Cytoplasmic polyadenylation in mammalian oocyte maturation

Granulosa cell transcription is similarly impacted by superovulation and aging and predicts early embryonic trajectories

In vitro fertilization efficiency is limited in part because a fraction of retrieved oocytes fails to fertilize. Accurately evaluating their quality could significantly improve in vitro fertilization efficiency, which would require better understanding how their maturation may be disrupted. Here, we quantitatively investigate the interplay between superovulation and aging in mouse oocytes and their paired granulosa cells using a newly adapted experimental methodology. We test the hypothesis that superovulation disrupts oocyte maturation, revealing the key intercellular communication pathways dysregulated at the transcriptional level by forced hormonal stimulation. We further demonstrate that granulosa cell transcriptional markers can prospectively predict an associated oocyte's early developmental potential. By using naturally ovulated old mice as a non-stimulated reference, we show that aging and superovulation dysregulate similar genes and interact with each other. By comparing mice and human transcriptional responses of granulosa cells, we find that age-related dysregulation of hormonal responses and cell cycle pathways are shared, though substantial divergence exists in other pathways.

NAT10-mediated mRNA N4-acetylation is essential for the translational regulation during oocyte meiotic maturation in mice

The precise translational regulation of maternal messenger RNAs (mRNAs) drives mammalian oocyte maturation. However, the function and mechanism of posttranscriptional chemical modifications, especially the newly identified N4-acetylcytidine (ac4C) modification catalyzed by N-acetyltransferase 10 (NAT10), are unknown. In this study, we developed a low-input ac4C sequencing technology, ac4C LACE-seq, and mapped 8241 ac4C peaks at the whole-transcriptome level using 50 mouse oocytes at the germinal vesicle stage. Oocyte-specific Nat10 knockout wiped out ac4C signals in oocytes and caused severe defects in meiotic maturation and female infertility. Mechanically, Nat10 deletion led to a failure of ac4C deposition on mRNAs encoding key maternal factors, which regulate transcriptome stability and maternal-to-zygotic transition. Nat10-deleted oocytes showed decreased mRNA translation efficiency due to the direct inhibition of ac4C sites on specific transcripts during meiotic maturation. In summary, we developed a low-input, high-sensitivity mRNA ac4C profiling approach and highlighted the important physiological function of ac4C in the precise regulation of oocyte meiotic maturation by enhancing translation efficiency.

Dynamic R-loops at centromeres ensure chromosome alignment during oocyte meiotic divisions in mice

R-loops play various roles in many physiological processes, however, their role in meiotic division remains largely unknown. Here we show that R-loops and their regulator RNase H1 are present at centromeres during oocyte meiotic divisions. Proper centromeric R-loops are essential to ensure chromosome alignment in oocytes during metaphase I (MI). Remarkably, both Rnaseh1 knockout and overexpression in oocytes lead to severe spindle assembly defects and chromosome misalignment due to dysregulation of R-loops at centromeres. Furthermore, we find that replication protein A (RPA) is recruited to centromeric R-loops, facilitating the deposition of ataxia telangiectasia-mutated and Rad3-related (ATR) kinase at centromeres by interacting with the ATR-interaction protein (ATRIP). The ATR kinase deposition triggers the activity of CHK1, stimulating the phosphorylation of Aurora B to finally promote proper spindle assembly and chromosome alignment at the equatorial plate. Most importantly, the application of ATR, CHK1, and Aurora B inhibitors could efficiently rescue the defects in spindle assembly and chromosome alignment due to RNase H1 deficiency in oocytes. Overall, our findings uncover a critical role of R-loops during mouse oocyte meiotic divisions, suggesting that dysregulation of R-loops may be associated with female infertility. Additionally, ATR, CHK1, and Aurora B inhibitors may potentially be used to treat some infertile patients.

MARTRE family proteins negatively regulate CCR4-NOT activity to protect poly(A) tail length and promote translation of maternal mRNA

The mammalian early embryo development requires translation of maternal mRNA inherited from the oocyte. While poly(A) tail length influences mRNA translation efficiency during the oocyte-to-embryo transition (OET), molecular mechanisms regulating maternal RNA poly(A) tail length are not fully understood. In this study, we identified MARTRE, a previously uncharacterized protein family (MARTRE1-MARTRE6), as regulators expressed during mouse OET that modulate poly(A) tail length. MARTRE inhibits deadenylation through the direct interaction with the deadenylase CCR4-NOT, and ectopic expression of Martre stabilized mRNA by attenuating poly(A) tail shortening. Deletion of the Martre gene locus results in shortened poly(A) tails and decreased translation efficiency of actively translated mRNAs in mouse zygotes, but does not affect maternal mRNA decay. MARTRE proteins thus fine-tune maternal mRNA translation by negatively regulating the deadenylating activity of CCR4-NOT. Moreover, Martre knockout embryos show delayed 2-cell stage progression and compromised preimplantation development. Together, our findings highlight protection of long poly(A) tails from active deadenylation as an important mechanism to coordinate translation of maternal mRNA.

VPS34 Governs Oocyte Developmental Competence by Regulating Mito/Autophagy: A Novel Insight into the Significance of RAB7 Activity and Its Subcellular Location

Asynchronous nuclear and cytoplasmic maturation in human oocytes is believed to cause morphological anomalies after controlled ovarian hyperstimulation. Vacuolar protein sorting 34 (VPS34) is renowned for its pivotal role in regulating autophagy and endocytic trafficking. To investigate its impact on oocyte development, oocyte-specific knockout mice (ZcKO) are generated, and these mice are completely found infertile, with embryonic development halted at 2- to 4-cell stage. This infertility is related with a disruption on autophagic/mitophagic flux in ZcKO oocytes, leading to subsequent failure of zygotic genome activation (ZGA) in derived 2-cell embryos. The findings further elucidated the regulation of VPS34 on the activity and subcellular translocation of RAS-related GTP-binding protein 7 (RAB7), which is critical not only for the maturation of late endosomes and lysosomes, but also for initiating mitophagy via retrograde trafficking. VPS34 binds directly with RAB7 and facilitates its activity conversion through TBC1 domain family member 5 (TBC1D5). Consistent with the cytoplasmic vacuolation observed in ZcKO oocytes, defects in multiple vesicle trafficking systems are also identified in vacuolated human oocytes. Furthermore, activating VPS34 with corynoxin B (CB) treatment improved oocyte quality in aged mice. Hence, VPS34 activation may represent a novel approach to enhance oocyte quality in human artificial reproduction.

