PCBP1 is required for maintenance of the transcriptionally silent state in fully grown mouse oocytes

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 oocyte to acquire the developmental competence.

KAS-seq profiling captures transcription dynamics during oocyte maturation

In fully grown oocytes, the genome is considered to be globally transcriptionally silenced. However, this conclusion is primarily derived from the results obtained through immunofluorescence staining or inferred from the highly condensed state of chromosomes, lacking more direct evidence. Here, by using a kethoxal-assisted single-stranded DNA sequencing (KAS-seq) approach, we investigated the landscape of single-strand DNA (ssDNA) throughout the genome and provided a readout of the activity and dynamics of transcription during oocyte meiotic maturation. In non-surrounded nucleolus (NSN) oocytes, we observed a robust KAS-seq signal, indicating the high transcriptional activity. In surrounded nucleolus (SN) oocytes, the presence of ssDNA still persists although the KAS-seq signal was relatively weak, suggesting the presence of transcription. Accompanying with the meiotic resumption, the transcriptional activity gradually decreased, and global repression was detected in matured oocytes. Moreover, we preformed the integrative genomics analysis to dissect the transcriptional dynamics during mouse oocyte maturation. In sum, the present study delineates the detailed transcriptional activity during mammalian oocyte maturation.

Regulation of Oocyte mRNA Metabolism: A Key Determinant of Oocyte Developmental Competence

The regulation of mRNA transcription and translation is uncoupled during oogenesis. The reason for this uncoupling is two-fold. Chromatin is only accessible to the transcriptional machinery during the growth phase as it condenses prior to resumption of meiosis to ensure faithful segregation of chromosomes during meiotic maturation. Thus, transcription rates are high during this time period in order to produce all of the transcripts needed for meiosis, fertilization, and embryo cleavage until the newly formed embryonic genome becomes transcriptionally active. To ensure appropriate timing of key developmental milestones including chromatin condensation, resumption of meiosis, segregation of chromosomes, and polar body extrusion, the translation of protein from transcripts synthesized during oocyte growth must be temporally regulated. This is achieved by the regulation of mRNA interaction with RNA binding proteins and shortening and lengthening of the poly(A) tail. This chapter details the essential factors that regulate the dynamic changes in mRNA synthesis, storage, translation, and degradation during oocyte growth and maturation.

"Meiosis arrester" C-natriuretic peptide directly stimulates oocyte mtDNA accumulation and is implicated in aging-associated oocyte mtDNA loss

C-natriuretic peptide (CNP) is the central regulator of oocyte meiosis progression, thus coordinating synchronization of oocyte nuclear-cytoplasmic maturation. However, whether CNP can independently regulate cytoplasmic maturation has been long overlooked. Mitochondrial DNA (mtDNA) accumulation is the hallmark event of cytoplasmic maturation, but the mechanism underlying oocyte mtDNA replication remains largely elusive. Herein, we report that CNP can directly stimulate oocyte mtDNA replication at GV stage, and deficiency of follicular CNP may contribute largely to lower mtDNA copy number in in vitro matured oocytes. The mechanistic study showed that cAMP-PKA-CREB1 signaling cascade underlies the regulatory role of CNP in stimulating mtDNA replication and upregulating related genes. Of interest, we also report that CNP-NPR2 signaling is inhibited in aging follicles, and this inhibition is implicated in lower mtDNA copy number in oocytes from aging females. Together, our study provides the first direct functional link between follicular CNP and oocyte mtDNA replication, and identifies its involvement in aging-associated mtDNA loss in oocytes. These findings, not only update the current knowledge of the functions of CNP in coordinating oocyte maturation but also present a promising strategy for improving in vitro fertilization outcomes of aging females.

Chromatin Configuration in Diplotene Mouse and Human Oocytes during the Period of Transcriptional Activity Extinction

