The effects of a glyphosate-based herbicide on the bovine gametes during an in vitro embryo production model

Roundup® (R), while it is the most used herbicide globally, and its residues are ubiquitous in urban and suburban areas, its impact on vertebrates' safety remains highly debated. Here, in three in vitro experiments, we investigated the effects of a very low dose (1 ppm) of R on the fertilization capacity and embryo development in cattle. In the first experiment, frozen-thawed bull semen exposed to R for 1 h exhibited reduced motility parameters but unaffected fertilization ability. However, after in vitro fertilization, the rates of embryo formation were significantly lower compared to the untreated controls. In the second experiment, oocytes exposed to R during in vitro maturation showed reduced cleavage rates, and the embryo yield on days 7, 8, and 9 of embryo culture was significantly lower than that of the controls. In the third experiment, oocytes were matured in the presence of R and in a medium containing both R and Zinc, chosen to offer antioxidant protection to the oocytes. Day-7 blastocysts were analyzed for the expression of genes associated with oxidative stress, apoptosis, and epigenetic reprogramming. Exposure to R markedly suppressed embryo formation rates compared to the controls. The combination of R with Zinc restored the blastocyst yield, which on days 8 and 9 was comparable to that of the controls and higher than the groups exposed only to R on all days. The gene expression analysis revealed that R promotes oxidative stress development, triggers apoptosis, and induces epigenetic changes in developing embryos, while zinc presence alleviates these adverse effects of R. These findings imply that even at very low doses, R could be highly toxic, leading to functional abnormalities in both gametes, potentially affecting fertility in both genders.

Long-term exposure to 6-PPD quinone reduces reproductive capacity by enhancing germline apoptosis associated with activation of both DNA damage and cell corpse engulfment in Caenorhabditis elegans

Recently, 6-PPD quinone (6-PPDQ), a derivative of tire antioxidant 6-PPD, was reported to have acute toxicity for organisms. However, the possible reproductive toxicity of 6-PPDQ is still largely unclear. In this study, the reproductive toxicity of 6-PPDQ after long-term exposure was further investigated in Caenorhabditis elegans. Exposure to 1 and 10 μg/L 6-PPDQ reduced the reproductive capacity. Meanwhile, exposure to 1 and 10 μg/L 6-PPDQ enhanced the germline apoptosis, which was accompanied by upregulation of ced-3, ced-4, and egl-1 expressions and downregulation of ced-9 expression. The observed increase in germline apoptosis in 1 and 10 μg/L 6-PPDQ exposed nematodes was associated with the enhancement in DNA damage and increase in expressions of related genes of cep-1, clk-2, hus-1, and mrt-2. The detected enhancement in germline apoptosis in 1 and 10 μg/L 6-PPDQ exposed nematodes was further associated with the increase in expressions of ced-1 and ced-6 governing the cell corpse engulfment process. Molecular docking analysis indicated the binding potentials of 6-PPDQ with three DNA damage checkpoints (CLK-2, HUS-1, and MRT-2) and corpse-recognizing phagocytic receptor CED-1. Therefore, our data suggested the toxicity on reproductive capacity by 6-PPDQ at environmentally relevant concentrations by enhancing DNA damage- and cell corpse engulfment-induced germline apoptosis in organisms.

The emerging risk of microplastics and nanoplastics on the microstructure and function of reproductive organs in mammals: A systematic review of preclinical evidence

AIMS

Plastic particles (PP) pollution is a global environmental concern. Although the reproductive toxicity of PP is primarily understood for invertebrates, the evidence for mammals is still fragmented. We used a systematic review framework to investigate the reproductive impact of microplastics and nanoplastics (MNP) on mammals.

MATERIALS AND METHODS

Research records were screened from Embase, Medline, Scopus and Web of Science. Twelve original papers were identified and reviewed. Immunological, oxidative and morphofunctional outcomes, and the risk of bias in all studies reviewed were analyzed.

KEY FINDINGS

These studies indicated that PP can accumulate in the gonads, triggering seminiferous degeneration, Sertoli cells death, blood-testis barrier disruption, sperm degeneration, malformation, reduced number and mobility, ovarian cysts, reduced follicular growth and granulosa cells death. Gonadal damage was associated with upregulation of prooxidant mediators (oxygen reactive species, lipid and DNA oxidation), cell death, proinflammatory molecular pathways and cytokines, as well as inhibition of enzymatic and non-enzymatic antioxidant defense mechanisms. Spermatogenesis, folliculogenesis, testosterone, progesterone and estrogen levels were also impaired in PP-treated animals, which were potentially associated with down-regulation of molecules involved in germ cells microstructural organization (occludin, N-cadherin, β-catenin and connexin 43) and steroidogenesis, such as hydroxysteroid dehydrogenases, steroidogenic acute regulatory proteins, follicle stimulating and luteinizing hormones. Selection, performance and detection bias were the main limitations identified.

SIGNIFICANCE

Current evidence indicates that PP can induce dose-dependent microstructural and functional gonadal damage, which is orchestrated by pro-oxidant and pro-inflammatory mechanisms that disrupt genes, molecular effectors, and hormones that control spermatogenesis and folliculogenesis.

Follicle-stimulating hormone-mediated decline in miR-92a-3p expression in pubertal mice Sertoli cells is crucial for germ cell differentiation and fertility

Sertoli cells (Sc) are the sole target of follicle-stimulating hormone (FSH) in the testis and attain functional maturation post-birth to significantly augment germ cell (Gc) division and differentiation at puberty. Despite having an operational microRNA (miRNA) machinery, limited information is available on miRNA-mediated regulation of Sc maturation and male fertility. We have shown before that miR-92a-3p levels decline in pubertal rat Sc. In response to FSH treatment, the expressions of FSH Receptor, Claudin11 and Klf4 were found to be elevated in pubertal rat Sc coinciding with our finding of FSH-induced decline in miR-92a-3p levels. To investigate the association of miR-92a-3p and spermatogenesis, we generated transgenic mice where such pubertal decline of miR-92a-3p was prevented by its overexpression in pubertal Sc under proximal Rhox5 promoter, which is known to be activated specifically at puberty, in Sc. Our in vivo observations provided substantial evidence that FSH-induced decline in miR-92a-3p expression during Sc maturation acts as an essential prerequisite for the pubertal onset of spermatogenesis. Elevated expression of miR-92a-3p in post-pubertal testes results into functionally compromised Sc, leading to impairment of the blood-testis barrier formation and apoptosis of pre-meiotic Gc, ultimately culminating into infertility. Collectively, our data suggest that regulation of miR-92a-3p expression is crucial for Sc-mediated induction of active spermatogenesis at puberty and regulation of male fertility.

Intragenic recombination within the pun allele of the pink-eyed dilution locus in pre-melanocytes and primordial germ cells of embryonic mice treated with N-ethyl-N-nitrosourea

The forward or reverse processes of intragenic recombination (IGR), which occur through the addition or deletion of duplicated homologous exons of the p^un allele in Pun mice, was observed in vivo, after introducing an homozygous p^un allele in a C57BL/6 background. We assessed the frequency of IGR upon N-ethyl-N-nitrosourea (ENU) treatment of pre-melanocytes (PMCs: somatic cells) and primordial germ cells (PGCs: germ cells) of embryonic mice at 10.5 days of development (E10.5). We simultaneously examined IGR and other mutations at the p locus of PMCs responsible for coat color in the offspring obtained by crossing p^un/p^un with p^un/P mice. The frequencies of both spontaneous and ENU-induced IGR were markedly higher than that of the recessive mutation (RM) in PMCs obtained from crossing C57BL/6 and PW strains (Shibuya et al., 1982). ENU also induces IGR at a higher frequency in PGCs at E10.5, which was observed in the next generation. These results indicate that ENU, which preferentially induces gene mutations through base substitution, also induces IGR at a high frequency in the p^un allele in both somatic and germ cells of embryonic mice at the E10.5 developmental stage.

