Glucose metabolism during bovine preimplantation development: analysis of gene expression in single oocytes and embryos

Parameters to identify good quality oocytes and embryos in cattle

Oocyte/embryo selection methodologies are either invasive or noninvasive and can be applied at various stages of development from the oocyte to cleaved embryos and up to the blastocyst stage. Morphology and the proportion of embryos developing to the blastocyst stage are important criteria to assess developmental competence. Evaluation of morphology remains the method of choice for selecting viable oocytes for IVP or embryos prior to transfer. Although non-invasive approaches are improving, invasive ones have been extremely helpful in finding candidate genes to determine oocyte/embryo quality. There is still a strong need for further refinement of existing oocyte and embryo selection methods and quality parameters. The development of novel, robust and non-invasive procedures will ensure that only embryos with the highest developmental potential are chosen for transfer. In the present review, various methods for assessing the quality of oocytes and preimplantation embryos, particularly in cattle, are considered. These methods include assessment of morphology including different staining procedures, transcriptomic and proteomic analyses, metabolic profiling, as well as the use of artificial intelligence technologies.

Expression pattern of GLUT 1, 5, 8 and citrate synthase transcripts in buffalo (Bubalus bubalis) preimplantation embryos produced in vitro and derived in vivo

In vitro-produced (IVP) embryos are reported to be developmentally lesser competent than in vivo-derived (IVD) embryos and supposed to differ in the expression of genes related with glucose metabolism. So, the present study was conducted to analyse the expression pattern of GLUT 1, 5, 8 and citrate synthase (CS) in oocytes and embryos produced in vivo or in vitro in buffalo. IVD embryos were obtained from 18 superovulated buffaloes. IVP embryos were obtained from slaughterhouse-derived oocytes subsequently subjected to in vitro fertilization and culture. Total RNA was isolated from different stages of oocytes (immature and in vitro matured) and embryos (8-16 cell to blastocysts of IVP embryos and morula to blastocysts of IVD embryos). Results demonstrated that the expression of GLUT1, GLUT 8 increased from 8 to 16 cells to blastocyst and was significantly (p < .05) higher in IVP embryos. Expression of both genes was (p < .05) higher in IVD than in IVP blastocysts; though GLUT5 transcripts were not detected at 8- to 16-cell stage IVP embryos, significantly (p < .05) higher transcripts were found at morula and blastocyst stages irrespective of embryo source with significantly (p < .05) higher expression in IVD embryos compared to IVP embryos. No significant difference was observed in citrate synthase expression in embryos at morula stage irrespective of the embryo source while significantly (p < .05) higher transcript level was observed at blastocyst stage with no difference between in vivo and in vitro embryos. It can be concluded that expression of GLUTs and CS is upregulated with progression of embryonic stage and expression is higher in in vivo embryos than in vitro counter parts; thus, it can be said that in vivo-produced embryos are metabolically superior to in vitro embryos.

Temporally differential protein expression of glycolytic and glycogenic enzymes during in vitro preimplantation bovine embryo development

Proteomic analyses are useful for understanding the metabolic pathways governing embryo development. This study investigated the presence of enzymes involved in glycolysis and glycogenesis in in vitro-produced bovine embryos at five developmental stages leading up to blastocyst formation. The enzymes examined were: (1) glycolytic: hexokinase-I (HK-I), phosphofructokinase-1 (PFK-1), pyruvate kinase mutase 1/2 (PKM-1/2), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and (2) glycogenic: glycogen synthase kinase-3 isoforms α/ β (GSK-3α/β). Glucose transporter-1 (GLUT-1) was also analysed. The developmental stages examined were: (1) 2-4-cell, (2) 5-8-cell, (3) 16-cell, (4) morula and (5) expanded blastocyst. The enzymes HK-I, PFK-1, PKM-1/2, GAPDH and GLUT-1 were differentially expressed throughout all stages (P<0.05). GSK-3α and β were also differentially expressed from the 2-4-cell to the expanded blastocyst stage (P<0.05) and GLUT-1 was identified throughout. The general trend was that the abundance of PFK1, GAPDH and PKM-1/2 decreased whereas HK-I, phospho-GSK3α (P-GSK3α) and P-GSK3β levels increased as the embryo advanced. In contrast, GLUT-1 expression peaked at the 16-cell stage. These data combined suggest that in vitro bovine embryo metabolism switches from being glycolytic-centric to glycogenic-centric around the 16-cell stage, the developmental window also characterised by embryonic genome activation.

Different co-culture systems have the same impact on bovine embryo transcriptome

During the last few years, several co-culture systems using either BOEC or VERO feeder cells have been developed to improve bovine embryo development and these systems give better results at high oxygen concentration (20%). In parallel, the SOF medium, used at 5% O2, has been developed to mimic the oviduct fluid. Since 2010s, the SOF medium has become popular in improving bovine embryo development and authors have started to associate this medium to co-culture systems. Nevertheless, little is known about the putative benefit of this association on early development. To address this question, we have compared embryo transcriptomes in four different culture conditions: SOF with BOEC or VERO at 20% O2, and SOF without feeders at 5% or 20% O2. Embryos have been analyzed at 16-cell and blastocyst stages. Co-culture systems did not improve the developmental rate when compared to 5% O2. Direct comparison of the two co-culture systems failed to highlight major differences in embryo transcriptome at both developmental stages. Both feeder cell types appear to regulate the same cytokines and growth factors pathways, and thus to influence embryo physiology in the same way. In blastocysts, when compared to culture in SOF at 5% O2, BOEC or VERO seems to reduce cell survival and differentiation by, at least, negatively regulating STAT3 and STAT5 pathways. Collectively, in SOF medium both blastocysts rate and embryo transcriptome suggest no influence of feeder origin on bovine early development and no beneficial impact of co-culture systems when compared to 5% O2.

Oocyte aging-induced Neuronatin (NNAT) hypermethylation affects oocyte quality by impairing glucose transport in porcine

DNA methylation plays important roles in regulating many physiological behaviors; however, few studies were focused on the changes of DNA methylation during oocyte aging. Early studies showed that some imprinted genes’ DNA methylation had been changed in aged mouse oocytes. In this study, we used porcine oocytes to test the hypothesis that oocyte aging would alter DNA methylation pattern of genes and disturb their expression in age oocytes, which affected the developmental potential of oocytes. We compared several different types of genes and found that the expression and DNA methylation of Neuronatin (NNAT) were disturbed in aged oocytes significantly. Additional experiments demonstrated that glucose transport was impaired in aged oocytes and injection of NNAT antibody into fresh oocytes led to the same effects on glucose transport. These results suggest that the expression of NNAT was declined by elevating DNA methylation, which affected oocyte quality by decreasing the ability of glucose transport in aged oocytes.

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.

Increasing of blastocyst rate and gene expression in co-culture of bovine embryos with adult adipose tissue-derived mesenchymal stem cells

PURPOSE

Despite advances in the composition of defined embryo culture media, co-culture with somatic cells is still used for bovine in vitro embryo production (IVEP) in many laboratories worldwide. Granulosa cells are most often used for this purpose, although recent work suggests that co-culture with stem cells of adult or embryonic origin or their derived biomaterials may improve mouse, cattle, and pig embryo development.

MATERIALS AND METHODS

In experiment 1, in vitro produced bovine embryos were co-cultured in the presence of two concentrations of bovine adipose tissue-derived mesenchymal cells (b-ATMSCs; 10³ and 10⁴ cells/mL), in b-ATMSC preconditioned medium (SOF-Cond), or SOF alone (control). In experiment 2, co-culture with 10⁴ b-ATMSCs/mL was compared to the traditional granulosa cell co-culture system (Gran).

RESULTS

In experiment 1, co-culture with 10⁴ b-ATMSCs/mL improved blastocyst rates in comparison to conditioned and control media (p < 0.05). Despite that it did not show difference with 10³ b-ATMSCs/mL (p = 0.051), group 10⁴ b-ATMSCs/mL yielded higher results of blastocyst production. In experiment 2, when compared to group Gran, co-culture with 10⁴ b-ATMSCs/mL improved not only blastocyst rates but also quality as assessed by increased total cell numbers and mRNA expression levels for POU5F1 and G6PDH (p < 0.05).

