Effect of time interval from insemination to first cleavage on the developmental characteristics, sex ratio and pregnancy rate after transfer of bovine embryos

Relief of endoplasmic reticulum stress enhances DNA damage repair and improves development of pre-implantation embryos

Early-cleaving embryos are known to have better capacity to reach the blastocyst stage and produce better quality embryos compared to late-cleaving embryos. To investigate the significance of endoplasmic reticulum (ER) stress on early embryo cleavage kinetics and development, porcine embryos produced in vitro were separated into early- and late-cleaving groups and then cultured in the absence or presence of the ER stress inhibitor tauroursodeoxycholic acid (TUDCA). Developing embryos were collected at days 3 to 7 of culture for assessment of ER stress status, incidence of DNA double-strand breaks (DSBs), development and total cell number. In the absence of TUDCA treatment, late-cleaving embryos exhibited ER stress, higher incidence of DNA DSBs, as well as reductions in development to the blastocyst stage and total embryo cell numbers. Treatment of late-cleaving embryos with TUDCA mitigated these effects and markedly improved embryo quality and development. These results demonstrate the importance of stress coping responses in early developing embryos, and that reduction of ER stress is a potential means to improve embryo quality and developmental competence.

A mathematical model of the interaction between bovine blastocyst developmental stage and progesterone-stimulated uterine factors on differential embryonic development observed on Day 15 of gestation

A complex interaction between the developing bovine embryo and the growth potential of the uterine milieu it inhabits results in an embryo capable of developing past the maternal recognition stage and on to a successful pregnancy. Previously, we observed variation in the lengths of embryos recovered 8 d after bulk transfer of Day 7 in vitro-produced (IVP) blastocysts into the same uterus. Potential causes of the differential embryonic growth were examined and modeled using 2 rounds of bulk (n = 4-6) IVP transfers and recovery of these embryos 8 d later. Morphological and gene expression measurements of the embryos were determined and the progesterone concentration of the cows was measured throughout the reproductive cycle as a reflection of the status of the uterine environment. These data were used to develop and evaluate a model that describes the interaction between the uterine environment and the growth rate of the developing embryo. Expression of 6 trophectoderm genes (IFNT, TKDP1, PAG11, PTGS2, DKK1, and PDPN) was correlated with conceptus length. The model determined that if the embryo develops to blastocyst stage, the uterine environment, driven by progesterone, is a more important component than blastocyst size in the stimulation of embryonic growth rate to ensure adequate interferon tau (IFNT) for pregnancy recognition. We detected an effect of Day 7 progesterone on the expression of all 6 genes, embryonic disc size, and trophectoderm length on Day 15. We also found effects of embryo transfer size on trophectoderm length and expression of IFNT and PAG11 on Day 15. Lower energy balance over the period from transfer to recovery was associated with reduced embryo growth to Day 15, and this effect was independent of progesterone. Energy balance also affected expression of PDPN and TKDP1 on Day 15. We observed an effect of energy balance from transfer to recovery on embryo survival in cows with partial embryo losses, where embryo factors dominate embryo survival, with cows with greater energy balance having lower embryo losses. This effect was independent of energy balance 40 d before transfer and suggests that energy balance has direct, immediate effects on the embryo and maternal environment during this period. Furthermore, energy balance effects on embryo survival in cows with partial embryo losses were largely mediated by expression of TKDP1, PAG11, and PDPN. These results provide candidate signaling pathways for the effect of progesterone and energy balance on embryo growth and survival.

Spent culture medium analysis from individually cultured bovine embryos demonstrates metabolomic differences

Spent culture medium can provide valuable information regarding the physiological state of a bovine preimplantation embryos through non-invasive analysis of the sum/depleted metabolite constituents. Metabolomics has become of great interest as an adjunct technique to morphological and cleavage-rate assessment, but more importantly, in improving our understanding of metabolism. In this study, in vitro produced bovine embryos developing at different rates were evaluated using proton nuclear magnetic resonance (1H NMR). Spent culture medium from individually cultured embryos (2-cell to blastocyst stage) were divided into two groups based on their cleavage rate fast growing (FG) and slow growing (SG; developmentally delayed by 12-24 h), then analyzed by a 600 MHz NMR spectrometer. Sixteen metabolites were detected and investigated for sum/depletion throughout development. Data indicate distinct differences between the 4-cell SG and FG embryos for pyruvate (P < 0.05, n = 9) and at the 16-cell stage for acetate, tryptophan, leucine/isoleucine, valine and histidine. Overall sum/depletion levels of metabolites demonstrated that embryos produced glutamate, but consumed histidine, tyrosine, glycine, methionine, tryptophan, phenylalanine, lysine, arginine, acetate, threonine, alanine, pyruvate, valine, isoleucine/leucine, and lactate with an overall trend of higher consumption of these metabolites by FG groups. Principal component analysis revealed distinct clustering of the plain medium, SG, and FG group, signifying the uniqueness of the metabolomic signatures of each of these groups. This study is the first of its kind to characterize the metabolomic profiles of SG and FG bovine embryos produced in vitro using 1H NMR. Elucidating differences between embryos of varying developmental rates could contribute to a better understanding of embryonic health and physiology.

The contribution of efficient production of monozygotic twins to beef cattle breeding

Production of sires with high breeding potential is indispensable for prompt and reliable breeding using their semen in the cattle industry. Currently, in Japan, we aim to further the production of Japanese black sires via a new breeding system that uses genetically homologous monozygotic twins so that better growth performance and carcass traits can be translated to the increased production of beef with higher economic value. Several studies have reported that monozygotic twins are produced by embryo bisection. On the other hand, with the evolution and stabilization of in vitro fertilization technology, it has become possible to produce multiple monozygotic twin calves from blastomeres separated from a cleavage-stage embryo. This review attempts to clarify breeding practices through revalidation of the factors that affect the production efficiency of monozygotic twin calves by embryo bisection. Furthermore, the establishment of a system for monozygotic twin embryo production via the simplified technique of blastomere separation is reviewed while showing data from our previously performed studies.

Selection of viable in vitro-fertilized bovine embryos using time-lapse monitoring in microwell culture dishes

Conventionally, in vitro-fertilized (IVF) bovine embryos for transfer are morphologically evaluated at day 7–8 of embryo culture. This method is, however, subjective and results in unreliable selection. We previously described a novel selection system for IVF bovine blastocysts for transfer that traces the development of individual embryos with time-lapse monitoring in our specially developed microwell culture dishes (LinKID micro25). The system can noninvasively identify prognostic factors that reflect viability after transfer. By assessing a combination of identified prognostic factors —timing of the first cleavage; number of blastomeres at the end of the first cleavage; and number of blastomeres at the onset of lag-phase, which results in temporary developmental arrest during the fourth or fifth cell cycle— the pregnancy rate was improved over using conventional morphological evaluation. Time-lapse monitoring with LinKID micro25 could facilitate objective and reliable selection of healthy IVF bovine embryos. Here, we review the novel bovine embryo selection system that allows for prediction of viability after transfer.

