Isolation of a DEAD-family protein gene that encodes a murine homolog of Drosophila vasa and its specific expression in germ cell lineage

Germline-specific RNA helicase DDX4 forms cytoplasmic granules in cancer cells and promotes tumor growth

Cancer cells undergo major epigenetic alterations and transcriptomic changes, including ectopic expression of tissue- and cell-type-specific genes. Here, we show that the germline-specific RNA helicase DDX4 forms germ-granule-like cytoplasmic ribonucleoprotein granules in various human tumors, but not in cultured cancer cells. These cancerous DDX4 complexes contain RNA-binding proteins and splicing regulators, including many known germ granule components. The deletion of DDX4 in cancer cells induces transcriptomic changes and affects the alternative splicing landscape of a number of genes involved in cancer growth and invasiveness, leading to compromised capability of DDX4-null cancer cells to form xenograft tumors in immunocompromised mice. Importantly, the occurrence of DDX4 granules is associated with poor survival in patients with head and neck squamous cell carcinoma and higher histological grade of prostate cancer. Taken together, these results show that the germ-granule-resembling cancerous DDX4 granules control gene expression and promote malignant and invasive properties of cancer cells.

Characteristics of the Vasa Gene in Silurus asotus and Its Expression Response to Letrozole Treatment

The identification and expression of germ cells are important for studying sex-related mechanisms in fish. The vasa gene, encoding an ATP-dependent RNA helicase, is recognized as a molecular marker of germ cells and plays a crucial role in germ cell development. Silurus asotus, an important freshwater economic fish species in China, shows significant sex dimorphism with the female growing faster than the male. However, the molecular mechanisms underlying these sex differences especially involving in the vasa gene in this fish remain poorly understood. In this work, the vasa gene sequence of S. asotus (named as Savasa) was obtained through RT-PCR and rapid amplification of cDNA end (RACE), and its expression in embryos and tissues was analyzed using qRT-PCR and an in situ hybridization method. Letrozole (LT) treatment on the larvae fish was also conducted to investigate its influence on the gene. The results revealed that the open reading frame (ORF) of Savasa was 1989 bp, encoding 662 amino acids. The SaVasa protein contains 10 conserved domains unique to the DEAD-box protein family, showing the highest sequence identity of 95.92% with that of Silurus meridionalis. In embryos, Savasa is highly expressed from the two-cell stage to the blastula stage in early embryos, with a gradually decreasing trend from the gastrula stage to the heart-beating stage. Furthermore, Savasa was initially detected at the end of the cleavage furrow during the two-cell stage, later condensing into four symmetrical cell clusters with embryonic development. At the gastrula stage, Savasa-positive cells increased and began to migrate towards the dorsal side of the embryo. In tissues, Savasa is predominantly expressed in the ovaries, with almost no or lower expression in other detected tissues. Moreover, Savasa was expressed in phase I-V oocytes in the ovaries, as well as in spermatogonia and spermatocytes in the testis, implying a specific expression pattern of germ cells. In addition, LT significantly upregulated the expression of Savasa in a concentration-dependent manner during the key gonadal differentiation period of the fish. Notably, at 120 dph after LT treatment, Savasa expression was the lowest in the testis and ovary of the high concentration group. Collectively, findings from gene structure, protein sequence, phylogenetic analysis, RNA expression patterns, and response to LT suggest that Savasa is maternally inherited with conserved features, serving as a potential marker gene for germ cells in S.asotus, and might participate in LT-induced early embryonic development and gonadal development processes of the fish. This would provide a basis for further research on the application of germ cell markers and the molecular mechanisms of sex differences in S. asotus.

Neurotrophin-4 promotes in vitro development and maturation of human secondary follicles yielding metaphase II oocytes and successful blastocyst formation

STUDY QUESTION

Does a matrix-free culture system supplemented with neurotrophic factor 4 (NT4) improve human in vitro follicular development and meiotic maturation, ultimately resulting in fertilizable oocytes?

SUMMARY ANSWER

NT4 supplementation of in vitro culture significantly enhances the growth, steroid hormone production, and maturity potential of human secondary follicles derived from fresh ovarian medulla (from post- and pre-pubertal patients), thereby yielding fertilizable oocytes.

WHAT IS KNOWN ALREADY

Reconstituting folliculogenesis in vitro is of paramount importance in the realms of fertility preservation, reproductive biology research, and reproductive toxicity assessments. However, the efficiency of in vitro culture systems remains suboptimal, as the attainment of fertilizable oocytes from in vitro growth (IVG) of human follicles remains unachieved, with the data being particularly scant regarding follicles from prepubertal girls. We have previously found that mouse oocytes from secondary follicles derived from IVG are deficient in neuroendocrine regulation. NT4 and its corresponding receptor have been identified in human follicles. Significantly, the addition of NT4 during the IVG process markedly enhances both follicle growth and oocyte maturation rates in mice.

STUDY DESIGN SIZE DURATION

Fresh medulla tissue obtained during tissue preparation for ovarian tissue cryopreservation (OTC) were collected from 10 patients aged from 6 to 21 years old, all of whom had undergone unilateral oophorectomy as a means of fertility preservation. Isolated secondary follicles were individually cultured in vitro with or without NT4 in a matrix-free system.

PARTICIPANTS/MATERIALS SETTING METHODS

Secondary follicles, extracted via enzymatic digestion and mechanical disruption from each patient, were randomly allocated to either a control group or an NT4-supplemented group (100 ng/ml), followed by individual culture on an ultra-low attachment plate. Follicle growth and viability were assessed by microscopy. Levels of anti-Müllerian hormone (AMH), estradiol, and progesterone in the medium were quantified. An oocyte-specific marker was identified using confocal fluorescence microscopy following DEAD box polypeptide 4 (DDX4) staining. The competence of individual oocytes for maturation and fertilization were assessed after IVM and ICSI with donated sperm samples.

MAIN RESULTS AND THE ROLE OF CHANCE

Overall, isolated follicles from both groups survived up to 6 weeks with increasing diameters over the duration (P < 0.05), reaching terminal diameters of almost 1 mm with confirmed steroidogenesis and expression of oocyte marker (DDX4), and producing morphologically normal MII oocytes. When compared with the control group, the NT4 group had a similar initial follicular diameter (206 ± 61.3 vs 184 ± 93.4 μm) but exhibited a significant increase in follicular diameter from the ninth day of culture onwards (P < 0.05). From Week 3, estradiol and progesterone production were significantly increased in the NT4 group, while no significant difference was observed in AMH production between groups. The proportion of 'fast-growth' follicles in the NT4 group was significantly higher than that in the control group (13/23 vs 6/24, P < 0.05). An increased efficiency of MII oocyte maturation per live follicle in the NT4 group was also observed (control group vs NT4 group, 4/24 vs 10/23, P < 0.05). It is noteworthy that an MII oocyte obtained from the control group exhibited abnormal fertilization after ICSI. In contrast, an MII oocyte acquired from the NT4 group progressed to the blastocyst stage and showed potential for transfer.

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

The cohort examined in this study was all patients diagnosed with beta-thalassemia major. Whether this culture system is effective for patients with other diseases remains unknown. Since the chosen dose of NT4 was established based on dose finding in mice, the optimal dose for use in a human IVG system needs further confirmation. The oocytes and embryos procured from this study have not been quantified for ploidy status or epigenetic signatures.

WIDER IMPLICATIONS OF THE FINDINGS

Fresh medulla tissue obtained during tissue preparation for OTC may serve as a precious source of fertilizable oocytes for female fertility preservation, even for pre-pubertal girls, without the threat of tumour reintroduction. After further characterization and optimization of the system, this culture system holds the potential to provide a powerful future research tool, for the comprehensive exploration of human follicular development mechanisms and for conducting reproductive toxicity evaluations.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the National Key R&D Program of China (grant number 2022YFC2703000) and National Natural Science Foundation of China (grant numbers 82271651 and 81871214). The medium used in human follicle in vitro culture in this study has been applied for a national invention patent in China (No. 202211330660.7). The inventors of the patent, in order, are: Y.G., C.F., and X.L.

Germ plasm dynamics during oogenesis and early embryonic development in Xenopus and zebrafish

Specification of the germline and its segregation from the soma mark one of the most crucial events in the lifetime of an organism. In different organisms, this specification can occur through either inheritance or inductive mechanisms. In species such as Xenopus and zebrafish, the specification of primordial germ cells relies on the inheritance of maternal germline determinants that are synthesized and sequestered in the germ plasm during oogenesis. In this review, we discuss the formation of the germ plasm, how germline determinants are recruited into the germ plasm during oogenesis, and the dynamics of the germ plasm during oogenesis and early embryonic development.

