Mammalian nucleolar protein DCAF13 is essential for ovarian follicle maintenance and oocyte growth by mediating rRNA processing

The chromatin accessibility landscape of mouse oocytes during configuration transition

The transition of chromatin configuration in mammalian oocytes from a non-surrounded nucleolus (NSN) to a surrounded nucleolus (SN) is critical for acquiring the developmental competence. However, the genomic and epigenomic features underlying this process remain poorly understood. In the present study, we first establish the chromatin accessibility landscape of mouse oocytes from NSN to SN stage. Through the integrative analysis of multi-omics, we find that the establishment of DNA methylation in oocytes is independent of the dynamics of chromatin accessibility. In contrast, histone H3K4me3 status is closely associated with the dynamics of accessible regions during configuration transition. Furthermore, by focusing on the actively transcribed genes in NSN and SN oocytes, we discover that chromatin accessibility coupled with histone methylation (H3K4me3 and H3K27me3) participates in the transcriptional control during phase transition. In sum, our data provide a comprehensive resource for probing configuration transition in oocytes, and offer insights into the mechanisms determining chromatin dynamics and oocyte quality.

Oocyte-specific deletion of eukaryotic translation initiation factor 5 causes apoptosis of mouse oocytes within the early-growing follicles by mitochondrial fission defect-reactive oxygen species-DNA damage

BACKGROUND

Mutations in several translation initiation factors are closely associated with premature ovarian insufficiency (POI), but the underlying pathogenesis remains largely unknown.

METHODS AND RESULTS

We generated eukaryotic translation initiation factor 5 (Eif5) conditional knockout mice aiming to investigate the function of eIF5 during oocyte growth and follicle development. Here, we demonstrated that Eif5 deletion in mouse primordial and growing oocytes both resulted in the apoptosis of oocytes within the early-growing follicles. Further studies revealed that Eif5 deletion in oocytes downregulated the levels of mitochondrial fission-related proteins (p-DRP1, FIS1, MFF and MTFR) and upregulated the levels of the integrated stress response-related proteins (AARS1, SHMT2 and SLC7A1) and genes (Atf4, Ddit3 and Fgf21). Consistent with this, Eif5 deletion in oocytes resulted in mitochondrial dysfunction characterized by elongated form, aggregated distribution beneath the oocyte membrane, decreased adenosine triphosphate content and mtDNA copy numbers, and excessive accumulation of reactive oxygen species (ROS) and mitochondrial superoxide. Meanwhile, Eif5 deletion in oocytes led to a significant increase in the levels of DNA damage response proteins (γH2AX, p-CHK2 and p-p53) and proapoptotic proteins (PUMA and BAX), as well as a significant decrease in the levels of anti-apoptotic protein BCL-xL.

CONCLUSION

These findings indicate that Eif5 deletion in mouse oocytes results in the apoptosis of oocytes within the early-growing follicles via mitochondrial fission defects, excessive ROS accumulation and DNA damage. This study provides new insights into pathogenesis, genetic diagnosis and potential therapeutic targets for POI.

KEY POINTS

Eif5 deletion in oocytes leads to arrest in oocyte growth and follicle development. Eif5 deletion in oocytes impairs the translation of mitochondrial fission-related proteins, followed by mitochondrial dysfunction. Depletion of Eif5 causes oocyte apoptosis via ROS accumulation and DNA damage response pathway.

MIB2 Functions in Oocyte Meiosis by Modulating Chromatin Configuration

Chromatin configuration serves as a principal indicator of GV (germinal vesicle)-stage oocyte quality. However, the underlying mechanisms governing the chromatin configuration transition from NSN (non-surrounded nucleolus) to SN (surrounded nucleolus) remain unclear. In this study, by conducting a quantitative proteomic analysis, we identified an increased expression of the MIB2 (MIB E3 ubiquitin protein ligase 2) protein in SN oocytes. Specific depletion of MIB2 in SN oocytes not only leads to severe disruption of the meiotic apparatus and a higher incidence of aneuploidy but also adversely affects meiotic maturation and early embryo development. Notably, overexpression of MIB2 in NSN oocytes facilitates the chromatin configuration transition. Meantime, we observed that forced expression of MIB2 in NSN oocytes significantly mitigates spindle/chromosome disorganization and aneuploidy. In summary, our results suggest that chromatin configuration transition regulated by MIB2 is crucial for oocytes to acquire developmental competence.

CRL4DCAF13 E3 ubiquitin ligase targets MeCP2 for degradation to prevent DNA hypermethylation and ensure normal transcription in growing oocytes

The DNA methylation is gradually acquired during oogenesis, a process sustained by successful follicle development. However, the functional roles of methyl-CpG-binding protein 2 (MeCP2), an epigenetic regulator displaying specifical binding with methylated DNA, remains unknown in oogenesis. In this study, we found MeCP2 protein was highly expressed in primordial and primary follicle, but was almost undetectable in secondary follicles. However, in aged ovary, MeCP2 protein is significantly increased in both oocyte and granulosa cells. Overexpression of MeCP2 in growing oocyte caused transcription dysregulation, DNA hypermethylation, and genome instability, ultimately leading to follicle growth arrest and apoptosis. MeCP2 is targeted by DCAF13, a substrate recognition adaptor of the Cullin 4-RING (CRL4) E3 ligase, and polyubiquitinated for degradation in both cells and oocytes. Dcaf13-null oocyte exhibited an accumulation of MeCP2 protein, and the partial rescue of follicle growth arrest induced by Dcaf13 deletion was observed following MeCP2 knockdown. The RNA-seq results revealed that large amounts of genes were regulated by the DCAF13-MeCP2 axis in growing oocytes. Our study demonstrated that CRL4DCAF13 E3 ubiquitin ligase targets MeCP2 for degradation to ensure normal DNA methylome and transcription in growing oocytes. Moreover, in aged ovarian follicles, deceased DCAF13 and DDB1 protein were observed, indicating a potential novel mechanism that regulates ovary aging.

Genetic mechanisms of fertilization failure and early embryonic arrest: a comprehensive review

BACKGROUND

Infertility and pregnancy loss are longstanding problems. Successful fertilization and high-quality embryos are prerequisites for an ongoing pregnancy. Studies have proven that every stage in the human reproductive process is regulated by multiple genes and any problem, at any step, may lead to fertilization failure (FF) or early embryonic arrest (EEA). Doctors can diagnose the pathogenic factors involved in FF and EEA by using genetic methods. With the progress in the development of new genetic technologies, such as single-cell RNA analysis and whole-exome sequencing, a new approach has opened up for us to directly study human germ cells and reproductive development. These findings will help us to identify the unique mechanism(s) that leads to FF and EEA in order to find potential treatments.

OBJECTIVE AND RATIONALE

The goal of this review is to compile current genetic knowledge related to FF and EEA, clarifying the mechanisms involved and providing clues for clinical diagnosis and treatment.

