Inhibition of Skp1-Cullin-F-box complexes during bovine oocyte maturation and preimplantation development leads to delayed development of embryos†

Inhibition of neddylation disturbs zygotic genome activation through histone modification change and leads to early development arrest in mouse embryos

Post-translational modification and fine-tuned protein turnover are of great importance in mammalian early embryo development. Apart from the classic protein degradation promoting ubiquitination, new forms of ubiquitination-like modification are yet to be fully understood. Here, we demonstrate the function and potential mechanisms of one ubiquitination-like modification, neddylation, in mouse preimplantation embryo development. Treated with specific inhibitors, zygotes showed a dramatically decreased cleavage rate and almost all failed to enter the 4-cell stage. Transcriptional profiling showed genes were differentially expressed in pathways involving cell fate determination and cell differentiation, including several down-regulated zygotic genome activation (ZGA) marker genes. A decreased level of phosphorylated RNA polymerase II was detected, indicating impaired gene transcription inside the embryo cell nucleus. Proteomic data showed that differentially expressed proteins were enriched in histone modifications. We confirmed the lowered in methyltransferase (KMT2D) expression and a decrease in histone H3K4me3. At the same time, acetyltransferase (CBP/p300) reduced, while deacetylase (HDAC6) increased, resulting in an attenuation in histone H3K27ac. Additionally, we observed the up-regulation in YAP1 and RPL13 activities, indicating potential abnormalities in the downstream response of Hippo signaling pathway. In summary, we found that inhibition of neddylation induced epigenetic changes in early embryos and led to abnormalities in related downstream signaling pathways. This study sheds light upon new forms of ubiquitination regulating mammalian embryonic development and may contribute to further investigation of female infertility pathology.

Enhanced branched-chain amino acid metabolism improves age-related reproduction in C. elegans

Reproductive ageing is one of the earliest human ageing phenotypes, and mitochondrial dysfunction has been linked to oocyte quality decline; however, it is not known which mitochondrial metabolic processes are critical for oocyte quality maintenance with age. To understand how mitochondrial processes contribute to Caenorhabditis elegans oocyte quality, we characterized the mitochondrial proteomes of young and aged wild-type and long-reproductive daf-2 mutants. Here we show that the mitochondrial proteomic profiles of young wild-type and daf-2 worms are similar and share upregulation of branched-chain amino acid (BCAA) metabolism pathway enzymes. Reduction of the BCAA catabolism enzyme BCAT-1 shortens reproduction, elevates mitochondrial reactive oxygen species levels, and shifts mitochondrial localization. Moreover, bcat-1 knockdown decreases oocyte quality in daf-2 worms and reduces reproductive capability, indicating the role of this pathway in the maintenance of oocyte quality with age. Notably, oocyte quality deterioration can be delayed, and reproduction can be extended in wild-type animals both by bcat-1 overexpression and by supplementing with vitamin B1, a cofactor needed for BCAA metabolism.

Impact of media supplements FGF2, LIF and IGF1 on the genome activity of porcine embryos produced in vitro

In this article, we focused on the impact of precisely chemically modified FLI maturation medium enriched with fibroblast growth factor 2 (FGF2), leukemia inhibitory factor (LIF), insulin-like growth factor 1 (IGF1), and polyvinyl alcohol (PVA) and its potential to improve the efficiency of in vitro production of porcine embryos. We hypothesized that enhancing the composition of the maturation medium could result in an elevated production of embryos in vitro and can affect EGA. FLI medium resulted in a significantly higher rate of oocyte blastocyst maturation and formation compared to the control DMEM medium. In addition, immunocytochemical labelling confirmed the detection of UBF in 4-cell FLI parthenogenic embryos, suggesting similarities with natural embryo development. Through RNAseq analysis, upregulated genes present in 4-cell FLI embryos were found to play key roles in important biological processes such as cell proliferation, cell differentiation, and transcriptional regulation. Based on our findings, we demonstrated the positive influence of FLI medium in the evaluation of in vitro embryo production, EGA detection, transcriptomic and proteomic profile, which was confirmed by the positive activation of the embryonal genome in the 4-cell stage of parthenogenetically activated embryos.

