Zygote arrest 1 (Zar1) is an evolutionarily conserved gene expressed in vertebrate ovaries

De Novo Assembly, Characterization and Comparative Transcriptome Analysis of the Mature Male and Female Gonads in Acrossocheilus parallens

Acrossocheilus parallens has become an important commercial aquaculture species in southern China due to its high nutritional content and ornamental value. However, at present, there is very little research on its gonad development and reproductive regulation, which has restricted the development of its aquaculture industry. In this research, the gonadal transcriptome sequencing data of female and male A. parallens were first analyzed and compared. A total of 67,251 unigenes were successfully assembled and a total of 34,069 unigenes were annotated. After the comparative transcriptome analysis, a sum of 14,514 differentially expressed genes (DEGs) were identified between the male and female gonads, with 9111 having significantly high expression in the testes and 5403 having high expression in the ovaries. Additionally, 82 DEGs related to reproduction, gonad development and differentiation in the gonads were identified and the differential expression profiles of partial genes were further validated using real-time fluorescence quantitative PCR. These results provide basic data for further research on the functions of the genes and pathways related to sex differentiation and gonad development in A. parallens.

ZAR1/2-Regulated Epigenetic Modifications are Essential for Age-Associated Oocyte Quality Maintenance and Zygotic Activation

The developmental competence and epigenetic progression of oocytes gradually become dysregulated with increasing maternal age. However, the mechanisms underlying age-related epigenetic regulation in oocytes remain poorly understood. Zygote arrest proteins 1 and 2 (ZAR1/2) are two maternal factors with partially redundant roles in maintaining oocyte quality, mainly known by regulating mRNA stability. In addition to this known function, it is found that ZAR1/2 is required for oocyte epigenetic maturation and zygotic reprogramming. Zar1/2-deleted oocytes exhibited reduced levels of multiple histone modifications and of the expression of corresponding histone modifiers, along with over-condensed chromatin, leading to compromised minor zygotic genome activation and deficient embryo development following fertilization. Cytoplasmic ZAR1/2 participated in intranuclear epigenetic maturation by binding the transcripts encoding histone modifiers and regulating their stability and translational activity. Moreover, oocytes from aged mice exhibited similar histone-modification deficiencies as the Zar1/2-deleted oocytes. ZAR1/2 mRNA and protein levels are downregulated in oocytes from mice and women with advanced ages, suggesting ZAR1/2 as regulators of epigenetic changes with reproductive aging. This study presents a new nucleo-cytoplasmic interaction mechanism that is involved in preventing oocyte epigenetic aging. Further, ZAR1/2 represents potential gene targets for diagnosis and clinical interventions in age-associated deficiencies in oocyte and embryo development.

How germ granules promote germ cell fate

Germ cells are the only cells in the body capable of giving rise to a new organism, and this totipotency hinges on their ability to assemble membraneless germ granules. These specialized RNA and protein complexes are hallmarks of germ cells throughout their life cycle: as embryonic germ granules in late oocytes and zygotes, Balbiani bodies in immature oocytes, and nuage in maturing gametes. Decades of developmental, genetic and biochemical studies have identified protein and RNA constituents unique to germ granules and have implicated these in germ cell identity, genome integrity and gamete differentiation. Now, emerging research is defining germ granules as biomolecular condensates that achieve high molecular concentrations by phase separation, and it is assigning distinct roles to germ granules during different stages of germline development. This organization of the germ cell cytoplasm into cellular subcompartments seems to be critical not only for the flawless continuity through the germline life cycle within the developing organism but also for the success of the next generation.

Systemic low-dose anti-fibrotic treatment attenuates ovarian aging in the mouse

The female reproductive system is one of the first to age in humans, resulting in infertility and endocrine disruptions. The aging ovary assumes a fibro-inflammatory milieu which negatively impacts gamete quantity and quality as well as ovulation. Here, we tested whether the systemic delivery of anti-inflammatory (Etanercept) or anti-fibrotic (Pirfenidone) drugs attenuates ovarian aging in mice. We first evaluated the ability of these drugs to decrease the expression of fibro-inflammatory genes in primary ovarian stromal cells treated with a pro-fibrotic or a pro-inflammatory stimulus. Whereas Etanercept did not block Tnf expression in ovarian stromal cells, Pirfenidone significantly reduced Col1a1 expression. We then tested Pirfenidone in vivo where the drug was delivered systemically via mini-osmotic pumps for 6 weeks. Pirfenidone mitigated the age-dependent increase in ovarian fibrosis without impacting overall health parameters. Ovarian function was improved in Pirfenidone-treated mice as evidenced by increased follicle and corpora lutea number, AMH levels, and improved estrous cyclicity. Transcriptomic analysis revealed that Pirfenidone treatment resulted in an upregulation of reproductive function-related genes at 8.5 months and a downregulation of inflammatory genes at 12 months of age. These findings demonstrate that reducing the fibroinflammatory ovarian microenvironment improves ovarian function, thereby supporting modulating the ovarian environment as a therapeutic avenue to extend reproductive longevity.

Acquisition of 2C-like totipotency through defined maternal-effect factors

Fully grown oocytes have the natural ability to transform 2 terminally differentiated gametes into a totipotent zygote representing the acquisition of totipotency. This process wholly depends on maternal-effect factors (MFs). MFs stored in the eggs are therefore likely to be able to induce cellular reprogramming to a totipotency state. Here we report the generation of totipotent-like stem cells from mESCs using 4MFs Hsf1, Zar1, Padi6, and Npm2, designated as MFiTLSCs. MFiTLSCs exhibited a unique and inherent capability to differentiate into embryonic and extraembryonic derivatives. Transcriptomic analysis revealed that MFiTLSCs are enriched with 2-cell-specific genes that appear to synergistically induce a transcriptional repressive state, in that parental genomes are remodeled to a poised transcriptional repression state while totipotency is established following fertilization. This method to derive MFiTLSCs could help advance the understanding of fate determinations of totipotent stem cells in a physiological context and establish a foundation for the development of oocyte biology-based reprogramming technology.

Systemic low-dose anti-fibrotic treatment attenuates ovarian aging in the mouse

The female reproductive system is one of the first to age in humans, resulting in infertility and endocrine disruptions. The aging ovary assumes a fibro-inflammatory milieu which negatively impacts gamete quantity and quality as well as ovulation. Here we tested whether the systemic delivery of anti-inflammatory (Etanercept) or anti-fibrotic (Pirfenidone) drugs attenuates ovarian aging in mice. We first evaluated the ability of these drugs to decrease the expression of fibro-inflammatory genes in primary ovarian stromal cells. Whereas Etanercept did not block Tnf expression in ovarian stromal cells, Pirfenidone significantly reduced Col1a1 expression. We then tested Pirfenidone in vivo where the drug was delivered systemically via mini-osmotic pumps for 6-weeks. Pirfenidone mitigated the age-dependent increase in ovarian fibrosis without impacting overall health parameters. Ovarian function was improved in Pirfenidone-treated mice as evidenced by increased follicle and corpora lutea number, AMH levels, and improved estrous cyclicity. Transcriptomic analysis revealed that Pirfenidone treatment resulted in an upregulation of reproductive function-related genes at 8.5 months and a downregulation of inflammatory genes at 12 months of age. These findings demonstrate that reducing the fibroinflammatory ovarian microenvironment improves ovarian function, thereby supporting modulating the ovarian environment as a therapeutic avenue to extend reproductive longevity.

Gonadal transcriptome analysis of genes related to sex differentiation and sex development in the Pomacea canaliculata

As an invasive alien animal, Pomacea canaliculata poses a great danger to the ecology and human beings. Recently, there has been a gradual shift towards bio-friendly control. Based on the development of RNA interference and CRISPR technology as molecular regulatory techniques for pest control, it was determined if the knockout of genes related to sex differentiation in P. canaliculata could induce sterility, thereby helping in population control. However, the knowledge of sex differentiation- and development-related genes in P. canaliculata is currently lacking. Here, transcriptomic approaches were used to study the genes expressed in the two genders of P. canaliculata at various developmental stages. Gonad transcriptomes of immature or mature males and females were compared, revealing 12,063 genes with sex-specific expression, of which 6066 were male- and 5997 were female-specific. Among the latter, 581 and 235 genes were up-regulated in immature and mature females, respectively. The sex-specific expressed genes identified included GnRHR2 and TSSK3 in males and ZAR1 and WNT4 in females. Of the genes, six were involved in reproduction: CCNBLIP1, MND1, DMC1, DLC1, MRE11, and E(sev)2B. Compared to immature snail gonads, the expression of HSP90 and CDK1 was markedly reduced in gonadal. It was hypothesized that the two were associated with the development of females. These findings provided new insights into crucial genetic information on sex differentiation and development in P. canaliculata. Additionally, some candidate genes were explored, which can contribute to future studies on controlling P. canaliculata using molecular regulatory techniques.