Microplastics hamper the fertilization success of a broadcast spawning bivalve through reducing gamete collision and gamete fusion efficiency

By employing external fertilization (broadcast spawning) as a mating strategy, the gametes and subsequent fertilization of various marine invertebrates are directly subjected to pollution. Although microplastics (MPs) are ubiquitous in marine environments, their potential effects on the fertilization of broadcast spawners remain largely unknown. Therefore in this study, the impacts of polystyrene MPs on the fertilization success of broadcast spawning bivalve (Tegillarca granosa) were investigated. In order to reveal the underlying mechanisms affecting fertilization, the sperm swimming performance, sperm ATP status, sperm viability, DNA integrity, gamete collision probability, gamete fusion efficiency, enzymatic antioxidants, and key ion transport enzyme activities were analyzed. The results showed that MPs weakened the sperm swimming performance through reducing ATP production and cell viability, thus leading to the decreased probability of gamete collision. Furthermore, MPs affected ion transport in the gametes by inducing oxidative stress, which resulted in gamete fusion failure. In conclusion, this study demonstrates that MPs could significantly decrease the fertilization success of T. granosa through reducing gamete collision and lowering gamete fusion efficiency.

In vivo and in vitro protective effects of the Wuzi Yanzong pill against experimental spermatogenesis disorder by promoting germ cell proliferation and suppressing apoptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Wuzi Yanzong pill (WZYZP) is a classical traditional Chinese medicine (TCM) formula originated from the Tang dynasty. WZYZP has a long history of use for reinforcing kidney and alleviating male infertility in China.

AIM OF THE STUDY

The effect of WZYZP on male infertility and the mechanism underlying this effect was not clarified clearly. Therefore, this study aimed to investigate the protective effect of WZYZP in experimental spermatogenesis disorder via in vivo and in vitro studies, to promote the use of this formula for the treatment of spermatogenesis disorder.

MATERIAL AND METHODS

Male SD rats were exposed to tripterygium glycosides to induce experimental spermatogenesis disorder, and WZYZP was subsequently administrated at different dosages for treatment. Sperm counts, sperm motility, and serum hormone levels were detected. HE staining and TUNEL staining were performed to evaluate the pathological lesions and apoptosis of testes, respectively. Next, germ cells were isolated from spermatogenesis disorder-model rats and treated with WZYZP- containing serum at different concentrations. CCK-8 assay and flow cytometry assay were performed to detect cell proliferation and apoptosis. Immunofluorescence assay, qRT-PCR and Western blotting analyses were performed to detect the expression of Beclin 1, LC3 and TGF-β-PI3k/AKT-mTOR pathway - related factors, including TGF-β, PI3K, AKT, mTOR, 4 EBP-1 and p70S6K.

RESULTS

In vivo experiments showed that WZYZP protected against spermatogenesis disorder in model rats by improving sperm count and motility, as well as restoring serum hormone levels. HE and TUNEL staining demonstrated that the pathological injuries and cell apoptosis in testes of the model rats were alleviated by WZYZP treatment. Moreover, in vitro experiments of germ cells isolated from spermatogenesis disorder-model rats showed that WZYZP treatment increased the cell proliferation, inhibited cell apoptosis and autophagy. qRT-PCR and Western blotting assay results showed that this protective effect was associated with the regulation of the TGF-β/PI3K/AKT/mTOR signaling pathway. The expression levels of p-PI3K/PI3K, p-AKT/AKT, p-mTOR/mTOR, 4 EBP-1 and p70S6K were increased, while TGF-β was inhibited in the WZYZP treated groups.

CONCLUSION

The results showed that WZYZP could protect against experimental spermatogenesis disorder by increasing the germ cell proliferation and inhibiting their apoptosis. Our support the clinical use of this formula for the management of spermatogenesis disorder.

Chemical Genetic Screen in Drosophila Germline Uncovers Small Molecule Drugs That Sensitize Stem Cells to Insult-Induced Apoptosis

Cancer stem cells, in contrast to their more differentiated daughter cells, can endure genotoxic insults, escape apoptosis, and cause tumor recurrence. Understanding how normal adult stem cells survive and go to quiescence may help identify druggable pathways that cancer stem cells have co-opted. In this study, we utilize a genetically tractable model for stem cell survival in the Drosophila gonad to screen drug candidates and probe chemical-genetic interactions. Our study employs three levels of small molecule screening: (1) a medium-throughput primary screen in male germline stem cells (GSCs), (2) a secondary screen with irradiation and protein-constrained food in female GSCs, and (3) a tertiary screen in breast cancer organoids in vitro. Herein, we uncover a series of small molecule drug candidates that may sensitize cancer stem cells to apoptosis. Further, we have assessed these small molecules for chemical-genetic interactions in the germline and identified the NF-κB pathway as an essential and druggable pathway in GSC quiescence and viability. Our study demonstrates the power of the Drosophila stem cell niche as a model system for targeted drug discovery.

Multi Species Analyses Reveal Testicular T3 Metabolism and Signalling as a Target of Environmental Pesticides

Thyroid hormones (THs) regulate many biological processes in vertebrates, including reproduction. Testicular somatic and germ cells are equipped with the arrays of enzymes (deiodinases), transporters, and receptors necessary to locally maintain the optimal level of THs and their signalling, needed for their functions and spermatogenesis. Pesticides, as chlorpyrifos (CPF) and ethylene thiourea (ETU), impair the function of thyroid and testis, affecting male fertility. However, their ability to disarrange testicular T3 (t-T3) metabolism and signalling is poorly considered. Here, a multi-species analysis involving zebrafish and mouse suggests the damage of t-T3 metabolism and signalling as a mechanism of gonadic toxicity of low-doses CPF and ETU. Indeed, the developmental exposure to both compounds reduces Dio2 transcript in both models, as well as in ex-vivo cultures of murine seminiferous tubules, and it is linked to alteration of steroidogenesis and germ cell differentiation. A major impact on spermatogonia was confirmed molecularly by the expression of their markers and morphologically evidenced in zebrafish. The results reveal that in the adopted models, exposure to both pesticides alters the t-T3 metabolism and signalling, affecting the reproductive capability. Our data, together with previous reports suggest zebrafish as an evaluable model in assessing the action of compounds impairing locally T3 signalling.

Improving In Vitro Culture of Human Male Fetal Germ Cells

Male human fetal germ cells (hFGCs) give rise to spermatogonial stem cells (SSCs), which are the adult precursors of the male gametes. Human SSCs are a promising (autologous) source of cells for male fertility preservation; however, in contrast to mouse SSCs, we are still unable to culture them in the long term. Here, we investigated the effect of two different culture media and four substrates (laminin, gelatin, vitronectin and matrigel) in the culture of dissociated second trimester testes, enriched for hFGCs. After 6 days in culture, we quantified the presence of POU5F1 and DDX4 expressing hFGCs. We observed a pronounced difference in hFGC number in different substrates. The combination of gelatin-coated substrate and medium containing GDNF, LIF, FGF2 and EGF resulted in the highest percentage of hFGCs (10% of the total gonadal cells) after 6 days of culture. However, the vitronectin-coated substrate resulted in a comparable percentage of hFGCs regardless of the media used (3.3% of total cells in Zhou-medium and 4.8% of total cells in Shinohara-medium). We provide evidence that not only the choices of culture medium but also choices of the adequate substrate are crucial for optimizing culture protocols for male hFGCs. Optimizing culture conditions in order to improve the expansion of hFGCs will benefit the development of gametogenesis assays in vitro.

