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.

Transcriptional regulation of the alternative sex hormone-binding globulin promoter by KLF4

In most mammals the major site of sex hormone-binding globulin (SHBG) synthesis is the liver wherefrom it is secreted into the bloodstream and is the primary determinant of sex steroid access to target tissues. The minor site of SHBG synthesis is the testis and in lower mammals testicular SHBG has long been known to be synthesized and secreted by Sertoli cells. However, human testicular SHBG is expressed in developing germ cells from an upstream alternative promoter (altP-SHBG). Transcripts arising from this region comprise an alternative first exon (1A) with the resultant protein confined to the acrosomal compartment of the mature spermatozoa. I have dissected the regulatory components of the alternative SHBG promoter and identified motifs that are required for optimal transcriptional activity from this region. Transcriptional activity is driven by two CACCC elements that appear to be functionally redundant. The transcription factor KLF4 interacts with promoter the region spanning these elements in vivo. Knockdown of Klf4 results in decreased altP-SHBG activity, while Klf4 overexpression relieves the effects of knockdown. Based on their shared patterns of expression in vivo, I conclude that KLF4 is a transcriptional regulator of SHBG in male germ cells.

The role of CoQ10 in embryonic development

Coenzyme Q10 (CoQ10) is a natural component widely present in the inner membrane of mitochondria. CoQ10 functions as a key cofactor for adenosine triphosphate (ATP) production and exhibits antioxidant properties in vivo. Mitochondria, as the energy supply center of cells, play a crucial role in germ cell maturation and embryonic development, a complicated process of cell division and cellular differentiation that transforms from a single cell (zygote) to a multicellular organism (fetus). Here, we discuss the effects of CoQ10 on oocyte maturation and the important role of CoQ10 in the growth of various organs during different stages of fetal development. These allowed us to gain a deeper understanding of the pathophysiology of embryonic development and the potential role of CoQ10 in improving fertility quality. They also provide a reference for further developing its application in clinical treatments.

BORIS/CTCFL epigenetically reprograms clustered CTCF binding sites into alternative transcriptional start sites

BACKGROUND

Pervasive usage of alternative promoters leads to the deregulation of gene expression in carcinogenesis and may drive the emergence of new genes in spermatogenesis. However, little is known regarding the mechanisms underpinning the activation of alternative promoters.

RESULTS

Here we describe how alternative cancer-testis-specific transcription is activated. We show that intergenic and intronic CTCF binding sites, which are transcriptionally inert in normal somatic cells, could be epigenetically reprogrammed into active de novo promoters in germ and cancer cells. BORIS/CTCFL, the testis-specific paralog of the ubiquitously expressed CTCF, triggers the epigenetic reprogramming of CTCF sites into units of active transcription. BORIS binding initiates the recruitment of the chromatin remodeling factor, SRCAP, followed by the replacement of H2A histone with H2A.Z, resulting in a more relaxed chromatin state in the nucleosomes flanking the CTCF binding sites. The relaxation of chromatin around CTCF binding sites facilitates the recruitment of multiple additional transcription factors, thereby activating transcription from a given binding site. We demonstrate that the epigenetically reprogrammed CTCF binding sites can drive the expression of cancer-testis genes, long noncoding RNAs, retro-pseudogenes, and dormant transposable elements.

CONCLUSIONS

Thus, BORIS functions as a transcription factor that epigenetically reprograms clustered CTCF binding sites into transcriptional start sites, promoting transcription from alternative promoters in both germ cells and cancer cells.

Glial cell line-derived neurotrophic factor (GDNF) is essential for colonization and expansion of turbot (Scophthalmus maximus) germ cells in recipients and in vitro culture

Germ cell transplantation (GCT) is a promising biotechnology that enables the production of donor-derived gametes in surrogate recipients. It plays a crucial role in the protection of endangered species, the propagation of elite species with desired traits, and long-term preservation of genetic resources. This significance is particularly pronounced when GCT is synergistically employed with cryopreservation techniques. However, GCT often encounters challenges due to low colonization rates and, in some cases, complete loss of donor cells in recipients. Glial cell line-derived neurotrophic factor (GDNF) plays a pivotal role in sustaining the self-renewal of spermatogonial stem cells (SSCs) in mammals. Additionally, it has been shown to promote the proliferation of spermatogonia in vitro cultures in certain animal species. In turbot (Scophthalmus maximus), we found that the expressions of gdnf and gfrα1a were predominantly observed in spermatogonia rather than somatic cells, which differed from their expression patterns in mammals. The efficiency of exogenous spermatogonia transplantation in Japanese flounder (Paralichthys olivaceus) larvae could be substantially enhanced by incubating donor cells from turbot with 100 ng/ml GDNF prior to transplantation. This led to a noteworthy increase in the colonization rate, rising from 33%-50%-61.5%. Additionally, the addition of 20 ng/ml GDNF in cell medium could also promote the proliferation of turbot germ cells in vitro. These results demonstrated the gdnf in turbot testis expression characteristics and suggested that addition of GNDF could be an effective way to improve the GCT efficiency and promote the germ cells expansion during in vitro culture.

Organogenetic transcriptomes of the Drosophila embryo at single cell resolution

To gain insight into the transcription programs activated during the formation of Drosophila larval structures, we carried out single cell RNA sequencing during two periods of Drosophila embryogenesis: stages 10-12, when most organs are first specified and initiate morphological and physiological specialization; and stages 13-16, when organs achieve their final mature architectures and begin to function. Our data confirm previous findings with regards to functional specialization of some organs - the salivary gland and trachea - and clarify the embryonic functions of another - the plasmatocytes. We also identify two early developmental trajectories in germ cells and uncover a potential role for proteolysis during germline stem cell specialization. We identify the likely cell type of origin for key components of the Drosophila matrisome and several commonly used Drosophila embryonic cell culture lines. Finally, we compare our findings with other recent related studies and with other modalities for identifying tissue-specific gene expression patterns. These data provide a useful community resource for identifying many new players in tissue-specific morphogenesis and functional specialization of developing organs.

Reproductive toxicity induced by lead exposure: Effects on gametogenesis and sex steroid signaling in teleost fish

Lead (Pb) is an emerging contaminant widely distributed in aquatic environments, which has serious effects on human and animal health. In this study, we determined whether Pb exposure affects gametogenesis, sex steroids, estrogen (ERα and ERβ), and androgen (AR) receptors. Adult specimens of Astyanax bimaculatus were exposed in duplicate to 15, 50, and 100 μg/L of lead acetate, whereas the control group was not exposed. After 28 days of exposure, fish were euthanized and samples of the gonads, liver, and blood were collected for analysis. The results indicated a reduction in the gonadosomatic index as well as the diameters of the vitellogenic follicles and seminiferous tubules in the exposed groups. Morphometry of gametogenesis revealed inhibition of the secondary oocyte growth and a reduction in the number of spermatozoa in the 50 and 100 μg/L Pb-treated groups. In females, plasma 17β-estradiol (E2) increased following 15 and 50 μg/L Pb treatment, whereas males exhibited an increase in E2 and 11-ketotestosterone following treatment with 15 and 100 μg/L Pb, respectively. Vitellogenin was significantly reduced in females exposed to 100 μg/L Pb, but metallothionein levels were unchanged. ERα, ERβ, and AR were immunolocalized in the somatic and germ cells, with increased ovarian expression of ERα and Erβ in the 100 μg/L Pb-treated group, but no significant difference in AR among the groups. In males, only ERα increased in the 100 μg/L Pb-treated group. These results indicate that Pb exposure impairs gametogenesis, disrupts estrogen receptor signaling, and affects the expression of major reproductive biomarkers in A. bimaculatus.

