Nanos genes and their role in development and beyond

Depletion of Gtsf1L impairs development of eupyrene sperm and ovary in Gtsf1L

Sperm delivers genetic information from the male to the ovum, playing vital roles in sexual reproduction. Like other Lepidoptera, Bombyx mori exhibits dimorphic spermatogenesis, generating coexisting nucleated eupyrene sperm and anucleated apyrene sperm. The mechanism of dimorphic spermatogenesis is still to be clarified. In a previous study, we demonstrated that Gametocyte-specific factor1 (Gtsf1) is essential for female sex determination and PIWI-interacting RNA (piRNA) mediated transposon silencing in B. mori. Here, we performed functional analysis of the Gtsf1 paralog BmGtsf1L using a binary transgenic CRISPR/Cas9 system. BmGtsf1L is dispensable for sex determination but critical for fertility in both males and females. We separated different types of sperm and found that BmGtsf1L is highly expressed in both types of sperm. BmGtsf1L deficiency (△BmGtsf1L) impaired the formation and migration of eupyrene sperm, whereas the development and movement of apyrene sperm were normal. Furthermore, through a sperm culture experiment, we confirmed that eupyrene spermatogenesis defects appeared before the elongation stage. Double copulations of a female with △BmGtsf1L and Sex-lethal mutant males can rescue infertility phenotypes, revealing that the apyrene sperm of BmGtsf1L mutants is functional. We also found that the depletion of BmGtsf1L impacted proper oogenesis. This study provided the first functional analysis of Gtsf1 paralogs on physiology, demonstrating the critical role of BmGtsf1L in the development of eupyrene sperm and the ovary.

Whole-genome sequencing identifies novel loci for keratoconus and facilitates risk stratification in a Han Chinese population

BACKGROUND

Keratoconus (KC) is a prevalent corneal condition with a modest genetic basis. Recent studies have reported significant genetic associations in multi-ethnic cohorts. However, the situation in the Chinese population remains unknown. This study was conducted to identify novel genetic variants linked to KC and to evaluate the potential applicability of a polygenic risk model in the Han Chinese population.

METHODS

A total of 830 individuals diagnosed with KC and 779 controls from a Chinese cohort were enrolled and genotyped by whole-genome sequencing (WGS). Common and rare variants were respectively subjected to single variant association analysis and gene-based burden analysis. Polygenic risk score (PRS) models were developed using top single-nucleotide polymorphisms (SNPs) identified from a multi-ethnic meta-analysis and then evaluated in the Chinese cohort.

RESULTS

The characterization of germline variants entailed correction for population stratification and validation of the East Asian ancestry of the included samples via principal component analysis. For rare protein-truncating variants (PTVs) with minor allele frequency (MAF) < 5%, ZC3H11B emerged as the top prioritized gene, albeit failing to reach the significance threshold. We detected three common variants reaching genome-wide significance (P ≤ 5 × 10-8), all of which are novel to KC. Our study validated three well known predisposition loci, COL5A1, EIF3A and FNDC3B. Additionally, a significant correlation of allelic effects was observed for suggestive SNPs between the largest multi-ethnic meta-genome-wide association study (GWAS) and our study. The PRS model, generated using top SNPs from the meta-GWAS, stratified individuals in the upper quartile, revealing up to a 2.16-fold increased risk for KC.

CONCLUSIONS

Our comprehensive WGS-based GWAS in a large Chinese cohort enhances the efficiency of array-based genetic studies, revealing novel genetic associations for KC and highlighting the potential for refining clinical decision-making and early prevention strategies.

Retinoic acid, an essential component of the roof plate organizer, promotes the spatiotemporal segregation of dorsal neural fates

Dorsal neural tube-derived retinoic acid promotes the end of neural crest production and transition into a definitive roof plate. Here, we analyze how this impacts the segregation of central and peripheral lineages, a process essential for tissue patterning and function. Localized in ovo inhibition in quail embryos of retinoic acid activity followed by single-cell transcriptomics unraveled a comprehensive list of differentially expressed genes relevant to these processes. Importantly, progenitors co-expressed neural crest, roof plate and dI1 interneuron markers, indicating a failure in proper lineage segregation. Furthermore, separation between roof plate and dI1 interneurons is mediated by Notch activity downstream of retinoic acid, highlighting their crucial role in establishing the roof plate-dI1 boundary. Within the peripheral branch, where absence of retinoic acid resulted in neural crest production and emigration extending into the roof plate stage, sensory progenitors failed to separate from melanocytes, leading to formation of a common glia-melanocyte cell with aberrant migratory patterns. In summary, the implementation of single-cell RNA sequencing facilitated the discovery and characterization of a molecular mechanism responsible for the segregation of dorsal neural fates during development.

Interplay of RNA-binding proteins controls germ cell development in zebrafish

The specification of germ cells in zebrafish mostly relies on an inherited mechanism by which localized maternal determinants, called germ plasm, confer germline fate in the early embryo. Extensive studies have partially allowed the identification of key regulators governing germ plasm formation and subsequent germ cell development. RNA-binding proteins, acting in concert with other germ plasm components, play essential roles in the organization of the germ plasm and the specification, migration, maintenance, and differentiation of primordial germ cells. The loss of their functions impairs germ cell formation and causes sterility or sexual conversion. Evidence is emerging that they instruct germline development through differential regulation of mRNA fates in somatic and germ cells. However, the challenge remains to decipher the complex interplay of maternal germ plasm components in germ plasm compartmentalization and germ cell specification. Because failure to control the developmental outcome of germ cells disrupts the formation of gametes, it is important to gain a complete picture of regulatory mechanisms operating in the germ cell lineage. This review sheds light on the contributions of RNA-binding proteins to germ cell development in zebrafish and highlights intriguing questions that remain open for future investigation.

Nanos2 marks precursors of somatic lineages and is required for germline formation in the sea anemone Nematostella vectensis

In animals, stem cell populations of varying potency facilitate regeneration and tissue homeostasis. Notably, germline stem cells in both vertebrates and invertebrates express highly conserved RNA binding proteins, such as nanos, vasa, and piwi. In highly regenerative animals, these genes are also expressed in somatic stem cells, which led to the proposal that they had an ancestral role in all stem cells. In cnidarians, multi- and pluripotent interstitial stem cells have only been identified in hydrozoans. Therefore, it is currently unclear if cnidarian stem cell systems share a common evolutionary origin. We, therefore, aimed to characterize conserved stem cell marker genes in the sea anemone Nematostella vectensis. Through transgenic reporter genes and single-cell transcriptomics, we identify cell populations expressing the germline-associated markers piwi1 and nanos2 in the soma and germline, and gene knockout shows that Nanos2 is indispensable for germline formation. This suggests that nanos and piwi genes have a conserved role in somatic and germline stem cells in cnidarians.

Transcriptomic and metabolomic analyses reveal sex-related differences in the gonads of Pinctada fucata martensii

Pinctada fucata martensii is an economically important bivalve mollusk, as this species makes a major contribution to seawater pearl production. Pearl production efficiency varies between the sexes of P. f. martensii, but many aspects of the molecular mechanisms underlying sex determination and sex differentiation in P. f. martensii remain unclear. Here, transcriptomic and metabonomic analyses were conducted to identify the major genes and metabolic changes associated with sex determination and gametogenesis. We identified a total of 3426 differentially expressed genes (DEGs) between females and males. These included Fem-1c and Foxl2, which are involved in sex determination and sex differentiation, and SOHLH2, Nanos1 and TSSK4, which are involved in gametogenesis. We also identified a total of 5231 significant differential metabolites (SDMs) between females and males. These DEGs were enriched in 47 metabolic pathways, including "ABC transporters," "purine metabolism," and "glycerophospholipid metabolism." Our findings provide new insights into the molecular mechanisms underlying sex determination, sex differentiation, and gametogenesis and will aid future studies of P. f. martensii.