SEARCH METHODS

PubMed was used to search for relevant research articles and reviews, primarily focusing on English-language publications from January 1978 to June 2023. The search terms included fertilization failure, early embryonic arrest, genetic, epigenetic, whole-exome sequencing, DNA methylation, chromosome, non-coding RNA, and other related keywords. Additional studies were identified by searching reference lists. This review primarily focuses on research conducted in humans. However, it also incorporates relevant data from animal models when applicable. The results were presented descriptively, and individual study quality was not assessed.

OUTCOMES

A total of 233 relevant articles were included in the final review, from 3925 records identified initially. The review provides an overview of genetic factors and mechanisms involved in the human reproductive process. The genetic mutations and other genetic mechanisms of FF and EEA were systematically reviewed, for example, globozoospermia, oocyte activation failure, maternal effect gene mutations, zygotic genome activation abnormalities, chromosome abnormalities, and epigenetic abnormalities. Additionally, the review summarizes progress in treatments for different gene defects, offering new insights for clinical diagnosis and treatment.

WIDER IMPLICATIONS

The information provided in this review will facilitate the development of more accurate molecular screening tools for diagnosing infertility using genetic markers and networks in human reproductive development. The findings will also help guide clinical practice by identifying appropriate interventions based on specific gene mutations. For example, when an individual has obvious gene mutations related to FF, ICSI is recommended instead of IVF. However, in the case of genetic defects such as phospholipase C zeta1 (PLCZ1), actin-like7A (ACTL7A), actin-like 9 (ACTL9), and IQ motif-containing N (IQCN), ICSI may also fail to fertilize. We can consider artificial oocyte activation technology with ICSI to improve fertilization rate and reduce monetary and time costs. In the future, fertility is expected to be improved or restored by interfering with or supplementing the relevant genes.

DCAF13 inhibits the p53 signaling pathway by promoting p53 ubiquitination modification in lung adenocarcinoma

BACKGROUND

Lung cancer is a malignant tumor with the highest mortality worldwide. Abnormalities in the ubiquitin proteasome system are considered to be contributed to lung cancer progression with deleterious effects. DDB1 and CUL4 associated factor 13 (DCAF13) is a substrate receptor of the E3 ubiquitin ligase CRL4, but its role in lung cancer remains unknown. In this study, we aimed to investigate the regulatory mechanisms of DCAF13 in lung adenocarcinoma (LUAD).

METHODS

So as to investigate the effect of DCAF13 on lung adenocarcinoma cell function using in vivo and in vitro. Mechanistically, we have identified the downstream targets of DCAF13 by using RNA-sequencing, as well as ubiquitination assays, co-immunoprecipitation, immunofluorescence, immunohistochemistry and chromatin immunoprecipitation - qPCR experiments.

RESULTS

Our findings reveal that DCAF13 is a carcinogenic factor in LUAD, as it is highly expressed and negatively correlated with clinical outcomes in LUAD patients. Through RNA-sequencing, it has been shown that DCAF13 negatively regulates the p53 signaling pathway and inhibits p53 downstream targets including p21, BAX, FAS, and PIDD1. We also demonstrate that DCAF13 can bind to p53 protein, leading to K48-linked ubiquitination and degradation of p53. Functionally, we have shown that DCAF13 knockdown inhibits cell proliferation and migration. Our results highlight the significant role of DCAF13 in promoting LUAD progression by inhibiting p53 protein stabilization and the p53 signaling pathway. Furthermore, our findings suggest that high DCAF13 expression is a poor prognostic indicator in LUAD, and DCAF13 may be a potential therapeutic target for treating with this aggressive cancer.

CONCLUSIONS

The DCAF13 as a novel negative regulator of p53 to promote LUAD progression via facilitating p53 ubiquitination and degradation, suggesting that DCAF13 might be a novel biomarker and therapeutical target for LUAD.

Cordycepin delays postovulatory aging of oocytes through inhibition of maternal mRNAs degradation via DCP1A polyadenylation suppression

Postovulatory aging leads to the decline in oocyte quality and subsequent impairment of embryonic development, thereby reducing the success rate of assisted reproductive technology (ART). Potential preventative strategies preventing oocytes from aging and the associated underlying mechanisms warrant investigation. In this study, we identified that cordycepin, a natural nucleoside analogue, promoted the quality of oocytes aging in vitro, as indicated by reduced oocyte fragmentation, improved spindle/chromosomes morphology and mitochondrial function, as well as increased embryonic developmental competence. Proteomic and RNA sequencing analyses revealed that cordycepin inhibited the degradation of several crucial maternal proteins and mRNAs caused by aging. Strikingly, cordycepin was found to suppress the elevation of DCP1A protein by inhibiting polyadenylation during postovulatory aging, consequently impeding the decapping of maternal mRNAs. In humans, the increased degradation of DCP1A and total mRNA during postovulatory aging was also inhibited by cordycepin. Collectively, our findings demonstrate that cordycepin prevents postovulatory aging of mammalian oocytes by inhibition of maternal mRNAs degradation via suppressing polyadenylation of DCP1A mRNA, thereby promoting oocyte developmental competence.

T cell proliferation requires ribosomal maturation in nucleolar condensates dependent on DCAF13

T cells require rapid proliferation to initiate adaptive immunity to prevent pathogen attacks. The nucleolus, a distinct subnuclear membrane-less compartment for ribosomal biogenesis, is indispensable for cell proliferation. However, specific nucleolar proteins involved in rapid T cell proliferation and their underlying molecular regulatory mechanism remain elusive. Here, we identified an essential nucleolar protein, DCAF13, in T cells and revealed its significant regulation of rapid T cell proliferation. Its depletion drastically impairs T cell proliferation due to severe 18S rRNA maturation failure, consequent abnormal ribosome assembly in nucleoli, and insufficient production of nascent proteins. Mechanistically, we propose that DCAF13 promotes NPM1 phase separation to accelerate pre-RNA enrichment and its endonuclease UTP23 for 18S rRNA maturation during T cell proliferation. Our findings reveal the modulatory effect of nucleolar NPM1/DCAF13 phase separation on ribosomal maturation to ensure rapid T cell proliferation and further pathogen clearance for the first time.

Nucleolar condensates: A cellular machinery necessary for T cell activation

Naive T cells must shift from a state of quiescence to an active metabolic state. To do this, T cells must ramp up their production of ribosomes. In this issue, Zhou et al. (2023. J. Cell Biol.https://doi.org/10.1083/jcb.202201096) identify DDB1 and Cul4-associated factor 13 (DCAF13) as a T cell activation-induced nucleolar protein that functions to enhance ribosome biosynthesis. DCAF13 binds to nucleophosmin 1 (NPM1) to form a biomolecular condensate that functions, in part, by recruiting the endonuclease UTP23 into the nucleolus.