Wnt10a downregulation contributes to MEHP-induced disruption of self-renewal and differentiation balance and proliferation inhibition in GC-1 cells: Insights from multiple transcriptomic profiling

Di (2-ethylhexyl) phthalate (DEHP), one of phthalic acid esters, has been widely used in daily products. Its main metabolite, mono (2-ethylhexyl) phthalate (MEHP) was reported to possess higher testicular toxicity than DEHP. To explore the precise mechanism in MEHP-induced testis damage, multiple transcriptomic sequencing was employed in spermatogonia cell line GC-1 cells treated with MEHP (0, 100, and 200 μM) for 24 h. Integrative omics analysis and empirical validation revealed that Wnt signaling pathway was downregulated and wnt10a, one of hub genes, may be the key player in this process. Similar results were observed in DEHP-exposed rats. MEHP-induced disturbance of self-renewal and differentiation was dose-dependent. Moreover, self-renewal proteins were downregulated; the differentiation level was stimulated. Meanwhile, GC-1 proliferation was decreased. Stable transformation strain of wnt10a overexpression GC-1 cell line constructed from lentivirus was utilized in this study. The upregulation of Wnt10a significantly reversed the dysfunction of self-renewal and differentiation and promoted the cell proliferation. Finally, retinol, predicted to be useful in CONNECTIVITY MAP (cMAP), failed to rescue the damage caused by MEHP. Cumulatively, our findings revealed that the downregulation of Wnt10a induced the imbalance of self-renew and differentiation, and inhibition of cell proliferation in GC-1 cells after MEHP exposure.

Recent advances in chromosome capture techniques unraveling 3D genome architecture in germ cells, health, and disease

In eukaryotes, the genome does not emerge in a specific shape but rather as a hierarchial bundle within the nucleus. This multifaceted genome organization consists of multiresolution cellular structures, such as chromosome territories, compartments, and topologically associating domains, which are frequently defined by architecture, design proteins including CTCF and cohesin, and chromatin loops. This review briefly discusses the advances in understanding the basic rules of control, chromatin folding, and functional areas in early embryogenesis. With the use of chromosome capture techniques, the latest advancements in technologies for visualizing chromatin interactions come close to revealing 3D genome formation frameworks with incredible detail throughout all genomic levels, including at single-cell resolution. The possibility of detecting variations in chromatin architecture might open up new opportunities for disease diagnosis and prevention, infertility treatments, therapeutic approaches, desired exploration, and many other application scenarios.

Norethindrone suppress the germ cell development via androgen receptor resulting in male bias

Progestins are widely used and detected in surface waters, and can affect gonad development and sexual differentiation in fish. However, the toxicological mechanisms of sexual differentiation induced by progestins are not well understood. Here, we investigated the effects of norethindrone (NET) and androgen receptor (AR) antagonist flutamide (FLU) on gonadal differentiation in zebrafish from 21 dpf (days post-fertilization) to 49 dpf. The results showed that NET caused male bias, while FLU resulted in female bias at 49 dpf. The NET and FLU mixtures significantly decreased the percentage of males compared to the NET single exposure. Molecular docking analysis showed that FLU and NET had similar docking pocket and docking posture with AR resulting in competitively forming the hydrogen bond with Thr334 of AR. These results suggested that binding to AR was the molecular initiating event of sex differentiation induced by NET. Moreover, NET strongly decreased transcription of biomarker genes (dnd1, ddx4, dazl, piwil1 and nanos1) involved in germ cell development, while FLU significantly increased transcription of these target genes. There was an increase in the number of juvenile oocytes, which was consistent with the female bias in the combined groups. The bliss independence model analysis further showed that NET and FLU had antagonistic effect on transcription and histology during gonadal differentiation. Thus, NET suppressed the germ cell development via AR, resulting in male bias. Understanding the molecular initiation of sex differentiation in progestins is essential to provide a comprehensive biological basis for ecological risk assessment.

Multipotent fetal stem cells in reproductive biology research

Due to the limited accessibility of the in vivo situation, the scarcity of the human tissue, legal constraints, and ethical considerations, the underlying molecular mechanisms of disorders, such as preeclampsia, the pathological consequences of fetomaternal microchimerism, or infertility, are still not fully understood. And although substantial progress has already been made, the therapeutic strategies for reproductive system diseases are still facing limitations. In the recent years, it became more and more evident that stem cells are powerful tools for basic research in human reproduction and stem cell-based approaches moved into the center of endeavors to establish new clinical concepts. Multipotent fetal stem cells derived from the amniotic fluid, amniotic membrane, chorion leave, Wharton´s jelly, or placenta came to the fore because they are easy to acquire, are not associated with ethical concerns or covered by strict legal restrictions, and can be banked for autologous utilization later in life. Compared to adult stem cells, they exhibit a significantly higher differentiation potential and are much easier to propagate in vitro. Compared to pluripotent stem cells, they harbor less mutations, are not tumorigenic, and exhibit low immunogenicity. Studies on multipotent fetal stem cells can be invaluable to gain knowledge on the development of dysfunctional fetal cell types, to characterize the fetal stem cells migrating into the body of a pregnant woman in the context of fetomaternal microchimerism, and to obtain a more comprehensive picture of germ cell development in the course of in vitro differentiation experiments. The in vivo transplantation of fetal stem cells or their paracrine factors can mediate therapeutic effects in preeclampsia and can restore reproductive organ functions. Together with the use of fetal stem cell-derived gametes, such strategies could once help individuals, who do not develop functional gametes, to conceive genetically related children. Although there is still a long way to go, these developments regarding the usage of multipotent fetal stem cells in the clinic should continuously be accompanied by a wide and detailed ethical discussion.

Single-cell transcriptomics allows novel insights into the endocrine-disrupting chemicals induced mammalian reproductive disorder

Increasing environmental pollution has led to the spread of many endocrine-disrupting chemicals (EDCs) around the world, which are toxic substances in the form of compounds that pose a great threat to the reproductive health of mammals and become a potential cause of many reproductive function-related diseases. In the past decade, the rapid development of single-cell RNA sequencing (scRNA-seq) technology has greatly promoted the study of the toxic mechanisms of EDCs in the mammalian reproductive system, including DEHP, ZEN, BPA, and BDE47. These studies aim to resolve the interference of EDCs in critical stages of reproductive development, including prepubertal and pubertal in males, meiosis I and early follicle formation in females. This paper introduces the sequencing process and analysis methods of current mainstream scRNA-seq technology, systematically reviews the outstanding contributions and specific research ideas of this technology in the study of reproductive system toxicity, lists representative cases of using this technology to explore reproductive damage caused by EDCs, and summarizes in detail the connection between environmental pollution and reproductive development disorders. It provides an important theoretical basis and direction for further exploring the mechanism of damage to the physiological functions of toxic substances on the reproductive system and the prevention and treatment of reproductive diseases.

Review: Embryonic stem cells as tools for in vitro gamete production in livestock

The goal of in vitro gametogenesis is to reproduce the events of sperm and oocyte development in the laboratory. Significant advances have been made in the mouse in the last decade, but evolutionary divergence from the murine developmental program has prevented the replication of these advances in large mammals. In recent years, intensive work has been done in humans, non-human primates and livestock to elucidate species-specific differences that regulate germ cell development, due to the number of potential applications. One of the most promising applications is the use of in vitro gametes to optimize the spread of elite genetics in cattle. In this context, embryonic stem cells have been posed as excellent candidates for germ cell platforms. Here, we present the most relevant advances in in vitro gametogenesis of interest to livestock science, including new types of pluripotent stem cells with potential for germline derivation, characterization of the signaling environment in the gonadal niche, and experimental systems used to reproduce different stages of germ cell development in the laboratory.

Touch print smear of testicular tissue with thionine stain for intraoperative diagnosis in azoospermic men

PURPOSE

To compare the diagnostic value of testicular tissue touch print smear (TPS) conducted on azoospermic patients with results obtained from histopathology and in vitro fertility (IVF) lab findings.