In the oocyte nucleus, called the germinal vesicle (GV) at the prolonged diplotene stage of the meiotic prophase, chromatin undergoes a global rearrangement, which is often accompanied by the cessation of its transcriptional activity. In many mammals, including mice and humans, chromatin condenses around a special nuclear organelle called the atypical nucleolus or formerly nucleolus-like body. Chromatin configuration is an important indicator of the quality of GV oocytes and largely predicts their ability to resume meiosis and successful embryonic development. In mice, GV oocytes are traditionally divided into the NSN (non-surrounded nucleolus) and SN (surrounded nucleolus) based on the specific chromatin configuration. The NSN-SN transition is a key event in mouse oogenesis and the main prerequisite for the normal development of the embryo. As for humans, there is no single nomenclature for the chromatin configuration at the GV stage. This often leads to discrepancies and misunderstandings, the overcoming of which should expand the scope of the application of mouse oocytes as a model for developing new methods for assessing and improving the quality of human oocytes. As a first approximation and with a certain proviso, the mouse NSN/SN classification can be used for the primary characterization of human GV oocytes. The task of this review is to analyze and discuss the existing classifications of chromatin configuration in mouse and human GV oocytes with an emphasis on transcriptional activity extinction at the end of oocyte growth.

Single-cell transcriptome and translatome dual-omics reveals potential mechanisms of human oocyte maturation

The combined use of transcriptome and translatome as indicators of gene expression profiles is usually more accurate than the use of transcriptomes alone, especially in cell types governed by translational regulation, such as mammalian oocytes. Here, we developed a dual-omics methodology that includes both transcriptome and translatome sequencing (T&T-seq) of single-cell oocyte samples, and we used it to characterize the transcriptomes and translatomes during mouse and human oocyte maturation. T&T-seq analysis revealed distinct translational expression patterns between mouse and human oocytes and delineated a sequential gene expression regulation from the cytoplasm to the nucleus during human oocyte maturation. By these means, we also identified a functional role of OOSP2 inducing factor in human oocyte maturation, as human recombinant OOSP2 induced in vitro maturation of human oocytes, which was blocked by anti-OOSP2. Single-oocyte T&T-seq analyses further elucidated that OOSP2 induces specific signaling pathways, including small GTPases, through translational regulation.

Development of methods for simultaneous single cell analysis of transcription and translation is still underway. Here, Hu et al. develop single-cell transcriptome and translatome dual-omics on human oocytes, which enables them to identify OOSP2 as an induction factor during human oocyte maturation.

Proteostasis Regulators in Cystic Fibrosis: Current Development and Future Perspectives

In cystic fibrosis (CF), the deletion of phenylalanine 508 (F508del) in the CF transmembrane conductance regulator (CFTR) leads to misfolding and premature degradation of the mutant protein. These defects can be targeted with pharmacological agents named potentiators and correctors. During the past years, several efforts have been devoted to develop and approve new effective molecules. However, their clinical use remains limited, as they fail to fully restore F508del-CFTR biological function. Indeed, the search for CFTR correctors with different and additive mechanisms has recently increased. Among them, drugs that modulate the CFTR proteostasis environment are particularly attractive to enhance therapy effectiveness further. This Perspective focuses on reviewing the recent progress in discovering CFTR proteostasis regulators, mainly describing the design, chemical structure, and structure-activity relationships. The opportunities, challenges, and future directions in this emerging and promising field of research are discussed, as well.

Single-cell multiomic analysis of in vivo and in vitro matured human oocytes

STUDY QUESTION

Are there any differences between in vivo (IVV) and in vitro (IVT) matured metaphase II (MII) oocytes at the molecular level?

SUMMARY ANSWER

Between IVV and IVT oocytes, 507 differentially expressed genes (DEGs) were identified; the non-CpG methylomes were significantly different, but the CpG methylomes and genomic copy number variations (CNVs) were similar.

WHAT IS KNOWN ALREADY

A previous study using microarray and single-cell RNA-seq analysis revealed that numerous genes were differentially expressed between IVV and IVT oocytes. Independent studies of DNA methylation profiling in human oocytes have revealed negative correlations between gene transcription and the DNA methylation level at gene promoter regions. No study has compared global CpG or non-CpG methylation between these two groups of oocytes. Although a high level of aneuploidy has been reported in MII oocytes, no direct comparison of IVV and IVT oocytes based on single-cell sequencing data has been performed.