Spermatogonial stem cell transplantation into nonablated mouse recipient testes

Spermatogonial transplantation has been used as a standard assay for spermatogonial stem cells (SSCs). After transplantation into the seminiferous tubules, SSCs transmigrate through the blood-testis barrier (BTB) between Sertoli cells and settle in a niche. Unlike in the repair of other self-renewing systems, SSC transplantation is generally performed after complete destruction of endogenous spermatogenesis. Here, we examined the impacts of recipient conditioning on SSC homing. Germ cell ablation downregulated the expression of glial cell line-derived neurotrophic factor, which has been shown to attract SSCs to niches, implying that nonablated niches would attract SSCs more efficiently. As expected, SSCs colonized nonablated testes when transplanted into recipients with the same genetic background. Moreover, although spermatogenesis was arrested at the spermatocyte stage in Cldn11-deficient mice without a BTB, transplantation not only enhanced donor colonization but also restored normal spermatogenesis. The results show promise for the development of a new transplantation strategy to overcome male infertility.

Stability of Imprinting and Differentiation Capacity in Naïve Human Cells Induced by Chemical Inhibition of CDK8 and CDK19

Pluripotent stem cells can be stabilized in vitro at different developmental states by the use of specific chemicals and soluble factors. The naïve and primed states are the best characterized pluripotency states. Naïve pluripotent stem cells (PSCs) correspond to the early pre-implantation blastocyst and, in mice, constitute the optimal starting state for subsequent developmental applications. However, the stabilization of human naïve PSCs remains challenging because, after short-term culture, most current methods result in karyotypic abnormalities, aberrant DNA methylation patterns, loss of imprinting and severely compromised developmental potency. We have recently developed a novel method to induce and stabilize naïve human PSCs that consists in the simple addition of a chemical inhibitor for the closely related CDK8 and CDK19 kinases (CDK8/19i). Long-term cultured CDK8/19i-naïve human PSCs preserve their normal karyotype and do not show widespread DNA demethylation. Here, we investigate the long-term stability of allele-specific methylation at imprinted loci and the differentiation potency of CDK8/19i-naïve human PSCs. We report that long-term cultured CDK8/19i-naïve human PSCs retain the imprinting profile of their parental primed cells, and imprints are further retained upon differentiation in the context of teratoma formation. We have also tested the capacity of long-term cultured CDK8/19i-naïve human PSCs to differentiate into primordial germ cell (PGC)-like cells (PGCLCs) and trophoblast stem cells (TSCs), two cell types that are accessible from the naïve state. Interestingly, long-term cultured CDK8/19i-naïve human PSCs differentiated into PGCLCs with a similar efficiency to their primed counterparts. Also, long-term cultured CDK8/19i-naïve human PSCs were able to differentiate into TSCs, a transition that was not possible for primed PSCs. We conclude that inhibition of CDK8/19 stabilizes human PSCs in a functional naïve state that preserves imprinting and potency over long-term culture.

Histological and transcriptional effects of androstenedione in adult zebrafish (Danio rerio)

As a natural androgen, androstenedione (AED) may pose potential risks to aquatic organisms due to its ubiquitousness in aquatic environments. Here we assessed the adverse effects of AED on histology of gonads, as well as mRNA expression levels of 34 genes concerned with hypothalamic-pituitary-gonadal (HPG) axis, germ-cell differentiation and sex differentiation in zebrafish (Danio rerio). Adult zebrafish were exposed to solvent control and three measured concentrations of 0.2, 2.3 and 23.7 μg/L AED for 60 days. The results showed that AED did not induce any obvious histological effects in the ovaries and testes. Of the investigated genes, transcriptional expression levels of amh and cyp11c1 genes in the ovaries of females were significantly increased by AED at 2.3 or 23.7 μg/L. However, different exposure concentrations of AED significantly inhibited mRNA expression of gnrh3, atf4b1 and cyp19a1b in the brain of males. In the testes of males, AED at 2.3 μg/L led to a significant induction of sox9b gene, but it at 23.7 μg/L down-regulated nr5a1b gene. These observed transcriptional changes indicated that AED could pose potential androgenic effects in zebrafish.

In vitro reduction of Plasmodium falciparum gametocytes: Artemisia spp. tea infusions vs. artemisinin

ETHNOPHARMACOLOGICAL RELEVANCE

Artemisia annua has a long history of use in Southeast Asia where it was used to treat "fever", and A. afra has a similar history in southern Africa. Since their discovery, A. annua use, in particular, has expanded globally with millions of people using the plant in therapeutic tea infusions, mainly to treat malaria.

AIM OF THE STUDY

In this study, we used in vitro studies to query if and how A. annua and A. afra tea infusions being used across the globe affect asexual Plasmodium falciparum parasites, and their sexual gametocytes.

MATERIALS AND METHODS

P. falciparumstrain NF54 was grown in vitro, synchronized, and induced to form gametocytes using N-acetylglucosamine. Cultures during asexual, early, and late stage gametocytogenesis were treated with artemisinin, methylene blue, and A. annua and A. afra tea infusions (5 g DW/L) using cultivars that contained 0-283 μM artemisinin. Asexual parasitemia and gametocytemia were analyzed microscopically. Gametocyte morphology also was scored. Markers of early (PfGEXP5) and late stage (Pfs25) gametocyte gene expression also were measured using RT-qPCR.

RESULTS

Both A. annua and A. afra tea infusions reduced gametocytemia in vitro, and the effect was mainly artemisinin dependent. Expression levels of both marker genes were reduced and also occurred with the effect mainly attributed to artemisinin content of four tested Artemisia cultivars. Tea infusions of both species also inhibited asexual parasitemia and although mainly artemisinin dependent, there was a weak antiparasitic effect from artemisinin-deficient A. afra.

CONCLUSIONS

These results showed that A. annua and to a lesser extent, A. afra, inhibited parasitemia and gametocytemia in vitro.

Comprehensive review of genotoxicity data for diclofenac

Diclofenac is a non-steroidal anti-inflammatory drug discovered several decades ago, which has since been used by an estimated one billion patients and has demonstrated an acceptable safety profile. In support of its marketing approval, a comprehensive set of genotoxicity studies were conducted in vitro and in vivo. Despite the fact that these studies preceded both Good Laboratory Practice (GLP) requirements and International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) guidelines on genotoxicity testing, they were conducted using the best scientific principles and are considered appropriate by contemporary standards. In addition to bacterial mutagenicity and mammalian in vitro assays, repeat-dose somatic, germ cell and dominant lethal assays were conducted. These data are made available for the first time to offer researchers an opportunity to review the existing data set that unequivocally demonstrates that diclofenac sodium is not genotoxic. This is further substantiated by long-term bioassay data demonstrating that diclofenac sodium has no carcinogenic potential in rodents. However, more recently, new studies have been published showing a genotoxic potential for diclofenac in novel or modified in vitro test systems. These new publications are discussed in the context of the existing comprehensive data package.

