CAG-TagRFP DNA were co-injected into the cytoplasm, TagRFP fluorescence was observed after the 2-cell stage; when 30 ng/µl pPB-CAG-TagRFP DNA and 30 ng/µl hyPBase mRNA were co-injected, 94.4% of blastocysts were TagRFP positive. Furthermore, a high concentration of hyPBase mRNA resulted in creation of mosaic embryos in which the TagRFP signals partially disappeared. However, suitable concentrations of injected DNA and hyPBase mRNA produced embryos in which almost all blastomeres were TagRFP positive. Thus, the hyperactive piggyBac transposon system is an easy-to-implement and highly effective method that can contribute to production of transgenic mice.

Expression profile of genes as indicators of developmental competence and quality of in vitro fertilization and somatic cell nuclear transfer bovine embryos

Reproductive biotechnologies such as in vitro fertilization (IVF) and somatic cell nuclear transfer (SCNT) enable improved reproductive efficiency of animals. However, the birth rate of in vitro-derived embryos still lags behind that of their in vivo counterparts. Thus, it is critical to develop an accurate evaluation and prediction system of embryo competence, both for commercial purposes and for scientific research. Previous works have demonstrated that in vitro culture systems induce alterations in the relative abundance (RA) of diverse transcripts and thus compromise embryo quality. The aim of this work was to analyze the RA of a set of genes involved in cellular stress (heat shock protein 70-kDa, HSP70), endoplasmic reticulum (ER) stress (immunoglobulin heavy chain binding protein, Bip; proteasome subunit β5, PSMB5) and apoptosis (BCL-2 associated X protein, Bax; cysteine aspartate protease-3, Caspase-3) in bovine blastocysts produced by IVF or SCNT and compare it with that of their in vivo counterparts. Poly (A) ⁺ mRNA was isolated from three pools of 10 blastocysts per treatment and analyzed by real-time RT-PCR. The RA of three of the stress indicators analyzed (Bax, PSMB5 and Bip) was significantly increased in SCNT embryos as compared with that of in vivo-derived blastocysts. No significant differences were found in the RA of HSP70 and Caspase-3 gene transcripts. This study could potentially complement morphological analyses in the development of an effective and accurate technique for the diagnosis of embryo quality, ultimately aiding to improve the efficiency of assisted reproductive techniques (ART).

Molecular signatures of bovine embryo developmental competence

Assessment of the developmental capacity of early bovine embryos is still an obstacle. Therefore, the present paper reviews all current knowledge with respect to morphological criteria and environmental factors that affect embryo quality. The molecular signature of an oocyte or embryo is considered to reflect its quality and to predict its subsequent developmental capacity. Therefore, the primary aim of the present review is to provide an overview of reported correlations between molecular signatures and developmental competence. A secondary aim of this paper is to present some new strategies to enable concomitant evaluation of the molecular signatures of specific embryos and individual developmental capacity.

Melatonin improves the quality of in vitro produced (IVP) bovine embryos: implications for blastocyst development, cryotolerance, and modifications of relevant gene expression

To evaluate the potential effects of melatonin on the kinetics of embryo development and quality of blastocyst during the process of in vitro bovine embryo culture. Bovine cumulus–oocyte complexes (COCs) were fertilized after in vitro maturation. The presumed zygotes were cultured in in vitro culture medium supplemented with or without 10⁻⁷ M melatonin. The cleavage rate, 8-cell rate and blastocyst rate were examined to identify the kinetics of embryo development. The hatched blastocyst rate, mortality rate after thawing and the relevant transcript abundance were measured to evaluate the quality of blastocyst. The results showed that melatonin significantly promoted the cleavage rate and 8-cell embryo yield of in vitro produced bovine embryo. In addition, significantly more blastocysts were observed by Day 7 of embryo culture at the presence of melatonin. These results indicated that melatonin accelerated the development of in vitro produced bovine embryos. Following vitrification at Day 7 of embryo culture, melatonin (10⁻⁷ M) significantly increased the hatched blastocyst rate from 24 h to 72 h and decreased the mortality rate from 48 h to 72 h after thawing. The presence of melatonin during the embryo culture resulted in a significant increase in the gene expressions of DNMT3A, OCC, CDH1 and decrease in that of AQP3 after thawing. In conclusion, melatonin not only promoted blastocyst yield and accelerated in vitro bovine embryo development, but also improved the quality of blastocysts which was indexed by an elevated cryotolerance and the up-regulated expressions of developmentally important genes.