CONCLUSIONS

Co-culture of bovine embryos with b-ATMSCs was more beneficial than the traditional co-culture system with granulosa cells. We speculate that the microenvironmental modulatory potential of MSCs, by means of soluble substances and exosome secretions, could be responsible for the positive effects observed. Further experiments must be done to evaluate if this beneficial effect in vitro also translates to an increase in offspring following embryo transfer. Moreover, this study provides an interesting platform to study the basic requirements during preimplantation embryo development, which, in turn, may aid the improvement of embryo culture protocols in bovine and other species.

Differential developmental competence and gene expression patterns in buffalo (Bubalus bubalis) nuclear transfer embryos reconstructed with fetal fibroblasts and amnion mesenchymal stem cells

The developmental ability and gene expression pattern at 8- to 16-cell and blastocyst stages of buffalo (Bubalus bubalis) nuclear transfer (NT) embryos from fetal fibroblasts (FFs), amnion mesenchymal stem cells (AMSCs) and in vitro fertilized (IVF) embryos were compared in the present studies. The in vitro expanded buffalo FFs showed a typical "S" shape growth curve with a doubling time of 41.4 h and stained positive for vimentin. The in vitro cultured undifferentiated AMSCs showed a doubling time of 39.5 h and stained positive for alkaline phosphatase, and these cells also showed expression of pluripotency markers (OCT 4, SOX 2, NANOG), and mesenchymal stem cell markers (CD29, CD44) and were negative for haematopoietic marker (CD34) genes at different passages. Further, when AMSCs were exposed to corresponding induction conditions, these cells differentiated into adipogenic, chondrogenic and osteogenic lineages which were confirmed through oil red O, alcian blue and alizarin staining, respectively. Donor cells at 3-4 passage were employed for NT. The cleavage rate was significantly (P < 0.05) higher in IVF than in FF-NT and AMSC-NT embryos (82.6 ± 8.2 vs. 64.6 ± 1.3 and 72.3 ± 2.2 %, respectively). However, blastocyst rates in IVF and AMSC-NT embryos (30.6 ± 2.7 and 28.9 ± 3.1 %) did not differ and were significantly (P < 0.05) higher than FF-NT (19.5 ± 1.8 %). Total cell number did not show significant (P > 0.05) differences between IVF and AMSC-NT embryos (186.7 ± 4.2, 171.2 ± 3.8, respectively) but were significantly (P < 0.05) higher than that from FF-NT (151.3 ± 4.1). Alterations in the expression pattern of genes implicated in transcription and pluripotency (OCT4, STAT3, NANOG), DNA methylation (DNMT1, DNMT3A), histone deacetylation (HDAC2), growth factor signaling and imprinting (IGF2, IGF2R), apoptosis (BAX, BCL2), metabolism (GLUT1) and oxidative stress (MnSOD) regulation were observed in cloned embryos. The transcripts or expression patterns in AMSC-NT embryos more closely followed that of the in vitro derived embryos compared with FF-NT embryos. The results demonstrate that multipotent amnion MSCs have a greater potential as donor cells than FFs in achieving enhanced production of cloned buffalo embryos.

Metabolic control of oocyte development: linking maternal nutrition and reproductive outcomes

Obesity, diabetes, and related metabolic disorders are major health issues worldwide. As the epidemic of metabolic disorders continues, the associated medical co-morbidities, including the detrimental impact on reproduction, increase as well. Emerging evidence suggests that the effects of maternal nutrition on reproductive outcomes are likely to be mediated, at least in part, by oocyte metabolism. Well-balanced and timed energy metabolism is critical for optimal development of oocytes. To date, much of our understanding of oocyte metabolism comes from the effects of extrinsic nutrients on oocyte maturation. In contrast, intrinsic regulation of oocyte development by metabolic enzymes, intracellular mediators, and transport systems is less characterized. Specifically, decreased acid transport proteins levels, increased glucose/lipid content and elevated reactive oxygen species in oocytes have been implicated in meiotic defects, organelle dysfunction and epigenetic alteration. Therefore, metabolic disturbances in oocytes may contribute to the diminished reproductive potential experienced by women with metabolic disorders. In-depth research is needed to further explore the underlying mechanisms. This review also discusses several approaches for metabolic analysis. Metabolomic profiling of oocytes, the surrounding granulosa cells, and follicular fluid will uncover the metabolic networks regulating oocyte development, potentially leading to the identification of oocyte quality markers and prevention of reproductive disease and poor outcomes in offspring.

Developmental competence and expression pattern of bubaline (Bubalus bubalis) oocytes subjected to elevated temperatures during meiotic maturation in vitro

OBJECTIVE

To determine the direct effect of physiologically relevant high temperatures (40.5 and 41.5 °C) for two time periods (12 and 24 h) on bubaline oocytes during in vitro maturation.

METHOD

The control group oocytes were cultured at 38.5 °C for 24 h. The treatment 1 (T1) and 3 (T3) group oocytes were cultured at 40.5 and 41.5 °C respectively, for the first 12 h and at 38.5 °C for rest of the 12 h. However, treatment 2 (T2) and 4 (T4) group oocytes were cultured at 40.5 and 41.5 °C for complete 24 h.

RESULTS

Development of oocytes to blastocyst was severely compromised (p < 0.001) when matured at 40.5 and 41.5 °C for both exposure periods (12 h and 24 h). It was found that the cleavage rates, blastocyst yield and mean cell number decreased remarkably (p < 0.001) in the treatment groups compared to control. The relative mRNA expression of heat shock protein (Hsp 70.1, 70.2, 70.8, 60, 10 and HSF1), pro-apoptotic (caspases-3, -7, -8, Bid and Bax) and oxidative stress (iNOS) related genes was significantly higher (p < 0.05) in all the treatment groups compared to control. However, mRNA abundance of anti-apoptotic (Bcl-2, Mcl-1, Bcl-xl), glucose transport (Glut1, Glut3 and IGF1R), developmental competence (ZAR1 and BMP15) and oxidative stress (MnSOD) related genes was significantly decreased (p < 0.05) in the treatment groups compared to control.

CONCLUSION

The present study clearly establishes that physiologically relevant elevated temperatures during in vitro meiotic maturation reduce developmental competence of bubaline oocytes.

Evaluation of reference genes in mouse preimplantation embryos for gene expression studies using real-time quantitative RT-PCR (RT-qPCR)

Background

Real-time quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) is the most sensitive, and valuable technique for rare mRNA detection. However, the expression profiles of reference genes under different experimental conditions, such as different mouse strains, developmental stage, and culture conditions have been poorly studied.

Results

mRNA stability of the actb, gapdh, sdha, ablim, ywhaz, sptbn, h2afz, tgfb1, 18 s and wrnip genes was analyzed. Using the NormFinder program, the most stable genes are as follows: h2afz for the B6D2F-1 and C57BL/6 strains; sptbn for ICR; h2afz for KOSOM and CZB cultures of B6D2F-1 and C57BL/6 strain-derived embryos; wrnip for M16 culture of B6D2F-1 and C57BL/6 strain-derived embryos; ywhaz, tgfb1, 18 s, 18 s, ywhaz, and h2afz for zygote, 2-cell, 4-cell, 8-cell, molular, and blastocyst embryonic stages cultured in KSOM medium, respectively; h2afz, wrnip, wrnip, h2afz, ywhaz, and ablim for zygote, 2-cell, 4-cell, 8-cell, molular, and blastocyst stage embryos cultured in CZB medium, respectively; 18 s, h2afz, h2afz, actb, h2afz, and wrnip for zygote, 2-cell, 4-cell, 8-cell, molular, and blastocyst stage embryos cultured in M16 medium, respectively.

Conclusions

These results demonstrated that candidate reference genes for normalization of target gene expression using RT-qPCR should be selected according to mouse strains, developmental stage, and culture conditions.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-0500-7-675) contains supplementary material, which is available to authorized users.

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.

Insulin influences developmental competence of bovine oocytes cultured in α-MEM plus follicle-simulating hormone

The aim of this study was to evaluate the dose-response effect of insulin, plus follicle-simulating hormone (FSH) at a fixed concentration, in a serum-free defined culture medium (DCM) on the in vitro maturation of bovine cumulus-oocyte complexes (COCs). For oocyte nuclear maturation, the expression levels of GDF9, GLUT1, PRDX1 and HSP70.1 transcripts related to oocyte and embryo developmental competence were analysed. For in vitro maturation (IVM), cumulus-oocyte complexes from slaughterhouse ovaries were distributed into four groups based on insulin concentration added to serum-free DCM, which was composed of alpha minimum essential medium (α-MEM), as basal medium: (1) DCM control: 0 ng/ml; (2) DCM1: 1 ng/ml; (3) DCM10: 10 ng/ml; and (4) DCM100: 100 ng/ml. After IVM, the nuclear status of a sample of oocytes was analysed and the other oocytes were submitted for in vitro fertilization (IVF) and in vitro culture (IVC). Different concentrations of insulin did not affect significantly the nuclear maturation and cleavage rate (72 h post-insemination) across all groups. Blastocyst rate (192 h post-insemination) did not differ in DCM control (24.3%), DCM1 (27.0%) and DCM10 (26.3%) groups, but the DCM100 (36.1%) group showed a greater blastocyst rate (P 0.05) was observed at the different insulin concentrations. The results indicated that insulin added to DCM influenced levels of transcripts related to cellular stress (HSP70-1 and PRDX1) and oocyte competence (GDF9) in bovine oocytes and at higher concentrations enhanced blastocyst production.

