Chromatin analysis in human early development reveals epigenetic transition during ZGA

ACSS2 mediates an epigenetic pathway to regulate β-cell adaptation during gestation in mice

Maternal pancreatic β-cells undergo adaptive changes to meet the metabolic demands of pregnancy, and disruptions in this adaptation can lead to gestational diabetes mellitus. However, the mechanisms governing this adaptation remain largely unexplored. Using single-cell transcriptome combined with genetic analyses, we identified a precise process of β-cell adaptation in mice, characterized by progressive metabolic stress-related β-cell dysfunction, increased acetyl-CoA biosynthesis, and gene element-specific histone acetylation. STAT3 recruits p300 to promote histone acetylation of pregnancy-associated genes, a process enhanced by Acetyl-CoA Synthetase 2 (ACSS2). High-fat feeding induces hyperacetylation of chromatin regions specifically opened during pregnancy, leading to the overexpression of genes that impair β-cell function. However, these impairments can be rescued by β-cell-specific deletion of Acss2. Notably, ACSS2 is functionally implicated in the early establishment of β-cell adaptation in HFD-fed mice but does not appear to play a role in standard diet-fed mice until after the initiation of adaptation. Our study uncovers a finely regulated β-cell adaptation process at the single-cell level during pregnancy and identifies a specific epigenetic pathway that governs this process. These findings provide insights into β-cell plasticity and potential therapeutic strategies for gestational diabetes mellitus.

Single-cell proteomics analysis of human oocytes during GV-to-MI transition

STUDY QUESTION

Which proteins are involved in the transition of human oocytes from the germinal vesicle (GV) to metaphase I (MI) phase?

SUMMARY ANSWER

A total of 2369 proteins were identified, including 149 with significantly differential expression, 79 with upregulated expression in MI oocytes and 70 with downregulated expression.

WHAT IS KNOWN ALREADY

During oocyte maturation, maternal proteins and RNA are stored to support early embryo development. However, GV oocytes matured in vitro have a lower chance of developing into blastocysts than MI oocytes. Therefore, identifying key differentially expressed proteins between the GV and MI stages can provide a better understanding of human oocyte development and maturation mechanisms and improve the utilization of oocytes.

STUDY DESIGN, SIZE, DURATION

In total, 16 oocytes at the GV and MI stages were collected from female patients who underwent ovulation induction due to male factor infertility requiring embryo retrieval for ICSI. Differential proteins were identified in 16 oocytes using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis, and the expression of several differential proteins was verified by immunofluorescence (IF). RNA interference was employed to identify the functions of specific proteins during oocyte maturation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

16 immature human oocytes discarded during ICSI cycles (eight GV oocytes and eight MI oocytes) were collected from 10 female patients. Two cohorts of oocytes underwent zona pellucida removal, lysis, and enzymatic digestion prior to peptide detection using LC-MS/MS methodology. Peptide detection outcomes were subjected to differential protein screening and functional annotation employing distinct analytical algorithms and datasets. To corroborate the sequencing findings, proteins exhibiting notable differential expression were authenticated via IF. Concerning protein functionality, siRNA was introduced during the GV phase, and oocyte maturation was evaluated through observation of polar body extrusion, alongside assessment of siRNA interference efficacy via IF analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 2369 proteins were identified, including 149 with significantly differential expression, 79 with upregulated expression in MI oocytes and 70 with downregulated expression. Gene ontology functional annotation and functional analysis revealed that these differentially expressed proteins are involved mainly in organic matter and cell metabolism, biological regulation, primary metabolism, nitrogen compound metabolism, and other biological processes. Kyoto Encyclopedia of Genes and Genomes analysis revealed that the differentially expressed genes were involved mainly in the following pathways: transport and catabolism, signal transduction, protein folding, and energy and amino acid metabolism. The differentially expressed proteins included actin-related protein 2 (ACTR2), NADH: Ubiquinone Oxidoreductase Core Subunit S1 (NDUFS1), Tubulin Gamma Complex Component 3 (TUBGCP3), Heat Shock Protein Family B (Small) Member 1 (HSPB1), and Eukaryotic Translation Initiation Factor 3 Subunit B, which are involved mainly in mitochondrial function, cell division, and signal transduction. ACTR2, HSPB1, NDUFS1, and TUBGCP3 were selected for IF staining, and the difference in fluorescence intensity between GV and MI oocytes was consistent with the sequencing results. Three pairs of primers were designed for each gene corresponding to the top 10 differentially upregulated and downregulated proteins (with siRNAs successfully designed for eight upregulated and seven downregulated proteins) to study their function, and the results revealed that the protein expression of TUBGCP3 was downregulated after RNA interference.

LARGE SCALE DATA

See supplementary tables.

LIMITATIONS, REASONS FOR CAUTION

Although we have identified some differentially expressed proteins during the transition from human oocyte GV to MI stage, their crucial roles in oocyte maturation remain elusive. To elucidate the functions of these proteins in oocyte maturation, we have generated conditional knockout mice targeting selected proteins.

WIDER IMPLICATIONS OF THE FINDINGS

We conducted single-cell level analysis to identify differentially expressed proteins between the human oocyte GV and MI stages. Our objective is to ascertain the potential of supplementing these proteins in the in vitro maturation culture medium to augment both oocyte maturation rates and quality.

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by the National Natural Science Foundation of China (82171599 and 82471657, B.X., 82301871, L.L.); China Postdoctoral Science Foundation (2024M763169, S.B.); and the National Key Research and Development Project of China (2029YFA0802600, B.X.). None of the authors has any conflict of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Combining ATAC-seq and RNA-seq reveals key genes for gonadal abnormalities in one-month-old XX-DSD pigs

BACKGROUND

Disorders of Sex Development (DSD) are caused by congenital abnormalities in the chromosomes, and subsequent development of gonads or sexual anatomy. XX-DSD pigs exhibit a series of adverse symptoms such as sterility, genital infections, and decline in meat quality, leading to significant economic losses in the breeding industry. However, the understanding of the etiology and pathogenesis of XX-DSD in pigs remains limited. To investigate the molecular mechanisms underlying abnormal gonadal development in XX-DSD pigs, we analyzed the gonads of 1-month-old XX-DSD pigs, normal females, and normal males using RNA-seq and ATAC-seq techniques.

RESULTS

From RNA-seq, we identified potential genes involved in gonadal development in XX-DSD pigs, including SOX9, HSD3B1, CYP19A1, CCNB2, CYP11A1, DMRT1, and MGP. Following this, we analyzed ATAC-seq data and identified 14,820 differential accessible chromatin peaks. Then, by integrating the ATAC-seq and RNA-seq analysis results, we identified several candidate genes (SOX9, COL1A1, COL1A2, FDX1, COL6A1, HSD3B1, FSHR, and CYP17A1) that might be associated with sex development. Through PPI (Protein-Protein Interaction Networks) analysis, we found that SOX9 gene was the top hub gene. Furthermore, we confirmed the effect of the open chromatin region on SOX9 gene expression by a dual-luciferase reporter assay, thus further validating the critical role of this open region in regulating SOX9 expression.

CONCLUSIONS

This study elucidates the critical regulatory role of specific open chromatin structures in the SOX9 gene promoter region (8647563-8648475) in gonadal development of XX-DSD pigs. Additionally, we identify that genes such as SOX9, HSD3B1, and CYP19A1 act in concert to participate in gonadal development. These findings provide molecular evidence for the dynamic chromatin regulatory network underlying gonadal dysgenesis in XX-DSD and lay the foundation for subsequent mechanistic studies.

Tracking single-cell evolution using clock-like chromatin accessibility loci

Single-cell chromatin accessibility sequencing (scATAC-seq) reconstructs developmental trajectory by phenotypic similarity. However, inferring the exact developmental trajectory is challenging. Previous studies showed age-associated DNA methylation (DNAm) changes in specific genomic regions, termed clock-like differential methylation loci (ClockDML). Age-associated DNAm could either result from or result in chromatin accessibility changes at ClockDML. As cells undergo mitosis, the heterogeneity of chromatin accessibility on clock-like loci is reduced, providing a measure of mitotic age. In this study, we developed a method, called EpiTrace, that counts the fraction of opened clock-like loci from scATAC-seq data to determine cell age and perform lineage tracing in various cell lineages and animal species. It shows concordance with known developmental hierarchies, correlates well with DNAm-based clocks and is complementary with mutation-based lineage tracing, RNA velocity and stemness predictions. Applying EpiTrace to scATAC-seq data reveals biological insights with clinically relevant implications, ranging from hematopoiesis, organ development, tumor biology and immunity to cortical gyrification.