METHODS

Microdissection testicular sperm extraction was performed on a group of 148 azoospermic patients and testicular samples obtained intraoperatively. Using TPS, the samples were smeared onto a sterile slide, followed with staining using thionine. The testis tissue bulk samples were also transferred to the IVF lab, and determinations of sperm presence or absence obtained from IVF lab tests were compared with the TPS sample results. Needle testis biopsy was separately performed on a group of 360 azoospermic patients, and results of pathohistology review on the biopsies were further compared with determinations of spermatogenesis stage obtained from TPS for those patients.

RESULTS

When compared with IVF lab results, TPS was found to have 100% (126/126) positive predictive value and 95.5% (25/26) negative predictive value for predicting sperm presence or absence, respectively. Furthermore, TPS was further found to have a 93.6% correlation (337 of 360 biopsies) with results of histological diagnoses performed by needle biopsy. Results from histology and TPS for the detection of sperm presence were concordant in 96.1% (346/360) of biopsies. Diagnosis of SCO by TPS shows the highest correlation with histopathology (98.6%), followed by complete spermatogenesis (97.5%), early maturation arrest (78.9%), and late maturation arrest (27.3%).

CONCLUSIONS

The results support the continued use of TPS in testicular tissue analysis for more rapid assessment of spermatogenesis and for detection of spermatozoa in azoospermic subjects.

Immunohistochemistry and immunocytochemistry analysis of PLZF and VASA in mice testis during spermatogenesis

Spermatogonial stem cells (SSCs) are the basis of male spermatogenesis and fertility. SSCs are distinguished by their ability to self-renew and differentiate into spermatozoa throughout the male reproductive life and pass genetic information to the next generation. Immunohistochemistry (IHC), immunocytochemistry (ICC) and Fluidigm reverse transcriptase-polymerase chain reaction (RT-PCR) were used to analyze the expression of PLZF and VASA in mice testis tissue. In this experimental study, whereas undifferentiated spermatogonial cells sharply expressed PLZF, other types of germ cells located in the seminiferous tubule were negative for this marker. Conversely, the germ cells near the basal membrane of the seminiferous tubule showed VASA expression, whereas the undifferentiated germ cells located on the basal membrane were negative. The ICC analysis indicated higher expression of PLZF in the isolated undifferentiated cells compared with differentiated germ cells. Fluidigm real-time RT-PCR results demonstrated a significant expression (P < 0.05) of VASA in the SSCs compared with differentiated cells and also showed expression of PLZF in undifferentiated spermatogonia. These results clearly proved the role of PLZF as a specific marker for SSCs, and can be beneficial for advanced research on in vitro differentiation of SSCs to functional sperms.

Development of Ovaries and Sex Change in Fish: Bringing Potential into Action

BACKGROUND

Encompassing about half of the 60,000 species of vertebrates, fish display the greatest diversity of sex determination mechanisms among metazoans. As such that phylum offers a unique playground to study the impressive variety of gonadal morphogenetic strategies, ranging from gonochorism, with either genetic or environmental sex determination, to unisexuality, with either simultaneous or consecutive hermaphroditism.

SUMMARY

From the two main types of gonads, the ovaries embrace the important role to produce the larger and non-motile gametes, which is the basis for the development of a future organism. The production of the egg cells is complex and involves the formation of follicular cells, which are necessary for the maturation of the oocytes and the production of feminine hormones. In this vein, our review focuses on the development of ovaries in fish with special emphasis on the germ cells, including those that transition from one sex to the other as part of their life cycle and those that are capable of transitioning to the opposite sex depending on environmental cues.

KEY MESSAGES

Clearly, establishing an individual as either a female or a male is not accomplished by the sole development of two types of gonads. In most cases, that dichotomy, be it final or transient, is accompanied by coordinated transformations across the entire organism, leading to changes in the physiological sex as a whole. These coordinated transformations require both molecular and neuroendocrine networks, but also anatomical and behavioural adjustments. Remarkably, fish managed to tame the ins and outs of sex reversal mechanisms to take the most advantages of changing sex as adaptive strategies in some situations.

Endocannabinoid system and epigenetics in spermatogenesis and testicular cancer

In mammals, male germ cell development starts during fetal life and is carried out in postnatal life with the formation of sperms. Spermatogenesis is the complex and highly orderly process during which a group of germ stem cells is set at birth, starts to differentiate at puberty. It proceeds through several stages: proliferation, differentiation, and morphogenesis and it is strictly regulated by a complex network of hormonal, autocrine and paracrine factors and it is associated with a unique epigenetic program. Altered epigenetic mechanisms or inability to respond to these factors can impair the correct process of germ development leading to reproductive disorders and/or testicular germ cell cancer. Among factors regulating spermatogenesis an emerging role is played by the endocannabinoid system (ECS). ECS is a complex system comprising endogenous cannabinoids (eCBs), their synthetic and degrading enzymes, and cannabinoid receptors. Mammalian male germ cells have a complete and active ECS which is modulated during spermatogenesis and that crucially regulates processes such as germ cell differentiation and sperm functions. Recently, cannabinoid receptor signaling has been reported to induce epigenetic modifications such as DNA methylation, histone modifications and miRNA expression. Epigenetic modifications may also affect the expression and function of ECS elements, highlighting the establishment of a complex mutual interaction. Here, we describe the developmental origin and differentiation of male germ cells and testicular germ cell tumors (TGCTs) focusing on the interplay between ECS and epigenetic mechanisms involved in these processes.

Epigenetic developmental programming and intergenerational effects of thyroid hormones

Mounting evidence is showing that altered signaling through the nuclear hormone receptor superfamily can cause abnormal, long-term epigenetic changes which translate into pathological modifications and susceptibility to disease. These effects seem to be more prominent if the exposure occurs early in life, when transcriptomic profiles are rapidly changing. At this time, the coordination of the complex coordinated processes of cell proliferation and differentiation that characterize mammalian development. Such exposures may also alter the epigenetic information of the germ line, potentially leading to developmental changes and abnormal outcomes in subsequent generations. Thyroid hormone (TH) signaling is mediated by specific nuclear receptors, which have the ability to markedly change chromatin structure and gene transcription, and can also regulate other determinants of epigenetic marks. TH exhibits pleiotropic effects in mammals, and during development, its action is regulated in a highly dynamic manner to suit the rapidly evolving needs of multiple tissues. Their molecular mechanisms of action, timely developmental regulation and broad biological effects place THs in a central position to play a role in the developmental epigenetic programming of adult pathophysiology and, through effects on the germ line, in inter- and trans-generational epigenetic phenomena. These areas of epigenetic research are in their infancy, and studies regarding THs are limited. In the context of their characteristics as epigenetic modifiers and their finely tuned developmental action, here we review some of the observations underscoring the role that altered TH action may play in the developmental programming of adult traits and in the phenotypes of subsequent generations via germ line transmission of altered epigenetic information. Considering the relatively high prevalence of thyroid disease and the ability of some environmental chemicals to disrupt TH action, the epigenetic effects of abnormal levels of TH action may be important contributors to the non-genetic etiology of human disease.

Developmental toxicity window of fetal testicular injury in offspring mice induced by prenatal amoxicillin exposure at different time, doses and courses

Amoxicillin is widely used in the clinical treatment of syphilis, gonorrhea and other infectious diseases during pregnancy, but the effects of prenatal amoxicillin exposure (PAmE) on fetal testicular development have not been reported. Based on the characteristics of clinical medication, Kunming mice were orally gavaged with amoxicillin during pregnancy at different time (mid- or late-pregnancy), doses (75, 150 or 300 mg/kg·d) or courses (single- or multi-course). The results showed that compared with the control group, PAmE resulted in fetal testicular abnormal morphological development, cell proliferation inhibition and apoptosis enhancement, Leydig cell steroid synthase system (SF1, StAR, P450scc, CYP17a1) expression inhibition, and fetal blood testosterone levels decreased. Among them, the late-pregnancy and high-dose amoxicillin groups had severe damage, while the damage in different course groups was basically the same. Meanwhile, PAmE could damage the number and function of germ cells at all time, doses and courses, but had no obvious effect on Sertoli cells. It was further found that PAmE inhibited fetal testis AKT and ERK signaling pathways in late pregnancy and high dose, while the damage in different course groups was basically the same. In summary, this study proposed the developmental toxicity window of fetal testicular injury induced by PAmE in late-pregnancy and high-dose and its related mechanism of AKT and ERK signaling pathway, which provided a theoretical and experimental basis for guiding rational drug use during pregnancy and effectively evaluating the risk of fetal testicular developmental toxicity.