Deoxynivalenol exposure disturbs the cytoplasmic maturation in porcine oocytes

Deoxynivalenol (DON) is a secondary metabolite of Fusarium fungi and belonged to trichothecenes, and it widely presents in various food commodities. Previous studies have highlighted its potent toxicity, adversely affecting the growth, development, and reproductive in both humans and animals. However, the potential impact of DON on porcine oocyte organelles remains elusive. In present study, we delved into the toxic effects of DON on mitochondria, endoplasmic reticulum, Golgi during the porcine oocyte maturation. Our findings revealed that DON exposure significantly impeded granulosa cell diffusion and the expulsion of the first polar body. Additionally, mitochondrial fluorescence intensity and membrane potential underwent notable alterations under DON exposure. Notably, lysosomal fluorescence intensity decreased significantly, suggesting protein degradation and potential autophagy, which was further corroborated by the enhanced fluorescence intensity of LC3. Furthermore, endoplasmic reticulum fluorescence intensity declined, and DON exposure elevated endoplasmic reticulum stress levels, evident from the upregulated expression of GRP78. Concurrently, we observed disruption in the fusiform cortex distribution of the Golgi apparatus, characterized by reduced Golgi apparatus fluorescence intensity and GM130 expression. Collectively, our results indicate that DON exposure profoundly affects the fundamental functions of porcine oocyte organelles during meiosis and maturation.

Decoding molecular features of bovine oocyte fate during antral follicle growth via single-cell multi-omics analysis†

Antral follicle size is a useful predictive marker of the competency of enclosed oocytes for yielding an embryo following in vitro maturation and fertilization. However, the molecular mechanisms underpinning oocyte developmental potential during bovine antral follicle growth are still unclear. Here, we used a modified single-cell multi-omics approach to analyze the transcriptome, DNA methylome, and chromatin accessibility in parallel for oocytes and cumulus cells collected from bovine antral follicles of different sizes. Transcriptome profiling identified three types of oocytes (small, medium, and large) that underwent different developmental trajectories, with large oocytes exhibiting the largest average follicle size and characteristics resembling metaphase-II oocytes. Differential expression analysis and real-time polymerase chain reaction assay showed that most replication-dependent histone genes were highly expressed in large oocytes. The joint analysis of multi-omics data revealed that the transcription of 20 differentially expressed genes in large oocytes was associated with both DNA methylation and chromatin accessibility. In addition, oocyte-cumulus interaction analysis showed that inflammation, DNA damage, and p53 signaling pathways were active in small oocytes, which had the smallest average follicle sizes. We further confirmed that p53 pathway inhibition in the in vitro maturation experiments using oocytes obtained from small antral follicles could improve the quality of oocytes and increased the blastocyte rate after in vitro fertilization and culture. Our work provides new insights into the intricate orchestration of bovine oocyte fate determination during antral folliculogenesis, which is instrumental for optimizing in vitro maturation techniques to optimize oocyte quality.

Beyond simple tails: poly(A) tail-mediated RNA epigenetic regulation

The poly(A) tail is an essential structural component of mRNA required for the latter's stability and translation. Recent technologies have enabled transcriptome-wide profiling of the length and composition of poly(A) tails, shedding light on their overlooked regulatory capacities. Notably, poly(A) tails contain not only adenine but also uracil, cytosine, and guanine residues. These findings strongly suggest that poly(A) tails could encode a wealth of regulatory information, similar to known reversible RNA chemical modifications. This review aims to succinctly summarize our current knowledge on the composition, dynamics, and regulatory functions of RNA poly(A) tails. Given their capacity to carry rich regulatory information beyond the genetic code, we propose the concept of 'poly(A) tail epigenetic information' as a new layer of RNA epigenetic regulation.

HT-2 toxin impairs porcine oocyte in vitro maturation through disruption of endomembrane system

HT-2 toxin is a type of mycotoxin which is shown to affect gastric and intestinal lesions, hematopoietic and immunosuppressive effects, anorexia, lethargy, nausea. Recently, emerging evidences indicate that HT-2 also disturbs the reproductive system. In this study, we investigated the impact of HT-2 toxin exposure on the organelles of porcine oocytes. Our results found that the abnormal distribution of endoplasmic reticulum increased after HT-2 treatment, with the perturbation of ribosome protein RPS3 and GRP78 expression; Golgi apparatus showed diffused localization pattern and GM130 localization was also impaired, thereby affecting the Rab10-based vesicular transport; Due to the impairment of ribosomes, ER, and Golgi apparatus, the protein supply to lysosomes was hindered, resulting in lysosomal damage, which further disrupted the LC3-based autophagy. Moreover, the results indicated that the function and distribution of mitochondria were also affected by HT-2 toxin, showing with fragments of mitochondria, decreased TMRE and ATP level. Taken together, our study suggested that HT-2 toxin exposure induces damage to the organelles for endomembrane system, which further inhibited the meiotic maturation of porcine oocytes.

Maternal mRNA deadenylation is defective in in vitro matured mouse and human oocytes

Oocyte in vitro maturation is a technique in assisted reproductive technology. Thousands of genes show abnormally high expression in in vitro maturated metaphase II (MII) oocytes compared to those matured in vivo in bovines, mice, and humans. The mechanisms underlying this phenomenon are poorly understood. Here, we use poly(A) inclusive RNA isoform sequencing (PAIso-seq) for profiling the transcriptome-wide poly(A) tails in both in vivo and in vitro matured mouse and human oocytes. Our results demonstrate that the observed increase in maternal mRNA abundance is caused by impaired deadenylation in in vitro MII oocytes. Moreover, the cytoplasmic polyadenylation of dormant Btg4 and Cnot7 mRNAs, which encode key components of deadenylation machinery, is impaired in in vitro MII oocytes, contributing to reduced translation of these deadenylase machinery components and subsequently impaired global maternal mRNA deadenylation. Our findings highlight impaired maternal mRNA deadenylation as a distinct molecular defect in in vitro MII oocytes.

CPEB3 Maintains Developmental Competence of the Oocyte

Mammalian oocyte development depends on the temporally controlled translation of maternal transcripts, particularly in the coordination of meiotic and early embryonic development when transcription has ceased. The translation of mRNA is regulated by various RNA-binding proteins. We show that the absence of cytoplasmic polyadenylation element-binding protein 3 (CPEB3) negatively affects female reproductive fitness. CPEB3-depleted oocytes undergo meiosis normally but experience early embryonic arrest due to a disrupted transcriptome, leading to aberrant protein expression and the subsequent failure of embryonic transcription initiation. We found that CPEB3 stabilizes a subset of mRNAs with a significantly longer 3'UTR that is enriched in its distal region with cytoplasmic polyadenylation elements. Overall, our results suggest that CPEB3 is an important maternal factor that regulates the stability and translation of a subclass of mRNAs that are essential for the initiation of embryonic transcription and thus for embryonic development.

Revealing the hidden RBP-RNA interactions with RNA modification enzyme-based strategies

RNA-binding proteins (RBPs) are powerful and versatile regulators in living creatures, playing fundamental roles in organismal development, metabolism, and various diseases by the regulation of gene expression at multiple levels. The requirements of deep research on RBP function have promoted the rapid development of RBP-RNA interplay detection methods. Recently, the detection method of fusing RNA modification enzymes (RME) with RBP of interest has become a hot topic. Here, we reviewed RNA modification enzymes in adenosine deaminases that act on RNA (ADAR), terminal nucleotidyl transferase (TENT), and activation-induced cytosine deaminase/ApoB mRNA editing enzyme catalytic polypeptide-like (AID/APOBEC) protein family, regarding the biological function, biochemical activity, and substrate specificity originated from enzyme selves, their domains and partner proteins. In addition, we discussed the RME activity screening system, and the RME mutations with engineered enzyme activity. Furthermore, we provided a systematic overview of the basic principles, advantages, disadvantages, and applications of the RME-based and cross-linking and immunopurification (CLIP)-based RBP target profiling strategies, including targets of RNA-binding proteins identified by editing (TRIBE), RNA tagging, surveying targets by APOBEC-mediated profiling (STAMP), CLIP-seq, and their derivative technology. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Recognition RNA Processing > RNA Editing and Modification.