Super RNA Pol II domains enhance minor ZGA through 3D interaction to ensure the integrity of major transcriptional waves in late-ZGA mammals

Zygotic genome activation (ZGA) occurs at distinct stages across mammals, with mice initiating ZGA at the 2-cell stage and bovines and humans activating the process in the 4- to 8-cell stages. RNA polymerase II (RNA Pol II) gradually initiates ZGA in mice, but regulation in late-ZGA species remains unclear. Here, RNA Pol II profiling in bovine embryos identified strong intergenic clusters that boost minor ZGA gene expression via chromatin interactions and are named super RNA Pol II domains (SPDs). CRISPRi perturbation of SPDs in bovine embryos decreases the expression of minor ZGA genes, whereas the knockdown of these genes disrupts major ZGA and embryogenesis. Rapid enhancement of minor ZGA genes also occurs in human embryos. Alternatively, mouse and porcine oocytes precociously express these minor ZGA genes without SPDs. Thus, SPDs appear to be an adaptation in bovine embryos, promoting minor ZGA gene expression to comparable levels as early-ZGA species, illuminating species-specific regulation of ZGA timing.

Moving toward totipotency: the molecular and cellular features of totipotent and naive pluripotent stem cells

BACKGROUND

Dissecting the key molecular mechanism of embryonic development provides novel insights into embryogenesis and potential intervention strategies for clinical practices. However, the ability to study the molecular mechanisms of early embryo development in humans, such as zygotic genome activation and lineage segregation, is meaningfully constrained by methodological limitations and ethical concerns. Totipotent stem cells have an extended developmental potential to differentiate into embryonic and extraembryonic tissues, providing a suitable model for studying early embryo development. Recently, a series of ground-breaking results on stem cells have identified totipotent-like cells or induced pluripotent stem cells into totipotent-like cells.

OBJECTIVE AND RATIONALE

This review followed the PRISMA guidelines, surveys the current works of literature on totipotent, naive, and formative pluripotent stem cells, introduces the molecular and biological characteristics of those stem cells, and gives advice for future research.

SEARCH METHODS

The search method employed the terms 'totipotent' OR 'naive pluripotent stem cell' OR 'formative pluripotent stem cell' for unfiltered search on PubMed, Web of Science, and Cochrane Library. Papers included were those with information on totipotent stem cells, naive pluripotent stem cells, or formative pluripotent stem cells until June 2024 and were published in the English language. Articles that have no relevance to stem cells, or totipotent, naive pluripotent, or formative pluripotent cells were excluded.

OUTCOMES

There were 152 records included in this review. These publications were divided into four groups according to the species of the cells included in the studies: 67 human stem cell studies, 70 mouse stem cell studies, 9 porcine stem cell studies, and 6 cynomolgus stem cell studies. Naive pluripotent stem cell models have been established in other species such as porcine and cynomolgus. Human and mouse totipotent stem cells, e.g. human 8-cell-like cells, human totipotent blastomere-like cells, and mouse 2-cell-like cells, have been successfully established and exhibit high developmental potency for both embryonic and extraembryonic contributions. However, the observed discrepancies between these cells and real embryos in terms of epigenetics and transcription suggest that further research is warranted. Our results systematically reviewed the established methods, molecular characteristics, and developmental potency of different naive, formative pluripotent, and totipotent stem cells. Furthermore, we provide a parallel comparison between animal and human models, and offer recommendations for future applications to advance early embryo research and assisted reproduction technologies.

WIDER IMPLICATIONS

Totipotent cell models provide a valuable resource to understand the underlying mechanisms of embryo development and forge new paths toward future treatment of infertility and regenerative medicine. However, current in vitro cell models exhibit epigenetic and transcriptional differences from in vivo embryos, and many cell models are unstable across passages, thus imperfectly recapitulating embryonic development. In this regard, standardizing and expanding current research on totipotent stem cell models are essential to enhance our capability to resemble and decipher embryogenesis.

DUX-mediated configuration of p300/CBP drives minor zygotic genome activation independent of its catalytic activity

Maternal-deposited factors initiate zygotic genome activation (ZGA), driving the maternal-to-zygotic transition; however, the coordination between maternal coactivators and transcription factors (TFs) in this process remains unclear. In this study, by profiling the dynamic landscape of p300 during mouse ZGA, we reveal its role in promoting RNA polymerase II (Pol II) pre-configuration at ZGA gene regions and sequentially establishing enhancer activity and regulatory networks. Moreover, p300/CBP-catalyzed acetylation drives Pol II elongation and minor ZGA gene expression by inducing pivotal TFs such as Dux. Remarkably, the supplementation of exogenous Dux rescues ZGA failure and developmental defects caused by the loss of p300/CBP acetylation. DUX functions as a pioneer factor, guiding p300 and Pol II to minor ZGA gene regions and activating them in a manner dependent on the non-catalytic functions of p300/CBP. Together, our findings reveal a mutual dependency between p300/CBP and DUX, highlighting their coordinated role in regulating minor ZGA activation.

Human oocyte quality and reproductive health

Declining female fertility is a health issue that has received broad global attention. Oocyte quality is the key limiting factor of female fertility, and key processes affecting oocyte quality involve the secretion of and response to hormones, ovarian function, oogenesis, oocyte maturation, and meiosis. However, compared with other species, the research and understanding of human oocyte quality and human reproductive health is limited. This review highlights our current understanding of the physiological factors and pathological factors related to human oocyte quality and discusses potential treatments. In terms of physiology, we discuss the regulation of the hypothalamic-pituitary-gonadal axis, granulosa cells, key subcellular structures, maternal mRNA homeostasis, the extracellular matrix, the maternal microenvironment, and multi-omics resources related to human oocyte quality. In terms of pathology, we review hypothalamic-pituitary-gonadal defects, ovarian dysfunction (including premature ovarian insufficiency and polycystic ovary syndrome), human oocyte development defects, and aging. In terms of the pathological aspects of human oocyte development and quality defects, nearly half of the reported pathogenic genes are involved in meiosis, while the remainder are involved in maternal mRNA regulation, the subcortical maternal complex, zona pellucida formation, ion channels, protein transport, and mitochondrial function. Furthermore, we outline the emerging scientific prospects and challenges for future explorations of the biological mechanisms behind infertility and the development of clinical treatments. This review seeks to deepen our understanding of the mechanisms regulating human oocyte quality and to provide novel insights into clinical female infertility characterized by defects in oocyte quality and oocyte development.

Epigenome dynamics in early mammalian embryogenesis

During early embryonic development in mammals, the totipotency of the zygote - which is reprogrammed from the differentiated gametes - transitions to pluripotency by the blastocyst stage, coincident with the first cell fate decision. These changes in cellular potency are accompanied by large-scale alterations in the nucleus, including major transcriptional, epigenetic and architectural remodelling, and the establishment of the DNA replication programme. Advances in low-input genomics and loss-of-function methodologies tailored to the pre-implantation embryo now enable these processes to be studied at an unprecedented level of molecular detail in vivo. Such studies have provided new insights into the genome-wide landscape of epigenetic reprogramming and chromatin dynamics during this fundamental period of pre-implantation development.