Autophagy regulation and protein kinase activity of PIK3C3 controls sertoli cell polarity through its negative regulation on SCIN (scinderin)

Sertoli cells are highly polarized testicular cells that provide a nurturing environment for germ cell development and maturation during spermatogenesis. The class III phosphatidylinositol 3-kinase (PtdIns3K) plays core roles in macroautophagy in various cell types; however, its role in Sertoli cells remains unclear. Here, we generated a mouse line in which the gene encoding the catalytic subunit, Pik3c3, was specifically deleted in Sertoli cells (cKO) and found that after one round of normal spermatogenesis, the cKO mice quickly became infertile and showed disruption of Sertoli cell polarity and impaired spermiogenesis. Subsequent proteomics and phosphoproteomics analyses enriched the F-actin cytoskeleton network involved in the disorganized Sertoli-cell structure in cKO testis which we identified a significant increase of the F-actin negative regulator SCIN (scinderin) and the reduced phosphorylation of HDAC6, an α-tubulin deacetylase. Our results further demonstrated that the accumulation of SCIN in cKO Sertoli cells caused the disorder and disassembly of the F-actin cytoskeleton, which was related to the failure of SCIN degradation through the autophagy-lysosome pathway. Additionally, we found that the phosphorylation of HDAC6 at site S59 by PIK3C3 was essential for its degradation through the ubiquitin-proteasome pathway. As a result, the HDAC6 that accumulated in cKO Sertoli cells deacetylated SCIN at site K189 and led to a disorganized F-actin cytoskeleton. Taken together, our findings elucidate a new mechanism for PIK3C3 in maintaining the polarity of Sertoli cells, in which both its autophagy regulation or protein kinase activities are required for the stabilization of the actin cytoskeleton.Abbreviations: ACTB: actin, beta; AR: androgen receptor; ATG14: autophagy related 14; BafA1: bafilomycin A1; BECN1: beclin 1, autophagy related; BTB: blood-testis barrier; CASP3: caspase 3; CDC42: cell division cycle 42; CDH2: cadherin 2; CHX: cycloheximide; CTNNA1: catenin (cadherin associated protein), alpha 1; CYP11A1: cytochrome P450, family 11, subfamily A, polypeptide 1; EBSS: Earle's balanced salt solution; ES: ectoplasmic specialization; FITC: fluorescein isothiocyanate; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GCNA: germ cell nuclear acidic protein; GJA1: gap junction protein, alpha 1; H2AX: H2A.X variant histone; HDAC6: histone deacetylase 6; KIT: KIT proto-oncogene, receptor tyrosine kinase; LAMP1: lysosomal associated membrane protein 1; MAP3K5: mitogen-activated protein kinase kinase kinase 5; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; OCLN: occludin; PIK3C3: phosphatidylinositol 3-kinase catalytic subunit type 3; PIK3R4: phosphoinositide-3-kinase regulatory subunit 4; PNA: arachis hypogaea lectin; RAC1: Rac family small GTPase 1; SCIN: scinderin; SQSTM1/p62: sequestosome 1; SSC: spermatogonia stem cell; STK11: serine/threonine kinase 11; TJP1: tight junction protein 1; TubA: tubastatin A; TUBB3: tubulin beta 3 class III; TUNEL: TdT-mediated dUTP nick-end labeling; UB: ubiquitin; UVRAG: UV radiation resistance associated gene; VIM: vimentin; WT1: WT1 transcription factor; ZBTB16: zinc finger and BTB domain containing 16.

In vitro culture of reptile PGCS to preserve endangered species

Primordial germ cells (PGCs), are the source of gametes in vertebrates. There are similarities in the development of PGCs of reptiles with avian and mammalian species PGCs development. PGCs culture has been performed for avian and mammalian species but there is no report for reptilian PGCs culture. In vitro culture of PGCs is needed to produce transgenic animals, preservation of endangered animals and for studies on cell behaviour and research on fertility. Reptiles are traded as exotic pets and a source of food and they are valuable for their skin and they are useful as model for medical research. Transgenic reptile has been suggested to be useful for pet industry and medical research. In this research different aspects of PGCs development was compared in three main classes of vertebrates including mammalian, avian and reptilian species. It is proposed that a discussion on similarities between reptilian PGCs development with avian and mammalian species helps to find clues for studies of reptilian PGCs development details and finding an efficient protocol for in vitro culture of reptilian PG.

RNA Helicase Vasa as a Multifunctional Conservative Regulator of Gametogenesis in Eukaryotes

Being a conservative marker of germ cells across metazoan species, DEAD box RNA helicase Vasa (DDX4) remains the subject of worldwide investigations thanks to its multiple functional manifestations. Vasa takes part in the preformation of primordial germ cells in a group of organisms and contributes to the maintenance of germline stem cells. Vasa is an essential player in the piRNA-mediated silencing of harmful genomic elements and in the translational regulation of selected mRNAs. Vasa is the top hierarchical protein of germ granules, liquid droplet organelles that compartmentalize RNA processing factors. Here, we survey current advances and problems in the understanding of the multifaceted functions of Vasa proteins in the gametogenesis of different eukaryotic organisms, from nematodes to humans.

Sertoli cells are the source of stem cell factor for spermatogenesis

Several cell types have been proposed to create the required microenvironment for spermatogenesis. However, expression patterns of the key growth factors produced by these somatic cells have not been systematically studied and no such factor has been conditionally deleted from its primary source(s), raising the question of which cell type(s) are the physiological sources of these growth factors. Here, using single-cell RNA sequencing and a series of fluorescent reporter mice, we found that stem cell factor (Scf), one of the essential growth factors for spermatogenesis, was broadly expressed in testicular stromal cells, including Sertoli, endothelial, Leydig, smooth muscle and Tcf21-CreER+ stromal cells. Both undifferentiated and differentiating spermatogonia were associated with Scf-expressing Sertoli cells in the seminiferous tubule. Conditional deletion of Scf from Sertoli cells, but not any other Scf-expressing cells, blocked the differentiation of spermatogonia, leading to complete male infertility. Conditional overexpression of Scf in Sertoli cells, but not endothelial cells, significantly increased spermatogenesis. Our data reveal the importance of anatomical localization for Sertoli cells in regulating spermatogenesis and that SCF produced specifically by Sertoli cells is essential for spermatogenesis.

Characterization of Oogonial Stem Cells in Adult Mouse Ovaries with Age and Comparison to In Silico Data on Human Ovarian Aging

Many adult somatic stem cell lineages are comprised of subpopulations that differ in gene expression, mitotic activity, and differentiation status. In this study, we explored if cellular heterogeneity also exists within oogonial stem cells (OSCs), and how chronological aging impacts OSCs. In OSCs isolated from mouse ovaries by flow cytometry and established in culture, we identified subpopulations of OSCs that could be separated based on differential expression of stage-specific embryonic antigen 1 (SSEA1) and cluster of differentiation 61 (CD61). Levels of aldehyde dehydrogenase (ALDH) activity were inversely related to OSC differentiation, whereas commitment of OSCs to differentiation through transcriptional activation of stimulated by retinoic acid gene 8 was marked by a decline in ALDH activity and in SSEA1 expression. Analysis of OSCs freshly isolated from ovaries of mice between 3 and 20 months of age revealed that these subpopulations were present and persisted throughout adult life. However, expression of developmental pluripotency associated 3 (Dppa3), an epigenetic modifier that promotes OSC differentiation into oocytes, was lost as the mice transitioned from a time of reproductive compromise (10 months) to reproductive failure (15 months). Further analysis showed that OSCs from aged females could be established in culture, and that once established the cultured cells reactivated Dppa3 expression and the capacity for oogenesis. Analysis of single-nucleus RNA sequence data sets generated from ovaries of women in their 20s versus those in their late 40s to early 50s showed that the frequency of DPPA3-expressing cells decreased with advancing age, and this was paralleled by reduced expression of several key meiotic differentiation genes. These data support the existence of OSC subpopulations that differ in gene expression profiles and differentiation status. In addition, an age-related decrease in Dppa3/DPPA3 expression, which is conserved between mice and humans, may play a role in loss of the ability of OSCs to maintain oogenesis with age.