Arthropod promoters for genetic control of disease vectors

Vector-borne diseases (VBDs) impose devastating effects on human health and a heavy financial burden. Malaria, Lyme disease, and dengue fever are just a few examples of VBDs that cause severe illnesses. The current strategies to control VBDs consist mainly of environmental modification and chemical use, and to a small extent, genetic approaches. The genetic approaches, including transgenesis/genome modification and gene-drive technologies, provide the basis for developing new tools for VBD prevention by suppressing vector populations or reducing their capacity to transmit pathogens. The regulatory elements such as promoters are required for a robust sex-, tissue-, and stage-specific transgene expression. As discussed in this review, information on the regulatory elements is available for mosquito vectors but is scant for other vectors.

NANOS1 restricts oral cancer cell motility and TGF-ß signaling

Oral squamous cell carcinoma (OSCC) is the most frequent type of cancer of the head and neck area accounting for approx. 377,000 new cancer cases every year. The epithelial-to-mesenchymal transition (EMT) program plays an important role in OSCC progression and metastasis therefore contributing to a poor prognosis in patients with advanced disease. Transforming growth factor beta (TGF-ß) is a powerful inducer of EMT thereby increasing cancer cell aggressiveness. Here, we aimed at identifying RNA-binding proteins (RBPs) that affect TGF-ß-induced EMT. To this end we treated oral cancer cells with TGF-ß and identified a total of 643 significantly deregulated protein-coding genes in response to TGF-ß. Of note, 19 genes encoded RBPs with NANOS1 being the most downregulated RBP. Subsequent cellular studies demonstrated a strong inhibitory effect of NANOS1 on migration and invasion of SAS oral cancer cells. Further mechanistic studies revealed an interaction of NANOS1 with the TGF-ß receptor 1 (TGFBR1) mRNA, leading to increased decay of this transcript and a reduced TGFBR1 protein expression, thereby preventing downstream TGF-ß/SMAD signaling. In summary, we identified NANOS1 as negative regulator of TGF-ß signaling in oral cancer cells.

P-body-like condensates in the germline

P-bodies are cytoplasmic condensates that accumulate low-translation mRNAs for temporary storage before translation or degradation. P-bodies have been best characterized in yeast and mammalian tissue culture cells. We describe here related condensates in the germline of animal models. Germline P-bodies have been reported at all stages of germline development from primordial germ cells to gametes. The activity of the universal germ cell fate regulator, Nanos, is linked to the mRNA decay function of P-bodies, and spatially-regulated condensation of P-body like condensates in embryos is required to localize mRNA regulators to primordial germ cells. In most cases, however, it is not known whether P-bodies represent functional compartments or non-functional condensation by-products that arise when ribonucleoprotein complexes saturate the cytoplasm. We speculate that the ubiquity of P-body-like condensates in germ cells reflects the strong reliance of the germline on cytoplasmic, rather than nuclear, mechanisms of gene regulation.

Divergent epigenetic responses to perinatal asphyxia in severe mental disorders

Epigenetic modifications influenced by environmental exposures are molecular sources of phenotypic heterogeneity found in schizophrenia and bipolar disorder and may contribute to shared etiopathogenetic mechanisms of these two disorders. Newborns who experienced perinatal asphyxia have suffered reduced oxygen delivery to the brain around the time of birth, which increases the risk of later psychiatric diagnosis. This study aimed to investigate DNA methylation in blood cells for associations with a history of perinatal asphyxia, a neurologically harmful condition occurring within the biological environment of birth. We utilized prospective data from the Medical Birth Registry of Norway to identify incidents of perinatal asphyxia in 643 individuals with schizophrenia or bipolar disorder and 676 healthy controls. We performed an epigenome wide association study to distinguish differentially methylated positions associated with perinatal asphyxia. We found an interaction between methylation and exposure to perinatal asphyxia on case-control status, wherein having a history of perinatal asphyxia was associated with an increase of methylation in healthy controls and a decrease of methylation in patients on 4 regions of DNA important for brain development and function. The differentially methylated regions were observed in genes involved in oligodendrocyte survival and axonal myelination and functional recovery (LINGO3); assembly, maturation and maintenance of the brain (BLCAP;NNAT and NANOS2) and axonal transport processes and neural plasticity (SLC2A14). These findings are consistent with the notion that an opposite epigenetic response to perinatal asphyxia, in patients compared with controls, may contribute to molecular mechanisms of risk for schizophrenia and bipolar disorder.

Germ Line/Multipotency Genes Show Differential Expression during Embryonic Development of the Annelid Enchytraeus coronatus

Germ line development and the origin of the primordial germ cells (PGCs) are very variable and may occur across a range of developmental stages and in several developmental contexts. In establishing and maintaining germ line, a conserved set of genes is involved. On the other hand, these genes are expressed in multipotent/pluripotent cells that may give rise to both somatic and germline cells. To begin elucidating mechanisms by which the germ line is specified in Enchytraeus coronatus embryos, we identified twenty germline/multipotency genes, homologs of Vasa, PL10, Piwi, Nanos, Myc, Pumilio, Tudor, Boule, and Bruno, using transcriptome analysis and gene cloning, and characterized their expression by whole-mount in situ hybridization. To answer the question of the possible origin of PGCs in this annelid, we carried out an additional description of the early embryogenesis. Our results suggest that PGCs derive from small cells originating at the first two divisions of the mesoteloblasts. PGCs form two cell clusters, undergo limited proliferation, and migrate to the developing gonadal segments. In embryos and juvenile E. coronatus, homologs of the germline/multipotency genes are differentially expressed in both germline and somatic tissue including the presumptive germ cell precursors, posterior growth zone, developing foregut, and nervous system.

Rhox6 regulates the expression of distinct target genes to mediate mouse PGCLC formation and ESC self-renewal

BACKGROUND

Mouse embryonic stem cells (mESCs) not only retain the property of self-renewal but also have the ability to develop into primordial germ cell-like cells (PGCLCs). However, knowledge about the mechanisms of transcriptional regulation is still limited. Rhox6, a member of the homeobox family that is located on the X chromosome, is highly expressed within PGCLCs in vivo and in vitro. However, the detailed effects of Rhox6 on PGCLC specification and mESC maintenance remain unclear.

RESULTS

In this study, we found that overexpression of Rhox6 favors the formation of PGCLCs, while depletion of Rhox6 inhibits the generation of PGCLCs. Mechanistically, Rhox6 directly induces the expression of Nanos3 during the specification of PGCLCs. Subsequently, downregulation of Nanos3 expression is sufficient to decrease the ability of Rhox6 to induce PGCLC formation. Moreover, we found that depletion of Rhox6 expression facilitates the self-renewal of mESCs. High-throughput sequencing revealed that suppression of Rhox6 transcription significantly increases the expression of pluripotency genes. Functional studies further demonstrated that Rhox6 directly represses the transcription of Tbx3. Therefore, knockdown of the expression of the latter impairs the self-renewal of mESCs promoted by Rhox6 downregulation.

CONCLUSIONS

Our study reveals that overexpression of Rhox6 is beneficial for PGCLC generation through induction of Nanos3, while downregulation of Rhox6 contributes to mESC self-renewal by increasing Tbx3. These findings help elucidate the early development of mouse embryos.