Chromatin accessibility landscape of mouse early embryos revealed by single-cell NanoATAC-seq2

In mammals, fertilized eggs undergo genome-wide epigenetic reprogramming to generate the organism. However, our understanding of epigenetic dynamics during preimplantation development at single-cell resolution remains incomplete. Here, we developed scNanoATAC-seq2, a single-cell assay for transposase-accessible chromatin using long-read sequencing for scarce samples. We present a detailed chromatin accessibility landscape of mouse preimplantation development, revealing distinct chromatin signatures in the epiblast, primitive endoderm, and trophectoderm during lineage segregation. Differences between zygotes and two-cell embryos highlight reprogramming in chromatin accessibility during the maternal-to-zygotic transition. Single-cell long-read sequencing enables in-depth analysis of chromatin accessibility in noncanonical imprinting, imprinted X chromosome inactivation, and low-mappability genomic regions, such as repetitive elements and paralogs. Our data provide insights into chromatin dynamics during mammalian preimplantation development and lineage differentiation.

The expression order determines the pioneer functions of NGN3 and NEUROD1 in pancreatic endocrine differentiation

Pioneer transcription factors (TFs) initiate chromatin remodeling, which is crucial for gene regulation and cell differentiation. In this study, we investigated how the sequential expression of neurogenin 3 (NGN3) and NEUROD1 affects their pioneering functions during pancreatic endocrine differentiation. Using a genetically engineered mouse model, we mapped NGN3-binding sites, confirming the pivotal role of this molecule in regulating chromatin accessibility. The pioneering function of NGN3 involves dose tolerance, and low doses are sufficient. Although NEUROD1 generally acts as a conventional TF, it can assume a pioneering role in the absence of NGN3. The sequential expression of NeuroD1 and Ngn3 predominantly drives α cell generation, which may explain the inefficient β cell induction observed in vitro. Our findings demonstrate that pioneer activity is dynamically shaped by temporal TF expression and inter-TF interactions, providing insights into transcriptional regulation and its implications for disease mechanisms and therapeutic targeting and enhancing in vitro differentiation strategies.

IL-24 promotes atopic dermatitis-like inflammation through driving MRSA-induced allergic responses

Atopic dermatitis (AD) is a prevalent inflammatory skin disorder in which patients experience recurrent eczematous lesions and intense itching. The colonization of Staphylococcus aureus (S. aureus) is correlated with the severity of the disease, but its role in AD development remains elusive. Using single-cell RNA sequencing, we uncovered that keratinocytes activate a distinct immune response characterized by induction of Il24 when exposed to methicillin-resistant S. aureus (MRSA). Further experiments using animal models showed that the administration of recombinant IL-24 protein worsened AD-like pathology. Genetic ablation of Il24 or the receptor Il20rb in keratinocytes alleviated allergic inflammation and atopic march. Mechanistically, IL-24 acted through its heterodimeric receptors on keratinocytes and augmented the production of IL-33, which in turn aggravated type 2 immunity and AD-like skin conditions. Overall, these findings establish IL-24 as a critical factor for onset and progression of AD and a compelling therapeutic target.

Methionine regulates maternal-fetal immune tolerance and endometrial receptivity by enhancing embryonic IL-5 secretion

Endometrial receptivity and maternal-fetal immune tolerance are two crucial processes for a successful pregnancy. However, the molecular mechanisms of nutrition involved are largely unexplored. Here, we showed that maternal methionine supply significantly improved pregnancy outcomes, which was closely related to interleukin-5 (IL-5) concentration. Mechanistically, methionine induced embryonic IL-5 secretion, which enhanced the conversion of CD4+ T cells to IL-5+ Th2 cells in the uterus, thereby improving maternal-fetal immune tolerance. Meanwhile, methionine-mediated IL-5 secretion activated the nuclear factor κB (NF-κB) pathway and enhanced integrin αvβ3 expression in endometrial cells, which improved endometrial receptivity. Further, methionine strongly influenced the DNA methylation and transcription levels of the transcription factor eomesodermin (Eomes), which bound directly to the IL-5 promoter region and inhibited IL-5 transcription. Methionine modulated IL-5 transcription, maternal-fetal immune tolerance, and endometrial receptivity via its effects on Eomes. This study reveals the crucial functions of methionine and IL-5 and offers a potential nutritional strategy for successful pregnancy.

Comparative proteomic landscapes elucidate human preimplantation development and failure

Understanding mammalian preimplantation development, particularly in humans, at the proteomic level remains limited. Here, we applied our comprehensive solution of ultrasensitive proteomic technology to measure the proteomic profiles of oocytes and early embryos and identified nearly 8,000 proteins in humans and over 6,300 proteins in mice. We observed distinct proteomic dynamics before and around zygotic genome activation (ZGA) between the two species. Integrative analysis with translatomic data revealed extensive divergence between translation activation and protein accumulation. Multi-omic analysis indicated that ZGA transcripts often contribute to protein accumulation in blastocysts. Using mouse embryos, we identified several transcriptional regulators critical for early development, thereby linking ZGA to the first lineage specification. Furthermore, single-embryo proteomics of poor-quality embryos from over 100 patient couples provided insights into preimplantation development failure. Our study may contribute to reshaping the framework of mammalian preimplantation development and opening avenues for addressing human infertility.

MicroRNAs bta-novel-miR-117, bta-novel-miR-234 and bta-novel-miR-417 have adverse effects on blastocyst formation

In a previous study we found that the levels of the novel microRNAs (miRNAs) bta-novel-miR-117 bta-novel-miR-234 and bta-novel-miR-417 (P < 0.001) are significantly up-regulated in extracellular vesicles (EVs) in the culture medium of degenerating embryos compared to blastocysts. Because the functions of these novel miRNAs are still unknown, we investigated their regulatory roles during bovine blastocyst development by adding their mimics and inhibitors to the culture medium. The addition of mimics for bta-novel-miR-117, bta-novel-miR-234 and bta-novel-miR-417 resulted in a decreased blastocyst rate, and supplementation of bta-novel-miR-234 inhibitors increased the cleavage rate significantly (P < 0.001). Low-input transcriptome analysis and RT-qPCR results revealed that bta-novel-miR-117, bta-novel-miR-234 and bta-novel-miR-417 co-target genes such as ANKEF1, HAND2 and SLC2A2, downregulated their expression significantly (P < 0.001). These genes associated with glucose transmembrane transport and plasma membrane raft metabolism play crucial roles in embryonic development. The results suggest that overexpressing of these three novel miRNAs impairs embryonic development, and they might serve as biomarkers to detect failing bovine embryos.

The nuclear matrix stabilizes primed-specific genes in human pluripotent stem cells

The nuclear matrix, a proteinaceous gel composed of proteins and RNA, is an important nuclear structure that supports chromatin architecture, but its role in human pluripotent stem cells (hPSCs) has not been described. Here we show that by disrupting heterogeneous nuclear ribonucleoprotein U (HNRNPU) or the nuclear matrix protein, Matrin-3, primed hPSCs adopted features of the naive pluripotent state, including morphology and upregulation of naive-specific marker genes. We demonstrate that HNRNPU depletion leads to increased chromatin accessibility, reduced DNA contacts and increased nuclear size. Mechanistically, HNRNPU acts as a transcriptional co-factor that anchors promoters of primed-specific genes to the nuclear matrix with POLII to promote their expression and their RNA stability. Overall, HNRNPU promotes cell-type stability and when reduced promotes conversion to earlier embryonic states.

TBP bookmarks and preserves neural stem cell fate memory by orchestrating local chromatin architecture

Mitotic bookmarking has been posited as an important strategy for cells to faithfully propagate their fate memory through cell generations. However, the physiological significance and regulatory mechanisms of mitotic bookmarking in neural development remain unexplored. Here, we identified TATA-binding protein (TBP) as a crucial mitotic bookmarker for preserving the fate memory of Drosophila neural stem cells (NSCs). Phosphorylation by the super elongation complex (SEC) is important for TBP to retain as discrete foci at mitotic chromosomes of NSCs to effectively transmit their fate memory. TBP depletion leads to drastic NSC loss, whereas TBP overexpression enhances the ability of SEC to induce neural progenitor dedifferentiation and tumorigenesis. Importantly, TBP achieves its mitotic retention through recruiting the chromatin remodeler EP400, which in turn increases local chromatin accessibility via depositing H2A.Z. Thus, local chromatin remodeling ensures mitotic bookmarking, which may represent a general principle underlying the preservation of cell fate memory.