In vitro spermatogenesis: In search of fully defined conditions

A complete reconstruction of spermatogenesis in vitro under fully defined conditions still has not been achieved. However, many techniques have been proposed to get closer to that aim. Here we review the current progress in the field. At first, we describe the most successful technique, the organ culture method, which allows to produce functional haploid cells. However, this method is based on the culturing of intact testis tissue with unknown factors acting inside it. Then we discuss different types of 3D-cultures where specific testicular cell populations may be aggregated and the impact of each cell population may be examined. Unfortunately, germ cell development does not proceed further than the pachytene stage of meiosis there, with rare exceptions. Finally, we describe recent studies that focus on germ cells in a conventional adherent cell culture. Such studies thoroughly examine issues with in vitro meiosis and provide insight into the mechanisms of meiotic initiation.

Single-cell RNA-sequencing analysis of early sea star development

Echinoderms represent a broad phylum with many tractable features to test evolutionary changes and constraints. Here, we present a single-cell RNA-sequencing analysis of early development in the sea star Patiria miniata, to complement the recent analysis of two sea urchin species. We identified 20 cell states across six developmental stages from 8 hpf to mid-gastrula stage, using the analysis of 25,703 cells. The clusters were assigned cell states based on known marker gene expression and by in situ RNA hybridization. We found that early (morula, 8-14 hpf) and late (blastula-to-mid-gastrula) cell states are transcriptionally distinct. Cells surrounding the blastopore undergo rapid cell state changes that include endomesoderm diversification. Of particular import to understanding germ cell specification is that we never see Nodal pathway members within Nanos/Vasa-positive cells in the region known to give rise to the primordial germ cells (PGCs). The results from this work contrast the results of PGC specification in the sea urchin, and the dataset presented here enables deeper comparative studies in tractable developmental models for testing a variety of developmental mechanisms.

AIRE in Male Fertility: A New Hypothesis

Male infertility affects approximately 14% of all European men, of which ~44% are characterized as idiopathic. There is an urgency to identify the factors that affect male fertility. One such factor, Autoimmune Regulator (AIRE), a protein found in the thymus, has been studied in the context of central tolerance functioning as a nuclear transcription modulator, responsible for the expression of tissue-restricted antigens in specialized thymic cells that prevent autoimmunity. While its expression in the testes remains enigmatic, we recently observed that sterility in mice correlates with the absence of Aire in the testes, regardless of the deficient expression in medullary thymic epithelial cells or cells of the hematopoietic system. By assessing the Aire transcript levels, we discovered that Sertoli cells are the exclusive source of Aire in the testes, where it most likely plays a non-immune role, suggesting an unknown mechanism by which testicular Aire regulates fertility. Here, we discuss these results in the context of previous reports which have suggested that infertility observed in Aire deficient mice is of an autoimmune aetiology. We present an alternative point of view for the role of Aire in testes in respect to fertility altering the perspective of how Aire's function in the testes is currently perceived.

Vasa identifies germ cells in embryos and gonads of Oryzias celebensis

Vasa is the most studied germ cell marker that is indispensable for germ cell development in teleost fishes. Here, a vasa full-length cDNA from Oryzias celebensis was isolated. Analysis of gene expression by reversed transcription polymerase chain reaction and in situ hybridization showed the vasa transcript was maternally inherited and specifically expressed in germ cells during embryogenesis and in adult gonads. During embryogenesis, vasa mRNA was widely distributed in the embryos until the somitogenesis stage and then specifically expressed in primordial germ cells (PGCs). In the testis, vasa expression was highest in spermatogonia and gradually decreased during spermatogenesis. In ovary, vasa expression was present predominantly in immature oocytes and persisted throughout oogenesis. Constructs containing green or red fluorescence proteins and vasa 3' UTR or dnd 3' UTR, confirmed stable vasa expression in the PGCs of O. celebensis and co-expression of the two genes. In summary, the conservation of vasa expression in embryonic and adult germ cells of both sexes compared to other vertebrates suggests its function is also widely conserved.

Soma-to-germline transformation in chromatin-linked neurodevelopmental disorders?

Mutations in numerous chromatin regulators cause neurodevelopmental disorders (NDDs) with unknown mechanisms. Understandably, most research has focused on how chromatin regulators control gene expression that is directly relevant to brain development and function, such as synaptic genes. However, some NDD models surprisingly show ectopic expression of germline genes in the brain. These germline genes are usually expressed only in the primordial germ cells, testis, and ovaries for germ cell development and sexual reproduction. Such ectopic germline gene expression has been reported in several NDDs, including immunodeficiency, centromeric instability, facial anomalies syndrome 1; Kleefstra syndrome 1; MeCP2 duplication syndrome; and mental retardation, X-linked syndromic, Claes-Jensen type. The responsible genes, DNMT3B, G9A/GLP, MECP2, and KDM5C, all encode chromatin regulators for gene silencing. These mutations may therefore lead to germline gene derepression and, in turn, a severe identity crisis of brain cells-potentially interfering with normal brain development. Thus, the ectopic expression of germline genes is a unique hallmark defining this NDD subset and further implicates the importance of germline gene silencing during brain development. The functional impact of germline gene expression on brain development, however, remains undetermined. This perspective article explores how this apparent soma-to-germline transformation arises and how it may interfere with neurodevelopment through genomic instability and impaired sensory cilium formation. Furthermore, we also discuss how to test these hypotheses experimentally to ultimately determine the contribution of ectopic germline transcripts to chromatin-linked NDDs.

Immunolocalization of Vasa, PIWI, and TDRKH proteins in male germ cells during spermatogenesis of the teleost fish Poecilia reticulata

Vasa, PIWI and TDRKH are conserved components of germ granules that in metazoans are involved in germline specification and differentiation, as documented by mutational experiments in some model animals. So far, investigations on PIWI during spermatogenesis of fish has been limited to a few species, and no information is available for TDRKH, another protein involved in the piRNA pathway. In this study, the immunolocalization of these three germline determinants was analyzed in male gonads of the teleost fish Poecilia reticulata to document their localization pattern in the different stages of germ cell differentiation. To analyze their distribution pattern during the different stages of spermatogenesis we performed immunohistochemistry (IHC) and immunofluorescence (IF) assays using primary polyclonal antibodies after testing their specificity with Western Blot. Moreover, sections of testis stained with haematoxylin and eosin clarified the structural organization of P. reticulata testis, while the use of the confocal microscope and the nuclear staining clarified the different stages of germ cell differentiation during spermatogenesis. The results showed that Vasa, PIWI and TDRKH were specifically immunolocalized in the germ cells of P. reticulata, with no specific signal detected in Sertoli cells and in other somatic cells of the gonad. These markers were detected in all stages of differentiation from early spermatogonia to advanced spermatids. Vasa staining was the strongest in spermatogonia, and then decreases throughout differentiation. Instead, both PIWI and TDRKH staining increases during differentiation, and their distribution pattern, similar to what observed in the mouse, suggests their concerted participation in the piRNA pathway also in this fish.

Instructing Mouse Germ Cells to Adopt a Female Fate

BACKGROUND

Germ cells are critical for the survival of our species. They are the only cells that undergo meiosis - the reductive form of cell division that is necessary for genetic reassortment of chromosomes and production of the haploid gametes, the sperm and eggs. Remarkably, the initial female/male fate decision in fetal germ cells does not depend on whether they are chromosomally XX or XY; rather, initial sexual fate is imposed by influences from the surrounding tissue. In mammals, the female germline is particularly precious: despite recent suggestions that germline stem cells exist in the ovary, it is still generally accepted that the ovarian reserve is finite, and its size is dependant on germ cells of the fetal ovary initiating meiosis in a timely manner.

SUMMARY

Prior to 2006, evidence suggested that gonadal germ cells initiate meiotic prophase I by default, but more recent data support a key role for the signalling molecule retinoic acid (RA) in instructing female germ cell fate. Newer findings also support a key meiosis-inducing role for another signalling molecule, bone morphogenic protein (BMP). Nonetheless, many questions remain.

KEY MESSAGES

Here, we review knowledge thus far regarding extrinsic and intrinsic determinants of a female germ cell fate, focusing on the mouse model.