Mtor inhibition by INK128 extends functions of the ovary reconstituted from germline stem cells in aging and premature aging mice

Stem cell transplantation has been generally considered as promising therapeutics in preserving or recovering functions of lost, damaged, or aging tissues. Transplantation of primordial germ cells (PGCs) or oogonia stem cells (OSCs) can reconstitute ovarian functions that yet sustain for only short period of time, limiting potential application of stem cells in preservation of fertility and endocrine function. Here, we show that mTOR inhibition by INK128 extends the follicular and endocrine functions of the reconstituted ovaries in aging and premature aging mice following transplantation of PGCs/OSCs. Follicular development and endocrine functions of the reconstituted ovaries by transplanting PGCs into kidney capsule of the recipient mice were maintained by INK128 treatment for more than 12 weeks, in contrast to the controls for only about 4 weeks without receiving the mTOR inhibitors. Comparatively, rapamycin also can prolong the ovarian functions but for limited time. Furthermore, our data reveal that INK128 promotes mitochondrial function in addition to its known function in suppression of immune response and inflammation. Taken together, germline stem cell transplantation in combination with mTOR inhibition by INK128 improves and extends the reconstituted ovarian and endocrine functions in reproductive aging and premature aging mice.

Decabromodiphenyl ether (BDE-209) exposure to lactating mice perturbs steroidogenesis and spermatogenesis in adult male offspring

Decabromodiphenyl ether (BDE-209) is widely used as a flame retardant in many products like electronic equipments, plastics, furniture and textiles. BDE-209, a thyroid hormones (THs)-disrupting chemical, affects male reproductive health through altered THs status in mouse model. The present study was designed in continuation to our earlier work to elucidate whether early life exposure to BDE-209 has a long term potential risk to male reproductive health. This study, therefore, aimed to evaluate the effect of maternal BDE-209 exposure during lactation and to elucidate possible mechanism(s) of its action on male reproduction in adult Parkes mice offspring. Lactating female Parkes mice were orally gavaged with 500, and 700 mg/kg body weight of BDE-209 in corn oil from postnatal day (PND) 1 to PND 28 along with 6-propyl-2-thiouracil (PTU)-treated positive controls and vehicle-treated controls. Male pups of lactating dams were euthanized at PND 75. Maternal BDE-209 exposure during lactation markedly affected histoarchitecture of testis and testosterone production with concomitant down-regulation in the expression of various steroidogenic markers in adult offspring. Maternal exposure to BDE-209 during lactation also interfered with germ cell dynamics and oxidative status in testes of adult mice offspring. A decreased expression of connexin 43 and androgen receptor was also evident in testes of these mice offspring; further, number, motility and viability of spermatozoa were also adversely affected in these mice. The results thus provide evidences that maternal exposure to BDE-209 during lactation causes reproductive toxicity in adult mice offspring.

The 28 + 28 day design is an effective sampling time for analyzing mutant frequencies in rapidly proliferating tissues of MutaMouse animals

The Organisation for Economic Co-Operation and Development Test Guideline 488 (TG 488) uses transgenic rodent models to generate in vivo mutagenesis data for regulatory submission. The recommended design in TG 488, 28 consecutive daily exposures with tissue sampling three days later (28 + 3d), is optimized for rapidly proliferating tissues such as bone marrow (BM). A sampling time of 28 days (28 + 28d) is considered more appropriate for slowly proliferating tissues (e.g., liver) and male germ cells. We evaluated the impact of the sampling time on mutant frequencies (MF) in the BM of MutaMouse males exposed for 28 days to benzo[a]pyrene (BaP), procarbazine (PRC), isopropyl methanesulfonate (iPMS), or triethylenemelamine (TEM) in dose–response studies. BM samples were collected + 3d, + 28d, + 42d or + 70d post exposure and MF quantified using the lacZ assay. All chemicals significantly increased MF with maximum fold increases at 28 + 3d of 162.9, 6.6, 4.7 and 2.8 for BaP, PRC, iPMS and TEM, respectively. MF were relatively stable over the time period investigated, although they were significantly increased only at 28 + 3d and 28 + 28d for TEM. Benchmark dose (BMD) modelling generated overlapping BMD confidence intervals among the four sampling times for each chemical. These results demonstrate that the sampling time does not affect the detection of mutations for strong mutagens. However, for mutagens that produce small increases in MF, sampling times greater than 28 days may produce false-negative results. Thus, the 28 + 28d protocol represents a unifying protocol for simultaneously assessing mutations in rapidly and slowly proliferating somatic tissues and male germ cells.

Ceramide mediates radiation-induced germ cell apoptosis via regulating mitochondria function and MAPK factors in Caenorhabditis elegans

Studies about radiation damage in vivo are very significant for healthy risk assessment as well as cancer radiotherapy. Ceramide as a second messenger has been found to be related to radiation-induced apoptosis. However, the detailed mechanisms in living systems are still not fully understood. In the present study, the effects of ceramide in gamma radiation-induced response were investigated using Caenorhabditis elegans. Our results indicated that ceramide was required for gamma radiation-induced whole-body germ cell apoptosis by the production of radical oxygen species and decrease of mitochondrial transmembrane potential. Using genetic ceramide synthase-related mutated strains and exogenous C₁₆-ceramide, we illustrated that ceramide could regulate DNA damage response (DDR) pathway to mediate radiation-induced germ cell apoptosis. Moreover, ceramide was found to function epistatic to pmk-1 and mpk-1 in MAPK pathway to promote radiation-induced apoptosis in Caenorhabditis elegans. These results demonstrated ceramide could potentially mediated gamma radiation-induced apoptosis through regulating mitochondrial function, DDR pathway and MAPK pathway.

A novel glucokinase activator TMG-123 causes long-lasting hypoglycemia and impairs spermatogenesis irreversibly in rats

The importance of glucose is well known as an energy source in testes. In order to evaluate the effects of long-lasting hypoglycemia on testes, a novel glucokinase activator, TMG-123, was dosed to rats at 5, 20 and 100 mg/kg for 13 weeks. As a result, plasma glucose levels decreased for several hours with increasing doses over the dose range of 5 to 100 mg/kg. No toxicological findings attributable to the test article were observed in clinical observation, measurements of body weight and food consumption, necropsy, and organ weight measurement. Histopathology showed scattered degeneration of seminiferous tubules in testes, and exfoliation of germ cells related to the degeneration of seminiferous tubules was observed in the lumen of both epididymides in the same animals at the end of the dosing period. Similar histopathological findings were noted at the end of the recovery period. In addition, a fertility study was conducted at the same doses for 13 weeks for males and 5 weeks for females. Sperm analysis showed decreases in the sperm concentration and the motility index and an increase in the incidences of sperm malformations. However, there were no abnormalities in the copulation or fertility rate. These results suggest that long-lasting hypoglycemia in rats is harmful to spermatogenesis and the testicular damage does not recover.

Epigenetic response to nanopolystyrene in germline of nematode Caenorhabditis elegans

microRNAs (miRNAs) provide an epigenetic regulation mechanism for the response to environmental toxicants. mir-38, a germline miRNA, was increased by exposure to nanopolystyrene (100 nm). In this study, we further found that germline overexpression of mir-38 decreased expressions of nhl-2 encoding a miRISC cofactor, ndk-1 encoding a homolog of NM23-H1, and wrt-3 encoding a homolog of PPIL-2. Meanwhile, germline-specific RNAi knockdown of nhl-2, ndk-1, or wrt-3 caused the resistance to nanopolystyrene toxicity. Additionally, mir-38 overexpression suppressed the resistance of nematodes overexpressing germline nhl-2, ndk-1, or wrt-3 containing 3'UTR, suggesting the role of NHL-2, NDK-1, and WRT-3 as the targets of germline mir-38 in regulating the response to nanopolystyrene. Moreover, during the control of response to nanopolystyrene, EKL-1, a Tudor domain protein, was identified as the downstream target of germline NHL-2, kinase suppressors of Ras (KSR-1 and KSR-2) were identified as the downstream targets of germline NDK-1, and ASP-2, a homolog of BACE1, was identified as the downstream target of germline WRT-3. Our results raised a mir-38-mediated molecular network in the germline in response to nanopolystyrene in nematodes. Our data provided an important basis for our understanding the response of germline of organisms to nanoplastic exposure.