The molecular mechanisms underpinning maternal mRNA dormancy

A large number of mRNAs of maternal origin are produced during oogenesis and deposited in the oocyte. Since transcription stops at the onset of meiosis during oogenesis and does not resume until later in embryogenesis, maternal mRNAs are the only templates for protein synthesis during this period. To ensure that a protein is made in the right place at the right time, the translation of maternal mRNAs must be activated at a specific stage of development. Here we summarize our current understanding of the sophisticated mechanisms that contribute to the temporal repression of maternal mRNAs, termed maternal mRNA dormancy. We discuss mechanisms at the level of the RNA itself, such as the regulation of polyadenine tail length and RNA modifications, as well as at the level of RNA-binding proteins, which often block the assembly of translation initiation complexes at the 5' end of an mRNA or recruit mRNAs to specific subcellular compartments. We also review microRNAs and other mechanisms that contribute to repressing translation, such as ribosome dormancy. Importantly, the mechanisms responsible for mRNA dormancy during the oocyte-to-embryo transition are also relevant to cellular quiescence in other biological contexts.

Control of poly(A)-tail length and translation in vertebrate oocytes and early embryos

During oocyte maturation and early embryogenesis, changes in mRNA poly(A)-tail lengths strongly influence translation, but how these tail-length changes are orchestrated has been unclear. Here, we performed tail-length and translational profiling of mRNA reporter libraries (each with millions of 3' UTR sequence variants) in frog oocytes and embryos and in fish embryos. Contrasting to previously proposed cytoplasmic polyadenylation elements (CPEs), we found that a shorter element, UUUUA, together with the polyadenylation signal (PAS), specify cytoplasmic polyadenylation, and we identified contextual features that modulate the activity of both elements. In maturing oocytes, this tail lengthening occurs against a backdrop of global deadenylation and the action of C-rich elements that specify tail-length-independent translational repression. In embryos, cytoplasmic polyadenylation becomes more permissive, and additional elements specify waves of stage-specific deadenylation. Together, these findings largely explain the complex tapestry of tail-length changes observed in early frog and fish development, with strong evidence of conservation in both mice and humans.

Poly(A) tale: From A to A; RNA polyadenylation in prokaryotes and eukaryotes

Most eukaryotic mRNAs and different non-coding RNAs undergo a form of 3' end processing known as polyadenylation. Polyadenylation machinery is present in almost all organisms except few species. In bacteria, the machinery has evolved from PNPase, which adds heteropolymeric tails, to a poly(A)-specific polymerase. Differently, a complex machinery for accurate polyadenylation and several non-canonical poly(A) polymerases are developed in eukaryotes. The role of poly(A) tail has also evolved from serving as a degradative signal to a stabilizing modification that also regulates translation. In this review, we discuss poly(A) tail emergence in prokaryotes and its development into a stable, yet dynamic feature at the 3' end of mRNAs in eukaryotes. We also describe how appearance of novel poly(A) polymerases gives cells flexibility to shape poly(A) tail. We explain how poly(A) tail dynamics help regulate cognate RNA metabolism in a context-dependent manner, such as during oocyte maturation. Finally, we describe specific mRNAs in metazoans that bear stem-loops instead of poly(A) tails. We conclude with how recent discoveries about poly(A) tail can be applied to mRNA technology. This article is categorized under: RNA Evolution and Genomics > RNA and Ribonucleoprotein Evolution RNA Processing > 3' End Processing RNA Turnover and Surveillance > Regulation of RNA Stability.

An extended wave of global mRNA deadenylation sets up a switch in translation regulation across the mammalian oocyte-to-embryo transition

Without new transcription, gene expression across the oocyte-to-embryo transition (OET) relies instead on regulation of mRNA poly(A) tails to control translation. However, how tail dynamics shape translation across the OET in mammals remains unclear. We perform long-read RNA sequencing to uncover poly(A) tail lengths across the mouse OET and, incorporating published ribosome profiling data, provide an integrated, transcriptome-wide analysis of poly(A) tails and translation across the entire transition. We uncover an extended wave of global deadenylation during fertilization in which short-tailed, oocyte-deposited mRNAs are translationally activated without polyadenylation through resistance to deadenylation. Subsequently, in the embryo, mRNAs are readenylated and translated in a surge of global polyadenylation. We further identify regulation of poly(A) tail length at the isoform level and stage-specific enrichment of mRNA sequence motifs among regulated transcripts. These data provide insight into the stage-specific mechanisms of poly(A) tail regulation that orchestrate gene expression from oocyte to embryo in mammals.

The translational oscillation in oocyte and early embryo development

Translation is critical for development as transcription in the oocyte and early embryo is silenced. To illustrate the translational changes during meiosis and consecutive two mitoses of the oocyte and early embryo, we performed a genome-wide translatome analysis. Acquired data showed significant and uniform activation of key translational initiation and elongation axes specific to M-phases. Although global protein synthesis decreases in M-phases, translation initiation and elongation activity increases in a uniformly fluctuating manner, leading to qualitative changes in translation regulation via the mTOR1/4F/eEF2 axis. Overall, we have uncovered a highly dynamic and oscillatory pattern of translational reprogramming that contributes to the translational regulation of specific mRNAs with different modes of polysomal occupancy/translation that are important for oocyte and embryo developmental competence. Our results provide new insights into the regulation of gene expression during oocyte meiosis as well as the first two embryonic mitoses and show how temporal translation can be optimized. This study is the first step towards a comprehensive analysis of the molecular mechanisms that not only control translation during early development, but also regulate translation-related networks employed in the oocyte-to-embryo transition and embryonic genome activation.

Identification of nonfunctional PABPC1L causing oocyte maturation abnormalities and early embryonic arrest in female primary infertility

Oocyte maturation arrest, fertilization failure, and early embryonic arrest are important causes of female infertility, whereas the genetic events that contribute to these processes are largely unknown. Loss-of-function of PABPC1L in mice has been suggested to cause female infertility involved in the absence of mature oocytes or embryos in vivo or in vitro. However, the role of PABPC1L in human female reproduction remains largely elusive. In this study, we identified a homozygous missense mutation (c.536G>A, p.R179Q) and a compound heterozygous mutation (c.793C>T, p.R265W; c.1201C>T, p.Q401*) in PABPC1L in two unrelated infertile females characterized by recurrent oocyte maturation abnormalities and early embryonic arrest. These variants resulted in nonfunctional PABPC1L protein and were associated with impaired chromatin configuration and transcriptional silencing in GV oocytes. Moreover, the binding capacity of mutant PABPC1L to mRNAs related to oocyte maturation and early embryonic development was decreased significantly. Our findings revealed novel PABPC1L mutations causing oocyte maturation abnormalities and early embryonic arrest, confirming the essential role of PABPC1L in human female fertility.

