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Context: Maternal-effect genes (MEGs) play a critical role in modulating both cellular and molecular biology events in preimplantation embryonic development. Damage-specific DNA binding protein 1 (DDB1) is a gene that participates in meiotic resumption, ovulation, and embryonic stem cell maintenance. Its function in preimplantation development is not well-studied., Aims: We aimed to explore the expression pattern, genomic heritage, and potential molecular mechanisms of DDB1 in preimplantation embryos in porcine., Methods: In this study, RNA interference, microinjection, RT-qPCR, immunofluorescence staining and single-cell RNA sequencing were used to explore the molecular function of DDB1 in porcine preimplantation embryos., Key Results: DDB1 was found to be expressed in germinal vesicle (GV) and Meiosis II (MII) oocytes and in preimplantation embryos. We confirmed it is a MEG. DDB1 -deficient blastocysts had a significantly reduced number of trophectoderm cells, an increased apoptotic cell number and increased apoptosis index. According to a next-generation sequencing (NGS) analysis, 236 genes (131 upregulated and 105 downregulated) significantly changed in the DDB1 -deficient morula. The myeloid leukaemia factor 1 (MLF1 ) and yes-associated protein 1 (YAP1 ) expressions were significantly upregulated and downregulated respectively, in the DDB1 -deficient morula. In combination with the decreased expression of TEAD4 , CDX2 , GATA3 , OCT4 , and NANOG and the increased expression of SOX2 in the blastocyst, DDB1 may play a role in determining lineage differentiation and pluripotency maintenance., Conclusions: DDB1 is a MEG and it plays a crucial role in porcine preimplantation embryonic development., Implications: This study provides a theoretical basis for further understanding the molecular mechanisms of preimplantation embryo development.

Maternal metabolic stress conditions are of growing importance in both human and dairy cattle settings as they can have significant repercussions on fertility. Upregulated lipolysis is a common trait associated with metabolic disorders and results in systemically elevated concentrations of non-esterified fatty acids (NEFAs). The effects of high NEFA concentrations on the follicular environment, oocyte and embryo development is well documented. However, knowledge on the effects of NEFAs within the oviduct, representing the initial embryonic growth environment, is currently lacking. Therefore, the experiments outlined here were designed to obtain fundamental insights into both the direct and indirect interactions between NEFAs, bovine oviductal cells and developing zygotes. Hence, zygotes were co-cultured with NEFA-pre-exposed bovine oviductal cells or subjected to simultaneous NEFA exposure during the co-culture period. The outcome parameters assessed were embryo development with cleavage (48h post insemination (pi)), morula (120-126h pi) and blastocyst (192h pi) rates, as well as morula intracellular lipid content and blastocyst quality using Bodipy and differential staining respectively. Our data suggest a direct embryotoxicity of NEFAs as well as impaired embryo development through a reduced oviductal ability to support and protect early embryo development.

The advent of metabolomics technology and its application to small samples has allowed us to non-invasively monitor the metabolic activity of embryos in a complex culture environment. The aim of this study was to apply metabolomics technology to the analysis of individual embryos from several species during in vitro development to gain an insight into the metabolomics pathways used by embryos and their relationship with embryo quality. Alanine is produced by both in vivo- and in vitro-derived human, murine, bovine and porcine embryos. Glutamine is also produced by the embryos of these four species, but only those produced in vitro. Across species, blastocysts significantly consumed amino acids from the culture medium, whereas glucose was not significantly taken up. There are significant differences in the metabolic profile of in vivo- compared with in vitro-produced embryos at the blastocyst stage. For example, in vitro-produced murine embryos consume arginine, asparagine, glutamate and proline, whereas in vivo-produced embryos do not. Human embryos produce more alanine, glutamate and glutamine, and consume less pyruvate, at the blastocyst compared with cleavage stages. Glucose was consumed by human blastocysts, but not at a high enough level to reach significance. Consumption of tyrosine by cleavage stage human embryos is indicative of blastocyst development, although tyrosine consumption is not predictive of blastocyst quality. Similarly, although in vivo-produced murine blastocysts consumed less aspartate, lactate, taurine and tyrosine than those produced in vitro, consumption of these four amino acids by in vitro-derived embryos with high octamer-binding transcription factor 4 (Oct4) expression, indicative of high quality, did not differ from those with low Oct4 expression. Further application of metabolomic technologies to studies of the consumption and/or production of metabolites from individual embryos in a complete culture medium could transform our understanding of embryo physiology and improve our ability to produce developmentally competent embryos in vitro.