Bovine embryo-oviduct interaction in vitro reveals an early cross talk mediated by BMP signaling

Signaling components of bone morphogenetic proteins (BMPs) are expressed in an anatomically and temporally regulated fashion in bovine oviduct. However, a local response of this signaling to the presence of the embryo has yet to be elucidated. The aim of the present study was to evaluate if early embryo-oviduct interaction induces changes in the gene expression of BMP signaling components. For this purpose, we used an in vitro co-culture system to investigate the local interaction between bovine oviductal epithelial cells (BOEC) from the isthmus region with early embryos during two developmental periods: before (from the 2-cell to 8-cell stage) or during (from the 8-cell to 16-cell stage) the main phase of embryonic genome activation (EGA). Exposure to embryos, irrespective of the period, significantly reduced the relative abundance of BMPR1B, BMPR2, SMAD1, SMAD6 and ID2 mRNAs in BOEC. In contrast, embryos that interacted with BOEC before EGA showed a significant increase in the relative abundance of SMAD1 mRNA at the 8-cell stage compared to embryos cultured without BOEC. Moreover, embryos at the 16-cell stage that interacted with BOEC during EGA showed a significant increase in BMPR1B, BMPR2 and ID2 mRNA. These results demonstrate that embryo-oviduct interaction in vitro induces specific changes in the transcriptional levels of BMP signaling, causing a bidirectional response that reduces the expression levels of this signaling in the oviductal cells while increases them in the early embryo. This suggests that BMP signaling pathway could be involved in an early cross talk between the bovine embryo and the oviduct during the first stages of development.

Zygote injection of CRISPR/Cas9 RNA successfully modifies the target gene without delaying blastocyst development or altering the sex ratio in pigs

The CRISPR/Cas9 genome editing tool has increased the efficiency of creating genetically modified pigs for use as biomedical or agricultural models. The objectives were to determine if DNA editing resulted in a delay in development to the blastocyst stage or in a skewing of the sex ratio. Six DNA templates (gBlocks) that were designed to express guide RNAs that target the transmembrane protease, serine S1, member 2 (TMPRSS2) gene were in vitro transcribed. Pairs of CRISPR guide RNAs that flanked the start codon and polyadenylated Cas9 were co-injected into the cytoplasm of zygotes and cultured in vitro to the blastocyst stage. Blastocysts were collected as they formed on days 5, 6 or 7. PCR was performed to determine genotype and sex of each embryo. Separately, embryos were surgically transferred into recipient gilts on day 4 of estrus. The rate of blastocyst development was not significantly different between CRISPR injection embryos or the non-injected controls at day 5, 6 or 7 (p = 0.36, 0.09, 0.63, respectively). Injection of three CRISPR sets of guides resulted in a detectable INDEL in 92-100 % of the embryos analyzed. There was not a difference in the number of edits or sex ratio of male to female embryos when compared between days 5, 6 and 7 to the controls (p > 0.22, >0.85). There were 12 resulting piglets and all 12 had biallelic edits of TMRPSS2. Zygote injection with CRISPR/Cas9 continues to be a highly efficient tool to genetically modify pig embryos.

In vivo and in vitro maturation of rabbit oocytes differently affects the gene expression profile, mitochondrial distribution, apoptosis and early embryo development

In vivo-matured cumulus–oocyte complexes are valuable models in which to assess potential biomarkers of rabbit oocyte quality that contribute to enhanced IVM systems. In the present study we compared some gene markers of oocytes and cumulus cells (CCs) from immature, in vivo-matured and IVM oocytes. Moreover, apoptosis in CCs, nuclear maturation, mitochondrial reallocation and the developmental potential of oocytes after IVF were assessed. In relation to cumulus expansion, gene expression of gap junction protein, alpha 1, 43 kDa (Gja1) and prostaglandin-endoperoxide synthase 2 (Ptgs2) was significantly lower in CCs after in vivo maturation than IVM. In addition, there were differences in gene expression after in vivo maturation versus IVM in both oocytes and CCs for genes related to cell cycle regulation and apoptosis (V-Akt murine thymoma viral oncogene homologue 1 (Akt1), tumour protein 53 (Tp53), caspase 3, apoptosis-related cysteine protease (Casp3)), oxidative response (superoxide dismutase 2, mitochondrial (Sod2)) and metabolism (glucose-6-phosphate dehydrogenase (G6pd), glyceraldehyde-3-phosphate dehydrogenase (Gapdh)). In vivo-matured CCs had a lower apoptosis rate than IVM and immature CCs. Meiotic progression, mitochondrial migration to the periphery and developmental competence were higher for in vivo-matured than IVM oocytes. In conclusion, differences in oocyte developmental capacity after IVM or in vivo maturation are accompanied by significant changes in transcript abundance in oocytes and their surrounding CCs, meiotic rate, mitochondrial distribution and apoptotic index. Some of the genes investigated, such as Gja1, could be potential biomarkers for oocyte developmental competence in the rabbit model, helping improve in vitro culture systems in these species.

Differences in developmental competence and gene expression profiles between buffalo (Bubalus bubalis) preimplantation embryos cultured in three different embryo culture media

The objective of this study was to compare effects of in vitro culture systems on embryonic development and expression patterns of developmentally important genes in preimplantation buffalo embryos. After IVM/IVF presumptive zygotes were cultured in one of three systems: undefined TCM-199, mCR2aa medium supplemented with 10 % FBS and defined PVA-myo-inositol-phosphate-EGF medium. No (P > 0.05) differences at 2-cell, 4-cell and 8-cell to 16- cell stages were observed among the three cultured media used, however, increased (P < 0.05) blastocyst yield, cell number and hatching rate were found in defined medium compared to undefined media. The expression patterns of genes implicated in embryo metabolism (GLUT-1), anti-apoptosis (BCL-2), imprinting (IGF-2R), DNA methylation (DNMT-3A) and maternal recognition of pregnancy (IFNT) were increased (P < 0.05) in hatched blastocysts derived from defined medium compared to undefined media. In conclusion, serum-free, defined medium improved developmental competence of in vitro cultured buffalo embryos. Whether these differences in morphological development and gene expression have long-term effects on buffalo calves born after embryo transfer remains unknown. However, it is possible that early adaptations of the preimplantation embryo to its environment persist during fetal and post-natal development.

