H3S10 phosphorylation marks constitutive heterochromatin during interphase in early mouse embryos until the 4-cell stage

Strategies to Improve the Efficiency of Somatic Cell Nuclear Transfer

Mammalian oocytes can reprogram differentiated somatic cells into a totipotent state through somatic cell nuclear transfer (SCNT), which is known as cloning. Although many mammalian species have been successfully cloned, the majority of cloned embryos failed to develop to term, resulting in the overall cloning efficiency being still low. There are many factors contributing to the cloning success. Aberrant epigenetic reprogramming is a major cause for the developmental failure of cloned embryos and abnormalities in the cloned offspring. Numerous research groups attempted multiple strategies to technically improve each step of the SCNT procedure and rescue abnormal epigenetic reprogramming by modulating DNA methylation and histone modifications, overexpression or repression of embryonic-related genes, etc. Here, we review the recent approaches for technical SCNT improvement and ameliorating epigenetic modifications in donor cells, oocytes, and cloned embryos in order to enhance cloning efficiency.

Current status of assisted reproductive technologies in buffaloes

Buffaloes are raised by small farm holders primarily as source of draft power owing to its resistance to hot climate, disease, and stress conditions. Over the years, transformation of these animals from draft to dairy was deliberately carried out through genetic improvement program leading to the development of buffalo-based enterprises. Buffalo production is now getting more attention and interest from buffalo raisers due to its socioeconomic impact as well as its contribution to propelling the livestock industry in many developing countries. Reproduction of buffaloes, however, is confronted with huge challenge and concern as being generally less efficient to reproduce compared with cattle due to both intrinsic and extrinsic factors such as poor estrus manifestation, silent heat, marked seasonal infertility, postpartum anestrus, long calving interval, delayed puberty, inherently low number of primordial follicles in their ovaries, high incidence of atresia, and apoptosis. Assisted reproductive technologies (ARTs) are major interventions for the efficient utilization of follicle reserve in buffaloes. The present review focuses on estrus and ovulation synchronization for fixed time artificial insemination, in vitro embryo production, intracytoplasmic sperm injection, cryopreservation of oocytes and embryos, somatic cell nuclear transfer, the factors affecting utilization in various ARTs, and future perspectives in buffaloes.

Histone Modifications in Mouse Pronuclei and Consequences for Embryo Development

Epigenetic marks, such as DNA methylation and posttranslational modifications of core histones, are the key regulators of gene expression. In the mouse, many of these marks are erased during gamete formation and must be introduced de novo after fertilization. Some of them appear synchronously, but the others are deposited asynchronously and/or remain differently distributed on maternal and paternal chromatin. Although the mechanisms regulating these processes are not entirely understandable, it is commonly accepted that epigenetic reprogramming occurring during the first cell cycle of a mouse embryo is crucial for its further development. This chapter focuses on selected epigenetic modifications, such as DNA methylation, the introduction of histone variants, histones acetylation, phosphorylation, and methylation. Properly depositing these marks on maternal and paternal chromatin is crucial for normal embryonic development.

NOTCH signaling pathway is required for bovine early embryonic development†

The NOTCH signaling pathway plays an important role in regulating various biological processes, including lineage specification and apoptosis. Multiple components of the NOTCH pathway have been identified in mammalian preimplantation embryos. However, the precise role of the NOTCH pathway in early embryonic development is poorly understood, especially in large animals. Here, we show that the expression of genes encoding key transcripts of the NOTCH pathway is dynamic throughout early embryonic development. We also confirm the presence of active NOTCH1 and RBPJ. By using pharmacological and RNA interference tools, we demonstrate that the NOTCH pathway is required for the proper development of bovine early embryos. This functional consequence could be partly attributed to the major transcriptional mediator, Recombination Signal Binding Protein For Immunoglobulin Kappa J Region (RBPJ), whose deficiency also compromised the embryo quality. Indeed, both NOTCH1 and RBPJ knockdown cause a significant increase of histone H3 serine 10 phosphorylation (pH3S10, a mitosis marker) positive blastomeres, suggesting a cell cycle arrest at mitosis. Importantly, RNA sequencing analyses reveal that either NOTCH1 or RBPJ depletion triggers a reduction in H1FOO that encodes the oocyte-specific linker histone H1 variant. Interestingly, depleting H1FOO results in detrimental effects on the developmental competence of early embryos, similar with NOTCH1 inhibition. Overall, our results reveal a crucial role for NOTCH pathway in regulating bovine preimplantation development, likely by controlling cell proliferation and maintaining H1FOO expression.

AURKB promotes gastric cancer progression via activation of CCND1 expression

Aurora kinase B (AURKB) triggers the phosphorylation of serine 10 on histone H3 (H3S10ph), which is important for chromosome condensation and cytokinesis during mitosis in mammals. However, how exactly AURKB controls cell cycle and contributes to tumorigenesis as an oncoprotein under pathological conditions remains largely unknown. Here, we report that AURKB promotes gastric cancer cell proliferation in vitro and in vivo. Silencing AURKB expression inhibits gastric cell proliferation and arrests the cell cycle in G₂/M phase. We demonstrate that cyclin D1 (CCND1) is a direct downstream target of AURKB that plays a key role in gastric cancer cell proliferation. AURKB is able to activate the expression of CCND1 through mediating H3S10ph in the promoter of the CCND1 gene. Furthermore, we show that AZD1152, a specific inhibitor of AURKB, can suppress the expression of CCND1 in the gastric cancer cells and inhibit cell proliferation in vitro and in vivo. Importantly, we found that high AURKB and CCND1 expression levels are correlated with shorter overall survival of gastric cancer patients. This study demonstrates that AURKB promotes gastric tumorigenesis potentially through epigenetically activating CCND1 expression, suggesting AURKB as a promising therapeutic target in gastric cancer.