Selection of the in vitro culture media influences mRNA expression of Hedgehog genes, Il-6, and important genes regarding reactive oxygen species in single murine preimplantation embryos

Background. The aim of this paper was to determine the influence of different in vitro culture media on mRNA expression of Hedgehog genes, il-6, and important genes regarding reactive oxygen species in single mouse embryos. Methods. Reverse transcription of single embryos either cultured in vitro from day 0.5 until 3.5 (COOK's Cleavage medium or Vitrolife's G-1 PLUS medium) or in vivo until day 3.5 post coitum. PCR was carried out for β-actin followed by nested-PCR for shh, ihh, il-6, nox, gpx4, gpx1, and prdx2. Results. The number of murine blastocysts cultured in COOK medium which expressed il-6, gpx4, gpx1, and prdx2 mRNA differed significantly compared to the in vivo group. Except for nox, the mRNA profile of the Vitrolife media group embryos varied significantly from the in vivo ones regarding the number of blastocysts expressing the mRNA of shh, ihh, il-6, gpx4, gpx1 and prdx2. Conclusions. The present study shows that different in vitro culture media lead to different mRNA expression profiles during early development. Even the newly developed in vitro culture media are not able to mimic the female reproductive tract. The question of long-term consequences for children due to assisted reproduction techniques needs to be addressed in larger studies.

Oxidative stress and redox regulation on in vitro development of mammalian embryos

Many factors affect development of mammalian preimplantation embryos in vitro. It is well known that in vitro development of bovine embryos is highly affected by culture condition including energy source, growth factors, pH or gas environment. Many efforts have been made towards the suitable environments which can successfully support embryo development in vitro. For a rapid growth and differentiation, embryo requires energy by utilizing ATP, NADPH with oxygen molecules. These energy substrates are produced from the electron transport chain in the mitochondria. In addition to energy production, reactive oxygen species (ROS) are also generated as by-product of such energy production system. ROS production is sensitively controlled by the balance of oxidizing and reducing status and affected by several antioxidant enzymes such as superoxide dismutase (SOD), Catalase, glutathione peroxidase (GPx) or low molecular weight thiols such as glutathione (GSH). Imbalance of oxidation and reduction causes production of excess ROS, which causes the developmental arrest, physical DNA damage, apoptosis induction or lipid peroxidation. Environmental oxygen condition during embryo culture also highly affects embryo development as well as intracellular redox balance. Several studies have revealed that regulation of intra- and extra- cellular reducing environment by reducing excess ROS by using antioxidants, reducing oxygen concentration are effective for improving embryo development. Also, recent studies have demonstrated the difference in gene expression affected by oxidative stress. This review briefly summarizes the effects of ROS and the role of redox balance on preimplantation embryos for improving the efficiency of in vitro production of mammalian embryos.

Molecular and subcellular characterisation of oocytes screened for their developmental competence based on glucose-6-phosphate dehydrogenase activity

Oocyte selection based on glucose-6-phosphate dehydrogenase (G6PDH) activity has been successfully used to differentiate between competent and incompetent bovine oocytes. However, the intrinsic molecular and subcellular characteristics of these oocytes have not yet been investigated. Here, we aim to identify molecular and functional markers associated with oocyte developmental potential when selected based on G6PDH activity. Immature compact cumulus-oocyte complexes were stained with brilliant cresyl blue (BCB) for 90 min. Based on their colouration, oocytes were divided into BCB(-) (colourless cytoplasm, high G6PDH activity) and BCB(+) (coloured cytoplasm, low G6PDH activity). The chromatin configuration of the nucleus and the mitochondrial activity of oocytes were determined by fluorescence labelling and photometric measurement. The abundance and phosphorylation pattern of protein kinases Akt and MAP were estimated by Western blot analysis. A bovine cDNA microarray was used to analyse the gene expression profiles of BCB(+) and BCB(-) oocytes. Consequently, marked differences were found in blastocyst rate at day 8 between BCB(+) (33.1+/-3.1%) and BCB(-) (12.1+/-1.5%) oocytes. Moreover, BCB(+) oocytes were found to show higher phosphorylation levels of Akt and MAP kinases and are enriched with genes regulating transcription (SMARCA5), cell cycle (nuclear autoantigenic sperm protein, NASP) and protein biosynthesis (RPS274A and mRNA for elongation factor 1alpha, EF1A). BCB(-) oocytes, which revealed higher mitochondrial activity and still nucleoli in their germinal vesicles, were enriched with genes involved in ATP synthesis (ATP5A1), mitochondrial electron transport (FL405), calcium ion binding (S100A10) and growth factor activity (bone morphogenetic protein 15, BMP15). This study has evidenced molecular and subcellular organisational differences of oocytes with different G6PDH activity.

Presence and distribution of E-cadherin in the 4-cell golden hamster embryo. Effect of maternal age and parity

Maternal age dependency of gestation time in hamster and in other mammals is a well demonstrated fact. We have recently shown that adult nulliparous and multiparous hamster females show significant asynchrony and retard on early embryo development (from two blastomeres to morula stages) when compared with nulliparous young females. The number of cell–cell adhesions between blastomeres in early embryo development has been reported to be a good indication of the ability of embryos to cleave and develop. In this work we studied, by indirect immunofluorescence, the presence and distribution of E-cadherin in 4-cell embryos obtained from nulliparous young (NYF), nulliparous adult (NAF) and multiparous adult (MAF) hamster females. Distribution and intensity of fluorescence was observed and registered using confocal microscopy. Staining intensities for E-cadherin were quantified by computed densitometry in the free membrane regions, in the cytoplasm region and in the cell–cell adhesion zones of each embryo. E-Cadherin in all the studied zones was significantly higher (p< 0.01) in NYF. Cadherin concentration in the intercellular membranes was always statistically higher (p< 0.05) than in the free membrane regions. An appreciable concentration of E-cadherin was found in the cytoplasm of the 4-cell embryos obtained from the three groups of females, but was significantly higher in NYF. No statistical differences were observed in any of the parameters studied between NAF and MAF. Our results seem to indicate that changes in the reproductive behavior related to age and/or multiparity may be correlated with changes in the processes related to intercellular adhesions during early cleavage.