Trophoblast Major Histocompatibility Complex Class I Expression Is Associated with Immune-Mediated Rejection of Bovine Fetuses Produced by Cloning

Trophoblast cells from bovine somatic cell nuclear transfer (SCNT) conceptuses express major histocompatibility complex class I (MHC-I) proteins early in gestation, and this may be one cause of the significant first-trimester embryonic mortality observed in these pregnancies. MHC-I homozygous-compatible (n = 9), homozygous-incompatible (n = 8), and heterozygous-incompatible (n = 5) SCNT pregnancies were established. The control group consisted of eight pregnancies produced by artificial insemination. Uterine and placental samples were collected on Day 35 ± 1 of pregnancy, and expression of MHC-I, leukocyte markers, and cytokines were examined by immunohistochemistry. Trophoblast cells from all SCNT pregnancies expressed MHC-I, while trophoblast cells from age-matched control pregnancies were negative for MHC-I expression. Expression of MHC-I antigens by trophoblast cells from SCNT pregnancies was associated with lymphocytic infiltration in the endometrium. Furthermore, MHC-I-incompatible conceptuses, particularly the heterozygous-incompatible ones, induced a more pronounced lymphocytic infiltration than MHC-I-compatible conceptuses. Cells expressing cluster of differentiation (CD) 3, gamma/deltaTCR, and MHC-II were increased in the endometrium of SCNT pregnancies compared to the control group. CD4⁺ lymphocytes were increased in MHC-I-incompatible pregnancies compared to MHC-I-compatible and control pregnancies. CD8⁺, FOXP3⁺, and natural killer cells were increased in MHC-I heterozygous-incompatible SCNT pregnancies compared to homozygous SCNT and control pregnancies.

Crocetin improves the quality of in vitro-produced bovine embryos: Implications for blastocyst development, cryotolerance, and apoptosis

The aim of this work was to assess the effect of supplementation of bovine culture medium with the natural antioxidant crocetin on in vitro blastocyst development and quality. This was evaluated as cryotolerance, apoptosis index, and total cells number and allocation. Abattoir-derived oocytes were matured and fertilized in vitro according to standard procedure. Twenty hours after IVF, presumptive zygotes were cultured in synthetic oviduct fluid medium, supplemented with 0, 1, 2.5, and 5 μM crocetin (experiment 1) at 39 °C under humidified air with 5% CO2, 7% O2, and 88% N2. On Day 7, embryo yields were assessed and the blastocysts were vitrified by Cryotop method in 16.5% ethylene glycol, 16.5% DMSO, and 0.5 M sucrose. Finally, blastocysts produced on Day 8 in the absence (control) and presence of 1 μM crocetin were used for terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling and differential staining to evaluate, respectively, the apoptotic rate and the allocation of cells into inner cell mass (ICM) and trophectoderm (TE) lineages (experiment 2). Embryo development was higher in the 1 μM crocetin group compared to the control, both in terms of total embryo output (37.7 ± 4.2%, 52.9 ± 6.3%, 40.9 ± 7.6%, and 42.4 ± 8.7%, respectively, with 0, 1, 2.5, and 5 μM; P < 0.01) and grade 1 and 2 blastocysts (33.6 ± 4.9%, 46.1 ± 7.3%, 37.8 ± 7.9%, and 39.4 ± 7.9%, respectively, with 0, 1, 2.5, and 5 μM; P < 0.05). Moreover, the percentage of fast-developing embryos increased in 1 μM crocetin group compared to the control (23.4 ± 4.7%, 32.7 ± 6.6%, 27.2 ± 6.6%, and 30.1 ± 7.2%, respectively, with 0, 1, 2.5, and 5 μM; P < 0.05). In addition, the enrichment of culture medium with 1 μM crocetin improved embryo cryotolerance compared to the control, as indicated by higher hatching rates recorded after 48 hours postwarming culture (46.5% vs. 60.4%; P < 0.05). Furthermore, 1 μM crocetin decreased both the average number (9.9 ± 0.4 vs. 7.1 ± 0.3) and the percentage of apoptotic cells (7.1 ± 0.4 vs. 4.2 ± 0.2) in blastocysts compared to the control (P < 0.01). However, no differences were recorded in the average number of ICM, TE, and total cells between 1 μM crocetin and control groups. In conclusion, the enrichment of bovine culture medium with 1 μM crocetin increased both blastocyst yield and quality, as indicated by the improved chronology of embryo development, increased resistance to cryopreservation, and reduced incidence of apoptosis.

Insulin exposure during in vitro bovine oocyte maturation changes blastocyst gene expression and developmental potential

Metabolic imbalance impairs fertility, because changes in concentrations of metabolites and hormones in the blood and follicular fluid create an unfavourable environment for early embryonic development. Insulin is a key metabolic hormone known for its effects on fertility: insulin concentrations are increased during energy balance disturbances in diabetes or metabolic syndrome. Still, insulin is frequently used at supraphysiological concentrations for embryo in vitro culture with unknown consequences for the developmental potential of the offspring. In the present study we investigated the effects of insulin exposure during in vitro bovine oocyte maturation on developmental rates, embryo quality and gene expression. Supplementation of the maturation media with insulin at 10 or 0.1 µg mL-1 decreased blastocyst rates compared with an insulin-free control (19.8 ± 1.3% and 20.4 ± 1.3% vs 23.8 ± 1.3%, respectively; P < 0.05) and led to increased cell numbers (nearly 10% more cells on Day 8 compared with control; P < 0.05). Transcriptome analysis revealed significant upregulation of genes involved in lipid metabolism, nuclear factor (erythroid-derived 2)-like 2 (NRF2) stress response and cell differentiation, validated by quantitative polymerase chain reaction. To conclude, the results of the present study demonstrate that insulin exposure during in vitro oocyte maturation has a lasting effect on the embryo until the blastocyst stage, with a potential negative effect in the form of specific gene expression perturbations.

In vitro fertilization (IVF) in mammals: epigenetic and developmental alterations. Scientific and bioethical implications for IVF in humans

The advent of in vitro fertilization (IVF) in animals and humans implies an extraordinary change in the environment where the beginning of a new organism takes place. In mammals fertilization occurs in the maternal oviduct, where there are unique conditions for guaranteeing the encounter of the gametes and the first stages of development of the embryo and thus its future. During this period a major epigenetic reprogramming takes place that is crucial for the normal fate of the embryo. This epigenetic reprogramming is very vulnerable to changes in environmental conditions such as the ones implied in IVF, including in vitro culture, nutrition, light, temperature, oxygen tension, embryo-maternal signaling, and the general absence of protection against foreign elements that could affect the stability of this process. The objective of this review is to update the impact of the various conditions inherent in the use of IVF on the epigenetic profile and outcomes of mammalian embryos, including superovulation, IVF technique, embryo culture and manipulation and absence of embryo-maternal signaling. It also covers the possible transgenerational inheritance of the epigenetic alterations associated with assisted reproductive technologies (ART), including its phenotypic consequences as is in the case of the large offspring syndrome (LOS). Finally, the important scientific and bioethical implications of the results found in animals are discussed in terms of the ART in humans.