Targeting neddylation sensitizes colorectal cancer to topoisomerase I inhibitors by inactivating the DCAF13-CRL4 ubiquitin ligase complex

Colorectal cancers (CRCs) are prevalent worldwide, yet current treatments remain inadequate. Using chemical genetic screens, we identify that co-inhibition of topoisomerase I (TOP1) and NEDD8 is synergistically cytotoxic in human CRC cells. Combination of the TOP1 inhibitor irinotecan or its bioactive metabolite SN38 with the NEDD8-activating enzyme inhibitor pevonedistat exhibits synergy in CRC patient-derived organoids and xenografts. Mechanistically, we show that pevonedistat blocks the ubiquitin/proteasome-dependent repair of TOP1 DNA-protein crosslinks (TOP1-DPCs) induced by TOP1 inhibitors and that the CUL4-RBX1 complex (CRL4) is a prominent ubiquitin ligase acting on TOP1-DPCs for proteasomal degradation upon auto-NEDD8 modification during replication. We identify DCAF13, a DDB1 and Cullin Associated Factor, as the receptor of TOP1-DPCs for CRL4. Our study not only uncovers a replication-coupled ubiquitin-proteasome pathway for the repair of TOP1-DPCs but also provides molecular and translational rationale for combining TOP1 inhibitors and pevonedistat for CRC and other types of cancers.

A biallelic variant of DCAF13 implicated in a neuromuscular disorder in humans

Neuromuscular disorders encompass a broad range of phenotypes and genetic causes. We investigated a consanguineous family in which multiple patients had a neuromuscular disorder characterized by a waddling gait, limb deformities, muscular weakness and facial palsy. Exome sequencing was completed on the DNA of three of the four patients. We identified a novel missense variant in DCAF13, ENST00000612750.5, NM_015420.7, c.907 G > A;p.(Asp303Asn), ENST00000616836.4, NM_015420.6, c.1363 G > A:p.(Asp455Asn) (rs1209794872) segregating with this phenotype; being homozygous in all four affected patients and heterozygous in the unaffected individuals. The variant was extremely rare in the public databases (gnomAD allele frequency 0.000007081); was absent from the DNA of 300 ethnically matched controls and affected an amino acid which has been conserved across 1-2 billion years of evolution in eukaryotes. DCAF13 contains three WD40 domains and is hypothesized to have roles in both rRNA processing and in ubiquitination of proteins. Analysis of DCAF13 with the p.(Asp455Asn) variant predicted that the amino acid change is deleterious and affects a β-hairpin turn, within a WD40 domain of the protein which may decrease protein stability. Previously, a heterozygous variant of DCAF13 NM_015420.6, c.20 G > C:p.(Trp7Ser) with or without a heterozygous missense variant in CCN3, was suggested to cause inherited cortical myoclonic tremor with epilepsy. In addition, a heterozygous DCAF13 variant has been associated with autism spectrum disorder. Our study indicates a potential role of biallelic DCAF13 variants in neuromuscular disorders. Screening of additional patients with similar phenotype may broaden the allelic and phenotypic spectrum due to DCAF13 variants.

Zebrafish ambra1b knockout reveals a novel role for Ambra1 in primordial germ cells survival, sex differentiation and reproduction

BACKGROUND

AMBRA1 is an intrinsically disordered protein, working as a scaffold molecule to coordinate, by protein-protein interaction, many cellular processes, including autophagy, mitophagy, apoptosis and cell cycle progression. The zebrafish genome contains two ambra1 paralogous genes (a and b), both involved in development and expressed at high levels in the gonads. Characterization of the zebrafish paralogous genes mutant lines generated by CRISPR/Cas9 approach showed that ambra1b knockout leads to an all-male population.

RESULTS

We demonstrated that the silencing of the ambra1b gene determines a reduction of primordial germ cells (PGCs), a condition that, in the zebrafish, leads to the development of all-male progeny. PGC reduction was confirmed by knockdown experiments and rescued by injection of ambra1b and human AMBRA1 mRNAs, but not ambra1a mRNA. Moreover, PGC loss was not rescued by injection with human AMBRA1 mRNA mutated in the CUL4-DDB1 binding region, thus suggesting that interaction with this complex is involved in PGC protection from loss. Results from zebrafish embryos injected with murine Stat3 mRNA and stat3 morpholino suggest that Ambra1b could indirectly regulate this protein through CUL4-DDB1 interaction. According to this, Ambra1+/- mice showed a reduced Stat3 expression in the ovary together with a low number of antral follicles and an increase of atretic follicles, indicating a function of Ambra1 in the ovary of mammals as well. Moreover, in agreement with the high expression of these genes in the testis and ovary, we found significant impairment of the reproductive process and pathological alterations, including tumors, mainly limited to the gonads.

CONCLUSIONS

By exploiting ambra1a and ambra1b knockout zebrafish lines, we prove the sub-functionalization between the two paralogous zebrafish genes and uncover a novel function of Ambra1 in the protection from excessive PGC loss, which seems to require binding with the CUL4-DDB1 complex. Both genes seem to play a role in the regulation of reproductive physiology.

A multidimensional pan-cancer analysis of DCAF13 and its protumorigenic effect in lung adenocarcinoma

DCAF13 is a substrate recognition protein in the ubiquitin-proteasome system with oncogenic effects in several malignant tumors. However, it is unclear that the relationship between DCAF13 expression pattern and prognosis across different cancer types. Also unknown is the biological function or effects on the immune microenvironment of DCAF13. In this study, we parsed multiple public databases to explore the potential tumorigenic actions of DCAF13, including correlations with prognosis, microsatellite instability (MSI), tumor mutational burden (TMB), immune checkpoint genes, immune cell infiltration, and immunotherapy response in pan-cancer. Moreover, we validated DCAF13 expression in a tissue microarray by immunohistochemistry and investigate its effects in vitro and in vivo. The results showed that DCAF13 was upregulated in 17 cancer types and correlated with poor prognosis in many cancers. Also, the correlation between DCAF13 and TMB was found in 14 cancers as well as MSI in nine. The expression level of DCAF13 was found to be notably correlated with immune cell infiltration, showing a negative correlation with CD4 T cell infiltration and a positive correlation with neutrophil infiltration. The oncogene DCAF13 expression was shown to have a positive correlation with CD274 or ADORA2A and negative correlation with VSIR, TNFRSF4, or TNFRSF14 across large subsets of human cancers. Finally, we observed that DCAF13 was highly expressed in a tissue microarray of lung cancer. In immunocompromised mouse models, xenograft growth of human lung cancer cells was significantly inhibited by DCAF13 knockdown. Our results highlighted the value of DCAF13 as a promising independent predictor of poor prognosis through numerous biological processes. High DCAF13 expression often predicts suppressive immune microenvironment and immunotherapy resistance in a pan-cancer context.

HucMSC-EVs Facilitate In Vitro Development of Maternally Aged Preantral Follicles and Oocytes

Follicle developmental capacity and oocyte quality decline with advanced maternal age. Extracellular vesicles from human umbilical cord mesenchymal stem cells (HucMSC-EVs) act as a potential therapeutic product in the treatment of age-related ovarian dysfunction. In vitro culture (IVC) of preantral follicles is a useful method for understanding the mechanism of follicle development and is a promising means for improving female fertility. However, whether HucMSC-EVs have beneficial effects on aged follicle development during IVC has not yet been reported. Our research demonstrated that follicular development with single-addition withdrawal of HucMSC-EVs was better than that with continuous treatment with HucMSC-EVs. HucMSC-EVs facilitated the survival and growth of follicles, promoted the proliferation of granulosa cells (GCs), and improved the steroid hormone secretion of GCs during IVC of aged follicles. Both GCs and oocytes could uptake HucMSC-EVs. Moreover, we observed elevated cellular transcription in GCs and oocytes after treatment with HucMSC-EVs. The RNA sequencing (RNA-seq) results further validated that the differentially expressed genes are related to the promotion of GC proliferation, cell communication, and oocyte spindle organization. Additionally, the aged oocytes displayed a higher maturation rate, presented less aberrant spindle morphology, and expressed a higher level of the antioxidant protein Sirtuin 1 (SIRT1) after treatment with HucMSC-EVs. Our findings suggested that HucMSC-EVs can improve the growth and quality of aged follicles and oocytes in vitro through the regulation of gene transcription, which provides evidence for HucMSC-EVs as potential therapeutic reagents to restore female fertility with advanced age.