The molecular regulatory mechanisms of meiotic arrest and resumption in Oocyte development and maturation

In human female primordial germ cells, the transition from mitosis to meiosis begins from the fetal stage. In germ cells, meiosis is arrested at the diplotene stage of prophase in meiosis I (MI) after synapsis and recombination of homologous chromosomes, which cannot be segregated. Within the follicle, the maintenance of oocyte meiotic arrest is primarily attributed to high cytoplasmic concentrations of cyclic adenosine monophosphate (cAMP). Depending on the specific species, oocytes can remain arrested for extended periods of time, ranging from months to even years. During estrus phase in animals or the menstrual cycle in humans, the resumption of meiosis occurs in certain oocytes due to a surge of luteinizing hormone (LH) levels. Any factor interfering with this process may lead to impaired oocyte maturation, which in turn affects female reproductive function. Nevertheless, the precise molecular mechanisms underlying this phenomenon has not been systematically summarized yet. To provide a comprehensive understanding of the recently uncovered regulatory network involved in oocyte development and maturation, the progress of the cellular and molecular mechanisms of oocyte nuclear maturation including meiosis arrest and meiosis resumption is summarized. Additionally, the advancements in understanding the molecular cytoplasmic events occurring in oocytes, such as maternal mRNA degradation, posttranslational regulation, and organelle distribution associated with the quality of oocyte maturation, are reviewed. Therefore, understanding the pathways regulating oocyte meiotic arrest and resumption will provide detailed insight into female reproductive system and provide a theoretical basis for further research and potential approaches for novel disease treatments.

Single-cell multi-omics profiling reveals key regulatory mechanisms that poise germinal vesicle oocytes for maturation in pigs

The molecular mechanisms controlling the transition from meiotic arrest to meiotic resumption in mammalian oocytes have not been fully elucidated. Single-cell omics technology provides a new opportunity to decipher the early molecular events of oocyte growth in mammals. Here we focused on analyzing oocytes that were collected from antral follicles in different diameters of porcine pubertal ovaries, and used single-cell M&T-seq technology to analyze the nuclear DNA methylome and cytoplasmic transcriptome in parallel for 62 oocytes. 10× Genomics single-cell transcriptomic analyses were also performed to explore the bi-directional cell-cell communications within antral follicles. A new pipeline, methyConcerto, was developed to specifically and comprehensively characterize the methylation profile and allele-specific methylation events for a single-cell methylome. We characterized the gene expressions and DNA methylations of individual oocyte in porcine antral follicle, and both active and inactive gene's bodies displayed high methylation levels, thereby enabled defining two distinct types of oocytes. Although the methylation levels of Type II were higher than that of Type I, Type II contained nearly two times more of cytoplasmic transcripts than Type I. Moreover, the imprinting methylation patterns of Type II were more dramatically divergent than Type I, and the gene expressions and DNA methylations of Type II were more similar with that of MII oocytes. The crosstalk between granulosa cells and Type II oocytes was active, and these observations revealed that Type II was more poised for maturation. We further confirmed Insulin Receptor Substrate-1 in insulin signaling pathway is a key regulator on maturation by in vitro maturation experiments. Our study provides new insights into the regulatory mechanisms between meiotic arrest and meiotic resumption in mammalian oocytes. We also provide a new analytical package for future single-cell methylomics study.

Maternal NAT10 orchestrates oocyte meiotic cell-cycle progression and maturation in mice

In mammals, the production of mature oocytes necessitates rigorous regulation of the discontinuous meiotic cell-cycle progression at both the transcriptional and post-transcriptional levels. However, the factors underlying this sophisticated but explicit process remain largely unclear. Here we characterize the function of N-acetyltransferase 10 (Nat10), a writer for N4-acetylcytidine (ac4C) on RNA molecules, in mouse oocyte development. We provide genetic evidence that Nat10 is essential for oocyte meiotic prophase I progression, oocyte growth and maturation by sculpting the maternal transcriptome through timely degradation of poly(A) tail mRNAs. This is achieved through the ac4C deposition on the key CCR4-NOT complex transcripts. Importantly, we devise a method for examining the poly(A) tail length (PAT), termed Hairpin Adaptor-poly(A) tail length (HA-PAT), which outperforms conventional methods in terms of cost, sensitivity, and efficiency. In summary, these findings provide genetic evidence that unveils the indispensable role of maternal Nat10 in oocyte development.

Advances in Oocyte Maturation In Vivo and In Vitro in Mammals

The quality and maturation of an oocyte not only play decisive roles in fertilization and embryo success, but also have long-term impacts on the later growth and development of the fetus. Female fertility declines with age, reflecting a decline in oocyte quantity. However, the meiosis of oocytes involves a complex and orderly regulatory process whose mechanisms have not yet been fully elucidated. This review therefore mainly focuses on the regulation mechanism of oocyte maturation, including folliculogenesis, oogenesis, and the interactions between granulosa cells and oocytes, plus in vitro technology and nuclear/cytoplasm maturation in oocytes. Additionally, we have reviewed advances made in the single-cell mRNA sequencing technology related to oocyte maturation in order to improve our understanding of the mechanism of oocyte maturation and to provide a theoretical basis for subsequent research into oocyte maturation.

Regulation of adult stem cell quiescence and its functions in the maintenance of tissue integrity

Adult stem cells are important for mammalian tissues, where they act as a cell reserve that supports normal tissue turnover and can mount a regenerative response following acute injuries. Quiescent stem cells are well established in certain tissues, such as skeletal muscle, brain, and bone marrow. The quiescent state is actively controlled and is essential for long-term maintenance of stem cell pools. In this Review, we discuss the importance of maintaining a functional pool of quiescent adult stem cells, including haematopoietic stem cells, skeletal muscle stem cells, neural stem cells, hair follicle stem cells, and mesenchymal stem cells such as fibro-adipogenic progenitors, to ensure tissue maintenance and repair. We discuss the molecular mechanisms that regulate the entry into, maintenance of, and exit from the quiescent state in mice. Recent studies revealed that quiescent stem cells have a discordance between RNA and protein levels, indicating the importance of post-transcriptional mechanisms, such as alternative polyadenylation, alternative splicing, and translation repression, in the control of stem cell quiescence. Understanding how these mechanisms guide stem cell function during homeostasis and regeneration has important implications for regenerative medicine.

Preimplantation embryo gene expression: 56 years of discovery, and counting

The biology of preimplantation embryo gene expression began 56 years ago with studies of the effects of protein synthesis inhibition and discovery of changes in embryo metabolism and related enzyme activities. The field accelerated rapidly with the emergence of embryo culture systems and progressively evolving methodologies that have allowed early questions to be re-addressed in new ways and in greater detail, leading to deeper understanding and progressively more targeted studies to discover ever more fine details. The advent of technologies for assisted reproduction, preimplantation genetic testing, stem cell manipulations, artificial gametes, and genetic manipulation, particularly in experimental animal models and livestock species, has further elevated the desire to understand preimplantation development in greater detail. The questions that drove enquiry from the earliest years of the field remain drivers of enquiry today. Our understanding of the crucial roles of oocyte-expressed RNA and proteins in early embryos, temporal patterns of embryonic gene expression, and mechanisms controlling embryonic gene expression has increased exponentially over the past five and a half decades as new analytical methods emerged. This review combines early and recent discoveries on gene regulation and expression in mature oocytes and preimplantation stage embryos to provide a comprehensive understanding of preimplantation embryo biology and to anticipate exciting future advances that will build upon and extend what has been discovered so far.