Developmental kinetics of in vitro-produced bovine embryos: An aid for making decisions

Embryo developmental kinetics and embryo survival after cryopreservation have been correlated with embryo quality and viability. The main objectives of this work were to analyze developmental ability and quality of in vitro-produced bovine embryos in relation to their kinetics and to establish a criterion of quality to predict further viability. Embryos were classified and grouped by their specific stage of development (2, 3-4, or ≥ 5 cells) at 44 hours post insemination (hpi) and cultured separately up to Day 8. On Days 7 and 8, good quality expanded blastocysts were vitrified or frozen. Cryopreserved surviving hatched embryos were stained for cell counts. Embryos at a more advanced stage (3-4 cells, and ≥5 cells) developed to morulae (P < 0.001) and blastocysts (P < 0.01) at higher rates than those embryos that had cleaved once by 44 hpi. Vitrification improved the hatching rates of blastocysts at 48 hours (P < 0.001) when compared with slow-rate freezing within each group of embryos (3-4 cells and ≥5 cells). After vitrification/warming, blastocysts coming from 3- to 4-cell embryos had higher hatching rates at 48 hours than those that came from ≥5-cell embryos. With regard to differential cell counts, no effect of the initial developmental stage was observed after warming/thawing. However, trophectoderm and total cells were higher in vitrified/warmed than in the frozen/thawed embryos (P < 0.001). These data show that selecting IVF embryos at 44 hpi, after the evaluation of their in vitro embryo development, could be used as noninvasive markers of embryo developmental competence and may help to select IVF embryos that would be more suitable for cryopreservation.

Maternal PCBP1 determines the normal timing of pronucleus formation in mouse eggs

In mammals, pronucleus formation, a landmark event for egg activation and fertilization, is critical for embryonic development. However, the mechanisms underlying pronucleus formation remain unclear. Increasing evidence has shown that the transition from a mature egg to a developing embryo and the early steps of development are driven by the control of maternal cytoplasmic factors. Herein, a two-dimensional-electrophoresis-based proteomic approach was used in metaphase II and parthenogenetically activated mouse eggs to search for maternal proteins involved in egg activation, one of which was poly(rC)-binding protein 1 (PCBP1). Phosphoprotein staining indicated that PCBP1 displayed dephosphorylation in parthenogenetically activated egg, which possibly boosts its ability to bind to mRNAs. We identified 75 mRNAs expressed in mouse eggs that contained the characteristic PCBP1-binding CU-rich sequence in the 3'-UTR. Among them, we focused on H2a.x mRNA, as it was closely related to pronucleus formation in Xenopus oocytes. Further studies suggested that PCBP1 could bind to H2a.x mRNA and enhance its stability, thus promoting mouse pronucleus formation during parthenogenetic activation of murine eggs, while the inhibition of PCBP1 evidently retarded pronucleus formation. In summary, these data propose that PCBP1 may serve as a novel maternal factor that is required for determining the normal timing of pronucleus formation.

The ART of selecting the best embryo: A review of early embryonic mortality and bovine embryo viability assessment methods

Animal reproductive biotechnology is continually evolving. Significant advances have been made in our understanding of early embryonic mortality and embryo development in domestic animals, which has improved the selection and success of in vitro technologies. Yet our knowledge is still relatively limited such that identifying a single embryo with the highest chance of survival and development for transfer remains challenging. While invasive methods such as embryo biopsy can provide useful information regarding the genetic status of the embryos, morphological assessment remains the most common evaluation. A recent shift, however, favors alternative, adjunct approaches for non-invasive assessment of an embryo's viability and developmental potential. Various analytical techniques have facilitated the evaluation of cellular health through the metabolome, the assessment of end products of cellular metabolism, or by analyzing spent media for small RNAs. This review discusses the application of noninvasive approaches for ascertaining the health and viability of in vitro-produced bovine embryos. A comparative analysis of noninvasive techniques for embryo assessment currently being investigated in cattle and humans is also discussed.

The Incidence of DNA Double-Strand Breaks Is Higher in Late-Cleaving and Less Developmentally Competent Porcine Embryos

Studies in different species, including human, mice, bovine, and swine, demonstrated that early-cleaving embryos have higher capacity to develop to the blastocyst stage and produce better quality embryos with superior capacity to establish pregnancy than late-cleaving embryos. It has also been shown that experimentally induced DNA damage delays embryo cleavage kinetics and reduces blastocyst formation. To gain additional insights into the effects of genome damage on embryo cleavage kinetics and development, the present study compared the occurrence of DNA double-strand breaks (DSBs) with the expression profile of genes involved in DNA repair and cell cycle control between early- and late-cleaving embryos. Porcine oocytes matured in vitro were activated, and then early-cleaving (before 24 h) and late-cleaving (between 24 and 48 h) embryos were identified and cultured separately. Developing embryos, on Days 3, 5, and 7, were used to evaluate the total cell number and presence of DSBs (by counting the number of immunofluorescent foci for phosphorylated histone H2A.x [H2AX139ph] and RAD51 proteins) and to quantify transcripts of genes involved in DNA repair and cell cycle control by quantitative RT-PCR. Early-cleaving embryos had fewer DSBs, lower transcript levels for genes encoding DNA repair and cell cycle checkpoint proteins, and more cells than late-cleaving embryos. Interestingly, at the blastocyst stage, embryos that developed from early- and late-cleaving groups had similar number of DSBs as well as transcript levels of genes induced by DNA damage. This indicates that only embryos with less DNA damage and/or superior capacity for DNA repair are able to progress to the blastocyst stage. Collectively, findings in this study revealed a negative correlation between the occurrence of DSBs and embryo cleavage kinetics and embryo developmental capacity to the blastocyst stage.

Comparison of different fertilisation media for an in vitro maturation?fertilisation?culture system using flow-cytometrically sorted X chromosome-bearing spermatozoa for bovine embryo production

High demand exists among commercial cattle producers for in vitro-derived bovine embryos fertilised with female sex-sorted spermatozoa from high-value breeding stock. The aim of this study was to evaluate three fertilisation media, namely M199, synthetic oviductal fluid (SOF) and Tyrode's albumin-lactate-pyruvate (TALP), on IVF performance using female sex-sorted spermatozoa. In all, 1143, 1220 and 1041 cumulus-oocyte complexes were fertilised in M199, SOF and TALP, respectively. There were significant differences among fertilisation media (P < 0.05) in cleavage rate (M199 = 57%, SOF = 71% and TALP = 72%), blastocyst formation (M199 = 9%, SOF = 20% and TALP = 19%), proportion of Grade 1 blastocysts (M199 = 15%, SOF = 52% and TALP = 51%), proportion of Grade 3 blastocysts (M199 = 58%, SOF = 21% and TALP = 20%) and hatching rates (M199 = 29%, SOF = 60% and TALP = 65%). The inner cell mass (ICM) and trophectoderm (TE) cells of Day 7 blastocysts were also affected by the fertilisation medium. Embryos derived from SOF and TALP fertilisation media had higher numbers of ICM, TE and total cells than those fertilised in M199. In conclusion, fertilisation media affected cleavage rate, as well as subsequent embryo development, quality and hatching ability. SOF and TALP fertilisation media produced significantly more embryos of higher quality than M199.