Zygotic gene activation and maternal factors in mammals

Zygotic gene activation (ZGA) is the first event of gene expression after fertilization. Following fertilization, ZGA occurs within a short time interval depending on the animal species. Until ZGA, maternal proteins and transcripts stored in oocytes control embryonic development, indicating the importance of maternal factors for development. Somatic cell cloning also proves the potential of oocyte to reprogram the differentiated cell nuclei to embryonic nuclei. Recent studies show that the epigenetic modifications of nuclei play important roles in controlling gene expression during ZGA. However, the mechanisms that control ZGA remain largely unknown. This review will cover the current understanding of ZGA. Specifically, it will focus on the maternal factors that control gene expression during early embryogenesis.

Zygotically activated genes are suppressed in mouse nuclear transferred embryos

Mammalian oocytes have the ability to confer totipotency to terminally differentiated somatic cell nuclei. Viable cloned animals have been produced by somatic cell nuclear transfer (NT) into oocytes in many mammalian species including mouse. However, the success rates of the production were quite low in all species. Many studies have measured differences in gene expression between NT and fertilized embryos in relatively advanced stages of development such as pre- and post-natal stages or the blastocyst stage. In the present study, we compared gene expression patterns using differential display RT-PCR (DDRT-PCR) between the NT and IVF embryos at the 2-cell stage to detect some abnormalities affecting later development of NT embryos. Aberrant gene expression was detected in NT embryos compared with IVF embryos, and MuERV-L and Dnaja2 genes were down-regulated and Inpp5b and Chst12 genes were up-regulated in the NT embryos. Further analysis showed that the expression of zygotically activated genes such as Interferon-gamma, Dub-1, Spz1, DD2106 (unknown gene), and DD2111 (unknown gene) were suppressed in NT embryos, suggesting that the cellular process involved in the nuclear reprogramming of somatic nucleus is not appropriately regulated.

Role of oocyte-specific genes in the development of mammalian embryos

Studies on oocyte-specific genes are important in understanding the genetic pathways essential for folliculogenesis, oogenesis and early embryogenesis. Although the molecular mechanisms regulating oocyte growth and embryo development in mammals have partially been unraveled by gene knockout studies, many aspects concerning reproduction remain to be determined. Development of mammalian embryos starts with the fusion of sperm and egg. After fertilization, the first major developmental transition, maternal to zygotic transition, occurs at the specific stages of preimplantation development in each mammal. The transition is called zygotic gene activation (ZGA) or embryonic genome activation. The ZGA is one of the most important events that occur during preimplantation development; however, the mechanism of the event remains unknown. Because the development until the transition is maintained by maternally inherited proteins and transcripts stored in the oocytes, it is highly likely that these products play an important role in the initiation of ZGA. Several maternal-effects genes that are specifically expressed in oocytes have been identified and their involvement in preimplantation development has been revealed. Therefore, to study oocyte-specific gene regulation would help not only to understand the precise mechanisms of mammalian development, but also to show the mechanisms of reproductive disorders, such as premature ovarian failure and infertility. (Reprod Med Biol 2006; 5: 175-182).

Oog1, an oocyte-specific protein, interacts with Ras and Ras-signaling proteins during early embryogenesis

We previously identified an oocyte-specific gene, Oogenesin 1 (Oog1), that encodes 326 amino acids containing a leucine zipper structure and a leucine-rich repeat. In the present study, to identify the interacting proteins of Oog1, we performed a yeast two-hybrid screening using a GV-oocyte cDNA library and found that Ral guanine nucleotide dissociation stimulator (RalGDS) is the binding partner of Oog1. Coimmunoprecipitation assay confirmed the interaction between Oog1 and RalGDS proteins. Colocalization experiments provide the evidence that the nuclear localization of RalGDS depends on the expression of Oog1. Interestingly, RalGDS protein localized in the nucleus rather than the cytoplasm between late 1-cell and early 2-cell stages, the time when Oog1 localizes in the nucleus. We also examined the interaction between Oog1 and Ras by GST pull-down assay and revealed that Oog1 interacts with Ras in a GTP-dependent manner. These findings suggest a role of Oog1 as a Ras-binding protein.