Disruption of Zar1 leads to arrested oogenesis by regulating polyadenylation via Cpeb1 in tilapia (Oreochromis niloticus)

Oogenesis is a complex process regulated by precise coordination of multiple factors, including maternal genes. Zygote arrest 1 (zar1) has been identified as an ovary-specific maternal gene that is vital for oocyte-to-embryo transition and oogenesis in mouse and zebrafish. However, its function in other species remains to be elucidated. In the present study, zar1 was identified with conserved C-terminal zinc finger domains in Nile tilapia. zar1 was highly expressed in the ovary and specifically expressed in phase I and II oocytes. Disruption of zar1 led to the failed transition from oogonia to phase I oocytes, with somatic cell apoptosis. Down-regulation and failed polyadenylation of figla, gdf9, bmp15 and wee2 mRNAs were observed in the ovaries of zar1-/- fish. Cpeb1, a gene essential for polyadenylation that interacts with Zar1, was down-regulated in zar1-/- fish. Moreover, decreased levels of serum estrogen and increased levels of androgen were observed in zar1-/- fish. Taken together, zar1 seems to be essential for tilapia oogenesis by regulating polyadenylation and estrogen synthesis. Our study shows that Zar1 has different molecular functions during gonadal development by the similar signaling pathway in different species.

Characterization of Two Gonadal Genes, zar1 and wt1b, in Hermaphroditic Fish Asian Seabass (Lates calcarifer)

Zygote arrest-1 (Zar1) and Wilms' tumor 1 (Wt1) play an important role in oogenesis, with the latter also involved in testicular development and gender differentiation. Here, Lczar1 and Lcwt1b were identified in Asian seabass (Lates calcarifer), a hermaphrodite fish, as the valuable model for studying sex differentiation. The cloned cDNA fragments of Lczar1 were 1192 bp, encoding 336 amino acids, and contained a zinc-binding domain, while those of Lcwt1b cDNA were 1521 bp, encoding a peptide of 423 amino acids with a Zn finger domain belonging to Wt1b family. RT-qPCR analysis showed that Lczar1 mRNA was exclusively expressed in the ovary, while Lcwt1b mRNA was majorly expressed in the gonads in a higher amount in the testis than in the ovary. In situ hybridization results showed that Lczar1 mRNA was mainly concentrated in oogonia and oocytes at early stages in the ovary, but were undetectable in the testis. Lcwt1b mRNA was localized not only in gonadal somatic cells (the testis and ovary), but also in female and male germ cells in the early developmental stages, such as those of previtellogenic oocytes, spermatogonia, spermatocytes and spermatids. These results indicated that Lczar1 and Lcwt1b possibly play roles in gonadal development. Therefore, the findings of this study will provide a basis for clarifying the mechanism of Lczar1 and Lcwt1b in regulating germ cell development and the sex reversal of Asian seabass and even other hermaphroditic species.

Embryonic arrest: causes and implications

PURPOSE OF REVIEW

Embryonic arrest is a key determinant of the number of euploid blastocysts obtained after IVF. Here, we review factors that are implicated in the developmental arrest of preimplantation embryos and their relevance for assisted reproduction outcomes.

RECENT FINDINGS

Among the treatment options available to infertile women, IVF is the one associated with most favorable outcomes. The cumulative pregnancy rates in women undergoing IVF are determined by aneuploidy rate (age), ovarian response to stimulation (ovarian reserve), and the rate of embryo developmental arrest. Mutations in maternal effect genes, especially those encoding for subcortical maternal complex, have been implicated in human embryo developmental arrest. In addition, perturbation of biological processes, such as mitochondrial unfolded protein response and long noncoding RNA regulatory pathways, may play a role. However, how each of these factors contributes to embryos' arrest in different cohorts and age groups has not been determined.

SUMMARY

Arrest of human embryos during preimplantation development is a common occurrence and is partly responsible for the limited number of euploid blastocysts obtained in assisted reproduction cycles. Although genetic and metabolic causes have been implicated, the mechanisms responsible for human embryo developmental arrest remain poorly characterized.

Landscape of pathogenic mutations in premature ovarian insufficiency

Premature ovarian insufficiency (POI) is a major cause of female infertility due to early loss of ovarian function. POI is a heterogeneous condition, and its molecular etiology is unclear. To identify genetic variants associated with POI, here we performed whole-exome sequencing in a cohort of 1,030 patients with POI. We detected 195 pathogenic/likely pathogenic variants in 59 known POI-causative genes, accounting for 193 (18.7%) cases. Association analyses comparing the POI cohort with a control cohort of 5,000 individuals without POI identified 20 further POI-associated genes with a significantly higher burden of loss-of-function variants. Functional annotations of these novel 20 genes indicated their involvement in ovarian development and function, including gonadogenesis (LGR4 and PRDM1), meiosis (CPEB1, KASH5, MCMDC2, MEIOSIN, NUP43, RFWD3, SHOC1, SLX4 and STRA8) and folliculogenesis and ovulation (ALOX12, BMP6, H1-8, HMMR, HSD17B1, MST1R, PPM1B, ZAR1 and ZP3). Cumulatively, pathogenic and likely pathogenic variants in known POI-causative and novel POI-associated genes contributed to 242 (23.5%) cases. Further genotype-phenotype correlation analyses indicated that genetic contribution was higher in cases with primary amenorrhea compared to that in cases with secondary amenorrhea. This study expands understanding of the genetic landscape underlying POI and presents insights that have the potential to improve the utility of diagnostic genetic screenings.

The translation regulator Zar1l controls timing of meiosis in Xenopus oocytes

Oocyte maturation and early embryo development occur in vertebrates in the near absence of transcription. Thus, sexual reproduction of vertebrates critically depends on the timely translation of mRNAs already stockpiled in the oocyte. Yet how translational activation of specific mRNAs is temporally coordinated is still incompletely understood. Here, we elucidate the function of Zar1l, a yet uncharacterized member of the Zar RNA-binding protein family, in Xenopus oocytes. Employing TRIM-Away, we demonstrate that loss of Zar1l accelerates hormone-induced meiotic resumption of Xenopus oocytes due to premature accumulation of the M-phase-promoting kinase cMos. We show that Zar1l is a constituent of a large ribonucleoparticle containing the translation repressor 4E-T and the central polyadenylation regulator CPEB1, and that it binds directly to the cMos mRNA. Partial, hormone-induced degradation of Zar1l liberates 4E-T from CPEB1, which weakens translational repression of mRNAs encoding cMos and likely additional M-phase-promoting factors. Thus, our study provides fundamental insights into the mechanisms that ensure temporally regulated translation of key cell cycle regulators during oocyte maturation, which is essential for sexual reproductivity.

De novo gonad transcriptome analysis of elongate loach (Leptobotia elongata) provides novel insights into sex-related genes

Elongate loach (Leptobotia elongata) is endemic in middle and upper reaches of the Yangtze River in China. Because of many anthropogenic factors such as overfishing and dam construction, the loach has become a highly endangered species. So far, the genomic resources which benefit for species conservation and utilization are still lacking in elongate loach. Therefore, the first gonad transcriptome analysis of the loach was conducted in this study, providing novel insights into sex-related genes. A total of 286,800,660 clean reads with a total length of 42.02 Gb were obtained. 18,975 differentially expressed genes (DEGs) were identified, where 12,976 DEGs, especially Sox9a, Sox9b, Igf2 and Fgfr2, were upregulated in the testis, and 5999 DEGs, especially Zp3, Eg2, Plk1, Ccnb1, Cdc20 and Mos, were upregulated in the ovary. Meanwhile, some testis-specific genes (i.e. Cald1, Atp1a, Muc2 and Ca2) and ovary-specific genes (i.e. Ca4, Tuba, Acp5, Ccna, Larp6 and Nop4) were identified and verified. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses of DEGs, we found a series of enrichment pathways related to reproduction in elongate loach, such as the MAPK signaling pathway, oxytocin signaling pathway and oocyte meiosis pathway. Twelve DEGs were randomly selected to verify RNA-seq results by qPCR. In conclusion, this study provides a data source to study the molecular characteristics and regulatory mechanisms of sex-related genes in elongate loach, which has a potential to improve the resource protection and aquaculture production of the loach.