Developmental abnormalities and epigenetic alterations in medaka (Oryzias latipes) embryos induced by triclosan exposure

Triclosan (TCS), an antibacterial and antifungal agent present in some consumer products, has been detected in the environment at varying concentrations. TCS exposure has been found to cause developmental abnormalities and endocrine disruption in various species of fish. It is not clearly understood whether TCS exposure causes epigenetic alterations in developing embryos and their germ cells. In the present study, we examined the effects of TCS exposure (0, 50, 100 and, 200 μg/L) on embryonic development and primordial germ cells (PGCs), which are precursors of sperm and eggs, in medaka (Oyzias latipes). Developmental TCS exposure from 8 h post-fertilization through 15 days post-fertilization (dpf) resulted in several developmental abnormalities, including enlarged yolk sac, decreased head trunk angle (HTA), and severe edema in the pericardial region. The male ratio increased in the 100 μg/L TCS exposure group, which was negatively correlated with the expression of cyp19ala (a gene encoding aromatase) and arα (androgen receptor alpha). Developmental 50 μg/L TCS exposure resulted in global hypomethylation in the whole body but not in the isolated PGCs. Expression of the gene encoding DNA methyltransferases (dnmt1 and dnmt3aa) was decreased by 50 μg/L TCS exposure both in the whole body and PGCs. TCS altered the expression of genes encoding enzymes involved in DNA methylation and demethylation in PGCs, suggesting epigenetic effects on germ cells. The present results demonstrate that the embryos exposed to the tested concentrations of TCS develop deformities during the early life stages and that the TCS within this range possesses endocrine disrupting properties potential enough to alter sex ratios of developing embryos.

Sex-dependent effects of preconception exposure to arsenite on gene transcription in parental germ cells and on transcriptomic profiles and diabetic phenotype of offspring

Chronic exposure to inorganic arsenic (iAs) has been linked to diabetic phenotypes in both humans and mice. However, diabetogenic effects of iAs exposure during specific developmental windows have never been systematically studied. We have previously shown that in mice, combined preconception and in utero exposures to iAs resulted in impaired glucose homeostasis in male offspring. The goal of the present study was to determine if preconception exposure alone can contribute to this outcome. We have examined metabolic phenotypes in male and female offspring from dams and sires that were exposed to iAs in drinking water (0 or 200 μg As/L) for 10 weeks prior to mating. The effects of iAs exposure on gene expression profiles in parental germ cells, and pancreatic islets and livers from offspring were assessed using RNA sequencing. We found that iAs exposure significantly altered transcript levels of genes, including diabetes-related genes, in the sperm of sires. Notably, some of the same gene transcripts and the associated pathways were also altered in the liver of the offspring. The exposure had a more subtle effect on gene expression in maternal oocytes and in pancreatic islets of the offspring. In female offspring, the preconception exposure was associated with increased adiposity, but lower blood glucose after fasting and after glucose challenge. HOMA-IR, the indicator of insulin resistance, was also lower. In contrast, the preconception exposure had no effects on blood glucose measures in male offspring. However, males from parents exposed to iAs had higher plasma insulin after glucose challenge and higher insulinogenic index than control offspring, indicating a greater requirement for insulin to maintain glucose homeostasis. Our results suggest that preconception exposure may contribute to the development of diabetic phenotype in male offspring, possibly mediated through germ cell-associated inheritance. Future research can investigate role of epigenetics in this phenomenon. The paradoxical outcomes in female offspring, suggesting a protective effect of the preconception exposure, warrant further investigation.

Heritable hazards of smoking: Applying the "clean sheet" framework to further science and policy

All the cells in our bodies are derived from the germ cells of our parents, just as our own germ cells become the bodies of our children. The integrity of the genetic information inherited from these germ cells is of paramount importance in establishing the health of each generation and perpetuating our species into the future. There is a large and growing body of evidence strongly suggesting the existence of substances that may threaten this integrity by acting as human germ cell mutagens. However, there generally are no absolute regulatory requirements to test agents for germ cell effects. In addition, the current regulatory testing paradigms do not evaluate the impacts of epigenetically mediated intergenerational effects, and there is no regulatory framework to apply new and emerging tests in regulatory decision making. At the 50th annual meeting of the Environmental Mutagenesis and Genomics Society held in Washington, DC, in September 2019, a workshop took place that examined the heritable effects of hazardous exposures to germ cells, using tobacco smoke as the example hazard. This synopsis provides a summary of areas of concern regarding heritable hazards from tobacco smoke exposures identified at the workshop and the value of the Clean Sheet framework in organizing information to address knowledge and testing gaps.

Neonicotinoid-containing insecticide disruption of growth, locomotion, and fertility in Caenorhabditis elegans

Neonicotinoids, a class of insecticides structurally similar to nicotine that target biting and sucking insects, are the most widely used insecticides today, in part due to their supposed low toxicity in other organisms. However, a growing body of research has found that even low doses of neonicotinoids can induce unexpected negative effects on the physiology and survival of a wide range of non-target organisms. Importantly, no work has been done on the commercial formulations of pesticides that include imidacloprid as the active ingredient, but that also contain many other components. The present study examines the sublethal effects of "Tree and Shrub"™ ("T+S"), a commercial insecticide containing the neonicotinoid imidacloprid as its active ingredient, on Caenorhabditis elegans. We discovered that "T+S" significantly stunted the overall growth in wildtype nematodes, an effect that was exacerbated by concurrent exposure to heat stress. "T+S" also negatively impacted fecundity as measured by increased germline apoptosis, a decrease in egg-laying, and fewer viable offspring. Lastly, exposure to "T+S" resulted in degenerative changes in nicotinic cholinergic neurons in wildtype nematodes. As a whole, these findings demonstrate widespread toxic effects of neonicotinoids to critical functions in nematodes.

Toxic Effects of Nonylphenol on Neonatal Testicular Development in Mouse Organ Culture

Nonylphenol (NP) is an alkylphenol that is widely used in chemical manufacturing. Exposure to this toxic environmental contaminant has been shown to negatively affect the reproductive system. Herein, we evaluated the toxicity of NP in mouse testes, while using in vitro organ culture. Mouse testicular fragments (MTFs), derived from five-day postpartum neonatal mouse testes, were exposed to different concentrations of NP (1-50 μM) for 30 days. The results showed that NP impaired germ cell development and maintenance. Furthermore, NP significantly downregulated the transcript levels of both undifferentiated and differentiated germ cell marker genes relative to those in controls. In particular, a high dose of NP (50 µM) led to complete germ cell depletion and resulted in spermatogenic failure, despite the presence of Sertoli and Leydig cells. In addition, the mRNA expression of steroidogenic enzymes, such as steroidogenic acute regulatory protein (STAR), Cytochrome P450 Family 11 Subfamily A Member 1 (Cyp11α1), Cytochrome P450 17A1 (Cyp17α1), and androgen receptor (AR), increased with increasing concentration of NP. Conversely, the expression of estrogen receptor alpha (ESR1) and Cytochrome P450 family 19 subfamily A member 1 (Cyp19α1) in NP-exposed MTFs decreased when compared to that of the control. Taken together, this study demonstrates that NP has a negative effect on prepubertal spermatogenesis and germ cell maintenance and it disrupts steroidogenesis and induces hormonal imbalance in MTFs.