Gene expression in bovine embryos derived from oocytes with different developmental competence collected at the defined follicular developmental stage

The aim of this study was to compare the expression of selected genes in bovine embryos developed from oocytes with different developmental competence. Four oocyte populations were collected, separately either from small (2-5 mm) or medium (6-10 mm) follicles, in the growth/stagnation (G/S) or dominance/regression (D/R) stage of the first follicular wave. They were matured, fertilized and cultured to D7 or D8 blastocysts by a standard protocol. Poly (A)+ mRNA was extracted from pooled blastocysts and the expression of bax-alpha (Bax), connexin 43 (Cx 43) and connexin 31 (Cx 31) was estimated using real-time RT-PCR. The cleavage rates were significantly higher in oocytes collected from both medium and small follicles, (p < or = 0.05 and p < or = 0.01, respectively) in the G/S than in the D/R stage. There were no significant differences in the D7 blastocyst rates between oocytes from both medium and small follicles in the G/S or D/R stage. But the D8 blastocyst rate was significantly higher in oocytes from small follicles in the G/S stage compared with those in the D/R stage. The relative abundance of Bax and Cx 31 made no significant difference in both D7 and D8 blastocysts developed from oocytes collected from medium or small follicles in the G/S or D/R stages. But the relative abundance of the Cx 43 transcript was significantly higher in D8 blastocysts developed from oocytes collected from both medium and small follicles in the G/S stage compared with those in the D/R stage. We conclude that the relative abundance of Cx 43 can be used as a marker of developmental potential for embryos derived from oocytes with different developmental competence because the level of Cx 43 transcript was greater in embryos derived from oocytes with greater developmental competence compared with those derived from oocytes with lesser developmental competence.

The impact of oocyte maturation media on early bovine embryonic development

Successful production of high quality blastocysts in vitro depends on the use of a culture system that ensures the acquisition of developmental competence by the maturing oocyte. It is now clear that the in vitro maturation environment has a major influence on the oocyte's ability to acquire the potential to develop into blastocysts. In this work we examine the impact of oocyte culture media on the quality of blastocysts by comparing developmental rates, cell number and their allocation to embryonic cell lineages, apoptosis, and expression of developmentally important genes. Higher total cell count and ICM:TCN ratio, which are indicative of embryo viability, were observed in embryos derived from oocyte maturation in TCM-199 supplemented with serum when compared to blastocysts derived from oocyte maturation in SOF BSA. Moreover, oocyte maturation in TCM-199 supplemented with serum-generated embryos of higher morphological quality and producing higher levels of Interferon Tau transcripts when compared to embryos derived from oocyte maturation in SOF BSA. In conclusion, the oocyte maturation regimen affected the morphological feature of blastocysts, including total cell count and allocation of cells to trophectoderm (TE) and inner cell mass (ICM) lineages and the expression profiles of genes involved in various embryo functions such as early embryonic growth, regulation of gene transcription, trophoblast differentiation and function, embryo-maternal communication, and stress response. Our results show that the oocyte culture media have strong impact on the quality of embryos produced in vitro and emphasize the need for more in depth evaluation of oocyte maturation protocols.

Gene expression signatures of seven individual human embryonic stem cell lines

Identification of molecular components that define a pluripotent human embryonic stem cell (hESC) provides the basis for understanding the molecular mechanisms regulating the maintenance of pluripotency and induction of differentiation. We compared the gene expression profiles of seven genetically independent hESC lines with those of nonlineage-differentiated cells derived from each line. A total of 8,464 transcripts were expressed in all hESC lines. More than 45% of them have no yet-known biological function, which indicates that a high number of unknown factors contribute to hESC pluripotency. Among these 8,464 transcripts, 280 genes were specific for hESCs and 219 genes were more than twofold differentially expressed in all hESC lines compared with nonlineage-differentiated cells. They represent genes implicated in the maintenance of pluripotency and those involved in early differentiation. The chromosomal distribution of these hESC-enriched genes showed over-representation in chromosome 19 and under-representation in chromosome 18. Although the overall gene expression profiles of the seven hESC lines were markedly similar, each line also had a subset of differentially expressed genes reflecting their genetic variation and possibly preferential differentiation potential. Limited overlap between gene expression profiles illustrates the importance of cross-validation of results between different ESC lines.

The TCL1 family of oncoproteins: co-activators of transformation

The T-cell leukaemia/lymphoma 1 (TCL1)-family oncoproteins augment AKT signal transduction and enhance cell proliferation and survival. Chromosome rearrangements, faulty developmental silencing and Epstein-Barr virus infection appear to dysregulate the expression of TCL1-family genes, provoking several important types of lymphocyte cancer. A key role for TCL1 proteins in cell transformation has been established in studies of transgenic mouse models, which develop a unique spectrum of T- and B-cell malignancies. How TCL1 proteins are regulated and dysregulated, how they promote transformation and the potential for therapies modelled on TCL1 interactions have important implications for understanding and treating lymphocyte cancers.

