Highly rigid H3.1/H3.2–H3K9me3 domains set a barrier for cell fate reprogramming in trophoblast stem cells

The placenta is a highly evolved, specialized organ in mammals. It differs from other organs in that it functions only for fetal maintenance during gestation. Therefore, there must be intrinsic mechanisms that guarantee its unique functions. To address this question, we comprehensively analyzed epigenomic features of mouse trophoblast stem cells (TSCs). Our genome-wide, high-throughput analyses revealed that the TSC genome contains large-scale (>1-Mb) rigid heterochromatin architectures with a high degree of histone H3.1/3.2–H3K9me3 accumulation, which we termed TSC-defined highly heterochromatinized domains (THDs). Importantly, depletion of THDs by knockdown of CAF1, an H3.1/3.2 chaperone, resulted in down-regulation of TSC markers, such as Cdx2 and Elf5, and up-regulation of the pluripotent marker Oct3/4, indicating that THDs maintain the trophoblastic nature of TSCs. Furthermore, our nuclear transfer technique revealed that THDs are highly resistant to genomic reprogramming. However, when H3K9me3 was removed, the TSC genome was fully reprogrammed, giving rise to the first TSC cloned offspring. Interestingly, THD-like domains are also present in mouse and human placental cells in vivo, but not in other cell types. Thus, THDs are genomic architectures uniquely developed in placental lineage cells, which serve to protect them from fate reprogramming to stably maintain placental function.

Genome-wide mapping of histone modification H3K4me3 in bovine oocytes and early embryos

Reprogramming of histone modifications is critical to safeguard correct gene expression profile during preimplantation development. Of interest, trimethylation of lysine 4 on histone 3 (H3K4me3) exhibits a unique and dynamic landscape with a potential species-specific feature. Here, we address how it is reprogrammed and its functional significance during oocyte maturation and early embryonic development in cows. Notably, the overall signal of H3K4me3 decreased sharply during embryonic genome activation (EGA). By using low input ChIP-seq technology, we find widespread broad H3K4me3 domains in oocytes and early cleaved embryos. The broad domains are gradually removed after fertilization, which is obviously seen during EGA. Meanwhile, H3K4me3 become enriched at promoter regions. Interestingly, the gene expression level displays a positive correlation with the relative H3K4me3 signal of their promoters when embryos reach 16-cell stage. Importantly, disruption of H3K4me3 demethylases KDM5A-5C increases H3K4me3 level, decreases the embryonic developmental rate and results in dysregulation of over a thousand genes. Meanwhile, KDM5 deficiency causes a re-destribution of H3K4me3 across genome. In particular, the positive correlation between promoter H3K4me3 enrichment and gene expression level disappear. Overall, we describe the genomic reprogramming of H3K4me3 in a greater resolution during bovine preimplantation development and propose that KDM5-mediated re-distribution of H3K4me3 plays an important role in modulating oocyte-to-embryonic transition.

Comparative Analysis of Histone H3K4me3 Distribution in Mouse Liver in Different Diets Reveals the Epigenetic Efficacy of Cyanidin-3-O-glucoside Dietary Intake

Background: Different diets result in significantly different phenotypes through metabolic and genomic reprogramming. Epigenetic marks, identified in humans and mouse models through caloric restriction, a high-fat diet or the intake of specific bioactives, suggest that genomic reprogramming drives this metabolic reprogramming and mediates the effect of nutrition on health. Histone modifications encode the epigenetic signal, which adapts genome functions to environmental conditions, including diets, by tuning the structure and properties of chromatin. To date, the effect of different diets on the genome-wide distribution of critical histone marks has not been determined. Methods: Using chromatin immunoprecipitation sequencing, we investigated the distribution of the trimethylation of lysine 4 of histone H3 in the liver of mice fed for one year with five different diets, including: chow containing yellow corn powder as an extra source of plant bioactives or specifically enriched with cyanidin-3-O-Glucoside, high-fat-enriched obesogenic diets, and caloric-restricted pro-longevity diets. Conclusions: Comparison of the resulting histone mark profiles revealed that functional food containing cyanidin determines a broad effect.

Epigenetic abnormalities associated with somatic cell nuclear transfer

Twenty-five years have passed since the birth of Dolly the sheep, the first mammalian clone produced by adult somatic cell nuclear transfer (SCNT). During that time, the main thrust of SCNT-related research has been the elucidation of SCNT-associated epigenetic abnormalities and their correction, with the aim of improving the efficiency of cloned animal production. Through these studies, it has become clear that some epigenomic information can be reprogrammed by the oocyte, while some cannot. Now we know that the imprinting memories in the donor genome, whether canonical (DNA-methylation-dependent) or noncanonical (H3K27me3-dependent), are not reprogrammed by SCNT. Thus, SCNT-derived embryos have the normal canonical imprinting and the erased noncanonical imprinting, both being inherited from the donor cells. The latter can cause abnormal phenotypes in SCNT-derived placentas arising from biallelic expressions of noncanonically imprinted genes. By contrast, repressive epigenomic information, such as DNA methylation and histone modifications, might be more variably reprogrammed, leaving room for technical improvements. Low-input analytical technologies now enable us to analyze the genome of gametes and embryos in a high-throughput, genome-wide manner. These technologies are being applied rapidly to the SCNT field, providing evidence for incomplete reprogramming of the donor genome in cloned embryos or offspring. Insights from the study of epigenetic phenomena in SCNT are highly relevant for our understanding of the mechanisms of genomic reprogramming that can induce totipotency in the mammalian genome.