Dibutyl phthalate (DBP), a widely used phthalate, is known to cause many serious diseases, especially in the reproductive system. However, little is known about the effects of its metabolite, mono-n-butyl phthalate (MBP), on preimplantation embryo development. In the present study, we found that treatment of embryos with 10⁻³ M MBP impaired developmental competency, whereas exposure to 10⁻⁴ M MBP delayed the progression of preimplantation embryos to the blastocyst stage. Furthermore, reactive oxygen species (ROS) levels in embryos were significantly increased following treatment with 10⁻³ M MBP. In addition, 10⁻³ M MBP increased apoptosis via the release of cytochrome c, whereas immunofluorescent analysis revealed that exposure of preimplantation embryos to MBP concentration-dependently (10⁻⁵, 10⁻⁴ and 10⁻³ M) decreased DNA methylation. Together, the results indicate a possible relationship between MBP exposure and developmental failure in preimplantation embryos.

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

The main objective of the present study was to analyse the quantitative expression pattern of genes from a subtracted blastocyst transcriptome throughout the preimplantation developmental stages of in vitro-produced bovine oocytes and embryos. For this purpose, Day 5 morula (M) cDNAs were subtracted from Day 7 blastocyst (B) cDNAs (B-M) and used to establish a B-M subtracted cDNA library, as reported previously. From the total generated clones, 19 were analysed quantitatively. The mRNA samples isolated from pools of immature oocytes (n = 150), mature oocytes (n = 150) and two-cell (n = 80), four-cell (n = 40), eight-cell (n = 20), morula (n = 6) and blastocyst (n = 3) embryos were reverse transcribed and subjected to real-time polymerase chain reaction (PCR) using sequence-specific primers and SYBR green as the DNA dye. A relative standard curve method was used to analyse the real-time data taking the morula stage as a calibrator. Applying suppression subtractive hybridisation (SSH), a total of 71 clones, which represent 33 different expressed sequence tags, were generated and available for analysis. Most transcripts were analysed for the first time in bovine embryogenesis. The real-time PCR has validated the results of SSH positively for 84% (16/19) of transcripts, whereas 16% (3/19) showed deviation in the expression pattern from the one seen during SSH. Several transcript-specific expression patterns were observed for genes that play decisive roles in bovine embryogenesis. In addition to identification, accurately quantifying the expression profiles of transcripts during development will pave the way towards understanding the molecular mechanisms of embryogenesis and their potential role in early embryo development. Most importantly, the present study has contributed to the enrichment of bovine embryo gene collection by generating new transcripts involved in bovine embryo development.

The presence of inhibin subunits (alpha, betaA and betaB), activin binding protein follistatin and activin receptors (ActR-I, ActR-IB, ActR-II and ActR-IIB) mRNA transcripts in bovine oocytes and preimplantation embryos was examined by reverse transcription-polymerase chain reaction. Immature and matured oocytes, zygotes, 2-cell, 3-4-cell, 5-8-cell, 9-16-cell embryos, morulae, blastocysts and hatched blastocysts were produced by in vitro maturation, fertilization and culture for this study. Activin betaA subunit and follistatin transcripts were detected in all of the stages tested. However, alpha subunit transcripts were detected only in oocytes (immature and matured), blastocysts and hatched blastocysts, and no betaB subunit transcripts were found in any of the stages. Whereas ActR-I transcripts were detectable in all stages, ActR-IB transcripts were not detectable in oocytes or embryos except in matured oocytes. Activin type II receptors (ActR-II and ActR-IIB) transcripts were detectable in oocytes and embryos except for ActR-IIB, which was not found in the 5-8-cell stage embryos. The results suggest that bovine embryos may produce activin A (homodimer of the betaA subunits) at least from zygotes to morulae. Furthermore, bovine oocytes and embryos express the activin receptors mainly by the combination of ActR-I and either ActR-II or ActR-IIB.

