Transcriptome profiling of bovine inner cell mass and trophectoderm derived from in vivo generated blastocysts

Bta-miR-665 improves bovine blastocyst development through its influence on microtubule dynamics and apoptosis

Extracellular vesicles (EVs) contain microRNAs (miRNAs), which are important regulators of embryonic development. Nevertheless, little is known about the precise molecular processes controlling blastocyst development and quality. In a previous study, we identified bta-miR-665 as one of the miRNAs more abundantly present in extracellular vesicles of embryo-conditioned culture media of blastocysts compared to degenerate ones. Here, we investigated the effect and regulatory roles of bta-miR-665 in blastocyst development by supplementation of bta-miR-665 mimics or inhibitors to the culture media. Supplementation of bta-miR-665 mimics improved cleavage and blastocyst rate (P < 0.01), and blastocyst quality as indicated by increased inner cell mass rates and reduced apoptotic cell ratios (P < 0.01). Furthermore, supplementation of bta-miR-665 inhibitors had the opposite effect on these phenotypes. Low input transcriptome analysis and RT-qPCR revealed that bta-miR-665 acts on genes linked to microtubule formation and apoptosis/cell proliferation. These insights not only elucidate the important role of bta-miR-665 in embryo development, but also underscore its potential in improving reproductive efficiency in bovine embryo culture.

Early Cell Lineage Formation in Mammals: Complexity, Species Diversity, and Susceptibility to Disruptions Impacting Embryo Viability

The emergence of the earliest cell lineages in mammalian embryos is a complex process that utilizes an extensive network of chromatin regulators, transcription factors, cell polarity regulators, and cellular signaling pathways. These factors and pathways operate over a protracted period of time as embryos cleave, undergo compaction, and form blastocysts. The first cell fate specification event separates the pluripotent inner cell mass from the trophectoderm lineage. The second event separates pluripotent epiblast from hypoblast. This review summarizes over 50 years of study of these early lineage forming events, addressing the complexity of the network of interacting molecules, cellular functions and pathways that drive them, interspecies differences, and aspects of these mechanisms that likely underlie their high susceptibility to disruption by numerous environmental factors that can compromise embryo viability, such as maternal health and diet, environmental toxins, and other stressors.

Transverse and vertical incisions affect the viability of in vitro-produced embryos submitted to a simplified microsurgery approach

Integrating in vitro embryo production with embryonic microsurgery facilitates the generation of monozygotic twins. However, despite their potential benefits, these methods have not been widely adopted in commercial settings because of their substantial costs. Hence, there is a need to streamline the bisection procedure while ensuring efficient production of viable demi-embryos. In this study, we investigated the impact of different orientations of microsurgical incisions in relation to inner cell mass on embryonic development, morphology, viability, and expression of cell fate protein markers using a simplified microsurgery approach. Ovaries were transported from the slaughterhouse to the laboratory and aspirated to obtain oocytes that were selected and subjected to in vitro embryo production. The selected expanded blastocysts (n = 204) underwent microsurgery. The blastocysts were immobilized to facilitate incision using an adapted microblade, yielding demi-embryos (vertical incision) and viable embryonic fragments (transverse incision). The structures were then re-cultured for 12 h. Viability was assessed by measuring the re-expansion rate after re-culture, followed by immunofluorescence analysis of proteins (CDX2 and NANOG) and apoptosis analysis using terminal deoxynucleotyl transferase dUTP nick end-labeling (TUNEL). Microsurgically derived embryos exhibited remarkable plasticity, as evidenced by a slight reduction (P < 0.05) in the re-expansion rate (transverse 64.2 % and vertical 57.2 %) compared to that of the control group (blastocysts without microsurgery) (86.7 %). They also demonstrated the ability of morphological reconstitution after culturing. Despite the anticipated decrease (P < 0.05) in the total number of cells and embryo volume, microsurgery did not result in a significant increase (P > 0.05) in the number of apoptotic cells. Furthermore, microsurgery led to higher (P < 0.05) expression of markers associated with pluripotency, indicating its efficiency in preserving regenerative capacity. Moreover, microsurgery, whether followed by immunosurgery or not, made the isolation of embryonic cells easier. In conclusion, both transverse and vertical microsurgery incisions enabled the production of identical demi-embryos and served as tools for isolating embryonic cells without compromising the resumption of development and the apoptotic index.

Influence of choline and follistatin supplementation during in vitro bovine oocyte maturation on oocyte competence and blastocyst development

Metabolite supplementation during in vitro embryo development improves blastocyst quality, however, our understanding of the incorporation of metabolites during in vitro maturation (IVM) is limited. Two important metabolites, follistatin and choline, have beneficial impacts during in vitro culture; however, effects of supplementation during IVM are unknown. The objective of this study was to investigate combining choline and follistatin during IVM on bovine oocytes and subsequent early embryonic development. We hypothesized that supplementation of choline with follistatin would synergistically improve oocyte quality and subsequent early embryonic development. Small follicles were aspirated from slaughterhouse ovaries to obtain cumulus oocyte complexes for IVM with choline (0, 1.3 or 1.8 mM) and follistatin (0 or 10 ng/mL) supplementation in a 3 × 2 design. A subset of oocytes underwent transcriptomic analysis, the remaining oocytes were used for IVF and in vitro culture (IVC). Transcript abundance of CEPT1 tended to be reduced in oocytes supplemented with 1.8 mM choline and follistatin compared to control oocytes (P = 0.07). Combination of follistatin with 1.8 mM choline supplementation during maturation, tended (P = 0.08) to reduce CPEB4 in oocytes. In the blastocysts, HDCA8, NANOG, SAV1 and SOX2 were increased with choline 1.8 mM supplementation without follistatin (P < 0.05), while HDCA8 and SOX2 were increased when follistatin was incorporated (P < 0.05). The combination of choline and follistatin during oocyte maturation may provide a beneficial impact on early embryonic development. Further research is warranted to investigate the interaction between these two metabolites during early embryonic development and long-term influence on fetal development.

In vitro developmental competence of bovine demi-embryos generated by blastomere separation and blastocyst bisection

The efficiency of bovine in vitro embryo production can be significantly improved by splitting embryos at different stages. However, the blastocyst quality of in vitro-produced demi-embryos remains unexplored. The objective of this research was to compare embryo developmental rates and quality of bovine demi-embryos produced by two different strategies: (a) embryo bisection (BSEC) and (b) 2-cell blastomere separation (BSEP). To determine demi-embryos quality, we evaluated total blastocyst cell number and proportion of SOX2+ cells. Additionally, the expression of SOX2, NANOG, OCT4, CDX2, IFNT, BAX and BCL genes and let-7a and miRNA-30c Micro RNAs was analysed. BSEP resulted in improved blastocyst development, higher ICM cells and a significantly higher expression of IFNΤ than demi-embryos produced by BSEC. Let-7a, which is associated with low pregnancy establishment was detected in BSEC, while miRNA-30c expression was observed in all treatments. In conclusion, BSEP of 2-cell embryos is more efficient to improve in vitro bovine embryo development and to produce good quality demi-embryos based on ICM cell number and the expression pattern of the genes explored compared to BSEC.

Developmental, cytogenetic and epigenetic consequences of removing complex proteins and adding melatonin during in vitro maturation of bovine oocytes

Background

In vitro maturation (IVM) of germinal vesicle intact oocytes prior to in vitro fertilization (IVF) is practiced widely in animals. In human assisted reproduction it is generally reserved for fertility preservation or where ovarian stimulation is contraindicated. Standard practice incorporates complex proteins (CP), in the form of serum and/or albumin, into IVM media to mimic the ovarian follicle environment. However, the undefined nature of CP, together with batch variation and ethical concerns regarding their origin, necessitate the development of more defined formulations. A known component of follicular fluid, melatonin, has multifaceted roles including that of a metabolic regulator and antioxidant. In certain circumstances it can enhance oocyte maturation. At this stage in development, the germinal-vesicle intact oocyte is prone to aneuploidy and epigenetic dysregulation.

Objectives

To determine the developmental, cytogenetic and epigenetic consequences of removing CP and including melatonin during bovine IVM.

Materials and methods

The study comprised a 2 x 2 factorial arrangement comparing (i) the inclusion or exclusion of CP, and (ii) the addition (100 nM) or omission of melatonin, during IVM. Cumulus-oocyte complexes (COCs) were retrieved from stimulated cycles. Following IVM and IVF, putative zygotes were cultured to Day 8 in standard media. RNAseq was performed on isolated cumulus cells, cytogenetic analyses (SNP-based algorithms) on isolated trophectoderm cells, and DNA methylation analysis (reduced representation bisulfite sequencing) on isolated cells of the inner-cell mass.