Intrauterine hyponutrition reduces fetal testosterone production and postnatal sperm count in the mouse

Although intrauterine hyponutrition is regarded as a risk factor for the development of "testicular dysgenesis syndrome" (TDS) in the human, underlying mechanism(s) remain largely unknown. To clarify the underlying mechanism(s), we fed vaginal plug-positive C57BL/6N female mice with regular food ad libitum throughout the pregnant course (control females) (C-females) or with 50% of the mean daily intake of the C-females from 6.5 dpc (calorie-restricted females) (R-females), and compared male reproductive findings between 17.5-dpc-old male mice delivered from C-females (C-fetuses) and those delivered from R-females (R-fetuses) and between 6-week-old male mice born to C-females (C-offspring) and those born to R-females (R-offspring). Compared with the C-fetuses, the R-fetuses had (1) morphologically normal external genitalia with significantly reduced anogenital distance index, (2) normal numbers of testicular component cells, and (3) significantly low intratesticular testosterone, in association with significantly reduced expressions of steroidogenic genes. Furthermore, compared with the C-offspring, the R-offspring had (1) significantly increased TUNEL-positive cells and normal numbers of other testicular component cells, (2) normal intratesticular testosterone, in association with normal expressions of steroidogenic genes, (3) significantly reduced sperm count, and normal testis weight and sperm motility, and (4) significantly altered expressions of oxidation stress-related, apoptosis-related, and spermatogenesis-related genes. The results, together with the previous data including the association between testosterone deprivation and oxidative stress-evoked apoptotic activation, imply that reduced fetal testosterone production is the primary underlying factor for the development of TDS in intrauterine hyponutrition, and that TDS is included in the clinical spectrum of Developmental Origins of Health and Disease.

Characterization of vasa and dnd homologs in summer flounder, Paralichthys dentatus: Expression analysis and colocalization of PGCs during embryogenesis

Specification of primordial germ cells (PGCs) is particularly important for germline formation. Many maternal-effect genes such as vasa, dnd, and nanos have been identified. However, the research on distribution patterns of PGCs in marine fish is limited. Vasa has been widely used as a germ cell marker to identify its origination in teleosts because vasa RNA is a component of germ plasm. Dnd is known to be an RNA binding protein that protects germline-specific RNAs from degradation. In this study, we isolated full-length vasa and dnd cDNA from summer flounder to track germ cell origination and their expression patterns by RT-PCR and ISH. The results demonstrated that deduced amino acid sequence of Pdvas and Pddnd shared typically conserved motifs of their homologues and demonstrated high identities with other teleosts. Both vasa and dnd transcripts were exclusively detected in germ cells of the gonads. During embryogenesis, vasa and dnd RNA were located at the cleavage furrows of early cleavage stages, and then through proliferation and migration they eventually moved to a location at the predetermined genital ridge. Phylogenetic analysis revealed that summer flounder belongs to the Euteleostei species, but vasa/dnd transcripts localized at the cleavage furrows was similar to that in zebrafish (Osteriophysans). This suggests that germ cells differentiating at early embryogenesis have no direct relation with phylogenesis. At the same time, we found the spatio-temporal expression pattern of dnd was highly consistent with vasa during this process, which indicated the important function of dnd in keeping the target RNA from being degraded to maintain germ cell fate. These results will provide further understanding of germ plasm localization and PGC differentiation in teleosts, and facilitate germ cell manipulation in marine fishes.

Building RNA-protein germ granules: insights from the multifaceted functions of DEAD-box helicase Vasa/Ddx4 in germline development

The segregation and maintenance of a dedicated germline in multicellular organisms is essential for species propagation in the sexually reproducing metazoan kingdom. The germline is distinct from somatic cells in that it is ultimately dedicated to acquiring the "totipotency" and to regenerating the offspring after fertilization. The most striking feature of germ cells lies in the presence of characteristic membraneless germ granules that have recently proven to behave like liquid droplets resulting from liquid-liquid phase separation (LLPS). Vasa/Ddx4, a faithful DEAD-box family germline marker highly conserved across metazoan species, harbors canonical DEAD-box motifs and typical intrinsically disordered sequences at both the N-terminus and C-terminus. This feature enables it to serve as a primary driving force behind germ granule formation and helicase-mediated RNA metabolism (e.g., piRNA biogenesis). Genetic ablation of Vasa/Ddx4 or the catalytic-dead mutations abolishing its helicase activity led to sexually dimorphic germline defects resulting in either male or female sterility among diverse species. While recent efforts have discovered pivotal functions of Vasa/Ddx4 in somatic cells, especially in multipotent stem cells, we herein summarize the helicase-dependent and -independent functions of Vasa/Ddx4 in the germline, and discuss recent findings of Vasa/Ddx4-mediated phase separation, germ granule formation and piRNA-dependent retrotransposon control essential for germline development.

Cell-fate transition and determination analysis of mouse male germ cells throughout development

Mammalian male germ cell development is a stepwise cell-fate transition process; however, the full-term developmental profile of male germ cells remains undefined. Here, by interrogating the high-precision transcriptome atlas of 11,598 cells covering 28 critical time-points, we demonstrate that cell-fate transition from mitotic to post-mitotic primordial germ cells is accompanied by transcriptome-scale reconfiguration and a transitional cell state. Notch signaling pathway is essential for initiating mitotic arrest and the maintenance of male germ cells' identities. Ablation of HELQ induces developmental arrest and abnormal transcriptome reprogramming of male germ cells, indicating the importance of cell cycle regulation for proper cell-fate transition. Finally, systematic human-mouse comparison reveals potential regulators whose deficiency contributed to human male infertility via mitotic arrest regulation. Collectively, our study provides an accurate and comprehensive transcriptome atlas of the male germline cycle and allows for an in-depth understanding of the cell-fate transition and determination underlying male germ cell development.

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.

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.

TRIM71 Deficiency Causes Germ Cell Loss During Mouse Embryogenesis and Is Associated With Human Male Infertility

Mutations affecting the germline can result in infertility or the generation of germ cell tumors (GCT), highlighting the need to identify and characterize the genes controlling germ cell development. The RNA-binding protein and E3 ubiquitin ligase TRIM71 is essential for embryogenesis, and its expression has been reported in GCT and adult mouse testes. To investigate the role of TRIM71 in mammalian germ cell embryonic development, we generated a germline-specific conditional Trim71 knockout mouse (cKO) using the early primordial germ cell (PGC) marker Nanos3 as a Cre-recombinase driver. cKO mice are infertile, with male mice displaying a Sertoli cell-only (SCO) phenotype which in humans is defined as a specific subtype of non-obstructive azoospermia characterized by the absence of germ cells in the seminiferous tubules. Infertility in male Trim71 cKO mice originates during embryogenesis, as the SCO phenotype was already apparent in neonatal mice. The in vitro differentiation of mouse embryonic stem cells (ESCs) into PGC-like cells (PGCLCs) revealed reduced numbers of PGCLCs in Trim71-deficient cells. Furthermore, TCam-2 cells, a human GCT-derived seminoma cell line which was used as an in vitro model for PGCs, showed proliferation defects upon TRIM71 knockdown. Additionally, in vitro growth competition assays, as well as proliferation assays with wild type and CRISPR/Cas9-generated TRIM71 mutant NCCIT cells showed that TRIM71 also promotes proliferation in this malignant GCT-derived non-seminoma cell line. Importantly, the PGC-specific markers BLIMP1 and NANOS3 were consistently downregulated in Trim71 KO PGCLCs, TRIM71 knockdown TCam-2 cells and TRIM71 mutant NCCIT cells. These data collectively support a role for TRIM71 in PGC development. Last, via exome sequencing analysis, we identified several TRIM71 variants in a cohort of infertile men, including a loss-of-function variant in a patient with an SCO phenotype. Altogether, our work reveals for the first time an association of TRIM71 deficiency with human male infertility, and uncovers further developmental roles for TRIM71 in the germline during mouse embryogenesis.

A transgenic DND1GFP fusion allele reports in vivo expression and RNA-binding targets in undifferentiated mouse germ cells†

In vertebrates, the RNA-binding protein (RBP) dead end 1 (DND1) is essential for primordial germ cell (PGC) survival and maintenance of cell identity. In multiple species, Dnd1 loss or mutation leads to severe PGC loss soon after specification or, in some species, germ cell transformation to somatic lineages. Our investigations into the role of DND1 in PGC specification and differentiation have been limited by the absence of an available antibody. To address this problem, we used CRISPR/Cas9 gene editing to establish a transgenic mouse line carrying a DND1GFP fusion allele. We present imaging analysis of DND1GFP expression showing that DND1GFP expression is heterogeneous among male germ cells (MGCs) and female germ cells (FGCs). DND1GFP was detected in MGCs throughout fetal life but lost from FGCs at meiotic entry. In postnatal and adult testes, DND1GFP expression correlated with classic markers for the premeiotic spermatogonial population. Utilizing the GFP tag for RNA immunoprecipitation (RIP) analysis in MGCs validated this transgenic as a tool for identifying in vivo transcript targets of DND1. The DND1GFP mouse line is a novel tool for isolation and analysis of embryonic and fetal germ cells, and the spermatogonial population of the postnatal and adult testis.