Bovine embryos produced in vitro from the putative zygote stage to the blastocyst stage, and blastocysts freshly flushed from the uterus, were cultured in a physiological mixture of amino acids. Depletion of amino acids from the medium and, in a few cases, their appearance, was measured by high performance liquid chromatography. Amino acids were depleted at widely differing rates. The depletion of amino acids was higher when embryos at later developmental stages were cultured, implying an increase in amino acid requirement with development. Threonine was the only amino acid to be depleted at all stages of development; depletion increased from 0.18 +/- 0.07 pmol embryo-1 h-1 at the putative zygote stage to 1.96 +/- 0.49 pmol embryo-1 h-1 at the blastocyst stage. Glutamine was depleted at the putative zygote stage and the 4-cell stage (0.76 +/- 0.05 and 0.94 +/- 0.10 pmol embryo-1 h-1 respectively), but was not significantly depleted at the later stages. Alanine was the only amino acid that appeared consistently in the medium and its production increased progressively throughout development. Aspartate, glutamate, threonine and lysine were depleted significantly by blastocysts derived both in vitro and in vivo; the embryos in vivo also depleted arginine, phenylalanine, isoleucine and tyrosine. These results indicate that individual amino acids are depleted at different rates by bovine preimplantation embryos and suggest that amino acid requirements change during development.

The production of radiolabelled CO2 from [U-14C]glucose, [1-14C]lactate, and [U-14C]acetate was used to study the oxidative metabolism of embryos recovered from sheep, mice and cattle. Sheep embryos showed an increasing capacity to oxidize glucose after the 4- to 8-cell stage and oxidative turnover of this substrate at the blastocyst stage was four times that at the early stages. Decarboxylation of carbon-1 of lactate followed a pattern similar to that seen for glucose oxidation, but acetate oxidation was low and did not follow the trends with development seen for the other substrates. Furthermore, estimates of incorporation of acetate into the macromolecules of sheep embryos were low compared with similar estimates for glucose and, unlike glucose, did not increase with development. Oxidation of all three substrates by mouse embryos increased with development but the rate of CO2 production from acetate was low compared with that from the other substrates. A combination of lactate or glucose with acetate had no influence on the utilization of acetate by mouse morulae/early blastocysts, nor did acetate influence utilization of the other substrates. Cattle morulae/early blastocysts also produced more CO2 from glucose and lactate than from acetate and the incorporation of carbon from acetate into the macromolecules of these embryos was less than from glucose. Overall, cattle embryos showed the greatest ability to metabolize acetate but were not as effective in using the other substrates as either sheep or mouse embryos at the same stage.

The metabolism of, and retention of radioactivity from, radiolabelled glucose, glutamine and pyruvate were measured in individual cattle embryos produced in vitro from the 2-cell to hatched blastocyst stage. Uptake was defined as the numeric sum of metabolism and retention of radiolabel. Glucose metabolism increased significantly between the 8- and 16-cell stages, but was accompanied by a much larger increase in glucose uptake. Consequently, the proportion of glucose uptake that was metabolized through the pentose-phosphate and Embden-Meyerhof pathways reached a minimum at those stages. From the compacted morula stage onward, the calculated uptake of [14C]glucose was only 25 to 33% of that calculated for [5-3H]glucose. This suggests that 66 to 75% of glucose carbon leaves the embryo, after metabolism to phosphoenolpyruvate, in some form other than CO2. Little or no glucose metabolism by the Krebs cycle could be detected at any stage. Both glutamine and pyruvate metabolism were relatively high at the 2- and 4-cell stages, declined to a minimum at the compacted morula stage and then increased with blastulation. Glutamine metabolism continued to increase with expansion and hatching of the blastocyst, but pyruvate metabolism did not. This suggest that, relative to the activity of the pathway from pyruvate to 2-oxoglutarate, the activity of the 2-oxoglutarate-to-oxaloacetate segment of the Krebs cycle is of increasing significance during expansion and hatching of the cattle blastocyst.