RNA surveillance by the RNA helicase MTR4 determines volume of mouse oocytes

Oocytes are the largest cell type in multicellular animals. Here, we show that mRNA transporter 4 (MTR4) is indispensable for oocyte growth and functions as part of the RNA surveillance mechanism, which is responsible for nuclear waste RNA clearance. MTR4 ensures the normal post-transcriptional processing of maternal RNAs, their nuclear export to the cytoplasm, and the accumulation of properly processed transcripts. Oocytes with Mtr4 knockout fail to accumulate sufficient and normal transcripts in the cytoplasm and cannot grow to normal sizes. MTR4-dependent RNA surveillance has a previously unrecognized function in maintaining a stable nuclear environment for the establishment of non-canonical histone H3 lysine-4 trimethylation and chromatin reorganization, which is necessary to form a nucleolus-like structure in oocytes. In conclusion, MTR4-dependent RNA surveillance activity is a checkpoint that allows oocytes to grow to a normal size, undergo nuclear and cytoplasmic maturation, and acquire developmental competence.

Rise and SINE: roles of transcription factors and retrotransposons in zygotic genome activation

In sexually reproducing organisms, life begins with the fusion of transcriptionally silent gametes, the oocyte and sperm. Although initiation of transcription in the embryo, known as zygotic genome activation (ZGA), is universally required for development, the transcription factors regulating this process are poorly conserved. In this Perspective, we discuss recent insights into the mechanisms of ZGA in totipotent mammalian embryos, namely ZGA regulation by several transcription factors, including by orphan nuclear receptors (OrphNRs) such as the pioneer transcription factor NR5A2, and by factors of the DUX, TPRX and OBOX families. We performed a meta-analysis and compiled a list of pan-ZGA genes, and found that most of these genes are indeed targets of the above transcription factors. Remarkably, more than a third of these ZGA genes appear to be regulated both by OrphNRs such as NR5A2 and by OBOX proteins, whose motifs co-occur in SINE B1 retrotransposable elements, which are enriched near ZGA genes. We propose that ZGA in mice is activated by recruitment of multiple transcription factors to SINE B1 elements that function as enhancers, and discuss a potential relevance of this mechanism to Alu retrotransposable elements in human ZGA.

Exploring key embryonic developmental morphokinetic parameters that affect clinical outcomes during the PGT cycle using time-lapse monitoring systems

RESEARCH QUESTION

Is it possible to predict blastocyst quality, embryo chromosomal ploidy, and clinical pregnancy outcome after single embryo transfer from embryo developmental morphokinetic parameters?

DESIGN

The morphokinetic parameters of 1011 blastocysts from 227 patients undergoing preimplantation genetic testing were examined. Correlations between the morphokinetic parameters and the quality of blastocysts, chromosomal ploidy, and clinical pregnancy outcomes following the transfer of single blastocysts were retrospectively analyzed.

RESULTS

The morphokinetic parameters of embryos in the high-quality blastocyst group were significantly shorter than those in the low-quality blastocyst group (p < 0.05). In contrast, the CC2 time was significantly prolonged (p < 0.05). On chromosomal analysis of biopsy blastocysts nourished by trophectoderm cells, in comparison to euploid embryos, aneuploid embryos exhibited significant extensions in tPNa, S3, tSC, tM, tSB, and tB (p < 0.05), with a simultaneous significant reduction in CC2 time (p < 0.05). After adjusting for age and body mass index through logistic regression analysis, late morphokinetic parameters, namely tM (OR 0.96; 95% CI 0.93-0.99), tSB (OR 0.94; 95% CI 0.90-0.97), and tB (OR 0.93; 95% CI 0.90-0.97), emerged as independent risk factors influencing the development of embryos into high-quality blastocysts. S3 (< 12.01 h), t8 (< 62.48 h), and tPB2 (< 3.36 h) were potential predictors of a successful clinical pregnancy after blastocyst transfer.

CONCLUSION

Morphokinetic parameters showed correlations with blastocyst quality, chromosomal status, and clinical pregnancy outcomes post-transfer, making them effective predictors for clinical results. Embryos with relatively rapid development tended to exhibit better blastocyst quality, chromosomal ploidy, and improved clinical pregnancy outcomes. The late morphokinetic parameter, S3, demonstrated a strong predictive effect on blastocyst quality, chromosomal ploidy, and clinical pregnancy outcomes.

Chromatin accessibility: biological functions, molecular mechanisms and therapeutic application

The dynamic regulation of chromatin accessibility is one of the prominent characteristics of eukaryotic genome. The inaccessible regions are mainly located in heterochromatin, which is multilevel compressed and access restricted. The remaining accessible loci are generally located in the euchromatin, which have less nucleosome occupancy and higher regulatory activity. The opening of chromatin is the most important prerequisite for DNA transcription, replication, and damage repair, which is regulated by genetic, epigenetic, environmental, and other factors, playing a vital role in multiple biological progresses. Currently, based on the susceptibility difference of occupied or free DNA to enzymatic cleavage, solubility, methylation, and transposition, there are many methods to detect chromatin accessibility both in bulk and single-cell level. Through combining with high-throughput sequencing, the genome-wide chromatin accessibility landscape of many tissues and cells types also have been constructed. The chromatin accessibility feature is distinct in different tissues and biological states. Research on the regulation network of chromatin accessibility is crucial for uncovering the secret of various biological processes. In this review, we comprehensively introduced the major functions and mechanisms of chromatin accessibility variation in different physiological and pathological processes, meanwhile, the targeted therapies based on chromatin dynamics regulation are also summarized.

The impact of retrotransposons on zygotic genome activation and the chromatin landscape of early embryos

In mammals, fertilization is followed by extensive reprogramming and reorganization of the chromatin accompanying the transcriptional activation of the embryo. This reprogramming results in blastomeres with the ability to give rise to all cell types and a complete organism, including extra-embryonic tissues, and is known as totipotency. Transcriptional activation occurs in a process known as zygotic genome activation (ZGA) and is tightly linked to the expression of transposable elements, including endogenous retroviruses (ERVs) such as endogenous retrovirus with leucine tRNA primer (ERVL). Recent studies discovered the importance of ERVs in this process, yet the race to decipher the network surrounding these elements is still ongoing, and the molecular mechanism behind their involvement remains a mystery. Amid a recent surge of studies reporting the discovery of various factors and pathways involved in the regulation of ERVs, this review provides an overview of the knowns and unknowns in the field, with a particular emphasis on the chromatin landscape and how ERVs shape preimplantation development in mammals. In so doing, we highlight recent discoveries that have advanced our understanding of how these elements are involved in transforming the quiescent zygote into the most powerful cell type in mammals.

Mechanistic insights into zinc oxide nanoparticles induced embryotoxicity via H3K9me3 modulation

The widespread application of nanoparticles (NPs) in various fields has raised health concerns, especially in reproductive health. Our research has shown zinc oxide nanoparticles (ZnONPs) exhibit the most significant toxicity to pre-implantation embryos in mice compared to other common NPs. In patients undergoing assisted reproduction technology (ART), a significant negative correlation was observed between Zn concentration and clinical outcomes. Therefore, this study explores the impact of ZnONPs exposure on pre-implantation embryonic development and its underlying mechanisms. We revealed that both in vivo and in vitro exposure to ZnONPs impairs pre-implantation embryonic development. Moreover, ZnONPs were found to reduce the pluripotency of mouse embryonic stem cells (mESCs), as evidenced by teratoma and diploid chimera assays. Employing multi-omics approaches, including RNA-Seq, CUT&Tag, and ATAC-seq, the embryotoxicity mechanisms of ZnONPs were elucidated. The findings indicate that ZnONPs elevate H3K9me3 levels, leading to increased heterochromatin and consequent inhibition of gene expression related to development and pluripotency. Notably, Chaetocin, a H3K9me3 inhibitor, sucessfully reversed the embryotoxicity effects induced by ZnONPs. Additionally, the direct interaction between ZnONPs and H3K9me3 was verified through pull-down and immunoprecipitation assays. Collectively, these findings offer new insights into the epigenetic mechanisms of ZnONPs toxicity, enhancing our understanding of their impact on human reproductive health.