EPCO-06. MOLECULAR DETERMINANTS OF EVOLUTION AND PROGNOSIS AMONG DIFFUSE LOWER GRADE ASTROCYTOMAS

Gliomas with wild type (WT) isocitrate dehydrogenase (IDH) are considerably more aggressive than those with mutant IDH. To identify putative drivers of the distinct progression trajectories of IDH WT and mutant disease, we analyzed transcriptomes of lower grade astrocytomas (LGAs; grade 2–3) with retention of 1p and 19q from The Cancer Genome Atlas (TCGA; n = 347). Compared to IDH mutant LGAs, we found that PDGF signaling was significantly enriched in IDH WT LGAs and that PDGFA was the top overexpressed gene in this pathway. We identified copy number gains of chromosome 7 in WT LGAs, and methylation of the PDGFA promoter in mutant LGAs, as candidate mechanisms for the differential expression of PDGFA. High PDGFA expression and low PDGFA promoter methylation were significantly associated with poor survival in all LGAs. We also found that PDGFA expression was positively associated with aneuploidy and extracellular matrix-related immunosuppressive features in WT LGAs, underscoring the role of PDGFA as a secreted mitogen. Finally, we show that the proportion of p53 pathway mutations increase significantly with grade in IDH WT gliomas. Taken together, our findings suggest that IDH WT LGAs evolve to higher grades, and ultimately to GBM, by progressive inactivation of the p53 pathway - functioning in concert with a background of increased PDGFA expression. These data emphasize the scope of genomic reprogramming that occurs in gliomas in relation to IDH mutations and further highlight the role of PDGFA in glioma formation, progression, and prognosis. Going forward, this work provides critical biological insight that may inspire new therapeutic strategies to suppress the transformation of IDH WT LGAs to higher-grade cancers.

Influence of oocyte selection, activation with a zinc chelator and inhibition of histone deacetylases on cloned porcine embryo and chemically activated oocytes development

SummaryThe aim of this study was to evaluate the effects of alternative protocols to improve oocyte selection, embryo activation and genomic reprogramming on in vitro development of porcine embryos cloned by somatic cell nuclear transfer (SCNT). In Experiment 1, in vitro-matured oocytes were selected by exposure to a hyperosmotic sucrose solution prior to micromanipulation. In Experiment 2, an alternative chemical activation protocol using a zinc chelator as an adjuvant (ionomycin + N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) + N-6-dimethylaminopurine (6-DMAP)) was compared with a standard protocol (ionomycin + 6-DMAP) for the activation of porcine oocytes or SCNT embryos. In Experiment 3, presumptive cloned zygotes were incubated after chemical activation in a histone deacetylase inhibitor (Scriptaid) for 15 h, with the evaluation of embryo yield and total cell number in day 7 blastocysts. In Experiment 1, cleavage rates tended to be higher in sucrose-treated oocytes than controls (123/199, 61.8% vs. 119/222, 53.6%, respectively); however, blastocyst rates were similar between groups. In Experiment 2, cleavage rates were higher in zygotes treated with TPEN than controls but no difference in blastocyst rates between groups occurred. For Experiment 3, the exposure to Scriptaid did not improve embryo development after cloning. Nevertheless, the total number of cells was higher in cloned zygotes treated with Scriptaid than SCNT controls. In conclusion, oocyte selection by sucrose as well as treatments with zinc chelator and an inhibitor of histone deacetylases did not significantly improve blastocyst yield in cloned and parthenotes. However, the histone deacetylases inhibitor produced a significant improvement in the blastocyst quality.

Neuroprotection Mechanisms in Cerebral Hypothermia (Review)

The review focuses on the neuroprotective mechanisms of therapeutic hypothermia from the standpoint of metabolic depression and genomic reprogramming of neurons that develop when brain temperature decreases.The concept of hypothermic pre-conditioning based on the development of typical nonspecific reactions for the formation of the cytoprotective phenotype of neurons due to potentially dangerous stimuli, such as ischemia, reperfusion, and hypothermia, was used to explain the effects of low temperatures. The data confirming the role of therapeutic cerebral hypothermia as a technique of selective brain exposure to mild cold for the neuroprotection and correction of temperature balance disorders are shown.The approach to therapeutic hypothermia as a hypothermic pre-conditioning allows to significantly expand the scope of its use in various procedural variants.

RNA sequencing reveals novel macrophage transcriptome favoring neurovascular plasticity after ischemic stroke

Blood monocytes/macrophages infiltrate the brain after ischemic stroke and critically influence brain injury and regeneration. We investigated stroke-induced transcriptomic changes of monocytes/macrophages by RNA sequencing profiling, using a mouse model of permanent focal cerebral ischemia. Compared to non-ischemic conditions, brain ischemia induced only moderate genomic changes in blood monocytes, but triggered robust genomic reprogramming in monocytes/macrophages invading the brain. Surprisingly, functional enrichment analysis of the transcriptome of brain macrophages revealed significant overrepresentation of biological processes linked to neurovascular remodeling, such as angiogenesis and axonal regeneration, as early as five days after stroke, suggesting a previously underappreciated role for macrophages in initiating post-stroke brain repair. Upstream Regulator analysis predicted peroxisome proliferator-activated receptor gamma (PPARγ) as a master regulator driving the transcriptional reprogramming in post-stroke brain macrophages. Importantly, myeloid cell-specific PPARγ knockout (mKO) mice demonstrated lower post-stroke angiogenesis and neurogenesis than wild-type mice, which correlated significantly with the exacerbation of post-stroke neurological deficits in mKO mice. Collectively, our findings reveal a novel repair-enhancing transcriptome in brain macrophages during post-stroke neurovascular remodeling. As a master switch controlling genomic reprogramming, PPARγ is a rational therapeutic target for promoting and maintaining beneficial macrophage functions, facilitating neurorestoration, and improving long-term functional recovery after ischemic stroke.