Translation regulatory factor BZW1 regulates preimplantation embryo development and compaction by restricting global non-AUG Initiation

Protein synthesis is an essential step in gene expression during the development of mammalian preimplantation embryos. This is a complex and highly regulated process. The accuracy of the translation initiation codon is important in various gene expression programs. However, the mechanisms that regulate AUG and non-AUG codon initiation in early embryos remain poorly understood. BZW1 is a key factor in determining the mRNA translation start codon. Here, we show that BZW1 is essential for early embryonic development in mice. Bzw1-knockdown embryos fail to undergo compaction, and show decreased blastocyst formation rates. We also observe defects in the differentiation capacity and implantation potential after Bzw1 interference. Further investigation revealed that Bzw1 knockdown causes the levels of translation initiation with CUG as the start codon to increase. The decline in BZW1 levels result in a decrease in protein synthesis in preimplantation embryos, whereas the total mRNA levels are not altered. Therefore, we concluded that BZW1 contributes to protein synthesis during early embryonic development by restricting non-AUG translational initiation.

PABPN1 functions as a hub in the assembly of nuclear poly(A) domains that are essential for mouse oocyte development

Growing oocytes store a large amount of maternal mRNA to support the subsequent "maternal-zygotic transition" process. At present, it is not clear how the growing oocytes store and process the newly transcribed mRNA under physiological conditions. In this study, we report non-membrane-bound compartments, nuclear poly(A) domains (NPADs), as the hub for newly transcribed mRNA, in developing mouse oocytes. The RNA binding protein PABPN1 promotes the formation of NPAD through its N-terminal disordered domain and RNA-recognized motif by means of liquid phase separation. Pabpn1-null growing oocytes cannot form NPAD normally in vivo and have defects in stability of oocyte growing-related transcripts and formation of long 3' untranslated region isoform transcripts. Ultimately, Pabpn1^fl/fl;Gdf9-Cre mice are completely sterile with primary ovarian insufficiency. These results demonstrate that NPAD formed by the phase separation properties of PABPN1-mRNA are the hub of the newly transcribed mRNA and essential for the development of oocytes and female reproduction.

DCAF-13 is required for C. elegans growth, development, and fertility

DCAF13 (DDB1 and CUL4 associated factor 13) is a potential oncogene but little is understood about the developmental roles of this highly conserved gene. We characterized the RNAi phenotypes of dcaf-13 , the C. elegans homolog of DCAF13, and show that compared to age-matched control worms, body length is decreased in dcaf-13 (RNAi) C. elegans larvae, suggesting a role of dcaf-13 in larval development. In addition, dcaf-13 (RNAi) worms display either a failure or delay in reaching the L4 and adult stages. Our data also indicates that dcaf-13 (RNAi) treatment beginning at L4 stage does not increase embryonic lethality in progeny; however, progeny production was significantly decreased in dcaf-13 (RNAi) worms, suggesting a general role in fertility and perhaps oocyte development.

Glyphosate exposure deteriorates oocyte meiotic maturation via induction of organelle dysfunctions in pigs

Background

Recently, defects in mammalian oocytes maturation induced by environmental pollution results in the decreasing animal reproduction. Animal exposed to glyphosate is largely unavoidable because glyphosate is one of the most widely used herbicide worldwide due to its high-efficiency and broad-spectrum effects, which causes glyphosate an environmental contaminant found in soil, water and food. During the last few years, the growing and wider use of glyphosate has raised great concerns about its effects of reproductive toxicity. In this study, using porcine models, we investigated effects of glyphosate on organelle functions during oocyte meiosis.

Results

The results showed glyphosate exposure disrupted porcine oocyte maturation. Expression levels of cumulus expansion-related genes were interfered, further indicating the meiotic defects. The damaging effects were mediated by destruction of mitochondrial distribution and functions, which induced ROS accumulation and oxidative stress, also indicated by the decreased mRNA expression of related antioxidant enzyme genes. We also found an interference of endoplasmic reticulum (ER) distribution, disturbance of Ca²⁺ homeostasis, as well as fluctuation of ER stress, showing with the reduced ER stress-related mRNA or protein expression, which could indicate the dysfunction of ER for protein processing and signal transduction in glyphosate-exposed oocytes. Moreover, glyphosate exposure induced the disruption of lysosome function for autophagy, showing with the decrease of LAMP2 expression and autophagy-related genes mRNA expression. Additionally, our data showed the distribution of Golgi apparatus and the functions of ribosome were disturbed after glyphosate exposure, which might affect protein synthesis and transport.

Conclusions

Collectively, our study showed that exposed to glyphosate could affect animal reproduction by compromising the quality of oocytes through its wide toxic effects on organelle functions.

Ppan is essential for preimplantation development in mice†

PETER PAN (PPAN), located to nucleoli and mitochondria, is a member of the Brix domain protein family, involved in rRNA processing through its rRNA binding motif and mitochondrial apoptosis by protecting mitochondria structure and suppressing basal autophagic flux. Ppan is important for cell proliferation and viability, and mutation of Ppan in Drosophila caused larval lethality and oogenesis failure. Yet, its role in mammalian reproduction remains unclear. In this study, we explored the function of Ppan in oocyte maturation and early embryogenesis using conditional knockout mouse model. Deficiency of maternal Ppan significantly downregulated the expression level of 5.8S rRNA, 18S rRNA, and 28S rRNA, though it had no effect on oocyte maturation or preimplantation embryo development. However, depletion of both maternal and zygotic Ppan blocked embryonic development at morula stage. Similar phenotype was obtained when only zygotic Ppan was depleted. We further identified no DNA binding activity of PPAN in mouse embryonic stem cells, and depletion of Ppan had minimum impact on transcriptome but decreased expression of 5.8S rRNA, 18S rRNA, and 28S rRNA nevertheless. Our findings demonstrate that Ppan is indispensable for early embryogenesis in mice.