Remodeling of maternal mRNA through poly(A) tail orchestrates human oocyte-to-embryo transition

Poly(A)-tail-mediated post-transcriptional regulation of maternal mRNAs is vital in the oocyte-to-embryo transition (OET). Nothing is known about poly(A) tail dynamics during the human OET. Here, we show that poly(A) tail length and internal non-A residues are highly dynamic during the human OET, using poly(A)-inclusive RNA isoform sequencing (PAIso-seq). Unexpectedly, maternal mRNAs undergo global remodeling: after deadenylation or partial degradation into 3'-UTRs, they are re-polyadenylated to produce polyadenylated degradation intermediates, coinciding with massive incorporation of non-A residues, particularly internal long consecutive U residues, into the newly synthesized poly(A) tails. Moreover, TUT4 and TUT7 contribute to the incorporation of these U residues, BTG4-mediated deadenylation produces substrates for maternal mRNA re-polyadenylation, and TENT4A and TENT4B incorporate internal G residues. The maternal mRNA remodeling is further confirmed using PAIso-seq2. Importantly, maternal mRNA remodeling is essential for the first cleavage of human embryos. Together, these findings broaden our understanding of the post-transcriptional regulation of maternal mRNAs during the human OET.

Application of Single-Cell RNA Sequencing in Ovarian Development

The ovary is a female reproductive organ that plays a key role in fertility and the maintenance of endocrine homeostasis, which is of great importance to women's health. It is characterized by a high heterogeneity, with different cellular subpopulations primarily containing oocytes, granulosa cells, stromal cells, endothelial cells, vascular smooth muscle cells, and diverse immune cell types. Each has unique and important functions. From the fetal period to old age, the ovary experiences continuous structural and functional changes, with the gene expression of each cell type undergoing dramatic changes. In addition, ovarian development strongly relies on the communication between germ and somatic cells. Compared to traditional bulk RNA sequencing techniques, the single-cell RNA sequencing (scRNA-seq) approach has substantial advantages in analyzing individual cells within an ever-changing and complicated tissue, classifying them into cell types, characterizing single cells, delineating the cellular developmental trajectory, and studying cell-to-cell interactions. In this review, we present single-cell transcriptome mapping of the ovary, summarize the characteristics of the important constituent cells of the ovary and the critical cellular developmental processes, and describe key signaling pathways for cell-to-cell communication in the ovary, as revealed by scRNA-seq. This review will undoubtedly improve our understanding of the characteristics of ovarian cells and development, thus enabling the identification of novel therapeutic targets for ovarian-related diseases.

Characterization of MicroRNAs Associated with Reproduction in the Brown Planthopper, Nilaparvata lugens

Insects have a robust capacity to produce offspring for propagation, and the reproductive events of female insects have been achieved at the molecular and physiological levels via regulatory gene pathways. However, the roles of MicroRNAs (miRNAs) in the reproductive development of the brown planthopper (BPH), Nilaparvata lugens, remain largely unexplored. To understand the roles of miRNAs in reproductive development, miRNAs were identified by Solexa sequencing in short-winged (SW) female adults of BPH. Small RNA libraries derived from three developmental phases (1 day, 3 days, and 5 days after emergence) were constructed and sequenced. We identified 905 miRNAs, including 263 known and 642 novel miRNAs. Among them, a total of 43 miRNAs were differentially expressed in the three developmental phases, and 14,568 putative targets for 43 differentially expressed miRNAs (DEMs) were predicted by TargetScan and miRanda. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the predicted miRNA targets illustrated the putative roles for these DEMs in reproduction. The progress events were annotated, including oogenesis, lipid biosynthetic process, and related pathways such as apoptosis, ABC transporters, and amino acid metabolism. Four highly abundant DEMs (miR-9a-5p, miR-34-5p, miR-275-3p, and miR-317-3p) were further screened, and miR-34-5p was confirmed to be involved in the regulation of reproduction. Overexpression of miR-34-5p via injecting its mimics reduced fecundity and decreased Vg expression. Moreover, target genes prediction for miR-34-5p showed they might be involved in 20E signaling cascades, apoptosis, and gonadal development, including hormone receptor 4 (HR4), caspase-1 (Cp-1), and spermatogenesis-associated protein 20 (SPATA20). These findings provide a valuable resource for future studies on the role of miRNAs in BPH reproductive development.

Single-cell quantitative proteomic analysis of human oocyte maturation revealed high heterogeneity in in vitro matured oocytes

Oocyte maturation is pertinent to the success of in vitro maturation (IVM), which is used to overcome female infertility, and produced over 5000 live births worldwide. However, the quality of human IVM oocytes has not been investigated at single-cell proteome level. Here, we quantified 2094 proteins in human oocytes during in vitro and in vivo maturation (IVO) by single-cell proteomic analysis and identified 176 differential proteins between IVO and germinal vesicle oocytes and 45 between IVM and IVO oocytes including maternal effect proteins, with potential contribution to the clinically observed decreased fertilization, implantation, and birth rates using human IVM oocytes. IVM and IVO oocytes showed separate clusters in principal component analysis, with higher inter-cell variability among IVM oocytes, and have little correlation between mRNA and protein changes during maturation. The patients with the most aberrantly expressed proteins in IVM oocytes had the lowest level of estradiol per mature follicle on trigger day. Our data provide a rich resource to evaluate effect of IVM on oocyte quality and study mechanism of oocyte maturation.

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Single-cell proteomic profiling of human oocytes matured in vitro and in vivo.

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Low correlation between protein and mRNA levels during human oocyte maturation.

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In vitro matured (IVM) oocytes exhibit higher heterogeneity at the proteome level.

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45 differentially expressed proteins between IVM and in vivo matured (IVO) oocytes.

Exposure of mouse oocytes to N,N-dimethylformamide impairs mitochondrial functions and reduces oocyte quality

N,N-dimethylformamide (DMF) is a widely-used solvent for the synthesis of synthetic fibers such as polyacrylonitrile fiber, and can also be used to make medicine. Although this organic solvent has multipurpose applications, its biological toxicity cannot be ignored and its impact on mammalian reproduction remains largely unexplored. Our study found that DMF exposure inhibited oocyte maturation and fertilization ability. Transcriptomic analysis indicated that DMF exposure changed the expression of genes and transposable elements in oocytes. Subcellular structure examination found that DMF exposure caused mitochondrial dysfunction, abnormal aggregation of mitochondria and decreased mitochondrial membrane potential in mouse oocytes. Its exposure also caused abnormal distribution of Golgi apparatus and endoplasmic reticulum which formed large number of clusters. In addition, oxidative stress occurs in oocytes exposed to DMF, which was manifested by an increase in the level of reactive oxygen species. We found that DMF exposure induced disordered spindle and chromosomes abnormality. Meanwhile, we examined various histone modification levels in oocytes exposed to DMF and found that DMF exposure reduced H3K9me3, H3K9ac, H3K27ac, and H4K16ac levels in mouse oocytes. Moreover, DMF-treated oocytes failed to form pronuclei after fusion with normal sperm. Collectively, DMF exposure caused mitochondrial damage, oxidative stress, spindle assembly and chromosome arrangement disorder, leading to oocyte maturation arrest and fertilization failure.