Role of Phosphorylated Gonadotropin-Regulated Testicular RNA Helicase (GRTH/DDX25) in the Regulation of Germ Cell Specific mRNAs in Chromatoid Bodies During Spermatogenesis

GRTH/DDX25 is a member of the DEAD-box family of RNA helicases that play an essential role in spermatogenesis. GRTH knock-in (KI) mice with the human mutant GRTH gene (R242H) show loss of the phospho-species from cytoplasm with preservation of the non-phospho form in the cytoplasm and nucleus. GRTH KI mice are sterile and lack elongated spermatids and spermatozoa, with spermatogenic arrest at step 8 of round spermatids which contain chromatoid body (CB) markedly reduced in size. We observed an absence of phospho-GRTH in CB of GRTH KI mice. RNA-Seq analysis of mRNA isolated from CB revealed that 1,421 genes show differential abundance, of which 947 genes showed a decrease in abundance and 474 genes showed an increase in abundance in GRTH KI mice. The transcripts related to spermatid development, differentiation, and chromatin remodeling (Tnp1/2, Prm1/2/3, Spem1/2, Tssk 2/3/6, Grth, tAce, and Upf2) were reduced, and the transcripts encoding for factors involved in RNA transport, regulation, and surveillance and transcriptional and translational regulation (Eef1a1, Ppp1cc, Pabpc1, Ybx3, Tent5b, H2al1m, Dctn2, and Dync1h1) were increased in the CB of KI mice and were further validated by qPCR. In the round spermatids of wild-type mice, mRNAs of Tnp2, Prm2, and Grth were abundantly co-localized with MVH protein in the CB, while in GRTH KI mice these were minimally present. In addition, GRTH binding to Tnp1/2, Prm1/2, Grth, and Tssk6 mRNAs was found to be markedly decreased in KI. These results demonstrate the importance of phospho-GRTH in the maintenance of the structure of CB and its role in the storage and stability of germ cell-specific mRNAs during spermiogenesis.

Both of marine fish species Oryzias melastigma and Pagrus major all failing in early localization at embryo stage by vasa RNA

Germ cells are essential for gonadal development. As precursors of germ cells, primordial germ cells (PGCs) are particularly important for germline formation. However, the research on distribution patterns of PGCs in marine fish is very limited, especially for economic species. The vasa gene has been widely used as marker to identify PGCs origination and migration because of vasa RNA is a component of germ plasm. In this study, we isolated full-length vasa cDNA (Omvas and Pmvas) from marine medaka (Oryzias melastigma) and red seabream (Pagrus major), detected vasa transcripts in different tissues by RT-PCR and described vasa expression patterns during embryogenesis and gametogenesis by in situ hybridization. At the same time, we also explored the relationship between early distribution of germ plasm components and species evolution. The results demonstrated that deduced amino acid sequence of Omvas and Pmvas shared several conserved motifs of Vasa homologues and high identity with other teleost, and vasa transcripts were exclusively detected in early germ cells of gonad. During embryogenesis, vasa RNA of both fishes, like medaka (Oryzias latipes), failed to localize at cleavage furrows and distributed uniformly throughout each blastomere. This study firstly discovered that the marine economic fish, red seabream, lost vasa RNA early specific localization at cleavage furrows and distinctive distribution in germ cells. In addition, compared with other teleost, we found that early distribution of germ plasm might not relate to species evolution. This will improve our understanding of vasa localization modes in teleost, and facilitate fish germ cell manipulation.

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.

Automatic three-dimensional segmentation of mouse embryonic stem cell nuclei by utilising multiple channels of confocal fluorescence images

Time-lapse confocal fluorescence microscopy images from mouse embryonic stem cells (ESCs) carrying reporter genes, histone H2B-mCherry and Mvh-Venus, have been used to monitor dynamic changes in cellular/differentiation characteristics of live ESCs. Accurate cell nucleus segmentation is required to analyse the ESC dynamics and differentiation at a single cell resolution. Several methods used concavities on nucleus contours to segment overlapping cell nuclei. Our proposed method evaluates not only the concavities but also the size and shape of every 2D nucleus region to determine if any of the strait, extrusion, convexity and large diameter criteria is satisfied to segment overlapping nuclei inside the region. We then use a 3D segmentation method to reconstruct simple, convex, and reasonably sized 3D nuclei along the image stacking direction using the radius and centre of every segmented region in respective microscopy images. To avoid false concavities on nucleus boundaries, fluorescence images of the H2B-mCherry reporter are used for localisation of cell nuclei and Venus fluorescence images are used for determining the cell colony ranges. We use a series of image preprocessing procedures to remove noise outside and inside cell colonies, and in respective nuclei, and to smooth nucleus boundaries based on the colony ranges.  We propose dynamic data structures to record every segmented nucleus region and solid in sets (volumes) of 3D confocal images. The experimental results show that the proposed image preprocessing method preserves the areas of mouse ESC nuclei on microscopy images and that the segmentation method effectively segment out every nucleus with a reasonable size and shape. All 3D nuclei in a set (volume) of confocal microscopy images can be accessed by the dynamic data structures for 3D reconstruction. The 3D nuclei in time-lapse confocal microscopy images can be tracked to calculate cell movement and proliferation in consecutive volumes for understanding the dynamics of the differentiation characteristics about ESCs. LAY DESCRIPTION: Embryonic stem cells (ESCs) are considered as an ideal source for basic cell biology study and producing medically useful cells in vitro. This study uses time-lapse confocal fluorescence microscopy images from mouse ESCs carrying reporter gene to monitor dynamic changes in cellular/differentiation characteristics of live ESCs. To automate analyses of ESC differentiation behaviours, accurate cell nucleus segmentation to distinguish respective cells are required. A series of image preprocessing procedures are implemented to remove noise in live-cell fluorescence images but yield overlapping cell nuclei. A segmentation method that evaluates boundary concavities and the size and shape of every nucleus is then used to determine if any of the strait, extrusion, convexity, large and local minimum diameter criteria satisfied to segment overlapping nuclei. We propose a dynamic data structure to record every newly segmented nucleus. The experimental results show that the proposed image preprocessing method preserves the areas of mouse ESC nuclei and that the segmentation method effectively detects overlapping nuclei. All segmented nuclei in confocal images can be accessed using the dynamic data structures to be visualised and manipulated for quantitative analyses of the ESC differentiation behaviours. The manipulation can be tracking of segmented 3D cell nuclei in time-lapse images to calculate their dynamics of differentiation characteristics.

Cyclin A2 is essential for mouse gonocyte maturation

In mammals, male gonocytes are derived from primordial germ cells during embryogenesis, enter a period of mitotic proliferation, and then become quiescent until birth. After birth, the gonocytes proliferate and migrate from the center of testicular cord toward the basement membrane to form the pool of spermatogonial stem cells (SSCs) and establish the SSC niche architecture. However, the molecular mechanisms underlying gonocyte proliferation, migration and differentiation are largely unknown. Cyclin A2 is a key component of the cell cycle and required for cell proliferation. Here, we show that cyclin A2 is required in mouse male gonocyte development and the establishment of spermatogenesis in the neonatal testis. Loss of cyclin A2 function in embryonic gonocytes by targeted gene disruption affected the regulation of the male gonocytes to SSC transition, resulting in the disruption of SSC pool formation, imbalance between SSC self-renewal and differentiation, and severely abnormal spermatogenesis in the adult testis.