STUDY DESIGN, SIZE, DURATION

We collected eight IVV oocytes from six patients and seven IVT oocytes from seven patients and then analysed each oocyte using the previously established single-cell triple omics sequencing (scTrioseq) analysis to determine associations among the transcriptome, DNA methylome and chromosome ploidy in the oocytes.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All IVV oocytes were donated by patients who received 150 IU gonadotropin per day from the third day of their menstrual cycle, followed by GnRH antagonist after 5 days of gonadotropin stimulation. All IVT oocytes were from immature oocytes which were donated by volunteers undergoing delivery by caesarean section then cultured in oocyte maturation medium containing 75 mIU/ml hMG for 24 to 48 h. Every single oocyte was analysed using the previously established single-cell multiomic sequencing analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

There were 507 genes differentially expressed between the IVV (n = 8) and IVT (n = 7) oocytes, even though their global transcriptome profiles were similar. The enriched genes in IVV oocytes were related to the cell cycle process while those in IVT oocytes were related to mitochondrial respiration biogenesis. Although the global CpG methylation of the two groups of oocytes was similar, the non-CpG methylation level in IVV oocytes was higher than that in IVT oocytes. A high aneuploidy ratio was found in both groups, but the aneuploidy did not affect transcription according to the correlation analysis.

LARGE-SCALE DATA

N/A.

LIMITATIONS AND REASONS FOR CAUTION

Due to the difficulty in collecting MII oocytes, especially IVV matured oocytes, the sample size was limited.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings indicate that single-cell multiomic sequencing can be utilised to examine the similarity and differences between IVV and IVT matured MII oocytes.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Ministry of Science and Technology of China, National Key R&D Program of China (No. 2017YFC1001601). The donated oocytes were collected by Shanghai Tenth People's Hospital. The authors declare no competing interests.

Coenzyme Q10 supplement rescues postovulatory oocyte aging by regulating SIRT4 expression

BACKGROUND

High-quality of the oocyte is crucial for embryo development and the success of human assisted reproduction. The postovulatory aged oocytes lose the developmental competence with mitochondrial dysfunction and oxidative stress. Coenzyme Q10 (CoQ10) is widely distributed in the membranes of cells, and has an important role in the mitochondrial respiration chain, against oxidative stress and modulation of gene expression.

OBJECTIVE

To investigate the functions and mechanisms of CoQ10 on delaying postovulatory oocyte aging.

METHODS

Quantitative real-time PCR and Immunofluorescence staining were used to determine the expression patterns of the biogenesis genes of CoQ10 in postovulatory aged oocytes compared with fresh oocytes. The mitochondrial function, apoptosis, reactive oxygen species (ROS) accumulation and spindle abnormalities were investigated after treatment with 10 μM CoQ10 in aged groups. SIRT4 siRNA or capped RNA was injected into oocytes to investigate the function of SIRT4 on postovulatory oocyte aging and the relationship between CoQ10 and SIRT4.

RESULTS

Multiple CoQ10 biosynthesis enzymes are insufficient, and supplement of CoQ10 can improve oocyte quality and elevate the development competency of postovulatory aged oocytes. CoQ10 can attenuate the aging-induced abnormalities including mitochondrial dysfunction, ROS accumulation, spindle abnormalities, and apoptosis in postovulatory aged oocytes. Furthermore, SIRT4, which was first found to be up-regulated in postovulatory aged oocytes, decreased following CoQ10 treatment. Finally, knockdown of SIRT4 can rescue aging-induced dysfunction of mitochondria, and the efficiency of CoQ10 rescuing dysfunction of mitochondria can be weakened by SIRT4 overexpression.

CONCLUSION

Supplement of CoQ10 protects oocytes from postovulatory aging by inhibiting SIRT4increase.

Heterochromatin Morphodynamics in Late Oogenesis and Early Embryogenesis of Mammals

During the period of oocyte growth, chromatin undergoes global rearrangements at both morphological and molecular levels. An intriguing feature of oogenesis in some mammalian species is the formation of a heterochromatin ring-shaped structure, called the karyosphere or surrounded "nucleolus", which is associated with the periphery of the nucleolus-like bodies (NLBs). Morphologically similar heterochromatin structures also form around the nucleolus-precursor bodies (NPBs) in zygotes and persist for several first cleavage divisions in blastomeres. Despite recent progress in our understanding the regulation of gene silencing/expression during early mammalian development, as well as the molecular mechanisms that underlie chromatin condensation and heterochromatin structure, the biological significance of the karyosphere and its counterparts in early embryos is still elusive. We pay attention to both the changes of heterochromatin morphology and to the molecular mechanisms that can affect the configuration and functional activity of chromatin. We briefly discuss how DNA methylation, post-translational histone modifications, alternative histone variants, and some chromatin-associated non-histone proteins may be involved in the formation of peculiar heterochromatin structures intimately associated with NLBs and NPBs, the unique nuclear bodies of oocytes and early embryos.

