Perturbation of maternal PIASy abundance disrupts zygotic genome activation and embryonic development via SUMOylation pathway

Unraveling the mysteries of early embryonic arrest: genetic factors and molecular mechanisms

Early embryonic arrest (EEA) is a critical impediment in assisted reproductive technology (ART), affecting 40% of infertile patients by halting the development of early embryos from the zygote to blastocyst stage, resulting in a lack of viable embryos for successful pregnancy. Despite its prevalence, the molecular mechanism underlying EEA remains elusive. This review synthesizes the latest research on the genetic and molecular factors contributing to EEA, with a focus on maternal, paternal, and embryonic factors. Maternal factors such as irregularities in follicular development and endometrial environment, along with mutations in genes like NLRP5, PADI6, KPNA7, IGF2, and TUBB8, have been implicated in EEA. Specifically, PATL2 mutations are hypothesized to disrupt the maternal-zygotic transition, impairing embryo development. Paternal contributions to EEA are linked to chromosomal variations, epigenetic modifications, and mutations in genes such as CFAP69, ACTL7A, and M1AP, which interfere with sperm development and lead to infertility. Aneuploidy may disrupt spindle assembly checkpoints and pathways including Wnt, MAPK, and Hippo signaling, thereby contributing to EEA. Additionally, key genes involved in embryonic genome activation-such as ZSCAN4, DUXB, DUXA, NANOGNB, DPPA4, GATA6, ARGFX, RBP7, and KLF5-alongside functional disruptions in epigenetic modifications, mitochondrial DNA, and small non-coding RNAs, play critical roles in the onset of EEA. This review provides a comprehensive understanding of the genetic and molecular underpinnings of EEA, offering a theoretical foundation for the diagnosis and potential therapeutic strategies aimed at improving pregnancy outcomes.

MiR-290 Family Maintains Pluripotency and Self-Renewal by Regulating MAPK Signaling Pathway in Intermediate Pluripotent Stem Cells

Mouse embryonic stem cells (ESCs) and epiblast stem cells (EpiSCs) are derived from pre- and post-implantation embryos, representing the initial "naïve" and final "primed" states of pluripotency, respectively. In this study, novel reprogrammed pluripotent stem cells (rPSCs) were induced from mouse EpiSCs using a chemically defined medium containing mouse LIF, BMP4, CHIR99021, XAV939, and SB203580. The rPSCs exhibited domed clones and expressed key pluripotency genes, with both X chromosomes active in female cells. Furthermore, rPSCs differentiated into cells of all three germ layers in vivo through teratoma formation. Regarding epigenetic modifications, the DNA methylation of Oct4, Sox2, and Nanog promoter regions and the mRNA levels of Dnmt3a, Dnmt3b, and Dnmt1 were reduced in rPSCs compared with EpiSCs. However, the miR-290 family was significantly upregulated in rPSCs. After removing SB203580, an inhibitor of the p38 MAPK pathway, the cell colonies changed from domed to flat, with a significant decrease in the expression of pluripotency genes and the miR-290 family. Conversely, overexpression of pri-miR-290 reversed these changes. In addition, Map2k6 was identified as a direct target gene of miR-291b-3p, indicating that the miR-290 family maintains pluripotency and self-renewal in rPSCs by regulating the MAPK signaling pathway.

Global SUMOylation in mouse oocytes maintains oocyte identity and regulates chromatin remodeling and transcriptional silencing at the end of folliculogenesis

Meiotically competent oocytes in mammals undergo cyclic development during folliculogenesis. Oocytes within ovarian follicles are transcriptionally active, producing and storing transcripts required for oocyte growth, somatic cell communication and early embryogenesis. Transcription ceases as oocytes transition from growth to maturation and does not resume until zygotic genome activation. Although SUMOylation, a post-translational modification, plays multifaceted roles in transcriptional regulation, its involvement during oocyte development remains poorly understood. In this study, we generated an oocyte-specific knockout of Ube2i, encoding the SUMO E2 enzyme UBE2I, using Zp3-cre+ to determine how loss of oocyte SUMOylation during folliculogenesis affects oocyte development. Ube2i Zp3-cre+ female knockout mice were sterile, with oocyte defects in meiotic competence, spindle architecture and chromosome alignment, and a premature arrest in metaphase I. Additionally, fully grown Ube2i Zp3-cre+ oocytes exhibited sustained transcriptional activity but downregulated maternal effect genes and prematurely activated genes and retrotransposons typically associated with zygotic genome activation. These findings demonstrate that UBE2I is required for the acquisition of key hallmarks of oocyte development during folliculogenesis, and highlight UBE2I as a previously unreported orchestrator of transcriptional regulation in mouse oocytes.