Vitrification of the ovarian tissue in sturgeons

The aim of this study was to test whether vitrification of sterlet Acipenser ruthenus and Russian sturgeon Acipenser gueldenstaedtii ovarian tissue through needle-immersed vitrification (NIV) is an efficient strategy for the preservation of oogonia (OOG) in order to supplement the current conservation efforts for these endangered fish species. Histological analyses of the gonads displayed that the ovaries of both species were immature and contained predominantly OOG and primary oocytes. The germline origin of these cells was verified by localization of the vasa protein through immunocytochemistry. NIV protocol was optimized by testing different equilibration (ES) and vitrification solutions (VS) containing various concentrations of dimethyl sulfoxide (Me₂SO), propylene glycol (PG) or methanol (MeOH). In sterlet, the highest average viability (55.7 ± 11.5%) was obtained by using a combination of 1.5 M PG and 1.5 M Me₂SO in the ES, and 1.5 M MeOH and 5.5 M Me₂SO in the VS. In Russian sturgeon, the highest average viability (49.4 ± 17.1%) was obtained by using a combination of 1.5 M MeOH and 1.5 M Me₂SO in the ES, and 3 M PG and 3 M Me₂SO in the VS. To test whether vitrified/warmed OOG are functional, we have conducted an intra-specific transplantation assay to verify whether transplanted sterlet OOG will colonize the gonads of recipient fish. Fluorescently labelled cells were detected within recipient gonads at 2 and 3 months post-fertilization (mpf). Colonization rates of vitrified/warmed OOG (70% at 2 mpf and 61% at 3 mpf) were similar to those of fresh OOG (80% at 2 mpf and 70% at 3 mpf). This study has demonstrated that vitrification of ovarian tissue is an effective method for the preservation of OOG, and that the vitrified/warmed cells are functional and are able to colonize recipient gonads after transplantation similarly to the fresh cells. Since the vitrification procedure displayed in this study is simple and does not require complex and expensive laboratory equipment, it can be readily applied in field conditions, and therefore it can be invaluable for the conservation efforts of the critically endangered sturgeon species. However, care needs to be taken that despite the research conducted so far, donor-derived progeny was not yet obtained in sturgeons.

Isolation and Culture Techniques for Fetal Mouse Germ Cells

The fetal gonad contains a great variety of differentiating cell populations, of which germ cells make up a relatively small percentage. In order to study germ cell-specific gene and protein expression, as well as determine direct effects of signaling molecules, it is necessary to prepare enriched populations of germ cells and maintain them in culture for several hours to multiple days. The protocols in this chapter are designed to provide a guide for the isolation or enrichment of primordial germ cells (from 9.5 days post coitum (dpc) to 18.5 dpc) by flow cytometry (Subheading 3.1) or magnetic sorting (Subheading 3.2), followed by feeder-free primary germ cell culture (Subheading 3.3).

Role of mesonephric contribution to mouse testicular development revisited

The role of the mesonephros in testicular development was re-evaluated by growing embryonic day 11.5 (E11.5) mouse testes devoid of mesonephros for 8-21 days in vivo under the renal capsule of castrated male athymic nude mice. This method provides improved growth conditions relative to previous studies based upon short-term (4-7 days) organ culture. Meticulous controls involved wholemount examination of dissected E11.5 mouse testes as well as serial sections of dissected E11.5 mouse testes which were indeed shown to be devoid of mesonephros. As expected, grafts of E11.5 mouse testes with mesonephros attached formed seminiferous tubules and also contained mesonephric derivatives. Grafts of E11.5 mouse testes without associated mesonephros also formed seminiferous tubules and never contained mesonephric derivatives. The consistent absence of mesonephric derivatives in grafts of E11.5 mouse testes grafted alone is further proof of the complete removal of the mesonephros from the E11.5 mouse testes. The testicular tissues that developed in grafts of E11.5 mouse testes alone contained canalized seminiferous tubules composed of Sox9-positive Sertoli cells as well as GENA-positive germ cells. The seminiferous tubules were surrounded by α-actin-positive myoid cells, and the interstitial space contained 3βHSD-1-positive Leydig cells. Grafts of E11.5 GFP mouse testes into wild-type hosts developed GFP-positive vasculature indicating that E11.5 mouse testes contain vascular precursors. These results indicate that the E11.5 mouse testis contains precursor cells for Sertoli cells, Leydig cells, myoid cells and vasculature whose development and differentiation are independent of cells migrating from the E11.5 mesonephros.

elegans to Analyze Transgenerational Epigenetic Phenotypes Inherited from Germ Cells

The last several years have seen an increasing number of examples of transgenerational epigenetic inheritance, in which phenotypes are inherited for three or more generations without changes to the underlying DNA sequence. One model system that has been particularly useful for studying transgenerational epigenetic inheritance is C. elegans. Their short generation time and hermaphroditic reproduction have allowed multiple transgenerational phenotypes to be identified, including aging, fertility, and behavior. However, it is still not clear how transgenerational epigenetic inheritance from the germline affects embryogenesis. Fortunately, the C. elegans embryo has a unique property that makes it ideal for addressing this question: they develop via an invariant lineage, with each cell undergoing stereotypical cell divisions to adopt the same cell fate in every individual embryo. Because of this invariant cell lineage, automated lineage tracing and single-cell RNA-seq can be employed to determine how transgenerational epigenetic inheritance from the germline affects developmental timing and cell fate. Unfortunately, difficulties with these techniques have severely limited their adoption in the community. Here, we provide a practical guide to automated lineage tracing coupled with single-cell RNA-seq to facilitate their use in studying transgenerational epigenetic inheritance in C. elegans embryos.

ATAC-Seq Analysis of Accessible Chromatin: From Experimental Steps to Data Analysis

Accessible chromatin often represents gene regulatory elements, including promoters and enhancers, essential for gene expression. Assay for Transposase Accessible Chromatin sequencing (ATAC-seq) is one of the most popular techniques to investigate chromatin accessibility across the genome. Here we describe, step by step, a series of optimized experimental methods and bioinformatics pipelines for ATAC-seq analysis. As an example, we present an analysis of murine spermatogenic cells: a method to isolate germ cells, a reaction step using Tn5 transposase to insert sequencing adapters into accessible DNA, a library preparation method for high-throughput sequencing, and bioinformatics analysis of sequencing data. Overall, we introduce a framework of ATAC-seq analysis that can be applied to any cell population to identify cell-type-specific gene regulatory elements and their cis-regulatory networks.

Human Endogenous Retroviruses: Friends and Foes in Urology Clinics

Human endogenous retroviruses (HERVs) are originated from ancient exogenous retroviruses, which infected human germ line cells millions of years ago. HERVs have generally lost their replication and retrotransposition abilities, but adopted physiological roles in human biology. Though mostly inactive, HERVs can be reactivated by internal and external factors such as inflammations and environmental conditions. Their aberrant expression can participate in various human malignancies with complex etiology. This review describes the features and functions of HERVs in urological subjects, such as urological cancers and human reproduction. It provides the current knowledge of the HERVs and useful insights helping practice in urology clinics.