The interplay between translational efficiency, poly(A) tails, microRNAs, and neuronal activation

Neurons provide a rich setting for studying post-transcriptional control. Here, we investigate the landscape of translational control in neurons and search for mRNA features that explain differences in translational efficiency (TE), considering the interplay between TE, mRNA poly(A)-tail lengths, microRNAs, and neuronal activation. In neurons and brain tissues, TE correlates with tail length, and a few dozen mRNAs appear to undergo cytoplasmic polyadenylation upon light or chemical stimulation. However, the correlation between TE and tail length is modest, explaining <5% of TE variance, and even this modest relationship diminishes when accounting for other mRNA features. Thus, tail length appears to affect TE only minimally. Accordingly, miRNAs, which accelerate deadenylation of their mRNA targets, primarily influence target mRNA levels, with no detectable effect on either steady-state tail lengths or TE. Larger correlates with TE include codon composition and predicted mRNA folding energy. When combined in a model, the identified correlates explain 38%-45% of TE variance. These results provide a framework for considering the relative impact of factors that contribute to translational control in neurons. They indicate that when examined in bulk, translational control in neurons largely resembles that of other types of post-embryonic cells. Thus, detection of more specialized control might require analyses that can distinguish translation occurring in neuronal processes from that occurring in cell bodies.

Pervasive 3'-UTR Isoform Switches During Mouse Oocyte Maturation

Oocyte maturation is the foundation for developing healthy individuals of mammals. Upon germinal vesicle breakdown, oocyte meiosis resumes and the synthesis of new transcripts ceases. To quantitatively profile the transcriptomic dynamics after meiotic resumption throughout the oocyte maturation, we generated transcriptome sequencing data with individual mouse oocytes at three main developmental stages: germinal vesicle (GV), metaphase I (MI), and metaphase II (MII). When clustering the sequenced oocytes, results showed that isoform-level expression analysis outperformed gene-level analysis, indicating isoform expression provided extra information that was useful in distinguishing oocyte stages. Comparing transcriptomes of the oocytes at the GV stage and the MII stage, in addition to identification of differentially expressed genes (DEGs), we detected many differentially expressed transcripts (DETs), some of which came from genes that were not identified as DEGs. When breaking down the isoform-level changes into alternative RNA processing events, we found the main source of isoform composition changes was the alternative usage of polyadenylation sites. With detailed analysis focusing on the alternative usage of 3′-UTR isoforms, we identified, out of 3,810 tested genes, 512 (13.7%) exhibiting significant switches of 3′-UTR isoforms during the process of moues oocyte maturation. Altogether, our data and analyses suggest the importance of examining isoform abundance changes during oocyte maturation, and further investigation of the pervasive 3′-UTR isoform switches in the transition may deepen our understanding on the molecular mechanisms underlying mammalian early development.

Toxic effects of patulin on mouse oocytes and its possible mechanisms

Patulin is a secondary metabolite mainly secreted by fungi and is the most common mycotoxin found in apples and apple-based products. For the past few years, numerous studies suggested the wide distribution and toxicity of patulin. In this study, we investigated the toxic effect of patulin on mouse oocytes and its possible mechanisms. The results showed that patulin treatment did not affect meiotic resumption, but inhibited oocyte maturation as indicated by failure of first polar body extrusion. Further mechanistic study showed that patulin treatment disturbed normal spindle assembly, chromosome alignment and morphology. We also found increased oxidative stress by testing the level of ROS and decreased mitochondrial membrane potential, indicating mitochondria dysfunction. In summary, our results suggest that patulin treatment causes oocyte meiotic arrest by disturbing normal spindle assembly and chromosome alignment, which may be caused by dysfunctions of mitochondria.

The effects of aging on molecular modulators of human embryo implantation

Advancing age has a negative impact on female fertility. As implantation rates decline during the normal maternal life course, age-related, embryonic factors are altered and our inability to monitor these factors in an unbiased genome-wide manner in vivo has severely limited our understanding of early human embryo development and implantation. Our high-throughput methodology uses trophectoderm samples representing the full spectrum of maternal reproductive ages with embryo implantation potential examined in relation to trophectoderm transcriptome dynamics and reproductive maternal age. Potential embryo-endometrial interactions were tested using trophectoderm sampled from young women, with the receptive uterine environment representing the most 'fertile' environment for successful embryo implantation. Potential roles for extracellular exosomes, embryonic metabolism and regulation of apoptosis were revealed. These biomarkers are consistent with embryo-endometrial crosstalk/developmental competency, serving as a mediator for successful implantation. Our data opens the door to developing a diagnostic test for predicting implantation success in women undergoing fertility treatment.

Podophyllotoxin Exposure Affects Organelle Distribution and Functions in Mouse Oocyte Meiosis

Podophyllotoxin (POD) is one of the most characterized lignans that is commonly found in podophyllum, and its preparations and derivatives are widely used in clinical treatment due to strong antitumor and antivirus activities. POD has been reported for its neurotoxicity, liver toxicity, and potential reproductive toxicity. In the present study, we investigated the effects of POD on the organelles of mouse oocytes during meiosis. Our results showed that exposure to POD significantly reduced the developmental competence of mouse oocytes. Further analysis revealed that the endoplasmic reticulum (ER) failed to accumulate to the spindle periphery, suggesting that POD exposure might affect protein synthesis during oocyte meiotic maturation. Similarly, abnormal Golgi apparatus distribution was found after POD exposure, which could be confirmed by the aberrant localization of Rab11a-related vesicles, indicating that POD induced vesicle-based protein transport disorder. We also found the aberrant accumulation of lysosomes in the cytoplasm of POD-exposed oocytes, which implied that POD might lead to aberrant protein degradation. Moreover, the perinuclear distribution of mitochondria was also significantly disturbed, indicating the mitochondrial dysfunction after POD exposure. In all, our study illustrated that exposure to POD might disrupt protein synthesis, transport, degradation, and ATP production by its effects on the distribution and functions of organelles during mouse oocyte meiotic maturation.

Loss of Arf Guanine Nucleotide Exchange Factor GBF1 Activity Disturbs Organelle Dynamics in Mouse Oocytes

GBF1 [Golgi brefeldin A (BFA) resistance factor 1] is a member of the guanine nucleotide exchange factors Arf family. GBF1 localizes at the cis-Golgi and endoplasmic reticulum (ER)-Golgi intermediate compartment where it participates in ER-Golgi traffic by assisting in the recruitment of the coat protein COPI. However, the roles of GBF1 in oocyte meiotic maturation are still unknown. In the present study, we investigated the regulatory functions of GBF1 in mouse oocyte organelle dynamics. In our results, GBF1 was stably expressed during oocyte maturation, and GBF1 localized at the spindle periphery during metaphase I. Inhibiting GBF1 activity led to aberrant accumulation of the Golgi apparatus around the spindle. This may be due to the effects of GBF1 on the localization of GM130, as GBF1 co-localized with GM130 and inhibiting GBF1 induced condensation of GM130. Moreover, the loss of GBF1 activity affected the ER distribution and induced ER stress, as shown by increased GRP78 expression. Mitochondrial localization and functions were affected, as the mitochondrial membrane potential was altered. Taken together, these results suggest that GBF1 has wide-ranging effects on the distribution and functions of Golgi apparatus, ER, and mitochondria as well as normal polar body formation in mouse oocytes.