Expression and knockdown analysis of glucose phosphate isomerase in chicken primordial germ cells

Glucose is an important monosaccharide required to generate energy in all cells. After entry into cells, glucose is phosphorylated to glucose-6-phosphate and then transformed into glycogen or metabolized to produce energy. Glucose phosphate isomerase (GPI) catalyzes the reversible isomerization of glucose-6-phosphate and fructose-6-phosphate. Without GPI activity or fructose-6-phosphate, many steps of glucose metabolism would not occur. The requirement for GPI activity for normal functioning of primordial germ cells (PGCs) needs to be identified. In this study, we first examined the expression of chicken GPI during early embryonic development and germ cell development. GPI expression was strongly and ubiquitously detected in chicken early embryos and embryonic tissues at Embryonic Day 6.5 (E6.5). Continuous GPI expression was detected in PGCs and germ cells of both sexes during gonadal development. Specifically, GPI expression was stronger in male germ cells than in female germ cells during embryonic development and the majority of post-hatching development. Then, we used siRNA-1499 to knock down GPI expression in PGCs. siRNA-1499 caused an 85% knockdown in GPI, and PGC proliferation was also affected 48 h after transfection. We further examined the knockdown effects on 28 genes related to the glycolysis/gluconeogenesis pathway and the endogenous glucose level in chicken PGCs. Among genes related to glycolysis/gluconeogenesis, 20 genes showed approximately 3-fold lower expression, 4 showed approximately 10-fold lower, and 2 showed approximately 100-fold lower expression in knockdown PGCs. The endogenous glucose level was significantly reduced in knockdown PGCs. We conclude that the GPI gene is crucial for maintaining glycolysis and supplying energy to developing PGCs.

DNA methylation and mRNA expression profiles in bovine oocytes derived from prepubertal and adult donors

The developmental capacity of oocytes from prepubertal cattle is reduced compared with their adult counterparts, and epigenetic mechanisms are thought to be involved herein. Here, we analyzed DNA methylation in three developmentally important, nonimprinted genes (SLC2A1, PRDX1, ZAR1) and two satellite sequences, i.e. ‘bovine testis satellite I’ (BTS) and ‘Bos taurus alpha satellite I’ (BTαS). In parallel, mRNA expression of the genes was determined by quantitative real-time PCR. Oocytes were retrieved from prepubertal calves and adult cows twice per week over a 3-week period by ultrasound-guided follicular aspiration after treatment with FSH and/or IGF1. Both immature and in vitro matured prepubertal and adult oocytes showed a distinct hypomethylation profile of the three genes without differences between the two types of donors. The methylation status of the BTS sequence changed according to the age and treatment while the methylation status of BTαS sequence remained largely unchanged across the different age and treatment groups. Relative transcript abundance of the selected genes was significantly different in immature and in vitro matured oocytes; only minor changes related to origin and treatment were observed. In conclusion, methylation levels of the investigated satellite sequences were high (>50%) in all groups and showed significant variation depending on the age, treatment, or in vitro maturation. To what extent this is involved in the acquisition of developmental competence of bovine oocytes needs further study.

Effect of ovarian stimulation on oocyte gene expression in cattle

The objective was to analyze the impact of follicle stimulating hormone (FSH, ovarian stimulation) on the transcriptome of in vivo bovine oocytes three times around the luteinizing hormone (LH) surge. In vivo bovine oocytes were collected 2 h pre-LH surge, 6 h post-LH surge, and 22 h post-LH surge in both naturally ovulating and superovulated animals. To assess potential changes in gene levels, samples were hybridized using a custom bovine microarray. Two series of hybridizations were performed: the first comparing natural vs. stimulated cycles, the second according to time of collection. Among the potential candidates, 13 genes were selected according to their degree of differential expression and their potential link to oocyte competence. Measurements of their relative mRNA levels was made using QPCR. Gene candidates BTG4 (P = 0.0006), PTTG1 (P = 0.0027), PAPOLA (P = 0.0245), and LEO1 (P = 0.0393) had higher mRNA levels in oocytes treated with FSH for all collection times when compared to oocytes produced through the natural cycle. Among our selected candidates, only one gene, GDF9 (P = 0.0261), was present at a higher level in oocytes collected at -2 h and 6 h than 22 h post-LH for all treatments, regardless of the presence of FSH. Although the number of genes influenced by ovarian stimulation seemed low, the observed differences occurred at a time of minimal transcriptional activity and supported the potential impact on the future embryo. These impacts could have been epigenetic in nature, as embryo quality was not reported to be different from stimulated animals.

A novel approach to sexing bovine blastocysts using male-specific gene expression

When examining gene expression profiles for the purposes of assessing embryo quality, it is imperative that sex be considered, because many embryonic transcripts have sex-related expression patterns. The objective of this study was to systematically examine eight Y chromosome linked genes (DDX3Y, EIF1AY, HSFY, SRY, TSPY, USP9Y, ZFY, and ZRSR2Y) to characterize their expression in bovine blastocysts and to examine the usefulness of this expression for the purpose of RNA-based embryo sexing. In order to examine the expression of these genes, pools of blastocysts (groups of 10 and 20) as well as single embryos (N = 50) were analyzed with reverse transcriptase polymerase chain reaction (RT-PCR) and reverse transcriptase quantitative PCR (RT-qPCR). Of the 50 single embryos, 32 were concurrently sexed with DNA-based methods. Transcripts of DDX3Y, EIF1AY, TSPY, USP9Y, ZFY and ZRSR2Y were detected in the pooled and single blastocysts, but no transcripts were detected for HSFY or SRY. After performing DNA-based sexing experiments, we concluded that this expression was restricted to the male embryos. The consistency of the expression varied according to the gene as well as the specific primer set. Three genes were expressed in the full set of male embryos, DDX3Y, USP9Y, and ZRSR2Y and therefore represent good candidates for RNA-based sexing methods.

Developmental changes in thermoprotective actions of insulin-like growth factor-1 on the preimplantation bovine embryo

Insulin-like growth factor 1 (IGF1) is an important endocrine signal for regulation of early embryonic development. It increases the proportion of preimplantation embryos becoming blastocysts, alters blastocyst gene expression, improves resistance of embryos to various stresses and can enhance survival of embryos after transfer to recipients. The present study had two objectives. The first was to determine whether the thermoprotective actions of IGF1 on the preimplantation bovine embryo was developmentally regulated, with the two-cell embryo being refractory to IGF1. The second was to determine the molecular basis for the improved competence of embryos treated with IGF1 to establish pregnancy after transfer to heat-stressed recipients. Treatment of embryos with 100 ng/ml IGF1 reduced the effects of heat shock on embryos ≥16 cells at day 5 after insemination but did not provide thermoprotection to two-cell embryos. Failure of IGF1 to alter embryo survival after heat shock was not associated with reduced expression of genes involved in IGF1 signaling (IGF1R, RAF1, PI3K, and MAPK) or immunoreactive IGF1R protein. Treatment with IGF1 had little effect on the transcriptome at the blastocyst stage of development, with a total of 102 differentially expressed genes identified. Among the differentially expressed genes were several involved in apoptosis, protection against free radicals and development. Changes in gene expression were consistent with IGF1 acting to induce an anti-apoptotic state and inhibit neurulation. In conclusion, thermoprotective actions of IGF1 are developmentally regulated. Failure of IGF1 to protect the two-cell embryo from heat shock could reflect the fact that these embryos are maximally sensitive to damage caused by heat shock or reflect the quiescence of the embryonic genome at this stage of development. Changes in gene expression at the blastocyst stage induced by IGF1 could contribute to the increased survival of IGF1-treated embryos when transferred during periods of heat stress.