Long-range transcription factor binding sites clustered regions may mediate transcriptional regulation through phase-separation interactions in early human embryo

In mammals, during the post-fertilization pre-implantation phase, the expression of cell type-specific genes is crucial for normal embryonic development, which is regulated by cis-regulatory elements (CREs). TFs control gene expression by interacting with CREs. Research shows that transcription factor binding sites (TFBSs) reflect the general characteristics of the regulatory genome. Here, we identified TFBSs from chromatin accessibility data in five stages of early human embryonic development, and quantified transcription factor binding sites-clustered regions (TFCRs) and their complexity (TC). Assigning TC values to TFCRs has made it possible to assess the functionality of these regulatory elements in a more quantitative way. Our findings reveal a robust correlation between TFCR complexity and gene expression starting from the 8Cell stage, which is when the zygotic genome is activated in humans. Furthermore, we have defined long-range TFCRs (LR-TFCRs) and conjecture that LR-TFCRs may regulate gene expression through phase-separation mechanisms during the early stages of human embryonic development.

Kick-starting the zygotic genome: licensors, specifiers, and beyond

Zygotic genome activation (ZGA), the first transcription event following fertilization, kickstarts the embryonic program that takes over the control of early development from the maternal products. How ZGA occurs, especially in mammals, is poorly understood due to the limited amount of research materials. With the rapid development of single-cell and low-input technologies, remarkable progress made in the past decade has unveiled dramatic transitions of the epigenomes, transcriptomes, proteomes, and metabolomes associated with ZGA. Moreover, functional investigations are yielding insights into the key regulators of ZGA, among which two major classes of players are emerging: licensors and specifiers. Licensors would control the permission of transcription and its timing during ZGA. Accumulating evidence suggests that such licensors of ZGA include regulators of the transcription apparatus and nuclear gatekeepers. Specifiers would instruct the activation of specific genes during ZGA. These specifiers include key transcription factors present at this stage, often facilitated by epigenetic regulators. Based on data primarily from mammals but also results from other species, we discuss in this review how recent research sheds light on the molecular regulation of ZGA and its executors, including the licensors and specifiers.

A conserved germline-specific Dsn1 alternative splice isoform supports oocyte and embryo development

The chromosome segregation and cell division programs associated with somatic mitosis and germline meiosis display dramatic differences such as kinetochore orientation, cohesin removal, or the presence of a gap phase.1,2,3,4,5,6 These changes in chromosome segregation require alterations to the established cell division machinery.5,6 It remains unclear what aspects of kinetochore function and its regulatory control differ between the mitotic and meiotic cell divisions to rewire these core processes. Alternative RNA splicing can generate distinct protein isoforms to allow for the differential control of cell processes across cell types. However, alternative splice isoforms that differentially modulate distinct cell division programs have remained elusive. Here, we demonstrate that mammalian germ cells express an alternative mRNA splice isoform for the kinetochore component, DSN1, a subunit of the MIS12 complex that links the centromeres to spindle microtubules during chromosome segregation. This germline DSN1 isoform bypasses the requirement for Aurora kinase phosphorylation for its centromere localization due to the absence of a key regulatory region allowing DSN1 to display persistent centromere localization. Expression of the germline DSN1 isoform in somatic cells results in constitutive kinetochore localization, chromosome segregation errors, and growth defects, providing an explanation for its tight cell-type-specific expression. Reciprocally, precisely eliminating expression of the germline-specific DSN1 splice isoform in mouse models disrupts oocyte maturation and early embryonic divisions coupled with a reduction in fertility. Together, this work identifies a germline-specific splice isoform for a chromosome segregation component and implicates its role in mammalian fertility.

Distinct dynamics of parental 5-hydroxymethylcytosine during human preimplantation development regulate early lineage gene expression

The conversion of DNA 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) by TET enzymes represents a significant epigenetic modification, yet its role in early human embryos remains largely unknown. Here we showed that the early human embryo inherited a significant amount of 5hmCs from an oocyte, which unexpectedly underwent de novo hydroxymethylation during its growth. Furthermore, the generation of 5hmC in the paternal genome after fertilization roughly followed the maternal pattern, which was linked to DNA methylation dynamics and regions of sustained methylation. The 5hmCs persisted until the eight-cell stage and exhibited high enrichment at OTX2 binding sites, whereas knockdown of OTX2 in human embryos compromised the expression of early lineage genes. Specifically, the depletion of 5hmC affected the activation of embryonic genes, which was further evaluated by ectopically expressing mouse Tet3 in human early embryos. These findings revealed distinct dynamics of 5hmC and unravelled its multifaceted functions in early human embryonic development.

Epigenetic inheritance of acquired traits via stem cells dedifferentiation/differentiation or transdifferentiation cycles

Inheritance of acquired characteristics is the once widely accepted idea that multiple modifications acquired by an organism during its life, can be inherited by the offspring. This belief is at least as old as Hippocrates and became popular in early 19th century, leading Lamarck to suggest his theory of evolution. Charles Darwin, along with other thinkers of the time attempted to explain the mechanism of acquired traits' inheritance by proposing the theory of pangenesis. While later this and similar theories were rejected because of the lack of hard evidence, the studies aimed at revealing the mechanism by which somatic information can be passed to germ cells have continued up to the present. In this paper, we present a new theory and provide supporting literature to explain this phenomenon. We hypothesize existence of pluripotent adult stem cells that can serve as collectors and carriers of new epigenetic traits by entering different developmentally active organ/tissue compartments through blood circulation and acquiring new epigenetic marks though cycles of differentiation/dedifferentiation or transdifferentiation. During gametogenesis, these epigenetically modified cells are attracted by gonads, transdifferentiate into germ cells, and pass the acquired epigenetic modifications collected from the entire body's somatic cells to the offspring.

RNAseq analysis of oocyte maturation from the germinal vesicle stage to metaphase II in pig and human

During maturation oocytes at the germinal vesicle (GV) stage progress to metaphase II (MII). However, during in vitro maturation a proportion often fail to progress. To understand these processes, we employed RNA sequencing to examine the transcriptome profile of these three groups of oocytes from the pig. We compared our findings with similar public oocyte data from humans. The transcriptomes in oocytes that failed to progress was similar to those that did. We found in both species, the most upregulated genes in MII oocytes were associated with chromosome segregation and cell cycle processes, while the most down regulated genes were relevant to ribosomal and mitochondrial pathways. Moreover, those genes involved in chromosome segregation during GV to MII transition were conserved in pig and human. We also compared MII and GV oocyte transcriptomes at the isoform transcript level in both species. Several thousands of genes (including DTNBP1, MAPK1, RAB35, GOLGA7, ATP1A1 and ATP2B1) identified as not different in expression at a gene transcript level were found to have differences in isoform transcript levels. Many of these genes were involved in ATPase-dependent or GTPase-dependent intracellular transport in pig and human, respectively. In conclusion, our study suggests the failure to progress to MII in vitro may not be regulated at the level of the genome and that many genes are differentially regulated at the isoform level, particular those involved ATPase- or GTPase-dependent intracellular transport.

Functional Characterization of Ao4g24: An Uncharacterized Gene Involved in Conidiation, Trap Formation, Stress Response, and Secondary Metabolism in Arthrobotrys oligospora

Arthrobotrys oligospora is a typical nematode-trapping (NT) fungus, which can secrete food cues to lure, capture, and digest nematodes by triggering the production of adhesive networks (traps). Based on genomic and proteomic analyses, multiple pathogenic genes and proteins involved in trap formation have been characterized; however, there are numerous uncharacterized genes that play important roles in trap formation. The functional studies of these unknown genes are helpful in systematically elucidating the complex interactions between A. oligospora and nematode hosts. In this study, we screened the gene AOL_s00004g24 (Ao4g24). This gene is similar to the SWI/SNF chromatin remodeling complex, which was found to play a potential role in trap formation in our previous transcriptome analysis. Here, we characterized the function of Ao4g24 by gene disruption, phenotypic analysis, and metabolomics. The deletion of Ao4g24 led to a remarkable decrease in conidia yield, trap formation, and secondary metabolites. Meanwhile, the absence of Ao4g24 influenced the mitochondrial membrane potential, ATP content, autophagy, ROS level, and stress response. These results indicate that Ao4g24 has crucial functions in sporulation, trap formation, and pathogenicity in NT fungi. Our study provides a reference for understanding the role of unidentified genes in mycelium growth and trap formation in NT fungi.