Spatial and temporal expression pattern of sex-related genes in ovo-testis of the self-fertilizing mangrove killifish (Kryptolebias marmoratus)

In vertebrates, sex determination and differentiation comprehend a fine balance between female and male factors, leading the bipotential anlage to develop towards ovary or testis, respectively. Nevertheless, the mangrove killifish, (Kryptolebias marmoratus) a simultaneous hermaphroditic species, could overcome those antagonistic pathways and evolved to develop and maintain reproductively active ovarian and testicular tissues in the same organ. Morphological and mRNA localization analyzes of developing and adult gonads demonstrate that genes related to testis (dmrt1 and amh) and ovary differentiation (foxl2 and sox9a) follow the same expression pattern observed in gonochoristic species, thus functioning as two independent organs. In addition, Amh expression patterns make it a strong candidate for initiation of the formation and maintenance of the testicular tissue in the hermaphroditic gonad. Differently from described so far, foxl3 seems to have an important role in oogenesis as well as spermatogenesis and gonadal structure.

Single-cell analysis of human ovarian cortex identifies distinct cell populations but no oogonial stem cells

The human ovary orchestrates sex hormone production and undergoes monthly structural changes to release mature oocytes. The outer lining of the ovary (cortex) has a key role in defining fertility in women as it harbors the ovarian reserve. It has been postulated that putative oogonial stem cells exist in the ovarian cortex and that these can be captured by DDX4 antibody isolation. Here, we report single-cell transcriptomes and cell surface antigen profiles of over 24,000 cells from high quality ovarian cortex samples from 21 patients. Our data identify transcriptional profiles of six main cell types; oocytes, granulosa cells, immune cells, endothelial cells, perivascular cells, and stromal cells. Cells captured by DDX4 antibody are perivascular cells, not oogonial stem cells. Our data do not support the existence of germline stem cells in adult human ovaries, thereby reinforcing the dogma of a limited ovarian reserve.

A reviewed chronology of primordial germ cells migration in the chick embryo

INTRODUCTION

Primordial Germ Cells (PGCs) are present in all sexually reproducing animals. They differentiate into spermatozoa or oocytes and are therefore responsible for the transmission of genetic and epigenetic information across generations. In birds, PGCs are first observed in the center of the blastodisc at stage Eyal-Giladi X. With the formation of the primitive streak, germ cells are translocated anteriorly to the germinal crescent. At stage Hamburger- Hamilton 10-12, they enter the vasculature before migrating through the dorsal mesentery towards the genital ridges.

MATERIAL AND METHODS

Embryos from stages Hamburger-Hamilton (HH) 16 to 22 were collected. Blood samples were taken from the dorsal aorta and from the heart in order to perform blood smears and PAS staining. Embryos were dissected and fixed in Serra's medium. Sections were placed on slides for PAS staining. A sample of each embryo was collected for DNA extraction and PCR in order to determine the sex of the embryos.

RESULTS

PGCs were observed in blood circulation until stage HH 20 on blood smears and until stage HH 19 on histological sections. The first PGCs arrived in the genital ridges were observed from stage HH 17. A few germ cells were still migrating in the dorsal mesentery at stage HH 22. The aim of this study was to review the chronology of the migration of PGCs in chick embryos.

Is Vasa such a highly specific marker for primordial germ cells? A comparison of VASA and HSP90 proteins expression in young chicken embryos

INTRODUCTION

Primordial germ cells (PGCs) have been studied since the 19^th century with several different methods. The earliest works were based on the morphological criteria of these cells associated or not with a particular staining. Different markers have been proposed in immunohistochemistry among which we can quote the Stage-specific embryonic antigene-1 (SSEA-1), the embryonic mouse antigen-1 (EMA-1) or the heat shock protein 90. Unfortunately, none of them are germline specific. The VASA protein is considered as one of the most reliable marker for PGCs by some authors with its expression being considered to limited to the germ cells. However, other studies have reported its expression in somatic cells. Here, we described the expression of the heat shock protein, HSP90, and the VASA protein in the early chick embryo.

MATERIAL AND METHODS

Embryos from stages Hamburger-Hamilton (HH) 19, 21 and 28 were collected. Embryos were dissected and fixed in Serra's medium. Sections were placed on slides for PAS staining and for double immunohistochemistry with HSP90 and VASA.

RESULTS

VASA and HSP90 expression have been observed in germ cells but as well in other cell lineages with a spatio-temporal gradient in respect to the characteristics of development of each organ. The conclusion is that VASA expression is not limited to the germ line in chick embryo.

Mitochondria Associated Germinal Structures in Spermatogenesis: piRNA Pathway Regulation and Beyond

Multiple specific granular structures are present in the cytoplasm of germ cells, termed nuage, which are electron-dense, non-membranous, close to mitochondria and/or nuclei, variant size yielding to different compartments harboring different components, including intermitochondrial cement (IMC), piP-body, and chromatoid body (CB). Since mitochondria exhibit different morphology and topographical arrangements to accommodate specific needs during spermatogenesis, the distribution of mitochondria-associated nuage is also dynamic. The most relevant nuage structure with mitochondria is IMC, also called pi-body, present in prospermatogonia, spermatogonia, and spermatocytes. IMC is primarily enriched with various Piwi-interacting RNA (piRNA) proteins and mainly functions as piRNA biogenesis, transposon silencing, mRNA translation, and mitochondria fusion. Importantly, our previous work reported that mitochondria-associated ER membranes (MAMs) are abundant in spermatogenic cells and contain many crucial proteins associated with the piRNA pathway. Provocatively, IMC functionally communicates with other nuage structures, such as piP-body, to perform its complex functions in spermatogenesis. Although little is known about the formation of both IMC and MAMs, its distinctive characters have attracted considerable attention. Here, we review the insights gained from studying the structural components of mitochondria-associated germinal structures, including IMC, CB, and MAMs, which are pivotal structures to ensure genome integrity and male fertility. We discuss the roles of the structural components in spermatogenesis and piRNA biogenesis, which provide new insights into mitochondria-associated germinal structures in germ cell development and male reproduction.

Investigation of VASA Gene and Protein Expression in Neonate and Adult Testicular Germ Cells in Mice In Vivo and In Vitro

Objective

We aimed to examine the expression levels of the VASA gene and protein in testis sections of neonate and adult mice as well as testicular cell cultures.

Materials and Methods

In this experimental study, in order to investigate the expression of this germ cell marker gene in more detail, we analyzed the expression of VASA by immunocytochemistry, immunohistochemistry and fluidigm reverse transcription-polymerase chain reaction (RT-PCR).

Results

The immunohistochemical assays showed that the VASA protein was exclusively expressed in germ cells in the seminiferous tubules of the neonate and adult testis and not in somatic cells. VASA was not detectable in PLZF positive spermatogonial stem cells (SSCs), was weakly expressed in proliferating spermatogonia, and became abundant in spermatocytes and round spermatozoa. Counting VASA-positive cells in the seminiferous tubules of the neonate and adult testis depicted significant higher expression (P<0.05) of VASA in the adult testis in comparison to its neonate counterpart. SSC colonies were established in vitro after digestion of the testis and characterized by immunocytochemistry for CD90 and stage-specific embryonic antigens 3 (SSEA3). Immunocytochemistry confirmed that in contrast to the not detectable signal in vivo, VASA protein was strongly localized in the cytoplasm of both neonate and adult mouse SSCs under in vitro conditions. The results of Fluidigm RT-PCR revealed a significant higher expression of the germ cell gene VASA in adult SSCs in comparison to neonate SSCs in cell culture (P<0.05).

Conclusion

The VASA protein is, therefore, an extremely specific marker of testicular germ cell differentiation in vivo and mostly expressed in the adult testis in spermatocytes and round spermatids. The immunohistochemical signal in spermatogonia is very low. So, PLZF positive SSCs are negative for VASA in vivo, while in contrast, once isolated from the testicular niche VASA is also strongly expressed in SSCs under in vitro conditions.

Visualization of Turbot (Scophthalmus maximus) Primordial Germ Cells in vivo Using Fluorescent Protein Mediated by the 3' Untranslated Region of nanos3 or vasa Gene

Primordial germ cells (PGCs) as the precursors of germ cells are responsible for transmitting genetic information to the next generation. Visualization of teleost PGCs in vivo is essential to research the origination and development of germ cells and facilitate further manipulation on PGCs isolation, cryopreservation, and surrogate breeding. In this study, artificially synthesized mRNAs constructed by fusing fluorescent protein coding region to the 3' untranslated region (3'UTR) of nanos3 or vasa (mCherry-Smnanos3 3'UTR or mCherry-Smvasa 3'UTR mRNA) were injected into turbot (Scophthalmus maximus) fertilized eggs for tracing PGCs. The results demonstrated that the fluorescent PGCs differentiated from somatic cells and aligned on both sides of the trunk at the early segmentation period, then migrated and located at the dorsal part of the gut where the gonad would form. In the same way, we also found that the zebrafish (Danio rerio) vasa 3'UTR could trace turbot PGCs, while the vasa 3'UTR s of marine medaka (Oryzias melastigma) and red seabream (Pagrus major) failed, although they could label the marine medaka PGCs. In addition, through comparative analysis, we discovered that some potential sequence elements in the3 'UTRs of nanos3 and vasa, such as GCACs, 62-bp U-rich regions and nucleotide 187-218 regions might be involved in PGCs stabilization. The results of this study provided an efficient, rapid, and specific non-transgenic approach for visualizing PGCs of economical marine fish in vivo.