H3K27ac chromatin acetylation and gene expression analysis reveal sex- and situs-related differences in developing chicken gonads

BACKGROUND

Birds exhibit a unique asymmetry in terms of gonad development. The female left gonad generates a functional ovary, whereas the right gonad regresses. In males, both left and right gonads would develop into testes. How is this left/right asymmetry established only in females but not in males remains unknown. The epigenetic regulation of gonadal developmental genes may contribute to this sex disparity. The modification of histone tails such as H3K27ac is tightly coupled to chromatin activation and gene expression. To explore whether H3K27ac marked chromatin activation is involved in the asymmetric development of avian gonads, we probed genome-wide H3K27ac occupancy in left and right gonads from both sexes and related chromatin activity profile to the expression of gonadal genes. Furthermore, we validated the effect of chromatin activity on asymmetric gonadal development by manipulating the chromatin histone acetylation levels.

METHODS

The undifferentiated gonads from both sides of each sex were collected and subjected to RNA-Seq and H3K27ac ChIP-Seq experiments. Integrated analysis of gene expression and active chromatin regions were performed to identify the sex- and situs-specific regulation and expression of gonadal genes. The histone deacetylase inhibitor trichostatin A (TSA) was applied to the undifferentiated female right gonads to assess the effect of chromatin activation on gonadal gene expression and cell proliferation.

RESULTS

Even before sex differentiation, the gonads already show divergent gene expression between different sexes and between left/right sides in females. The sex-specific H3K27ac chromatin distributions coincide with the higher expression of male/female specification genes in each sex. Unexpectedly, the H3K27ac marked chromatin activation show a dramatic difference between left and right gonads in both sexes, although the left/right asymmetric gonadal development was observed only in females but not in males. In females, the side-specific H3K27ac occupancy instructs the differential expression of developmental genes between the pair of gonads and contributes to the development of left but not right gonad. However, in males, the left/right discrepancy of H3K27ac chromatin distribution does not drive the side-biased gene expression or gonad development. The TSA-induced retention of chromatin acetylation causes up-regulation of ovarian developmental genes and increases cell proliferation in the female right gonad.

CONCLUSIONS

We revealed that left/right asymmetry in H3K27ac marked chromatin activation exists in both sexes, but this discrepancy gives rise to asymmetric gonadal development only in females. Other mechanisms overriding the chromatin activation would control the symmetric development of male gonads in chicken.

Revisiting ZAR proteins: the understudied regulator of female fertility and beyond

Putative RNA-binding proteins (RBPs), zygote arrested-1 (ZAR1), and ZAR2 (also known as ZAR1L), have been identified as maternal factors that mainly function in oogenesis and embryogenesis. Despite divergence in their spatio-temporal expression among species, the CxxC structure of the C-terminus of ZAR proteins is highly conserved and is reported to be the functional domain for the activity of the RBPs of ZAR proteins. In oocytes from Xenopus laevis and zebrafish, ZAR proteins have been reported to bind to maternal transcripts and inhibit translation in immature growing oocytes, whereas in fully grown mouse oocytes, they promote the translation during meiotic maturation. Thus, ZAR1 and ZAR2 may be required for the maternal-to-zygotic transition by stabilizing the maternal transcriptome in oocytes with partial functional redundancy. In addition, recent studies have suggested non-ovarian expression and function of ZAR proteins, particularly their involvement in tumorigenesis. ZAR proteins are potentially associated with tumor suppressors and can serve as epigenetically inactivated cancer biomarkers. In this review, studies on Zar1/2 are systematically summarized, and some issues that require discussion and further investigation are introduced as perspectives.

Mating-Induced Trade-Offs upon Egg Production versus Fertilization and Offspring's Survival in a Sawfly with Facultative Parthenogenesis

Investigation of mating-induced trade-offs between reproduction and survival is conducive to provide evolutionary insights into reproductive strategies and aging. Here, we used RNAseq and bioinformatics to reveal mating-induced changes of genes and pathways related to reproduction and survival in female Cephalcia chuxiongica, a pine defoliator with facultative parthenogenesis and long larval dormancy. Results showed that mating induced substantial downregulation on genes and pathways associated to immunity, stress response, and longevity. However, mating induced divergent reproductive response, with downregulation on genes and pathways related to egg production while upregulation on genes and pathways related to egg fertilization. Considering the nature of limited resources in adults, low fecundity, and egg protection behavior in C. chuxiongica, we suggest that mating triggers trade-offs between reproduction and survival in this insect and females of this species may have evolved specific strategies to adapt to the environmental and hosts' conditions, e.g., restrict whole fecundity to ensure higher fertilization and offspring's survival. Moreover, mating induced significant responses on genes and pathways that play important roles in vertebrate reproduction while their function in insects are unclear, such as the progesterone-mediated oocyte maturation pathway; the significant regulation after mating suggests that their function may be evolutionarily conserved in animal kingdom.

Modulation of folliculogenesis in adult laying chickens by bisphenol A and bisphenol S: Perspectives on ovarian morphology and gene expression

Both bisphenol A (BPA) and its analog bisphenol S (BPS) are industrial chemicals that have been used to make certain plastic products applied in chicken farms, including food and water containers. They are endocrine disrupting chemicals (EDCs) with xenoestrogenic activities and affect reproductive success in many ways. It was hypothesized that BPA and BPS could adversely affect the folliculogenesis in chickens due to their disruption of the estrogen responses, using either genomic or non-genomic mechanisms. This study investigated the deleterious effects of BPA and BPS on the ovaries when adult layer chickens were orally treated with these EDCs at 50 μg/kg body weight, the reference dose for chronic oral exposure of BPA established by the U.S. EPA. The chickens in both BPA and BPS-treated groups showed a decreased number of the preovulatory follicles. BPA-treated chickens showed a significant decrease in the diameter of F1. Additionally, both BPA and BPS treatments increased the infiltrations of lymphocytes and plasma cells in ovaries. Moreover, it was found that the ovaries of BPS-treated chickens weighed the most among the groups. RNA sequencing and subsequent pathway enrichment analysis of differentially expressed genes revealed that both BPA- and BPS-treatment groups showed significant changes in gene expression and pathways related to reproduction, immune function and carcinogenesis. Taken together, both BPA and BPS are potentially carcinogenic and have deleterious effects on the fertility of laying chickens by inducing inflammation, suggesting that BPS may not be a safe replacement for BPA.

Transcriptome Profiling of the Ovarian Cells at the Single-Cell Resolution in Adult Asian Seabass

Single-cell RNA sequencing (scRNA-seq) is widely adopted for identifying the signature molecular markers or regulators in cells, as this would benefit defining or isolating various types of cells. Likewise, the signature transcriptome profile analysis at the single cell level would well illustrate the key regulators or networks involved in gametogenesis and gonad development in animals; however, there is limited scRNA-seq analysis on gonadal cells in lower vertebrates, especially in the sexual reversal fish species. In this study, we analyzed the molecular signature of several distinct cell populations of Asian seabass adult ovaries through scRNA-seq. We identified five cell types and also successfully validated some specific genes of germ cells and granulosa cells. Likewise, we found some key pathways involved in ovarian development that may concert germline-somatic interactions. Moreover, we compared the transcriptomic profiles across fruit fly, mammals, and fish, and thus uncovered the conservation and divergence in molecular mechanisms that might drive ovarian development. Our results provide a basis for studying the crucial features of germ cells and somatic cells, which will benefit the understandings of the molecular mechanisms behind gametogenesis and gonad development in fish.

FAX-RIC enables robust profiling of dynamic RNP complex formation in multicellular organisms in vivo

RNA-protein interaction is central to post-transcriptional gene regulation. Identification of RNA-binding proteins relies mainly on UV-induced crosslinking (UVX) followed by the enrichment of RNA-protein conjugates and LC-MS/MS analysis. However, UVX has limited applicability in tissues of multicellular organisms due to its low penetration depth. Here, we introduce formaldehyde crosslinking (FAX) as an alternative chemical crosslinking for RNA interactome capture (RIC). Mild FAX captures RNA-protein interaction with high specificity and efficiency in cell culture. Unlike UVX-RIC, FAX-RIC robustly detects proteins that bind to structured RNAs or uracil-poor RNAs (e.g. AGO1, STAU1, UPF1, NCBP2, EIF4E, YTHDF proteins and PABP), broadening the coverage. Applied to Xenopus laevis oocytes and embryos, FAX-RIC provided comprehensive and unbiased RNA interactome, revealing dynamic remodeling of RNA-protein complexes. Notably, translation machinery changes during oocyte-to-embryo transition, for instance, from canonical eIF4E to noncanonical eIF4E3. Furthermore, using Mus musculus liver, we demonstrate that FAX-RIC is applicable to mammalian tissue samples. Taken together, we report that FAX can extend the RNA interactome profiling into multicellular organisms.