Results

Removal of CP during IVM led to modest reductions in blastocyst development, whilst added melatonin was beneficial in the presence but detrimental in the absence of CP. The composition of IVM media did not affect the nature or incidence of chromosomal abnormalities but cumulus-cell transcript expression indicated altered metabolism (primarily lipid) in COCs. These effects preceded the establishment of distinct metabolic and epigenetic signatures several days later in expanded and hatching blastocysts.

Conclusions

These findings highlight the importance of lipid, particularly sterol, metabolism by the COC during IVM. They lay the foundation for future studies that seek to develop chemically defined systems of IVM for the generation of transferrable embryos that are both cytogenetically and epigenetically normal.

Adaptative response to changes in pyruvate metabolism on the epigenetic landscapes and transcriptomics of bovine embryos

The epigenetic reprogramming that occurs during the earliest stages of embryonic development has been described as crucial for the initial events of cell specification and differentiation. Recently, the metabolic status of the embryo has gained attention as one of the main factors coordinating epigenetic events. In this work, we investigate the link between pyruvate metabolism and epigenetic regulation by culturing bovine embryos from day 5 in the presence of dichloroacetate (DCA), a pyruvate analog that increases the pyruvate to acetyl-CoA conversion, and iodoacetate (IA), which inhibits the glyceraldehyde-3-phosphate dehydrogenase (GAPDH), leading to glycolysis inhibition. After 8 h of incubation, both DCA and IA-derived embryos presented higher mitochondrial membrane potential. Nevertheless, in both cases, lower levels of acetyl-CoA, ATP-citrate lyase and mitochondrial membrane potential were found in blastocysts, suggesting an adaptative metabolic response, especially in the DCA group. The metabolic alteration found in blastocysts led to changes in the global pattern of H3K9 and H3K27 acetylation and H3K27 trimethylation. Transcriptome analysis revealed that such alterations resulted in molecular differences mainly associated to metabolic processes, establishment of epigenetic marks, control of gene expression and cell cycle. The latter was further confirmed by the alteration of total cell number and cell differentiation in both groups when compared to the control. These results corroborate previous evidence of the relationship between the energy metabolism and the epigenetic reprogramming in preimplantation bovine embryos, reinforcing that the culture system is decisive for precise epigenetic reprogramming, with consequences for the molecular control and differentiation of cells.

Pre-Implantation Bovine Embryo Evaluation-From Optics to Omics and Beyond

Approximately 80% of the ~1.5 million bovine embryos transferred in 2021 were in vitro produced. However, only ~27% of the transferred IVP embryos will result in live births. The ~73% pregnancy failures are partly due to transferring poor-quality embryos, a result of erroneous stereomicroscopy-based morphological evaluation, the current method of choice for pre-transfer embryo evaluation. Numerous microscopic (e.g., differential interference contrast, electron, fluorescent, time-lapse, and artificial-intelligence-based microscopy) and non-microscopic (e.g., genomics, transcriptomics, epigenomics, proteomics, metabolomics, and nuclear magnetic resonance) methodologies have been tested to find an embryo evaluation technique that is superior to morphologic evaluation. Many of these research tools can accurately determine embryo quality/viability; however, most are invasive, expensive, laborious, technically sophisticated, and/or time-consuming, making them futile in the context of in-field embryo evaluation. However accurate they may be, using complex methods, such as RNA sequencing, SNP chips, mass spectrometry, and multiphoton microscopy, at thousands of embryo production/collection facilities is impractical. Therefore, future research is warranted to innovate field-friendly, simple benchtop tests using findings already available, particularly from omics-based research methodologies. Time-lapse monitoring and artificial-intelligence-based automated image analysis also have the potential for accurate embryo evaluation; however, further research is warranted to innovate economically feasible options for in-field applications.

Species-specific molecular differentiation of embryonic inner cell mass and trophectoderm: A systematic review

A wide-ranging review study regarding the molecular characterization of the first cell lineages of the developmental embryo is lacking, especially for the primary events during earliest differentiation which leads to the determination of cellular fate. Here, a systematic review and meta-analysis were conducted according to PRISMA guidelines. MEDLINE-PubMed was searched based on an established search strategy through April 2021. Thirty-six studies fulfilling the inclusion criteria were subjected to qualitative and quantitative analysis. Among the studies, 50 % (18/36) used mice as an animal model, 22.2 % (8/36) pigs, 16.7 % (6/36) cattle, 5.5 % (2/36) humans, and 2.8 % (1/36) goats as well as 2.8 % (1/36) equine. Our results demonstrated that each of the first cell lineages of embryos requires a certain pattern of expression to establish the cellular determination of fate. Moreover, these patterns are shared by many species, particularly for those molecules that have already been identified in the literature as biomarkers. In conclusion, the present study integrated carefully chosen studies regarding embryonic development and first cellular decisions in mammalian species and summarized the information about the differential characterization of the first cell lineages and their possible relationship with specific gene expression.

Disruption of CSF2RA in the bovine preimplantation embryo reduces development and affects embryonic gene expression in utero

The hypothesis that CSF2 plays a role in the preimplantation development of the bovine embryo was tested by evaluating consequences of inactivation of CSF2RA (the functional receptor in the embryo) for development of embryos in utero. CRISPR/Cas9 was used to alter sequences on exon 5 and intron 5 of CSF2RA, Control embryos were injected with Cas9 mRNA only. Embryos > 16 cells at day 5 after insemination were transferred to synchronized recipient females in groups of 7 to 24. Embryos were flushed from the uterus two days later. The proportion of recovered embryos that developed to the blastocyst stage was lower for knockout embryos (39%) than for control embryos (63%). RNA sequencing of individual morulae and blastocysts indicated a total of 27 (morula) or 15 (blastocyst) differentially-expressed genes (false discovery rate <0.05). Gene set enrichment analysis indicated that the knockout affected genes playing roles in several functions including cell signaling and glycosylation. It was concluded that signaling through CSF2RA is not obligatory for development of the bovine preimplantation embryo to the blastocyst stage but that CSF2 signaling does enhance the likelihood that the embryo can become a blastocyst and result in specific changes in gene expression.

Unhatched bovine blastocysts express all transcripts of the estrogen biosynthetic pathway, but steroid hormone synthesis could not yet be demonstrated

Early embryos of rodent species and rabbits but also farm animals such as pigs, horses and cattle produce estrogens, which are considered important regulators of the implantation process. In cattle, the exact stage at which embryonic estrogen synthesis commences is yet unknown. However, this information is regarded as important to consider a possible role of embryonic estrogens in preimplantation development. Therefore, in this study, we first used quantitative reverse transcription PCR to examine the mRNA expression of the enzymes required for the conversion of cholesterol into free and sulfonated estrogens (CYP11A1, CYP17A1, HSD3B, CYP19A1, and SULT1E1), the cholesterol carrier protein STAR, and the estrogen receptors ESR1 and ESR2 in in vitro produced morulae and unhatched blastocysts (d 6-9). Only in the blastocysts, were the mRNAs of the entire estrogen biosynthesis chain and of both estrogen receptors clearly present, whereas mRNA specific to ESRs was already detectable in the morulae. We also examined the expression of the corresponding enzymes in blastocysts at the protein level. None of the enzymes were detectable by capillary-based western analysis. Immunofluorescence methods were established for the detection of CYP17A1, CYP19A1, and SULT1E1. CYP17A1 was observed in the inner cell mass and trophectoderm, whereas CYP19A1 and SULT1E1 were present only in trophectoderm. An attempt to detect estrogen sulfotransferase activity was unsuccessful. Despite clear evidence that some elements of the estrogen biosynthetic pathway are also present at the protein level, it remains to be clarified whether the enzyme cascade underlying estrogen production is already functional in unhatched blastocysts.

