Follistatin treatment modifies DNA methylation of the CDX2 gene in bovine preimplantation embryos

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.

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.

Combined Exogenous Activation of Bovine Oocytes: Effects on Maturation-Promoting Factor, Mitogen-Activated Protein Kinases, and Embryonic Competence

Oocyte activation via dual inhibition of protein synthesis and phosphorylation has improved in vitro embryo production in different mammalian species. In this study, we evaluated the effects of the combination of cycloheximide (CHX), dimethyl amino purine (DMAP), and anisomycin (ANY) on the activation of bovine oocytes, particularly on dynamics of MPF and MAPKs, embryonic developmental potential, and quality. The results showed that the cleavage and blastocyst rates, as well as levels of CCNB1, CDK1, p-CDK1Thr161, and p-CDK1Thr14-Tyr15, were similar among groups; ANY and ANY + CHX reduced the expression of ERK1/2 compared to DMAP-combinations (p < 0.05), whereas ANY + DMAP, CHX + DMAP, and ANY + CHX + DMAP reduced p-ERK1/2 compared to ANY and ANY + CHX treatments (p < 0.05). The quality of blastocysts in terms of cell counts, their allocation, and the numbers of TUNEL-positive cells did not differ among groups. However, transcript levels of POU5F1 were higher in embryos derived from ANY + CHX + DMAP treatment compared to other groups, while expression levels of CDX2 did not show differences. In addition, the BCL2A1/BAX ratio of the ANY + CHX + DMAP treatment was significantly low compared to the ANY treatment (p < 0.05) and did not differ significantly from the other treatments. In conclusion, oocyte activation by dual inhibition of protein synthesis and phosphorylation induces MPF inactivation without degradation of CCNB1, while MAPK inactivation occurs differentially between these inhibitors. Thus, although the combined use of these inhibitors does not affect early developmental competence in vitro, it positively impacts the expression of transcripts associated with embryonic quality.

Glucocorticoid Exposure of Preimplantation Embryos Increases Offspring Anxiety-Like Behavior by Upregulating miR-211-5p via Trpm1 Demethylation

Most studies on mechanisms by which prenatal stress affects offspring behavior were conducted during late pregnancy using in vivo models; studies on the effect of preimplantation stress are rare. In vivo models do not allow accurate specification of the roles of different hormones and cells within the complicated living organism, and cannot verify whether hormones act directly on embryos or indirectly to alter progeny behavior. Furthermore, the number of anxiety-related miRNAs identified are limited. This study showed that both mouse embryculture with corticosterone (ECC) and maternal preimplantation restraint stress (PIRS) increased anxiety-like behavior (ALB) while decreasing hippocampal expression of glucocorticoid receptor (GR) and brain-derived neurotrophic factor (BDNF) in offspring. ECC/PIRS downregulated GR and BDNF expression by increasing miR-211-5p expression via promoter demethylation of its host gene Trpm1, and this epigenetic cell fate determination was exclusively perpetuated during development into mature hippocampus. Transfection with miR-211-5p mimic/inhibitor in cultured hippocampal cell lines confirmed that miR-211-5p downregulated Gr and Bdnf. Intrahippocampal injection of miR-211-5p agomir/antagomir validated that miR-211-5p dose-dependently increased ALB while decreasing hippocampal GR/BDNF expression. In conclusion, preimplantation exposure to glucocorticoids increased ALB by upregulating miR-211-5p via Trpm1 demethylation, and miR-211-5p may be used as therapeutic targets and biomarkers for anxiety-related diseases.

Nobiletin-induced partial abrogation of deleterious effects of AKT inhibition on preimplantation bovine embryo development in vitro

During preimplantational embryo development, PI3K/AKT regulates cell proliferation and differentiation and nobiletin modulates this pathway to promote cell survival. Therefore, we aimed to establish whether, when the AKT cascade is inhibited using inhibitors III and IV, nobiletin supplementation to in vitro culture media during the minor (2 to 8-cell stage, MNEGA) or major (8 to 16-cell stage, MJEGA) phases of EGA is able to modulate the development and quality of bovine embryos. In vitro zygotes were cultured during MNEGA or MJEGA phase in SOF + 5% FCS or supplemented with: 15 μM AKT-InhIII; 10 μM AKT-InhIV; 10 μM nobiletin; nobiletin+AKT-InhIII; nobiletin+AKT-InhIV; 0.03% DMSO. Embryo development was lower in treatments with AKT inhibitors, while combination of nobiletin with AKT inhibitors was able to recover their adverse developmental effect and also increase blastocyst cell number. The mRNA abundance of GPX1, NFE2L2, and POU5F1 was partially increased in 8- and 16-cell embryos from nobiletin with AKT inhibitors. Besides, nobiletin increased the p-rpS6 level whether or not AKT inhibitors were present. In conclusion, nobiletin promotes bovine embryo development and quality and partially recovers the adverse developmental effect of AKT inhibitors which infers that nobiletin probably uses another signalling cascade that PI3K/AKT during early embryo development in bovine.

Follistatin supplementation induces changes in CDX2 CpG methylation and improves in vitro development of bovine SCNT preimplantation embryos

Caudal Type Homeobox 2 (CDX2) is a key regulator of trophectoderm formation and maintenance in preimplantation embryos. We previously demonstrated that supplementation of exogenous follistatin, during in vitro culture of bovine IVF embryos, upregulates CDX2 expression, possibly, via alteration of the methylation status of CDX2 gene. Here, we further investigated the effects of exogenous follistatin supplementation on developmental competence and CDX2 methylation in bovine somatic cell nuclear transfer (SCNT) embryos. SCNT embryos were cultured with or without follistatin for 72h, then transferred into follistatin free media until d7 when blastocysts were collected and subjected to CDX2 gene expression and DNA methylation analysis for CDX2 regulatory regions by bisulfite sequencing. Follistatin supplementation significantly increased both blastocyst development as well as blastocyst CDX2 mRNA expression on d7. Three different CpG rich fragments within the CDX2 regulatory elements; proximal promoter (fragment P1, -1644 to -1180; P2, -305 to +126) and intron 1 (fragment I, + 3030 to + 3710) were identified and selected for bisulfite sequencing analysis. This analysis showed that follistatin treatment induced differential methylation (DM) at specific CpG sites within the analyzed fragments. Follistatin treatment elicited hypomethylation at six CpG sites at positions -1374, -279, -163, -23, +122 and +3558 and hypermethylation at two CpG sites at positions -243 and +20 in promoter region and first intron of CDX2 gene. Motif analysis using MatInspector revealed that differentially methylated CpG sites are putative binding sites for key transcription factors (TFs) known to regulate Cdx2 expression in mouse embryos and embryonic stem cells including OCT1, AP2F, KLF and P53, or TFs that have indirect link to CDX2 regulation including HAND and NRSF. Collectively, results of the present study together with our previous findings in IVF embryos support the hypothesis that alteration of CDX2 methylation is one of the epigenetic mechanisms by which follistatin may regulates CDX2 expression in preimplantation bovine embryos.