Crosstalk Between Retinoic Acid and Sex-Related Genes Controls Germ Cell Fate and Gametogenesis in Medaka

Sex determination (SD) is a highly diverse and complex mechanism. In vertebrates, one of the first morphological differences between the sexes is the timing of initiation of the first meiosis, where its initiation occurs first in female and later in male. Thus, SD is intimately related to the responsiveness of the germ cells to undergo meiosis in a sex-specific manner. In some vertebrates, it has been reported that the timing for meiosis entry would be under control of retinoic acid (RA), through activation of Stra8. In this study, we used a fish model species for sex determination and lacking the stra8 gene, the Japanese medaka (Oryzias latipes), to investigate the connection between RA and the sex determination pathway. Exogenous RA treatments act as a stress factor inhibiting germ cell differentiation probably by activation of dmrt1a and amh. Disruption of the RA degrading enzyme gene cyp26a1 induced precocious meiosis and oogenesis in embryos/hatchlings of female and even some males. Transcriptome analyzes of cyp26a1–/–adult gonads revealed upregulation of genes related to germ cell differentiation and meiosis, in both ovaries and testes. Our findings show that germ cells respond to RA in a stra8 independent model species. The responsiveness to RA is conferred by sex-related genes, restricting its action to the sex differentiation period in both sexes.

A story of birth and death: mRNA translation and clearance at the onset of maternal-to-zygotic transition in mammals†

In mammals, maternal-to-zygotic transition (MZT), or oocyte-to-embryo transition, begins with oocyte meiotic resumption due to the sequential translational activation and destabilization of dormant maternal transcripts stored in the ooplasm. It then continues with the elimination of maternal transcripts during oocyte maturation and fertilization and ends with the full transcriptional activation of the zygotic genome during embryonic development. A hallmark of MZT in mammals is its reliance on translation and the utilization of stored RNAs and proteins, rather than de novo transcription of genes, to sustain meiotic maturation and early development. Impaired maternal mRNA clearance at the onset of MZT prevents zygotic genome activation and causes early arrest of developing embryos. In this review, we discuss recent advances in our knowledge of the mechanisms whereby mRNA translation and degradation are controlled by cytoplasmic polyadenylation and deadenylation which set up the competence of maturing oocyte to accomplish MZT. The emphasis of this review is on the mouse as a model organism for mammals and BTG4 as a licensing factor of MZT under the translational control of the MAPK cascade.

The ZAR1 protein in cancer; from epigenetic silencing to functional characterisation and epigenetic therapy of tumour suppressors

ZAR1, zygote arrest 1, is a zinc finger protein (C-terminus), which was initially identified in mouse oocytes. Later it was found that its expression is present in various human tissues e.g. lung and kidney. Interestingly, it was observed that in various tumour types the ZAR1 transcript is missing due to hypermethylation of its CpG island promoter, but not ZAR2. Since methylation of the ZAR1 promoter is described as a frequent event in tumourigenesis, ZAR1 could serve as a useful diagnostic marker in cancer screens. ZAR1 was described as a useful prognostic/diagnostic cancer marker for lung cancer, kidney cancer, melanoma and possibly liver carcinoma. Furthermore, ZAR1 was reactivated as a tumour suppressor by epigenetic therapy using CRISPR-dCas9 method. This method holds the potential to precisely target not only ZAR1 and reactivate tumour suppressors in a tailored cancer therapy. ZAR1 is highly conserved amongst vertebrates, especially its zinc finger, which is the relevant domain for its protein and RNA binding ability. ZAR1 is implicated in various cellular mechanisms including regulation of oocyte/embryo development, cell cycle control and mRNA binding, though little was known about the underlying mechanisms. ZAR1 was reported to regulate and activate translation through the binding to TCS translation control sequences in the 3'UTRs of its target mRNA the kinase WEE1. ZAR1 has a tumour suppressing function by inhibiting cell cycle progression. Here we review the current literature on ZAR1 focusing on structural, functional and epigenetic aspects. Characterising the cellular mechanisms that regulate the signalling pathways ZAR1 is involved in, could lead to a deeper understanding of tumour development and, furthermore, to new strategies in cancer treatment.

Variation Screening of Zygote Arrest 1(ZAR1) in Women with Recurrent Zygote Arrest During IVF/ICSI Programs

Human zygote arrest during in vitro culture is rare and the etiology is unclear. The oocyte-specific gene Zar1 plays an essential role in oocyte-embryo transition, and most embryos from Zar1 knockout female mice arrest at the one-cell stage. This study investigates whether maternal ZAR1 gene variations play a role in human zygote arrest. Sequence analysis of ZAR1 was conducted for 47 women with recurrent uncleaved zygotes in in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) cycles (≥ 70% zygotes uncleaved in at least 2 cycles), 93 women from IVF/ICSI cycles with normal uncleaved rate and live birth (control subset I) and 188 women with spontaneous pregnancy and live birth (control subset II). One novel synonymous variation (c.516C>T) and one novel intron variation (c.964-55A>T) of ZAR1 were identified in the zygote arrest group but not in any of the 188 controls. However, the bioinformatics analysis revealed that neither of the mutations in ZAR1 has effect on ZAR1 protein function. Compared with control subset I, the allele frequencies of rare SNPs rs117545505 and rs17609740 were significantly different in patients with zygote arrest (P = 0.047, OR = 3.66). Allele frequencies of these two SNPs were also significantly different between the case group and control subset II (P = 0.024, OR = 3.28). In conclusion, two SNPs in ZAR1 are associated with human zygote arrest, although additional proof is needed for validation.

Characterizing transcriptome in female scallop Chlamys farreri provides new insights into the molecular mechanisms of reproductive regulation during ovarian development and spawn

Bivalve mollusks are descendants of an early-Cambrian lineage and have successfully evolved unique strategies for reproduction. Nonetheless, the molecular mechanisms underlying reproductive regulation in mollusks remain to be elucidated. In this study, transcriptomes of ovary at four reproductive stages in female Chlamys farreri were characterized by RNA-Seq. Regarding signaling pathways, ECM-receptor interaction pathway, mTOR signaling pathway, Fanconi anemia pathway, FoxO signaling pathway, Wnt signaling pathway and Hedgehog signaling pathway were enriched during ovarian development processes. In addition, pathways related to energy metabolism such as Nitrogen metabolism and Arachidonic acid metabolism were enriched at spawn stage. Interestingly, Neuroactive ligand-receptor interaction was significantly enriched involved in ovarian development and spawn, and indicated the potential functions of nervous system on reproductive regulation in C. farreri. What's more, this study identified and characterized fourteen genes involved in "sex hormones synthesis and regulation", "ovarian development and spawn" and "maternal immunity" during the four reproductive stages in C. farreri. We determined that CYP17 uniquely affected gamete release by influencing the physiological balance among the steroid hormones and showed that receptors of the 5-HT and GABA neurotransmitters were tightly associated with ovarian maturation. Furthermore, to the best of our knowledge, this is the first study to report the maternal effect gene Zar1 in bivalve mollusks, likewise the maternal immunity genes displayed coordinated and cooperative expression during reproductive periods, which strengthened the environmental adaptation mechanisms of bivalves. Taken together, this study provides the first dynamic transcriptomic analysis of C. farreri at four key reproductive stages, which will assist in revealing the molecular mechanisms underlying bivalves on reproductive regulation in ovarian development and spawn.

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.