Effects of Extra-Long-Acting Recombinant Bovine FSH (bscrFSH) on Cattle Superovulation

Over the last few years, several commercial FSH products have been developed for cattle superovulation (SOV) purposes in Multiple Ovulation and Embryo Transfer (MOET) programs. The SOV response is highly variable among individuals and remains one of the main limiting factors in obtaining a profitable number of transferable embryos. In this study, follicle stimulating hormone (FSH) from different origins was included in two SOV protocols, (a) FSH from purified pig pituitary extract (NIH-FSH-p; two doses/day, 12 h apart, four consecutive days); and (b) extra-long-acting bovine recombinant FSH (bscrFSH; a single dose/day, four consecutive days), to test the effects of bscrFSH on the ovarian response, hormone profile levels, in vivo embryo production and the pluripotency gene expression of the obtained embryos. A total of 68 healthy primiparous red Angus cows (Bos taurus) were randomly distributed into two experimental groups (n = 34 each). Blood sample collection for progesterone (P4) and cortisol (C) level determination was performed together with ultrasonographic assessment for ovarian size, follicles (FL) and corpora lutea (CL) quantification in each SOV protocol (Day 0, 4, 8, and 15). Moreover, FSH profiles were monitorised throughout both protocols (Day 0, 4, 5, 6, 7, 8, 9, 10, and 15). In vivo embryo quantity and quality (total structures, morulae, blastocysts, viable, degenerated and blocked embryos) were recorded in each SOV protocol. Finally, embryo quality in both protocols was assessed by the analysis of the expression level of crucial genes for early embryo development (OCT4, IFNt, CDX2, BCL2, and BAX). P4 and cortisol concentration peaks in both SOV protocols were obtained on Day 15 and Day 8, respectively, which were statistically different compared to the other time-points (p < 0.05). Ovarian dimensions increased from Day 0 to Day 15 irrespective of the SOV protocol considered (p < 0.05). Significant changes in CL number were observed over time till Day 15 irrespective of the SOV protocol applied (p < 0.05), being non- significantly different between SOV protocols within each time-point (p > 0.05). The number of CL was higher on Day 15 in the bscrFSH group compared to the NIH-FSH-p group (p < 0.05). The number of embryonic structures recovered was higher in the bscrFSH group (p = 0.025), probably as a result of a tendency towards a greater number of follicles developed compared to the NIH-FSH-p group. IFNt and BAX were overexpressed in embryos from the bscrFSH group (p < 0.05), with a fold change of 16 and 1.3, respectively. However, no statistical differences were detected regarding the OCT4, CDX2, BCL2, and BCL2/BAX expression ratio (p > 0.05). In conclusion, including bscrFSH in SOV protocols could be an important alternative by reducing the number of applications and offering an improved ovarian response together with better embryo quality and superior performance in embryo production compared to NIH-FSH-p SOV protocols.

How the environment affects early embryonic development

In the field of animal reproduction, the environment associated with gametes and embryos refers to the parents' condition as well as conditions surrounding gametes and embryos in vivo or in vitro . This environment is now known to influence not only the functionality of the early embryo but potentially the future phenotype of the offspring. Using transcriptomic and epigenetic molecular analysis, and the bovine model, recent research has shown that both the female and the male metabolic status, for example age, can affect gene expression and gene programming in the embryo. Evidence demonstrates that milking cows, which are losing weight at the time of conception, generates compromised embryos and offspring with a unique metabolic signature. A similar phenomenon has been associated with different culture conditions and the IVF procedure. The general common consequence of these situations is an embryo behaving on 'economy' mode where translation, cell division and ATP production is reduced, potentially to adapt to the perceived future environment. Few epidemiological studies have been done in bovines to assess if these changes result in a different phenotype and more studies are required to associate specific molecular changes in embryos with visible consequences later in life.

Cross-species meta-analysis of transcriptome changes during the morula-to-blastocyst transition: metabolic and physiological changes take center stage

The morula-to-blastocyst transition (MBT) culminates with formation of inner cell mass (ICM) and trophectoderm (TE) lineages. Recent studies identified signaling pathways driving lineage specification, but some features of these pathways display significant species divergence. To better understand evolutionary conservation of the MBT, we completed a meta-analysis of RNA sequencing data from five model species and ICMTE differences from four species. Although many genes change in expression during the MBT within any given species, the number of shared differentially expressed genes (DEGs) is comparatively small, and the number of shared ICMTE DEGs is even smaller. DEGs related to known lineage determining pathways (e.g., POU5F1) are seen, but the most prominent pathways and functions associated with shared DEGs or shared across individual species DEG lists impact basic physiological and metabolic activities, such as TCA cycle, unfolded protein response, oxidative phosphorylation, sirtuin signaling, mitotic roles of polo-like kinases, NRF2-mediated oxidative stress, estrogen receptor signaling, apoptosis, necrosis, lipid and fatty acid metabolism, cholesterol biosynthesis, endocytosis, AMPK signaling, homeostasis, transcription, and cell death. We also observed prominent differences in transcriptome regulation between ungulates and nonungulates, particularly for ICM- and TE-enhanced mRNAs. These results extend our understanding of shared mechanisms of the MBT and formation of the ICM and TE and should better inform the selection of model species for particular applications.

Mitochondrial maturation in the trophectoderm and inner cell mass regions of bovine blastocysts

Cellular differentiation induces various morphological changes, including elongation, in mitochondria. Preimplantation embryos have round-shaped mitochondria, characteristic of undifferentiated cells. However, there is controversy regarding the precise mitochondrial morphology in blastocyst embryos, which are generated from two cell lineages: undifferentiated inner cell mass (ICM) and differentiated trophectoderm (TE). This study attempted to precisely determine mitochondrial morphology in these two blastocyst regions. Transmission electron microscopy analyses were conducted using more than 1000 mitochondria from blastocyst embryos. No significant differences were observed in the configuration of mitochondrial cristae and frequencies of hooded mitochondria, which are specific to embryos of livestock animals, between the ICM and TE. To accurately compare mitochondrial roundness between the ICM and TE, oblateness was calculated based on both the major and minor axes. Average oblateness was significantly greater in the TE than in the ICM (P < 0.01). These results indicate tissue-specific mitochondrial maturation with complete elongation in the TE at the blastocyst stage. Since mitochondrial elongation is closely associated with cellular metabolism and differentiation, the present study provides new insights for better understanding of early embryonic development in cattle.

PGE2 Supplementation of Oocyte Culture Media Improves the Developmental and Cryotolerance Performance of Bovine Blastocysts Derived From a Serum-Free in vitro Production System, Mirroring the Inner Cell Mass Transcriptome

The culture media used throughout the in vitro production (IVP) of bovine embryos remain complex. The serum added to culture media in order to improve embryo development negatively impacts the cryotolerance of blastocysts. Periconceptional prostaglandin E2 (PGE2) signaling is known to exert prosurvival effects on in vitro-generated blastocysts. The purpose of the present study was to evaluate the effects on developmental and cryotolerance performance of a serum-free (SF) IVP system that included defined oocyte culture media supplemented or not with PGE2, versus serum-containing (SC) IVP. RNA-sequencing analysis was used to examine the gene expression of ICM derived under the different IVP conditions. We assessed the degree of cryotolerance of grade-I blastocysts during a three-day post-thaw culture by measuring survival and hatching rates, counting trophectoderm and inner cell mass (ICM) blastomere numbers. We also determined the proportion of ICM cells expressing octamer-binding transcription factor 4 protein (OCT4/POU5F1). We showed that grade-I blastocyst development rates under SF + PGE2 conditions were similar to those obtained under SC conditions, although the cleavage rate remained significantly lower. SC IVP conditions induced changes to ICM gene expression relative to several metabolic processes, catabolic activities, cell death and apoptosis. These alterations were associated with significantly higher levels of ICM cell death at day 7 post-fertilization, and lower survival and hatching rates after thawing. SF IVP conditions supplemented or not with PGE2 induced changes to ICM gene expression related to DNA replication, metabolism and double-strand break repair processes, and were associated with significantly larger ICM cell populations after thawing. SF + PGE2 IVP induced changes to ICM gene expression related to epigenetic regulation and were associated with a significantly higher proportion of ICM cells expressing OCT4. For the first time, our study thus offers a comprehensive analysis of the ICM transcriptome regulated by IVP culture conditions in terms of the cellular changes revealed during culture for three days after thawing.

The global gene expression outline of the bovine blastocyst: reflector of environmental conditions and predictor of developmental capacity

Background

Morphological evaluation of embryos has been used to screen embryos for transfer. However, the repeatability and accuracy of this method remains low. Thus, evaluation of an embryo’s gene expression signature with respect to its developmental capacity could provide new opportunities for embryo selection. Since the gene expression outline of an embryo is considered as an aggregate of its intrinsic characteristics and culture conditions, we have compared transcriptome profiles of in vivo and in vitro derived blastocysts in relation to pregnancy outcome to unravel the discrete effects of developmental competence and environmental conditions on bovine embryo gene expression outlines. To understand whether the gene expression patterns could be associated with blastocyst developmental competency, the global transcriptome profile of in vivo (CVO) and in vitro (CVT) derived competent blastocysts that resulted in pregnancy was investigated relative to that of in vivo (NVO) and in vitro (NVT) derived blastocysts which did not establish initial pregnancy, respectively while to unravel the effects of culture condition on the transcriptome profile of embryos, the transcriptional activity of the CVO group was compared to the CVT group and the NVO group was compared to the NVT ones.