Comparison of POU5F1 gene expression and protein localization in two differentiated and undifferentiated spermatogonial stem cells

The POU domain, class 5, transcription factor 1 (POU5F1), plays a vital role in creating pluripotency and maintaining self-renewal of the spermatogonial stem cells (SSCs). In this experimental research, the gene and protein expression of POU5F1 in two populations of differentiated and undifferentiated spermatogonia were examined, by immunohistochemistry (IMH), immunocytochemistry (ICC) and Fluidigm real-time RT-PCR. Our study was extended with online databases and the creation of PPI networks. The results indicated that the POU5F1 protein was localized in the basal compartment of seminiferous tubules. Under in vitro conditions, isolated SSC colonies were ICC-positive for the POU5F1, but the protein expression level of POU5F1 in the undifferentiated populations was higher than that in differentiated. A significant POU5F1 mRNA expression was seen in passage 4 compared to passage 0 for both populations. POU5F1 has a significantly higher mRNA expression in undifferentiated SSCs than that in differentiated SSCs, also in mESCs than in SSC-like cells. Bioinformatic analysis on POU5F1 shows its impressive connection with other genes involved in spermatogonia differentiation. These results support the advanced investigations of spermatogonia differentiation, both in vitro and in vivo. A better understanding of the POU5F1 gene and its function during differentiation will give the scientific community an open perspective for the development of direct differentiation of SSC to other male germline cells which is very important in infertility treatment.

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.

The positive predictive value of using fsh and Inhibin-B serum levels to diagnose gonadotropin insufficiency in bilateral cryptorchid boys is high

AIM OF STUDY

Despite early surgery, many boys with bilateral cryptorchidism at surgery have a reduced number of germ cells per tubular cross-section (G/T) in testicular biopsies and/or low inhibin-B with no elevated follicle-stimulating hormone (FSH) as expected based on a normal gonadotropin feed-back mechanism. Such boys have a high risk of later infertility because of insufficient gonadotropin stimulation and may benefit from adjuvant hormonal treatment. Testicular biopsies are not always wanted or accepted. The study aim was to investigate the value of a low inhibin-B and normal FSH to identify patients that might benefit from adjuvant hormonal treatment avoiding the need for testicular biopsy.

METHODS

A series of boys with cryptorchidism were evaluated with serum levels of inhibin-B and FSH in relation to G/T in testicular biopsies, which were compared to previously published age-matched normal control values.

RESULTS

A total of 365 boys who underwent bilateral orchidopexy between 0.4 and 7.8 (median: 2) years of age were included. Twenty-seven (7%) patients had increased FSH and low G/T, whereas 11 of these also had low inhibin-B indicating hypergonadotropic hypogonadism. Moreover, 85 (23%) patients between 0.75 and 7.5 (median: 2) years of age had both low G/T (median: 0.3) and low inhibin-B (median: 56 pg/ml) but normal FSH (median: 0.6 U/l) indicating a gonadotropin insufficiency. Three patients with normal FSH and low inhibin B had normal G/T.

DISCUSSION

Our study shows that if surgeons prefer to avoid testicular biopsies and only wish to rely on hormonal parameters (low inhibin-B and normal FSH) in order to diagnose a gonadotropin insufficiency as the cause of hypogonadism, they will identify only about 30% of such cases and overlook about 70% of patients sharing the same endocrinopathy. In addition, if surgeons treat patients for gonadotropin insufficiency only based on low inhibin-B and normal FSH they will solely treat patients with gonadotropin insufficiency and would not overtreat patients.

CONCLUSION

Adjuvant hormonal treatment was indicated by a gonadotropin insufficiency discerned in 23% of boys with bilateral cryptorchidism. Without histology, the clinicians are left with more difficult clinical judgments to identify patients for adjuvant hormonal treatment. The positive predictive value of low inhibin-B and normal FSH corroborated by low G/T was 0.97 (85/85 + 3), but the sensitivity was low (0.30).

Beyond Genes: Germline Disruption in the Etiology of Autism Spectrum Disorders

Investigations into the etiology of autism spectrum disorders have been largely confined to two realms: variations in DNA sequence and somatic developmental exposures. Here we suggest a third route-disruption of the germline epigenome induced by exogenous toxicants during a parent's gamete development. Similar to cases of germline mutation, these molecular perturbations may produce dysregulated transcription of brain-related genes during fetal and early development, resulting in abnormal neurobehavioral phenotypes in offspring. Many types of exposures may have these impacts, and here we discuss examples of anesthetic gases, tobacco components, synthetic steroids, and valproic acid. Alterations in parental germline could help explain some unsolved phenomena of autism, including increased prevalence, missing heritability, skewed sex ratio, and heterogeneity of neurobiology and behavior.

Loss of abnormal spindle-like, microcephaly-associated (Aspm) disrupts female folliculogenesis in mice during maturation and aging

The abnormal spindle-like, microcephaly-associated (ASPM) gene is a causative gene of autosomal recessive primary microcephaly (MCPH) 5 in humans, which is characterized by a reduction in brain volume. It was previously reported that truncated Aspm proteins in transgenic mice caused major defects in the germline, a severe reduction in ovary weight and the number of follicles accompanied by reduced fertility. However; it remains unknown whether a loss of Aspm induces abnormal ovarian function, resulting in female infertility. In order to assess the ovary function, we examined vaginal smear cytology from the age of 7 weeks to 100 weeks in CAG-mediated Cre-loxP conditional Aspm^-/- knockout mice and control female mice. In addition, we evaluated the ovarian size, fibrosis ratio and the number of follicles (primordial, primary, secondary, antral and atretic follicles) in mice from 15 weeks to 100 weeks old by image analyses. Mann-Whitney U-test was used for statistical analysis. The size of the ovary was significantly reduced in Aspm knockout mice at 15-20 weeks, 40-50 weeks and 70-80 weeks old compared with the control mice. Furthermore, at all stages, we found a severe decrease in the number of developing follicles at 10-15 weeks, 40-50 weeks and 70-80 weeks old, accompanied by disrupted cyclic changes of vaginal cytology and an aberrant upregulation of Foxo3, Kitl, and Lhcgr in Aspm knockout female. These results suggested that Aspm might play an important role in the folliculogenesis and estrous cyclicity of the postnatal ovary during maturation and aging.

Reproductive Hormones Imbalance, Germ Cell Apoptosis, Abnormal Sperm Morphophenotypes and Ultrastructural Changes in Testis of African Giant Rats (Cricetomys gambianus) Exposed to Sodium Metavanadate Intoxication

Environmental exposure to vanadium has been on the increase in recent time. This metal is a known toxicant. The current study was conducted to investigate the reproductive toxicity of sodium metavanadate (SMV) in male African giant rats. Administration of SMV was done intraperitoneally daily for 14 consecutive days at a dosage of 3 mg/kg body weight. Sterile water was administered to the control group. Serum reproductive hormones, sperm reserve and quality as well as testicular ultrastructural changes following SMV treatment were analysed. Results showed SMV-exposed AGR group had statistically decreased concentrations of testosterone (4.7 ng/ml), FSH (3.4 IU/L) and LH (3.8 IU/L). Also, SMV-treated group had statistically decreased sperm motility and mass activity with increased percentage of abnormal morphophenotypes of spermatozoa and upregulation of P53 immunopositive cells. Ultrastructural study revealed vacuolation of germ and Sertoli cells cytoplasm and nucleus, and mitochondrial swelling and vacuolations were also observed. There was severe disintegration of the seminiferous tubules, atrophy and degeneration of myeloid cells and apoptosis of the Leydig, Sertoli and germ cells. In conclusion, intraperitoneal SMV exposure exerts severe adverse effects on some serum reproductive hormones, reduction in the sperm reserve and quality, apoptosis and degenerative changes of the Leydig, Sertoli and germ cells which can lead to infertility.

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.

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.

Mapk activation drives male and female mouse teratocarcinomas from late PGCs

Germ cell tumors (GCTs) are rare tumors that can develop in both sexes, peaking in adolescents. To understand the mechanisms that underlie germ cell transformation, we established a GCT mouse model carrying germ cell-specific BRafV600E mutation with or without heterozygous Pten deletion. Both male and female mice developed monolateral teratocarcinomas containing embryonal carcinoma (EC) cells that showed an aggressive phenotype and metastatic ability. Germ cell transformation started in fetal gonads and progressed after birth leading to gonadal invasion. Early postnatal testes showed foci of tumor transformation, while ovaries showed increased number of follicles, multi-ovular follicles (MOFs) and scattered metaphase I oocytes containing follicles. Our results indicate that Mapk over-activation in fetal germ cells of both sexes can expand their proliferative window leading to neoplastic transformation and metastatic behavior.