Zebrafish as a model for studying ovarian development: Recent advances from targeted gene knockout studies

Ovarian development is a complex process controlled by precise coordination of multiple factors. The targeted gene knockout technique is a powerful tool to study the functions of these factors. The successful application of this technique in mice in the past three decades has significantly enhanced our understanding on the molecular mechanism of ovarian development. Recently, with the advent of genome editing techniques, targeted gene knockout research can be carried out in many species. Zebrafish has emerged as an excellent model system to study the control of ovarian development. Dozens of genes related to ovarian development have been knocked out in zebrafish in recent years. Much new information and perspectives on the molecular mechanism of ovarian development have been obtained from these mutant zebrafish. Some findings have challenged conventional views. Several genes have been identified for the first time in vertebrates to control ovarian development. Focusing on ovarian development, the purpose of this review is to briefly summarize recent findings using these gene knockout zebrafish models, and compare these findings with mammalian models. These established mutants and rapid development of gene knockout techniques have prompted zebrafish as an ideal animal model for studying ovarian development.

Comparative transcriptome analysis of male and female gonads reveals sex-biased genes in spotted scat (Scatophagus argus)

Scatophagus argus is a new emerging aquaculture fish in East and Southeast Asia. To date, research on reproductive development and regulation in S. argus is lacking. Additionally, genetic and genomic information about reproduction, such as gonadal transcriptome data, is also lacking. Herein, we report the first gonadal transcriptomes of S. argus and identify genes potentially involved in reproduction and gonadal development. A total of 136,561 unigenes were obtained by sequencing of testes (n = 3) and ovaries (n = 3) at stage III. Genes upregulated in males and females known to be involved in gonadal development and gametogenesis were identified, including male-biased dmrt1, amh, gsdf, wt1a, sox9b, and nanos2, and female-biased foxl2, gdf9, bmp15, sox3, zar1, and figla. Serum estradiol-17β and 11-ketotestosterone levels were biased in female and male fish, respectively. Sexual dimorphism of serum steroid hormone levels were interpreted after expression analysis of 20 steroidogenesis-related genes, including cyp19a1a and cyp11b2. This gonadal transcript dataset will help investigate functional genes related to reproduction in S. argus.

Gonadal transcriptome analysis of the common carp, Cyprinus carpio: Identification of differentially expressed genes and SSRs

Common carp (Cyprinus carpio) is a world-wide freshwater fish of eutrophic waters. C. carpio, have various reproductive traits, including early sexual maturity, that may make them excellent, large, realistic, aquaculture model species. In the present work, de novo assembly of gonadal (testicular and ovarian) transcriptomes from juvenile common carp was performed to identify genes involved in gonadal development. A total of 81,757 and 43,257 transcripts with average lengths of 769 and 856 bp, were obtained from the immature testicular and ovarian transcriptomes, respectively. About 84,367 unigenes were constructed after removing redundancy involving representation of transcripts in both gonadal transcriptomes. Gene ontology (39,171 unigenes), clusters of orthologous group's analysis (6651 unigenes) and Kyoto encyclopedia of genes, and genomes automatic annotation server analysis (4783 unigenes) were performed to identify potential genes along with their functions. Furthermore, 18,342 (testis) and 8693 (ovary) simple sequence repeats were identified. About 298 differentially expressed genes were identified, of which 171 and 127 genes were up-regulated in testis and ovary, respectively. Quantitative real-time reverse transcription PCR was performed to validate differential expression of selected genes in testis and ovary. Nearly 809 genes related to reproduction were identified, sex-wise expression pattern of genes related to steroid synthesis, endocrine regulation, germ cell maintenance and others factors related to gonadal differentiation was observed, and expression analysis of nanos, ad4bp/sf-1, and gdf9 was performed. The present study identified certain important genes/factors involved in the gonadal development of C. carpio which may provide insights into the understanding of sex-differentiation and gonadal development processes.

Gene-specific profiling of DNA methylation and mRNA expression in bovine oocytes derived from follicles of different size categories

Epigenetic changes, such as DNA methylation, play an essential role in the acquisition of full developmental competence by mammalian oocytes during the late follicular growth phase. Here we used the bovine model to investigate the DNA methylation profiles of seven candidate genes (imprinted: bH19, bSNRPN; non-imprinted: bZAR1, bDNMT3A, bOCT4, bDNMT3 Lo and bDNMT3 Ls) and the mRNA expression of nine candidate genes (imprinted: bSNRPN, bPEG3, bIGF2R; non-imprinted: bPRDX1, bDNMT1B, bDNMT3A, bZAR1, bHSF1 and bNLRP9) in oocytes from antral follicles of three different size classes (≤2mm, 3-5mm, ≥6mm) to unravel the epigenetic contribution to this process. We observed an increased number of aberrantly methylated alleles in bH19, bSNRPN and bDNMT3 Lo of oocytes from small antral follicles (≤2mm), correlating with lower developmental competence. Furthermore, we detected an increased frequency of CpG sites with an unclear methylation status for DNMT3 Ls, specifically in oocytes from follicles ≥6mm, predominantly at three CpG positions (CpG2, CpG7 and CpG8), of which CpG7 is a potential regulatory site. No major differences in mRNA expression were observed, indicating that the transcriptional machinery may not yet be active during the follicular growth phase. Our results support the notion that a follicle diameter of ~2mm is a critical stage for establishing DNA methylation profiles and indicate a link between DNA methylation and the acquisition of oocyte developmental competence.

Acquisition of oocyte competence to develop as an embryo: integrated nuclear and cytoplasmic events

Infertility affects ~7% of couples of reproductive age with little change in incidence in the last two decades. ART, as well as other interventions, have made major strides in correcting this condition. However, and in spite of advancements in the field, the age of the female partner remains a main factor for a successful outcome. A better understanding of the final stages of gamete maturation yielding an egg that can sustain embryo development and a pregnancy to term remains a major area for improvement in the field. This review will summarize the major cellular and molecular events unfolding at the oocyte-to-embryo transition. We will provide an update on the most important processes/pathways currently understood as the basis of developmental competence, including the molecular processes involved in mRNA storage, its recruitment to the translational machinery, and its degradation. We will discuss the hypothesis that the translational programme of maternal mRNAs plays a key role in establishing developmental competence. These regulations are essential to assemble the machinery that is used to establish a totipotent zygote. This hypothesis further supports the view that embryogenesis begins during oogenesis. A better understanding of the events required for developmental competence will guide the development of novel strategies to monitor and improve the success rate of IVF. Using this information, it will be possible to develop new biomarkers that may be used to better predict oocyte quality and in selection of the best egg for IVF.

ZAR1 knockdown promotes the differentiation of human neuroblastoma cells by suppression of MYCN expression

Although DNA hypermethylation at non-promoter region of the Zygote arrest 1 (ZAR1) gene has been observed in many types of tumor, including neuroblastoma (NB), the role of this gene in tumor development and/or progression is unclear. One reason is that knowledge about the function of ZAR1 protein is limited. Although it has been reported that ZAR1 plays a crucial role in early embryogenesis and may act as a transcriptional repressor for some transcripts, the detailed mechanism is still elusive. In the present study, we analyzed public data of NB patients and found that higher expression levels of ZAR1 were significantly associated with a shorter survival period. Consistent with this result, ZAR1-depleted NB cells showed well-differentiated phenotypes with elongated neurites and upregulated expression of TRKA and RET, which are markers for differentiated NB. Moreover, the expression level of MYCN protein was markedly suppressed in ZAR1-depleted NB cells. MYCN-depleted cells showed similar phenotypes to ZAR1-depleted cells. The present findings indicate that ZAR1 has oncogenic effects in NB by suppressing cell differentiation via regulation of MYCN expression.

Cloning and expression analysis of zygote arrest 1 (Zar1) in New Zealand white rabbits

Zygote arrest 1 (Zar1) is an oocyte-specific maternal-effect gene. Previous studies indicate that Zar1 plays important role in early embryo development, but little is known about its function in rabbit. The objectives of this study were to clone the New Zealand white rabbit Zar1 gene and to investigate its expression in various organs in groups of animals with different reproductive traits.We obtained a 709-bp Zar1 cDNA fragment consisting of an 8-bp exon 1, 161-bp exon 2, 75-bp exon 3, 271-bp exon 4 and 194-bp 3'sequences. The rabbit Zar1 nucleotide sequence showed per cent identities of 91, 88, 88, 87, 86, 87, 76 and 82% with Zar1 orthologues in human, cattle, sheep, pig, mouse, rat, zebrafish and Xenopus laevis, respectively, indicating a high homology with other species and evolutionary conservation. Quantitative real-time polymerase chain reaction analyses revealed nonoocyte-specific Zar1 expression, with expression in spleen, lung, ovary, uterus, heart, liver and kidney. The expression level was highest in the lung. This study may lay the theoretical foundation for the study of ZAR1's biological function.