Early cleavage of handmade cloned buffalo (Bubalus bubalis) embryos is an indicator of their developmental competence and quality

Following IVF, embryos which cleave early have been shown to have higher developmental competence and quality than those that cleave relatively later across many species. We investigated the effect of time of cleavage on the developmental competence, quality, epigenetic status and gene expression in buffalo embryos produced by handmade cloning (HMC). Following classification of embryos as early cleaving (EC) or late cleaving (LC) based on whether they had cleaved or not at 24 h post in vitro culture, 54% (164/303) were found to be EC and the rest to be LC. The blastocyst rate (58.1 ± 3.4 vs 36.9 ± 1.6%, p < 0.01) and the total cell number (285.5 ± 41.9 vs 141.4 ± 36.1, p < 0.05) were higher, whereas the apoptotic index (3.6 ± 0.6 vs 12.2 ± 1.7, p < 0.01) and the global level of H3K9ac and H3K27me3 were lower (p < 0.05) in the blastocysts produced from EC than in those produced from LC embryos. The relative transcript level of CASPASE3, CASPASE7, DNMT1, DNMT3a and CDX2 was higher (p < 0.05) and that of SOX2 was lower (p < 0.05) in blastocysts produced from LC than in those produced from EC embryos, whereas the expression level of CASPASE6, P53, P21, HDAC1, OCT4 and NANOG was not significantly different between the two groups. These results show that (i) following HMC, blastocysts produced from embryos that cleave early differ from those produced from late cleaving embryos in terms of epigenetic status and expression level of many important apoptosis-, pluripotency-, trophectoderm- and epigenetics-related genes, and (ii) EC embryos are superior to LC embryos in view of their higher developmental competence and quality.

Why we should not select the faster embryo: lessons from mice and cattle

Many studies have shown that in vitro culture can negatively impact preimplantation development. This necessitates some selection criteria for identifying the best-suited embryos for transfer. That said, embryo selection after in vitro culture remains a subjective process in most mammalian species, including cows, mice and humans. General consensus in the field is that embryos that develop in a timely manner have the highest developmental competence and viability after transfer. Herein lies the key question: what is a timely manner? With emerging data in bovine and mouse supporting increased developmental competency in embryos with moderate rates of development, it is time to question whether the fastest developing embryos are the best embryos for transfer in the human clinic. This is especially relevant to epigenetic gene regulation, including genomic imprinting, where faster developing embryos exhibit loss of imprinted methylation, as well as to sex selection bias, where faster developmental rates of male embryos may lead to biased embryo transfer and, in turn, biased sex ratios. In this review, we explore evidence surrounding the question of developmental timing as it relates to bovine embryo quality, mouse embryo quality and genomic imprint maintenance, and embryo sex.

Paternal influence of sperm DNA integrity on early embryonic development

STUDY QUESTION

Does sperm DNA damage affect early embryonic development?

SUMMARY ANSWER

Increased sperm DNA damage adversely affects embryo quality starting at Day 2 of early embryonic development and continuing after embryo transfer, resulting in reduced implantation rates and pregnancy outcomes.

WHAT IS KNOWN ALREADY

Abnormalities in the sperm DNA in the form of single and double strand breaks can be assessed by an alkaline Comet assay. Some prior studies have shown a strong paternal effect of sperm DNA damage on IVF outcome, including reduced fertilization, reduced embryo quality and cleavage rates, reduced numbers of embryos developing into blastocysts, increased percentage of embryos undergoing developmental arrest, and reduced implantation and pregnancy rates.

STUDY DESIGN, SIZE, DURATION

A cross-sectional study of 215 men from infertile couples undergoing assisted reproduction techniques at the University of Utah Center for Reproductive Medicine.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Sperm from men undergoing ART were analyzed for DNA damage using an alkaline Comet assay and classified into three groups: 'low damage' (0-30%), 'intermediate damage' (31-70%) and 'high damage' (71-100%). The cause of couples' infertility was categorized into one of the three types (male, female or unexplained). Each embryo was categorized as 'good', 'fair' or 'poor' quality, based on the number and grade of blastomeres. The influence of sperm DNA damage on early embryonic development was observed and classified into four stages: peri-fertilization effect (fertilization rate), early paternal effect (embryonic days 1-2), late paternal effect (embryonic days 3-5) and implantation stage effect.

MAIN RESULTS AND THE ROLE OF CHANCE

The paternal effect of sperm DNA damage was observed at each stage of early embryonic development. The peri-fertilization effect was higher in oocytes from patients with female infertility (20.85%) compared with male (8.22%; P < 0.001) and unexplained (7.30%; P < 0.001) infertility factors. In both the early and late paternal effect stages, the low DNA damage group had a higher percentage of good quality embryos (P < 0.05) and lower percentage of poor quality embryos (P < 0.05) compared with the high DNA damage group. Implantation was lower in the high DNA damage (33.33%) compared with intermediate DNA damage (55.26%; P < 0.001) and low DNA damage (65.00%; P < 0.001) groups. The implantation rate was higher following blastocyst transfer (58.33%), when compared with early stage blastocyst (53.85%; P = 0.554) and cavitating morula transfers (34.40%; P < 0.001). Implantation was higher when the female partner age was ≤35 years when compared with >35 year age group (52.75 versus 35.44%; P = 0.008).

LIMITATIONS, REASONS FOR CAUTION

A potential limitation of this study is that it is cross-sectional. Generally in such studies more than one variable could affect the outcome. Analyzing sperm is one part of the equation but a number of environmental and female factors also have the potential to influence embryo development and implantation. Furthermore, the selection of morphologically normal and physiologically motile sperm may result in isolation of sperm with reduced DNA damage. Therefore, selecting the best available sperm for ICSI may lead to experimental bias, as the selected sperm do not represent the overall sperm population in which the DNA damage is measured. Similar studies on selected sperm and with a larger sample size are now required.