Transcriptional Profiling of Pig Embryogenesis by Using a 15-K Member Unigene Set Specific for Pig Reproductive Tissues and Embryos1

Differential mRNA expression patterns were evaluated between germinal vesicle oocytes (pgvo), four-cell (p4civv), blastocyst (pblivv), and in vitro-produced four-cell (p4civp) and in vitro-produced blastocyst (pblivp) stage embryos to determine key transcripts responsible for early embryonic development in the pig. Five comparisons were made: pgvo to p4civv, p4civv to pblivv, pgvo to pblivv, p4civv to p4civp, and pblivv to pblivp. ANOVA (P < 0.05) was performed with the Benjamini and Hochberg false-discovery-rate multiple correction test on each comparison. A comparison of pgvo to p4civv, p4civv to pblivv, and pgvo to pblivv resulted in 3214, 1989, and 4528 differentially detected cDNAs, respectively. Real-time PCR analysis on seven transcripts showed an identical pattern of changes in expression as observed on the microarrays, while one transcript deviated at a single cell stage. There were 1409 and 1696 differentially detected cDNAs between the in vitro- and in vivo-produced embryos at the four-cell and blastocyst stages, respectively, without the Benjamini and Hochberg false-discovery-rate multiple correction test. Real-time polymerase chain reaction (PCR) analysis on four genes at the four-cell stage showed an identical pattern of gene expression as found on the microarrays. Real-time PCR analysis on four of five genes at the blastocyst stage showed an identical pattern of gene expression as found on the microarrays. Thus, only 1 of the 39 comparisons of the pattern of gene expression exhibited a major deviation between the microarray and the real-time PCR. These results illustrate the complex mechanisms involved in pig early embryonic development.

The problematic in-vitro embryo in the age of epigenetics

During use of many assisted reproductive technologies, the embryo spends time in vitro. The immediate and long-term epigenetic impacts of this exposure to an in-vitro environment are discussed in the context of the health of the offspring. Three exemplary types of possible epigenetic impact are discussed: embryonic cell numbers, mitochondria, and genomic imprints. There is evidence that all of these can be affected in the short term and that these short-term impacts can have heritable consequences across developmental cell generations into maturity. There is also evidence of association between the observed impact and pathology, but as yet no unequivocal evidence of causality for humans and mice. The problematic in-vitro embryo is considered paradigmatic for a central question facing biology: how does the environment interact epigenetically with the genome to produce variable phenotypic outcomes?

Effect of culture environment on embryo quality and gene expression - experience from animal studies

Recent studies comparing bovine oocyte maturation, fertilization and embryo culture in vivo and in vitro have demonstrated that the origin of the oocyte is the main factor affecting blastocyst yield, while the post-fertilization culture environment is critical in determining blastocyst quality, measured in terms of cryotolerance and relative transcript abundance, irrespective of the origin of the oocyte. Production of embryos in vitro, particularly when using an extended period of in-vitro culture, may predispose the embryo to phenomena such as the large offspring syndrome, which is likely to alter gene expression, particularly of imprinted genes. It is clear now that the post-fertilization culture environment has a profound effect on the relative abundance of gene transcripts within the embryo, and culture under suboptimal conditions for as little as 1 day can lead to perturbations in the pattern of expression.

Evaluation of gene expression in pigs selected for enhanced reproduction using differential display PCR: II. Anterior pituitary

The objective of this study was to identify differentially expressed genes in the anterior pituitary (AP) of sows selected for enhanced reproductive phenotypes. Selection in the Index (I) line was based on an index of ovulation rate and embryo survival, whereas random selection was used in the Control (C) line. Average numbers of fully formed piglets at birth were 12.5 +/- 1.5 and 9.9 +/- 2.0 for Line I and C sows used in this study, respectively. In order to induce luteolysis and synchronize follicle development, sows were injected (i.m.) with 2 mL of prostaglandin F2alpha analog between d 12 and 14 of the estrous cycle. Tissue was harvested 2 d (d2) or 4 d (d4) after injection, resulting in four experimental groups: Cd2 (n = 6), Cd4 (n = 4), Id2 (n = 6), and Id4 (n = 7). Differential display PCR (ddPCR) was used to search for transcriptional changes between selection lines in the AP, using samples within line but pooled across days. Northern hybridization was used to confirm ddPCR results. For ddPCR, two pools were used from each line (C and I). Three genes were confirmed to be differentially expressed between Lines I and C: G-beta like protein, ferritin heavy-chain, and follicle stimulating hormone beta subunit, whereas many other expressed sequence tags were observed to be differentially expressed but still require confirmation. Our findings indicate that long-term selection to increase ovulation rate and decrease embryo mortality has altered transcriptional patterns in the anterior pituitary, most likely as correlated responses.

Expression of stage-specific genes during zygotic gene activation in preimplantation mouse embryos

The expression of mouse two-cell stage specific genes was studied using the modified DDRT-PCR method, which overcame the paucity of the experimental materials of preimplantation embryos. Embryo tissues equivalent to that of four blastomeres are sufficient for amplification of target genes as visualized using polyacrylamide gel. Sequence analyses and reverse Northern blots indicate that the genes of ATPase 6 and Ywhaz are expressed specifically in two-cell embryos. ATPase 6 is essential for one-cell to two-cell transition and plays an important role in establishment of oxidative phosphorylation, while Ywhaz is related to initiating cellular communication system.