ZAR1 is a novel epigenetically inactivated tumour suppressor in lung cancer

BACKGROUND

Lung cancer is the leading cause of cancer-related deaths with 1.8 million new cases each year and poor 5-year prognosis. Promoter hypermethylation of tumour suppressors leads to their inactivation and thereby can promote cancer development and progression.

RESULTS

In this study, we analysed ZAR1 (zygote arrest 1), which has been said to be a maternal-effect gene and its expression mostly limited to certain reproductive tissues. Our study shows that ZAR1 is expressed in normal lung but inactivated by promoter methylation in lung cancer. ZAR1 is hypermethylated in primary lung cancer samples (22% small cell lung carcinoma (SCLC) and 76% non-small cell lung carcinoma (NSCLC), p < 0.001) vs. normal control lung tissue (11%). In lung cancer cell lines, ZAR1 was significantly methylated in 75% of SCLC and 83% of NSCLC vs. normal tissue (p < 0.005/0.05). In matching tumours and control tissues, we observed that NSCLC primary tumour samples exhibited a tumour-specific promoter methylation of ZAR1 in comparison to the normal control lung tissue. Demethylation treatment of various lung cancer cell lines reversed ZAR1 promoter hypermethylation and subsequently re-established ZAR1 expression. In addition, we could show the growth inhibitory potential of ZAR1 in lung cancer cell lines and cancer cell lines. Exogenous expression of ZAR1 not only inhibited colony formation but also blocked cell cycle progression of cancer cell lines.

CONCLUSIONS

Our study shows for the first time the lung tumour-specific epigenetic inactivation of ZAR1 due to DNA methylation of its CpG island promoter. Furthermore, ZAR1 was characterised by the ability to block tumour growth through the inhibition of cell cycle progression in cancer cell lines. We propose that ZAR1 could serve as an epigenetically inactivated biomarker in lung cancer.

Translation repression by maternal RNA binding protein Zar1 is essential for early oogenesis in zebrafish

A large amount of maternal RNA is deposited in oocytes and is reserved for later development. Control of maternal RNA translation during oocyte maturation has been extensively investigated and its regulatory mechanisms are well documented. However, translational regulation of maternal RNA in early oogenesis is largely unexplored. In this study, we generated zebrafish zar1 mutants that result in early oocyte apoptosis and fully penetrant male development. Loss of p53 suppresses the apoptosis in zar1 mutants and restores oocyte development. zar1 immature ovaries show upregulation of proteins implicated in endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). More importantly, loss of Zar1 causes marked upregulation of zona pellucida (ZP) family proteins, while overexpression of ZP proteins in oocytes causes upregulation of stress-related activating transcription factor 3 (atf3), arguing that tightly controlled translation of ZP proteins is essential for ER homeostasis during early oogenesis. Furthermore, Zar1 binds to ZP gene mRNAs and represses their translation. Together, our results indicate that regulation of translational repression and de-repression are essential for precisely controlling protein expression during early oogenesis.

Pipeline for contraceptive development

The high rates of unplanned pregnancy reflect an unmet need for effective contraceptive methods for women, especially for individuals with health risks such as obesity, diabetes, hypertension, and other conditions that may contraindicate use of an estrogen-containing product. Improvements in safety, user convenience, acceptability, and availability of products remain important goals of the contraceptive development program. Another important goal is to minimize the impact of the products on the environment. Development of new methods for male contraception has the potential to address many of these issues of safety for women who have contraindications to effective contraceptive methods but want to protect against pregnancy. It would also address a huge unmet need for men who want to control their fertility. Products under development for men would not introduce ecotoxic hormones into the water system.

Zygote arrest 1, nucleoplasmin 2, and developmentally associated protein 3 mRNA profiles throughout porcine embryo development in vitro

Maternal effect genes (MEGs) are expressed in oocytes and embryos and play an important role in activation of the embryonic genome. An abnormality in the expression of these genes may lead to arrest of embryonic cleavage or to altered transcription of factors responsible for further embryonic development. In vitro-produced porcine embryos have a lower developmental potential than embryos produced in vivo. We hypothesized that in vitro embryo culture conditions have an effect on the expression of MEGs at various developmental stages, which may affect their developmental potential. Here, using real-time polymerase chain reaction, we examined mRNA profiles of the MEGs, zygote arrest 1 (ZAR-1), nucleoplasmin 2 (NPM2), and developmentally associated pluripotency protein 3 (DPPA3), in porcine oocytes and embryos produced in vitro and in vivo. Further, we evaluated the effect of the combined addition of EGF, interleukin 1β, and leukemia inhibitory factor to the porcine in vitro embryo production system on mRNA profiles of selected MEGs. Finally, we studied localization of the MEG protein products in in vitro-obtained oocytes and embryos using confocal microscopy. We found that the ZAR-1 mRNA profile differed throughout in vitro and in vivo embryo development. In the embryos produced in vitro, the decrease in ZAR-1 mRNA levels was observed at the 2-cell stage, whereas in in vivo embryos, ZAR-1 mRNA levels declined significantly starting at the 4-cell stage (P < 0.05). In vitro culture conditions affected transiently also DPPA3 mRNA levels at the 4-cell stage (P < 0.05). There was no difference in the NPM2 mRNA profile during in vitro and in vivo embryo development. The ZAR-1 and DPPA3 proteins were localized in the cytoplasm of the oocytes and embryos, whereas the NPM2 protein was found both in the cytoplasm and in the nucleus. All proteins were expressed until blastocyst stage. The addition of EGF and cytokines to the culture medium decreased DPPA3 mRNA levels in 8-cell embryos (P < 0.05). This study indicated that IVC conditions affect ZAR-1 mRNA levels before the 4-cell stage, which may disturb the activation of the embryonic genome in pigs. The expression of the proteins after the 4-cell to 8-cell transition indicates that these factors play a role beyond activation of the embryonic genome. Supplementation of the culture media with EGF and cytokines affects DPPA3 mRNA levels after maternal to embryonic transition.

Expressão gênica em ovócitos suínos de diferentes classificações morfológicas

A produção in vitro de embriões suínos tem alcançado resultados insatisfatórios: ovócitos maturados in vivo produzem uma porcentagem maior de embriões em relação aos maturados in vitro. O sucesso da maturação in vitro está diretamente relacionado com a competência ovocitária. Somente ovócitos competentes são capazes de serem fecundados e terem desenvolvimento embrionário normal. A competência ovocitária pode ser avaliada por vários parâmetros. Recentemente têm sido utilizados como parâmetro os estudos da expressão de genes associados com a competência. O presente trabalho teve por objetivo avaliar diferenças na expressão dos genes BMP15, RYBP, MATER e ZAR1 em ovócitos imaturos de diferentes classes morfológicas, sendo elas: 1, 2, 3 e 4, com a finalidade de proporcionar importantes marcadores moleculares relacionados com a capacidade ovocitária. O RNA total dos ovócitos foi extraído e utilizado como molde para a síntese da primeira fita de cDNA. Os resultados da expressão gênica foram analisados utilizando-se modelo misto, considerando os dados de expressão gênica variável dependente e as classes ovocitárias variáveis independentes. Os genes BMP15, ZAR1 e RYBP apresentaram expressão semelhante nas classes ovocitárias 1, 2 e 3; somente a categoria 4 diferiu na expressão desses genes (P<0,05). O gene MATER foi expresso de forma semelhante em todas as classes ovocitárias estudadas (P>0,05). A técnica de RT-qPCR foi eficiente para detecção desses transcritos em ovócitos de diferentes classes. No entanto, para melhor entendimento do envolvimento desses transcritos na aquisição da competência ovocitária, são necessários mais estudos avaliando ovócitos de diferentes classes morfológicas, em diferentes fases de desenvolvimento, e implicação de outros genes envolvidos com a competência ovocitária.