The Price of Human Evolution: Cancer-Testis Antigens, the Decline in Male Fertility and the Increase in Cancer

The increasing frequency of general and particularly male cancer coupled with the reduction in male fertility seen worldwide motivated us to seek a potential evolutionary link between these two phenomena, concerning the reproductive transcriptional modules observed in cancer and the expression of cancer-testis antigens (CTA). The phylostratigraphy analysis of the human genome allowed us to link the early evolutionary origin of cancer via the reproductive life cycles of the unicellulars and early multicellulars, potentially driving soma-germ transition, female meiosis, and the parthenogenesis of polyploid giant cancer cells (PGCCs), with the expansion of the CTA multi-families, very late during their evolution. CTA adaptation was aided by retrovirus domestication in the unstable genomes of mammals, for protecting male fertility in stress conditions, particularly that of humans, as compensation for the energy consumption of a large complex brain which also exploited retrotransposition. We found that the early and late evolutionary branches of human cancer are united by the immunity-proto-placental network, which evolved in the Cambrian and shares stress regulators with the finely-tuned sex determination system. We further propose that social stress and endocrine disruption caused by environmental pollution with organic materials, which alter sex determination in male foetuses and further spermatogenesis in adults, bias the development of PGCC-parthenogenetic cancer by default.

Loss of Kmt2c in vivo leads to EMT, mitochondrial dysfunction and improved response to lapatinib in breast cancer

Deep sequencing of human tumours has uncovered a previously unappreciated role for epigenetic regulators in tumorigenesis. H3K4 methyltransferase KMT2C/MLL3 is mutated in several solid malignancies, including more than 10% of breast tumours. To study the tumour suppressor role of KMT2C in breast cancer, we generated mouse models of Erbb2/Neu, Myc or PIK3CA-driven tumorigenesis, in which the Kmt2c locus is knocked out specifically in the luminal lineage of mouse mammary glands using the Cre recombinase. Kmt2c knock out mice develop tumours earlier, irrespective of the oncogene, assigning a bona fide tumour suppressor role for KMT2C in mammary tumorigenesis. Loss of Kmt2c induces extensive epigenetic and transcriptional changes, which lead to increased ERK1/2 activity, extracellular matrix re-organization, epithelial-to-mesenchymal transition and mitochondrial dysfunction, the latter associated with increased reactive oxygen species production. Loss of Kmt2c renders the Erbb2/Neu-driven tumours more responsive to lapatinib. Publicly available clinical datasets revealed an association of low Kmt2c gene expression and better long-term outcome. Collectively, our findings solidify the role of KMT2C as a tumour suppressor in breast cancer and identify dependencies that could be therapeutically amenable.

Germline-related molecular phenotype in Metazoa: conservation and innovation highlighted by comparative transcriptomics

BACKGROUND

In Metazoa, the germline represents the cell lineage devoted to the transmission of genetic heredity across generations. Its functions intuitively evoke the crucial roles that it plays in organism development and species evolution, and its establishment is tightly tied to animal multicellularity itself. The molecular toolkit expressed in germ cells has a high degree of conservation between species, and it also shares many components with the molecular phenotype of some animal totipotent cell lineages, like planarian neoblasts and sponge archaeocytes. The present study stems from these observations and represents a transcriptome-wide comparative analysis between germline-related samples of 9 animal species (7 phyla), comprehending also totipotent lineages classically considered somatic.

RESULTS

Differential expression analyses were performed for each species between germline-related and control somatic tissues. We then compared the different germline-related transcriptional profiles across the species without the need for an a priori set of genes. Through a phylostratigraphic analysis, we observed that the proportion of phylum- and Metazoa-specific genes among germline-related upregulated transcripts was lower than expected by chance for almost all species. Moreover, homologous genes related to proper DNA replication resulted the most common when comparing the considered species, while the regulation of transcription and post-transcriptional mechanisms appeared more variable, showing shared upregulated functions and domains, but very few homologous whole-length sequences.

CONCLUSIONS

Our wide-scale comparative analysis mostly confirmed previous molecular characterizations of specific germline-related lineages. Additionally, we observed a consistent signal throughout the whole data set, therefore comprehending both canonically defined germline samples (germ cells), and totipotent cell lineages classically considered somatic (neoblasts and archaeocytes). The phylostratigraphic analysis supported the less probable involvement of novel molecular factors in the germline-related transcriptional phenotype and highlighted the early origin of such cell programming and its conservation throughout evolution. Moreover, the fact that the mostly shared molecular factors were involved in DNA replication and repair suggests how fidelity in genetic material inheritance is a strong and conserved driver of germline-related molecular phenotype, while transcriptional and post-transcriptional regulations appear differently tuned among the lineages.

Generation of germ cell-deficient pigs by NANOS3 knockout

NANOS3 is an evolutionarily conserved gene expressed in primordial germ cells that is important for germ cell development. Germ cell deletion by NANOS3 knockout has been reported in several mammalian species, but its function in pigs is unclear. In the present study, we investigated the germline effects of NANOS3 knockout in pigs using CRISPR/Cas9. Embryo transfer of CRISPR/Cas9-modified embryos produced ten offspring, of which one showed wild-type NANOS3 alleles, eight had two mutant NANOS3 alleles, and the other exhibited mosaicism (four mutant alleles). Histological analysis revealed no germ cells in the testes or ovaries of any of the nine mutant pigs. These results demonstrated that NANOS3 is crucial for porcine germ cell production.

A Germline-Specific Regulator of Mitochondrial Fusion is Required for Maintenance and Differentiation of Germline Stem and Progenitor Cells

Maintenance and differentiation of germline stem and progenitor cells (GSPCs) is important for sexual reproduction. Here, the authors identify zebrafish pld6 as a novel germline-specific gene by cross-analyzing different RNA sequencing results, and find that pld6 knockout mutants develop exclusively into infertile males. In pld6 mutants, GSPCs fail to differentiate and undergo apoptosis, leading to masculinization and infertility. Mitochondrial fusion in pld6-depleted GSPCs is severely impaired, and the mutants exhibit defects in piRNA biogenesis and transposon suppression. Overall, this work uncovers zebrafish Pld6 as a novel germline-specific regulator of mitochondrial fusion, and highlights its essential role in the maintenance and differentiation of GSPCs as well as gonadal development and gametogenesis.

Immunomodulatory Properties of Mouse Mesenchymal Stromal/Stem Cells Upon Ectopic Expression of Immunoregulator Nanos2

BACKGROUND

Mesenchymal stromal/stem cells (MSCs) are known for their involvement in modulating the immune system of mammals. This potency could be enhanced by different strategies, including regulation of key proteins, in order to meet desirable therapeutic properties. Nanos2, encoding an RNA-binding protein involved in regulation of key spermatogonial signaling pathways, has been demonstrated to downregulate a range of immune related genes in mouse embryonic fibroblasts (MEFs). Accordingly, it was hypothesized that Nanos2 functions as a potent immunosuppressing factor. This study was aimed to measure the expression profile of the immune-related genes in mouse mesenchymal stromal/stem cells (mMSCs) and assess their functional properties after Nanos2 ectopic expression.

METHODS

As inflammatory mediators, interferon (IFN-γ) and poly(I:C) were used to provoke an immune response. The interactions between the control and engineered mMSCs overexpressing Nanos2, with mouse peripheral blood mononuclear cells (mPBMCs) were then compared. The sensitivity of these cells to an inflammatory environment was assessed by using a conditioned medium containing high levels of inflammatory cytokines. Finally, the functional properties of the cells were investigated both in vivo and in vitro in presence of tumor and immune cells.