Fumonisin B1 exposure adversely affects porcine oocyte maturation in vitro by inducing mitochondrial dysfunction and oxidative stress

Fumonisin B₁ (FB₁), as the most toxic fumonisin, is a common Fusarium mycotoxin contaminant of feed stuff and food, posing a potential health hazard to animals and humans. FB₁ has been reported to cause hepatotoxicity, neurotoxicity, nephrotoxicity, immunotoxicity and embryotoxicity; however, little information is available on whether FB₁ has toxic effects on mammalian oocytes. Herein, we adopted porcine oocytes as models to explore the effects and potential mechanisms of FB₁ on mammalian oocytes during in vitro maturation. Porcine cumulus oocyte complexes (COCs) were exposed to 0, 20, 30 and 40 μM FB₁ for 44 h during in vitro maturation, and the results reported that first polar body (PB1) extrusion was significantly inhibited when the FB₁ concentration reached 30 (P < 0.01) or 40 μM (P < 0.001). Further cell cycle analysis revealed that meiotic progression was disrupted, with a larger proportion of the 30 μM FB₁-treated oocytes being arrested at the germinal vesicle breakdown (GVBD) stage (P < 0.01). After being treated with 30 μM FB₁ for 28 h, the percentage of oocytes with aberrant spindle assembly was observably increased (P < 0.01), and the distribution of actin filaments on the plasma membrane was significantly reduced (P < 0.05). Furthermore, an observably higher rate of abnormal mitochondrial distribution (P < 0.05) and significantly decreased mitochondrial membrane potential (MMP) (P < 0.05) were observed in FB₁-exposed oocytes. In addition, ROS generation in FB₁-treated oocytes was rapidly increased (P < 0.05), while the transcriptional levels of antioxidant-related genes (CAT, SOD2 and GSH-Px) were sharply decreased compared with those in the control group. Additionally, the incidence of early apoptosis in FB₁-treated oocytes was also significantly increased (P < 0.05), suggesting that FB₁ exposure induced oxidative stress and further triggered apoptosis in porcine oocytes. Thus, these results suggested that FB₁ adversely affected oocyte maturation by disturbing cell cycle progression, destroying cytoskeletal dynamics and damaging mitochondrial function, which eventually induced oxidative stress and apoptosis in porcine oocytes.

Molecular characteristics of oocytes and somatic cells of follicles at different sizes that influence in vitro oocyte maturation and embryo production

During the last 10 to 15 yr, in vitro research to predict antral follicle growth and oocyte maturation has delivered interesting advances in the knowledge of processes regulating follicle growth and developmental competence of oocytes. This review discusses the contribution of cumulus and mural granulosa cells in the process of oocyte maturation and cumulus expansion in cumulus-oocyte complexes (COCs) from follicles of different sizes and shows that differences in gene expression in oocytes, granulosa, and theca cells of small and large follicles impact the success of in vitro blastocyst development. In addition, the molecular mechanisms by which COC metabolism and antioxidant defense provide oocyte competence are highlighted. Furthermore, new insights and perspectives on molecular and cellular regulation of in vitro oocyte maturation are emphasized.

The toxic effects and possible mechanisms of decabromodiphenyl ethane on mouse oocyte

Decabromodiphenyl ethane (DBDPE), a widely used new brominated flame retardant, is added into flammable materials to achieve fire retardation. As it is continuously detected in the environment, it has become an emerging environmental pollutant. However, the effects of DBDPE exposure on oocyte maturation and its underlying mechanisms remain unknown. This study found that DBDPE exposure inhibited the rate of germinal vesicle breakdown (GVBD), first polar body extrusion (PBE) and fertilization of mouse oocytes. After 14 h of exposure to DBDPE, metaphase II (MII) oocytes showed that the hardness of zona pellucida (ZP) markedly increased and that the spindle morphology was abnormal. Moreover, DBDPE exposure induced abnormal mitochondrial distribution, mitochondrial dysfunction, and ATP deficiency. Simultaneously, DBDPE exposure down-regulated the expression of antioxidant-related genes (Sod2, Gpx1) and increased the level of reactive oxygen species (ROS) in oocytes. The results of immunofluorescence and qRT-PCR revealed that autophagy occurred in DBDPE-treated oocytes with high expression of autophagy-related protein (LC3) and genes (Lc3, Beclin1). Meanwhile, DBDPE significantly up-regulated the protein (Bax) and mRNA (Bax, Caspase3) levels of pro-apoptosis genes. However, the protein and mRNA expression of anti-apoptosis genes Bcl-2 was dramatically down-regulated in DBDPE-exposed oocytes. Collectively, DBDPE exposure impaired mitochondrial function, causing oxidative damage, autophagy and apoptosis in oocytes.

Positive Feedback Stimulation of Ccnb1 and Mos mRNA Translation by MAPK Cascade During Mouse Oocyte Maturation

In mammalian species, both the maturation promoting factor (MPF) and the mitogen-activated protein kinase (MAPK) cascade play critical roles in modulating oocyte meiotic cell-cycle progression. MPF is a critical heterodimer composed of CDK1 and cyclin B1. Activation of MPF and ERK1/2 requires the activation of maternal Ccnb1 and Mos mRNAs translation, respectively. The phosphorylation and degradation of CPEB1 that triggered by ERK1/2 is a principal mechanism of activating maternal mRNA translation. However, the interplay of these two key kinases in mediating mammalian translational activation of cytoplasmic mRNAs during oocyte maturation is unclear. We prove evidence that the translational activation of Ccnb1 transcripts containing a long 3'-UTR during meiotic resumption works in an ERK1/2-dependent way. A low level of ERK1/2 activation was detected prior to meiotic resumption. Precocious activation of MAPK signaling in germinal vesicle stage oocytes promotes the translation of Ccnb1 mRNA and meiotic maturation. Inhibition or precocious activation of CDK1 activity has an appreciable effect on the translation of Ccnb1 mRNA, suggesting that both kinases are required for Ccnb1 mRNA translational activation. CDK1 triggers phosphorylation, but not degradation, of CPEB1 in oocytes; the degradation of CPEB1 was only triggered by ERK1/2. Moreover, the translational activation of Mos mRNA is regulated by ERK1/2 and cytoplasmic polyadenylation elements too. Taken together, the cooperation and positive feedback activation of ERK1/2 and CDK1 lead to the fine-tuning of mRNA translation and cell-cycle progression during mouse oocyte maturation.