Mechanisms contributing to the reduced developmental competence of glucosamine-exposed mouse oocytes

Glucosamine (GlcN) is a widely used hyperglycaemia mimetic because of its ability to upregulate the ‘energy-sensing’ hexosamine biosynthesis pathway in a dose-dependent manner. A previous study demonstrated that addition of GlcN (2.5–5 mM) during IVM of cattle and pig cumulus–oocyte complexes (COC) inhibited development following fertilisation and early cleavage. In the present study, we demonstrate that the addition of 2.5 mM GlcN during IVM of mouse COCs similarly inhibits embryo development, with the degree of inhibition dependent upon the availability of glucose in the maturation medium. Furthermore, we determined that the effect of GlcN is likely mediated by the cumulus cell vestment, because we failed to observe inhibitory effects of GlcN following maturation of denuded (and therefore already developmentally compromised) oocytes. As with cattle oocytes, inhibition of O-linked glycosylation of unknown proteins within mouse cumulus cells significantly reversed the effects of GlcN. Finally, we also provide preliminary evidence that GlcN may inhibit the pentose phosphate metabolic pathway within the oocyte, an effect possibly mediated by cumulus cells in intact COCs. Collectively, our results demonstrate that GlcN inhibits the developmental competence of IVM mouse oocytes and suggest that this occurs via cumulus cell-mediated mechanisms. Therefore, the in vitro addition of GlcN is a useful experimental tool to determine the mechanisms of hyperglycaemic responses within COCs.

Expression of glucose transporter isoforms and the insulin receptor during hamster preimplantation embryo development

During preimplantation development, embryos of many species are known to express up to five isoforms of the facilitative glucose transporter proteins (GLUT). Development of hamster blastocysts is inhibited by glucose. We therefore investigated GLUT isoform and insulin receptor (IR) expression in hamster preimplantation embryos cultured in glucose-free medium from the 8-cell stage onwards. We show that GLUT1, 3 and 8 mRNA are constitutively expressed from the 8-cell to the blastocyst stage. The IR is expressed from the morula stage onwards. Messenger RNA of the insulin-responsive GLUT4 was not detected at any stage. GLUT1 and 3 were localised by immunocytochemistry. GLUT1 was expressed in both embryoblast and trophoblast, in the latter, mainly in basal and lateral membranes directed towards the blastocoel and embryoblast. GLUT3 was exclusively localised in the apical membrane of trophoblast cells. We show that hamster preimplantation embryos express several GLUT isoforms thus closely resembling embryos of other mammalian species. Despite endogenous IR expression, the insulin-sensitive isoform GLUT4 was not expressed, indicating that the insulin-mediated glucose uptake known from classical insulin target cells may not be relevant for hamster blastocysts.

Role of glucose in cloned mouse embryo development

Cloned mouse embryos display a marked preference for glucose-containing culture medium, with enhanced development to the blastocyst stage in glucose-containing medium attributable mainly to an early beneficial effect during the first cell cycle. This early beneficial effect of glucose is not displayed by parthenogenetic, fertilized, or tetraploid nuclear transfer control embryos, indicating that it is specific to diploid clones. Precocious localization of the glucose transporter SLC2A1 to the cell surface, as well as increased expression of glucose transporters and increased uptake of glucose at the one- and two-cell stages, is also seen in cloned embryos. To examine the role of glucose in early cloned embryo development, we examined glucose metabolism and associated metabolites, as well as mitochondrial ultrastructure, distribution, and number. Clones prepared with cumulus cell nuclei displayed significantly enhanced glucose metabolism at the two-cell stage relative to parthenogenetic controls. Despite the increase in metabolism, ATP content was reduced in clones relative to parthenotes and fertilized controls. Clones at both stages displayed elevated concentrations of glycogen compared with parthenogenetic controls. There was no difference in the number of mitochondria, but clone mitochondria displayed ultrastructural alterations. Interestingly, glucose availability positively affected mitochondrial structure and localization. We conclude that cloned embryos may be severely compromised in terms of ATP-dependent processes during the first two cell cycles and that glucose may exert its early beneficial effects via positive effects on the mitochondria.

Sequencing, characterization and genetic variation of the Bos indicus glucose-6-phosphate-dehydrogenase gene

The coding sequence of the bovine (Bos indicus) Glucose-6-phosphate-dehydrogenase (G6PD) gene was amplified by Reverse Transcriptase-PCR (RT-PCR), cloned, sequenced and characterized. The deduced amino acid sequence clustered the bovine G6PD sequence with the other mammalian G6PD proteins into a monophyletic group. The bovids (B. indicus and B. taurus) clustered clearly from the rodent (rat, mouse and hamster) subcluster and from humans. The multiple sequence alignment of the bovine G6PD with the mammalian species clearly revealed conservation of the substrate, coenzyme, catalytic and the dimer binding sites with the solved X-ray crystallographic structure of Homo sapiens. Also, four fragments of bovine (Bos indicus) G6PD gene viz. 118, 319, 683 and 408 bp were amplified and sequenced for the first time. A G/A and G/C single nucleotide polymorphisms in intron-9 and exon-10 were detected on PCR-RFLP of the 319 bp amplicon with Hae III and Pst I, respectively. This work is the first study on Bos indicus G6PD gene at the nucleotide level.

Total RNA and protein content, Cyclin B1 expression and developmental competence of prepubertal goat oocytes

The aim of this study was to examine the relationship between the developmental competence of oocytes and their total RNA and protein contents, and the level of Cyclin B1 transcription. Ovaries from prepubertal goats were collected from a slaughterhouse. Oocytes were recovered by slicing and those with two or more layers of cumulus cells and homogenous cytoplasm were matured in vitro (20-25 oocytes per drop) for 27 h. Both before and after IVM, samples of oocytes were denuded and categorised into four group treatments by diameter (<110 microm, 110-125 microm, 125-135 microm; >135 microm), separated into sub-groups of 10 oocytes per treatment-replicate and stored in liquid nitrogen until total RNA content analysis by spectophotometry, total protein content analysis by a colorimetric assay and Cyclin B1 transcription analysis by RT-PCR. For the study of developmental competence, the rest of the matured oocytes were fertilised in vitro in groups of 20-25 for 24 h. Presumptive zygotes were denuded, sorted into the four categories of diameter noted above, and placed into culture drops in groups of 18-25 for in vitro culture. Cleavage rate was evaluated at 48 hpi and embryo development at 8 d post-insemination. There were four replicates of each treatment for each assay or evaluation point of the experiment. There were no significant differences between the size categories of oocytes at collection in total RNA content, total protein content and Cyclin B1 mRNA. There were significant differences (P<0.05) in the expression of Cyclin B1 before IVM with oocytes in the >135 mm diameter category having the highest value for this variant. There were no significant differences in these characteristics between the categories of oocyte diameter after IVM except in respect of total RNA content, which was lower for the largest size of oocytes (>135 microm; mean+/-S.D.=12.3+/-1.84 ng/oocyte) than the other three size groups (19.2+/-1.38-22.1+/-4.44 ng/oocyte; P<0.05). Significant differences (P<0.05) in cleavage rate were observed between the different oocyte size categories (<110 microm, 3.0%; 110-125 microm, 32%; 125-135 microm, 50%; >135 microm, 73%). Only oocytes >125 microm diameter developed to the blastocyst stage (125-135 microm, 7%; >135 microm, 10%). This study showed that the RNA content and the Cyclin B1 RNA expression of prepubertal goat oocytes, and their development to embryos varied between the different size categories of the oocytes.

Identification of novel pregnancy-associated glycoproteins (PAG) expressed by the peri-implantation conceptus of domestic ruminants

Pregnancy-associated glycoproteins (PAG) are a multigene family, related to aspartic proteinases, expressed in the placenta of artiodactyls. Ruminant PAG expression varies spatially as well as temporally during gestation. The aim of this study was the identification of novel PAG expressed around implantation in domestic ruminants and to study their phylogenetic relationships. Day 12, 14, 17 (ovine); day 15, 18 (bovine); and day 12, 14, 15, 16, 18 (caprine) conceptuses were used for reverse transcription-polymerase chain reaction (RT-PCR) performed on RNA extracted from conceptuses pooled on each day of recovery. In ovine, a single PAG was detected on day 14, ovPAG2, from the PAG II group. On day 17, three more PAG were identified. One of them similar to ovPAG1 and two unknown named as ovPAG10 and ovPAG11, apparently from the PAG I group. In bovine, PAG expression was detected by day 15 and two transcripts were identified on day 18. One, boPAG2, from the PAG II group and other was previously unknown, boPAG22, closest to boPAG2. In goats, PAG expression was not detected on non-elongated conceptuses (days 12, 14 and 15). Two different transcripts were identified in both day 16 and 18 elongated conceptuses, one similar to caPAG2, from the PAG II group, whereas the other, caPAG12, apparently from the PAG I group, was previously unknown. Interestingly, the three new early PAG identified in sheep and goats are clustered together within the PAG I group. In summary, a complement of new PAGs expressed at implantation in domestic ruminants has been cloned.