Mouse Oocytes, A Complex Single Cell Transcriptome

Germinal vesicle (GV) stage is a critical transition point from growth to maturation in mammalian oocyte development. During the following meiotic maturation, active RNA degradation and absence of transcription significantly reprofile the oocyte transcriptome to determine oocyte quality. Oocyte RNA-seq has revealed transcriptome differences between two defined phases of GV stage, namely non-surrounded nucleolus (NSN) and surrounded nucleolus (SN) phases. In addition, oocyte RNA-seq has identified a variety of dysregulated genes upon genetic mutation or environmental perturbation. Historically, due to the low amount of RNA per oocyte, a few (20–200) oocytes were needed for a regular library construction in bulk RNA-seq. In recent years, development of single cell sequencing allows detailing the transcriptome of individual oocytes. Here in this study, different RNA-seq datasets from single and bulk of mouse oocytes are compared, and single oocyte RNA-seq (soRNA-seq) shows higher reproducibility. In addition, soRNA-seq better illustrates developmental progression of GV oocytes, revealing more complex gene changes than traditional views. Specially, an elevated level of ribosomal RNA 5′-ETS (5′ external transcribed spacer) has been shown to highly correlate with SN property. This study further demonstrates that UMI (unique molecular identifiers) based and other deduplication methods are limited in their ability to improve the precision of the soRNA-seq datasets. Finally, this study proposes that external spike-in molecules are useful for normalizing samples of different transcriptome sizes. A list of stable genes has been identified during oocyte maturation that are comparable to external spike-in molecules. These findings highlight the advantage of soRNA-seq, and have established ways for better clustering and cross-stage normalization, which can provide more insight into the biological features of oocyte maturation.

DCAF13 promotes breast cancer cell proliferation by ubiquitin inhibiting PERP expression

Evolutionarily conserved DDB1-and CUL4-associated factor 13 (DCAF13) is a recently discovered substrate receptor for the cullin RING-finger ubiquitin ligase 4 (CRL4) E3 ubiquitin ligase that regulates cell cycle progression. DCAF13 is overexpressed in many cancers, although its role in breast cancer is currently elusive. In this study we demonstrate that DCAF13 is overexpressed in human breast cancer and that its overexpression closely correlates with poor prognosis, suggesting that DCAF13 may serve as a diagnostic marker and therapeutic target. We knocked down DCAF13 in breast cancer cell lines using CRISPR/Cas9 and found that DCAF13 deletion markedly reduced breast cancer cell proliferation, clone formation, and migration both in vitro and in vivo. In addition, DCAF13 deletion promoted breast cancer cell apoptosis and senescence, and induced cell cycle arrest in the G1/S phase. Genome-wide RNAseq analysis and western blotting revealed that loss of DCAF13 resulted in both mRNA and protein accumulation of p53 apoptosis effector related to PMP22 (PERP). Knockdown of PERP partially reversed the hampered cell proliferation induced by DCAF13 knockdown. Co-immunoprecipitation assays revealed that DCAF13 and DNA damage-binding protein 1 (DDB1) directly interact with PERP. Overexpression of DDB1 significantly increased PERP polyubiquitination, suggesting that CRL4^DCAF13 E3 ligase targets PERP for ubiquitination and proteasomal degradation. In conclusion, DCAF13 and the downstream effector PERP occupy key roles in breast cancer proliferation and potentially serve as prognostics and therapeutic targets.

FGF2 Is Protective Towards Cisplatin-Induced KGN Cell Toxicity by Promoting FTO Expression and Autophagy

It is widely known that chemotherapy-induced apoptosis of granulosa was the main reason for premature ovarian failure (POF). In addition, accumulating evidence has demonstrated that autophagy was involved in it. Studies before have reported that fibroblast growth factor-2 (FGF2) could attenuate cell death via regulating autophagy. In our previous study, FGF2 could decrease granulosa cell apoptosis in cisplatin-induced POF mice. Furthermore, obesity-associated protein [fat mass and obesity-associated protein (FTO)], which decreased significantly in POF mice, could inhibit cell apoptosis via activating autophagy. Moreover, downregulation of FTO could decrease the expression of paracrine factor FGF2. However, the relationship between FTO and FGF2 in granulosa cell autophagy is still unknown. In the present study, Cell Counting Kit-8 (CCK-8) and 5-ethynyl-2-deoxyuridine (EdU) assays showed that exogenous addition of FGF2 could promote cisplatin-induced injured granulosa cell proliferation. Western blotting indicated that FGF2 could inhibit apoptosis of injured granulosa cells via autophagy. Inhibition of autophagy by chemicals suppressed the effect of FGF2 and promoted injured cell apoptosis. In addition, the expression of FTO was decreased in injured cells, and FGF2 addition could reverse it. Overexpression of FTO reduced injured cell apoptosis via activating the autophagy process. Our findings indicated that FGF2 activates autophagy by regulating the expression of FTO, thereby reducing the apoptosis of the injured cells.

Nuclear poly(A) binding protein 1 (PABPN1) mediates zygotic genome activation-dependent maternal mRNA clearance during mouse early embryonic development

An embryo starts its life with maternal mRNA clearance, which is crucial for embryonic development. The elimination of maternal transcripts occurs by the joint action of two pathways: the maternally encoded mRNA decay pathway (M-decay) and the zygotic genome activation (ZGA)-dependent pathway (Z-decay). However, zygotic factors triggering maternal mRNA decay in early mammalian embryos remain largely unknown. In this study, we identified the zygotically encoded nuclear poly(A) binding protein 1 (PABPN1) as a factor required for maternal mRNA turnover, with a previously undescribed cytoplasmic function. Cytoplasmic PABPN1 docks on 3'-uridylated transcripts, downstream of terminal uridylyl transferases TUT4 and TUT7, and recruits 3'-5' exoribonuclease DIS3L2 to its targets, facilitating maternal mRNA decay. Pabpn1-knockout in mice resulted in preimplantation stage mortality due to early developmental arrest at the morula stage. Maternal mRNAs to be eliminated via the Z-decay pathway failed to be removed from Pabpn1-depleted embryos. Furthermore, PABPN1-mediated Z-decay is essential for major ZGA and regulates the expression of cell fate-determining factors in mouse preimplantation embryos. This study revealed an unforeseen cytoplasmic function of PABPN1 coupled with early embryonic development, characterized the presence of a zygotic destabilizer of maternal mRNA, and elucidated the Z-decay process mechanisms, which potentially contribute to human fertility.

Biallelic mutations in MOS cause female infertility characterized by human early embryonic arrest and fragmentation

Early embryonic arrest and fragmentation (EEAF) is a common phenomenon leading to female infertility, but the genetic determinants remain largely unknown. The Moloney sarcoma oncogene (MOS) encodes a serine/threonine kinase that activates the ERK signaling cascade during oocyte maturation in vertebrates. Here, we identified four rare variants of MOS in three infertile female individuals with EEAF that followed a recessive inheritance pattern. These MOS variants encoded proteins that resulted in decreased phosphorylated ERK1/2 level in cells and oocytes, and displayed attenuated rescuing effects on cortical F-actin assembly. Using oocyte-specific Erk1/2 knockout mice, we verified that MOS-ERK signal pathway inactivation in oocytes caused EEAF as human. The RNA sequencing data revealed that maternal mRNA clearance was disrupted in human mature oocytes either with MOS homozygous variant or with U0126 treatment, especially genes relative to mitochondrial function. Mitochondrial dysfunction was observed in oocytes with ERK1/2 deficiency or inactivation. In conclusion, this study not only uncovers biallelic MOS variants causes EEAF but also demonstrates that MOS-ERK signaling pathway drives human oocyte cytoplasmic maturation to prevent EEAF.