Promising Loci and Genes for Yolk and Ovary Weight in Chickens Revealed by a Genome-Wide Association Study

Because it serves as the cytoplasm of the oocyte and provides a large amount of reserves, the egg yolk has biological significance for developing embryos. The ovary and its hierarchy of follicles are the main reproductive organs responsible for yolk deposition in chickens. However, the genetic architecture underlying the yolk and ovarian follicle weights remains elusive. Here, we measured the yolk weight (YW) at 11 age points from onset of egg laying to 72 weeks of age and measured the follicle weight (FW) and ovary weight (OW) at 73 weeks as part of a comprehensive genome-wide association study (GWAS) in 1,534 F₂ hens derived from reciprocal crosses between White Leghorn (WL) and Dongxiang chickens (DX). For all ages, YWs exhibited moderate single nucleotide polymorphism (SNP)-based heritability estimates (0.25–0.38), while the estimates for FW (0.16) and OW (0.20) were relatively low. Independent univariate genome-wide screens for each trait identified 12, 3, and 31 novel significant associations with YW, FW, and OW, respectively. A list of candidate genes such as ZAR1, STARD13, ACER1b, ACSBG2, and DHRS12 were identified for having a plausible function in yolk and follicle development. These genes are important to the initiation of embryogenesis, lipid transport, lipoprotein synthesis, lipid droplet promotion, and steroid hormone metabolism, respectively. Our study provides for the first time a genome-wide association (GWA) analysis for follicle and ovary weight. Identification of the promising loci as well as potential candidate genes will greatly advance our understanding of the genetic basis underlying dynamic yolk weight and ovarian follicle development and has practical significance in breeding programs for the alteration of yolk weight at different age points.

Extended in vitro maturation affects gene expression and DNA methylation in bovine oocytes

To mimic post-ovulatory ageing, we have extended the in vitro maturation (IVM) phase to 48 h and examined effects on (i) developmental potential, (ii) expression of a panel of developmentally important genes and (iii) gene-specific epigenetic marks. Results were compared with the 24 h IVM protocol (control) usually employed for bovine oocytes. Cleavage rates and blastocyst yields were significantly reduced in oocytes after extended IVM. No significant differences were observed in the methylation of entire alleles in oocytes for the genes bH19, bSNRPN, bZAR1, bOct4 and bDNMT3A. However, we found differentially methylated CpG sites in the bDNMT3Ls locus in oocytes after extended IVM and in embryos derived from them compared with controls. Moreover, embryos derived from the 48 h matured oocyte group were significantly less methylated at CpG5 and CpG7 compared with the 24 h group. CpG7 was significantly hypermethylated in embryos produced from the control oocytes, but not in oocytes matured for 48 h. Furthermore, methylation for CpG5-CpG8 of bDNMT3Ls was significantly lower in oocytes of the 24 h group compared with embryos derived therefrom, whereas no such difference was found for oocytes and embryos of the in vitro aged group. Expression of most of the selected genes was not affected by duration of IVM. However, transcript abundance for the imprinted gene bIGF2R was significantly reduced in oocytes analyzed after extended IVM compared with control oocytes. Transcript levels for bPRDX1, bDNMT3A and bBCLXL were significantly reduced in 4- to 8-cell embryos derived from in vitro aged oocytes. These results indicate that extended IVM leads to ageing-like alterations and demonstrate that epigenetic mechanisms are critically involved in ageing of bovine oocytes, which warrants further studies into epigenetic mechanisms involved in ageing of female germ cells, including humans.

X-Linked Retinitis Pigmentosa 2 Is a Novel Maternal-Effect Gene Required for Left-Right Asymmetry in Zebrafish

Retinitis pigmentosa 2 (RP2) gene is responsible for up to 20% of X-linked retinitis pigmentosa, a severe heterogeneous genetic disorder resulting in progressive retinal degeneration in humans. In vertebrates, several bodies of evidence have clearly established the role of Rp2 protein in cilia genesis and/or function. Unexpectedly, some observations in zebrafish have suggested the oocyte-predominant expression of the rp2 gene, a typical feature of maternal-effect genes. In the present study, we investigate the maternal inheritance of rp2 gene products in zebrafish eggs in order to address whether rp2 could be a novel maternal-effect gene required for normal development. Although both rp2 mRNA and corresponding protein are expressed during oogenesis, rp2 mRNA is maternally inherited, in contrast to Rp2 protein. A knockdown of the protein transcribed from both rp2 maternal and zygotic mRNA results in delayed epiboly and severe developmental defects, including eye malformations, that were not observed when only the protein from zygotic origin was knocked down. Moreover, the knockdown of maternal and zygotic Rp2 revealed a high incidence of left-right asymmetry establishment defects compared to only zygotic knockdown. Here we show that rp2 is a novel maternal-effect gene exclusively expressed in oocytes within the zebrafish ovary and demonstrate that maternal rp2 mRNA is essential for successful embryonic development and thus contributes to egg developmental competence. Our observations also reveal that Rp2 protein translated from maternal mRNA is important to allow normal heart loop formation, thus providing evidence of a direct maternal contribution to left-right asymmetry establishment.

Quantitative proteomics of Xenopus laevis embryos: expression kinetics of nearly 4000 proteins during early development

While there is a rich literature on transcription dynamics during the development of many organisms, protein data is limited. We used iTRAQ isotopic labeling and mass spectrometry to generate the largest developmental proteomic dataset for any animal. Expression dynamics of nearly 4,000 proteins of Xenopuslaevis was generated from fertilized egg to neurula embryo. Expression clusters into groups. The cluster profiles accurately reflect the major events that mark changes in gene expression patterns during early Xenopus development. We observed decline in the expression of ten DNA replication factors after the midblastula transition (MBT), including a marked decline of the licensing factor XCdc6. Ectopic expression of XCdc6 leads to apoptosis; temporal changes in this protein are critical for proper development. Measurement of expression in single embryos provided no evidence for significant protein heterogeneity between embryos at the same stage of development.

Zar1 represses translation in Xenopus oocytes and binds to the TCS in maternal mRNAs with different characteristics than Zar2

Maternal mRNAs are translationally regulated during early development. Zar1 and its closely related homolog, Zar2, are both crucial in early development. Xenopus laevis Zygote arrest 2 (Zar2) binds to the Translational Control Sequence (TCS) in maternal mRNAs and regulates translation. The molecular mechanism of Zar1 has not been described. Here we report similarities and differences between Xenopus Zar1 and Zar2. Analysis of Zar sequences in vertebrates revealed two Zar family members with conserved, characteristic amino acid differences in the C-terminal domain. The presence of only two vertebrate Zar proteins was supported by analyzing Zar1 synteny. We propose that the criteria for naming Zar sequences are based on the characteristic amino acids and the chromosomal context. We also propose reclassification of some Zar sequences. We found that Zar1 is expressed throughout oogenesis and is stable during oocyte maturation. The N-terminal domain of Zar1 repressed translation of a reporter construct in immature oocytes. Both Zar1 and Zar2 bound to the TCS in the Wee1 and Mos 3' UTRs using a zinc finger in the C-terminal domain. However, Zar1 had much higher affinity for RNA than Zar2. To show the functional significance of the conserved amino acid substitutions, these residues in Zar2 were mutated to those found in Zar1. We show that these residues contributed to the different RNA binding characteristics of Zar1 compared to Zar2. Our study shows that Zar proteins have generally similar molecular functions in the translational regulation of maternal mRNAs, but they may have different roles in early development.

Non-promoter DNA hypermethylation of Zygote Arrest 1 (ZAR1) in neuroblastomas

BACKGROUND

The comprehensive methylation analysis of tumor-specific differently methylated regions in malignant melanomas and brain tumors has led to the identification of non-promoter hypermethylation of zygote arrest 1 (ZAR1). To search the non-promoter ZAR1 hypermethylation in neuroblastomas, we analyzed the levels of the methylation and transcript expression of ZAR1.

METHODS

The MassARRAY® EpiTYPER (Sequenom Inc., San Diego, CA, USA) system was optimized to determine the quantitative methylation levels of ZAR1 for 12 neuroblastoma cell lines, 23 neuroblastoma samples and four adrenal samples. ZAR1 expression levels were evaluated through a quantitative, real-time reverse transcription-polymerase chain reaction. The quantitative methylation levels of ZAR1 were subjected to correlation studies with the established markers of progressive disease and outcome.

RESULTS

Strikingly, the hypermethylation of ZAR1 regions and ZAR1 expression levels was observed in the neuroblastoma cell lines and neuroblastoma samples, compared to the adrenal samples. Somatic changes in ZAR1 methylation and ZAR1 expression were found in all three neuroblastoma patients. In the ZAR1 regions, poor-outcome tumors that were MYCN-amplified and/or Stage 3 or 4 and/or the age at diagnosis was≥18months, and/or showed an unfavorable histology were frequently hypermethylated.

CONCLUSION

Our results indicate that the hypermethylation of ZAR1 regions is extremely frequent in neuroblastomas and correlates with established markers of progressive disease and outcome.