WIDER IMPLICATIONS OF THE FINDINGS

The paternal influence of damaged chromatin is more prominent after zygotic transcriptional activation. A prolonged paternal effect on the developing embryo may be due to the active repair mechanism present in oocytes that tends to overcome the damaged paternal chromatin. The probability of eliminating an embryo fertilized by a sperm with damaged DNA is higher at the blastocyst stage than the cleavage stage; therefore blastocyst transfer could be recommended for better implantation success. Finally, we recommend ICSI treatment for patients with a higher percentage of sperm with DNA damage as well as additional studies with a larger sample size aimed at assessing DNA damage analysis as a diagnostic tool for IVF.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the University of Utah internal funds. The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Impact of the periconceptional environment on the programming of adult disease

The periconceptional period of mammalian development has been identified as an early 'developmental window' during which environmental conditions may influence the pattern of future growth and physiology. Studies in humans and animal models have revealed that factors such as maternal nutritional status or in vitro culture and manipulation of developing gametes and preimplantation embryos can impact upon the long-term health and physiology of the offspring. However, the mechanisms involved in the programming of adult disease in response to altered periconceptional development require increased investigation. The role of epigenetic modifications to DNA and chromatin organisation has been identified as a likely mechanism through which environmental perturbations can affect gene expression patterns resulting in phenotypic change. This study will highlight the sensitivity of two critical stages in early mammalian development, gametogenesis and preimplantation development. We will detail how changes to the immediate environment can not only impact upon developmental processes taking place at that time, but can also affect long-term aspects of offspring health and physiology. We will also discuss the emerging role of epigenetics as a mechanistic link between the environment and the later phenotype of the developing organism.

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.

IGF-I slightly improves nuclear maturation and cleavage rate of bovine oocytes exposed to acute heat shock in vitro

An in vitro model of embryo production was used to examine the effects of insulin-like growth factor (IGF)-I on maturation and developmental competence of oocytes exposed to heat shock. Cumulus–oocyte complexes were matured at 38.5°C or exposed to acute heat shock (HS; 41.5°C), with or without 100 ng/ml IGF-I, for 22 h through in vitro maturation. The experimental groups were control (C), C + IGF-I, HS, and HS + IGF-I. Oocytes were fertilized at the end of maturation, and the proportion of cleaved embryos was recorded 44 h later. HS during maturation increased the proportion of TUNEL-positive oocytes (P < 0.05). HS did not have any effect on cortical granule translocation but impaired resumption of meiosis, expressed as a decreased proportion of oocytes with nuclei in metaphase I (P < 0.05) and metaphase II (MII; P < 0.05). HS decreased the proportion of oocytes that cleaved (P < 0.05), in particular those oocytes that further developed to 4-cell-stage embryos (P < 0.05). IGF-I alleviated, to some extent, the deleterious effects of HS on the oocytes as reflected by a reduced proportion of TUNEL-positive oocytes (P < 0.03). While not significant, IGF-I tended to increase the proportion of MII-stage oocytes (P < 0.08) and 4-cell-stage cleaved embryos (P < 0.06). Further examination is required to explore whether IGF-I also affects the developmental competence of oocytes exposed to HS.

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.

Recent progress in cryopreservation of bovine oocytes

Principle of oocyte cryoinjury is first overviewed and then research history of cryopreservation using bovine oocytes is summarized for the last two decades with a few special references to recent progresses. Various types of cryodevices have been developed to accelerate the cooling rate and applied to the oocytes from large domestic species enriched with cytoplasmic lipid droplets. Two recent approaches include the qualitative improvement of IVM oocytes prior to the vitrification and the short-term recovery culture of vitrified-warmed oocytes prior to the subsequent IVF. Supplementation of L-carnitine to IVM medium of bovine oocytes has been reported to reduce the amount of cytoplasmic lipid droplets and improve the cryotolerance of the oocytes, but it is still controversial whether the positive effect of L-carnitine is reproducible. Incidence of multiple aster formation, a possible cause for low developmental potential of vitrified-warmed bovine oocytes, was inhibited by a short-term culture of the postwarm oocytes in the presence of Rho-associated coiled-coil kinase (ROCK) inhibitor. Use of an antioxidant α-tocopherol, instead of the ROCK inhibitor, also supported the revivability of the postwarm bovine oocytes. Further improvements of the vitrification procedure, combined with pre- and postvitrification chemical treatment, would overcome the high sensitivity of bovine oocytes to cryopreservation.

Rapidly cleaving bovine two-cell embryos have better developmental potential and a distinctive mRNA pattern

Mammalian embryos that rapidly reach the two-cell stage in culture have a higher probability of becoming viable blastocysts. Our goal was to separate two-cell bovine embryos based on their zygotic cleavage timing, and to assess their global mRNA levels. Following in vitro fertilization, all embryos that cleaved by 29.5 hpi (early) were cultured separately from those that divided at 46 hpi (late). The blastocyst rates were 46.1 ± 3.7% and 6.1 ± 3.4% for early- and late-cleavers, respectively (P < 0.01). Seven replicates of selected two-cell embryos were collected at each time point for microarray characterization (n = 4) and quantitative reverse-transcriptase PCR (n = 3); the rest were left in culture for blastocyst evaluation. A total of 774 and 594 probes were preferentially present in early- and late-cleaving embryos, respectively (fold change ± 1.5, P < 0.05), with important contrasts related to cell cycle, gene expression, RNA processing, and protein degradation functions. A total of 12 transcripts were assessed by quantitative PCR, of which ATM, ATR, CTNNB1, MSH6, MRE11A, PCNA, APC, CENPE, and GRB2 were in agreement with the hybridization results. Since most of these molecules are directly or indirectly associated with cell-cycle regulation, DNA damage response, and transcription control, our results strongly suggest key roles for those biological functions in mammalian preimplantation development.

Energy substrate influences the effect of the timing of the first embryonic cleavage on the development of in vitro-produced porcine embryos in a sex-related manner

In vitro culture conditions and certain events during the earliest stages of development are linked to embryonic survival, possibly in a sex-related manner. In vitro-produced (IVP) porcine embryos cultured with glucose (IVC-Glu) or pyruvate-lactate (IVC-PL) were tested for any relationship between the timing of the first embryonic cleavage and development and sex ratio. The embryos were assigned to IVC-Glu or IVC-PL groups and classified depending on the timing of their first cleavage: 24, 26, 30, and 48 hr post-insemination (hpi). They were cultured separately in vitro and evaluated for cleavage rate and pattern, blastocyst rate and stage, cell number, apoptosis, and sex ratio. Regardless of energy source, the percentage of two-cell stage and fragmented embryos at the time of their first cleavage was, respectively, higher and lower in early-cleaving embryos. Those embryos cleaved by 24 hpi developed to blastocysts at a higher rate (IVC-Glu: 37.90 ± 3.06%; IVC-PL: 38.73 ± 4.08%) than those cleaved between 30 and 48 hpi (IVC-Glu: 5.87 ± 3.02%; IVC-PL: 8.41 ± 3.50%). Furthermore, a shift toward males was seen among embryos first cleaved before 30 hpi, versus towards females among those cleaved later. The early-cleaving embryos, only from the IVC-PL group, had a higher proportion of expanded blastocysts (81.05 ± 6.54% vs. 13.33 ± 13.33%) with higher cell numbers than their late-cleaving counterparts. Moreover, a shift toward males only appeared at the blastocyst stage in IVC-PL embryos. These findings confirm that the timing of the first cleavage influences development of IVP porcine embryos in a sex-related manner, and it depends on the main energy source of the in vitro culture medium.