Integrated analysis reveals the regulatory mechanism of the neddylation inhibitor MLN4924 on the metabolic dysregulation in rabbit granulosa cells

BACKGROUND

Neddylation, an important post-translational modification (PTM) of proteins, plays a crucial role in follicular development. MLN4924 is a small-molecule inhibitor of the neddylation-activating enzyme (NAE) that regulates various biological processes. However, the regulatory mechanisms of neddylation in rabbit ovarian cells have not been emphasized. Here, the transcriptome and metabolome profiles in granulosa cells (GCs) treated with MLN4924 were utilized to identify differentially expressed genes, followed by pathway analysis to precisely define the altered metabolisms.

RESULTS

The results showed that 563 upregulated and 910 downregulated differentially expressed genes (DEGs) were mainly enriched in pathways related to cancer, cell cycle, PI3K-AKT, progesterone-mediated oocyte maturation, and PPAR signaling pathway. Furthermore, we characterized that MLN4924 inhibits PPAR-mediated lipid metabolism, and disrupts the cell cycle by promoting the apoptosis and proliferation of GCs. Importantly, we found the reduction of several metabolites in the MLN4924 treated GCs, including glycerophosphocholine, arachidic acid, and palmitic acid, which was consistent with the deregulation of PPAR signaling pathways. Furthermore, the increased metabolites included 6-Deoxy-6-sulfo-D-glucono-1,5-lactone and N-Acetyl-D-glucosaminyldiphosphodolichol. Combined with transcriptome data analyses, we identified genes that strongly correlate with metabolic dysregulation, particularly those related to glucose and lipid metabolism. Therefore, neddylation inhibition may disrupt the energy metabolism of GCs.

CONCLUSIONS

These results provide a foundation for in-depth research into the role and molecular mechanism of neddylation in ovary development.

Neddylation inhibition affects early embryonic development by disrupting maternal-to-zygotic transition and mitochondrial function in mice

Post-translational modifications (PTMs) are critical for early development in mice because early cleavage-stage embryos are characterized by transcriptional inactivity. Neddylation is an important ubiquitin-like PTM that regulates multiple biophysical processes. However, the exact roles of neddylation in regulating early embryonic development remain largely unknown. In the present study, we found that inhibition of neddylation by specific inhibitor MLN4924 led to severe arrest of early embryonic development. Transcriptomic analysis showed that neddylation inhibition changed the expression of 3959 genes at the 2-cell stage. Importantly, neddylation inhibition blocked zygotic genome activation and maternal mRNA degradation, thus disrupting the maternal-to-zygotic transition. Moreover, inhibition of neddylation induced mitochondrial dysfunction including aberrant mitochondrial distribution, decreased mitochondrial membrane potential, and reduced ATP content. Further analysis showed that inhibition of neddylation resulted in the accumulation of reactive oxygen species and superoxide anion, thereby resulting in oxidative stress and severe DNA damage at the 2-cell stage. Overall, this study demonstrates that neddylation is vital for early embryonic development in mice. Our findings suggest that proper neddylation regulation is essential for the timely inter-stage transition during early embryonic development.

Enhanced Branched-Chain Amino Acid Metabolism Improves Age-Related Reproduction in C. elegans

Reproductive aging is one of the earliest human aging phenotypes, and mitochondrial dysfunction has been linked to oocyte quality decline. However, it is not known which mitochondrial metabolic processes are critical for oocyte quality maintenance with age. To understand how mitochondrial processes contribute to C. elegans oocyte quality, we characterized the mitochondrial proteomes of young and aged wild-type and long-reproductive daf-2 mutants. Here we show that the mitochondrial proteomic profiles of young wild-type and daf-2 worms are similar and share upregulation of branched-chain amino acid (BCAA) metabolism pathway enzymes. Reduction of the BCAA catabolism enzyme BCAT-1 shortens reproduction, elevates mitochondrial reactive oxygen species levels, and shifts mitochondrial localization. Moreover, bcat-1 knockdown decreases oocyte quality in daf-2 worms and reduces reproductive capability, indicating the role of this pathway in the maintenance of oocyte quality with age. Importantly, oocyte quality deterioration can be delayed, and reproduction can be extended in wild-type animals both by bcat-1 overexpression and by supplementing with Vitamin B1, a cofactor needed for BCAA metabolism.