Broad Heterochromatic Domains Open in Gonocyte Development Prior to De Novo DNA Methylation

Facultative heterochromatin forms and reorganizes in response to external stimuli. However, how the initial establishment of such a chromatin state is regulated in cell-cycle-arrested cells remains unexplored. Mouse gonocytes are arrested male germ cells, at which stage the genome-wide DNA methylome forms. Here, we discovered transiently accessible heterochromatin domains of several megabases in size in gonocytes and named them differentially accessible domains (DADs). Open DADs formed in gene desert and gene cluster regions, primarily at transposons, with the reprogramming of histone marks, suggesting DADs as facultative heterochromatin. De novo DNA methylation took place with two waves in gonocytes: the first region specific and the second genome-wide. DADs were resistant to the first wave and their opening preceded the second wave. In addition, the higher-order chromosome architecture was reorganized with less defined chromosome compartments in gonocytes. These findings suggest that multiple layers of chromatin reprogramming facilitate de novo DNA methylation.

Testis Development

Production of sperm and androgens is the main function of the testis. This depends on normal development of both testicular somatic cells and germ cells. A genetic program initiated from the Y chromosome gene sex-determining region Y (SRY) directs somatic cell specification to Sertoli cells that orchestrate further development. They first guide fetal germ cell differentiation toward spermatogenic destiny and then take care of the full service to spermatogenic cells during spermatogenesis. The number of Sertoli cells sets the limits of sperm production. Leydig cells secrete androgens that determine masculine development. Testis development does not depend on germ cells; that is, testicular somatic cells also develop in the absence of germ cells, and the testis can produce testosterone normally to induce full masculinization in these men. In contrast, spermatogenic cell development is totally dependent on somatic cells. We herein review germ cell differentiation from primordial germ cells to spermatogonia and development of the supporting somatic cells. Testicular descent to scrota is necessary for normal spermatogenesis, and cryptorchidism is the most common male birth defect. This is a mild form of a disorder of sex differentiation. Multiple genetic reasons for more severe forms of disorders of sex differentiation have been revealed during the last decades, and these are described along with the description of molecular regulation of testis development.

Extracellular Localisation of the C-Terminus of DDX4 Confirmed by Immunocytochemistry and Fluorescence-Activated Cell Sorting

Putative oogonial stem cells (OSCs) have been isolated by fluorescence-activated cell sorting (FACS) from adult human ovarian tissue using an antibody against DEAD-box helicase 4 (DDX4). DDX4 has been reported to be germ cell specific within the gonads and localised intracellularly. White et al. (2012) hypothesised that the C-terminus of DDX4 is localised on the surface of putative OSCs but is internalised during the process of oogenesis. This hypothesis is controversial since it is assumed that RNA helicases function intracellularly with no extracellular expression. To determine whether the C-terminus of DDX4 could be expressed on the cell surface, we generated a novel expression construct to express full-length DDX4 as a DsRed2 fusion protein with unique C- and N-terminal epitope tags. DDX4 and the C-terminal myc tag were detected at the cell surface by immunocytochemistry and FACS of non-permeabilised human embryonic kidney HEK 293T cells transfected with the DDX4 construct. DDX4 mRNA expression was detected in the DDX4-positive sorted cells by RT-PCR. This study clearly demonstrates that the C-terminus of DDX4 can be expressed on the cell surface despite its lack of a conventional membrane-targeting or secretory sequence. These results validate the use of antibody-based FACS to isolate DDX4-positive putative OSCs.

DDX5 plays essential transcriptional and post-transcriptional roles in the maintenance and function of spermatogonia

Mammalian spermatogenesis is sustained by mitotic germ cells with self-renewal potential known as undifferentiated spermatogonia. Maintenance of undifferentiated spermatogonia and spermatogenesis is dependent on tightly co-ordinated transcriptional and post-transcriptional mechanisms. The RNA helicase DDX5 is expressed by spermatogonia but roles in spermatogenesis are unexplored. Using an inducible knockout mouse model, we characterise an essential role for DDX5 in spermatogonial maintenance and show that Ddx5 is indispensable for male fertility. We demonstrate that DDX5 regulates appropriate splicing of key genes necessary for spermatogenesis. Moreover, DDX5 regulates expression of cell cycle genes in undifferentiated spermatogonia post-transcriptionally and is required for cell proliferation and survival. DDX5 can also act as a transcriptional co-activator and we demonstrate that DDX5 interacts with PLZF, a transcription factor required for germline maintenance, to co-regulate select target genes. Combined, our data reveal a critical multifunctional role for DDX5 in regulating gene expression programmes and activity of undifferentiated spermatogonia.

Sustained sperm production is dependent on activity of undifferentiated spermatogonia. Here, the authors demonstrate an essential role for RNA helicase DDX5 in maintenance of spermatogonia in adults through control of gene transcription plus RNA processing and export.

The timeline development of female canine germ cells

During the sex differentiation, the primordial germ cells (PGCs) pass through a differentiation, becoming spermatogonial cells in males and oocytes in females. In this phase, there is difference in gene expression and differentiation potency between males and females. Specific cell markers have been essential in the PGC meiosis beginning and become oocyte cells. However, there are few studies about germline in domestic animals. The domestic dog (Canis lupus familiaris) is an interesting animal model to be used in the investigation about the mammal development because it has several biochemical and physiological similarities to humans. In addition, some additional investigations about dogs may contribute to a better understanding of the biology and genetic components, improving clinical veterinary and zoological sciences. Here, we elucidated by immunofluorescence and quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR), the dynamics of the expression of pluripotent (POU5F1 and NANOG) and germline (DDX4, DAZL and DPPA3) markers that are very important in the development of female canine germ cells during 35-50 days post-fertilization (dpf). The female canine germ cells were positive for pluripotent markers during middle developmental period. The number of DDX4, DAZL and DPPA3 cells increased along the germ cell maturation from 45 to 50 dpf. We provided an expression analysis of the pluripotent and germline markers in paraffin sections using the middle and later periods in female canine germ cells. The results can contribute the understanding about the timeline of each marker along the maturation of female canine germ cells. These results have a great significance to demonstrate the germ cell profile changes because it may allow the development of protocols about in vitro germ cell derivation.

Evolutionarily conserved vasa identifies embryonic and gonadal germ cells in spinyhead croaker Collichthys lucidus

In this study, a 2198 bp full-length cDNA of spinyhead croaker Collichthys lucidus vasa gene encoding 616 amino-acid residues was obtained. Multiple alignment revealed that C. lucidus vasa has eight conserved characteristic motifs of the DEAD box protein family and has the highest identity to large yellow croaker Larimichthys croceas. Reverse-transcription (RT)-PCR and Western blot analyses indicated that the vasa messenger (m)RNA and Vasa protein are specifically expressed in the gonads in both sexes. In situ hybridisation (ISH) demonstrated that vasa RNA is exclusively detected in the germ cells in C. lucidus gonads and its temporospatial expression reveals a dynamic pattern during oogenesis. Surprisingly, C. lucidus vasa 3'UTR can direct stable and specific GFP expression in the primordial germ cells (PGC) of medaka Oryzias latipes embryos. Taken together, these results suggest that because C. lucidus vasa expression delineates critical stages of oogenesis, it may be a useful molecular marker for the identification of gonadal germ cells, facilitating the isolation and utilization of germ cells in future study.