Dynamics of DNA methylation during early development of the preimplantation bovine embryo

There is species divergence in control of DNA methylation during preimplantation development. The exact pattern of methylation in the bovine embryo has not been established nor has its regulation by gender or maternal signals that regulate development such as colony stimulating factor 2 (CSF2). Using immunofluorescent labeling with anti-5-methylcytosine and embryos produced with X-chromosome sorted sperm, it was demonstrated that methylation decreased from the 2-cell stage to the 6–8 cell stage and then increased thereafter up to the blastocyst stage. In a second experiment, embryos of specific genders were produced by fertilization with X- or Y-sorted sperm. The developmental pattern was similar to the first experiment, but there was stage × gender interaction. Methylation was greater for females at the 8-cell stage but greater for males at the blastocyst stage. Treatment with CSF2 had no effect on labeling for DNA methylation in blastocysts. Methylation was lower for inner cell mass cells (i.e., cells that did not label with anti-CDX2) than for trophectoderm (CDX2-positive). The possible role for DNMT3B in developmental changes in methylation was evaluated by determining gene expression and degree of methylation. Steady-state mRNA for DNMT3B decreased from the 2-cell stage to a nadir for D 5 embryos >16 cells and then increased at the blastocyst stage. High resolution melting analysis was used to assess methylation of a CpG rich region in an intronic region of DNMT3B. Methylation percent decreased between the 6–8 cell and the blastocyst stage but there was no difference in methylation between ICM and TE. Results indicate that DNA methylation undergoes dynamic changes during the preimplantation period in a manner that is dependent upon gender and cell lineage. Developmental changes in expression of DNMT3B are indicative of a possible role in changes in methylation. Moreover, DNMT3B itself appears to be under epigenetic control by methylation.

Factors affecting oocyte and embryo transcriptomes

The most important factor affecting the oocyte and early embryo transcriptome is the legacy from the follicular environment prior to meiotic resumption. Up to the 8-cell stage, the oocyte responds to maternal instructions stored before resumption of the meiotic division. Recent evidence suggests that properly prepared or programmed oocytes (in vivo) can achieve close to 100% blastocyst rates in standard in vitro conditions/media. Therefore, the optimal oocyte requires perfect follicular timing and differentiation, but the intra-oocyte mechanisms involved in such preparation are not completely understood. In addition, the influence of maternal mRNA storage and degradation, as well as the length of the poly A tail that influences the general pattern of the oocyte/early embryo transcriptome, is an important factor. Several hypotheses have been put forth to explain the depletion of the maternal store, including the potential role of microRNA (miRNA) in this process. The activation of the embryonic genome could be dependent on, or associated with, the process of maternal mRNA degradation, but obviously other functions are being activated at this critical time point. This review will focus on the period from full-size oocytes to the eight-cell stage and will summarize the impact of the important factors, that is, follicle, maternal RNA storage and embryonic genome activation, on the transcriptome.

HDAC inhibition decreases XIST expression on female IVP bovine blastocysts

During initial development, both X chromosomes are active in females, and one of them must be silenced at the appropriate time in order to dosage compensate their gene expression levels to male counterparts. Silencing involves epigenetic mechanisms, including histone deacetylation. Major X chromosome inactivation (XCI) in bovine occurs between hatching and implantation, although in vitro culture conditions might disrupt the silencing process, increasing or decreasing X-linked gene expression. In this study, we aimed to address the roles of histone deacetylase inhibition by trichostatin A (TSA) on female preimplantation development. We tested the hypothesis that by enhancing histone acetylation, TSA would increase the percentage of embryos achieving 16-cell stage, reducing percentage of embryos blocked at 8-cell stage, and interfere with XCI in IVF embryos. We noticed that after TSA treatment, acetylation levels in individual blastomeres of 8-16 cell embryos were increased twofold on treated embryos, and the same was detected for blastocysts. Changes among blastomere levels within the same embryo were diminished on TSA group, as low-acetylated blastomeres were no longer detected. The percentage of embryos that reached the 5th cleavage cycle 118 h after IVF, analyzed by Hoechst staining, remained unaltered after TSA treatment. Then, we assessed XIST and G6PD expression in individual female bovine blastocysts by quantitative real-time PCR. Even though G6PD expression remained unaltered after TSA exposure, XIST expression was eightfold decreased, and we also detected a major decrease in the percentage of blastocysts expressing detectable XIST levels after TSA treatment. Based on these results, we conclude that HDAC is involved on XCI process in bovine embryos, and its inhibition might delay X chromosome silencing and attenuate aberrant XIST expression described for IVF embryos.

Transcriptome fingerprint of bovine 2-cell stage blastomeres is directly correlated with the individual developmental competence of the corresponding sister blastomere

To date, gene expression profiles of bovine preimplantation embryos have only been indirectly related to developmental potential due to the invasive nature of such procedures. This study sought to find a direct correlation between transcriptome fingerprint of blastomeres of bovine 2-cell stage embryos with developmental competence of the corresponding sister blastomeres. Isolated blastomeres were classified according to the sister blastomere's development into three groups: two groups displayed developmental incompetency, including those blastomeres whose corresponding sister blastomeres either stopped cleaving after separation (2CB) or were blocked after two additional cleavages before embryonic genome activation (8CB). In the third group were competent blastomeres, which were defined as those whose sister blastomeres developed to the blastocyst stage (BL). As a result, developmental capacity of corresponding sister blastomeres was highly similar. Microarray analysis revealed 77 genes to be commonly differentially regulated among competent and incompetent blastomeres as well as blocked blastomeres. Clustering of differentially expressed genes according to molecular functions and pathways revealed antioxidant activity, NRF2-mediated oxidative stress response, and oxidative phosphorylation to be the main ontologies affected. Expression levels of selected candidate genes were further characterized in an independent model for developmental competence based on the time of first cleavage postfertilization. Moreover, overall results of this study were confirmed by higher developmental rates and more beneficial expression of CAT and PRDX1 when cultured in an antioxidative environment. These results will help us to understand molecular mechanisms defining developmental destination of individual bovine preimplantation embryos.