Identification of transcriptome differences in goat ovaries at the follicular phase and the luteal phase using an RNA-Seq method

The ovaries, the main female reproductive organs, directly mediate ovulation and reproductive hormone secretion. These complex physiological processes are regulated by multiple genes and pathways. However, there is a lack of research on goat ovaries, and the molecular mechanisms underlying the signaling pathways remain unclear. In this study, Illumina HiSeq 4000 sequencing was used to sequence the transcriptomes of goat ovaries. The expression patterns of differentially expressed mRNAs in goat ovaries at both the follicular and luteal phases were determined by bioinformatics analysis. A total of 1,122, 014, 112 clean reads were obtained, and 3770 differentially expressed mRNAs were identified for further analysis. There were 1727 and 2043 upregulated mRNAs in the luteal phase and follicular phase, respectively. According to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses, some mRNAs that were highly expressed in ovaries during the luteal phase, such as HSD17B7, 3BHSD, and SRD5A2, may be related to the synthesis of progesterone. In addition, some mRNAs that were highly expressed in ovaries during the follicular phase, such as RPL12, RPS13 and RPL10, are related to the growth and maturation of oocytes. Taken together, the findings of this study provide genome-wide mRNA expression profiles for goat ovaries at the follicular and luteal phases and identify mRNAs associated with goat hormone secretion and follicular development. In addition, this study provides a theoretical basis for further investigation of goat reproductive regulation.

RNA-Binding Protein Rbm24 as a Multifaceted Post-Transcriptional Regulator of Embryonic Lineage Differentiation and Cellular Homeostasis

RNA-binding proteins control the metabolism of RNAs at all stages of their lifetime. They are critically required for the post-transcriptional regulation of gene expression in a wide variety of physiological and pathological processes. Rbm24 is a highly conserved RNA-binding protein that displays strongly regionalized expression patterns and exhibits dynamic changes in subcellular localization during early development. There is increasing evidence that it acts as a multifunctional regulator to switch cell fate determination and to maintain tissue homeostasis. Dysfunction of Rbm24 disrupts cell differentiation in nearly every tissue where it is expressed, such as skeletal and cardiac muscles, and different head sensory organs, but the molecular events that are affected may vary in a tissue-specific, or even a stage-specific manner. Recent works using different animal models have uncovered multiple post-transcriptional regulatory mechanisms by which Rbm24 functions in key developmental processes. In particular, it represents a major splicing factor in muscle cell development, and plays an essential role in cytoplasmic polyadenylation during lens fiber cell terminal differentiation. Here we review the advances in understanding the implication of Rbm24 during development and disease, by focusing on its regulatory roles in physiological and pathological conditions.

What impact does oocyte vitrification have on epigenetics and gene expression?

Children conceived by assisted reproductive technologies (ART) have a moderate risk for a number of adverse events and conditions. The question whether this additional risk is associated with specific procedures used in ART or whether it is related to the intrinsic biological factors associated with infertility remains unresolved. One of the main hypotheses is that laboratory procedures could have an effect on the epigenome of gametes and embryos. This suspicion is linked to the fact that ART procedures occur precisely during the period when there are major changes in the organization of the epigenome. Oocyte freezing protocols are generally considered safe; however, some evidence suggests that vitrification may be associated with modifications of the epigenetic marks. In this manuscript, after describing the main changes that occur during epigenetic reprogramming, we will provide current information regarding the impact of oocyte vitrification on epigenetic regulation and the consequences on gene expression, both in animals and humans. Overall, the literature suggests that epigenetic and transcriptomic profiles are sensitive to the stress induced by oocyte vitrification, and it also underlines the need to improve our knowledge in this field.

Functions and mechanisms of RNA tailing by metazoan terminal nucleotidyltransferases

Termini often determine the fate of RNA molecules. In recent years, 3' ends of almost all classes of RNA species have been shown to acquire nontemplated nucleotides that are added by terminal nucleotidyltransferases (TENTs). The best-described role of 3' tailing is the bulk polyadenylation of messenger RNAs in the cell nucleus that is catalyzed by canonical poly(A) polymerases (PAPs). However, many other enzymes that add adenosines, uridines, or even more complex combinations of nucleotides have recently been described. This review focuses on metazoan TENTs, which are either noncanonical PAPs or terminal uridylyltransferases with varying processivity. These enzymes regulate RNA stability and RNA functions and are crucial in early development, gamete production, and somatic tissues. TENTs regulate gene expression at the posttranscriptional level, participate in the maturation of many transcripts, and protect cells against viral invasion and the transposition of repetitive sequences. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Recognition RNA Processing > 3' End Processing RNA Turnover and Surveillance > Regulation of RNA Stability.

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.

Citrinin exposure disrupts organelle distribution and functions in mouse oocytes

Citrinin (CTN) is a secondary fungal metabolite produced by several species of Aspergillins and Penicillins, and it is widely found in vegetable-derived foods such as cereals and fermented rice-based food supplements. Previous studies indicated that CTN had immunotoxicity, hepatotoxicity, nephrotoxicity, and reproductive toxicity, which caused severe effects on human and animal health. However, the potential toxicity of CTN on the organelles of mouse oocytes is still unclear. In this study, we showed that the exposure to 30 μM CTN significantly reduced the developmental capacity of mouse oocytes. Our results revealed that mitochondria exhibited abnormal distribution and mitochondrial membrane potential decreased under CTN exposure. And the endoplasmic reticulum (ER) failed to accumulate to the spindle periphery, which is accompanied by the occurrence of ER stress, showing with increased GRP78 expression. We also found that similar with ER, the Golgi apparatus showed homogenous localization pattern after CTN exposure, and the vesicle transport was disturbed, showing with aberrant expression and localization of Rab11a. Moreover, our results indicated that CTN exposure increased the expression of LAMP2, indicating the induction of lysosomal damage. In summary, our study showed that CTN exposure to mouse oocytes was toxic to the distribution and functions of organelles, which further led to a decrease of oocyte quality.

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.

CPEB1 deletion is not a common explanation for premature ovarian insufficiency in a Chinese cohort

Purpose

Premature ovarian insufficiency (POI), which is characterized by early menopause before the age of 40 years, affects approximately 1–5% of women. Cytoplasmic polyadenylation element binding protein 1 (CPEB1) is a post-transcriptional regulatory protein that is highly expressed in germ cells and promotes oocytes maturation, and several studies have found microdeletions of chromosome 15q25.2, which contains the CPEB1 gene, in POI patients. However, the deleted region also includes other plausible genes, and thus the contribution of CPEB1 to POI is uncertain. The present study aimed to determine the relationship between CPEB1 deletion and POI in a Chinese cohort.

Material and methods

Quantitative real-time polymerase chain reaction (qPCR) with primers for exon 4 and exon 11 of CPEB1 was performed to detect the CPEB1 deletion in 323 patients with POI and in 300 healthy controls. Subsequent qPCR with primers for each exon of CPEB1 was performed to precisely localize the deletion locus.

Results

One patient with primary amenorrhea was found to carry a heterozygous deletion of exons 8–12 of the CPEB1 gene.

Conclusion

Our study is the first to search for CPEB1 deletions in POI patients using a simple qPCR method, and we show that CPEB1 deletion is not a common cause for POI in a Chinese cohort.