A male germ cell assay and supporting somatic cells: its application for the detection of phase specificity of genotoxins in vitro

Male germ stem cells are responsible for transmission of genetic information to the next generation. Some chemicals exert a negative impact on male germ cells, either directly, or indirectly affecting them through their action on somatic cells. Ultimately, these effects might inhibit fertility, and may exhibit negative consequences on future offspring. Genotoxic anticancer agents may interact with DNA in germ cells potentially leading to a heritable germline mutation. Experimental information in support of this theory has not always been reproducible and suitable in vivo studies remain limited. Thus, alternative male germ cell tests, which are now able to detect phase specificity of such agents, might be used by regulatory agencies to help evaluate the potential risk of mutation. However, there is an urgent need for such approaches for identification of male reproductive genotoxins since this area has until recently been dependent on in vivo studies. Many factors drive alternative approaches, including the (1) commitment to the principles of the 3R's (Replacement, Reduction, and Refinement), (2) time-consuming nature and high cost of animal experiments, and (3) new opportunities presented by new molecular analytical assays. There is as yet currently no apparent appropriate model of full mammalian spermatogenesis in vitro, under the REACH initiative, where new tests introduced to assess genotoxicity and mutagenicity need to avoid unnecessary testing on animals. Accordingly, a battery of tests used in conjunction with the high throughput STAPUT gravity sedimentation was recently developed for purification of male germ cells to investigate genotoxicity for phase specificity in germ cells. This system might be valuable for the examination of phases previously only available in mammals with large-scale studies of germ cell genotoxicity in vivo. The aim of this review was to focus on this alternative approach and its applications as well as on chemicals of known in vivo phase specificities used during this test system development.

Rapamycin treatment maintains developmental potential of oocytes in mice and follicle reserve in human cortical fragments grafted into immune-deficient mice

The ovarian follicle pool size is limited; it decreases with age and following germ cell-damaging chemo- or radiation therapies. Due to a trend of delaying child-bearing age in the modern society, it is important to investigate the possibility to maintain the follicle reserve for middle-aged women and cancer-bearing patients subject to therapies. Earlier studies demonstrated the important role of the mammalian targets of the rapamycin (MTOR) signaling pathway in the activation of primordial follicles and suggested that treatment with the MTOR inhibitor rapamycin could maintain the follicle pool in rodents. Here, we confirmed the ability of rapamycin treatment for 3 weeks to suppress primordial follicle development and to maintain follicle pool size in mice. We further demonstrated that the developmental potential of oocytes was not affected by rapamycin treatment and the effect of rapamycin to decrease initial follicle recruitment is reversible. Using human ovarian cortical fragments grafted into immune-deficient mice, we demonstrated the ability of rapamycin to suppress follicle growth from the primordial stage. Our studies provide the basis for further studies on the possibility of using MTOR inhibitors to maintain follicle reserve in middle-aged women and cancer patients before/during germ cell-damaging therapies.

The progestin norethindrone alters growth, reproductive histology and gene expression in zebrafish (Danio rerio)

The aim of this study was to assess the long-term effects of synthetic progestin norethindrone (NET) on the growth, reproductive histology, and transcriptional expression profiles of genes associated with the hypothalamic-pituitary-gonadal (HPG) axis and germ cells in adult zebrafish. Adult zebrafish were exposed to 7, 84 and 810 ng/L NET for 90 days. The results showed that exposure to 810 ng/L NET caused a significant decrease in growth of females and males. The ovary weight and GSI was significantly reduced by NET at concentrations of 84 or 810 ng/L, which came along with the delay of ovary maturation in females. However, NET at all treatments resulted in acceleration of sperm maturation in males. In the ovaries of females, a strong inhibition of cyp19a1a gene was observed following exposure to NET at 810 ng/L. Similarly, NET at the highest treatment led to a significant down-regulation of cyp17, cyp19a1a, vasa, nanos1, dazl and dmc1 genes in the testes of males. Taken together, the overall results demonstrated that NET could impact growth and gonadal maturation, with significant alterations of transcriptional expression genes along HPG axis and germ cells.

Transcriptome profiling of laser-captured germ cells and functional characterization of zbtb40 during 17alpha-methyltestosterone-induced spermatogenesis in orange-spotted grouper (Epinephelus coioides)

BACKGROUND

Spermatogenesis is an intricate process regulated by a finely organized network. The orange-spotted grouper (Epinephelus coioides) is a protogynous hermaphroditic fish, but the regulatory mechanism of its spermatogenesis is not well-understood. In the present study, transcriptome sequencing of the male germ cells isolated from orange-spotted grouper was performed to explore the molecular mechanism underlying spermatogenesis.

RESULTS

In this study, the orange-spotted grouper was induced to change sex from female to male by 17alpha-methyltestosterone (MT) implantation. During the spermatogenesis, male germ cells (spermatogonia, spermatocytes, spermatids, and spermatozoa) were isolated by laser capture microdissection. Transcriptomic analysis for the isolated cells was performed. A total of 244,984,338 clean reads were generated from four cDNA libraries. Real-time PCR results of 13 genes related to sex differentiation and hormone metabolism indicated that transcriptome data are reliable. RNA-seq data showed that the female-related genes and genes involved in hormone metabolism were highly expressed in spermatogonia and spermatozoa, suggesting that these genes participate in the spermatogenesis. Interestingly, the expression of zbtb family genes showed significantly changes in the RNA-seq data, and their expression patterns were further examined during spermatogenesis. The analysis of cellular localization of Eczbtb40 and the co-localization of Eczbtb40 and Eccyp17a1 in different gonadal stages suggested that Eczbtb40 might interact with Eccyp17a1 during spermatogenesis.

CONCLUSIONS

Our study, for the first time, investigated the transcriptome of the male germ cells from orange-spotted grouper, and identified functional genes, GO terms, and KEGG pathways involved in spermatogenesis. Furthermore, Eczbtb40 was first characterized and its role during spermatogenesis was predicted. These data will contribute to future studies on the molecular mechanism of spermatogenesis in teleosts.

Transgenerational reproductive and developmental toxicity of tebuconazole in Caenorhabditis elegans

The transgenerational reproductive and developmental toxicity of tebuconazole (TEB) in Caenorhabditis elegans was investigated over five generations (P0 - F4). Only parental C.elegans (P0) were exposed to TEB (0, 0.01, 0.1, 1, and 10 μg/L) for 24 h and the subsequent offspring (F1-F4) were grown under TEB-free conditions. TEB exposure caused dose-dependent reproductive defects and developmental impairments in C.elegans. In the P0 generation reproductive defects were observed such as: reduced brood size and embryo hatchability, prolonged generation time, retarded gonadal development, and slower germline proliferation, even at 0.01 μg/L, together with developmental toxicity with significant reduced body length and narrowed body width at 10 μg/L. Additionally, the brood size significantly reduced in F2, which began to recover from F3, but was still lower than the control in F4. The proportion of abnormalities increased significantly in F2 and reduced from F3, but was still higher than the control, suggesting that TEB could have cumulative potential and be passed to offspring through parental exposure. Furthermore, exposure to TEB (10 μg/L) in P0 significantly reduced the body length in F1, which began to recover from F2, and was the same level as the control in F4. There was a concentration-dependent increase in body width in F1-F4, with a significant increase only observed in F1 at 10 μg/L. Thus, parental exposure to TEB induced transgenerational defects in both reproduction and development, emphasizing the significance of considering bio-toxicity over multiple generations to conduct accurate assessment of environmental risks of toxicants.