The developmental and evolutionary characteristics of transcription factor binding site clustered regions based on an explainable machine learning model

Gene expression is temporally and spatially regulated by the interaction of transcription factors (TFs) and cis-regulatory elements (CREs). The uneven distribution of TF binding sites across the genome poses challenges in understanding how this distribution evolves to regulate spatio-temporal gene expression and consequent heritable phenotypic variation. In this study, chromatin accessibility profiles and gene expression profiles were collected from several species including mammals (human, mouse, bovine), fish (zebrafish and medaka), and chicken. Transcription factor binding sites clustered regions (TFCRs) at different embryonic stages were characterized to investigate regulatory evolution. The study revealed dynamic changes in TFCR distribution during embryonic development and species evolution. The synchronization between TFCR complexity and gene expression was assessed across species using RegulatoryScore. Additionally, an explainable machine learning model highlighted the importance of the distance between TFCR and promoter in the coordinated regulation of TFCRs on gene expression. Our results revealed the developmental and evolutionary dynamics of TFCRs during embryonic development from fish, chicken to mammals. These data provide valuable resources for exploring the relationship between transcriptional regulation and phenotypic differences during embryonic development.

Histone H3K18 and Ezrin Lactylation Promote Renal Dysfunction in Sepsis-Associated Acute Kidney Injury

Histone lactylation is a metabolic stress-related histone modification. However, the role of histone lactylation in the development of sepsis-associated acute kidney injury (SA-AKI) remains unclear. Here, histone H3K18 lactylation (H3K18la) is elevated in SA-AKI, which is reported in this study. Furthermore, this lactate-dependent histone modification is enriched at the promoter of Ras homolog gene family member A (RhoA) and positively correlated with the transcription. Correction of abnormal lactate levels resulted in a reversal of abnormal histone lactylation at the promoter of RhoA. Examination of related mechanism revealed that histone lactylation promoted the RhoA/Rho-associated protein kinase (ROCK) /Ezrin signaling, the activation of nuclear factor-κB (NF-κB), inflammation, cell apoptosis, and aggravated renal dysfunction. In addition, Ezrin can undergo lactylation modification. Multiple lactylation sites are identified in Ezrin and confirmed that lactylation mainly occurred at the K263 site. The role of histone lactylation is revealed in SA-AKI and reportes a novel post-translational modification in Ezrin. Its potential role in regulating inflammatory metabolic adaptation of renal proximal tubule epithelial cells is also elucidated. The results provide novel insights into the epigenetic regulation of the onset of SA-AKI.

Technology to the rescue: how to uncover the role of transposable elements in preimplantation development

Transposable elements (TEs) are highly expressed in preimplantation development. Preimplantation development is the phase when the cells of the early embryo undergo the first cell fate choice and change from being totipotent to pluripotent. A range of studies have advanced our understanding of TEs in preimplantation, as well as their epigenetic regulation and functional roles. However, many questions remain about the implications of TE expression during early development. Challenges originate first due to the abundance of TEs in the genome, and second because of the limited cell numbers in preimplantation. Here we review the most recent technological advancements promising to shed light onto the role of TEs in preimplantation development. We explore novel avenues to identify genomic TE insertions and improve our understanding of the regulatory mechanisms and roles of TEs and their RNA and protein products during early development.

Capturing totipotency in human cells through spliceosomal repression

The cleavage of zygotes generates totipotent blastomeres. In human 8-cell blastomeres, zygotic genome activation (ZGA) occurs to initiate the ontogenesis program. However, capturing and maintaining totipotency in human cells pose significant challenges. Here, we realize culturing human totipotent blastomere-like cells (hTBLCs). We find that splicing inhibition can transiently reprogram human pluripotent stem cells into ZGA-like cells (ZLCs), which subsequently transition into stable hTBLCs after long-term passaging. Distinct from reported 8-cell-like cells (8CLCs), both ZLCs and hTBLCs widely silence pluripotent genes. Interestingly, ZLCs activate a particular group of ZGA-specific genes, and hTBLCs are enriched with pre-ZGA-specific genes. During spontaneous differentiation, hTBLCs re-enter the intermediate ZLC stage and further generate epiblast (EPI)-, primitive endoderm (PrE)-, and trophectoderm (TE)-like lineages, effectively recapitulating human pre-implantation development. Possessing both embryonic and extraembryonic developmental potency, hTBLCs can autonomously generate blastocyst-like structures in vitro without external cell signaling. In summary, our study provides key criteria and insights into human cell totipotency.

Pioneer Transcription Factors: The First Domino in Zygotic Genome Activation

Zygotic genome activation (ZGA) is a pivotal event in mammalian embryogenesis, marking the transition from maternal to zygotic control of development. During the ZGA process that is characterized by the intricate cascade of gene expression, who tipped the first domino in a meticulously arranged sequence is a subject of paramount interest. Recently, Dux, Obox and Nr5a2 were identified as pioneer transcription factors that reside at the top of transcriptional hierarchy. Through co-option of retrotransposon elements as hubs for transcriptional activation, these pioneer transcription factors rewire the gene regulatory network, thus initiating ZGA. In this review, we provide a snapshot of the mechanisms underlying the functions of these pioneer transcription factors. We propose that ZGA is the starting point where the embryo's own genome begins to influence development trajectory, therefore in-depth dissecting the functions of pioneer transcription factors during ZGA will form a cornerstone of our understanding for early embryonic development, which will pave the way for advancing our grasp of mammalian developmental biology and optimizing in vitro production (IVP) techniques.

Frameshift variants in C10orf71 cause dilated cardiomyopathy in human, mouse, and organoid models

Research advances over the past 30 years have confirmed a critical role for genetics in the etiology of dilated cardiomyopathies (DCMs). However, full knowledge of the genetic architecture of DCM remains incomplete. We identified candidate DCM causal gene, C10orf71, in a large family with 8 patients with DCM by whole-exome sequencing. Four loss-of-function variants of C10orf71 were subsequently identified in an additional group of492 patients with sporadic DCM from 2 independent cohorts. C10orf71 was found to be an intrinsically disordered protein specifically expressed in cardiomyocytes. C10orf71-KO mice had abnormal heart morphogenesis during embryonic development and cardiac dysfunction as adults with altered expression and splicing of contractile cardiac genes. C10orf71-null cardiomyocytes exhibited impaired contractile function with unaffected sarcomere structure. Cardiomyocytes and heart organoids derived from human induced pluripotent stem cells with C10orf71 frameshift variants also had contractile defects with normal electrophysiological activity. A rescue study using a cardiac myosin activator, omecamtiv mecarbil, restored contractile function in C10orf71-KO mice. These data support C10orf71 as a causal gene for DCM by contributing to the contractile function of cardiomyocytes. Mutation-specific pathophysiology may suggest therapeutic targets and more individualized therapy.

Lineage regulators TFAP2C and NR5A2 function as bipotency activators in totipotent embryos

During the first lineage segregation, a mammalian totipotent embryo differentiates into the inner cell mass (ICM) and trophectoderm (TE). However, how transcription factors (TFs) regulate this earliest cell-fate decision in vivo remains elusive, with their regulomes primarily inferred from cultured cells. Here, we investigated the TF regulomes during the first lineage specification in early mouse embryos, spanning the pre-initiation, initiation, commitment, and maintenance phases. Unexpectedly, we found that TFAP2C, a trophoblast regulator, bound and activated both early TE and inner cell mass (ICM) genes at the totipotent (two- to eight-cell) stages ('bipotency activation'). Tfap2c deficiency caused downregulation of early ICM genes, including Nanog, Nr5a2, and Tdgf1, and early TE genes, including Tfeb and Itgb5, in eight-cell embryos. Transcription defects in both ICM and TE lineages were also found in blastocysts, accompanied by increased apoptosis and reduced cell numbers in ICMs. Upon trophoblast commitment, TFAP2C left early ICM genes but acquired binding to late TE genes in blastocysts, where it co-bound with CDX2, and later to extra-embryonic ectoderm (ExE) genes, where it cooperatively co-occupied with the former ICM regulator SOX2. Finally, 'bipotency activation' in totipotent embryos also applied to a pluripotency regulator NR5A2, which similarly bound and activated both ICM and TE lineage genes at the eight-cell stage. These data reveal a unique transcription circuity of totipotency underpinned by highly adaptable lineage regulators.