First observations of ovary regeneration in an amphipod, Ampelisca eschrichtii Krøyer, 1842

Background

Females of the gammaridean amphipod Ampelisca eschrichtii with signs of regenerating, previously atrophied ovaries were recovered from the northeastern shelf of Sakhalin Island (Okhotsk Sea, Russia). Ovarian regeneration was previously unknown for any amphipod species. A. eschrichtii have a predominantly 2-year life cycle (from embryo to adult death) and reproduce once between late winter or early spring at the age of 2 years. Occasionally, females survive to a third year. An adaptive value of extended survival among these females is likely to require that they are also reproductive.

Methods

Histological sections from a second-year female with ovarian atrophy, a female with normal ovaries, a third-year female with ovarian regeneration, as well as testes of an immature and a sexually mature male were compared to determine the sources of cells of the germinal and somatic lines necessary for ovarian regeneration.

Results

Ovarian regeneration in the third-year female began with the formation of a new germinal zone from germ cells preserved in the atrophied ovaries and eosinophilic cells of the previously starving second-year female. Eosinophilic cells form the mesodermal component of the germinal zone. A mass of these cells appeared in the second-year female that had atrophied ovaries and in large numbers on the intestine wall of the third-year female with regenerating ovaries. These eosinophilic cells appear to migrate into the regenerating ovaries.

Conclusions

All germ cells of the second-year female are not lost during ovarian atrophy and can be involved in subsequent ovarian regeneration. Eosinophilic cells involved in ovarian regeneration are of mesodermal origin. The eosinophilic cell morphologies are similar to those of quiescence cells (cells in a reversible state that do not divide but retain the ability to re-enter cell division and participate in regeneration). These histological data thus indicate that eosinophilic and germ cells of third-year females can participate in the regeneration of the ovaries to reproduce a second brood. The precursors of these third-year females (a small number the second-year females with an asynchronous [summer] breeding period and ovaries that have atrophied due to seasonal starvation) appear to possess sources of somatic and germ cells that are sufficient for ovarian regeneration and that may be adaptations to starvation stress.

How Germ Cells Determine Their Own Sexual Fate in Mice

BACKGROUND

Whether to produce sperm or eggs is the most basic and important choice from the perspective of germ cell development and differentiation. However, the induction mechanism has not received much attention until relatively recently. This is because the issue of sexual differentiation has generally been considered a theme of somatic cells to make a testis or ovary. Basically, the sex of individual somatic cells and germ cells matches. Therefore, the sex of germ cells is thought to follow the sex of somatic cells once determined. However, researchers realized that a big, open question remained: What somatic cell signals actually induce the sexual differentiation of germ cells and what is the sex determinant in germ cells?

SUMMARY

In vitro experiments demonstrated that 2 somatic signals (BMP and RA) act directly on germ cells to induce oogonia. Therefore, these 2 signals may be referred to as oogonia inducers. From the viewpoint of germ cells, an independent experiment identified SMAD4 and STRA8, which are directly downstream of BMP and RA, respectively, acting in germ cells as female determinants. However, what about male? If these factors are female determinants, their absence may result in the induction of spermatogonia. This may be true in vivo because germ cells enter a male pathway if they do not receive these signals even in the ovary. However, this has not been confirmed in an in vitro culture system. There should be signals required for germ cells to enter a male pathway.

KEY MESSAGES

The important message is that although testis-specific factors secreted from the testis are considered to include male-inducing factors for germ cells, this may not be the case, and the male-inducing factor, if it exists, also exists in the ovary.

Effects of postnatal exposure to tetrabromobisphenol A on testis development in mice and early key events

Whether or not tetrabromobisphenol A (TBBPA) has reproductive developmental toxicity remains controversial. Here, we evaluated the effects of postnatal TBBPA exposure of dams (before weaning) and pups through drinking water (15, 150, 1500 ng/mL) on testis development in mice. On postnatal day (PND) 56, we found that TBBPA exerted little effects on testis weight, anogenital distance, sperm parameters, and the serum testosterone level, but resulted in dose-dependent reductions in the seminiferous tubule area coupled with decreased Sertoli cells and spermatogonia and the number of stage VII-VIII seminiferous tubules, and cytoskeleton damage in Sertoli cells, along with down-regulated expression of marker genes for Sertoli cells, spermatogonia and spermatocyte. Further study revealed that the reduced tubule area coupled decreased Sertoli cell and germ cell numbers and marker gene expression also occurred in TBBPA-treated testes on PND 7, along with reduced cell proliferation and disordered arrangement of Sertoli cell nuclei. On PND 15, most of these testicular alterations were still observed in TBBPA-treated males, and cytoskeleton damage in Sertoli cells became observable. All observations convincingly demonstrate that postnatal exposure to TBBPA disturbed testis development in early life and ultimately caused adverse outcomes in adult testes, and that cell proliferation inhibition, the reduction in the seminiferous tubule area coupled decreased Sertoli cell and germ cell numbers and marker gene expression, and cytoskeleton damage in Sertoli cells, are early events contributing to adverse outcomes in adult testes. Our study improves the understanding of reproductive developmental toxicity of TBBPA, highlighting its risk for human health.

Lifetime changes of the oocyte pool: Contributing factors with a focus on ovulatory inflammation

In mammalian species, females are born with a number of oocytes exceeding what they release via ovulation. In humans, an average girl is born with over a thousand times more oocytes than she will ovulate in her lifetime. The reason for having such an excessive number of oocytes in a neonatal female ovary is currently unknown. However, it is well established that the oocyte number decreases throughout the entire lifetime until the ovary loses them all. In this review, data published in the past 80 years were used to assess the current knowledge regarding the changing number of oocytes in humans and mice, as well as the reported factors that contribute to the decline of oocyte numbers. Briefly, a collective estimation indicates that an average girl is born with approximately 600,000 oocytes, which is 2,000 times more than the number of oocytes that she will ovulate in her lifetime. The oocyte number begins to decrease immediately after birth and is reduced to half of the initial number by puberty and almost zero by age 50 years. Multiple factors that are either intrinsic or extrinsic to the ovary contribute to the decline of the oocyte number. The inflammation caused by the ovulatory luteinizing hormone surge is discussed as a potential contributing factor to the decline of the oocyte pool during the reproductive lifespan.

ADAD2 regulates heterochromatin in meiotic and post-meiotic male germ cells via translation of MDC1

Male germ cells establish a unique heterochromatin domain, the XY-body, early in meiosis. How this domain is maintained through the end of meiosis and into post-meiotic germ cell differentiation is poorly understood. ADAD2 is a late meiotic male germ cell-specific RNA-binding protein, loss of which leads to post-meiotic germ cell defects. Analysis of ribosome association in Adad2 mouse mutants revealed defective translation of Mdc1, a key regulator of XY-body formation, late in meiosis. As a result, Adad2 mutants show normal establishment but failed maintenance of the XY-body. Observed XY-body defects are concurrent with abnormal autosomal heterochromatin and ultimately lead to severely perturbed post-meiotic germ cell heterochromatin and cell death. These findings highlight the requirement of ADAD2 for Mdc1 translation, the role of MDC1 in maintaining meiotic male germ cell heterochromatin and the importance of late meiotic heterochromatin for normal post-meiotic germ cell differentiation.

Metabolic Control of Germline Formation and Differentiation in Mammals

BACKGROUND

The germ cell lineage involves dynamic epigenetic changes during its formation and differentiation that are completely different from those of the somatic cell lineage. Metabolites and metabolic pathways have been reported as key factors related to the regulation of epigenetics as cofactors and substrates. However, our knowledge about the metabolic characteristics of germ cells, especially during the fetal stage, and their transition during differentiation is quite limited due to the rarity of the cells. Nevertheless, recent developments in omics technologies have made it possible to extract comprehensive metabolomic features of germ cells.