Mutation as a Toxicological Endpoint for Regulatory Decision-Making

Mutations induced in somatic cells and germ cells are responsible for a variety of human diseases, and mutation per se has been considered an adverse health concern since the early part of the 20th Century. Although in vitro and in vivo somatic cell mutation data are most commonly used by regulatory agencies for hazard identification, that is, determining whether or not a substance is a potential mutagen and carcinogen, quantitative mutagenicity dose-response data are being used increasingly for risk assessments. Efforts are currently underway to both improve the measurement of mutations and to refine the computational methods used for evaluating mutation data. We recommend continuing the development of these approaches with the objective of establishing consensus regarding the value of including the quantitative analysis of mutation per se as a required endpoint for comprehensive assessments of toxicological risk. Environ. Mol. Mutagen. 61:34-41, 2020. © 2019 Wiley Periodicals, Inc.

The mutagenesis moonshot: The propitious beginnings of the environmental mutagenesis and genomics society

A mutagenesis moonshot addressing the influence of the environment on our genetic wellbeing was launched just 2 months before astronauts landed on the moon. Its impetus included the discovery that X-rays (Muller HJ. [1927]: Science 64:84-87) and chemicals (Auerbach and Robson. [1946]: Nature 157:302) were germ-cell mutagens, the introduction of a growing number of untested chemicals into the environment after World War II, and an increasing awareness of the role of environmental pollution on human health. Due to mounting concern from influential scientists that germ-cell mutagens might be ubiquitous in the environment, Alexander Hollaender and colleagues founded in 1969 the Environmental Mutagen Society (EMS), now the Environmental Mutagenesis and Genomics Society (EMGS); Frits Sobels founded the European EMS in 1970. As Fred de Serres noted, such societies were necessary because protecting populations from environmental mutagens could not be addressed by existing scientific societies, and new multidisciplinary alliances were required to spearhead this movement. The nascent EMS gathered policy makers and scientists from government, industry, and academia who became advocates for laws requiring genetic toxicity testing of pesticides and drugs and helped implement those laws. They created an electronic database of the mutagenesis literature; established a peer-reviewed journal; promoted basic and applied research in DNA repair and mutagenesis; and established training programs that expanded the science worldwide. Despite these successes, one objective remains unfulfilled: identification of human germ-cell mutagens. After 50 years, the voyage continues, and a vibrant EMGS is needed to bring the mission to its intended target of protecting populations from genetic hazards. Environ. Mol. Mutagen. 61:8-24, 2020. © 2019 Wiley Periodicals, Inc.

A Return to the Origin of the EMGS: Rejuvenating the Quest for Human Germ Cell Mutagens and Determining the Risk to Future Generations

Fifty years ago, the Environmental Mutagen Society (now Environmental Mutagenesis and Genomics Society) was founded with a laser-focus on germ cell mutagenesis and the protection of "our most vital assets"-the sperm and egg genomes. Yet, five decades on, despite the fact that many agents have been demonstrated to induce inherited changes in the offspring of exposed laboratory rodents, there is no consensus on whether human germ cell mutagens exist. We argue that it is time to reevaluate the available data and conclude that we already have evidence for the existence of environmental exposures that impact human germ cells. What is missing are definite data to demonstrate a significant increase in de novo mutations in the offspring of exposed parents. We believe that with over two decades of research advancing knowledge and technologies in genomics, we are at the cusp of generating data to conclusively show that environmental exposures cause heritable de novo changes in the human offspring. We call on the research community to harness our technologies, synergize our efforts, and return to our Founders' original focus. The next 50 years must involve collaborative work between clinicians, epidemiologists, genetic toxicologists, genomics experts and bioinformaticians to precisely define how environmental exposures impact germ cell genomes. It is time for the research and regulatory communities to prepare to interpret the coming outpouring of data and develop a framework for managing, communicating and mitigating the risk of exposure to human germ cell mutagens. Environ. Mol. Mutagen. 61:42-54, 2020. © 2019 Her Majesty the Queen in Right of Canada.

[Reproductive toxicity of PBDE in males: Advances in studies]

Polybrominated biphenyl ether (PBDE) is a kind of brominated aromatic hydrocarbon commonly used as a flame retardant and now considered as one of the persistent organic pollutants, which generally exists in the environment and organisms. Studies have shown that PBDEs have an endocrine disrupting effect, neurotoxicity, developmental toxicity, reproductive toxicity, and the ability of inducing reproductive toxicity in men by reducing semen quality, affecting testis germ cells and interfering with reproductive hormone levels. Although PBDEs have been banned in some countries, they do exist in our environment. Therefore, more studies are needed to reveal their potential toxicity and mechanisms, so as to monitor, predict and prevent their pollution. This review focuses on the male reproductive toxicity of PBDEs.

Molecular mechanisms underlying nickel nanoparticle induced rat Sertoli-germ cells apoptosis

This study was done on SD rat Sertoli-germ co-cultured cells (Sertoli-germ cells) with nickel nanoparticles (Ni NPs). A series of investigations were performed to observe the role of Ni NPs on the apoptosis of Sertoli-germ cells and to explore the long-chain non-coding RNA (lncRNA) functions on key signaling pathways and regulatory mechanisms. We found that Ni NPs had an apoptotic effect on Sertoli-germ cells. Ni NPs-induced apoptosis in Sertoli-germ cells involves the LOC102551356, Insulin-like growth factor-binding protein 3 (Igfbp3), and mitochondrial apoptosis pathway. The specific mechanism may be: during the process of Ni NPs-induced apoptosis in Sertoli-germ cells, the expression of LOC102551356 is up-regulated, and LOC102551356 activates the mitochondrial apoptosis pathway through targeted regulation of the target gene Igfbp3 in the P53-reduced apoptosis pathway. The results of this study will be important for the safety evaluation of Ni NPs in the future, and could provide an approach for the prevention or alleviation of the toxicity induced by Ni NPs.

Acute exposure to perfluorononanoic acid in prepubertal mice: Effect on germ cell dynamics and an insight into the possible mechanisms of its inhibitory action on testicular functions

Perfluoroalkyl acids (PFAAs) are anthropogenic compounds used globally in a variety of commercial products. Perfluorononanoic acid (PFNA), a member of PFAAs, is detected in human blood and this has been reported to cause hepatotoxic, immunotoxic, and developmental and testicular toxic effects in laboratory animals. We have recently shown that the acute exposure to PFNA in prepubertal Parkes (P) mice impairs spermatogenesis by inducing oxidative stress and inhibiting testosterone biosynthesis in the testis. The present study was aimed to examine the effect of acute exposure to PFNA in prepubertal P mice on germ cell dynamics and to understand the possible mechanisms of action of this compound on testicular functions. PFNA (2 and 5 mg/kg body weight) was orally administered to male mice for 14 days from postnatal day 25-38. The treatment caused a decrease in overall germ cell transformation. The results also reveal that impairment in testicular functions in treated mice is associated with alterations in cholesterol and glucose homeostasis; further, an inhibition in expressions of growth hormone receptor (GHR), insulin-like growth factor-1 (IGF-1), insulin-like growth factor-1 receptor (IGF-1R), androgen receptor (AR), phosphorylated mammalian target of rapamycin (p-mTOR) and peroxisome proliferator activated receptor α (PPAR α) in the testis is also implicated in this action. The findings thus suggest involvement of multiple factors which altogether contribute to the alterations in spermatogenic process and testosterone production following acute exposure to PFNA in prepubertal mice.