The association of RBX1 and BAMBI gene expression with oocyte maturation in PCOS women

BACKGROUND

Polycystic ovarian syndrome (PCOS) is a common endocrine disorder that affects 6-20% of women of reproductive age. One of the symptoms of PCOS is hyperandrogenism, which can impair follicular development. This disruption can cause issues with the development of oocytes and the growth of embryos. Although the exact cause of PCOS is not yet fully understood, studying the gene expression pattern of cumulus cells, which play a crucial role in the maturation and quality of oocytes, could help identify the genes associated with oocyte maturation in PCOS women. Through indirect activation of APC/Cdc20, RBX1 enables oocytes to bypass the GV (germinal vesicles) stage and advance to the MII (metaphase II) stage. our other gene is the BAMBI gene which stimulates WNT signaling, that is a crucial pathway for healthy ovarian function. This study aims to explore the expression level of the RBX1 and BAMBI genes between GV and MII oocytes of PCOS and non-PCOS groups.

METHODS

In this experiment, we gathered the cumulus cells of MII (38 cases and 33 control) and GV (38 cases and 33 control) oocytes from women with/without PCOS. Besides, quantitative RT-PCR was used to assess the semi-quantitative expression of BAMBI and RBX1.

RESULTS

According to our research, the expression level of RBX1 and BAMBI in MII and GV cumulus cells of PCOS patients was significantly lower than that in non-PCOS ones.

CONCLUSION

This research raises the possibility of RBX1 and BAMBI involvement in oocyte quality in PCOS women.

Mammalian oocytes store proteins for the early embryo on cytoplasmic lattices

Mammalian oocytes are filled with poorly understood structures called cytoplasmic lattices. First discovered in the 1960s and speculated to correspond to mammalian yolk, ribosomal arrays, or intermediate filaments, their function has remained enigmatic to date. Here, we show that cytoplasmic lattices are sites where oocytes store essential proteins for early embryonic development. Using super-resolution light microscopy and cryoelectron tomography, we show that cytoplasmic lattices are composed of filaments with a high surface area, which contain PADI6 and subcortical maternal complex proteins. The lattices associate with many proteins critical for embryonic development, including proteins that control epigenetic reprogramming of the preimplantation embryo. Loss of cytoplasmic lattices by knocking out PADI6 or the subcortical maternal complex prevents the accumulation of these proteins and results in early embryonic arrest. Our work suggests that cytoplasmic lattices enrich maternally provided proteins to prevent their premature degradation and cellular activity, thereby enabling early mammalian development.

Neddylation Inhibition Causes Impaired Mouse Embryo Quality and Blastocyst Hatching Failure Through Elevated Oxidative Stress and Reduced IL-1β

Mammalian blastocyst hatching is an essential prerequisite for successful embryo implantation. As the rate-limiting step of current assisted reproductive technology, understanding the key factors regulating blastocyst hatching would be significantly helpful to improve the performance of the assisted reproductive practice. In early embryo development, the fine-tuned elimination of maternal materials and the balanced protein turnover are inevitable for the competent to hatch and implant into endometrium. Neddylation, a ubiquitination-like protein modification, has been shown to be involved in oocyte maturation and early embryo development. In this study, aiming to discover an unknown role of neddylation in the blastocyst hatching process, we provided functional evidence of neddylation in mammalian embryo quality and blastocyst hatching. Treatment with MLN4924, a specific neddylation inhibitor, lowered the embryo quality and dramatically reduced the hatching rate in mouse blastocysts. The transcriptional profile showed the upregulation of oxidative stress-related genes and aberrant expression of immune-related genes. The elevated oxidative stress was validated by qPCR and markers of apoptosis, DNA damage, reactive oxygen species, and cytoskeleton. Moreover, we found the secreted IL-1β level was reduced in an NF-κB-independent manner, leading to the final poor embryo quality and blastocyst hatching failure. This is the first report of neddylation being of great importance in the mammalian blastocyst hatching process. Further investigations uncovering more detailed molecular mechanisms of neddylation regulation in blastocyst hatching would greatly promote not only the understanding of this crucial biological process but also the clinical application in reproductive centers.