Sertoli cell-mediated differentiation of bovine fetal mesenchymal stem cells into germ cell lineage using an in vitro co-culture system

In vitro gamete derivation based on differentiation of germ cells (GC) from stem cells has emerged as a potential new strategy for the treatment of male infertility. This technology also has potential applications in animal reproduction as an alternative method for dissemination of elite animal genetics, production of transgenic animals, and conservation of endangered species. Mesenchymal stem cells (MSC) are multipotent progenitor cells defined by their ability to differentiate into mesodermal lineages. Under the effect of selected bioactive factors, MSC upregulate expression of pluripotent and GC specific-markers revealing their potential for GC differentiation. In addition to the effect of trophic factors, cell-to-cell interaction with Sertoli cells (SC) may be required to guide the sequential differentiation of MSC into GC. Thus, the aim of the present study was to investigate the effect of coculture with SC on the potential for in vitro GC differentiation of bovine fetal MSC (bfMSC) derived from bone marrow (BM-MSC) and adipose tissue (AT-MSC). bfMSC were isolated from male bovine fetuses and SC were collected from adult bull testes. The effect of SC interaction with BM-MSC or AT-MSC was analyzed on the expression of pluripotent factors OCT4 and NANOG, GC genes FRAGILLIS, STELLA and VASA and male GC markers DAZL, PIWIL2, STRA8 and SCP3 at Day 14 of coculture. Flow cytometry analyses detected that the majority (95,5% ± 2.5; P < 0.05) of the isolated population of SC cultures were positive for SC-specific marker WT1. Levels of mRNA of WT1 in BM-MSC and AT-MSC were lower (P < 0.05) compared to SC; whereas, WT1 expression was not detected in bovine fetal fibroblasts (FB). Cocultures of BM-MSC and AT-MSC with SC had higher (P < 0.05) OCT4 mRNA levels compared to monocultures of BM-MSC, AT-MSC and SC. Moreover, cocultures of BM-MSC with SC had higher (P < 0.05) proportion of cells positive for Oct4 and Nanog compared to monocultures of BM-MSC and SC. Levels of mRNA of DAZL, PIWIL2 and SCP3 were upregulated in cocultures of AT-MSC with SC compared to monocultures of AT-MSC and SC. Accordingly, the proportion of cells positive for Dazl were higher (P < 0.05) in cocultures of AT-MSC with SC compared to monocultures of AT-MSC and SC. Changes in gene expression profiles during coculture of SC with AT-MSC suggest that cell-to-cell interaction or bioactive factors provided by SC may induce progression of AT-MSC into early stages of GC differentiation.

Implications and Current Limitations of Oogenesis from Female Germline or Oogonial Stem Cells in Adult Mammalian Ovaries

A now large body of evidence supports the existence of mitotically active germ cells in postnatal ovaries of diverse mammalian species, including humans. This opens the possibility that adult stem cells naturally committed to a germline fate could be leveraged for the production of female gametes outside of the body. The functional properties of these cells, referred to as female germline or oogonial stem cells (OSCs), in ovaries of women have recently been tested in various ways, including a very recent investigation of the differentiation capacity of human OSCs at a single cell level. The exciting insights gained from these experiments, coupled with other data derived from intraovarian transplantation and genetic tracing analyses in animal models that have established the capacity of OSCs to generate healthy eggs, embryos and offspring, should drive constructive discussions in this relatively new field to further exploring the value of these cells to the study, and potential management, of human female fertility. Here, we provide a brief history of the discovery and characterization of OSCs in mammals, as well as of the in-vivo significance of postnatal oogenesis to adult ovarian function. We then highlight several key observations made recently on the biology of OSCs, and integrate this information into a broader discussion of the potential value and limitations of these adult stem cells to achieving a greater understanding of human female gametogenesis in vivo and in vitro.

Ceramide-1-phosphate has protective properties against cyclophosphamide-induced ovarian damage in a mice model of premature ovarian failure

STUDY QUESTION

Is ceramide-1-phosphate (C1P) an ovarian protective agent during alkylating chemotherapy?

SUMMARY ANSWER

Local administration of C1P drastically reduces ovarian damage induced by cyclophosphamide (Cy) via protection of follicular reserve, restoration of hormone levels, inhibition of apoptosis and improvement of stromal vasculature, while protecting fertility, oocyte quality and uterine morphology.

WHAT IS KNOWN ALREADY

Cancer-directed therapies cause accelerated loss of ovarian reserve and lead to premature ovarian failure (POF). Previous studies have demonstrated that C1P regulates different cellular processes including cell proliferation, cell migration, angiogenesis and apoptosis. This sphingolipid may be capable of modulating vascular development and apoptosis in ovaries affected by chemotherapy.

STUDY DESIGN, SIZE, DURATION

The 6-8-week-old mice were weighed and administered either a single intraperitoneal injection of Cy (75 mg/kg) or an equal volume of saline solution only for control mice. Control and Cy mice underwent sham surgery and received an intrabursal injection of saline solution, while Cy + C1P animal groups received 5 μl C1P, either 0.5 or 1 mM, under the bursa of both ovaries 1 h prior to Cy administration.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Animals were euthanized by cervical dislocation or cardiac puncture 2 weeks after surgery for collection of blood orovary and uterus samples, which were cleaned of adhering tissue in culture medium and used for subsequent assays. Ovaries were used for Western blotting or immunohistochemical and/or histological analyses or steroid extraction, as required (n = 5-8 per group). A set of mice (n = 3/group) was destined for oocyte recovery and IVF. Finally, another set (n = 5-6/group) was separated to study fertility parameters.

MAIN RESULTS AND THE ROLE OF CHANCE

The number of primordial (P < 0.01), primary (P < 0.05) and preantral follicles (P < 0.05) were decreased in Cy-treated mice compared to control animals, while atretic follicles were increased (P < 0.001). In Cy + C1P mice, the ovaries recovered control numbers of these follicular structures, in both C1P doses studied. Cy affected AMH expression, while it was at least partially recovered when C1P is administered as well. Cy caused an increase in serum FSH concentration (P < 0.01), which was prevented by C1P coadministration (P < 0.01). E2 levels in Cy-treated ovaries decreased significantly compared to control ovaries (P < 0.01), whilst C1P restored E2 levels to those of control ovaries (P < 0.01). Cy increased the expression of BAX (P < 0.01) and decreased the expression of BCLX-L compared to control ovaries (P < 0.01). The ovarian BCLX-L:BAX ratio was also lower in Cy-treated mice (P < 0.05). In the Cy + C1P group, the expression levels of BAX, BCLX-L and BCLX-L:BAX ratio were no different than those in control ovaries. In addition, acid sphingomyelinase (A-SMase) expression was higher in Cy-treated ovaries, whilst remaining similar to the control in the Cy + C1P group. Cy increased the apoptotic index (TUNEL-positive follicles/total follicles) in preantral and early antral stages, compared to control ovaries (P < 0.001 and P < 0.01, respectively). C1P protected follicles from this increase. No primordial or primary follicular cells stained for either cleaved caspase-3 or TUNEL when exposed to Cy, therefore, we have found no evidence for follicular reserve depletion in response to Cy being due to apoptosis. Cy caused evident vascular injury, especially in large cortical stromal vessels, and some neovascularization. In the Cy + C1P group, the disruptions in vascular wall continuity were less evident and the number of healthy stromal blood vessels seemed to be restored. In Cy-treated ovaries α-SMA-positive cells showed a less uniform distribution around blood vessels. C1P coadministration partially prevented this Cy-induced effect, with a higher presence of α-SMA-positive cells surrounding vessels. By H&E staining, Cy-treated mice showed endometrial alterations compared to controls, affecting both epithelial and stromal compartments. However, C1P allowed that the stromal tissue to maintain its loose quality and its glandular branches. Cy-treated animals had significantly lower pregnancy rates and smaller litter sizes compared with control mice (P = 0.013 and P < 0.05, respectively), whereas cotreatment with C1P preserved normal fertility. Furthermore, a higher (P < 0.05) proportion of abnormal oocytes was recovered from Cy-treated mice compared to the control, which was prevented by C1P administration.

LARGE SCALE DATA

N/A.

LIMITATIONS REASONS FOR CAUTION

The results of this study were generated from an in-vivo animal experimental model, already used by several authors. Further studies on C1P functions in female reproduction in pathological conditions such as chemotherapy-induced ovarian failure and on the safety of use of this sphingolipid are required.

WIDER IMPLICATIONS OF THE FINDINGS

The present findings showed that C1P administration prior to Cy might be a promising fertility preservation strategy in female patients who undergo chemotherapy.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from ANPCyT (PICT 2015-1117), CONICET (PIP 380), Cancer National Institute (INC) and Roemmers Foundation, Argentina. The authors declare no conflicts of interest.