RESULTS

Deep transcriptome analysis indicated that numerous genes were downregulated as a result of higher Nanos2 expression. Most of the genes subjected to gene expression alteration, were responsible for controlling responses to external stimuli, cell-cell adhesion, and wound healing. In comparison to the control cells, Nanos2-overexpressing cells showed lower expression of several immune-related genes after pretreatment with IFN-γ and poly(I:C). They also exhibited inhibitory effects against mPBMCs proliferation. Tumor growth rate, in B16-F0 administered mice was obviously increased upon their treatment with the Nanos2-mMSCs, while no tumor or very small ones were developed in the control group. In addition, the cytotoxic environment had no significant effects on Nanos2-mMSCs.

CONCLUSIONS

According to the literature, MSCs are believed to be tuned very precisely by their internal and external conditions to act as either pro-inflammatory or anti-inflammatory agents. We show here that Nanos2 plays a significant role in promoting anti-inflammatory properties when expressed at higher levels by MSCs. This approach could be adopted for controlling the excessive inflammatory conditions in clinical programs, however more experiments are required to confirm it. In Brief Viral transduction was used to over express Nanos2 in mouse mesenchymal stromal/stem cells (mMSCs). Induced expression of Nanos2 downregulated the expression of immune-related genes and proteins. These modified mMSCs switched to an immunosuppressive state, even in the presence of pro-inflammatory cytokines; and could also contribute to tumor progression in a mouse model.

Identification and expression analysis of sex biased miRNAs in chinese hook snout carp Opsariichthys bidens

As an economically important fish, Opsariichthys bidens has obvious sexual dimorphism and strong reproductive capacity, but no epigenetics study can well explain its phenotypic variations. In recent years, many microRNAs involved in the regulation of reproductive development have been explored. In this study, the small RNA libraries of O. bidens on the testis and ovary were constructed and sequenced. A total of 295 known miRNAs were obtained and 100 novel miRNAs were predicted. By comparing testis and ovary libraries, 115 differentially expressed (DE) miRNAs were selected, of which 53 were up-regulated and 62 were down-regulated. A total of 64 GO items (padj < 0.01) and 206 KEGG pathways (padj < 0.01) were enriched in the target gene of miRNA. After that, the expression levels of nine DE miRNAs, including let-7a, miR-146b, miR-18c, miR-202-5p, miR-135c, miR-9-5p, miR-34c-3p, miR-460-5p and miR-338 were verified by qRT-PCR. Furthermore, bidirectional prediction of DE miRNAs and sex-related genes was carried out and the targeting correlation between miR-9-5p and nanos1 was verified by Dual-Luciferase reporter assay. Our findings identified the differentially expressed miRNA and paved the way to new possibilities for the follow-up study on the mechanism of miRNA-mRNA interaction in the gonads of O. bidens.

A cooperative mechanism of target RNA selection via germ-cell-specific RNA-binding proteins NANOS2 and DND1

The germ-cell-specific RNA-binding protein (RBP) NANOS2 plays a pivotal role in male gonocyte differentiation and spermatogonial stem cell maintenance. Although NANOS2 interacts with the CNOT deadenylation complex and Dead end 1 (DND1) to repress target RNAs, the molecular mechanisms underlying target mRNA selection remain unclear because of the limited cell resource in vivo. Here, we demonstrate that exogenous NANOS2-DND1 suppresses target mRNAs in somatic cells. Using this somatic cell system, we find that NANOS2 interacts with RNA-bound DND1 and recruits the CNOT complex to the mRNAs. However, a fusion construct composed of the CNOT1-binding site of NANOS2 (NIM) and DND1 fails to repress the target gene expression. Therefore, NANOS2 is required not only for recruitment of the CNOT complex but also for selecting the target mRNA with DND1. This study reveals that NANOS2 functions as a second-layer RBP for the target recognition and functional adaptation of DND1.

Single-cell transcriptome reveals insights into the development and function of the zebrafish ovary

Zebrafish are an established research organism that has made many contributions to our understanding of vertebrate tissue and organ development, yet there are still significant gaps in our understanding of the genes that regulate gonad development, sex, and reproduction. Unlike the development of many organs, such as the brain and heart that form during the first few days of development, zebrafish gonads do not begin to form until the larval stage (≥5 days post-fertilization). Thus, forward genetic screens have identified very few genes required for gonad development. In addition, bulk RNA-sequencing studies that identify genes expressed in the gonads do not have the resolution necessary to define minor cell populations that may play significant roles in the development and function of these organs. To overcome these limitations, we have used single-cell RNA sequencing to determine the transcriptomes of cells isolated from juvenile zebrafish ovaries. This resulted in the profiles of 10,658 germ cells and 14,431 somatic cells. Our germ cell data represents all developmental stages from germline stem cells to early meiotic oocytes. Our somatic cell data represents all known somatic cell types, including follicle cells, theca cells, and ovarian stromal cells. Further analysis revealed an unexpected number of cell subpopulations within these broadly defined cell types. To further define their functional significance, we determined the location of these cell subpopulations within the ovary. Finally, we used gene knockout experiments to determine the roles of foxl2l and wnt9b for oocyte development and sex determination and/or differentiation, respectively. Our results reveal novel insights into zebrafish ovarian development and function, and the transcriptome profiles will provide a valuable resource for future studies.

Discovery of Nanos1 and Nanos2/3 as Germ Cell Markers During Scallop Gonadal Development

Nanos are conserved genes involved in germline cell specification and differentiation. However, little is known about the role of different members of Nanos family in germ cell development in mollusks. In the present study, we conducted genome-wide identification of Nanos family in an economically important scallop Patinopecten yessoensis, and detected their expression in adult tissues and during early development. Two Nanos genes (PyNanos1, PyNanos2/3) were identified, both of which have the N-terminal NOT1-interacting motif and C-terminal (CCHC)₂ zinc finger domain. Expression profiles showed that PyNanos1 and PyNanos2/3 were primarily expressed in the gonads, with PyNanos1 being localized in the oogonia, oocytes, and spermatogonia, while PyNanos2/3 being specifically in spermatogonia. The results suggest that PyNanos are germ cell specific and may play crucial roles in gametogenesis in the scallop. PyNanos1 is a maternal gene, which is distributed uniformly at early cleavage, and restricted to 2-3 cell clusters from blastulae to trochophore larvae, suggesting its potential role in the formation of PGCs. Zygotically expressed PyNanos2/3 displayed a similar signal with PyNanos1 in the trochophore larvae, suggesting it may also participate in the formation and/or maintenance of PGCs. This study will benefit germplasm exploitation and conservation in bivalves, and facilitate a better understanding of the evolution of Nanos family and the role of different Nanos in germ cell development in mollusks.

Nanos Is Expressed in Somatic and Germline Tissue during Larval and Post-Larval Development of the Annelid Alitta virens

Nanos is a translational regulator that is involved in germline development in a number of diverse animals and is also involved in somatic patterning in several model organisms, including insects. Neither germline development nor somatic stem cell lines/undifferentiated multipotent cells have been characterized in the development of the annelid Alitta virens, nor is the mechanism of germ/stem-line specification generally well-understood in annelids. Here, I have cloned an Avi-nanos ortholog from A. virens and determined the spatial and temporal expression of Nanos. The results revealed that transcripts of nanos are expressed during differentiation of multiple tissues, including those that are derived from the 2d and 4d cells. In late embryonic stages and during larval development, these transcripts are expressed in the presumptive brain, ventral nerve cord, mesodermal bands, putative primordial germ cells (PGCs), and developing foregut and hindgut. During metamorphosis of the nectochaete larva into a juvenile worm, a posterior growth zone consisting of nanos-positive cells is established, and the PGCs begin to migrate. Later, the PGCs stop migrating and form a cluster of four nanos-expressing cells located immediately behind the jaws (segments 4–5). During posterior regeneration following caudal amputation, a robust Avi-nanos expression appears de novo at the site of injury and further accompanies all steps of regeneration. The obtained data suggest that blastemal cells are mostly derived from cells of the segment adjacent to the amputation site; this is consistent with the idea that the cluster of PGCs do not participate in regeneration.