Using the histone H2a transcript as an endogenous standard to study relative transcript abundance during bovine early development

The requirement for sample standardization is basic to any relative RNA abundance assessment. In 2002, we published on the RNA abundance profiling of several housekeeping targets during early bovine embryonic development. It was then concluded that histone H2a was the most stable transcript across the studied developmental period. Since that time, several teams have applied this information, yet neglected to use the published set of primers. Here, we show that these other primer sets do not target the same histone H2a variant. Within the present report, the RNA abundance profiles of their respective targets, for example, histone H2a.1, H2a.z, and H2a.o were measured in developmental series spanning the immature oocyte to the blastocyst stage embryo. In order to more clearly define the conditions that impact the RNA abundance level measurement of these candidates, the state of polyadenylation and the origin of the transcript either from de novo transcription or from maternal stocks were taken into consideration. The histone H2a.z transcript is principally regulated by de novo transcription following embryonic genome activation, whereas the levels of H2a.1 and H2a.o variants are largely of maternal origin, conferring a more stable profile throughout the studied developmental window. The histone H2a.z was found solely in a polyadenylated state whereas the H2a.1 and H2a.o were found to be more abundant in a nonadenylated form. The presence of serum in the in vitro embryo production system also had some impact on the histone H2a.1 RNA level at the blastocyst stage.

Expression pattern of oxygen and stress-responsive gene transcripts at various developmental stages of in vitro and in vivo preimplantation bovine embryos

The present study examined the expression pattern of oxygen (O(2)) and stress-responsive gene transcripts at various preimplantation developmental stages of in vitro produced (IVP) and in vivo derived (IVD) bovine embryos. Embryos were produced in vitro from oocytes matured, fertilized and cultured in synthetic oviductal fluid (SOF) medium under low (5%) and high (20%) O(2) concentrations. In vivo embryos were derived from 18 superovulated and artificially inseminated cows. In IVP and IVD groups, embryos were collected at 2-, 4-, 8-, 16-cell morula and blastocyst stages at specific time points for gene expression analysis. The cleavage rates (69.8+/-4.8%) did not differ significantly, but blastocyst rates were significantly higher (28.5+/-3.7%) in low O(2) than those in high O(2) group (18.7+/-3.9%). Mean cell number in low O(2) (145+/-12) and high O(2) (121+/-73) IVP blastocyst were lower (P<0.05) than those of IVD blastocyst (223+/-25). The ICM ratio of IVD blastocyst (26+/-4) was lower (P<0.05) than that of IVP embryos under 5% O(2) (33+/-5) and 20% O(2) (34+/-4) concentrations, respectively. Using real time PCR, for the set of target transcripts (Glut1, Glut5, Sox, G6PD, MnSOD, PRDX5, NADH and Hsp 70.1) analyzed, there were differences in the mRNA expression pattern at 2-, 4-, 8-, 16-cell morula and Day 7 blastocyst stages between the two embryo sources. It can be concluded that, although in vitro bovine embryo culture in SOF medium under low (5%) O(2) concentration provided a more conducive environment in terms of blastocyst formation; differences in the total cell number and gene expression pattern between the IVP and IVD embryos reflected the effect of O(2) concentration.

A comparative analysis of metabolism and viability in porcine oocytes during in vitro maturation

The importance of oocyte quality cannot be overstated, because it impacts all subsequent events during development of the embryo, the fetus and even the resulting offspring. Oocyte metabolism plays a critical role in supporting developmental competence via multiple mechanisms. It is beginning to be understood that metabolic pathways not only affect cytoplasmic maturation but may control nuclear maturation as well. A complete understanding of the precise roles that metabolism plays in determining oocyte quality is crucial for developing efficient in vitro maturation systems to support acquisition of oocyte competence. To date, this pursuit has not been entirely successful. Work in our laboratory on porcine oocyte metabolism has elucidated some of the intricate control mechanisms at work within the oocyte, not only for energy production, but also encompassing progression of nuclear maturation, mitochondrial activity and distribution, and oxidative and ionic stresses. We hypothesize that by utilizing oocyte metabolic data, we can develop more appropriate in vitro maturation systems that result in increased oocyte and embryo developmental competence.

Effect of oocyte diameter on meiotic competence, embryo development, p34 (cdc2) expression and MPF activity in prepubertal goat oocytes

The aim of this study was to analyze the relationship between oocyte diameter, meiotic and embryo developmental competence and the expression of the catalytic subunit of MPF, the p34(cdc2), at mRNA, RNA and protein level, as well as its kinase activity, in prepubertal (1-2 months old) goat oocytes. MPF is the main meiotic regulator and a possible regulator of cytoplasmic maturation; therefore, it could be a key factor in understanding the differences between competent and incompetent oocytes. Oocytes were classified according to oocyte diameter in four categories: <110, 110-125, 125-135 and >135 microm and matured, fertilized and cultured in vitro. The p34(cdc2) was analyzed in oocytes at the time of collection (0 h) and after 27 h of IVM (27 h) in each of the oocyte diameter categories. The oocyte diameter was positively related to the percentage of oocytes at MII after IVM (0, 20.7, 58 and 78%, respectively) and the percentage of blastocysts obtained at 8 days postinsemination (0, 0, 1.95 and 12.5%, respectively). The expression of RNA and mRNA p34(cdc2) did not vary between oocyte diameters at 0 and 27h. Protein expression of p34(cdc2) increased in each oocyte category after 27 h of maturation. MPF activity among diameter groups did not vary at 0h but after IVM there was a clear and statistically significant increase of MPF activity in the biggest oocytes.

Somatic cell nuclei in cloning: strangers traveling in a foreign land

The recent successes in producing cloned offspring by somatic cell nuclear transfer are nothing short of remarkable. This process requires the somatic cell chromatin to substitute functionally for both the egg and the sperm genomes, and indeed the processing of the transferred nuclei shares aspects in common with processing of both parental genomes in normal fertilized embryos. Recent studies have yielded new information about the degree to which this substitution is accomplished. Overall, it has become evident that multiple aspects of genome processing and function are aberrant, indicating that the somatic cell chromatin only infrequently manages the successful transition to a competent surrogate for gamete genomes. This review focuses on recent results revealing these limitations and how they might be overcome.

The effect of glucosamine concentration on the development and sex ratio of bovine embryos

Glucosamine is a component of hyaluronic acid and an alternative substrate to glucose for the extracellular matrix synthesis of COCs. Its addition to an IVM medium reduces the glucose consumption of bovine COCs. Glucosamine is also metabolized to UDP-N-acetyl glucosamine (UDP-GlcNAc) via the hexosamine biosynthesis pathway and is utilized for O-linked glycosylation by the X-linked enzyme, O-linked GlcNAc transferase (OGT). Moreover, the inactivation of the second X chromosome in female embryos is influential in producing the sex ratio bias observed in vitro when embryos are cultured in the presence of glucose above 2.5mM. Accordingly, the aim of this study is to examine whether the presence of glucosamine during maturation or embryo culture causes a sex ratio bias in bovine blastocysts. Glucosamine was added to the medium in three different embryo developmental periods: in vitro maturation, the one-cell to eight-cell stage (before the maternal-zygotic transition, MZT), and the eight-cell to blastocyst stage (after MZT). When glucosamine was added during in vitro maturation, the developmental competence of oocytes was severely compromised. However, the sex ratio of embryos was not influenced. When glucosamine was added to embryo culture medium during development from one-cell to eight-cell stage (before MZT), it affected neither the development nor the sex ratio of bovine embryos. Finally, when glucosamine was added after MZT, the development rate of embryos was severely decreased, and the sex ratio was skewed toward males. Moreover, an inhibitor of OGT, benzyl-2-acetamido-2-deoxy-alpha-D-galactopyranoside (BADGP), negated the effect of glucosamine on the sex ratio when it was added to embryo culture medium from the eight-cell to blastocyst stage (after MZT). These results suggest that, like glucose, the supplementation of glucosamine into the medium skewed the sex ratio to males and that OGT, an X-linked enzyme, was involved in this phenomenon. Moreover, this effect of glucosamine was limited only to when it was present in the embryo culture medium after MZT.