Doxorubicin promotes breast cancer cell migration and invasion via DCAF13

DDB1 and CUL4 associated factor 13 (DCAF13) is a substrate receptor in the CUL4-DDB1 E3 ligase, and its expression is associated with the prognosis of certain cancers. In the present study, we report evidence that DCAF13 is aberrantly overexpressed in human breast cancer and its expression is positively associated with cancer progression. Further analysis showed that the DCAF13 expression level is significantly higher in triple-negative breast cancer compared to non-triple-negative breast cancer, indicating a positive correlation between its expression and the aggressiveness of breast cancer. Subsequent studies revealed that DCAF13 regulates cancer cell migration, invasion and epithelial-mesenchymal transition in human breast cancer, whereas it has no significant impact on breast cancer cell proliferation, cell cycle progressionor apoptosis. Taken together, our results demonstrate that DCAF13 promotes the epithelial-mesenchymal transition in human breast cancer cells, indicating an involvement in breast cancer metastasis. Furthermore, we report that doxorubicin, a widely used chemotherapy drug, increases DCAF13 expression in breast cancer cells, leading to enhanced cancer cell migration and invasion. These results suggest that doxorubicin chemotherapy may increase the risk of metastasis of drug-resistant breast cancer cells, and future therapeutics targeting DCAF13 may help reduce the risk, especially for patients undergoing chemotherapy.

Analysing a Novel RNA-Binding-Protein-Related Prognostic Signature Highly Expressed in Breast Cancer

BACKGROUND

Breast cancer (BRCA) is one of the most common cancers and the leading cause of cancer-related death in women. RNA-binding proteins (RBPs) play an important role in the emergence and pathogenesis of tumors. The target RNAs of RBPs are very diverse; in addition to binding to mRNA, RBPs also bind to noncoding RNA. Noncoding RNA can cause secondary structures that can bind to RBPs and regulate multiple processes such as splicing, RNA modification, protein localization, and chromosomes remodeling, which can lead to tumor initiation, progression, and invasion.

METHODS

(1) BRCA data were downloaded from The Cancer Genome Atlas (TCGA) and the International Cancer Genome Consortium (ICGC) databases and were used as training and testing datasets, respectively. (2) The prognostic RBPs-related genes were screened according to the overlapping differentially expressed genes (DEGs) from the TCGA database. (3) Univariate Cox proportional hazard regression was performed to identify the genes with significant prognostic value. (4) Further, we used the LASSO regression to construct a prognostic signature and validated the signature in the TCGA and ICGC cohort. (5) Besides, we also performed prognostic analysis, expression level verification, immune cell correlation analysis, and drug correlation analysis of the genes in the model.

RESULTS

Four genes (MRPL13, IGF2BP1, BRCA1, and MAEL) were identified as prognostic gene signatures. The prognostic model has been validated in the TCGA and ICGC cohorts. The risk score calculated with four genes signatures could largely predict overall survival for 1, 3, and 5 years in patients with BRCA. The calibration plot demonstrated outstanding consistency between the prediction and actual observation. The findings of online database verification revealed that these four genes were significantly highly expressed in tumors. Also, we observed their significant correlations with some immune cells and also potential correlations with some drugs.

CONCLUSION

We constructed a 4-RBPs-based prognostic signature to predict the prognosis of BRCA patients, and it has the potential for treating and diagnosing BRCA.

Oocyte meiosis-coupled poly(A) polymerase α phosphorylation and activation trigger maternal mRNA translation in mice

Mammalian oocyte maturation is driven by strictly regulated polyadenylation and translational activation of maternal mRNA stored in the cytoplasm. However, the poly(A) polymerase (PAP) that directly mediates cytoplasmic polyadenylation in mammalian oocytes has not been determined. In this study, we identified PAPα as the elusive enzyme that catalyzes cytoplasmic mRNA polyadenylation implicated in mouse oocyte maturation. PAPα was mainly localized in the germinal vesicle (GV) of fully grown oocytes but was distributed to the ooplasm after GV breakdown. Inhibition of PAPα activity impaired cytoplasmic polyadenylation and translation of maternal transcripts, thus blocking meiotic cell cycle progression. Once an oocyte resumes meiosis, activated CDK1 and ERK1/2 cooperatively mediate the phosphorylation of three serine residues of PAPα, 537, 545 and 558, thereby leading to increased activity. This mechanism is responsible for translational activation of transcripts lacking cytoplasmic polyadenylation elements in their 3′-untranslated region (3′-UTR). In turn, activated PAPα stimulated polyadenylation and translation of the mRNA encoding its own (Papola) through a positive feedback circuit. ERK1/2 promoted Papola mRNA translation in a 3′-UTR polyadenylation signal-dependent manner. Through these mechanisms, PAPα activity and levels were significantly amplified, improving the levels of global mRNA polyadenylation and translation, thus, benefiting meiotic cell cycle progression.

DDB1- and CUL4-associated factor 8 plays a critical role in spermatogenesis

Cullin-RING E3 ubiquitin ligase (CRL)-4 is a member of the large CRL family in eukaryotes. It plays important roles in a wide range of cellular processes, organismal development, and physiological and pathological conditions. DDB1- and CUL4-associated factor 8 (DCAF8) is a WD40 repeat-containing protein, which serves as a substrate receptor for CRL4. The physiological role of DCAF8 is unknown. In this study, we constructed Dcaf8 knockout mice. Homozygous mice were viable with no noticeable abnormalities. However, the fertility of Dcaf8-deficient male mice was markedly impaired, consistent with the high expression of DCAF8 in adult mouse testis. Sperm movement characteristics, including progressive motility, path velocity, progressive velocity, and track speed, were significantly lower in Dcaf8 knockout mice than in wild-type (WT) mice. However, the total motility was similar between WT and Dcaf8 knockout sperm. More than 40% of spermatids in Dcaf8 knockout mice showed pronounced morphological abnormalities with typical bent head malformation. The acrosome and nucleus of Dcaf8 knockout sperm looked similar to those of WT sperm. In vitro tests showed that the fertilization rate of Dcaf8 knockout mice was significantly reduced. The results demonstrated that DCAF8 plays a critical role in spermatogenesis, and DCAF8 is a key component of CRL4 function in the reproductive system.

Bcl-2 Associated Athanogene 2 (BAG2) is Associated With Progression and Prognosis of Hepatocellular Carcinoma: A Bioinformatics-Based Analysis

Background: Bcl-2 associated athanogene2 (BAG2) is reported to act as an oncogene or a tumor-suppressor in tumors in a context-dependent way; however, its function in hepatocellular carcinoma (HCC) remains unclear.

Methods: Immunohistochemistry (IHC) staining, cell counting kit-8 (CCK-8) assay, apoptotic assay, cell invasion assay and a set of bioinformatics tools were integrated to analyze the role of BAG2 in hepatocellular carcinoma.