The Dynamic Regulation of mRNA Translation and Ribosome Biogenesis During Germ Cell Development and Reproductive Aging

The regulation of mRNA translation, both globally and at the level of individual transcripts, plays a central role in the development and function of germ cells across species. Genetic studies using flies, worms, zebrafish and mice have highlighted the importance of specific RNA binding proteins in driving various aspects of germ cell formation and function. Many of these mRNA binding proteins, including Pumilio, Nanos, Vasa and Dazl have been conserved through evolution, specifically mark germ cells, and carry out similar functions across species. These proteins typically influence mRNA translation by binding to specific elements within the 3′ untranslated region (UTR) of target messages. Emerging evidence indicates that the global regulation of mRNA translation also plays an important role in germ cell development. For example, ribosome biogenesis is often regulated in a stage specific manner during gametogenesis. Moreover, oocytes need to produce and store a sufficient number of ribosomes to support the development of the early embryo until the initiation of zygotic transcription. Accumulating evidence indicates that disruption of mRNA translation regulatory mechanisms likely contributes to infertility and reproductive aging in humans. These findings highlight the importance of gaining further insights into the mechanisms that control mRNA translation within germ cells. Future work in this area will likely have important impacts beyond germ cell biology.

Development of a novel embryonic germline gene-related prognostic model of lung adenocarcinoma

BACKGROUND

Emerging evidence implicates the correlation of embryonic germline genes with the tumor progress and patient's outcome. However, the prognostic value of these genes in lung adenocarcinoma (LUAD) has not been fully studied. Here we systematically evaluated this issue, and constructed a novel signature and a nomogram associated with embryonic germline genes for predicting the outcomes of lung adenocarcinoma.

METHODS

The LUAD cohorts retrieved from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) database were used as training set and testing set, respectively. The embryonic germline genes were downloaded from the website https://venn.lodder.dev. Then, the differentially expressed embryonic germline genes (DEGGs) between the tumor and normal samples were identified by limma package. The functional enrichment and pathway analyses were also performed by clusterProfiler package. The prognostic model was constructed by the least absolute shrinkage and selection operator (LASSO)-Cox regression method. Survival and Receiver Operating Characteristic (ROC) analyses were performed to validate the model using training set and four testing GEO datasets. Finally, a prognostic nomogram based on the signature genes was constructed using multivariate regression method.

RESULTS

Among the identified 269 DEGGs, 249 were up-regulated and 20 were down-regulated. GO and KEGG analyses revealed that these DEGGs were mainly enriched in the process of cell proliferation and DNA damage repair. Then, 103 DEGGs with prognostic value were identified by univariate Cox regression and further filtered by LASSO method. The resulting sixteen DEGGs were included in step multivariate Cox regression and an eleven embryonic germline gene related signature (EGRS) was constructed. The model could robustly stratify the LUAD patients into high-risk and low-risk groups in both training and testing sets, and low-risk patients had much better outcomes. The multi-ROC analysis also showed that the EGRS model had the best predictive efficacy compared with other common clinicopathological factors. The EGRS model also showed robust predictive ability in four independent external datasets, and the area under curve (AUC) was 0.726 (GSE30219), 0.764 (GSE50081), 0.657 (GSE37745) and 0.668 (GSE72094). More importantly, the expression level of some genes in EGRS has a significant correlation with the progression of LUAD clinicopathology, suggesting these genes might play an important role in the progression of LUAD. Finally, based on EGRS genes, we built and calibrated a nomogram for conveniently evaluating patients' outcomes.

Primordial Germ Cell Specification in Vertebrate Embryos: Phylogenetic Distribution and Conserved Molecular Features of Preformation and Induction

The differentiation of primordial germ cells (PGCs) occurs during early embryonic development and is critical for the survival and fitness of sexually reproducing species. Here, we review the two main mechanisms of PGC specification, induction, and preformation, in the context of four model vertebrate species: mouse, axolotl, Xenopus frogs, and zebrafish. We additionally discuss some notable molecular characteristics shared across PGC specification pathways, including the shared expression of products from three conserved germline gene families, DAZ (Deleted in Azoospermia) genes, nanos-related genes, and DEAD-box RNA helicases. Then, we summarize the current state of knowledge of the distribution of germ cell determination systems across kingdom Animalia, with particular attention to vertebrate species, but include several categories of invertebrates - ranging from the "proto-vertebrate" cephalochordates to arthropods, cnidarians, and ctenophores. We also briefly highlight ongoing investigations and potential lines of inquiry that aim to understand the evolutionary relationships between these modes of specification.

Pharyngeal endoderm expression of nanos1 is dispensable for craniofacial development

Nanos proteins are essential for developing primordial germ cells (PGCs) in both invertebrates and vertebrates. In invertebrates, also contribute to the patterning of the anterior-posterior axis of the embryo and the neural development. In vertebrates, however, besides the role of Nanos proteins in PGC development, the biological functions of the proteins in normal development have not yet been identified. Here, we analyzed the expression and function of nanos1 during craniofacial development in zebrafish. nanos1 was expressed in the pharyngeal endoderm and endodermal pouches essential for the development of facial skeletons and endocrine glands in the vertebrate head. However, no craniofacial defects, such as abnormal pouches, hypoplasia of the thymus, malformed facial skeletons, have been found in nanos1 knockout animals. The normal craniofacial development of nanos1 knockout animals is unlikely a consequence of the genetic redundancy of Nanos1 with Nanos2 or Nanos3 or a result of the genetic compensation for the loss of Nanos1 by Nanos2 or Nanos3 because the expression of nanos2 and nanos3 was rarely seen in the pharyngeal endoderm and endodermal pouches in wild-type and nanos1 mutant animals during craniofacial development. Our findings suggest that nanos1 expression in the pharyngeal endoderm might be dispensable for craniofacial development in zebrafish.

NANOS2 is a sequence-specific mRNA-binding protein that promotes transcript degradation in spermatogonial stem cells

Spermatogonial stem cells (SSCs) sustain spermatogenesis and fertility throughout adult male life. The conserved RNA-binding protein NANOS2 is essential for the maintenance of SSCs, but its targets and mechanisms of function are not fully understood. Here, we generated a fully functional epitope-tagged Nanos2 mouse allele and applied the highly stringent cross-linking and analysis of cDNAs to define NANOS2 RNA occupancy in SSC lines. NANOS2 recognizes the AUKAAWU consensus motif, mostly found in the 3' untranslated region of defined messenger RNAs (mRNAs). We find that NANOS2 is a regulator of key signaling and metabolic pathways whose dosage or activity are known to be critical for SSC maintenance. NANOS2 interacts with components of CCR4-NOT deadenylase complex in SSC lines, and consequently, NANOS2 binding reduces the half-lives of target transcripts. In summary, NANOS2 contributes to SSC maintenance through the regulation of target mRNA stability and key self-renewal pathways.

mRNPs: Structure and role in development

In eukaryotic cells, mRNA molecules are coated with numerous RNA-binding proteins and so exist in ribonucleoproteins (mRNPs). The proteins associated with the mRNA regulate the fate of mRNA, including its localization, translation and decay. Before activation of translation, the mRNA does not display any template functions-it is masked. The coordinated activity of certain RNA-binding proteins determines the future fate of each mRNA individually. In embryo development, the temporal and spatial regulation of translation can cause a situation when the mRNA and the encoded protein are localized in different compartments and so the differentiation of the cells can be determined. The fundamentals of regulation of the mRNAs fate and functioning in nerves are similar to those already described for oo- and embryogenesis. Disorders in the mRNA masking and demasking result in the emergence of various diseases, in particular cancers and neuro-degenerative diseases.

