Selective Translation of Maternal mRNA by eIF4E1B Controls Oocyte to Embryo Transition

PGC7 regulates maternal mRNA translation via AKT1-YBX1 interactions in mouse oocytes

Timely and accurate translation of maternal mRNA is essential for oocyte maturation and early embryonic development. Previous studies have highlighted the importance of Primordial Germ cell 7 (PGC7) as a maternal factor in maintaining DNA methylation of maternally imprinted loci in zygotes. However, it is still unknown whether PGC7 is involved in the regulation of Maternal mRNA Translation. In this study, we have identified that PGC7-AKT1-YBX1 axis is involved in promoting the translation of maternal mRNAs. PGC7 not only sustains AKT1 activity by counteracting PP2A dephosphorylation and facilitating PDK1-AKT1 binding but also assists AKT1 in phosphorylating the translation inhibitor YBX1. In the absence of PGC7, despite increased PIK3CA expression and AKT1 phosphorylation, AKT1 is unable to phosphorylate YBX1. PGC7 facilitates the interaction between AKT1 and YBX1, enhancing YBX1-Serine 100 phosphorylation, which leads to YBX1 dissociation from eIF4E, thereby activating the translation of maternal Cyclin B1 and YAP1. The findings demonstrate the indispensability of PGC7 for translation activation in mammalian oocytes and provide a potential network regulated by PGC7 in early oogenesis.

Premeiotic deletion of Eif2s2 causes oocyte arrest at the early diplotene stage and apoptosis in mice

Eukaryotic translation initiation factor 2 subunit 2 (EIF2S2), a subunit of the heterotrimeric G protein EIF2, is involved in the initiation of translation. Our findings demonstrate that the depletion of Eif2s2 in premeiotic germ cells causes oocyte arrest at the pachytene and early diplotene stages at 1 day postpartum (dpp) and 5 dpp, respectively, and eventually leads to oocyte apoptosis and failure of primordial follicle formation. Further studies reveal that Eif2s2 deletion downregulates homologous recombination-related and mitochondrial fission-related protein levels, and upregulates the integrated stress response-related proteins and mRNA levels. Consistently, Eif2s2 deletion significantly decreases the expression of dictyate genes and compromises mitochondrial function, characterized by elongated shapes, decreased ATP levels and mtDNA copy number, along with an excessive accumulation of reactive oxygen species (ROS) and mitochondrial superoxide. Furthermore, DNA damage response and proapoptotic protein levels increase, while anti-apoptotic protein levels decrease in Eif2s2-deleted mice. An increase in oocytes with positive cleaved-Caspase-3 and TUNEL signals, alongside reduced Lamin B1 intensity, further indicates oocyte apoptosis. Collectively, Eif2s2 deletion in premeiotic germ cells causes oocyte meiotic arrest at the early diplotene stage by impairing homologous recombination, and eventually leads to oocyte apoptosis mainly through the downregulation of mitochondrial fission-related proteins, ROS accumulation and subsequent DNA damage.

Role of RNA-binding Proteins in Regulating Cell Adhesion and Progression of the Atherosclerotic Plaque and Plaque Erosion

PURPOSE OF REVIEW

RNA-binding proteins (RBPs) have emerged as crucial regulators of post-transcriptional processes, influencing the fate of RNA. This review delves into the biological functions of RBPs and their role in alternative splicing concerning atherosclerosis (AS), highlighting their participation in essential cellular processes. Our goal is to offer new insights for cardiovascular disease research and treatment.

RECENT FINDING

Dysregulation of RBPs is associated with various human diseases, including autoimmune and neurological disorders. The role of RBPs in the pathogenesis of AS is progressively being elucidated, as they influence plaque formation and disease progression by regulating cell function and gene expression. RBPs play intricate biological roles in regulating pre-mRNA, including editing, splicing, stability and translation. Alternative splicing has been demonstrated to enhance biological complexity and diversity. Our findings indicate that alternative splicing is extensively involved in the pathogenesis of AS. The dysregulated expression of specific RBPs in AS is linked to the production of adhesion molecules and vascular endothelium damage. Further research on RBPs could pave the way for the development of novel therapeutic targets.