Post-ovulatory aging is associated with altered patterns for small ubiquitin-like modifier (SUMO) proteins and SUMO-specific proteases

Mammalian oocytes are ovulated arrested at metaphase of the second meiotic division. If they are not fertilized within a short period, the oocyte undergoes several progressive morphological, structural, and molecular changes during a process called oocyte aging. Herein, we focused on those functional events associated with proper cytoskeleton organization and those that correlate with spindle displacement and chromosome misalignment or scatter. Post-translational modifications by Small Ubiquitin-like Modifier (SUMO) proteins are involved in spindle organization and here we demonstrate that the SUMO pathway is involved in spindle morphology changes and chromosome movements during oocyte aging. SUMO-2/3 as well as the SUMO-specific proteases SENP-2 localization are affected by postovulatory aging in vitro. Consistent with these findings, UBC9 decreases during oocyte aging while differential ubiquitination patterns also correlate with in vitro oocyte aging. These results are consistent with postovulatory aging-related alterations in the posttranslational modifications of the spindle apparatus by SUMO and its SENP proteases. These findings are suggestive that such age-related changes in SUMOylation and the deSUMOylation of key target proteins in the spindle apparatus and kinetochore may be involved with spindle and chromosome alignment defects during mammalian oocyte postovulatory aging. Such findings may have implications for ART-related human oocyte aging in vitro regarding the activities of the SUMO pathway and fertilization success.

The Conceivable Functions of Protein Ubiquitination and Deubiquitination in Reproduction

Protein ubiquitination with general existence in virtually all eukaryotic cells serves as a significant post-translational modification of cellular proteins, which leads to the degradation of proteins via the ubiquitin-proteasome system. Deubiquitinating enzymes (DUBs) can reverse the ubiquitination effect by removing the ubiquitin chain from the target protein. Together, these two processes participate in regulating protein stability, function, and localization, thus modulating cell cycle, DNA repair, autophagy, and transcription regulation. Accumulating evidence indicates that the ubiquitination/deubiquitination system regulates reproductive processes, including the cell cycle, oocyte maturation, oocyte-sperm binding, and early embryonic development, primarily by regulating protein stability. This review summarizes the extensive research concerning the role of ubiquitin and DUBs in gametogenesis and early embryonic development, which helps us to understand human pregnancy further.

SCF Ligases and Their Functions in Oogenesis and Embryogenesis-Summary of the Most Important Findings throughout the Animal Kingdom

SCF-dependent proteolysis was first discovered via genetic screening of budding yeast almost 25 years ago. In recent years, more and more functions of SCF (Skp1-Cullin 1-F-box) ligases have been described, and we can expect the number of studies on this topic to increase. SCF ligases, which are E3 ubiquitin multi-protein enzymes, catalyse protein ubiquitination and thus allow protein degradation mediated by the 26S proteasome. They play a crucial role in the degradation of cell cycle regulators, regulation of the DNA repair and centrosome cycle and play an important role in several diseases. SCF ligases seem to be needed during all phases of development, from oocyte formation through fertilization, activation of the embryonic genome to embryo implantation. In this review, we summarize known data on SCF ligase-mediated degradation during oogenesis and embryogenesis. In particular, SCFβTrCP and SCFSEL-10/FBXW7 are among the most important and best researched ligases during early development. SCFβTrCP is crucial for the oogenesis of Xenopus and mouse and also in Xenopus and Drosophila embryogenesis. SCFSEL-10/FBXW7 participates in the degradation of several RNA-binding proteins and thereby affects the regulation of gene expression during the meiosis of C. elegans. Nevertheless, a large number of SCF ligases that are primarily involved in embryogenesis remain to be elucidated.