Amplifiers co-translationally enhance CFTR biosynthesis via PCBP1-mediated regulation of CFTR mRNA

BACKGROUND

Cystic fibrosis (CF) is a recessive disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. We previously described a first-in-class CFTR modulator that functions as an amplifier to selectively increase CFTR expression and function. The amplifier mechanism is distinct from and complementary to corrector and potentiator classes of CFTR modulators. Here we characterize the mechanism by which amplifiers increase CFTR mRNA, protein, and activity.

METHODS

Biochemical studies elucidated the action of amplifiers on CFTR mRNA abundance and translation and defined the role of an amplifier-binding protein that was identified using chemical proteomics.

RESULTS

Amplifiers stabilize CFTR mRNA through a process that requires only the translated sequence of CFTR and involves translational elongation. Amplifiers enrich ER-associated CFTR mRNA and increase its translational efficiency through increasing the fraction of CFTR mRNA associated with polysomes. Pulldowns identified the poly(rC)-binding protein 1 (PCBP1) as directly binding to amplifier. A PCBP1 consensus element was identified within the CFTR open reading frame that binds PCBP1. This sequence proved necessary for amplifier responsiveness.

CONCLUSIONS

Small molecule amplifiers co-translationally increase CFTR mRNA stability. They enhance translation through addressing the inherently inefficient membrane targeting of CFTR mRNA. Amplifiers bind directly to PCBP1, show enhanced affinity in the presence of bound RNA, and require a PCBP1 consensus element within CFTR mRNA to elicit translational effects. These modulators represent a promising new and mechanistically novel class of CFTR therapeutic. They may be useful as a monotherapy or in combination with other CFTR modulators.

KH-Domain Poly(C)-Binding Proteins as Versatile Regulators of Multiple Biological Processes

Five known members of the family of KH-domain poly(C)-binding proteins (Pcbp1-4, hnRNP-K) have an unusually broad spectrum of cellular functions that include regulation of gene transcription, regulation of pre-mRNA processing, splicing, mRNA stability, translational silencing and enhancement, the control of iron turnover, and many others. Mechanistically, these proteins act via nucleic acid binding and protein-protein interactions. Through performing these multiple tasks, the KH-domain poly(C)-binding family members are involved in a wide variety of biological processes such as embryonic development, cell differentiation, and cancer. Deregulation of KH-domain protein expression is frequently associated with severe developmental defects and neoplasia. This review summarizes progress in studies of the KH-domain proteins made over past two decades. The review also reports our recent finding implying an involvement of the KH-factor Pcbp1 into control of transition from naïve to primed pluripotency cell state.

Actin depolymerization disrupts karyosphere capsule integrity but not residual transcription in late oocytes of the grass frog Rana temporaria

Late diplotene oocytes are characterized by an essential decrease in transcriptional activity. At this time, chromosomes condense and form a compact structure named a karyosphere. The karyosphere of grass frogs Rana temporaria is surrounded by a fibrillar karyosphere capsule (KC). One of the main protein constituents of R. temporaria KC is actin. In this study, we used antibodies against different actin epitopes to trace different forms of actin in the KC. We also investigated the effect of F-actin depolymerization on the oocyte nuclear structures and transcription of chromatin DNA and rDNA in the amplified nucleoli. It was determined that disruption of actin filaments leads to chromosome shrinkage, nucleoli fusion, and distortion of the KC structure, but does not inhibit residual transcription in both the karyosphere and the nucleoli.

Chromatin Modification and Global Transcriptional Silencing in the Oocyte Mediated by the mRNA Decay Activator ZFP36L2

Global transcriptional silencing is a highly conserved mechanism central to the oocyte-to-embryo transition. We report the unexpected discovery that global transcriptional silencing in oocytes depends on an mRNA decay activator. Oocyte-specific loss of ZFP36L2 an RNA-binding protein that promotes AU-rich element-dependent mRNA decay prevents global transcriptional silencing and causes oocyte maturation and fertilization defects, as well as complete female infertility in the mouse. Single-cell RNA sequencing revealed that ZFP36L2 downregulates mRNAs encoding transcription and chromatin modification regulators, including a large group of mRNAs for histone demethylases targeting H3K4 and H3K9, which we show are bound and degraded by ZFP36L2. Oocytes lacking Zfp36l2 fail to accumulate histone methylation at H3K4 and H3K9, marks associated with the transcriptionally silent, developmentally competent oocyte state. Our results uncover a ZFP36L2-dependent mRNA decay mechanism that acts as a developmental switch during oocyte growth, triggering wide-spread shifts in chromatin modification and global transcription.