Results

A total of 700 differentially expressed genes (DEGs) were identified between CVO and NVO blastocysts. These gene transcripts represent constitutive regions, indel variants, 3′-UTR sequence variants and novel transcript regions. The majority (82%) of these DEGs, including gene clusters like ATP synthases, eukaryotic translation initiation factors, ribosomal proteins, mitochondrial ribosomal proteins, NADH dehydrogenase and cytochrome c oxidase subunits were enriched in the CVO group. These DEGs were involved in pathways associated with glycolysis/glycogenesis, citrate acid cycle, pyruvate metabolism and oxidative phosphorylation. Similarly, a total of 218 genes were differentially expressed between CVT and NVT groups. Of these, 89%, including TPT1, PDIA6, HSP90AA1 and CALM, were downregulated in the CVT group and those DEGs were overrepresented in pathways related to protein processing, endoplasmic reticulum, spliceasome, ubiquitone mediated proteolysis and steroid biosynthesis. On the other hand, although both the CVT and CVO blastocyst groups resulted in pregnancy, a total of 937 genes were differential expressed between the two groups. Compared to CVO embryos, the CVT ones exhibited downregulation of gene clusters including ribosomal proteins, mitochondrial ribosomal protein, eukaryotic translation initiation factors, ATP synthases, NADH dehydrogenase and cytochrome c oxidases. Nonetheless, downregulation of these genes could be associated with pre and postnatal abnormalities observed after transfer of in vitro embryos.

Conclusion

The present study provides a detailed inventory of differentially expressed gene signatures and pathways specifically reflective of the developmental environment and future developmental capacities of bovine embryos suggesting that transcriptome activity observed in blastocysts could be indicative of further pregnancy success but also adaptation to culture environment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07693-0.

Strategy to Establish Embryo-Derived Pluripotent Stem Cells in Cattle

Stem cell research is essential not only for the research and treatment of human diseases, but also for the genetic preservation and improvement of animals. Since embryonic stem cells (ESCs) were established in mice, substantial efforts have been made to establish true ESCs in many species. Although various culture conditions were used to establish ESCs in cattle, the capturing of true bovine ESCs (bESCs) has not been achieved. In this review, the difficulty of establishing bESCs with various culture conditions is described, and the characteristics of proprietary induced pluripotent stem cells and extended pluripotent stem cells are introduced. We conclude with a suggestion of a strategy for establishing true bESCs.

Oocyte maturation under lipotoxic conditions induces carryover transcriptomic and functional alterations during post-hatching development of good-quality blastocysts: novel insights from a bovine embryo-transfer model

STUDY QUESTION

Does oocyte maturation under lipolytic conditions have detrimental carry-over effects on post-hatching embryo development of good-quality blastocysts after transfer?

SUMMARY ANSWER

Surviving, morphologically normal blastocysts derived from bovine oocytes that matured under lipotoxic conditions exhibit long-lasting cellular dysfunction at the transcriptomic and metabolic levels, which coincides with retarded post-hatching embryo development.

WHAT IS KNOWN ALREADY

There is increasing evidence showing that following maturation in pathophysiologically relevant lipotoxic conditions (as in obesity or metabolic syndrome), surviving blastocysts of good (transferable) morphological quality have persistent transcriptomic and epigenetic alteration even when in vitro embryo culture takes place under standard conditions. However, very little is known about subsequent development in the uterus after transfer.

STUDY DESIGN, SIZE, DURATION

Bovine oocytes were matured in vitro in the presence of pathophysiologically relevant, high non-esterified fatty acid (NEFA) concentrations (HIGH PA), or in basal NEFA concentrations (BASAL) as a physiological control. Eight healthy multiparous non-lactating Holstein cows were used for embryo transfers. Good-quality blastocysts (pools of eight) were transferred per cow, and cows were crossed over for treatments in the next replicate. Embryos were recovered 7 days later and assessed for post-hatching development, phenotypic features and gene expression profile. Blastocysts from solvent-free and NEFA-free maturation (CONTROL) were also tested for comparison.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Recovered Day 14 embryos were morphologically assessed and dissected into embryonic disk (ED) and extraembryonic tissue (EXT). Samples of EXT were cultured for 24 h to assess cellular metabolic activity (glucose and pyruvate consumption and lactate production) and embryos' ability to signal for maternal recognition of pregnancy (interferon-τ secretion; IFN-τ). ED and EXT samples were subjected to RNA sequencing to evaluate the genome-wide transcriptome patterns.

MAIN RESULTS AND THE ROLE OF CHANCE

The embryo recovery rate at Day 14 p.i. was not significantly different among treatment groups (P > 0.1). However, higher proportions of HIGH PA embryos were retarded in growth (in spherical stage) compared to the more elongated tubular stage embryos in the BASAL group (P < 0.05). Focusing on the normally developed tubular embryos in both groups, HIGH PA exposure resulted in altered cellular metabolism and altered transcriptome profile particularly in pathways related to redox-regulating mechanisms, apoptosis, cellular growth, interaction and differentiation, energy metabolism and epigenetic mechanisms, compared to BASAL embryos. Maturation under BASAL conditions did not have any significant effects on post-hatching development and cellular functions compared to CONTROL.

LARGE-SCALE DATA

The datasets of RNA sequencing analysis are available in the NCBI's Gene Expression Omnibus (GEO) repository, series accession number GSE127889 (https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE127889). Datasets of differentially expressed genes and their gene ontology functions are available in the Mendeley datasets at http://dx.doi.org/10.17632/my2z7dvk9j.2.

LIMITATIONS, REASONS FOR CAUTION

The bovine model was used here to allow non-invasive embryo transfer and post-hatching recovery on Day 14. There are physiological differences in some characteristics of post-hatching embryo development between human and cows, such as embryo elongation and trophoblastic invasion. However, the main carry-over effects of oocyte maturation under lipolytic conditions described here are evident at the cellular level and therefore may also occur during post-hatching development in other species including humans. In addition, post-hatching development was studied here under a healthy uterine environment to focus on carry-over effects originating from the oocyte, whereas additional detrimental effects may be induced by maternal metabolic disorders due to adverse changes in the uterine microenvironment. RNA sequencing results were not verified by qPCR, and no solvent control was included.

WIDER IMPLICATIONS OF THE FINDINGS

Our observations may increase the awareness of the importance of maternal metabolic stress at the level of the preovulatory oocyte in relation to carry-over effects that may persist in the transferrable embryos. It should further stimulate new research about preventive and protective strategies to optimize maternal metabolic health around conception to maximize embryo viability and thus fertility outcome.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Flemish Research Fund (FWO grant 11L8716N and FWO project 42/FAO10300/6541). The authors declare there are no conflicts of interest.

Effects of choline on the phenotype of the cultured bovine preimplantation embryo

Choline is a precursor of acetylcholine, phosphatidylcholine, and the methyl-donor betaine. Reports indicate that supplementation with rumen-protected choline improves postpartum reproductive function of dairy cows. The objective was to determine whether addition of choline to culture medium of in vitro-produced embryos alters the phenotype of the resultant blastocysts. Treatments were choline chloride (ChCl; 0.004, 1.3, 1.8, and 6.37 mM) and phosphatidylcholine (1.3 mM). Treatment with 0.004 mM ChCl improved development to the blastocyst stage, increased blastocyst cell number, and increased the percentage of blastocysts that were hatching or hatched. Development was not affected by higher concentrations of ChCl but was reduced by 1.3 mM phosphatidylcholine. Treatment of embryos with 1.3 mM ChCl (but not other concentrations) increased expression in blastocysts of 11 of 165 genes examined (AMOT, NANOG, HDAC8, HNF4A, STAT1, MBNL3, SOX2, STAT3, KDM2B, SAV1, and GPAM) and decreased expression of one gene (ASS1). Treatment with 1.3 mM ChCl decreased global DNA methylation at d 3.5 of development and increased DNA methylation at d 7.5 in blastocysts. Treatment with 1.8 mM ChCl also increased methylation in blastocysts. In conclusion, addition of choline to the culture medium alters the phenotype of preimplantation bovine embryos produced in vitro. Choline chloride can act in a concentration-dependent manner to alter development, expression of specific genes, and DNA methylation.

Notch signaling in mouse blastocyst development and hatching

Background

Mammalian early embryo development requires a well-orchestrated interplay of cell signaling pathways. Notch is a major regulatory pathway involved in cell-fate determination in embryonic and adult scenarios. However, the role of Notch in embryonic pre-implantation development is controversial. In particular, Notch role on blastocyst development and hatching remains elusive, and a complete picture of the transcription and expression patterns of Notch components during this time-period is not available.