Cell division- and DNA replication-free reprogramming of somatic nuclei for embryonic transcription

Nuclear transfer systems represent the efficient means to reprogram a cell and in theory provide a basis for investigating the development of endangered species. However, conventional nuclear transfer using oocytes of laboratory animals does not allow reprogramming of cross-species nuclei owing to defects in cell divisions and activation of embryonic genes. Here, we show that somatic nuclei transferred into mouse four-cell embryos arrested at the G2/M phase undergo reprogramming toward the embryonic state. Remarkably, genome-wide transcriptional reprogramming is induced within a day, and ZFP281 is important for this replication-free reprogramming. This system further enables transcriptional reprogramming of cells from Oryx dammah, now extinct in the wild. Thus, our findings indicate that arrested mouse embryos are competent to induce intra- and cross-species reprogramming. The direct induction of embryonic transcripts from diverse genomes paves a unique approach for identifying mechanisms of transcriptional reprogramming and genome activation from a diverse range of species.

Post-Translational Modifications in Oocyte Maturation and Embryo Development

Mammalian oocyte maturation and embryo development are unique biological processes regulated by various modifications. Since de novo mRNA transcription is absent during oocyte meiosis, protein-level regulation, especially post-translational modification (PTM), is crucial. It is known that PTM plays key roles in diverse cellular events such as DNA damage response, chromosome condensation, and cytoskeletal organization during oocyte maturation and embryo development. However, most previous reviews on PTM in oocytes and embryos have only focused on studies of Xenopus laevis or Caenorhabditis elegans eggs. In this review, we will discuss the latest discoveries regarding PTM in mammalian oocytes maturation and embryo development, focusing on phosphorylation, ubiquitination, SUMOylation and Poly(ADP-ribosyl)ation (PARylation). Phosphorylation functions in chromosome condensation and spindle alignment by regulating histone H3, mitogen-activated protein kinases, and some other pathways during mammalian oocyte maturation. Ubiquitination is a three-step enzymatic cascade that facilitates the degradation of proteins, and numerous E3 ubiquitin ligases are involved in modifying substrates and thus regulating oocyte maturation, oocyte-sperm binding, and early embryo development. Through the reversible addition and removal of SUMO (small ubiquitin-related modifier) on lysine residues, SUMOylation affects the cell cycle and DNA damage response in oocytes. As an emerging PTM, PARlation has been shown to not only participate in DNA damage repair, but also mediate asymmetric division of oocyte meiosis. Each of these PTMs and external environments is versatile and contributes to distinct phases during oocyte maturation and embryo development.

Retinoic acid induces NELFA-mediated 2C-like state of mouse embryonic stem cells associates with epigenetic modifications and metabolic processes in chemically defined media

OBJECTIVES

Mouse embryonic stem cells (ESCs) are derived from the inner cell mass of blastocyst-stage embryos and cultured in different culture media with varied pluripotency. Sporadically, a small population of ESCs exhibit 2-cell stage embryonic features in serum containing medium. However, whether ESCs can transit into 2-cell embryo-like (2C-like) cells in the chemically defined media remains largely unknown.

MATERIALS AND METHODS

We established a robust in vitro induction system, based on retinoic acid (RA) containing chemically defined media, which can efficiently increase the subpopulation of 2C-like cells. Further test the pluripotency and 2C features of ESCs cultured in RA. 2C reporter-positive cells were selected by FACS; the level of protein was detected via immunofluorescence staining and western blot; the level gene expressions were measured by RNA-seq.

RESULTS

Retinoic acid drives a NELFA (negative elongation factor A)-mediated 2C-like state in mouse ESCs, characterized with 2C-specific transcriptional networks and the ability to contribute trophectoderm (TE) when injected into developing embryos. In addition, RA treatment triggers DNA hypomethylation, active histone modification, suppressed glycolysis metabolism and reduced protein synthesis activity of ESCs.