Glucose utilization and the PI3-K pathway: mechanisms for cell survival in preimplantation embryos

The maintenance of optimal glucose utilization during the preimplantation period is critical for embryo survival. A decrease in glucose transport during preimplantation development has been linked to the early steps of programmed cell death in these embryos. Decreased glucose transport is not thought to be simply a consequence of cell death, rather it is thought to be a trigger that can initiate the apoptotic cascade. Extensive apoptosis during the preimplantation period may manifest later in pregnancy as a malformation – or miscarriage, if cell loss is excessive. Phosphatidylinositol 3-kinase (PI3-K) is a known regulator of a number of physiologic responses including cellular proliferation, growth, and survival as well as glucose metabolism. Studies performed in other cell systems have demonstrated that the PI3-K pathway plays a critical role in maintaining glucose transport and metabolism. This review will present the current evidence that suggests that PI3-K is vital for preimplantation embryo survival and development. In addition, data demonstrating that PI3-K activity is important for glucose metabolism during this early developmental period will be discussed.

Messenger RNA expression patterns in bovine embryos derived from in vitro procedures and their implications for development

The preimplantation bovine embryo is initially under the control of maternal genomic information that is accumulated during oogenesis. The genetic programme of development soon becomes dependent on new transcripts derived from activation of the embryonic genome. The early steps in development, including the timing of the first cleavage, activation of the embryonic genome, compaction and blastocyst formation, can be affected by the culture media and conditions, as well as the production procedure itself. These perturbations can possibly result in a marked decrease in the quality of the resulting blastocysts and may even affect the viability of offspring born after transfer. In vitro procedures such as in vitro production and somatic nuclear transfer of bovine embryos have been shown to be correlated with significant up- or downregulation, de novo induction or silencing of genes critical for undisturbed fetal and neonatal development. These alterations are likely to be caused by epigenetic modifications, such as DNA methylation and histone modifications. Analysis of perturbed epigenetic reprogramming and of the related phenomena, such as genomic imprinting and X-chromosome inactivation, in bovine embryos is promising for understanding the underlying mechanisms of developmental abnormalities, such as large offspring syndrome.

Gene Expression and Developmental Competence of Bovine Embryos Produced In Vitro with Different Serum Concentrations

The objective of this study was to determine the developmental rates and relative abundance of Hsp 70.1 and Glut-1 transcripts in in vivo- and in vitro-produced (IVP) bovine embryos in media supplemented with bovine serum albumin (BSA) or different oestrous cow serum concentrations. In experiment 1, in vitro maturation and culture media were supplemented with 0.4% BSA or 1, 5, 10 or 20% of oestrous cow serum (ECS). The analysis of the expression of Hsp 70.1 and Glut-1 was carried out in individual days 7 and 8 embryos by a semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assay. In experiment 2, in vivo-produced morulae were collected on day 7 of the oestrous cycle and employed for the comparison of the relative abundances of Hsp 70.1 and Glut-1 transcripts with IVP morulae produced using two protein sources (10% ECS or 0.4% BSA). No differences were observed in cleavage rate among groups, but blastocyst formation (27%) and hatching rates (78%) were significantly higher in IVP embryos produced with 20% ECS than the other groups (p<0.05). No significant differences were observed in the relative abundances of Hsp 70.1 and Glut-1 mRNA in days 7 and 8 blastocysts expanded blastocysts between groups. The abundances of mRNA for those genes were similar between IVP and in vivo-produced morulae. In spite of the alterations observed in embryonic development, the presence of serum at distinct concentrations did not appear to alter the relative abundance profiles of Hsp 70.1 and Glut-1 compared with controls or the BSA supplementation to the IVP media.

Gene expression and developmental competence of bovine embryos produced in vitro under varying embryo density conditions

The objective of this study was to determine the effects of oocyte/embryo density (embryo number:medium volume ratio) on developmental competence and relative transcription of developmentally important genes in in vitro-produced bovine embryos. Using standard procedures, bovine oocytes were matured, fertilized and cultured in vitro in groups of 5, 10, 20 or 30 oocytes/embryos per 100 microL medium drop (embryo number/medium volume ratios of 1:20, 1:10, 1:5 and 1:3.3, respectively). A semi-quantitative RT-PCR assay was used to determine the relative abundance of Hsp 70.1 and Glut-1 transcripts in Day-6 morulae, and in Day-7 and Day-8 blastocysts and expanded blastocysts. Cleavage rates (55.9, 49.1, 47.1 and 34.6%, respectively) and blastocyst developmental rates (24.1, 18.9, 20.4 and 12.6%, respectively) were higher in groups containing 5, 10 and 20 embryos versus 30 embryos per drop, but there were no significant differences among groups in hatching rates. The relative abundance of Hsp 70.1 transcripts in Day-7 blastocysts was higher in embryos produced in the 20-embryo than in the 5-embryo groups. There were no differences among embryos from all groups in the amount of Glut-1 mRNA (regardless of embryonic stage). However, there were differences in the pattern of Hsp 70.1 gene expression between distinct stages of embryo development and embryo density; these dissimilarities appeared to be associated with compromised development at higher embryo densities. In conclusion, the increase in embryo density during IVM, IVF, and IVC phases of in vitro embryo production might negatively affect embryo development and the pattern of gene expression of in vitro-produced bovine embryos.

Relationships between maternal hormone secretion and embryo development on day 5 of pregnancy in dairy cows

In cattle, increasing early embryonic losses are associated with inadequate progesterone concentrations within the first three weeks of pregnancy. The aim of this study was to investigate the complex relationship between early maternal progesterone concentration and embryo development early within the first week of pregnancy, specifically, on day 5 post-oestrus in dairy cows. Twenty Holstein-Friesian cows at the end of lactation were inseminated at oestrus (day 0) and on day 5 post-oestrus cows were slaughtered and the reproductive tract flushed to determine the presence and stage of embryo development. Three cows that had failed to synchronise correctly were excluded from analysis while in the remaining 17 cows 11 (65%) were pregnant with embryos at the morula (n = 3), 9-16 (n = 3) and 8-cell (n = 5) stages of development. No differences in day 5 plasma progesterone concentrations or corpus luteum (CL) size or progesterone content were observed between pregnant (n = 11) and non-pregnant (n = 6) cows. In cows with embryos beyond the 8-cell stage of development (n = 6) plasma progesterone concentration (P < 0.001) and CL weight (P < 0.01) were higher and plasma insulin concentrations lower (P < 0.001) than in cows with 8-cell embryos (n = 5). In addition there was a negative relationship between plasma progesterone and plasma insulin in pregnant cows (R(2) = 0.65; P < 0.005). In cows with an embryo present in the oviduct, oviductal glucose concentrations were lower (P < 0.05) than in cows with no embryo present. These results confirm progesterone is not only directly associated with embryo development, but that it may indirectly modulate embryo development via changes in the oviductal environment. In summary, the association between maternal progesterone concentration and embryo development exists as early as day 5 of pregnancy in dairy cows.

Involvement of the pentose phosphate pathway and redox regulation in fertilization in the mouse

Glucose metabolism is necessary for successful fertilization in the mouse. Both spermatozoa and oocytes metabolize glucose through the pentose phosphate pathway (PPP), and NADPH appears required for gamete fusion. The aims of this study were to further characterize the utilization of glucose by the fertilizing spermatozoon and the fertilized oocyte, to demonstrate the importance of the PPP in different steps of fertilization, and to examine whether the beneficial effect of glucose could be mediated by a NADPH-dependent enzyme involved in redox regulation. By using a fluorescent analog of 2-deoxyglucose, glucose uptake was evidenced in both the head and flagellum of motile spermatozoa. After sperm-oocyte fusion, an increase in glucose uptake by the fertilized oocyte was observed but not before the formation of the male and female pronuclei. By using a microphotometric technique, activity of glucose 6-phosphate dehydrogenase (G6PDH), the key enzyme of the PPP, was localized to the sperm head and midpiece. When epididymal spermatozoa were released into a glucose-containing medium, the NADPH/NADP ratio increased with capacitation. Sperm-oocyte fusion and meiosis reinitiation of the fertilized oocyte was inhibited by the PPP inhibitor 6-aminonicotinamide (6-AN); inhibition of sperm-oocyte fusion was relieved by NADPH. Sperm-oocyte fusion and meiosis reinitiation were also inhibited by diphenylamine iodonium, which is a flavoenzyme inhibitor reported to prevent reactive oxygen species (ROS) generation in mouse spermatozoa and embryos. These findings indicate that the PPP is involved in different steps of fertilization. Subsequent regulation of a NADPH-dependent flavoenzyme responsible of ROS production is envisaged.