SUMMARY

In this review, we present the latest researches on the metabolic properties of germ cells in 4 stages: primordial germ cell specification, fetal germ cell differentiation, spermatogenesis, and oogenesis. At every stage, extensive published data has been accumulated on energy metabolism, and it is possible to describe its changes during germ cell differentiation in detail. As pluripotent stem cells differentiate into germ cells, energy metabolism shifts from glycolysis to oxidative phosphorylation; however, in spermatogenesis, glycolytic pathways are also temporarily dominant in spermatogonial stem cells. Although the significance of metabolic pathways other than energy metabolism in germ cell differentiation is largely unknown, the relation of the pentose phosphate pathway and Ser-Gly-one-carbon metabolism with germ cell properties has been suggested at various stages. We further discuss the relationship between these characteristic metabolic pathways and epigenetic regulation during germ cell specification and differentiation. Finally, the relevance of dietary and supplemental interventions on germ cell function and epigenomic regulation is also discussed. Key Messages: Comprehensive elucidation of metabolic features and metabolism-epigenome crosstalk in germ cells is important to reveal how the characteristic metabolic pathways are involved in the germ cell regulation. The accumulation of such insights would lead to suggestions for optimal diets and supplements to maintain reproductive health through modulating metabolic and epigenetic status of germ cells.

INO80 requires a polycomb subunit to regulate the establishment of poised chromatin in murine spermatocytes

INO80 is the catalytic subunit of the INO80-chromatin remodeling complex that is involved in DNA replication, repair and transcription regulation. Ino80 deficiency in murine spermatocytes (Ino80cKO) results in pachytene arrest of spermatocytes due to incomplete synapsis and aberrant DNA double-strand break repair, which leads to apoptosis. RNA-seq on Ino80cKO spermatocytes revealed major changes in transcription, indicating that an aberrant transcription program arises upon INO80 depletion. In Ino80WT spermatocytes, genome-wide analysis showed that INO80-binding sites were mostly promoter proximal and necessary for the regulation of spermatogenic gene expression, primarily of premeiotic and meiotic genes. Furthermore, most of the genes poised for activity, as well as those genes that are active, shared INO80 binding. In Ino80cKO spermatocytes, most poised genes demonstrated de-repression due to reduced H3K27me3 enrichment and, in turn, showed increased expression levels. INO80 interacts with the core PRC2 complex member SUZ12 and promotes its recruitment. Furthermore, INO80 mediates H2A.Z incorporation at the poised promoters, which was reduced in Ino80cKO spermatocytes. Taken together, INO80 is emerging as a major regulator of the meiotic transcription program by mediating poised chromatin establishment through SUZ12 binding.

CRISPR-Mediated Activation of Transposable Elements in Embryonic Stem Cells

Mounting evidence has established that subsets of transposable elements (TEs) function as gene regulatory elements in a cell type- and species-specific manner. Here we describe an in vitro system to ectopically activate TEs using CRISPR-mediated activation (CRISPRa) for functional studies in mouse embryonic stem cells (ESCs). We established a stable mouse CRISPRa ESC line, in which expression of guide RNA enables the activation of TE-derived enhancers and the expression of their adjacent genes. We show an example of ectopic activation of TE-derived enhancers that function in male meiosis, as well as the expression of adjacent germline genes in ESCs. This system can also be applied to functional studies of TEs that are not active in ESCs.

Ultrastructure characteristics of primordial germ cells in stage X of pheasant (Phasianus colchicus) embryo

Stage X is one of the formation stages in birds at which the blastoderm area is distinguished by two areas of area pellucida being responsible for formation of embryonic tissues and primordial germ cells, and area opaca forming the extra-embryonic tissues. Primordial germ cells are multi-potent stem cells giving rise to spermatogonia or oogonia. The present study was carried out to describe the characteristics of primordial germ cells in stage X of pheasants' embryo using a transmission electron microscope. The blastoderm was dissected out from embryos which were already incubated for 12 hr. Toluidine blue was used for staining semi-thin sections; lead citrate and uranyl acetate were also used to stain ultra-thin sections. Images of primordial germ cells elucidated that the nucleus was situated eccentrically and had a compact spherical structure. Moreover, the nucleolus appeared elongated and was located eccentrically. The cytoplasm was composed of yolk granules and glycogen particles. Mitochondria were observed as round structures in the cytoplasm. The most important finding was that the primordial germ cells contained yolk granules, mitochondria and small amount of glycogen at this stage.

Meiotic sex chromosome inactivation and the XY body: a phase separation hypothesis

In mammalian male meiosis, the heterologous X and Y chromosomes remain unsynapsed and, as a result, are subject to meiotic sex chromosome inactivation (MSCI). MSCI is required for the successful completion of spermatogenesis. Following the initiation of MSCI, the X and Y chromosomes undergo various epigenetic modifications and are transformed into a nuclear body termed the XY body. Here, we review the mechanisms underlying the initiation of two essential, sequential processes in meiotic prophase I: MSCI and XY-body formation. The initiation of MSCI is directed by the action of DNA damage response (DDR) pathways; downstream of the DDR, unique epigenetic states are established, leading to the formation of the XY body. Accumulating evidence suggests that MSCI and subsequent XY-body formation may be driven by phase separation, a physical process that governs the formation of membraneless organelles and other biomolecular condensates. Thus, here we gather literature-based evidence to explore a phase separation hypothesis for the initiation of MSCI and the formation of the XY body.

Metabolic pathways regulating the development and non-genomic heritable traits of germ cells

Metabolism is an important cellular process necessary not only for producing energy and building blocks for cells, but also for regulating various cell functions, including intracellular signaling, epigenomic effects, and transcription. The regulatory roles of metabolism have been extensively studied in somatic cells, including stem cells and cancer cells, but data regarding germ cells are limited. Because germ cells produce individuals of subsequent generations, understanding the role of metabolism and its regulatory functions in germ cells is important. Although limited information concerning the specific role of metabolism in germ cells is available, recent advances in related research have revealed specific metabolic states of undifferentiated germ cells in embryos as well as in germ cells undergoing oogenesis and spermatogenesis. Studies have also elucidated the functions of some metabolic pathways associated with germ cell development and the non-genomic heritable machinery of germ cells. In this review, we summarized all the available knowledge on the characteristic metabolic pathways in germ cells, focusing on their regulatory functions, while discussing the issues that need to be addressed to enhance the understanding of germ cell metabolism.

Curcumin nanocrystals attenuate cyclophosphamide-induced testicular toxicity in mice

The cancer therapy using cyclophosphamide (CP) has been associated with adverse effects on the testicular function that raises concerns about the future fertility potential among cancer survivors. Curcumin, a polyphenol, has shown to possess a plethora of biological functions including tissue protective effects. In the present study, we investigated the protective effects of curcumin nanocrystals (NC) in mitigation of CP-induced testicular toxicity. Healthy adult (8-10 week) and prepubertal (2 week) male Swiss albino mice were injected with a single dose of CP (200 mg/kg) intraperitoneally (i.p). NC (4 mg/kg, i.p.) was administered every alternate day, for 35 days in adult mice while, a single dose of NC was injected intraperitoneally to prepubertal mice 1 h prior to CP. Administration of multiple doses of NC ameliorated CP-induced testicular toxicity in adult mice, which was evident from the improved sperm functional competence, sperm chromatin condensation, seminiferous tubule architecture and decreased apoptosis in testicular cells. Further, administration of NC 1 h prior to CP in prepubertal mice modulated the expression of genes pertaining to proliferation, pluripotency, DNA damage and DNA repair in spermatogonial cells at 24 h after the treatment. Overall, these results suggest that NC could be a promising chemoprotective agent, which can have potential application in male fertility preservation.