Results

This study provided a comprehensive view on the dynamics of individual embryo gene transcription and protein expression patterns of Notch components (receptors Notch1–4; ligands Dll1 and Dll4, Jagged1–2; and effectors Hes1–2), and their relationship with transcription of gene markers of pluripotency and differentiation (Sox2, Oct4, Klf4, Cdx2) during mouse blastocyst development and hatching. Transcription of Notch1–2, Jagged1–2 and Hes1 was highly prevalent and dynamic along stages of development, whereas transcription of Notch3–4, Dll4 and Hes2 had a low prevalence among embryos. Transcription levels of Notch1, Notch2, Jagged2 and Hes1 correlated with each other and with those of pluripotency and differentiation genes. Gene transcription was associated to protein expression, except for Jagged2, where high transcription levels in all embryos were not translated into protein. Presence of Notch signaling activity was confirmed through nuclear NICD and Hes1 detection, and downregulation of Hes1 transcription following canonical signaling blockade with DAPT. In vitro embryo culture supplementation with Jagged1 had no effect on embryo developmental kinetics. In contrast, supplementation with Jagged2 abolished Jagged1 transcription, downregulated Cdx2 transcription and inhibited blastocyst hatching. Notch signaling blockade by DAPT downregulated transcription of Sox2, and retarded embryo hatching.

Conclusion

Transcription of Notch genes showed a dynamic pattern along blastocyst development and hatching. Data confirmed Notch signaling activity, and lead to the suggestion that Notch canonical signaling may be operating through Notch1, Notch3, Jagged1 and Hes1. Embryo culture supplementation with Jagged1 and Jagged2 unveiled a possible regulatory effect between Jagged1, Cdx2 and blastocyst hatching. Overall, results indicate that a deregulation in Notch signaling, either by its over or under-activation, affects blastocyst development and hatching.

The maternal-to-zygotic transition in bovine in vitro-fertilized embryos is associated with marked changes in small non-coding RNAs†

In mammals, small non-coding RNAs (sncRNAs) have been reported to be important during early embryo development. However, a comprehensive assessment of the inventory of sncRNAs during the maternal-to-zygotic transition (MZT) has not been performed in an animal model that better represents the sncRNA biogenesis pathway in human oocytes and embryos. The objective of this study was to examine dynamic changes in expression of sncRNAs during the MZT in bovine embryos produced by in vitro fertilization (IVF), which occurs at the 8-cell stage. An unbiased, discovery-based approach was employed using small RNAseq to profile sncRNAs in bovine oocytes, 8-cell stage embryos and blastocyst stage embryos followed by network and ontology analyses to explore the functional relevance of differentially expressed micro-RNAS (miRNAs). The relative abundance of miRNAs was markedly higher in 8-cell stage embryos compared to oocytes or blastocyst stage embryos. This shift in miRNA population was largely associated with upregulation of miRNAs predicted to target genes involved in the biological processes of cell development, cell division, Wnt signaling, and pluripotency, among others. Distinct populations of piwi-interacting-like RNAs (pilRNAs) were identified in bovine oocytes and blastocyst stage embryos, though pilRNAs were nearly absent in 8-cell stage embryos. Also, small nucleolar RNAs were highly expressed in 8-cell stage embryos. Overall, these data reveal a strong dynamic shift in the relative abundance of sncRNAs associated with the MZT in bovine oocytes and embryos, suggesting that these molecules may play important roles in the shift from maternal to zygotic control of gene expression.

Genome-wide histone modification profiling of inner cell mass and trophectoderm of bovine blastocysts by RAT-ChIP

Chromatin immunoprecipitation coupled with next-generation sequencing (ChIP-seq) has revolutionized our understanding of chromatin-related biological processes. The method, however, requires thousands of cells and has therefore limited applications in situations where cell numbers are limited. Here we describe a novel method called Restriction Assisted Tagmentation Chromatin Immunoprecipitation (RAT-ChIP) that enables global histone modification profiling from as few as 100 cells. The method is simple, cost-effective and takes a single day to complete. We demonstrate the sensitivity of the method by deriving the first genome-wide maps of histone H3K4me3 and H3K27me3 modifications of inner cell mass and trophectoderm of bovine blastocyst stage embryos.

Dynamic status of lysosomal cathepsin in bovine oocytes and preimplantation embryos

Lysosomal cathepsin, in particular cathepsin B (CTSB), plays an important role in implantation, pregnancy, and embryonic development. However, little is known about the mechanism related to the dynamic status of lysosomal cathepsins in bovine oocytes and preimplantation embryos. In the present study, we investigated the dynamics of gene expression, activity, and immunolocalization of CTSB, as well as the activities of lysosome, in bovine oocytes and preimplantation embryos. After gene expression analysis of several cathepsin-related genes, transcript levels of CTSB, CTSD and CTSZ were highest in Metaphase II (MII) oocytes followed by a significant decrease from the 8-cell embryo stage. Activity of CTSB showed a significant increase in 1-cell and morula stage embryos. Lysosomal activity was also significant higher in 1-cell and morula stages, which was consistent with CTSB activities. However, immunolocalization of CTSB did not show the similar pattern of CTSB and lysosomal activities. We also found significantly higher expression levels of CTSB transcript in the trophectoderm (TE) compared to inner cell mass (ICM), whereas activity and immunolocalization of CTSB showed an opposite pattern, i.e. significantly higher in ICM than TE. These patterns were confirmed by the same analysis using separated ICM and TE. Our results suggest that lysosomal CTSB has a pivotal role during embryonic development and differentiation, especially fertilization and the differentiation period.

Can trophectoderm RNA analysis predict human blastocyst competency?

A systematic review of the literature showed that trophectoderm biopsy could assist in the selection of healthy embryos for uterine transfer without affecting implantation rates. However, previous studies attempting to establish the relationship between trophectoderm gene expression profiles and implantation competency using either microarrays or RNA sequencing strategies, were not sufficiently optimized to handle the exceptionally low RNA inputs available from biopsied material. In this pilot study, we report that differential gene expression in human trophectoderm biopsies assayed by an ultra-sensitive next generation RNA sequencing strategy could predict blastocyst implantation competence. RNA expression profiles from isolated human trophectoderm cells were analysed with established clinical pregnancy being the primary endpoint. Following RNA sequencing, a total of 47 transcripts were found to be significantly differentially expressed between the trophectoderm cells from successfully implanted (competent) versus unsuccessful (incompetent) blastocysts. Of these, 36 transcripts were significantly down-regulated in the incompetent blastocysts, including Hydroxysteroid 17-Beta Dehydrogenase 1 (HSD17B1) and Cytochrome P450 Family 11 Subfamily A Member 1 (CYP11A1), while the remaining 11 transcripts were significantly up-regulated, including BCL2 Antagonist/Killer 1 (BAK1) and KH Domain Containing 1 Pseudogene 1 (KHDC1P1) of which the latter was always detected in the incompetent and absent in all competent blastocysts. Ontological analysis of differentially expressed RNAs revealed pathways involved in steroidogenic processes with high confidence. Novel differentially expressed transcripts were also noted by reference to a de novo sequence assembly. The selection of the blastocyst with the best potential to support full-term pregnancy following single embryo transfer could reduce the need for multiple treatment cycles and embryo transfers. The main limitation was the low sample size (N = 8). Despite this shortcoming, the pilot suggests that trophectoderm biopsy could assist with the selection of healthy embryos for embryo transfer. A larger cohort of samples is needed to confirm these findings. Abbreviations: AMA: advanced maternal age; ART: assisted reproductive technology; CP: clinical pregnancy; DE: differential expression; FDR: false discovery rate; IVF: in vitro fertilization; LD PCR: long distance PCR; qRT-PCR: quantitative real-time PCR; SET: single embryo transfer; TE: trophectoderm.

Specification of trophoblast from embryonic stem cells exposed to BMP4

Trophoblast (TB) comprises the outer cell layers of the mammalian placenta that make direct contact with the maternal uterus and, in species with a highly invasive placenta, maternal blood. It has its origin as trophectoderm, a single epithelial layer of extra-embryonic ectoderm that surrounds the embryo proper at the blastocyst stage of development. Here, we briefly compare the features of TB specification and determination in the mouse and the human. We then review research on a model system that has been increasingly employed to study TB emergence, namely the BMP4 (bone morphogenetic protein-4)-directed differentiation of human embryonic stem cells (ESCd), and discuss why outcomes using it have proved so uneven. We also examine the controversial aspects of this model, particularly the issue of whether or not the ESCd represents TB at all. Our focus here has been to explore similarities and potential differences between the phenotypes of ESCd, trophectoderm, placental villous TB, and human TB stem cells. We then explore the role of BMP4 in the differentiation of human pluripotent cells to TB and suggest that it converts the ESC into a totipotent state that is primed for TB differentiation when self-renewal is blocked. Finally we speculate that the TB formed from ESC is homologous to the trophectoderm-derived, invasive TB that envelopes the implanting conceptus during the second week of pregnancy.