Tead4 and Tfap2c generate bipotency and a bistable switch in totipotent embryos to promote robust lineage diversification

The mouse and human embryo gradually loses totipotency before diversifying into the inner cell mass (ICM, future organism) and trophectoderm (TE, future placenta). The transcription factors TFAP2C and TEAD4 with activated RHOA accelerate embryo polarization. Here we show that these factors also accelerate the loss of totipotency. TFAP2C and TEAD4 paradoxically promote and inhibit Hippo signaling before lineage diversification: they drive expression of multiple Hippo regulators while also promoting apical domain formation, which inactivates Hippo. Each factor activates TE specifiers in bipotent cells, while TFAP2C also activates specifiers of the ICM fate. Asymmetric segregation of the apical domain reconciles the opposing regulation of Hippo signaling into Hippo OFF and the TE fate, or Hippo ON and the ICM fate. We propose that the bistable switch established by TFAP2C and TEAD4 is exploited to trigger robust lineage diversification in the developing embryo.

Single-cell 3D genome structure reveals distinct human pluripotent states

BACKGROUND

Pluripotent states of embryonic stem cells (ESCs) with distinct transcriptional profiles affect ESC differentiative capacity and therapeutic potential. Although single-cell RNA sequencing has revealed additional subpopulations and specific features of naive and primed human pluripotent stem cells (hPSCs), the underlying mechanisms that regulate their specific transcription and that control their pluripotent states remain elusive.

RESULTS

By single-cell analysis of high-resolution, three-dimensional (3D) genomic structure, we herein demonstrate that remodeling of genomic structure is highly associated with the pluripotent states of human ESCs (hESCs). The naive pluripotent state is featured with specialized 3D genomic structures and clear chromatin compartmentalization that is distinct from the primed state. The naive pluripotent state is achieved by remodeling the active euchromatin compartment and reducing chromatin interactions at the nuclear center. This unique genomic organization is linked to enhanced chromatin accessibility on enhancers and elevated expression levels of naive pluripotent genes localized to this region. In contradistinction, the primed state exhibits intermingled genomic organization. Moreover, active euchromatin and primed pluripotent genes are distributed at the nuclear periphery, while repressive heterochromatin is densely concentrated at the nuclear center, reducing chromatin accessibility and the transcription of naive genes.

CONCLUSIONS

Our data provide insights into the chromatin structure of ESCs in their naive and primed states, and we identify specific patterns of modifications in transcription and chromatin structure that might explain the genes that are differentially expressed between naive and primed hESCs. Thus, the inversion or relocation of heterochromatin to euchromatin via compartmentalization is related to the regulation of chromatin accessibility, thereby defining pluripotent states and cellular identity.

Disruption of maternal vascular remodeling by a fetal endoretrovirus-derived gene in preeclampsia

BACKGROUND

Preeclampsia, one of the most lethal pregnancy-related diseases, is associated with the disruption of uterine spiral artery remodeling during placentation. However, the early molecular events leading to preeclampsia remain unknown.

RESULTS

By analyzing placentas from preeclampsia, non-preeclampsia, and twin pregnancies with selective intrauterine growth restriction, we show that the pathogenesis of preeclampsia is attributed to immature trophoblast and maldeveloped endothelial cells. Delayed epigenetic reprogramming during early extraembryonic tissue development leads to generation of excessive immature trophoblast cells. We find reduction of de novo DNA methylation in these trophoblast cells results in selective overexpression of maternally imprinted genes, including the endoretrovirus-derived gene PEG10 (paternally expressed gene 10). PEG10 forms virus-like particles, which are transferred from the trophoblast to the closely proximate endothelial cells. In normal pregnancy, only a low amount of PEG10 is transferred to maternal cells; however, in preeclampsia, excessive PEG10 disrupts maternal vascular development by inhibiting TGF-beta signaling.

CONCLUSIONS

Our study reveals the intricate epigenetic mechanisms that regulate trans-generational genetic conflict and ultimately ensure proper maternal-fetal interface formation.

Differential sperm histone retention in normozoospermic ejaculates of infertile men negatively affects sperm functional competence and embryo quality

BACKGROUND

The unique epigenetic architecture that sperm cells acquire during spermiogenesis by retaining <15% of either canonical or variant histone proteins in their genome is essential for normal embryogenesis. Whilst heterogeneous levels of retained histones are found in morphologically normal spermatozoa, their effect on reproductive outcomes is not fully understood.

METHODS

Processed spermatozoa (n = 62) were tested for DNA integrity by sperm chromatin dispersion assay, and retained histones were extracted and subjected to dot-blot analysis. The impact of retained histone modifications in normozoospermic patients on sperm functional characteristics, embryo quality, metabolic signature in embryo spent culture medium and pregnancy outcome was studied.

RESULTS

Dot-blot analysis showed heterogeneous levels of retained histones in the genome of normozoospermic ejaculates. Post-wash sperm yield was affected by an increase in H3K27Me3 and H4K20Me3 levels in the sperm chromatin (p < 0.05). Also, spermatozoa with higher histone H3 retention had increased DNA damage (p < 0.05). Spermatozoa from these cohorts, when injected into donor oocytes, correlated to a significant decrease in the fertilisation rate with an increase in sperm histone H3 (p < 0.05) and H3K27Me3 (p < 0.01). An increase in histone H3 negatively affected embryo quality (p < 0.01) and clinical pregnancy outcome post-embryo transfer (p < 0.05). On the other hand, spent culture medium metabolites assessed by high-resolution (800 MHz) nuclear magnetic resonance showed an increased intensity of the amino acid methionine in the non-pregnant group than in the pregnant group (p < 0.05) and a negative correlation with sperm histone H3 in the pregnant group (p < 0.05).

DISCUSSION AND CONCLUSION

Histone retention in spermatozoa can be one of the factors behind the development of idiopathic male infertility. Such spermatozoa may influence embryonic behaviour and thereby affect the success rate of assisted reproductive technology procedures. These results, although descriptive in nature, warrant further research to address the underlying mechanisms behind these clinically important observations.

The dynamic landscape of enhancer-derived RNA during mouse early embryo development

Enhancer-derived RNAs (eRNAs) play critical roles in diverse biological processes by facilitating their target gene expression. However, the abundance and function of eRNAs in early embryos are not clear. Here, we present a comprehensive eRNA atlas by systematically integrating publicly available datasets of mouse early embryos. We characterize the transcriptional and regulatory network of eRNAs and show that different embryo developmental stages have distinct eRNA expression and regulatory profiles. Paternal eRNAs are activated asymmetrically during zygotic genome activation (ZGA). Moreover, we identify an eRNA, MZGAe1, which plays an important function in regulating mouse ZGA and early embryo development. MZGAe1 knockdown leads to a developmental block from 2-cell embryo to blastocyst. We create an online data portal, M2ED2, to query and visualize eRNA expression and regulation. Our study thus provides a systematic landscape of eRNA and reveals the important role of eRNAs in regulating mouse early embryo development.

A conserved germline-specific Dsn1 alternative splice isoform supports oocyte and embryo development

Alternative mRNA splicing can generate distinct protein isoforms to allow for the differential control of cell processes across cell types. However, alternative splice isoforms that differentially modulate distinct cell division programs have remained elusive. Here, we demonstrate that mammalian germ cells express an alternate mRNA splice isoform for the kinetochore component, DSN1, a subunit of the MIS12 complex that links the centromeres to spindle microtubules during chromosome segregation. This germline DSN1 isoform bypasses the requirement for Aurora kinase phosphorylation for its centromere localization due to the absence of a key regulatory region allowing DSN1 to display persistent centromere localization. Expression of the germline DSN1 isoform in somatic cells results in constitutive kinetochore localization, chromosome segregation errors, and growth defects, providing an explanation for its tight cell type-specific expression. Reciprocally, precisely eliminating expression of the germline DSN1 splice isoform in mouse models disrupts oocyte maturation and early embryonic divisions coupled with a reduction in fertility. Together, this work identifies a germline-specific splice isoform for a chromosome segregation component and implicates its role in mammalian fertility.