Results: BAG2 was significantly up-regulated in HCC. Prognostic analysis indicated that HCC patients with high expression of BAG2 had significantly shorter overall survival, progression free survival and disease specific survival. Besides, silencing BAG2 in HCC cells impaired cell proliferation, facilitated apoptosis and repressed invasion of the cells. Bioinformatics analysis showed that BAG2 might regulate ribosome biogenesis in HCC.

Conclusion: This study revealed that the up-regulated BAG2 in HCC was associated with a worse prognosis and might favor the progression of the disease.

Mechanisms of Oocyte Maturation and Related Epigenetic Regulation

Meiosis is the basis of sexual reproduction. In female mammals, meiosis of oocytes starts before birth and sustains at the dictyate stage of meiotic prophase I before gonadotropins-induced ovulation happens. Once meiosis gets started, the oocytes undergo the leptotene, zygotene, and pachytene stages, and then arrest at the dictyate stage. During each estrus cycle in mammals, or menstrual cycle in humans, a small portion of oocytes within preovulatory follicles may resume meiosis. It is crucial for females to supply high quality mature oocytes for sustaining fertility, which is generally achieved by fine-tuning oocyte meiotic arrest and resumption progression. Anything that disturbs the process may result in failure of oogenesis and seriously affect both the fertility and the health of females. Therefore, uncovering the regulatory network of oocyte meiosis progression illuminates not only how the foundations of mammalian reproduction are laid, but how mis-regulation of these steps result in infertility. In order to provide an overview of the recently uncovered cellular and molecular mechanism during oocyte maturation, especially epigenetic modification, the progress of the regulatory network of oocyte meiosis progression including meiosis arrest and meiosis resumption induced by gonadotropins is summarized. Then, advances in the epigenetic aspects, such as histone acetylation, phosphorylation, methylation, glycosylation, ubiquitination, and SUMOylation related to the quality of oocyte maturation are reviewed.

DCAF13 promotes triple-negative breast cancer metastasis by mediating DTX3 mRNA degradation

DCAF13 is firstly identified as a substrate receptor of CUL4-DDB1 E3 ligase complex. This study disclosed that DCAF13 acted as a novel RNA binding protein (RBP) that contributed to triple-negative breast cancer (TNBC) metastasis. Clinical data obtained from TCGA and our collection showed that DCAF13 was closely correlated with poor clinicopathological characteristics and overall survival, which indicated DCAF13 may serve as a diagnostic marker for TNBC metastasis. Functionally, DCAF13 overexpression or suppression was sufficient to enhance or decrease breast cancer cell migration and invasion. Mechanistically, DCAF13 functioned as an RBP by binding with the AU-rich element (ARE) of DTX3 mRNA 3'UTR to accelerate its degradation. Moreover, we identified that DTX3 promoted the ubiquitination and degradation of NOTCH4. Finally, increased DCAF13 expression led to post-transcriptional decay of DTX3 mRNA and consequently activated of NOTCH4 signaling pathway in TNBC. In conclusion, these results identified that DCAF13 as a diagnostic marker and therapeutic target for TNBC treatment. Abbreviation: DCAF13: DDB1 and CUL4-associated factor 13; DDB1: DNA-binding protein 1; CUL4: Cullin 4; CRL4, Cullin-ring finger ligase 4; RBP: RNA binding protein; TNBC: triple-negative breast cancer; ARE: AU-rich element; DTX3: Deltex E3 ubiquitin ligase 3; HER2: human epidermal growth factor receptor 2; ER: estrogen receptor; PR: progesterone receptor; PTEN: phosphatase and tensin homolog deleted on chromosome 10; EMT: epithelial-mesenchymal transition.

Function and Regulation of Histone H3 Lysine-4 Methylation During Oocyte Meiosis and Maternal-to-Zygotic Transition

During oogenesis and fertilization, histone lysine methyltransferases (KMTs) and histone lysine demethylases (KDMs) tightly regulate the methylation of histone H3 on lysine-4 (H3K4me) by adding and removing methyl groups, respectively. Female germline-specific conditional knockout approaches that abolish the maternal store of target mRNAs and proteins are used to examine the functions of H3K4 KMTs and KDMs during oogenesis and early embryogenesis. In this review, we discuss the recent advances in information regarding the deposition and removal of histone H3K4 methylations, as well as their functional roles in sculpting and poising the oocytic and zygotic genomes. We start by describing the role of KMTs in establishing H3K4 methylation patterns in oocytes and the impact of H3K4 methylation on oocyte maturation and competence to undergo MZT. We then introduce the latest information regarding H3K4 demethylases that account for the dynamic changes in H3K4 modification levels during development and finish the review by specifying important unanswered questions in this research field along with promising future directions for H3K4-related epigenetic studies.

Ubiquitin ligases and medulloblastoma: genetic markers of the four consensus subgroups identified through transcriptome datasets

The ubiquitin proteasome system regulates key cellular processes in normal and in cancer cells. Herein, we review published data on the role of ubiquitin ligases in the four major subgroups of medulloblastoma (MB). While conventional literature serves as an initial source of information on cellular pathways in MB, large publicly available datasets of gene expression can be used to add information not previously identified in the literature. By analysing the publicly available Cavalli dataset, we show that increased expression of ZNRF3 characterizes the WNT subgroup of MB. The ZNRF3 gene codes for an E3 ligase associated with WNT receptors. Loss of a copy of chromosome 6 in a subtype of the WNT group was associated with decreased expression of the gene encoding the E3 ligase RNF146. While the E3 ligase SMURF regulates SHH receptors, increased expression of the gene encoding the Cullin Ring E3 adaptor PPP2R2C was statistically a better genetic marker of the SHH group. Genes whose expression was statistically strongly related to Group 3 included the E3 ligase gene TRIM58, and the gene for the E3 ligase adaptor, PPP2R2B. Group 4 MB was associated with expression of genes encoding several E3 ligases and E3 ligase adaptors involved in ribosome biogenesis. Increased expression of the genes encoding the E3 ligase adaptors and transcription repressors ZBTB18 and ZBTB38 were also noted in subgroup 4. These data suggest that several E3 ligases and their adaptors should be investigated as therapeutic targets for subgroup specific MB brain tumors.

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.

PABPN1L mediates cytoplasmic mRNA decay as a placeholder during the maternal-to-zygotic transition

Maternal mRNA degradation is a critical event of the maternal-to-zygotic transition (MZT) that determines the developmental potential of early embryos. Nuclear Poly(A)-binding proteins (PABPNs) are extensively involved in mRNA post-transcriptional regulation, but their function in the MZT has not been investigated. In this study, we find that the maternally expressed PABPN1-like (PABPN1L), rather than its ubiquitously expressed homolog PABPN1, acts as an mRNA-binding adapter of the mammalian MZT licensing factor BTG4, which mediates maternal mRNA clearance. Female Pabpn1l null mice produce morphologically normal oocytes but are infertile owing to early developmental arrest of the resultant embryos at the 1- to 2-cell stage. Deletion of Pabpn1l impairs the deadenylation and degradation of a subset of BTG4-targeted maternal mRNAs during the MZT. In addition to recruiting BTG4 to the mRNA 3'-poly(A) tails, PABPN1L is also required for BTG4 protein accumulation in maturing oocytes by protecting BTG4 from SCF-βTrCP1 E3 ubiquitin ligase-mediated polyubiquitination and degradation. This study highlights a noncanonical cytoplasmic function of nuclear poly(A)-binding protein in mRNA turnover, as well as its physiological importance during the MZT.