Oogenesin is a novel mouse protein expressed in oocytes and early cleavage-stage embryos

We describe a new gene (Oogenesin) that is expressed through oogenesis and early embryogenesis in the mouse. De novo expression starts at 15.5 dpc (days postcoitum) in the ovary, which coincides with the start of oogenesis. The isolated cDNA was 1387 base pairs (bp) in length with a single open reading frame of 326 amino acids corresponding to a predicted molecular mass of 37 kDa with no significant homology to previously reported sequences. A remarkable characteristic of the gene is the presence of a leucine zipper structure at amino acid positions 131-152 and a leucine-rich domain at positions 131-254. Northern blot analysis demonstrated that the mRNA was present only in the ovary, in which it was expressed as a single transcript of approximately 1.7 kb. In situ hybridization revealed distinct signals in the oocytes in follicles at all stages (primordial to antral follicles). Western blot analysis demonstrated that the protein is expressed from oocytes to four-cell-stage embryos and that it has a little larger size (46 kDa) than the predicted size of 37. Immunohistochemical analysis of ovary sections revealed that the protein is also expressed specifically in oocytes in follicles at all stages. Furthermore, immunostaining of preimplantation embryos revealed that the protein localizes in nuclei at the late one-cell and early two-cell stages. These results suggest that the gene has some roles in zygotic transcription of early preimplantation embryos as well as folliculogenesis and oogenesis in the mouse.

Relative messenger RNA abundance in bovine oocytes collected in vitro or in vivo before and 20 hr after the preovulatory luteinizing hormone surge

In the cyclic cow, final maturation of the ovulatory follicle is initiated by the preovulatory luteinizing hormone (LH) surge. During the subsequent 24 hr period, the oocyte nucleus undergoes meiotic progression to metaphase II and several changes in cytoplasmic organization take place. We have previously shown that oocytes recovered at the time of the LH peak and matured in vitro are less competent to reach the blastocyst stage than their counterparts recovered 20 hr later following in vivo maturation, despite both groups undergoing IVF and culture in parallel. The objective of this study was to compare, using real-time quantitative RT-PCR, the relative abundance of various developmentally important gene transcripts in these oocytes. The groups used were mature bovine oocytes originating from: (1) 2-6 mm follicles from slaughterhouse ovaries; (2) preovulatory follicles punctured by ovum pick-up just before the LH surge (i.e., immature) and matured in vitro; or (3) preovulatory follicles punctured 20 hr later, just prior to ovulation (i.e., in vivo matured). In addition, immature oocytes from 2-6 mm follicles were examined. We examined the relative mRNA expression of five enzymes involved in protection against free oxygen radicals (mitochondrial Mn-superoxide dismutase, MnSOD, cytosolic Cu/Zn superoxide dismutase, Cu/ZnSOD, gamma-glutamyl-cysteine transferase, GCS, glutathione peroxidase, GPX, sarcosine oxidase, SOX), a transcript involved in follicular development (growth differentiation factor-9, GDF-9), transcripts involved in glucose metabolism (glucose-6-phosphate dehydrogenase, G6PDH, glucose transporter type-1 and -8, Glut-1, Glut-8) and genes involved in cell cycle events, Cyclin A and B, and poly(A) polymerase (PAP). Transcripts for all genes were detected, irrespective of oocyte origin. While differences were not significant in all cases, variations in levels of transcript abundance between the groups were related to developmental competence. In particular, transcripts for GDF-9 were expressed at significantly higher levels in oocytes recovered at the LH peak and matured in vitro than in those matured in vivo. The observations with GDF-9 are interesting as this gene is believed to be essential for normal folliculogenesis and may be important in the regulation of early follicle and oocyte growth. In conclusion, the results of this study demonstrate differences in the relative mRNA abundance of several developmentally important gene transcripts in bovine oocytes which may be related to developmental competence.

Oocyte and embryo quality: effect of origin, culture conditions and gene expression patterns

In general, the majority of immature bovine oocytes fail to develop to the blastocyst stage following maturation, fertilization and culture in vitro. The evidence suggests that while culture conditions during in vitro embryo production can impact on the developmental potential of the early embryo, the intrinsic quality of the oocyte is the key factor determining the proportion of oocytes developing to the blastocyst stage. In addition, evidence suggests that the period of post-fertilization embryo culture is the most critical in determining blastocyst quality. This paper reviews the current literature, with emphasis on the bovine model, demonstrating evidence for an effect of oocyte origin and/or in vitro maturation conditions on the developmental capacity and gene expression patterns in the oocyte. Furthermore, the well-documented effects of post-fertilization culture environment on embryo gene expression and quality are highlighted.

Up, down and up again is a signature global gene expression pattern at the beginning of gymnosperm embryogenesis

Somatic embryogenesis of a gymnosperm, Picea abies, represents a sequence of specifically regulated developmental stages including proembryogenic mass (PEM), PEM-to-embryo transition, and early and late embryogeny. Here, we report cDNA array analysis of expression patterns of 373 genes in the beginning of P. abies embryo development. The analysis revealed a group of 107 genes (29% of arrayed cDNAs) which were upregulated upon PEM-to-embryo transition, then downregulated during early embryogeny and finally upregulated again at the beginning of late embryogeny. This major gene expression pattern was abrogated in a developmentally arrested cell line that is unable to pass through the PEM-to-embryo transition. Thirty-five genes (9.4% of arrayed cDNAs) were found to be differentially expressed during normal embryonic pattern formation. Among them, 22 genes (5.9% of arrayed cDNAs) were directly associated with embryo pattern formation and can be considered as marker genes for early stages of P. abies embryogenesis. The majority of the marker genes encode for proteins involved in translation and posttranslational modification. Among them, 18 genes displayed the major expression pattern.