Two mechanisms repress cyclin B1 translation to maintain prophase arrest in mouse oocytes

In mammals, oocytes are arrested in prophase of meiosis I for long periods of time. Prophase arrest is critical for reproduction because it allows oocytes to grow to their full size to support meiotic maturation and embryonic development. Prophase arrest requires the inhibitory phosphorylation of the mitotic kinase CDK1. Whether prophase arrest is also regulated at the translational level is unknown. Here, we show that prophase arrest is regulated by translational control of dormant cyclin B1 mRNAs. Using Trim-Away, we identify two mechanisms that maintain cyclin B1 dormancy and thus prophase arrest. First, a complex of the RNA-binding proteins DDX6, LSM14B and CPEB1 directly represses cyclin B1 translation through interacting with its 3'UTR. Second, cytoplasmic poly(A)-binding proteins (PABPCs) indirectly repress the translation of cyclin B1 and other poly(A)-tail-less or short-tailed mRNAs by sequestering the translation machinery on long-tailed mRNAs. Together, we demonstrate how RNA-binding proteins coordinately regulate prophase arrest, and reveal an unexpected role for PABPCs in controlling mRNA dormancy.

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.

Predictive modeling of oocyte maternal mRNA features for five mammalian species reveals potential shared and species-restricted regulators during maturation

Oocyte maturation is accompanied by changes in abundances of thousands of mRNAs, many degraded and many preferentially stabilized. mRNA stability can be regulated by diverse features including GC content, codon bias, and motifs within the 3'-untranslated region (UTR) interacting with RNA binding proteins (RBPs) and miRNAs. Many studies have identified factors participating in mRNA splicing, bulk mRNA storage, and translational recruitment in mammalian oocytes, but the roles of potentially hundreds of expressed factors, how they regulate cohorts of thousands of mRNAs, and to what extent their functions are conserved across species has not been determined. We performed an extensive in silico cross-species analysis of features associated with mRNAs of different stability classes during oocyte maturation (stable, moderately degraded, and highly degraded) for five mammalian species. Using publicly available RNA sequencing data for germinal vesicle (GV) and MII oocyte transcriptomes, we determined that 3'-UTR length and synonymous codon usage are positively associated with stability, while greater GC content is negatively associated with stability. By applying machine learning and feature selection strategies, we identified RBPs and miRNAs that are predictive of mRNA stability, including some across multiple species and others more species-restricted. The results provide new insight into the mechanisms regulating maternal mRNA stabilization or degradation.NEW & NOTEWORTHY Conservation across species of mRNA features regulating maternal mRNA stability during mammalian oocyte maturation was analyzed. 3'-Untranslated region length and synonymous codon usage are positively associated with stability, while GC content is negatively associated. Just three RNA binding protein motifs were predicted to regulate mRNA stability across all five species examined, but associated pathways and functions are shared, indicating oocytes of different species arrive at comparable physiological destinations via different routes.

eIF4E1b is a non-canonical eIF4E protecting maternal dormant mRNAs

Maternal mRNAs are essential for protein synthesis during oogenesis and early embryogenesis. To adapt translation to specific needs during development, maternal mRNAs are translationally repressed by shortening the polyA tails. While mRNA deadenylation is associated with decapping and degradation in somatic cells, maternal mRNAs with short polyA tails are stable. Here we report that the germline-specific eIF4E paralog, eIF4E1b, is essential for zebrafish oogenesis. eIF4E1b localizes to P-bodies in zebrafish embryos and binds to mRNAs with reported short or no polyA tails, including histone mRNAs. Loss of eIF4E1b results in reduced histone mRNA levels in early gonads, consistent with a role in mRNA storage. Using mouse and human eIF4E1Bs (in vitro) and zebrafish eIF4E1b (in vivo), we show that unlike canonical eIF4Es, eIF4E1b does not interact with eIF4G to initiate translation. Instead, eIF4E1b interacts with the translational repressor eIF4ENIF1, which is required for eIF4E1b localization to P-bodies. Our study is consistent with an important role of eIF4E1b in regulating mRNA dormancy and provides new insights into fundamental post-transcriptional regulatory principles governing early vertebrate development.

Eif4enif1 haploinsufficiency disrupts oocyte mitochondrial dynamics and leads to subfertility

Infertility affects couples worldwide. Premature ovarian insufficiency (POI) refers to loss of ovarian function before 40 years of age and is a contributing factor to infertility. Several case studies have reported dominant-inherited POI symptoms in families with heterozygous EIF4ENIF1 (4E-T) mutations. However, the effects of EIF4ENIF1 haploinsufficiency have rarely been studied in animal models to reveal the underlying molecular changes related to infertility. Here, we demonstrate that Eif4enif1 haploinsufficiency causes mouse subfertility, impairs oocyte maturation and partially arrests early embryonic development. Using dual-omic sequencing, we observed that Eif4enif1 haploinsufficiency significantly altered both transcriptome and translatome in mouse oocytes, by which we further revealed oocyte mitochondrial hyperfusion and mitochondria-associated ribonucleoprotein domain distribution alteration in Eif4enif1-deficient oocytes. This study provides new insights into the molecular mechanisms underlying clinical fertility failure and new avenues to pursue new therapeutic targets to address infertility.