A systems biology analysis of reproductive toxicity effects induced by multigenerational exposure to ionizing radiation in C. elegans

Understanding the effects of chronic exposure to pollutants over generations is of primary importance for the protection of humans and the environment; however, to date, knowledge on the molecular mechanisms underlying multigenerational adverse effects is scarce. We employed a systems biology approach to analyze effects of chronic exposure to gamma radiation at molecular, tissue and individual levels in the nematode Caenorhabditis elegans. Our data show a decrease of 23% in the number of offspring on the first generation F0 and more than 40% in subsequent generations F1, F2 and F3. To unveil the impact on the germline, an in-depth analysis of reproductive processes involved in gametes formation was performed for all four generations. We measured a decrease in the number of mitotic germ cells accompanied by increased cell-cycle arrest in the distal part of the gonad. Further impact on the germline was manifested by decreased sperm quantity and quality. In order to obtain insight in the molecular mechanisms leading to decreased fecundity, gene expression was investigated via whole genome RNA sequencing. The transcriptomic analysis revealed modulation of transcription factors, as well as genes involved in stress response, unfolded protein response, lipid metabolism and reproduction. Furthermore, a drastic increase in the number of differentially expressed genes involved in defense response was measured in the last two generations, suggesting a cumulative stress effect of ionizing radiation exposure. Transcription factor binding site enrichment analysis and the use of transgenic strain identified daf-16/FOXO as a master regulator of genes differentially expressed in response to radiation. The presented data provide new knowledge with respect to the molecular mechanisms involved in reproductive toxic effects and accumulated stress resulting from multigenerational exposure to ionizing radiation.

During infancy low levels of follicle-stimulating hormone may result in high rate of germ cell apoptosis

PURPOSE

It has been suggested that follicle-stimulating hormone (FSH) plays a role in preventing germ cell apoptosis. We aimed to compare apoptotic rate of boys with cryptorchidism having different levels of FSH in order to investigate its role in apoptosis.

METHODS

Hormonal profiles and testicular biopsies from 30 boys with unilateral cryptorchidism (age range: 4-14 months) were included. Based on FSH level, the boys were grouped into three (3 × 10) having high (>97.5percentile), low (<2.5percentile), or within normal range. Sections underwent immunohistochemical staining to analyze the number of germ cells and type A dark spermatogonia per cross-sectional tubule. One section was co-stained with immunofluorescent antibodies against an apoptotic marker (cleaved caspase-3), proliferation marker (Ki67), Sertoli cell marker (anti-Müllerian hormone) and processed by confocal imaging for analysis. Germ cell apoptosis was calculated as the apoptosis index (percentage caspase-3+ germ cells/total germ cell number).

RESULTS

Fifty percent (5/10) of the boys with low FSH had an apoptosis index above 90% compared with 15% (3/20) of the boys with normal or high FSH (p = 0.04). Caspase-3+ germ cells were most likely to be located on the basement membrane (p<0.05).

CONCLUSION

Our findings lead to trends proposing that FSH may play a role in preventing apoptosis.

TYPE OF STUDY

Prognosis Study LEVEL OF EVIDENCE: III.

Successful transplantation of spermatogonial stem cells into the seminiferous tubules of busulfan-treated mice

Background

Spermatogonial stem cells (SSCs) in the testis are crucial for transferring genetic information to the next generation. Successful transplantation of SSCs to infertile men is an advanced therapeutic application in reproductive biology research.

Methods

In this experimental research, both in vitro and in vivo characterization of undifferentiated and differentiated SSCs were performed by morphology—immunocytochemistry (ICC), immunohistochemistry (IMH), Fluidigm Real-Time polymerase chain reaction (RT-PCR) and flow cytometry analysis. The isolated SSCs were finally microinjected into the rete testis of busulfan-treated mice.

The compact undifferentiated and more loosely connected round differentiated SSCs were isolated during testicular cell expansion from their specific feeder layer.

Results

ICC analysis indicated high and low expression levels of Zbtb16 in undifferentiated and differentiated germ cells. Also, IMH analysis showed different expression levels of Zbtb16 in the two different germ stem cell populations of the testicular tissue. While Fluidigm RT-PCR analysis indicated overexpression of the TAF4B germ cell gene, the expression of DAZL, VASA, and Zbtb16 were down-regulated during the differentiation of SSCs (P < 0.05). Also, flow cytometry analysis confirmed the significant downregulation of Itgb1 and Itga4 during differentiation. By transplantation of SSCs into busulfan-treated NOD/SCID mice, GFP-labeled sperm cells developed.

Conclusions

In the current study, we performed a transplantation technique that could be useful for the future microinjection of SSCs during infertility treatment and for studying in vivo differentiation of SSCs into sperm.

Spermatogonia (SSCs) in the testis transmit genetic information to the next generation. Successful SSC transplantation into infertile men is an advanced therapeutic application in reproductive biology research. In this experimental research, both in vitro and in vivo characterization of undifferentiated and differentiated SSCs were performed by morphology—immunocytochemistry (ICC), immunohistochemistry (IMH), Fluidigm Real-Time polymerase chain reaction (RT-PCR) and flow cytometry analysis. The isolated SSCs were finally microinjected into the rete testis of busulfan-treated mice. ICC analysis indicated high and low expression levels of Zbtb16 in undifferentiated and differentiated germ cells. IMH analysis showed different expression levels of Zbtb16 in both populations. Fluidigm RT-PCR analysis indicated overexpression of the TAF4B germ cell gene and the down-regulated expression of DAZL, VASA, and Zbtb16 during SSCs differentiation of (P < 0.05). Flow cytometry analysis confirmed the significant downregulation of Itgb1 and Itga4 during differentiation. By transplantation of SSCs into busulfan-treated NOD/SCID mice, GFP-labeled sperm cells developed. We performed a transplantation technique that could be useful for the future microinjection of SSCs during infertility treatment and for studying in vivo differentiation of SSCs into sperm. Data analysis confirmed that zbtb16 is expressed in the undifferentiated germ cells located on the basal membrane of seminiferous tubules and SSCs in vitro. Also, spermatogenesis was resumed, and fertility improved after transplantation of undifferentiated cells into busulfan-treated mice; thus, improvements in vitro SSCs transplantation, isolation and culture would be helpful in future clinical treatments to solve the reproductive problems of families influenced by infertility.

Self-organising human gonads generated by a Matrigel-based gradient system

BACKGROUND

Advances in three-dimensional culture technologies have led to progression in systems used to model the gonadal microenvironment in vitro. Despite demonstrating basic functionality, tissue organisation is often limited. We have previously detailed a three-dimensional culture model termed the three-layer gradient system to generate rat testicular organoids in vitro. Here we extend the model to human first-trimester embryonic gonadal tissue.

RESULTS

Testicular cell suspensions reorganised into testis-like organoids with distinct seminiferous-like cords situated within an interstitial environment after 7 days. In contrast, tissue reorganisation failed to occur when mesonephros, which promotes testicular development in vivo, was included in the tissue digest. Organoids generated from dissociated female gonad cell suspensions formed loosely organised cords after 7 days. In addition to displaying testis-specific architecture, testis-like organoids demonstrated evidence of somatic cell differentiation. Within the 3-LGS, we observed the onset of AMH expression in the cytoplasm of SOX9-positive Sertoli cells within reorganised testicular cords. Leydig cell differentiation and onset of steroidogenic capacity was also revealed in the 3-LGS through the expression of key steroidogenic enzymes StAR and CYP17A1 within the interstitial compartment. While the 3-LGS generates a somatic cell environment capable of supporting germ cell survival in ovarian organoids germ cell loss was observed in testicular organoids.

CONCLUSION

The 3-LGS can be used to generate organised whole gonadal organoids within 7 days. The 3-LGS brings a new opportunity to explore gonadal organogenesis and contributes to the development of more complex in vitro models in the field of developmental and regenerative medicine.