The combined treatment of calcium ionophore with strontium improves the quality of ovine SCNT embryo development

Poor embryo quality is a major problem that contributes to the failure of pregnancy in somatic cell nuclear transfer (SCNT). The aims of this study were to improve the quality of ovine SCNT embryos by modifying the conventional activation protocol with the addition of SrCl2. In order to achieve this objective we conducted a series of experiments with in vitro-matured oocytes to optimize conditions for oocyte activation with strontium, and subsequently applied the protocol to SCNT embryos. The results showed that in vitro-matured oocytes could be activated effectively by 10 mM SrCl2 + 5 mg/ml cytochalasin B (CB) for 5 h in the absence of Ca2+ and that the blastocyst rate on day 7 (33.2%) was similar to that in the control group (31.0%) (5 M calcium ionophore [IP] A23187 for 5 min and cultured in CB/cycloheximide [CHX] for 5 h; P > 0.05). In SCNT experiments, the total cell number/blastocyst (104.12 ± 6.86) in the IP + SrCl2/CB-treatment group was, however, significantly higher than that in the control group (81.07 ± 3.39; P < 0.05). Apoptotic index (12.29 ± 1.22%) was significantly lower than the control (17.60 ± 1.39%; P < 0.05) when a combination of IP and SrCl2/CB was applied to SCNT embryos. In addition, karyotyping of the SCNT embryos showed that the percentage of diploid blastocysts in the IP + SrCl2/CB-treatment group was slightly higher than that in the control (P > 0.05). We conclude that the modified activation protocol with IP + SrCl2/CB can improve significantly the quality of ovine SCNT embryos in terms of total cell number, apoptosis and ploidy.

Messenger RNAs in metaphase II oocytes correlate with successful embryo development to the blastocyst stage

The mRNAs accumulated in oocytes provide support for embryo development until embryo genomic activation. We hypothesized that the maternal mRNA stock present in bovine oocytes is associated with embryo development until the blastocyst stage. To test our hypothesis, we analyzed the transcriptome of the oocyte and correlated the results with the embryo development. Our goal was to identify genes expressed in the oocyte that correlate with its ability to develop to the blastocyst stage. A fraction of oocyte cytoplasm was biopsied using micro-aspiration and stored for further expression analysis. Oocytes were activated chemically, cultured individually and classified according to their capacity to develop in vitro to the blastocyst stage. Microarray analysis was performed on mRNA extracted from the oocyte cytoplasm fractions and correlated with its ability to develop to the blastocyst stage (good quality oocyte) or arrest at the 8-16-cell stage (bad quality oocyte). The expression of 4320 annotated genes was detected in the fractions of cytoplasm that had been collected from oocytes matured in vitro. Gene ontology classification revealed that enriched gene expression of genes was associated with certain biological processes: 'RNA processing', 'translation' and 'mRNA metabolic process'. Genes that are important to the molecular functions of 'RNA binding' and 'translation factor activity, RNA binding' were also enriched in oocytes. We identified 29 genes with differential expression between the two groups of oocytes compared (good versus bad quality). The content of mRNAs expressed in metaphase II oocytes influences the activation of the embryonic genome and enables further develop to the blastocyst stage.

Vitrification of in vitro produced bovine embryos: effect of embryonic block and developmental kinetics

In order to investigate whether the kinetics and stage of embryo development affect cryosurvival of in vitro produced bovine embryos, cleaved embryos were categorized in six groups based on their developmental kinetics regarding the stage of embryonic block in bovine (8-16 cell stage): I and II--early (day 2) and late (day 3) 5-8 cell, III and IV--early (day 3) and late (day 4) 8-16 cell, and V and VI--early (day 4) and late (day 5) morula. The cryosurvival and developmental competence of these embryos were compared with each other and also with the corresponding control groups. The potential of 5-8 cell stage embryos to survive vitrification and further develop towards blastocyst stage was significantly lower than vitrified and un-vitrified 8-16 cell and morula stage embryos. These results suggest that, the survival rate and potential of embryos to develop towards blastocyst stage might be affected by the kinetic of the embryo development. Moreover, the results of this study indicated that the optimal stages of early embryo vitrification are post-embryonic block.

Homologous recombination and non-homologous end-joining repair pathways in bovine embryos with different developmental competence

This study investigated the expression of genes controlling homologous recombination (HR), and non-homologous end-joining (NHEJ) DNA-repair pathways in bovine embryos of different developmental potential. It also evaluated whether bovine embryos can respond to DNA double-strand breaks (DSBs) induced with ultraviolet irradiation by regulating expression of genes involved in HR and NHEJ repair pathways. Embryos with high, intermediate or low developmental competence were selected based on the cleavage time after in vitro insemination and were removed from in vitro culture before (36 h), during (72 h) and after (96 h) the expected period of embryonic genome activation. All studied genes were expressed before, during and after the genome activation period regardless the developmental competence of the embryos. Higher mRNA expression of 53BP1 and RAD52 was found before genome activation in embryos with low developmental competence. Expression of 53BP1, RAD51 and KU70 was downregulated at 72 h and upregulated at 168 h post-insemination in response to DSBs induced by ultraviolet irradiation. In conclusion, important genes controlling HR and NHEJ DNA-repair pathways are expressed in bovine embryos, however genes participating in these pathways are only regulated after the period of embryo genome activation in response to ultraviolet-induced DSBs.

Gene expression profile differences in embryos derived from prepubertal and adult Japanese Black cattle during in vitro development

The present study was carried out to compare the gene expression profiles of in vitro-generated embryos derived from adult and prepubertal Japanese Black cattle oocytes using GeneChip Bovine Genome Array (containing 24072 probe sets representing over 23000 transcripts). Microarray experiments were performed on populations of 8- to 16-cell stage embryos and blastocysts derived from adult (24-35 months old) versus prepubertal (9-10 months old) Japanese Black cattle oocytes matured and fertilised in vitro. In total, 591 (2.4%) and 490 (2.0%) genes were differentially expressed in prepubertal and adult bovine in 8- to 16-cell and blastocyst stage embryos, respectively. Out of these, 218 and 248 genes were upregulated, while 373 and 242 were downregulated in prepubertal and adult 8- to 16-cell and blastocysts stage embryos, respectively. Gene ontology classification regarding biological process, molecular functions and cellular component revealed diversity in transcript abundances between prepubertal and adult groups in both the distinct developmental stages. Quantitative reverse transcription-PCR validated the expression differences of some selected transcripts as identified by microarray analysis. To our knowledge, this is the first report indicating the significant number of genes differentially expression (>2-fold, P<0.01) in preimplantition embryos between adult and prepubertal Japanese Black cattle during in vitro development.