A multi-ethnic genome-wide association study implicates collagen matrix integrity and cell differentiation pathways in keratoconus

Keratoconus is characterised by reduced rigidity of the cornea with distortion and focal thinning that causes blurred vision, however, the pathogenetic mechanisms are unknown. It can lead to severe visual morbidity in children and young adults and is a common indication for corneal transplantation worldwide. Here we report the first large scale genome-wide association study of keratoconus including 4,669 cases and 116,547 controls. We have identified significant association with 36 genomic loci that, for the first time, implicate both dysregulation of corneal collagen matrix integrity and cell differentiation pathways as primary disease-causing mechanisms. The results also suggest pleiotropy, with some disease mechanisms shared with other corneal diseases, such as Fuchs endothelial corneal dystrophy. The common variants associated with keratoconus explain 12.5% of the genetic variance, which shows potential for the future development of a diagnostic test to detect susceptibility to disease.

Rbm46, a novel germ cell-specific factor, modulates meiotic progression and spermatogenesis

It has been suggested that many novel RNA-binding proteins (RBPs) are required for gametogenesis, but the necessity of few of these proteins has been functionally verified. Here, we identified one RBP, Rbm46, and investigated its expression pattern and role in zebrafish reproduction. We found that rbm46 is maternally provided and specifically expressed in the germ cells of gonadal tissues using in situ hybridization, reverse transcription-PCR, and quantitative real-time polymerase chain reaction (qRT-PCR). Two independent rbm46 mutant zebrafish lines were generated via the transcription activator-like effector nuclease technique. Specific disruption of rbm46 resulted in masculinization and infertility in the mutants. Although the spermatogonia appeared grossly normal in the mutants, spermatogenesis was impaired, and meiosis events were not observed. The introduction of a tp53M214K mutation could not rescue the female-to-male sex-reversal phenotype, indicating that rbm46 acts independently of the p53-dependent apoptotic pathway. RNA sequencing and qRT-PCR subsequently indicated that Rbm46 might be involved in the posttranscriptional regulation of functional genes essential for germ cell development, such as nanos3, dazl, and sycp3, during gametogenesis. Together, our results reveal for the first time the crucial role of rbm46 in regulating germ cell development in vivo through promotion of germ cell progression through meiosis prophase I.

Analysis of ovarian transcriptomes reveals thousands of novel genes in the insect vector Rhodnius prolixus

Rhodnius prolixus is a Triatominae insect species and a primary vector of Chagas disease. The genome of R. prolixus has been recently sequenced and partially assembled, but few transcriptome analyses have been performed to date. In this study, we describe the stage-specific transcriptomes obtained from previtellogenic stages of oogenesis and from mature eggs. By analyzing ~ 228 million paired-end RNA-Seq reads, we significantly improved the current genome annotations for 9206 genes. We provide extended 5' and 3' UTRs, complete Open Reading Frames, and alternative transcript variants. Strikingly, using a combination of genome-guided and de novo transcriptome assembly we found more than two thousand novel genes, thus increasing the number of genes in R. prolixus from 15,738 to 17,864. We used the improved transcriptome to investigate stage-specific gene expression profiles during R. prolixus oogenesis. Our data reveal that 11,127 genes are expressed in the early previtellogenic stage of oogenesis and their transcripts are deposited in the developing egg including key factors regulating germline development, genome integrity, and the maternal-zygotic transition. In addition, GO term analyses show that transcripts encoding components of the steroid hormone receptor pathway, cytoskeleton, and intracellular signaling are abundant in the mature eggs, where they likely control early embryonic development upon fertilization. Our results significantly improve the R. prolixus genome and transcriptome and provide novel insight into oogenesis and early embryogenesis in this medically relevant insect.

Why isn't sex optional? Stem-cell competition, loss of regenerative capacity, and cancer in metazoan evolution

Animals that can reproduce vegetatively by fission or budding and also sexually via specialized gametes are found in all five primary animal lineages (Bilateria, Cnidaria, Ctenophora, Placozoa, Porifera). Many bilaterian lineages, including roundworms, insects, and most chordates, have lost the capability of vegetative reproduction and are obligately gametic. We suggest a developmental explanation for this evolutionary phenomenon: obligate gametic reproduction is the result of germline stem cells winning a winner-take-all competition with non-germline stem cells for control of reproduction and hence lineage survival. We develop this suggestion by extending Hamilton's rule, which factors the relatedness between parties into the cost/benefit analysis that underpins cooperative behaviors, to include similarity of cellular state. We show how coercive or deceptive cell-cell signaling can be used to make costly cooperative behaviors appear less costly to the cooperating party. We then show how competition between stem-cell lineages can render an ancestral combination of vegetative reproduction with facultative sex unstable, with one or the other process driven to extinction. The increased susceptibility to cancer observed in obligately-sexual lineages is, we suggest, a side-effect of deceptive signaling that is exacerbated by the loss of whole-body regenerative abilities. We suggest a variety of experimental approaches for testing our predictions.

Multi-level analysis of reproduction in an Antarctic midge identifies female and male accessory gland products that are altered by larval stress and impact progeny viability

The Antarctic midge, Belgica antarctica, is a wingless, non-biting midge endemic to Antarctica. Larval development requires at least 2 years, but adults live only 2 weeks. The nonfeeding adults mate in swarms and females die shortly after oviposition. Eggs are suspended in a gel of unknown composition that is expressed from the female accessory gland. This project characterizes molecular mechanisms underlying reproduction in this midge by examining differential gene expression in whole males, females, and larvae, as well as in male and female accessory glands. Functional studies were used to assess the role of the gel encasing the eggs, as well as the impact of stress on reproductive biology. RNA-seq analyses revealed sex- and development-specific gene sets along with those associated with the accessory glands. Proteomic analyses were used to define the composition of the egg-containing gel, which is generated during multiple developmental stages and derived from both the accessory gland and other female organs. Functional studies indicate the gel provides a larval food source as well as a buffer for thermal and dehydration stress. All of these function are critical to juvenile survival. Larval dehydration stress directly reduces production of storage proteins and key accessory gland components, a feature that impacts adult reproductive success. Modeling reveals that bouts of dehydration may have a significant impact on population growth. This work lays a foundation for further examination of reproduction in midges and provides new information related to general reproduction in dipterans. A key aspect of this work is that reproduction and stress dynamics, currently understudied in polar organisms, are likely to prove critical in determining how climate change will alter their survivability.

MiR-210 regulates coelomocyte proliferation through targeting E2F3 in Apostichopus japonicus

MiR-210 plays a crucial role in cell survival, migration, and regeneration in vertebrates. In our previous work, the expression of miR-210 was considerably induced in diseased Apostichopus japonicus with skin ulcer syndrome (SUS). To further explore the mechanism of miR-210 in regulating the SUS, this study identified E2F transcription factor 3 (E2F3), a candidate target of miR-210, from the sea cucumber A. japonicus via RNA-seq and RACE (designated as AjE2F3). A 1992 bp fragment representing the full-length cDNA of AjE2F3 was obtained, which includes an ORF of 1194 bp encoding a polypeptide of 398 amino acids with a molecular weight of 44.43 kDa. Expression profiling analysis suggested that the expression of AjE2F3 decreased while that of miR-210 increased in Vibrio splendidus-challenged sea cucumber coelomocytes. Dual-luciferase reporter assay revealed that miR-210 targeted AjE2F3 via binding to the 3'UTR region from 108 nt to 128 nt. MiR-210 overexpression in cultured coelomocytes repressed AjE2F3 at the mRNA level and reduced cell proliferation in vitro. Consistently, AjE2F3 overexpression significantly promoted coelomocyte proliferation, as assessed by MTT in vitro. Overall, our results indicated that miR-210 can suppress coelomocyte proliferation by targeting AjE2F3 in pathogen-challenged sea cucumbers.