Transcriptome Analysis of Immune Response of mIgM+ B Lymphocytes in Japanese Flounder (Paralichthys olivaceus) to Lactococcus lactis in vitro Revealed That IFN I-3 Could Enhance Their Phagocytosis

B cells have recently been proven to have phagocytic activities, but few studies have explored the relevant regulation mechanisms. In this study, we showed that the Japanese flounder (Paralichthys olivaceus) membrane-bound (m)IgM⁺ B lymphocyte population could phagocytose inactivated Lactococcus lactis with a mean phagocytic rate of 25%. High-purity mIgM⁺ B lymphocytes were subsequently sorted to investigate the cellular response to L. lactis stimulation in vitro. Transcriptome analysis identified 1,375 differentially expressed genes (DEGs) after L. lactis stimulation, including 975 upregulated and 400 downregulated genes. Many of these DEGs were enriched in multiple pathways associated with phagocytosis such as focal adhesion, the phagosome, and actin cytoskeleton regulation. Moreover, many genes involved in phagolysosomal function and antigen presentation were also upregulated after stimulation, indicating that mIgM⁺ B lymphocytes may degrade the internalized bacteria and present processed antigenic peptides to other immune cells. Interestingly, the type I interferon 3 (IFN I-3) gene was upregulated after L. lactis stimulation, and further analysis showed that the recombinant (r)IFN I-3 significantly enhanced phagocytosis of L. lactis and Edwardsiella tarda by mIgM⁺ B lymphocytes. In addition, significantly higher intracellular reactive oxygen species (ROS) levels were detected in mIgM⁺ B lymphocytes following rIFN I-3 treatment. We also found that IFN I-3 significantly upregulated Stat1 expression in mIgM⁺ B lymphocytes, and the enhancing effect of IFN I-3 on mIgM⁺ B lymphocyte-mediated phagocytosis was suppressed by fludarabine treatment. Collectively, these results demonstrate that mIgM⁺ B cell-mediated phagocytosis in the Japanese flounder is effectively triggered by bacterial stimulation, and further enhanced by IFN I-3, which itself may be regulated by Stat1.

Role of yes-associated protein 1, angiomotin, and mitogen-activated kinase kinase 1/2 in development of the bovine blastocyst

The morula-stage embryo is transformed into a blastocyst composed of epiblast, hypoblast, and trophectoderm (TE) through mechanisms that, in the mouse, involve the Hippo signaling and mitogen-activated kinase (MAPK) pathways. Using the cow as an additional model, we tested the hypotheses that TE and hypoblast differentiation were regulated by the Hippo pathway regulators, yes-associated protein 1 (YAP1) and angiomotin (AMOT), and MAPK kinase 1/2 (MAPK1/2). The presence of YAP1 and CDX2 in the nucleus and cytoplasm of MII oocytes and embryos was evaluated by immunofluorescence labeling. For both molecules, localization changed from cytoplasmic to nuclear as development advanced. Inhibition of YAP1 activity, either by verteporfin or a YAP1 targeting GapmeR, reduced the percent of zygotes that became blastocysts, the proportion of blastocysts that hatched and numbers of CDX2+ cells in blastocysts. Moreover, the YAP1-targeting GapmeR altered expression of 15 of 91 genes examined in the day 7.5 blastocyst. Treatment of embryos with an AMOT targeting GapmeR did not affect blastocyst development or hatching but altered expression of 16 of 91 genes examined at day 7.5 and reduced the number of CDX2+ nuclei and YAP1+ nuclei in blastocysts at day 8.5 of development. Inhibition of MAPK1/2 with PD0325901 did not affect blastocyst development but increased the number of epiblast cells. Results indicate a role for YAP1 and AMOT in function of TE in the bovine blastocyst. YAP1 can also affect function of the epiblast and hypoblast, and MAPK signaling is important for inner cell mass differentiation by reducing epiblast numbers.

Physiological profile of undifferentiated bovine blastocyst-derived trophoblasts

Trophectoderm of blastocysts mediate early events in fetal-maternal communication, enabling implantation and establishment of a functional placenta. Inadequate or impaired developmental events linked to trophoblasts directly impact early embryo survival and successful implantation during a crucial period that corresponds with high incidence of pregnancy losses in dairy cows. As yet, the molecular basis of bovine trophectoderm development and signaling towards initiation of implantation remains poorly understood. In this study, we developed methods for culturing undifferentiated bovine blastocyst-derived trophoblasts and used both transcriptomics and proteomics in early colonies to categorize and elucidate their functional characteristics. A total of 9270 transcripts and 1418 proteins were identified and analyzed based on absolute abundance. We profiled an extensive list of growth factors, cytokines and other relevant factors that can effectively influence paracrine communication in the uterine microenvironment. Functional categorization and analysis revealed novel information on structural organization, extracellular matrix composition, cell junction and adhesion components, transcription networks, and metabolic preferences. Our data showcase the fundamental physiology of bovine trophectoderm and indicate hallmarks of the self-renewing undifferentiated state akin to trophoblast stem cells described in other species. Functional features uncovered are essential for understanding early events in bovine pregnancy towards initiation of implantation.

Effect of macromolecule supplement on nuclear and cytoplasmic maturation, cryosurvival and in vitro embryo development of dromedary camel oocytes

The current evaluation of oocyte vitro maturation (IVM) media has progressed toward more defined conditions in human and livestock. In this study, the replacement of fetal calf serum (FCS) with bovine serum albumin (BSA) and polyvinyl alcohol (PVA) was evaluated during IVM in dromedary camel. Nuclear maturation rates in presence of FCS and PVA were comparable (81.6 ± 1 and 75.5 ± 5%, respectively). BSA, whether used alone or in combination with FCS, significantly reduced nuclear maturation (51.6 ± 3.9 and 54.6 ± 1.1%, respectively), compared to FCS and PVA. BSA also increased the rates of chromosome aberrations compared to FCS and PVA (25.7 ± 7.4, 8.8 ± 2.3 and 6.0 ± 2.0%, respectively). IVM macromolecule differentially affected morphological aspects of cumulus expansion and FCS promoted the highest dissociation of cumulus cells, compared to all the other groups. FCS significantly increased mean lipid intensity of oocytes compared to BSA, FCS-BSA and PVA which could explain the lower cryo-survival of oocytes matured in presence of FCS compared to BSA and PVA (56.1 ± 5.2, 91.0 ± 19.5, and 87.8 ± 6.7%, respectively). Mitochondrial activity was not affected by macromolecules, but oocytes cultured with PVA had the best redox status, compared to other IVM groups. Cleavage was not affected by IVM macromolecule, but FCS promoted significantly higher rate of morula development (51.6 ± 5.2 vs. 33.6 ± 2.9% for PVA) and blastocyst development (36.8 ± 1.4 vs. 20.5 ± 2.0% for BSA). Although adding FCS during IVM supported highest hatching rate of the resulting blastocysts, differential cell number showed no long lasting effect of IVM macromolecules on blastocyst quality. Obtained results suggest the possibility to switch from undefined to more defined IVM systems for efficient in vitro maturation and subsequent vitrification of dromedary camel oocytes. Keywords: camel, oocyte maturation, protein supplement, cryosurvival.

Dynamics of The Expression of Pluripotency and Lineage Specific Genes in The Pre and Peri-Implantation Goat Embryo

Objective

Two critical points of early development are the first and second lineage segregations, which are regulated by a wide spectrum of molecular and cellular factors. Gene regulatory networks, are one of the important components which handle inner cell mass (ICM) and trophectoderm (TE) fates and the pluripotency status across different mammalian species. Considering the importance of goats in agriculture and biotechnology, this study set out to investigate the dynamics of expression of the core pluripotency markers at the mRNA and protein levels.

Materials and Methods

In this experimental study, the expression pattern of three pluripotency markers (Oct4, Nanog and Sox2) and the linage specific markers (Rex1, Gata4 and Cdx2) were quantitatively assessed in in vitro matured (MII) oocytes and embryos at three distinctive stages: 8-16 cell stage, day-7 (D7) blastocysts and D14 blastocysts. Moreover, expression of Nanog, Oct4, Sox2 proteins, and their localization in the goat blastocyst was observed through immunocytochemistry.