Neddylation inactivation affects cell cycle and apoptosis in sheep follicular granulosa cells

Protein neddylation inactivation is a novel topic in cancer research. However, there are few studies on the mechanism of neddylation underlying the development of sheep follicular granulosa cells (GCs). In this study, the development of follicular GCs in sheep was inactivated by MLN4924, a neddylation-specific inhibitor, which significantly attenuated the proliferation and cell index of sheep follicular GCs. Further, the inactivation of neddylation by MLN4924 caused the accumulation of the cullin ring ligase (CRLs) substrates Wee1 and c-Myc, which could upregulate NOXA protein expression. Meanwhile, the B-cell lymphoma/leukemia 2 (BCL2) family members Bcl-2 and MCL-1 were downregulated, subsequently inducing apoptosis in follicular GCs of sheep. Increasing Wee1 levels caused G2/M-phase arrest. The effects of neddylation inactivation on Akt, the JAK2/STAT3 signaling pathway, and Forkhead box class O(FOXO) family members were evaluated. Neddylation inactivation by MLN4924 increased the levels of phospho-Akt, JAK2, phospho-STAT3, and FOXO1 (p < 0.05) and decreased the levels of phospho-FOXO3a and STAT3 (p < 0.05). In addition, MLN4924 could alter the mitochondrial morphology of GCs, increase cellular glucose utilization and lactate production, increase reactive oxygen species (ROS) generation, and promote sheep follicular GCs glycolysis, thus causing changes in mitochondrial functions. Together, these findings point to an unrecognized role of neddylation in regulating follicular GCs proliferation in sheep.

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, SCF^βTrCP and SCF^SEL-10/FBXW7 are among the most important and best researched ligases during early development. SCF^βTrCP is crucial for the oogenesis of Xenopus and mouse and also in Xenopus and Drosophila embryogenesis. SCF^SEL-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.

Physiologically relevant miRNAs in mammalian oocytes are rare and highly abundant

miRNAs, ˜22nt small RNAs associated with Argonaute (AGO) proteins, are important negative regulators of gene expression in mammalian cells. However, mammalian maternal miRNAs show negligible repressive activity and the miRNA pathway is dispensable for oocytes and maternal-to-zygotic transition. The stoichiometric hypothesis proposed that this is caused by dilution of maternal miRNAs during oocyte growth. As the dilution affects miRNAs but not mRNAs, it creates unfavorable miRNA:mRNA stoichiometry for efficient repression of cognate mRNAs. Here, we report that porcine ssc-miR-205 and bovine bta-miR-10b are exceptional miRNAs, which resist the diluting effect of oocyte growth and can efficiently suppress gene expression. Additional analysis of ssc-miR-205 shows that it has higher stability, reduces expression of endogenous targets, and contributes to the porcine oocyte-to-embryo transition. Consistent with the stoichiometric hypothesis, our results show that the endogenous miRNA pathway in mammalian oocytes is intact and that maternal miRNAs can efficiently suppress gene expression when a favorable miRNA:mRNA stoichiometry is established.

Analysis of Expression Profiles of CircRNA and MiRNA in Oviduct during the Follicular and Luteal Phases of Sheep with Two Fecundity (FecB Gene) Genotypes

CircRNA and miRNA, as classes of non-coding RNA, have been found to play pivotal roles in sheep reproduction. There are many reports of circRNA and miRNA in the ovary and uterus, but few in the oviduct. In this study, RNA-Seq was performed to analyze the expression profile of circRNA and miRNA in the oviduct during the follicular phase and luteal phase of sheep with FecB^BB and FecB⁺⁺ genotypes. The results showed that a total of 3223 circRNAs and 148 miRNAs were identified. A total of 15 DE circRNAs and 40 DE miRNAs were found in the comparison between the follicular phase and luteal phase, and 1 DE circRNA and 18 DE miRNAs were found in the comparison between the FecB^BB genotype and FecB⁺⁺ genotype. GO and KEGG analyses showed that the host genes of DE circRNAs were mainly enriched in the Rap1 signaling pathway, PI3K-Akt signaling pathway and neuroactive ligand-receptor interactions. Novel_circ_0004065, novel_circ_0005109, novel_circ_0012086, novel_circ_0014274 and novel_circ_0001794 were found to be possibly involved in the oviductal reproduction process. GO and KEGG analyses showed that the target genes of DE miRNAs were mainly enriched in insulin secretion, the cAMP signaling pathway, the cGMP-PKG signaling pathway, the Rap1 signaling pathway and the TGF-β signaling pathway, and the target genes LPAR1, LPAR2, FGF18, TACR3, BMP6, SMAD4, INHBB, SKP1 and TGFBR2 were found to be associated with the reproductive process. Miranda software was used to identify 27 miRNAs that may bind to 13 DE circRNAs, including miR-22-3p (target to novel_circ_0004065), miR-127, miR-136 (target to novel_circ_0000417), miR-27a (target to novel_circ_0014274) and oar-miR-181a (target to novel_circ_ 0017815). The results of this study will help to elucidate the regulatory mechanisms of circRNAs and miRNAs in sheep reproduction. Our study, although not establishing direct causal relationships of the circRNA and miRNA changes, enriches the sheep circRNA and miRNA database and provides a basis for further studies on sheep reproduction.