The chromatin accessibility dynamics during cell fate specifications in zebrafish early embryogenesis

Chromatin accessibility plays a critical role in the regulation of cell fate decisions. Although gene expression changes have been extensively profiled at the single-cell level during early embryogenesis, the dynamics of chromatin accessibility at cis-regulatory elements remain poorly studied. Here, we used a plate-based single-cell ATAC-seq method to profile the chromatin accessibility dynamics of over 10 000 nuclei from zebrafish embryos. We investigated several important time points immediately after zygotic genome activation (ZGA), covering key developmental stages up to dome. The results revealed key chromatin signatures in the first cell fate specifications when cells start to differentiate into enveloping layer (EVL) and yolk syncytial layer (YSL) cells. Finally, we uncovered many potential cell-type specific enhancers and transcription factor motifs that are important for the cell fate specifications.

The identification and classification of candidate genes during the zygotic genome activation in the mammals

Zygotic genome activation (ZGA) is a critical event in early embryonic development, and thousands of genes are involved in this delicate and sophisticated biological process. To date, however, only a handful of these genes have revealed their core functions in this special process, and therefore the roles of other genes still remain unclear. In the present study, we used previously published transcriptome profiling to identify potential key genes (candidate genes) in minor ZGA and major ZGA in both human and mouse specimens, and further identified the conserved genes across species. Our results showed that 887 and 760 genes, respectively, were thought to be specific to human and mouse in major ZGA, and the other 135 genes were considered to be orthologous genes. Moreover, the conserved genes were most enriched in rRNA processing in the nucleus and cytosol, ribonucleoprotein complex biogenesis, ribonucleoprotein complex assembly and ribosome large subunit biogenesis. The findings of this first comprehensive identification and characterization of candidate genes in minor and major ZGA provide relevant insights for future studies on ZGA.

How should the best human embryo in vitro be? Current and future challenges for embryo selection

In-vitro fertilization (IVF) aims at overcoming the causes of infertility and lead to a healthy live birth. To maximize IVF efficiency, it is critical to identify and transfer the most competent embryo within a cohort produced by a couple during a cycle. Conventional static embryo morphological assessment involves sequential observations under a light microscope at specific timepoints. The introduction of time-lapse technology enhanced morphological evaluation via the continuous monitoring of embryo preimplantation in vitro development, thereby unveiling features otherwise undetectable via multiple static assessments. Although an association exists, blastocyst morphology poorly predicts chromosomal competence. In fact, the only reliable approach currently available to diagnose the embryonic karyotype is trophectoderm biopsy and comprehensive chromosome testing to assess non-mosaic aneuploidies, namely preimplantation genetic testing for aneuploidies (PGT-A). Lately, the focus is shifting towards the fine-tuning of non-invasive technologies, such as "omic" analyses of waste products of IVF (e.g., spent culture media) and/or artificial intelligence-powered morphologic/morphodynamic evaluations. This review summarizes the main tools currently available to assess (or predict) embryo developmental, chromosomal, and reproductive competence, their strengths, the limitations, and the most probable future challenges.

Chromatin region binning of gene expression for improving embryo cell subtype identification

Mammalian embryonic development is a complex process, characterized by intricate spatiotemporal dynamics and distinct chromatin preferences. However, the quick diversification in early embryogenesis leads to significant cellular diversity and the sparsity of scRNA-seq data, posing challenges in accurately determining cell fate decisions. In this study, we introduce a chromatin region binning method using scChrBin, designed to identify chromatin regions that elucidate the dynamics of embryonic development and lineage differentiation. This method transforms scRNA-seq data into a chromatin-based matrix, leveraging genomic annotations. Our results showed that the scChrBin method achieves high accuracy, with 98.0% and 89.2% on two single-cell embryonic datasets, demonstrating its effectiveness in analyzing complex developmental processes. We also systematically and comprehensively analysis of these key chromatin binning regions and their associated genes, focusing on their roles in lineage and stage development. The perspective of chromatin region binning method enables a comprehensive analysis of transcriptome data at the chromatin level, allowing us to unveil the dynamic expression of chromatin regions across temporal and spatial development. The tool is available as an application at https://github.com/liameihao/scChrBin.

Interaction network of human early embryonic transcription factors

Embryonic genome activation (EGA) occurs during preimplantation development and is characterized by the initiation of de novo transcription from the embryonic genome. Despite its importance, the regulation of EGA and the transcription factors involved in this process are poorly understood. Paired-like homeobox (PRDL) family proteins are implicated as potential transcriptional regulators of EGA, yet the PRDL-mediated gene regulatory networks remain uncharacterized. To investigate the function of PRDL proteins, we are identifying the molecular interactions and the functions of a subset family of the Eutherian Totipotent Cell Homeobox (ETCHbox) proteins, seven PRDL family proteins and six other transcription factors (TFs), all suggested to participate in transcriptional regulation during preimplantation. Using mass spectrometry-based interactomics methods, AP-MS and proximity-dependent biotin labeling, and chromatin immunoprecipitation sequencing we derive the comprehensive regulatory networks of these preimplantation TFs. By these interactomics tools we identify more than a thousand high-confidence interactions for the 21 studied bait proteins with more than 300 interacting proteins. We also establish that TPRX2, currently assigned as pseudogene, is a transcriptional activator.

DNA methylation dynamics during yak adipocyte differentiation

In mammals, epigenetic modifications involving DNA methylation are necessary for the completion of the cell differentiation process. However, the global DNA methylation landscape and its dynamics during yak adipocyte differentiation remain unexplored. Here, we performed whole-genome bisulfite sequencing (WGBS) to asses DNA methylation in yak preadipocytes and adipocytes, combining these results with those of our previous studies on changes in chromatin accessibility and gene expression during yak adipogenesis. The results showed that CG methylation levels were lower in promoter than in exon and intron, and gradually decreasing from the distal regions to transcription start site (TSS). There was a significant negative correlation between CG methylation levels located in promoter and gene expression levels. The 46 genes shared by CG differentially methylated regions (DMRs) and differential chromatin accessibility were significantly enriched in Hedgehog and PI3K-Akt signaling pathways. ATAC-seq peaks with high chromatin accessibility located in both promoter (≤ 2 kb from TSS) and distal (> 2 kb from TSS) regions corresponded to low methylation levels. Taken together, these findings demonstrated that DNA methylation and its interactions with chromatin accessibility regulate gene expression during yak adipocyte differentiation, contributing to the understanding of mechanisms of various epigenetic modifications and their interactions in adipogenesis.

Single-cell multi-omics profiling of human preimplantation embryos identifies cytoskeletal defects during embryonic arrest

Human in vitro fertilized embryos exhibit low developmental capabilities, and the mechanisms that underlie embryonic arrest remain unclear. Here using a single-cell multi-omics sequencing approach, we simultaneously analysed alterations in the transcriptome, chromatin accessibility and the DNA methylome in human embryonic arrest due to unexplained reasons. Arrested embryos displayed transcriptome disorders, including a distorted microtubule cytoskeleton, increased genomic instability and impaired glycolysis, which were coordinated with multiple epigenetic reprogramming defects. We identified Aurora A kinase (AURKA) repression as a cause of embryonic arrest. Mechanistically, arrested embryos induced through AURKA inhibition resembled the reprogramming abnormalities of natural embryonic arrest in terms of the transcriptome, the DNA methylome, chromatin accessibility and H3K4me3 modifications. Mitosis-independent sequential activation of the zygotic genome in arrested embryos showed that YY1 contributed to human major zygotic genome activation. Collectively, our study decodes the reprogramming abnormalities and mechanisms of human embryonic arrest and the key regulators of zygotic genome activation.