MuERV-L is one of the earliest transcribed genes in mouse one-cell embryos

The expression pattern and function of the murine endogenous retrovirus-like (MuERV-L) gene in mouse preimplantation embryos was investigated. MuERV-L was rapidly transcribed from the beginning of S phase (8 h after fertilization) in the first cell cycle. MuERV-L expression was completely repressed when transcription from the zygotic genome was inhibited by alpha-amanitin. These results reveal that MuERV-L is transcribed from the zygotic genome and that it is expressed earlier than any other genes previously reported. In addition, MuERV-L was expressed even when the first round of DNA synthesis was inhibited by aphidicolin, suggesting that its expression is controlled by the zygotic clock. The function of MuERV-L in the development of mouse embryos was also examined using antisense oligonucleotides. The developmental competence of embryos was markedly suppressed after the 4-cell stage when they were treated with antisense oligonucleotides. This result suggests that MuERV-L plays an important role in the development of mouse embryos at the early preimplantation stage.

Bovine embryo culture in the presence or absence of serum: implications for blastocyst development, cryotolerance, and messenger RNA expression

We have previously shown that, while the intrinsic quality of the oocyte is the main factor affecting blastocyst yield during bovine embryo development in vitro, the main factor affecting the quality of the blastocyst is the postfertilization culture conditions. Therefore, any improvement in the quality of blastocysts produced in vitro is likely to derive from the modification of the postfertilization culture conditions. The objective of this study was to examine the effect of the presence or absence of serum and the concentration of BSA during the period of embryo culture in vitro on 1) cleavage rate, 2) the kinetics of embryo development, 3) blastocyst yield, and 4) blastocyst quality, as assessed by cryotolerance and gene expression patterns. The quantification of all gene transcripts was carried out by real-time quantitative reverse transcription-polymerase chain reaction. Bovine blastocysts from four sources were used: 1) in vitro culture in synthetic oviduct fluid (SOF) supplemented with 3 mg/ml BSA and 10% fetal calf serum (FCS), 2) in vitro culture in SOF + 3 mg/ml BSA in the absence of serum, 3) in vitro culture in SOF + 16 mg/ml BSA in the absence of serum, and 4) in vivo blastocysts. There was no difference in overall blastocyst yield at Day 9 between the groups. However, significantly more blastocysts were present by Day 6 in the presence of 10% serum (20.0%) compared with 3 mg/ml BSA (4.6%, P < 0.001) or 16 mg/ml BSA (11.6%, P < 0.01). By Day 7, however, this difference had disappeared. Following vitrification, there was no difference in survival between blastocysts produced in the presence of 16 mg/ml BSA or those produced in the presence of 10% FCS; the survival of both groups was significantly lower than the in vivo controls at all time points and in terms of hatching rate. In contrast, survival of blastocysts produced in SOF + 3 mg/ml BSA in the absence of serum was intermediate, with no difference remaining at 72 h when compared with in vivo embryos. Differences in relative mRNA abundance among the two groups of blastocysts analyzed were found for genes related to apoptosis (Bax), oxidative stress (MnSOD, CuZnSOD, and SOX), communication through gap junctions (Cx31 and Cx43), maternal recognition of pregnancy (IFN-tau), and differentiation and implantation (LIF and LR-beta). The presence of serum during the culture period resulted in a significant increase in the level of expression of MnSOD, SOX, Bax, LIF, and LR-beta. The level of expression of Cx31 and Cu/ZnSOD also tended to be increased, although the difference was not significant. In contrast, the level of expression of Cx43 and IFN-tau was decreased in the presence of serum. In conclusion, using a combination of measures of developmental competence (cleavage and blastocyst rates) and qualitative measures such as cryotolerance and relative mRNA abundance to give a more complete picture of the consequences of modifying medium composition on the embryo, we have shown that conditions of postfertilization culture, in particular, the presence of serum in the medium, can affect the speed of embryo development and the quality of the resulting blastocysts. The reduced cryotolerance of blastocysts generated in the presence of serum is accompanied by deviations in the relative abundance of developmentally important gene transcripts. Omission of serum during the postfertilization culture period can significantly improve the cryotolerance of the blastocysts to a level intermediate between serum-generated blastocysts and those derived in vivo. The challenge now is to try and bridge this gap.