An Interaction Network of RNA-Binding Proteins Involved in Drosophila Oogenesis

During Drosophila oogenesis, the localization and translational regulation of maternal transcripts relies on RNA-binding proteins (RBPs). Many of these RBPs localize several mRNAs and may have additional direct interaction partners to regulate their functions. Using immunoprecipitation from whole Drosophila ovaries coupled to mass spectrometry, we examined protein-protein associations of 6 GFP-tagged RBPs expressed at physiological levels. Analysis of the interaction network and further validation in human cells allowed us to identify 26 previously unknown associations, besides recovering several well characterized interactions. We identified interactions between RBPs and several splicing factors, providing links between nuclear and cytoplasmic events of mRNA regulation. Additionally, components of the translational and RNA decay machineries were selectively co-purified with some baits, suggesting a mechanism for how RBPs may regulate maternal transcripts. Given the evolutionary conservation of the studied RBPs, the interaction network presented here provides the foundation for future functional and structural studies of mRNA localization across metazoans.

Nanos3, a cancer-germline gene, promotes cell proliferation, migration, chemoresistance, and invasion of human glioblastoma

Background

Radiotherapy, chemotherapy, and surgery have made crucial strides in glioblastoma treatment, yet they often fail; thus, new treatment and new detection methods are needed. Aberrant expression of Nanos3 has been functionally associated with various cancers. Here, we sought to identify the clinical significance and potential mechanisms of Nanos3 in human glioblastoma.

Methods

Nanos3 expression was studied in nude mouse glioblastoma tissues and glioblastoma cell lines by immunohistochemistry, Western blot, and RT-PCR. Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 gene editing assay was performed to generate the Nanos3 knockdown glioblastoma cell lines. The effects of Nanos3 on glioblastoma cells proliferation, migration, invasion, chemoresistance, germ cell characteristics, and tumor formation were analyzed by CCK8, transwell, cell survival experiments and alkaline phosphatase staining in vitro and in nude mouse models in vivo. Correlation between the expression of stemness proteins and the expression of Nanos3 was evaluated by Western blot.

Results

We found that Nanos3 was strongly expressed in both glioblastoma cell lines and tissues. Western blot and sequencing assays showed that the Nanos3 knockdown glioblastoma cell lines were established successfully, and we discovered that Nanos3 deletion reduced the proliferation, migration, and invasion of glioblastoma cells in vitro (P < 0.05). Nanos3 knockdown enhanced the sensitivity of glioblastoma cells to doxorubicin (DOX) and temozolomide (TMZ) (P < 0.05), and Nanos3^+/- glioblastoma cell lines did not show the characteristics of the germline cells. In addition, Nanos3 deletion inhibited subcutaneous xenograft tumor growth in vivo (P < 0.001). Moreover, the oncogenesis germline protein levels of CD133, Oct4, Ki67, and Dazl decreased significantly in glioblastoma cells following Nanos3 knockdown.

Conclusions

Both in vitro and in vivo assays suggest that Nanos3, which is a cancer-germline gene, initiates the tumorigenesis of glioblastoma via acquiring the oncogenesis germline traits. These data demonstrate that ectopic germline traits are necessary for glioblastoma growth.

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.

Human NANOS1 Represses Apoptosis by Downregulating Pro-Apoptotic Genes in the Male Germ Cell Line

While two mouse NANOS paralogues, NANOS2 and NANOS3, are crucial for maintenance of germ cells by suppression of apoptosis, the mouse NANOS1 paralogue does not seem to regulate these processes. Previously, we described a human NANOS1 p.[(Pro34Thr);(Ser83del)] mutation associated with the absence of germ cells in seminiferous tubules of infertile patients, which might suggest an anti-apoptotic role of human NANOS1. In this study, we aimed to determine a potential influence of human NANOS1 on the maintenance of TCam-2 model germ cells by investigating proliferation, cell cycle, and apoptosis. Constructs encoding wild-type or mutated human NANOS1 were used for transfection of TCam-2 cells, in order to investigate the effect of NANOS1 on cell proliferation, which was studied using a colorimetric assay, as well as apoptosis and the cell cycle, which were measured by flow cytometry. RNA-Seq (RNA sequencing) analysis followed by RT-qPCR (reverse transcription and quantitative polymerase chain reaction) was conducted for identifying pro-apoptotic genes repressed by NANOS1. Here, we show that overexpression of NANOS1 downregulates apoptosis in TCam-2 cells. Moreover, we found that NANOS1 represses a set of pro-apoptotic genes at the mRNA level. We also found that the infertility-associated p.[(Pro34Thr);(Ser83del)] mutation causes NANOS1 to functionally switch from being anti-apoptotic to pro-apoptotic in the human male germ cell line. Thus, this report is the first to show an anti-apoptotic role of NANOS1 exerted by negative regulation of mRNAs of pro-apoptotic genes.

A Novel Bioengineered miR-127 Prodrug Suppresses the Growth and Metastatic Potential of Triple-Negative Breast Cancer Cells

miR-127 is downregulated in breast cancer, where it has been shown to suppress the proliferation, migration, and invasion of breast cancer cells. In triple-negative breast cancer (TNBC), miR-127 downregulation correlates with decreased disease-free and overall patient survival. Tumor suppressor miRNAs may hold therapeutic promise but progress has been limited by several factors, including the lability and high cost of miRNA mimics. Here, we take a novel approach to produce a miR-127 prodrug (miR-127^PD), which we demonstrate is processed to mature, functional miR-127-3p in TNBC tumor cells. miR-127^PD decreased the viability and motility of TNBC cells, sensitized TNBC cells to chemotherapy, and restricted the TNBC stem cell population. Furthermore, systemic delivery of miR-127^PD suppressed tumor growth of MDA-MB-231 and MDA-MB-468 TNBC cells and spontaneous metastasis of MDA-MB-231 cells. In addition, CERK, NANOS1, FOXO6, SOX11, SOX12, FASN, and SUSD2 were identified as novel, functionally important targets of miR-127. In conclusion, our study demonstrates that miR-127 functions as a tumor and metastasis suppressor in TNBC and that delivery of miR-127 may hold promise as a novel therapy. SIGNIFICANCE: Exogenous administration of miR-127, which is functionally activated in target cells, inhibits growth and spontaneous metastasis of triple-negative breast cancer.

A low-complexity region in human XRN1 directly recruits deadenylation and decapping factors in 5'-3' messenger RNA decay

XRN1 is the major cytoplasmic exoribonuclease in eukaryotes, which degrades deadenylated and decapped mRNAs in the last step of the 5'-3' mRNA decay pathway. Metazoan XRN1 interacts with decapping factors coupling the final stages of decay. Here, we reveal a direct interaction between XRN1 and the CCR4-NOT deadenylase complex mediated by a low-complexity region in XRN1, which we term the 'C-terminal interacting region' or CIR. The CIR represses reporter mRNA deadenylation in human cells when overexpressed and inhibits CCR4-NOT and isolated CAF1 deadenylase activity in vitro. Through complementation studies in an XRN1-null cell line, we dissect the specific contributions of XRN1 domains and regions toward decay of an mRNA reporter. We observe that XRN1 binding to the decapping activator EDC4 counteracts the dominant negative effect of CIR overexpression on decay. Another decapping activator PatL1 directly interacts with CIR and alleviates the CIR-mediated inhibition of CCR4-NOT activity in vitro. Ribosome profiling revealed that XRN1 loss impacts not only on mRNA levels but also on the translational efficiency of many cellular transcripts likely as a consequence of incomplete decay. Our findings reveal an additional layer of direct interactions in a tightly integrated network of factors mediating deadenylation, decapping and 5'-3' exonucleolytic decay.