CONCLUSIONS

We showed that RA has a broader role in 2C-like cells state, not only is one of the upstream regulators of the 2C-like state in chemically defined media but also illuminates genetic and epigenetic regulations that govern ESCs to 2C-like transition.

Extensive SUMO Modification of Repressive Chromatin Factors Distinguishes Pluripotent from Somatic Cells

Post-translational modification by SUMO is a key regulator of cell identity. In mouse embryonic fibroblasts (MEFs), SUMO impedes reprogramming to pluripotency, while in embryonic stem cells (ESCs), it represses the emergence of totipotent-like cells, suggesting that SUMO targets distinct substrates to preserve somatic and pluripotent states. Using MS-based proteomics, we show that the composition of endogenous SUMOylomes differs dramatically between MEFs and ESCs. In MEFs, SUMO2/3 targets proteins associated with canonical SUMO functions, such as splicing, and transcriptional regulators driving somatic enhancer selection. In contrast, in ESCs, SUMO2/3 primarily modifies highly interconnected repressive chromatin complexes, thereby preventing chromatin opening and transitioning to totipotent-like states. We also characterize several SUMO-modified pluripotency factors and show that SUMOylation of Dppa2 and Dppa4 impedes the conversion to 2-cell-embryo-like states. Altogether, we propose that rewiring the repertoire of SUMO target networks is a major driver of cell fate decision during embryonic development.

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Endogenous SUMO2/3 proteomics in ESCs and MEFs uncovers drastic SUMOylome rewiring

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In ESCs, SUMO2/3 targets densely interconnected repressive chromatin proteins

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In MEFs, SUMO2/3 targets key determinants of fibroblastic cell identity

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SUMOylation of Dppa2/4 prevents conversion of ESCs to the 2C-like state

The role of SUMOylation during development

During the development of multicellular organisms, transcriptional regulation plays an important role in the control of cell growth, differentiation and morphogenesis. SUMOylation is a reversible post-translational process involved in transcriptional regulation through the modification of transcription factors and through chromatin remodelling (either modifying chromatin remodelers or acting as a ‘molecular glue’ by promoting recruitment of chromatin regulators). SUMO modification results in changes in the activity, stability, interactions or localization of its substrates, which affects cellular processes such as cell cycle progression, DNA maintenance and repair or nucleocytoplasmic transport. This review focuses on the role of SUMO machinery and the modification of target proteins during embryonic development and organogenesis of animals, from invertebrates to mammals.

A cell in hand is worth two in the embryo: recent advances in 2-cell like cell reprogramming

Multicellular organisms develop from a single cell, the zygote. This feature is referred to as totipotency. In the mouse, only the zygote and the 2-cell stage embryo display this attribute. Cells resembling the embryonic 2-cell stage blastomeres were identified in embryonic stem (ES) cell cultures as '2-cell-like cells' (2CLCs). This discovery brought the first cellular model with the possibility to investigate some features of the totipotent embryo and the molecular mechanisms regulating totipotency in vitro. In this article, we discuss the latest advancements on the research on 2CLCs, which have uncovered an intricate reprogramming process regulated by proteins as well as metabolites and ncRNAs. These recent findings have shed light on the combinatorial regulation of 2-cell-like cell emergence and the nature of their unique attributes.

SUMOylation in development and neurodegeneration

In essentially all eukaryotes, proteins can be modified by the attachment of small ubiquitin-related modifier (SUMO) proteins to lysine side chains to produce branched proteins. This process of 'SUMOylation' plays essential roles in plant and animal development by altering protein function in spatially and temporally controlled ways. In this Primer, we explain the process of SUMOylation and summarize how SUMOylation regulates a number of signal transduction pathways. Next, we discuss multiple roles of SUMOylation in the epigenetic control of transcription. In addition, we evaluate the role of SUMOylation in the etiology of neurodegenerative disorders, focusing on Parkinson's disease and cerebral ischemia. Finally, we discuss the possibility that SUMOylation may stimulate survival and neurogenesis of neuronal stem cells.