Embryos were collected from superovulated donors at various intervals from onset of oestrus, ranging from Day 1.5 to Day 6. In addition, blastocysts obtained from the culture of 1-cell embryos collected in vivo or of oocytes matured and fertilized in vitro were used to assess the effects of in vitro manipulation and culture on glucose utilization. Glycolytic activity was determined by the conversion of [5-3H]glucose to 3H2O, and oxidation of glucose was determined by the conversion of [U-14C]glucose to 14CO2. Glucose utilization increases significantly from the 8-cell stage and during compaction and blastulation. Glucose oxidation was at a relatively low level (5-12% of total utilization) compared with glycolysis. No difference was observed between the glycolytic activity of blastocysts derived from in vivo or in vitro sources. However, glucose oxidation was lower (P less than 0.05) in blastocysts derived from the culture of 1-cell embryos or from oocytes matured and fertilized in vitro. Exogenous tricarboxylic acid cycle substrates (i.e. pyruvate and lactate supplied in the medium) affected the level of glucose oxidation.

Day-4 mouse embryos grew well in culture media supplemented with macromolecular components of uterine fluids recovered on day 3, 4 or 5 of pregnancy and pseudopregnancy. Addition of these components to media during a 2-h pulse culture had no significant effect on the incorporation of glucose carbon by morulae/early blastocysts. However, various fractions of uterine luminal macro-molecules significantly increased the turnover of glucose carbon incorporated into acid-soluble and acid-insoluble glycogen, into nucleic acids and into proteins during a 24-h chase culture. These effects were due mainly to components with a molecular weight between 1000 and 10,000 Da and the activity was most marked in fluids collected on day 5 of pregnancy or pseudopregnancy. Oxidation of glucose during a 4-h incubation was inhibited in the presence of certain uterine macromolecules but most consistently by the large molecular weight component (greater than 300,000 Da). Some differences were noted in the inhibitory activity of macromolecules obtained from pregnant and pseudopregnant sources. There was little evidence of an effect of uterine-fluid components on lactate production from glucose.

The cleavage rate and development of two-cell mouse embryos to the morulae stage in co-culture with mouse oviduct cells was studied in vitro and compared with those achieved in vivo. Embryos were cultured in Whittingham's T6 (T6), T6 supplemented with fetal calf serum (FCS) and in co-culture with either Dulbecco's Modified Eagles Medium supplemented with sodium lactate (DMEM + 1a) or a modification of T6 medium containing vitamins and amino acids (T6 + v + aa). Co-culture of oviductal cells with DMEM + la medium supported two-cell mouse embryo development to eight cells at a rate significantly better (P less than 0.001) than T6, but the rate of embryo development was not equivalent to that in vivo. DMEM + la alone was inadequate as an embryo culture medium. Co-cultures using T6 + v + aa with mouse oviductal cells were prepared from mice at days 1, 2 or 3 of pseudopregnancy. Day 2 and 3 co-cultures allowed two-cell embryos to develop at a rate comparable to that in vivo up to the mid eight-cell stage (68 h after hCG), but by 76 h after hCG embryos were retarded. Transfer to pseudopregnant recipients of embryos co-cultured with day 2 oviductal cells until 68 h after hCG resulted in a rate of fetal development equivalent to that of embryos grown in vivo. Our results show that co-culture of early cleavage-stage embryos with mouse oviductal cells allows embryos to retain cleavage rates and viability comparable to in vivo development.

The utilization of the acid-soluble glycogen pool in pulse-labelled embryos was significantly enhanced during 24- and 48-h chase culture under low oxygen concentrations of 5, 2.5 and 1%. The lower the oxygen tension the greater was the turnover in the pool. The morphological development of embryos was equally as good at very low oxygen concentrations as when embryos were cultured in 5-20% oxygen. Reduction in oxygen concentration enhanced the oxidative utilization of substrate, as measured by rate of carbon dioxide production. The present study could provide an explanation for the discrepancy in glycogen content between mouse blastocysts developing in utero and in vitro and for the reported beneficial effects of low oxygen concentration during development of embryos in culture.