TGF-beta signaling in cancer: post-transcriptional regulation of EMT via hnRNP E1

The TGFβ signaling pathway is a critical regulator of cancer progression in part through induction of the epithelial to mesenchymal transition (EMT). This process is aberrantly activated in cancer cells, facilitating invasion of the basement membrane, survival in the circulatory system, and dissemination to distant organs. The mechanisms through which epithelial cells transition to a mesenchymal state involve coordinated transcriptional and post-transcriptional control of gene expression. One such mechanism of control is through the RNA binding protein hnRNP E1, which regulates splicing and translation of a cohort of EMT and stemness-associated transcripts. A growing body of evidence indicates a major role for hnRNP E1 in the control of epithelial cell plasticity, especially in the context of carcinoma progression. Here, we review the multiple mechanisms through which hnRNP E1 functions to control EMT and metastatic progression.

Karyosphere (Karyosome): A Peculiar Structure of the Oocyte Nucleus

The karyosphere, aka the karyosome, is a meiosis-specific structure that represents a "knot" of condensed chromosomes joined together in a limited volume of the oocyte nucleus. The karyosphere is an evolutionarily conserved but morphologically rather "multifaceted" structure. It forms at the diplotene stage of meiotic prophase in many animals, from hydra and Drosophila to human. Karyosphere formation is generally linked with transcriptional silencing of the genome. It is believed that karyosphere/karyosome is a prerequisite for proper completion of meiotic divisions and further development. Here, a brief review on the karyosphere features in some invertebrates and vertebrates is provided. Special emphasis is made on terminology, since current discrepancies in this field may lead to confusions. In particular, it is proposed to distinguish the karyosphere with a capsule and the karyosome (a karyosphere devoid of a capsule). The "inverted" karyospheres are also considered, in which the chromosomes situate externally to an extrachromosomal structure (e.g., in human oocytes).

Maternal PCBP1 determines the normal timing of pronucleus formation in mouse eggs

In mammals, pronucleus formation, a landmark event for egg activation and fertilization, is critical for embryonic development. However, the mechanisms underlying pronucleus formation remain unclear. Increasing evidence has shown that the transition from a mature egg to a developing embryo and the early steps of development are driven by the control of maternal cytoplasmic factors. Herein, a two-dimensional-electrophoresis-based proteomic approach was used in metaphase II and parthenogenetically activated mouse eggs to search for maternal proteins involved in egg activation, one of which was poly(rC)-binding protein 1 (PCBP1). Phosphoprotein staining indicated that PCBP1 displayed dephosphorylation in parthenogenetically activated egg, which possibly boosts its ability to bind to mRNAs. We identified 75 mRNAs expressed in mouse eggs that contained the characteristic PCBP1-binding CU-rich sequence in the 3'-UTR. Among them, we focused on H2a.x mRNA, as it was closely related to pronucleus formation in Xenopus oocytes. Further studies suggested that PCBP1 could bind to H2a.x mRNA and enhance its stability, thus promoting mouse pronucleus formation during parthenogenetic activation of murine eggs, while the inhibition of PCBP1 evidently retarded pronucleus formation. In summary, these data propose that PCBP1 may serve as a novel maternal factor that is required for determining the normal timing of pronucleus formation.

Sculpting the Transcriptome During the Oocyte-to-Embryo Transition in Mouse

In mouse, the oocyte-to-embryo transition entails converting a highly differentiated oocyte to totipotent blastomeres. This transition is driven by degradation of maternal mRNAs, which results in loss of oocyte identity, and reprogramming of gene expression during the course of zygotic gene activation, which occurs primarily during the two-cell stage and confers blastomere totipotency. Full-grown oocytes are transcriptionally quiescent and mRNAs are remarkably stable in oocytes due to the RNA-binding protein MSY2, which stabilizes mRNAs, and low activity of the 5' and 3' RNA degradation machinery. Oocyte maturation initiates a transition from mRNA stability to instability due to phosphorylation of MSY2, which makes mRNAs more susceptible to the RNA degradation machinery, and recruitment of dormant maternal mRNAs that encode for critical components of the 5' and 3' RNA degradation machinery. Small RNAs (miRNA, siRNA, and piRNA) play little, if any, role in mRNA degradation that occurs during maturation. Many mRNAs are totally degraded but a substantial fraction is only partially degraded, their degradation completed by the end of the two-cell stage. Genome activation initiates during the one-cell stage, is promiscuous, low level, and genome wide (and includes both inter- and intragenic regions) and produces transcripts that are inefficiently spliced and polyadenylated. The major wave of genome activation in two-cell embryos involves expression of thousands of new genes. This unique pattern of gene expression is the product of maternal mRNAs recruited during maturation that encode for transcription factors and chromatin remodelers, as well as dramatic changes in chromatin structure due to incorporation of histone variants and modified histones.