The CRL4-DCAF13 ubiquitin E3 ligase supports oocyte meiotic resumption by targeting PTEN degradation

Cullin ring-finger ubiquitin ligase 4 (CRL4) has multiple functions in the maintenance of oocyte survival and meiotic cell cycle progression. DCAF13, a novel CRL4 adaptor, is essential for oocyte development. But the mechanisms by which CRL4-DCAF13 supports meiotic maturation remained unclear. In this study, we demonstrated that DCAF13 stimulates the meiotic resumption-coupled activation of protein synthesis in oocytes, partially by maintaining the activity of PI3K signaling pathway. CRL4-DCAF13 targets the polyubiquitination and degradation of PTEN, a lipid phosphatase that inhibits PI3K pathway as well as oocyte growth and maturation. Dcaf13 knockout in oocytes caused decreased CDK1 activity and impaired meiotic cell cycle progression and chromosome condensation defects. As a result, chromosomes fail to be aligned at the spindle equatorial plate, the spindle assembly checkpoint is activated, and most Dcaf13 null oocytes are arrested at the prometaphase I. The DCAF13-dependent PTEN degradation mechanism fits in as a missing link between CRL4 ubiquitin E3 ligase and PI3K pathway, both of which are crucial for translational activation during oocyte GV-MII transition.

ZAR1 and ZAR2 are required for oocyte meiotic maturation by regulating the maternal transcriptome and mRNA translational activation

Zar1 was one of the earliest mammalian maternal-effect genes to be identified. Embryos derived from Zar1-null female mice are blocked before zygotic genome activation; however, the underlying mechanism remains unclear. By knocking out Zar1 and its homolog Zar2 in mice, we revealed a novel function of these genes in oocyte meiotic maturation. Zar1/2-deleted oocytes displayed delayed meiotic resumption and polar body-1 emission and a higher incidence of abnormal meiotic spindle formation and chromosome aneuploidy. The grown oocytes of Zar1/2-null mice contained decreased levels of many maternal mRNAs and displayed a reduced level of protein synthesis. Key maturation-associated changes failed to occur in the Zar1/2-null oocytes, including the translational activation of maternal mRNAs encoding the cell-cycle proteins cyclin B1 and WEE2, as well as maternal-to-zygotic transition (MZT) licensing factor BTG4. Consequently, maternal mRNA decay was impaired and MZT was abolished. ZAR1/2 bound mRNAs to regulate the translational activity of their 3′-UTRs and interacted with other oocyte proteins, including mRNA-stabilizing protein MSY2 and cytoplasmic lattice components. These results countered the traditional view that ZAR1 only functions after fertilization and highlight a previously unrecognized role of ZAR1/2 in regulating the maternal transcriptome and translational activation in maturing oocytes.

The repair of endo/exogenous DNA double-strand breaks and its effects on meiotic chromosome segregation in oocytes

Germ cell-derived genomic structure variants not only drive the evolution of species but also induce developmental defects in offspring. The genomic structure variants have different types, but most of them are originated from DNA double-strand breaks (DSBs). It is still not well known whether DNA DSBs exist in adult mammalian oocytes and how the growing and fully grown oocytes repair their DNA DSBs induced by endogenous or exogenous factors. In this study, we detected the endogenous DNA DSBs in the growing and fully grown mouse oocytes and found that the DNA DSBs mainly localized at the centromere-adjacent regions, which are also copy number variation hotspots. When the exogenous DNA DSBs were introduced by Etoposide, we found that Rad51-mediated homologous recombination (HR) was used to repair the broken DNA. However, the HR repair caused the chromatin intertwined and impaired the homologous chromosome segregation in oocytes. Although we had not detected the indication about HR repair of endogenous centromere-adjacent DNA DSBs, we found that Rad52 and RNA:DNA hybrids colocalized with these DNA DSBs, indicating that a Rad52-dependent DNA repair might exist in oocytes. In summary, our results not only demonstrated an association between endogenous DNA DSBs with genomic structure variants but also revealed one specific DNA DSB repair manner in oocytes.

The 5.8S pre-rRNA maturation factor, M-phase phosphoprotein 6, is a female fertility factor required for oocyte quality and meiosis

OBJECTIVES

M-phase phosphoprotein 6 (MPP6) is important for 5.8S pre-rRNA maturation in somatic cells and was screened as a female fertility factor. However, whether MPP6 functions in oocyte meiosis and fertility is not yet known. We aimed to address this.

MATERIALS AND METHODS

Mouse oocytes with surrounded nucleus (SN) or non-surrounded nucleus (NSN) were used for all experiments. Peptide nanoparticle-mediated antibody transfection was used to deplete MPP6. Immunofluorescence staining, immunohistochemistry and live tracker staining were used to examine MPP6 localization and characterize phenotypes after control or MPP6 depletion. High-fidelity PCR and fluorescence in situ hybridization (FISH) were used to examine the localization and level of 5.8S rRNAs. Western blot was used to examine the protein level. MPP6-EGFP mRNA microinjection was used to do the rescue.

RESULTS

MPP6 was enriched within ovaries and oocytes. MPP6 depletion significantly impeded oocyte meiosis. MPP6 depletion increased 5.8S pre-rRNA. The mRNA levels of MPP6 and 5.8S rRNA decreased within ageing oocytes, and MPP6 mRNA injection partially increased 5.8S rRNA maturation and improved oocyte quality.

CONCLUSIONS

MPP6 is required for 5.8S rRNA maturation, meiosis and quality control in mouse oocytes, and MPP6 level might be a marker for oocyte quality.

Maternal DCAF13 Regulates Chromatin Tightness to Contribute to Embryonic Development

Maternal-zygotic transition (MZT) is critical for the developmental control handed from maternal products to newly synthesized zygotic genome in the earliest stage of embryogenesis. However, the spatiotemporal dynamic regulation of MZT by maternal factors is largely unknown. Here, we reported a novel maternal factor, DCAF13, which was highly expressed in growing oocyte nucleolus and had key maternal effects on oocyte and zygotic chromatin tightness during maternal to zygotic transition. DCAF13 specifically deleted in oocytes resulted in loose chromatin structure in fully grown germinal vesicle oocytes. Despite normal nuclear maturation in maternal DCAF13-deleted oocytes, the chromosomes at MII stage were not properly condensed. Consequently, the nuclear and nucleolar structure reorganized abnormally, and transcription was inactive in zygotic embryos. RNA-seq analysis of MII oocytes and 2-cell embryos demonstrated that the transcriptomes between knockout and control oocyte were similar, but the maternal DCAF13 deleted two-cell embryos showed a significant decrease in transcription. In addition, the maternal DCAF13-deleted embryos displayed arrest at the two-cell stage, which could not be rescued by injecting flag-Dcaf13 mRNA in the zygote. This revealed that DCAF13 was a unique maternal effect factor regulating the nucleolus.