Developing landscapes: genome architecture during early embryogenesis

Early in development embryos undergo a transition, during which maternally deposited transcripts are replaced by zygotic transcripts. During this transition the zygotic genome is activated. Recently, the three-dimensional organization of the genome (3D genome) has been charted surrounding this transition phase in a number of species. A common feature of the 3D genome in all these species is that they go through a phase, during which architectural features of the 3D genome, such as TADs and compartments are lost and a uniform chromatin architecture is established. Here, we review the data regarding this enigmatic phase and discuss similarities and differences between species. We also consider mechanisms that may be responsible for the formation of the uniform chromatin architecture. The uniform organization of chromosomes during early development may serve as an important in vivo paradigm for the general study of the 3D genome.

Loss of 5-hydroxymethylcytosine and intratumoral heterogeneity as an epigenomic hallmark of glioblastoma

Glioblastoma (GBM) is the most malignant neoplasm with predominant astrocytic differentiation and the most frequent primary brain tumor of the adult. Here, we investigated 170 human GBM specimens deriving from 162 patients, as well as 66 healthy control tissue specimens deriving from 27 patients, and analyzed the amount of 5-hydroxymethylcytosine (5hmC) in GBMs compared to normal brain and tumor infiltration zones. Additionally, we correlated the amount of 5hmC with two different proliferation markers, Ki67 and H3S10p. Genetic characterization of GBMs enabled us to analyze the effect of isocitrate dehydrogenase 1 (IDH1) mutations, O6-methylguanin-DNA-methyltransferase (MGMT) promoter methylation, and loss of heterozygosity of chromosome 1p and 19q (LOH1p/19q) on 5hmC amount. We found that GBMs show a tremendous loss of 5hmC, and we observed that even the infiltration zones show reduced amounts of 5hmC. Interestingly, the amount of 5hmC was inversely proportional to the two investigated proliferation markers, Ki67 and H3S10p. Correlation of 5hmC amount and molecular genetic markers of GBMs showed that there are no correlations of 5hmC amount and IDH1 mutations, MGMT promoter methylation, and LOH1p/19q. Furthermore, we evaluated the intratumoral distribution of 5hmC in compact and infiltrating areas and found that the quantification of the 5hmC amount is a useful tool in evaluation of tumor infiltration. In summary, our data emphasize that GBMs show a disturbed hydroxymethylome that is disrupted by IDH1 independent pathways, and that loss of 5hmC shows astonishing intratumoral heterogeneity.

Comparison of epigenetic mediator expression and function in mouse and human embryonic blastomeres

A map of human embryo development that combines imaging, molecular, genetic and epigenetic data for comparisons to other species and across pathologies would be greatly beneficial for basic science and clinical applications. Here, we compared mRNA and protein expression of key mediators of DNA methylation and histone modifications between mouse and human embryos, embryos from fertile/infertile couples, and following growth factor supplementation. We observed that individual mouse and human embryos are characterized by similarities and distinct differences in DNA methylation and histone modification patterns especially at the single-cell level. In particular, while mouse embryos first exhibited sub-compartmentalization of different histone modifications between blastomeres at the morula stage and cell sub-populations in blastocysts, differential histone modification expression was detected between blastomeres earlier in human embryos at the four- to eight-cell stage. Likewise, differences in epigenetic mediator expression were also observed between embryos from fertile and infertile couples, which were largely equalized in response to growth factor supplementation, suggesting that select growth factors might prevent alterations in epigenetic profiles during prolonged embryo culture. Finally, we determined that reduced expression via morpholino technologies of a single histone-modifying enzyme, Rps6ka4/Msk2, resulted in cleavage-stage arrest as assessed by time-lapse imaging and was associated with aneuploidy generation. Taken together, data document differences in epigenetic patterns between species with implications for fertility and suggest functional roles for individual epigenetic factors during pre-implantation development.

Histone post-translational modifications in preimplantation mouse embryos and their role in nuclear architecture

In mammals, epigenetic modifications are globally rearranged after fertilization, when gametes fuse to form the embryo. While gametes carry special epigenetic signatures and a unique nuclear organization, they attain embryo-specific patterns after fertilization. This "reprogramming" is promoted by intimate contact between the parental inherited genomes and the oocyte cytoplasm over the first cell cycles of development. Although the mechanisms of this reprogramming remain poorly understood, it appears that the particular epigenetic landscape established after fertilization is essential for further development. This review looks at histone post-translational modifications, focusing on their functions in chromatin organization and their role in nuclear architecture during mouse embryonic development. Epigenetic changes linked to the use of assisted reproductive technologies are also considered.