A requirement for ERK-dependent Dicer phosphorylation in coordinating oocyte-to-embryo transition in C. elegans

Signaling pathways and small RNAs direct diverse cellular events, but few examples are known of defined signaling pathways directly regulating small RNA biogenesis. We show that ERK phosphorylates Dicer on two conserved residues in its RNase IIIb and double-stranded RNA (dsRNA)-binding domains and that phosphorylation of these residues is necessary and sufficient to trigger Dicer's nuclear translocation in worms, mice, and human cells. Phosphorylation of Dicer on either site inhibits Dicer function in the female germline and dampens small RNA repertoire. Our data demonstrate that ERK phosphorylates and inhibits Dicer during meiosis I for oogenesis to proceed normally in Caenorhabditis elegans and that this inhibition is released before fertilization for embryogenesis to proceed normally. The conserved Dicer residues, their phosphorylation by ERK, and the consequences of the resulting modifications implicate an ERK-Dicer nexus as a fundamental component of the oocyte-to-embryo transition and an underlying mechanism coupling extracellular cues to small RNA production.

Species-dependent neuropathology in transgenic SOD1 pigs

Mutations in the human copper/zinc superoxide dismutase 1 (hSOD1) gene cause familial amyotrophic lateral sclerosis (ALS). It remains unknown whether large animal models of ALS mimic more pathological events seen in ALS patients via novel mechanisms. Here, we report the generation of transgenic pigs expressing mutant G93A hSOD1 and showing hind limb motor defects, which are germline transmissible, and motor neuron degeneration in dose- and age-dependent manners. Importantly, in the early disease stage, mutant hSOD1 did not form cytoplasmic inclusions, but showed nuclear accumulation and ubiquitinated nuclear aggregates, as seen in some ALS patient brains, but not in transgenic ALS mouse models. Our findings revealed that SOD1 binds PCBP1, a nuclear poly(rC) binding protein, in pig brain, but not in mouse brain, suggesting that the SOD1-PCBP1 interaction accounts for nuclear SOD1 accumulation and that species-specific targets are key to ALS pathology in large mammals and in humans.

An oocyte-specific ELAVL2 isoform is a translational repressor ablated from meiotically competent antral oocytes

At the end of the growth phase, mouse antral follicle oocytes acquire full developmental competence. In the mouse, this event is marked by the transition from the so-called non-surrounded nucleolus (NSN) chromatin configuration into the transcriptionally quiescent surrounded nucleolus (SN) configuration, which is named after a prominent perinucleolar condensed chromatin ring. However, the SN chromatin configuration alone is not sufficient for determining the developmental competence of the SN oocyte. There are additional nuclear and cytoplamic factors involved, while a little is known about the changes occurring in the cytoplasm during the NSN/SN transition. Here, we report functional analysis of maternal ELAVL2 an AU-rich element binding protein. Elavl2 gene encodes an oocyte-specific protein isoform (denoted ELAVL2°), which acts as a translational repressor. ELAVL2° is abundant in fully grown NSN oocytes, is ablated during the NSN/SN transition and remains low during the oocyte-to-embryo transition (OET). ELAVL2° overexpression during meiotic maturation causes errors in chromosome segregation, indicating the significance of naturally reduced ELAVL2° levels in SN oocytes. On the other hand, during oocyte growth, prematurely reduced Elavl2 expression results in lower yields of fully grown and meiotically matured oocytes, suggesting that Elavl2 is necessary for proper oocyte maturation. Moreover, Elavl2 knockdown showed stimulating effects on translation in fully grown oocytes. We propose that ELAVL2 has an ambivalent role in oocytes: it functions as a pleiotropic translational repressor in efficient production of fully grown oocytes, while its disposal during the NSN/SN transition contributes to the acquisition of full developmental competence.