Effect of speed of development on mRNA expression pattern in early bovine embryos cultured in vivo or in vitro

Recent data have demonstrated that fast-cleaving embryos produced in vitro are more likely to develop to blastocyst stage, and that the postfertilization culture system used impacts considerably on the mRNA expression and quality of blastocysts produced. The present study is the first to investigate the relationship between the developmental speed of embryos produced in vivo or in vitro and the temporal transcription pattern. Genes related to important preimplantation events are monitored during the first 4 days of embryo development in embryos with fast or slow development. The set of genes analyzed in the present study characterizes several important physiological processes including: transport and metabolism of fructose (Glut-5), stress (SOX), mitochondrial activity and detoxification of reactive oxygen species (MnSOD), cell communication (Cx43), maternal recognition of pregnancy (IFN-tau), imprinting (IGF-II), apoptosis (Bax), growth factor binding and metabolism (IGF-IR), and oxidative stress (G6PD). Using real time PCR, we have found that for all the genes analyzed there are differences in mRNA expression between embryos with fast and slow developmental speed produced both in vitro and in vivo. Frequently, genes that may be stress induced such as SOX, MnSOD, BAX, IFtau, and G6PD were highly transcribed in in vitro produced embryos and in embryos with slow developmental speed. On the other side, transcripts from genes related with metabolism, growth, and differentiation (Glut-5, Cx 43, IGF-II, and IGF-IR) were detected in higher amounts in in vivo produced embryos and in embryos with fast developmental speed. Moreover, it is interesting to stand out that for some genetic markers (such as SOX and G6PD) there are in vivo and in vitro differences that can be observed even before materno-zygotic transition, which probably reflects a differential mRNA degradation. These transcription patterns reflects the embryonic response to the adverse in vitro culture conditions, and connect the low quality of embryos which slow developmental speed produced in vivo and in vitro, with the mRNA expression pattern of some embryonic genes.

Effect of stage of follicular growth during superovulation on developmental competence of bovine oocytes

The final steps of oocyte capacitation and maturation are critical for embryonic development but detailed information is scarce on how the oocyte is affected during this period. In this study, 2033 oocytes were collected from 106 superovulated cattle at four different time points before ovulation. Follicular characteristics were measured and oocyte quality was assessed by morphology, mRNA expression of eight marker genes or developmental ability after in vitro/in vivo maturation and subsequent in vitro fertilization and culture. Approaching ovulation, expected increases in follicular size and cumulus expansion suggested progression of oocyte maturation. No differences were found in the expression patterns of analyzed genes, except for heat-shock-protein (Hsp) that was lower in in vivo matured oocytes collected shortly before ovulation. Oocytes collected at this time also had higher developmental ability measured as blastocyst rates (57.6%) after in vitro production while no differences were found between oocytes recovered earlier at the first three time points (39.3-41.5%). We conclude that oocytes recovered late in the preovulatory period are more developmentally competent than oocytes recovered at the pre-capacitation and the capacitation period, probably due to the former having matured in vivo. However, a precisely defined time for aspirating immature oocytes for subsequent in vitro development seems not to be crucial.

Two insulin-responsive glucose transporter isoforms and the insulin receptor are developmentally expressed in rabbit preimplantation embryos

Glucose is the most important energy substrate for mammalian blastocysts. Its uptake is mediated by glucose transporters (GLUT). In muscle and adipocyte cells insulin stimulates glucose uptake by activation of the insulin receptor (IR) pathway and translocation of GLUT4. GLUT4 is expressed in bovine preimplantation embryos. A new insulin-responsive isoform, GLUT8, was recently described in mouse blastocysts. Thus, potentially, two insulin-responsive isoforms are expressed in early embryos. The mechanism of insulin action on embryonic cells, however, is still not clear. In the present study expression of IR, GLUT1, 2, 3, 4, 5 and 8 was studied in rabbit preimplantation embryos using RT-PCR, Western blotting and immunohistochemistry. The rabbit mRNA sequences for the complete coding region of IR, GLUT4 and a partial GLUT8 sequence were determined by RACE-PCR and sequencing. GLUT4 was expressed in 3-day-old morulae and in 4- and 6-day-old blastocysts. IR and GLUT8 transcripts were detectable only in blastocysts. Blastocysts also expressed GLUT1 and 3, but not GLUT2 and 5. Transcript numbers of GLUT4 and 8 were higher in trophoblast than in embryoblast cells. Translation of IR, GLUT4 and 8 proteins in blastocysts was confirmed by Western blotting. GLUT4 was localized mainly in the membrane and in the perinuclear region in trophoblast cells while in embryoblast cells its localization was predominantly in the perinuclear cytoplasm. The possible function(s) of two insulin-responsive isoforms, GLUT4 and GLUT8, in rabbit preimplantation embryos needs further investigation. It may not necessarily be linked to insulin-stimulated glucose transport.

Spatio-Temporal Expression of the Germ Cell Marker Genes MATER, ZAR1, GDF9, BMP15,andVASA in Adult Bovine Tissues, Oocytes, and Preimplantation Embryos1

We have cloned the bovine homologue of Mater (maternal antigen that embryos require) cDNA, potentially the first germ cell-specific maternal-effect gene in this species. The 3297 base-pair longest open reading frame encodes a putative protein of 1098 amino acids with a domain organization similar to its human counterpart. By reverse transcription coupled to polymerase chain reaction, we have analyzed the spatiotemporal expression of MATER, along with other potential markers of germ cells or oocytes: ZAR1 (zygotic arrest 1), GDF9 (growth and differentiation factor 9), BMP15 (bone morphogenetic protein 15), and VASA. In agreement with a preferential oocyte origin, MATER, ZAR1, GDF9, and BMP15 transcripts were detected in the oocyte itself at a much higher level than in the gonads, while no significant expression was detected in our panel of somatic tissues (uterus, heart, spleen, intestine, liver, lung, mammary gland, muscle). In situ hybridization confirmed oocyte-restricted expression of MATER and ZAR1 within the ovary, as early as preantral follicle stages. VASA was highly represented in the testis and the ovary, and still present in the oocyte from antral follicles. Maternal MATER, ZAR1, GDF9, and BMP15 transcripts persisted during oocyte in vitro maturation and fertilization and in preimplantation embryo until the five- to eight-cell or morula stage, but transcription was not reactivated at the time of embryonic genome activation.

Improvement of the Developmental Capacity of Oocytes from Prepubertal Cattle by Intraovarian Insulin-Like Growth Factor-I Application1

The developmental potential of oocytes from prepubertal cattle is decreased, compared with those from their adult counterparts. The aim of the present study was to improve the developmental capacity of oocytes from prepubertal cattle by either systemic application of recombinant bovine somatotropin (rbST) or intraovarian injection of insulin-like growth factor-I (IGF-I). Blastocyst yields and the mRNA expression pattern (relative abundance, RA) of three putative marker genes (i.e., glucose transporter-1, Glut-1; eukaryotic translation initiation factor-1A, eIF1A, and upstream binding factor, UBF) were selected as criteria to determine the success of the treatments. At 6-7 mo of age, 30 healthy Holstein calves were randomly assigned to three experimental groups. The first group served as control and received an intraovarian injection of 0.6 ml acetic acid. The second group received a single s.c. injection of 500 mg of rbST. The third group received an intraovarian injection of 6 microg recombinant human IGF-I. During the following 2 wk, follicles were aspirated four times via transvaginal ultrasound-guided technology. All animals were i.m. injected with 60 mg FSH 48 h prior to each aspiration. The treatments were repeated with the same animals at 9-10, 11-12, and 14-15 mo of age. For comparison, five adult cows were each i.m. injected with 100 mg FSH and underwent oocyte retrieval. The proportion of oocytes considered to be developmentally competent was higher in cows than calves (65% vs. 58%, 50%, 52%) for the control, rbST, and IGF-I groups, respectively. The rate of blastocysts was similar in IGF-I-treated calves and cows (28% and 25%) and was higher (P </= 0.05) than in the controls and the rbST group (11% and 16%). The RA for Glut-1 was lower (P </= 0.05) in two- to four- cell embryos from calves, compared with cows. At the 8- to 16- cell stage, Glut-1 RA was similar in IGF-I-treated calves and cows. The RA for eIF1A was higher (P </= 0.05) in 8- to 16-cell embryos derived from cows than those from the control group. Results show that IGF-I intraovarian injection increased blastocyst yields and mRNA expression of Glut-1 and eIF1A to levels found in embryos produced from adult cows. This treatment may at least partially overcome the developmental deficiency of oocytes derived from calves and could be a step forward toward the use of prepubertal animals in breeding programs aimed at shortening the generation interval.