Results

Relative levels of mRNA transcripts for Nanog and Sox2 in D3 (8-16 cell) embryos were significantly higher than D7 blastocysts and mature oocytes, while Oct4 was only significantly higher than D7 blastocysts. However, the expression pattern of Rex1, as an epiblast linage marker, decreased from the oocyte to the D14 stage. The expression pattern of Gata4 and Cdx2, as extra embryonic linage markers, also showed a similar trend from oocyte to D3 while their expressions were up-regulated in D14 blastocysts.

Conclusion

Reduction in Nanog, Oct4, Sox2 mRNA transcription and a late increase in extra embryonic linage markers suggests that the developmental program of linage differentiation is retarded in goat embryos compared to previously reported data on mice and humans. This is likely related to late the implantation in goats.

Interleukin-6 increases inner cell mass numbers in bovine embryos

Background

Work in other species suggests that interleukin-6 (IL6) promotes early embryo development. It was unclear whether IL6 serves as an embryokine in cultured bovine embryos. This work was undertaken to elucidate the role of IL6 during in vitro bovine embryo production.

Results

Transcripts for IL6 and its two cognate receptor subunits (IL6R, IL6ST) were confirmed in bovine embryos from the 1-cell to blastocyst stages. Supplementing 100 ng/ml recombinant bovine IL6 to in vitro-produced bovine embryos at day 1, 3 or 5 increased (P < 0.05) inner cell mass (ICM) cell number and the ICM:trophectoderm (TE) ratio but not TE cell number. No increase in ICM or TE cell number was observed after supplementation of 1 or 10 ng/ml IL6 beginning at either day 1 or 5. Sequential supplementation with 100 ng/ml IL6 at both day 1 and 5 (for a total of 200 ng/ml IL6) increased (P < 0.05) ICM cell number to a greater extent than supplementing IL6 at a single time period in one study but not a second study. Additionally, providing 200 ng/ml IL6 beginning at day 1 or 5 yielded no further increase on ICM cell numbers when compared to supplementing with 100 ng/ml IL6. IL6 treatment had no effect on cleavage or blastocyst formation in group culture. However, IL6 supplementation increased cleavage and day 8 blastocyst formation when bovine embryos were cultured individually.

Conclusions

These results implicate IL6 as an embryokine that specifically increases ICM cell numbers in bovine embryos and facilitates bovine blastocyst development in embryos cultured individually.

Simulated physiological oocyte maturation has side effects on bovine oocytes and embryos

PURPOSE

Oocyte maturation is a complex process involving nuclear and cytoplasmic modulations, during which oocytes acquire their ability to become fertilized and support embryonic development. The oocyte is apparently "primed" for maturation during its development in the dominant follicle. As bovine oocytes immediately resume meiosis when cultured, it was hypothesized that delaying resumption of meiosis with cyclic nucleotide modulators before in vitro maturation (IVM) would allow the oocytes to acquire improved developmental competence.

METHODS

We tested the Simulated Physiological Oocyte Maturation (SPOM) system that uses forskolin and 3-isobutyl-1-methylxanthine for 2 h prior to IVM against two different systems of conventional IVM (Con-IVM). We evaluated the ultrastructure of matured oocytes and blastocysts and also assessed the expression of 96 genes related to embryo quality in the blastocysts.

RESULTS

In summary, the SPOM system resulted in lower blastocyst rates than both Con-IVM systems (30 ± 9.1 vs. 35 ± 8.7; 29 ± 2.6 vs. 38 ± 2.8). Mature SPOM oocytes had significantly increased volume and number of vesicles, reduced volume and surface density of large smooth endoplasmic reticulum clusters, and lower number of mitochondria than Con-IVM oocytes. SPOM blastocysts showed only subtle differences with parallel undulations of adjacent trophectoderm plasma membranes and peripherally localized ribosomes in cells of the inner cell mass compared with Con-IVM blastocysts. SPOM blastocysts, however, displayed significant downregulation of genes related to embryonic developmental potential when compared to Con-IVM blastocysts.

CONCLUSIONS

Our results show that the use of the current version of the SPOM system may have adverse effects on oocytes and blastocysts calling for optimized protocols for improving oocyte competence.

Targeting αGal epitopes for multi-species embryo immunosurgery

Immunosurgical isolation of the inner cell mass (ICM) from blastocysts is based on complement-mediated lysis of antibody-coated trophectoderm (TE) cells. Conventionally, anti-species antisera, containing antibodies against multiple undefined TE-cell epitopes, have been used as the antibody source. We previously generated α-1,3-galactosyltransferase deficient (GTKO) pigs to prevent hyperacute rejection of pig-to-primate xenotransplants. Since GTKO pigs lack galactosyl-α-1,3-galactose (αGal) but are exposed to this antigen (e.g. αGal on gut bacteria), they produce anti-αGal antibodies. In this study, we examined whether serum from GTKO pigs could be used as a novel antibody source for multi-species embryo immunosurgery. Mouse, rabbit, pig and cattle blastocysts were used for the experiment. Expression of αGal epitopes on the surface of TE cells was detected in blastocysts of all species tested. GTKO pig serum contained sufficient anti-αGal antibodies to induce complement-mediated lysis of TE cells in blastocysts from all species investigated. Intact ICMs could be successfully recovered and the majority showed the desired level of purity. Our study demonstrates that GTKO pig serum is a reliable and effective source of antibodies targeting the αGal epitopes of TE cells for multi-species embryo immunosurgery.

Role of chemokine (C-C motif) ligand 24 in spatial arrangement of the inner cell mass of the bovine embryo

The process of spatial rearrangement of cells of the inner cell mass (ICM) that are destined to become hypoblast is not well understood. The observation that the chemokine (C-C motif) ligand 24 (CCL24) and several other genes involved in chemokine signaling are expressed more in the ICM than in the trophectoderm of the bovine embryo resulted in the hypothesis that CCL24 participates in spatial organization of the ICM. Temporally, expression of CCL24 in the bovine embryo occurs coincidently with blastocyst formation: transcript abundance was low until the late morula stage, peaked in the blastocyst at Day 7 of development and declined by Day 9. Treatment of embryos with two separate antagonists of C-C motif chemokine receptor 3 (the prototypical receptor for CCL24) decreased the percent of GATA6+ cells (hypoblast precursors) that were located in the outside of the ICM. Similarly, injection of zygotes with a CCL24-specific morpholino decreased the percent of GATA6+ cells in the outside of the ICM. In conclusion, CCL24 assists in spatial arrangement of the ICM in the bovine embryo. This experiment points to new functions of chemokine signaling in the bovine embryo and is consistent with the idea that cell migration is involved in the spatial organization of hypoblast cells in the blastocyst.

Long non-coding RNAs involved in the regulatory network during porcine pre-implantation embryonic development and iPSC induction

Long non-coding RNAs (lncRNA) play a key role in the orchestration of transcriptional regulation during development and many other cellular processes. The importance of the regulatory co-expression network was highlighted in the identification of the mechanism of these processes in humans and mice. However, elucidation of the properties of porcine lncRNAs involved in the regulatory network during pre-implantation embryonic development and fibroblast reprogramming to induced pluripotent stem cell (iPSC) has been limited to date. Using a weighted gene co-expression network analysis, we constructed the regulatory network and determined that the novel lncRNAs were functionally involved in key events of embryonic development during the pre-implantation period; moreover, reprogramming could be delineated by a small number of potentially functional modules of co-expressed genes. These findings indicate that lncRNAs may be involved in the transcriptional regulation of zygotic genome activation, first lineage segregation and somatic reprogramming to pluripotency. Furthermore, we performed a conservation and synteny analysis with the significant lncRNAs involved in these vital events and validated the results via experimental assays. In summary, the current findings provide a valuable resource to dissect the protein coding gene and lncRNA regulatory networks that underlie the progressive development of embryos and somatic reprogramming.

Single-cell gene expression of the bovine blastocyst

The first two differentiation events in the embryo result in three cell types - epiblast, trophectoderm (TE) and hypoblast. The purpose here was to identify molecular markers for each cell type in the bovine and evaluate the differences in gene expression among individual cells of each lineage. The cDNA from 67 individual cells of dissociated blastocysts was used to determine transcript abundance for 93 genes implicated as cell lineage markers in other species or potentially involved in developmental processes. Clustering analysis indicated that the cells belonged to two major populations (clades A and B) with two subpopulations of clade A and four of clade B. Use of lineage-specific markers from other species indicated that the two subpopulations of clade A represented epiblast and hypoblast respectively while the four subpopulations of clade B were TE. Among the genes upregulated in epiblast were AJAP1, DNMT3A, FGF4, H2AFZ, KDM2B, NANOG, POU5F1, SAV1 and SLIT2 Genes overexpressed in hypoblast included ALPL, FGFR2, FN1, GATA6, GJA1, HDAC1, MBNL3, PDGFRA and SOX17, while genes overexpressed in all four TE populations were ACTA2, CDX2, CYP11A1, GATA2, GATA3, IFNT, KRT8, RAC1 and SFN The subpopulations of TE varied among each other for multiple genes including the prototypical TE marker IFNT. New markers for each cell type in the bovine blastocyst were identified. Results also indicate heterogeneity in gene expression among TE cells. Further studies are needed to confirm whether subpopulations of TE cells represent different stages in the development of a committed TE phenotype.