Molecular characterization of genomic activities at the onset of zygotic transcription in mammals

In rabbit embryos, zygotic transcripts are required for the development of the embryo only from the 8- to 16-cell stage onward, more than 44 h after fertilization (i.e., zygotic gene activation; ZGA). In order to characterize the first zygotic transcripts expressed in this species we used a suppression subtractive hybridization approach to isolate RNA that was present after the major transcriptional activation (morula stage), but absent at the 1-cell stage as maternal transcripts. One hundred fourteen differentially expressed inserts were selected and sequenced. A statistical analysis of expression patterns throughout the preimplantation period of development shows that genes transcribed from ZGA onward follow different patterns of expression. Considering their early post-ZGA behavior, we describe at least two main patterns: a gradual increase from ZGA onward, and a sharp increase in expression at ZGA followed by a marked decrease at the morula stage. Our data show that both ZGA and some early post-ZGA events are involved in the establishment of specific patterns of embryonic gene expression.

TCL1 participates in early embryonic development and is overexpressed in human seminomas

Overexpression of the TCL1 oncogene has been shown to play a causative role in T cell leukemias of humans and mice. The characterization of Tcl1-deficient mice in these studies indicates an important developmental role for Tcl1 in early embryogenesis. In wild-type embryos, Tcl1 is abundant in the first three mitotic cycles, during which it shuttles between nuclei and the embryo cortical regions in a cell-cycle-dependent fashion. The absence of this protein in early embryogenesis results in reduced fertility of female mice. The present studies elucidate the mechanism responsible for the reduced female fertility through analysis of the oogenesis stages and early embryo development in Tcl1-deficient mice. Even though Tcl1(-/-) females display normal oogenesis and rates of oocyte maturation/ovulation and fertilization, the lack of maternally derived Tcl1 impairs the embryo's ability to undergo normal cleavage and develop to the morula stage, especially under in vitro culture conditions. Beyond this crisis point, differentiative traits of zygotic genome activation and embryo compaction can take place normally. In contrast with this unanticipated role in early embryogenesis, we observed an overexpression of TCL1 in human seminomas. This finding suggests that TCL1 dysregulation could contribute to the development of this germinal cell cancer as well as lymphoid malignancies.

Analysis of differential messenger RNA expression between bovine blastocysts produced in different culture systems: implications for blastocyst quality

Using reverse transcriptase-amplified fragment length polymorphism (RT-AFLP) analysis of differential mRNA expression and semiquantitative reverse transcriptase-polymerase chain reaction, we compared mRNA expression in bovine blastocysts from 4 sources, known to differ in quality in terms of their ability to withstand cryopreservation: 1) in vitro culture in synthetic oviduct fluid of in vitro-matured (IVM)/in vitro fertilized (IVF) zygotes; 2) in vitro culture in TCM-199 supplemented with granulosa cells (coculture) of IVM/IVF zygotes; 3) in vivo culture in the ewe oviduct of IVM/IVF zygotes; or 4) superovulation, artificial insemination, and nonsurgical embryo recovery. Total mRNA was isolated from pools of blastocysts and reverse transcription was performed. Triplicate reactions from each sample were displayed, and only consistent banding variations were recorded. Using AFLP-differential display assay, we found that cDNA banding patterns are highly conserved between the 4 groups of blastocysts studied; however, there was a difference of 7% in bands either missing or expressed across the groups. Fifty bands were reamplified, and a sequence comparison search revealed similarity of 14 isolated fragments to ribosomal and mitochondrial genes, 16 matched to described cDNA, and 20 corresponded to unknown sequences that may represent novel genes. The study of 7 differentially expressed mRNAs known to be involved in developmental process in the embryo suggests roles for apoptosis, oxidative stress, gap junctions, and differentiation in the determination of embryo quality. The aberrant transcription patterns detected in in vitro-produced bovine embryos compared with those produced in vivo may explain their reduced quality in terms of viability after cryopreservation.

Nuclear accumulation of cyclin B1 in mouse two-cell embryos is controlled by the activation of Cdc2

In the present study, the sequential expression and cellular localization of cyclin B1 was examined in two-cell mouse embryos to elucidate the mechanism of the two-cell block. One-cell embryos derived from in vitro fertilization were cultured with oviductal tissue (nonblocking condition) or without oviductal tissue (blocking condition) to establish the experimental conditions in which the embryos either overcome the two-cell block or do not. The amount of cyclin B1 gradually increased through the second cell cycle (through S to G2 phase). However, the difference was not observed between culture conditions. This showed that even embryos exhibiting the two-cell block normally synthesize cyclin B1 through the cell cycle. Cyclin B1 in embryos cultured under nonblocking condition accumulates in the nucleus during the transition from the G2 to the M phase, whereas that in embryos cultured in blocking condition localizes in the cytoplasm throughout the cell cycle. These data indicate that two-cell embryos cultured in blocking condition are able to normally synthesize cyclin B1 but have defects in nuclear accumulation of the protein. However, when two-cell blocked embryos were treated with okadaic acid, an activator of Cdc2 kinase, part of cyclin B1 in the embryos translocated into the nucleus. Moreover, treatment with butyrolactone I, a specific inhibitor of Cdc2 kinase, inhibits nuclear translocation of cyclin B1 in those embryos. These results suggest that Cdc2 kinase regulates the nuclear accumulation of cyclin B1 in mouse two-cell embryos.