A new mouse model to study the role of ectopic Nanos3 expression in cancer

BACKGROUND

NANOS3 is a gene conserved throughout evolution. Despite the quite low conservation of Nanos sequences between different organisms and even between Nanos paralogs, their role in germ cell development is remarkably universal. Human Nanos3 expression is normally restricted to the gonads and the brain. However, ectopic activation of this gene has been detected in various human cancers. Until now, Nanos3 and other Nanos proteins have been studied almost exclusively in germ cell development.

METHODS

Transgenic mice were generated by targeted insertion of a human Nanos3 cDNA into the ROSA26 locus. The transgene could be spatiotemporally induced by Cre recombinase activity removing an upstream floxed STOP cassette. A lung tumor model with ectopic Nanos3 expression was based on the lung-specific activation of the reverse tetracycline transactivator gene, in combination with a tetO-CMV promoter controlling Cre expression. When doxycycline was provided to the mice, Cre was activated leading to deletion of TP53 alleles and activation of both oncogenic KRas^G12D and Nanos3. Appropriate controls were foreseen. Tumors and tumor-derived cell cultures were analyzed in various ways.

RESULTS

We describe the successful generation of Nanos3^LSL/- and Nanos3^LSL/LSL mice in which an exogenous human NANOS3 gene can be activated in vivo upon Cre expression. These mice, in combination with different conditional and doxycycline-inducible Cre lines, allow the study of the role of ectopic Nanos3 expression in several cancer types. The Nanos3^LSL mice were crossed with a non-small cell lung cancer (NSCLC) mouse model based on conditional expression of oncogenic KRas and homozygous loss of p53. This experiment demonstrated that ectopic expression of Nanos3 in the lungs has a significant negative effect on survival. Enhanced bronchiolar dysplasia was observed when Nanos3-expressing NSCLC mice were compared with control NSCLC mice. An allograft experiment, performed with cell cultures derived from primary lung tumors of control and Nanos3-expressing NSCLC mice, revealed lymph node metastasis in mice injected with Nanos3-expressing NSCLC cells.

CONCLUSIONS

A new mouse model was generated allowing examination of Nanos3-associated pathways and investigation of the influence of ectopic Nanos3 expression in various cancer types. This model might identify Nanos3 as an interesting target in cancer therapeutics.

Molecular Cloning and Sexually Dimorphic Expression Analysis of nanos2 in the Sea Urchin, Mesocentrotus nudus

Sea urchin (Mesocentrotus nudus) is an economically important mariculture species in China and the gonads are the solely edible parts to human. The molecular mechanisms of gonad development have attracted increasing attention in recent years. Although the nanos2 gene has been identified as a germ cell marker in several invertebrates, little is known about nanos2 in adult sea urchins. Hereinto, we report the characterization of Mnnano2, an M. nudus nanos2 homology gene. Mnnanos2 is a maternal factor and can be detected continuously during embryogenesis and early ontogeny. Real-time quantitative PCR (RT-qPCR) and section in situ hybridization (ISH) analysis revealed a dynamic and sexually dimorphic expression pattern of Mnnano2 in the gonads. Its expression reached the maximal level at Stage 2 along with the gonad development in both ovary and testis. In the ovary, Mnnanos2 is specifically expressed in germ cells. In contrast, Mnnanos2 is expressed in both nutritive phagocytes (NP) cells and male germ cells in testis. Moreover, knocking down of Mnnanos2 by means of RNA interference (RNAi) reduced nanos2 and boule expression but conversely increased the expression of foxl2. Therefore, our data suggest that Mnnanos2 may serve as a female germ cell marker during gametogenesis and provide chances to uncover its function in adult sea urchin.

RNA N6-methyladenosine modification participates in miR-660/E2F3 axis-mediated inhibition of cell proliferation in gastric cancer

Increasing evidence has shown that dysregulation of mircoRNA (miRNA) is linked to the development and progression of human cancer, including gastric cancer (GC). In the current study, by analysing the GEO database (GSE78091), we found that miR-660 was significantly downregulated in GC. Consistently, quantitative real-time PCR (qRT-PCR) results showed that miR-660 was dramatically decreased in GC tissues and cell lines. Importantly, low miR-660 expression was closely related to larger tumor size (P =  0.008), lymph node metastasis (P =  0.006), advanced TNM stage (P =  0.029), and poor outcome (P = 0.023). Ectopic expression of miR-660 inhibited proliferation of MGC-803 and AGS cells and induced apoptosis. Further mechanism experiments suggested that the well-known oncogene E2F3 (E2F transcription factor 3) was a downstream target of miR-660. Overexpression of miR-660 reduced the activity of E2F3 by directly binding to the 3221˜3226 region of E2F3 3`-UTR, and there was a strong negative correlation between the expression of miR-660 and E2F3 in GC tissues (r = - 0.648, P <  0.001). Furthermore, E2F3 overexpression abrogated the anti-proliferation effect of miR-660 in GC cell lines. Of note, we found an N6-methyladenosine (m<sup>6</sup>A) motif at the 3063˜3067 region of E2F3 3`-UTR, and this m⁶A-modified motif was required for the interaction between miR-660 and E2F3 3`-UTR. Collectively, our findings reveal the compelling role of m⁶A in GC and highlight the regulatory function of the miR-660/E2F3 pathway in GC progression.

PUM1 and PUM2 exhibit different modes of regulation for SIAH1 that involve cooperativity with NANOS paralogues

Pumilio (PUM) proteins are RNA-binding proteins that posttranscriptionally regulate gene expression in many organisms. Their PUF domain recognizes specific PUM-binding elements (PBE) in the 3' untranslated region of target mRNAs while engaging protein cofactors such as NANOS that repress the expression of target mRNAs through the recruitment of effector complexes. Although the general process whereby PUM recognizes individual mRNAs has been studied extensively, the particulars of the mechanism underlying PUM-NANOS cooperation in mRNA regulation and the functional overlap among PUM and NANOS paralogues in mammals have not been elucidated. Here, using the novel PUM1 and PUM2 mRNA target SIAH1 as a model, we show mechanistic differences between PUM1 and PUM2 and between NANOS1, 2, and 3 paralogues in the regulation of SIAH1. Specifically, unlike PUM2, PUM1 exhibited PBE-independent repression of SIAH1 3'UTR-dependent luciferase expression. Concordantly, the PUF domains of PUM1 and PUM2 showed different EMSA complex formation patterns with SIAH1 3'UTRs. Importantly, we show direct binding of NANOS3, but not NANOS2, to SIAH1 3'UTR, which did not require PBEs or the PUF domain. To the best of our knowledge, this is the first report, showing that an NANOS protein directly binds RNA. Finally, using NANOS1 and NANOS3 constructs carrying mutations identified in infertile patients, we show that these mutations disrupt repression of the SIAH1-luciferase reporter and that the central region in NANOS1 appears to contribute to the regulation of SIAH1. Our findings highlight the mechanistic versatility of the PUM/NANOS machinery in mammalian posttranscriptional regulation.