Genomic rearrangements in sporadic lymphangioleiomyomatosis: an evolving genetic story

Sporadic lymphangioleiomyomatosis is a progressive pulmonary cystic disease resulting from the infiltration of smooth muscle-like lymphangioleiomyomatosis cells into the lung. The migratory/metastasizing properties of the lymphangioleiomyomatosis cell together with the presence of somatic mutations, primarily in the tuberous sclerosis complex gene (TSC2), lead many to consider this a low-grade malignancy. As malignant tumors characteristically accumulate somatic structural variations, which have not been well studied in sporadic lymphangioleiomyomatosis, we utilized mate pair sequencing to define structural variations within laser capture microdissected enriched lymphangioleiomyomatosis cell populations from five sporadic lymphangioleiomyomatosis patients. Lymphangioleiomyomatosis cells were confirmed in each tissue by hematoxylin eosin stain review and by HMB-45 immunohistochemistry in four cases. A mutation panel demonstrated characteristic TSC2 driver mutations in three cases. Genomic profiles demonstrated normal diploid coverage across all chromosomes, with no aneuploidy or detectable gains/losses of whole chromosomal arms typical of neoplastic diseases. However, somatic rearrangements and smaller deletions were validated in the two cases which lacked TSC2 driver mutations. Most significantly, one of these sporadic lymphangioleiomyomatosis cases contained two different size deletions encompassing the entire TSC1 locus. The detection of a homozygous deletion of TSC1 driving a predicted case of sporadic lymphangioleiomyomatosis, consistent with the common two-hit TSC2 mutation model, has never been reported for sporadic lymphangioleiomyomatosis. However, while no evidence of the hereditary tuberous sclerosis complex disease was reported for this patient, the potential for mosaicism and sub-clinical phenotype cannot be ruled out. Nevertheless, this study demonstrates that somatic structural rearrangements are present in lymphangioleiomyomatosis disease and provides a novel method of genomic characterization of sporadic lymphangioleiomyomatosis cells, aiding in defining cases with no detected mutations by conventional methodologies. These structural rearrangements could represent additional pathogenic mechanisms in sporadic lymphangioleiomyomatosis disease, potentially affecting response to therapy and adding to the complex genetic story of this rare disease.

Transcriptomic evaluation of bovine blastocysts obtained from peri-pubertal oocyte donors

Assisted reproduction technologies (ART) and high selection pressure in the dairy industry are leading towards the use of younger females for reproduction, thereby reducing the interval between generations. This situation may have a negative impact on embryo quality, thus reducing the success rate of the procedures. This study aimed to document the effects of oocyte donor age on embryo quality, at the transcriptomic level, in order to characterize the effects of using young females for reproduction purpose. Young Holstein heifers (n = 10) were used at three different ages for ovarian stimulation protocols and oocyte collections (at 8, 11 and 14 months). All of the oocytes were fertilized in vitro with the semen of one adult bull, generating three lots of embryos per animal. Each animal was its own control for the evaluation of the effects of age. The EmbryoGENE platform was used for the assessment of gene expression patterns at the blastocyst stage. Embryos from animals at 8 vs 14 months and at 11 vs 14 months were used for microarray hybridization. Validation was done by performing RT-qPCR on seven candidate genes. Age-related contrast analysis (8 vs 14 mo and 11 vs 14 mo) identified 242 differentially expressed genes (DEGs) for the first contrast, and 296 for the second. The analysis of the molecular and biological functions of the DEGs suggests a metabolic cause to explain the differences that are observed between embryos from immature and adult subjects. The mTOR and PPAR signaling pathways, as well as the NRF2-mediated oxidative stress response pathways were among the gene expression pathways affected by donor age. In conclusion, the main differences between embryos produced at peri-pubertal ages are related to metabolic conditions resulting in a higher impact of in vitro conditions on blastocyts from younger heifers.

Dynamic Pattern of HOXB9 Protein Localization during Oocyte Maturation and Early Embryonic Development in Mammals

Background

We previously showed that the homeodomain transcription factor HOXB9 is expressed in mammalian oocytes and early embryos. However, a systematic and exhaustive study of the localization of the HOXB9 protein, and HOX proteins in general, during mammalian early embryonic development has so far never been performed.

Results

The distribution of HOXB9 proteins in oocytes and the early embryo was characterized by immunofluorescence from the immature oocyte stage to the peri-gastrulation period in both the mouse and the bovine. HOXB9 was detected at all studied stages with a dynamic expression pattern. Its distribution was well conserved between the two species until the blastocyst stage and was mainly nuclear. From that stage on, trophoblastic cells always showed a strong nuclear staining, while the inner cell mass and the derived cell lines showed important dynamic variations both in staining intensity and in intra-cellular localization. Indeed, HOXB9 appeared to be progressively downregulated in epiblast cells and only reappeared after gastrulation had well progressed. The protein was also detected in the primitive endoderm and its derivatives with a distinctive presence in apical vacuoles of mouse visceral endoderm cells.

Conclusions

Together, these results could suggest the existence of unsuspected functions for HOXB9 during early embryonic development in mammals.

Stem cell insights into human trophoblast lineage differentiation

BACKGROUND

The human placenta is vital for fetal development, yet little is understood about how it forms successfully to ensure a healthy pregnancy or why this process is inadequate in 1 in 10 pregnancies, leading to miscarriage, intrauterine growth restriction or preeclampsia. Trophoblasts are placenta-specific epithelial cells that maximize nutrient exchange. All trophoblast lineages are thought to arise from a population of trophoblast stem cells (TSCs). However, whilst the isolation of murine TSC has led to an explosion in understanding murine placentation, the isolation of an analogous human TSC has proved more difficult. Consequently, alternative methods of studying human trophoblast lineage development have been employed, including human embryonic stem cells (hESCs), induced pluripotent stem cells (iPS) and transformed cell lines; but what do these proxy models tell us about what is happening during early placental development?

OBJECTIVE AND RATIONALE

In this systematic review, we evaluate current approaches to understanding human trophoblast lineage development in order to collate and refine these models and inform future approaches aimed at establishing human TSC lines.

SEARCH METHODS

To ensure all relevant articles were analysed, an unfiltered search of Pubmed, Embase, Scopus and Web of Science was conducted for 25 key terms on the 13th May 2016. In total, 47 313 articles were retrieved and manually filtered based on non-human, non-English, non-full text, non-original article and off-topic subject matter. This resulted in a total of 71 articles deemed relevant for review in this article.

OUTCOMES

Candidate human TSC populations have been identified in, and isolated from, both the chorionic membrane and villous tissue of the placenta, but further investigation is required to validate these as 'true' human TSCs. Isolating human TSCs from blastocyst trophectoderm has not been successful in humans as it was in mice, although recently the first reported TSC line (USFB6) was isolated from an eight-cell morula. In lieu of human TSC lines, trophoblast-like cells have been induced to differentiate from hESCs and iPS. However, differentiation in these model systems is difficult to control, culture conditions employed are highly variable, and the extent to which they accurately convey the biology of 'true' human TSCs remains unclear, particularly as a consensus has not been met among the scientific community regarding which characteristics a human TSC must possess.

WIDER IMPLICATIONS

Human TSC models have the potential to revolutionize our understanding of trophoblast differentiation, allowing us to make significant gains in understanding the underlying pathology of pregnancy disorders and to test potential therapeutic interventions on cell function in vitro. In order to do this, a collaborative effort is required to establish the criteria that define a human TSC to confirm the presence of human TSCs in both primary isolates and to determine how accurately trophoblast-like cells derived from current model systems reflect trophoblast from primary tissue. The in vitro systems currently used to model early trophoblast lineage formation have provided insights into early human placental formation but it is unclear whether these trophoblast-like cells are truly representative of primary human trophoblast. Consequently, continued refinement of current models, and standardization of culture protocols is essential to aid our ability to identify, isolate and propagate 'true' human TSCs from primary tissue.