PolyC-binding protein 1 interacts with 5'-untranslated region of enterovirus 71 RNA in membrane-associated complex to facilitate viral replication

Enterovirus 71 (EV71) is one causative agent of hand, foot, and mouth disease (HFMD), which may lead to severe neurological disorders and mortality in children. EV71 genome is a positive single-stranded RNA containing a single open reading frame (ORF) flanked by 5'-untranslated region (5'UTR) and 3'UTR. The 5'UTR is fundamentally important for virus replication by interacting with cellular proteins. Here, we revealed that poly(C)-binding protein 1 (PCBP1) specifically binds to the 5'UTR of EV71. Detailed studies indicated that the RNA-binding K-homologous 1 (KH1) domain of PCBP1 is responsible for its binding to the stem-loop I and IV of EV71 5'UTR. Interestingly, we revealed that PCBP1 is distributed in the nucleus and cytoplasm of uninfected cells, but mainly localized in the cytoplasm of EV71-infected cells due to interaction and co-localization with the viral RNA. Furthermore, sub-cellular distribution analysis showed that PCBP1 is located in ER-derived membrane, in where virus replication occurred in the cytoplasm of EV71-infected cells, suggesting PCBP1 is recruited in a membrane-associated replication complex. In addition, we found that the binding of PCBP1 to 5'UTR resulted in enhancing EV71 viral protein expression and virus production so as to facilitate viral replication. Thus, we revealed a novel mechanism in which PCBP1 as a positive regulator involved in regulation of EV71 replication in the host specialized membrane-associated replication complex, which provides an insight into cellular factors involved in EV71 replication.

The role of RING box protein 1 in mouse oocyte meiotic maturation

RING box protein-1 (RBX1) is an essential component of Skp1-cullin-F-box protein (SCF) E3 ubiquitin ligase and participates in diverse cellular processes by targeting various substrates for degradation. However, the physiological function of RBX1 in mouse oocyte maturation remains unknown. Here, we examined the expression, localization and function of RBX1 during mouse oocyte meiotic maturation. Immunofluorescence analysis showed that RBX1 displayed dynamic distribution during the maturation process: it localized around and migrated along with the spindle and condensed chromosomes. Rbx1 knockdown with the appropriate siRNAs led to a decreased rate of first polar body extrusion and most oocytes were arrested at metaphase I. Moreover, downregulation of Rbx1 caused accumulation of Emi1, an inhibitor of the anaphase-promoting complex/cyclosome (APC/C), which is required for mouse meiotic maturation. In addition, we found apparently increased expression of the homologue disjunction-associated protein securin and cyclin B1, which are substrates of APC/C E3 ligase and need to be degraded for meiotic progression. These results indicate the essential role of the SCF^βTrCP-EMI1-APC/C axis in mouse oocyte meiotic maturation. In conclusion, we provide evidence for the indispensable role of RBX1 in mouse oocyte meiotic maturation.

Maternal factors required for oocyte developmental competence in mice: transcriptome analysis of non-surrounded nucleolus (NSN) and surrounded nucleolus (SN) oocytes

During mouse antral follicle development, the oocyte chromatin gradually transforms from a less condensed state with no Hoechst-positive rim surrounding the nucleolus (NSN) to a fully condensed chromatin state with a Hoechst-positive rim surrounding the nucleolus (SN). Compared with SN oocytes, NSN oocytes display a higher gene transcription activity and a lower rate of meiosis resumption (G2/M transition), and they are mostly arrested at the two-cell stage after in vitro fertilization. To explore the differences between NSN and SN oocytes, and the maternal factors required for oocyte developmental competence, we compared the whole-transcriptome profiles between NSN and SN oocytes. First, we found that the NSN and SN oocytes were different in their metabolic pathways. In the phosphatidylinositol signaling pathway, the SN oocytes tend to produce diacylglycerol, whereas the NSN oocytes tend to produce phosphatidylinositol (3,4,5)-trisphosphate. For energy production, the SN oocytes and NSN oocytes differed in the gluconeogenesis and in the synthesis processes. Second, we also found that the key genes associated with oocyte meiosis and/or preimplantation embryo development were differently expressed in the NSN and SN oocytes. Our results illustrate that during the NSN-SN transition, the oocytes change their metabolic activities and accumulate maternal factors for further oocyte maturation and post-fertilization embryo development.