FBXO34 Regulates the G2/M Transition and Anaphase Entry in Meiotic Oocytes

There are two important events in oocyte meiotic maturation, the G2/M transition and metaphase I progression. Thousands of proteins participate in regulating oocyte maturation, which highlights the importance of the ubiquitin proteasome system (UPS) in regulating protein synthesis and degradation. Skp1–Cullin–F-box (SCF) complexes, as the best characterized ubiquitin E3 ligases in the UPS, specifically recognize their substrates. F-box proteins, as the variable adaptors of SCF, can bind substrates specifically. Little is known about the functions of the F-box proteins in oocyte maturation. In this study, we found that depletion of FBXO34, an F-box protein, led to failure of oocyte meiotic resumption due to a low activity of MPF, and this phenotype could be rescued by exogenous overexpression of CCNB1. Strikingly, overexpression of FBXO34 promoted germinal vesicle breakdown (GVBD), but caused continuous activation of spindle assembly checkpoint (SAC) and MI arrest of oocytes. Here, we demonstrated that FBXO34 regulated both the G2/M transition and anaphase entry in meiotic oocytes.

MicroRNA dilution during oocyte growth disables the microRNA pathway in mammalian oocytes

MicroRNAs (miRNAs) are ubiquitous small RNAs guiding post-transcriptional gene repression in countless biological processes. However, the miRNA pathway in mouse oocytes appears inactive and dispensable for development. We propose that marginalization of the miRNA pathway activity stems from the constraints and adaptations of RNA metabolism elicited by the diluting effects of oocyte growth. We report that miRNAs do not accumulate like mRNAs during the oocyte growth because miRNA turnover has not adapted to it. The most abundant miRNAs total tens of thousands of molecules in growing (∅ 40 μm) and fully grown (∅ 80 μm) oocytes, a number similar to that observed in much smaller fibroblasts. The lack of miRNA accumulation results in a 100-fold lower miRNA concentration in fully grown oocytes than in somatic cells. This brings a knock-down-like effect, where diluted miRNAs engage targets but are not abundant enough for significant repression. Low-miRNA concentrations were observed in rat, hamster, porcine and bovine oocytes, arguing that miRNA inactivity is not mouse-specific but a common mammalian oocyte feature. Injection of 250,000 miRNA molecules was sufficient to restore reporter repression in mouse and porcine oocytes, suggesting that miRNA inactivity comes from low-miRNA abundance and not from some suppressor of the pathway.

The neglected part of early embryonic development: maternal protein degradation

The degradation of maternally provided molecules is a very important process during early embryogenesis. However, the vast majority of studies deals with mRNA degradation and protein degradation is only a very little explored process yet. The aim of this article was to summarize current knowledge about the protein degradation during embryogenesis of mammals. In addition to resuming of known data concerning mammalian embryogenesis, we tried to fill the gaps in knowledge by comparison with facts known about protein degradation in early embryos of non-mammalian species. Maternal protein degradation seems to be driven by very strict rules in terms of specificity and timing. The degradation of some maternal proteins is certainly necessary for the normal course of embryonic genome activation (EGA) and several concrete proteins that need to be degraded before major EGA have been already found. Nevertheless, the most important period seems to take place even before preimplantation development-during oocyte maturation. The defects arisen during this period seems to be later irreparable.