Up-regulation of glucose metabolism during male pronucleus formation determines the early onset of the s phase in bovine zygotes

After in vitro fertilization with spermatozoa from bulls with high in vitro fertility, a beneficial paternal effect is manifested during the G1 phase of the first cell cycle. This benefit determines an earlier onset of the first S phase, and then a successful morula-blastocyst transition 7 days later. We hypothesized that the origin of the paternal effect could be a shift of the metabolism of the fertilized oocyte, because in mice, sperm decondensation is responsible for a dramatic increase in glucose metabolism. In this study we investigated the interaction between both pronuclei and compared glycolysis and pentose phosphate pathway (PPP) activities in bovine oocytes fertilized with spermatozoa from bulls of high or low fertility. Here we demonstrate that male pronucleus formation is necessary for the onset of the S phase in the female pronucleus, and that the component promoting an early S phase in both pronuclei is metabolic and linked to an up-regulation of the PPP during the male pronucleus formation. This long-lasting paternal effect is more evidence of the important role of epigenetic control during early embryo development.

Use of heterologous complementary DNA array screening to analyze bovine oocyte transcriptome and its evolution during in vitro maturation

We have analyzed gene expression in bovine oocytes before and after in vitro maturation (IVM) using heterologous hybridization onto cDNA array. Total RNA was purified from pools of over 200 oocytes either immediately after aspiration from follicles at the surface of slaughterhouse cow ovaries or following in vitro maturation. Radiolabeled cDNA probes were generated by reverse-transcription followed by linear PCR amplification and were hybridized to Atlas human cDNA arrays. To our knowledge, this is the first report of gene expression profiling by this technology in the mammalian female germ cell. Our results demonstrate that cDNA array screening is a suitable method for analyzing the transcription pattern in oocytes. About 300 identified genes were reproducibly shown to be expressed in the bovine oocyte, the largest profile available so far in this model. The relative abundance of most messenger RNAs appeared stable during IVM. However, 70 transcripts underwent a significant differential regulation (by a factor of at least two). Their potential role in the context of oocyte maturation is discussed. Together they constitute a molecular signature of the degree of oocyte cytoplasmic maturation achieved in vitro.

Messenger RNA stockpile of cyclin B, insulin-like growth factor I, insulin-like growth factor II, insulin-like growth factor receptor Ib, and p53 in the rainbow trout oocyte in relation with developmental competence

In the present study, correlations between the oocyte messenger RNA (mRNA) stockpile of Cyclin B, insulin-like growth factor I (IGF-I), insulin-like growth factor (IGF-II), insulin-like growth factor receptor Ib (IGFR Ib), and p53 transcripts and the developmental competence of the oocyte were studied. For this purpose, post-ovulatory ageing was used as a tool to generate oocytes of varying developmental competence. Mature female rainbow trout were held at 12 degrees C and periodically checked for ovulation. Oocytes were collected from each female at ovulation and 5, 14, 21 days later. For each collected egg batch, the abundance of several mRNAs in the oocyte was analyzed by real-time PCR and embryo development was monitored after fertilization. Egg quality was estimated not only through embryonic survival but also by studying the occurrence of specific morphological abnormalities. The present study showed that oocyte post-ovulatory ageing was associated with variations of the relative abundance of several studied transcripts within the oocyte. In addition, the abundance of specific mRNAs could be correlated with either the embryonic survival or the occurrence of malformations. Thus, the abundance of IGFR Ib and Cyclin B transcripts in the oocyte was correlated with the occurrence of morphological abnormalities observed at yolk-sac resorption (negatively for IGFR Ib and positively for Cyclin B), while the maternal stockpile of IGF-I, IGF-II, and IGFR Ib mRNAs was positively correlated with embryonic survival.

Evolution of mRNA polyadenylation between oocyte maturation and first embryonic cleavage in cattle and its relation with developmental competence

In this study we analyzed the pattern of polyadenylation changes that takes place between the resumption of meiosis and the first cleavage of bovine oocytes. Moreover, we investigated whether the delayed occurrence of the first cleavage division, which characterizes embryos of low developmental competence, is accompanied by an altered polyadenylation pattern of individual transcripts. We determined the polyadenylation status of a group of genes that characterize physiological processes, involved in early differentiation (Oct-4), compaction, and cavitation (beta-actin, plakophilin, connexin-32, connexin-43), energy metabolism (glucose transporter type 1, pyruvate dehydrogenase phosphatase), RNA processing (RNA poly(A) polymerase), and stress (heat shock protein 70). RNA was isolated from pools of 20 oocytes or embryos at the germinal vesicle (GV) stage, at the end of in vitro maturation, at the end of in vitro fertilization, and at the time of the first cleavage. Cleavage was assessed 27, 30, 36, 42 hr post insemination (hpi), and at the latter time the remaining uncleaved oocytes were retained as a group. Between oocyte isolation and first cleavage at 27 hpi (best quality embryos), the poly(A) tail of individual transcripts followed four patterns: no changes (beta-actin, PDP); gradual reduction (Cx-43, Oct-4, Plako); gradual elongation (Cx-32, TPA); reduction followed by elongation (PAP, HSP-70, Glut-1). If the interval between insemination and first cleavage was longer than 27 hpi (progressively lower quality embryos) further changes of polyadenylation were observed, which differed for each gene considered. These data indicated that specific changes in polyadenylation contribute to the modulation of gene expression in bovine embryos at this stage of development. Defective developmental competence is accompanied by abnormal polyadenylation levels of specific maternal mRNAs with synchrony between polyadenylation and cleavage emerging as an apparently important factor.

Quantification of cyclin B1 and p34(cdc2) in bovine cumulus-oocyte complexes and expression mapping of genes involved in the cell cycle by complementary DNA macroarrays

Although high amounts of cyclin B1 mRNA are present in bovine oocytes arrested at the germinal vesicle (GV) stage, the protein is not detectable. Furthermore, there is a depletion of the stored cyclin B1 mRNA in the oocyte as follicular growth progresses. To assess the effect of follicular growth on the accumulation of M-phase promoting factor (MPF) components, mRNA and protein levels of cyclin B1 and p34(cdc2) were measured in GV oocytes collected from diverse follicle size groups (<2 mm, 3-5 mm, and >6 mm). Because oocytes collected from very small follicles have high levels of cyclin B1 mRNA, the onset of its accumulation in the oocytes was evaluated by in situ hybridization of fetal ovaries. Also, a comparative expression map of cell cycle-related genes expressed in the oocyte and cumulus cells was established using nylon-based cDNA arrays, which allowed the detection of 35 different genes transcribed mostly in oocytes. Both components of the pre-MPF complex were expressed at the mRNA level in GV oocytes, whereas p34(cdc2) was the only pre-MPF protein detected at that stage, thus indicating that meiosis resumption in bovine oocytes is differentially regulated as compared with other mammals, and meiosis resumption seems to be regulated by the translation of cyclin B1 mRNA.

Quantification of housekeeping transcript levels during the development of bovine preimplantation embryos

In mammals, the study of gene expression in the preimplantation embryo has been difficult because the standard procedures used to quantify mRNA generally require large amounts of starting material. The development of protocols using different quantitative strategies generally involving the polymerase chain reaction (PCR) has provided new tools for exploration of gene expression in preimplantation embryos. However, the use of an internal standard, often referred as a housekeeping gene, is essential to normalize the mRNA levels. RNA levels of eight housekeeping genes were quantified using real time PCR throughout the preimplantation period of the bovine embryo to find the most suitable gene to be used as standard. Histone H2a was the best internal standard because the transcript levels were constant across the preimplantation period. Linear amplification of antisense RNA using the T7 promotor for in vitro transcription of the entire RNA pool was evaluated as a suitable way to preamplify the starting material prior to quantification and was effective in providing accurate RNA abundance profiles throughout the preimplantation period. However, the amplification appears to be template dependent because the amplification factors were higher for some genes.