Histone deacetylase 2 (HDAC2) regulates chromosome segregation and kinetochore function via H4K16 deacetylation during oocyte maturation in mouse

Changes in histone acetylation occur during oocyte development and maturation, but the role of specific histone deacetylases in these processes is poorly defined. We report here that mice harboring Hdac1^−/+/Hdac2^−/− or Hdac2^−/− oocytes are infertile or sub-fertile, respectively. Depleting maternal HDAC2 results in hyperacetylation of H4K16 as determined by immunocytochemistry—normal deacetylation of other lysine residues of histone H3 or H4 is observed—and defective chromosome condensation and segregation during oocyte maturation occurs in a sub-population of oocytes. The resulting increased incidence of aneuploidy likely accounts for the observed sub-fertility of mice harboring Hdac2^−/− oocytes. The infertility of mice harboring Hdac1^−/+/Hdac2^−/−oocytes is attributed to failure of those few eggs that properly mature to metaphase II to initiate DNA replication following fertilization. The increased amount of acetylated H4K16 likely impairs kinetochore function in oocytes lacking HDAC2 because kinetochores in mutant oocytes are less able to form cold-stable microtubule attachments and less CENP-A is located at the centromere. These results implicate HDAC2 as the major HDAC that regulates global histone acetylation during oocyte development and, furthermore, suggest HDAC2 is largely responsible for the deacetylation of H4K16 during maturation. In addition, the results provide additional support that histone deacetylation that occurs during oocyte maturation is critical for proper chromosome segregation.

Oocyte development is becoming of increasing interest not only in the broad research community but also within the general public due, in part, to the ever increasing demand for and use of assisted reproductive technologies (ART) to treat human infertility, and because the oocyte-to-embryo transition encompasses a natural reprogramming of gene expression, a process central to forming iPS cells. Dramatic changes in chromatin structure and gene expression occur during oocyte development, but the role of such changes in generating oocytes that are capable of maturing, being fertilized, and giving rise to offspring is very poorly understood. Histone deacetylases (HDACs) are critically involved in modulating chromatin structure. Here, we describe the effect of specifically deleting the gene encoding Hdac2 in mouse oocytes and find the fertility of female mice harboring such oocytes is compromised. Although such mutant oocytes can grow they fail to mature properly to become an egg. The primary defect is that histone H4 acetylated on lysine 16 fails to become deacetylated as the oocyte matures to become an egg, with the consequence that the ability of chromosomes to interact with spindle microtubules is compromised, which in turn leads to improper chromosome segregation.

Contraception technology: past, present and future

Steady progress in contraception research has been achieved over the past 50 years. Hormonal and nonhormonal modern contraceptives have improved women's lives by reducing different health conditions that contributed to considerable morbidity. However, the contraceptives available today are not suitable to all users, and the need to expand contraceptive choices still exists. Novel products such as new implants, contraceptive vaginal rings, transdermal patches and newer combinations of oral contraceptives have recently been introduced in family planning programs, and hormonal contraception is widely used for spacing and limiting births. Concerns over the adverse effects of hormonal contraceptives have led to research and development of new combinations with improved metabolic profile. Recent developments include use of natural compounds such as estradiol and estradiol valerate with the hope to decrease thrombotic risk, in combination with newer progestins derived from the progesterone structure or from spirolactone, in order to avoid the androgenic effects. Progesterone antagonists and progesterone receptor modulators are highly effective in blocking ovulation and preventing follicular rupture and are undergoing investigations in the form of oral pills and in semi-long-acting delivery systems. Future developments also include the combination of a contraceptive with an antiretroviral agent for dual contraception and protection against sexually transmitted diseases, to be used before intercourse or on demand, as well as for continuous use in dual-protection rings. Although clinical trials of male contraception have reflected promising results, limited involvement of industry in that area of research has decreased the likelihood of having a male method available in the current decade. Development of nonhormonal methods is still at an early stage of research, with the identification of specific targets within the reproductive system in ovaries and testes, as well as interactions between spermatozoa and ova. It is hoped that the introduction of new methods with additional health benefits would help women and couples with unmet needs to obtain access to a wider range of contraceptives with improved acceptability.

Xenopus laevis zygote arrest 2 (zar2) encodes a zinc finger RNA-binding protein that binds to the translational control sequence in the maternal Wee1 mRNA and regulates translation

Zygote arrest (Zar) proteins are crucial for early embryonic development, but their molecular mechanism of action is unknown. The Translational Control Sequence (TCS) in the 3' untranslated region (UTR) of the maternal mRNA, Wee1, mediates translational repression in immature Xenopus oocytes and translational activation in mature oocytes, but the protein that binds to the TCS and mediates translational control is not known. Here we show that Xenopus laevis Zar2 (encoded by zar2) binds to the TCS in maternal Wee1 mRNA and represses translation in immature oocytes. Using yeast 3 hybrid assays and electrophoretic mobility shift assays, Zar2 was shown to bind specifically to the TCS in the Wee1 3'UTR. RNA binding required the presence of Zn(2+) and conserved cysteines in the C-terminal domain, suggesting that Zar2 contains a zinc finger. Consistent with regulating maternal mRNAs, Zar2 was present throughout oogenesis, and endogenous Zar2 co-immunoprecipitated endogenous Wee1 mRNA from immature oocytes, demonstrating the physiological significance of the protein-RNA interaction. Interestingly, Zar2 levels decreased during oocyte maturation. Dual luciferase reporter tethered assays showed that Zar2 repressed translation in immature oocytes. Translational repression was relieved during oocyte maturation and this coincided with degradation of Zar2 during maturation. This is the first report of a molecular function of zygote arrest proteins. These data show that Zar2 contains a zinc finger and is a trans-acting factor for the TCS in maternal mRNAs in immature Xenopus oocytes.

Molecular control of oogenesis

Oogenesis is a complex process regulated by a vast number of intra- and extra-ovarian factors. Oogonia, which originate from primordial germ cells, proliferate by mitosis and form primary oocytes that arrest at the prophase stage of the first meiotic division until they are fully-grown. Within primary oocytes, synthesis and accumulation of RNAs and proteins throughout oogenesis are essential for oocyte growth and maturation; and moreover, crucial for developing into a viable embryo after fertilization. Oocyte meiotic and developmental competence is gained in a gradual and sequential manner during folliculogenesis and is related to the fact that the oocyte grows in interaction with its companion somatic cells. Communication between oocyte and its surrounding granulosa cells is vital, both for oocyte development and for granulosa cells differentiation. Oocytes depend on differentiated cumulus cells, which provide them with nutrients and regulatory signals needed to promote oocyte nuclear and cytoplasmic maturation and consequently the acquisition of developmental competence.The purpose of this article is to summarize recent knowledge on the molecular aspects of oogenesis and oocyte maturation, and the crucial role of cumulus-cell interactions, highlighting the valuable contribution of experimental evidences obtained in animal models. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

Loss of maternal CTCF is associated with peri-implantation lethality of Ctcf null embryos

CTCF is a highly conserved, multifunctional zinc finger protein involved in critical aspects of gene regulation including transcription regulation, chromatin insulation, genomic imprinting, X-chromosome inactivation, and higher order chromatin organization. Such multifunctional properties of CTCF suggest an essential role in development. Indeed, a previous report on maternal depletion of CTCF suggested that CTCF is essential for pre-implantation development. To distinguish between the effects of maternal and zygotic expression of CTCF, we studied pre-implantation development in mice harboring a complete loss of function Ctcf knockout allele. Although we demonstrated that homozygous deletion of Ctcf is early embryonically lethal, in contrast to previous observations, we showed that the Ctcf nullizygous embryos developed up to the blastocyst stage (E3.5) followed by peri-implantation lethality (E4.5–E5.5). Moreover, one-cell stage Ctcf nullizygous embryos cultured ex vivo developed to the 16–32 cell stage with no obvious abnormalities. Using a single embryo assay that allowed both genotype and mRNA expression analyses of the same embryo, we demonstrated that pre-implantation development of the Ctcf nullizygous embryos was associated with the retention of the maternal wild type Ctcf mRNA. Loss of this stable maternal transcript was temporally associated with loss of CTCF protein expression, apoptosis of the developing embryo, and failure to further develop an inner cell mass and trophoectoderm ex vivo. This indicates that CTCF expression is critical to early embryogenesis and loss of its expression rapidly leads to apoptosis at a very early developmental stage. This is the first study documenting the presence of the stable maternal Ctcf transcript in the blastocyst stage embryos. Furthermore, in the presence of maternal CTCF, zygotic CTCF expression does not seem to be required for pre-implantation development.