Retinoic acid-stimulated ERK1/2 pathway regulates meiotic initiation in cultured fetal germ cells

In murine fetal germ cells, retinoic acid (RA) is an extrinsic cue for meiotic initiation that stimulates transcriptional activation of the Stimulated by retinoic acid gene 8 (Stra8), which is required for entry of germ cells into meiotic prophase I. Canonically, the biological activities of RA are mediated by nuclear RA receptors. Recent studies in somatic cells found that RA noncanonically stimulates intracellular signal transduction pathways to regulate multiple cellular processes. In this study, using a germ cell culture system, we investigated (1) whether RA treatment activates any mitogen-activated protein kinase (MAPK) pathways in fetal germ cells at the time of sex differentiation, and (2) if this is the case, whether the corresponding RA-stimulated signaling pathway regulates Stra8 expression in fetal germ cells and their entry into meiosis. When XX germ cells at embryonic day (E) 12.5 were cultured with RA, the extracellular-signal-regulated kinase (ERK) 1/2 pathway was predominantly activated. MEK1/2 inhibitor (U0126) treatment suppressed the mRNA expressions of RA-induced Stra8 and meiotic marker genes (Rec8, Spo11, Dmc1, and Sycp3) in both XX and XY fetal germ cells. Furthermore, U0126 treatment dramatically reduced STRA8 protein levels and numbers of meiotic cells among cultured XX and XY fetal germ cells even in the presence of RA. Taken together, our results suggest the novel concept that the RA functions by stimulating the ERK1/2 pathway and that this activity is critical for Stra8 expression and meiotic progression in fetal germ cells.

The comet assay in Ceraeochrysa claveri (Neuroptera: Chrysopidae): A suitable approach for detecting somatic and germ cell genotoxicity induced by agrochemicals

Some agrochemicals are genotoxic to several organisms. Nevertheless, few protocols are currently available for measuring the toxicogenetic effects of these compounds in target and non-target field-collected species of insects important to agriculture. Herein, we used the species Ceraeochrysa claveri (Neuroptera: Chrysopidae), a non-target predator insect, to investigate the ability of an azadirachtin-based biopesticide (Azamax™) to induce DNA damage. The alkaline version of the comet assay was standardized to evaluate genetic instability caused by the toxicant in somatic (gut) and germ (nurse cells and oocytes) cells of C. claveri. For this, C. claveri larvae were distributed into three groups (10/each) and treated with Azamax™ at 0, 0.3% or 0.5% throughout the larval stage. DNA damage (tail intensity) was measured in adult insects, four days after emerged. The data showed that both doses of Azamax™ (0.3% and 0.5%) were able to significantly (p < 0.05) increase DNA damage in somatic and germ cells of C. claveri. In conclusion, C. claveri (intestinal and ovarian cells) was a sensitive bioindicator for identifying Azamax™ genotoxic potential, whereas the comet assay was a useful tool for detecting the genotoxic hazard of the pesticide in the field-collected insect species. Given that estimation of adverse effects of pollutants on ecosystems is an essential component of environmental risk assessment, the approach used can be recommended to estimate the ecotoxicity of agricultural chemicals.

Gliadin Intake Causes Disruption of the Intestinal Barrier and an Increase in Germ Cell Apoptosis in A Caenorhabditis Elegans Model

Gliadin is a major protein component of gluten and causes gluten toxicity through intestinal stress. We previously showed that gliadin intake induces oxidative stress in the intestine and reduces fertility in a Caenorhabditis elegans model. To elucidate the possible link between intestinal stress and reproduction, changes in the intestine and germ cells of C. elegans after gliadin intake were examined at the molecular level. Gliadin intake increased reactive oxygen species (ROS) production in the intestine, decreased intestinal F-actin levels, and increased germ cell apoptosis. These gliadin-triggered effects were suppressed by antioxidant treatment. These results suggest that ROS production in the intestine induced by gliadin intake causes disruption of intestinal integrity and increases germ cell apoptosis. Gliadin-induced germ cell apoptosis (GIGA) was suppressed by depletion of cep-1, ced-13, egl-1, or mpk-1. However, HUS-1 was not activated, suggesting that GIGA is activated through the mitogen-activated protein kinase (MAPK) pathway and is CEP-1-dependent but is a separate pathway from that controlling the DNA damage response. Taken together, our results suggest that gliadin causes intestinal barrier disruption through ROS production and interacts with the germ cells to reduce fertility through GIGA.

Ghrelin alleviates endoplasmic reticulum stress and inflammation-mediated reproductive dysfunction induced by stress

PURPOSE

Psychological stress exists widely in modern society and results in the disruption of testicular tight junctions, germ cell apoptosis, and the disorder of fertility hormones and even causes infertility. Ghrelin (GHRL), a 28-amino acid peptide secreted mainly by the stomach and pancreas, has been reported to alleviate male reproductive injury through inhibiting apoptosis. However, whether GHRL has a beneficial effect on psychological stress-induced testicular injury and the possible mechanisms remain poorly understood.

METHODS

Male mice were immobilized in Decapicone bags for 3 h daily for 14 days treated with or without GHRL (i.p. 100 mg/kg body weight). Body weight and testicular weight were measured. Histological alterations and apoptosis were examined by H.E. staining and TUNEL staining, respectively. The expression of endoplasmic reticulum (ER) stress markers, inflammatory cytokines, Toll-like receptor 4 (TLR4), and nuclear factor-κB (NF-κB) in the testes was investigated.

RESULTS

Exposure to stress caused testicular histological alterations, an elevation of the Johnsen score, and germ cell apoptosis, while GHRL partially alleviated the adverse effects. The expression of ER stress marker proteins, including GRP78, CHOP, ATF6, p-JNK, and XBP-1, was upregulated in the stress group; however, GHRL treatment significantly suppressed the activation of ER stress in the testes. GHRL also inhibited the expression of TNF-α, IL-1β, IL-6, IL-10, TLR4, and NF-κB.

CONCLUSIONS

GHRL alleviated testicular injury induced by ER stress and inflammation which is associated with the TLR4/NF-κB signaling pathway, and these findings may provide a novel strategy for preventing and treating reproductive dysfunction.

p53-Dependent pathway and the opening of mPTP mediate the apoptosis of co-cultured Sertoli-germ cells induced by microcystin-LR

Microcystin-LR (MC-LR), a potent endotoxin, can induce reproductive toxicity. In order to investigate the role and mechanisms of apoptosis (p53-dependent and mitochondrial pathways) of germ cells induced by MC-LR, the co-cultured primary Sertoli-germ cells from Sprague-Dawley rats were used for the experiments. Expression levels of proteins, genes, and mitochondrial membrane potential (MMP) were obtained after exposing co-cultured Sertoli-germ cells to MC-LR with or without the addition of the p53 inhibitor, pifithrin-α (PFT-α), and MMP inhibitor, cyclosporin A (CsA). Results indicated that MC-LR could activate p53-dependent pathway-associated proteins in Sertoli-germ cells, leading to a decrease in MMP (indicating the opening of mitochondrial permeability transition pore [mPTP] and the release of Cytochrome-c [Cyt-c]) from the mitochondria into the cytoplasm and eventually the induction of apoptosis. PFT-α inhibited the expression ofp53, ameliorated the MMP of the co-cultured Sertoli-germ cells, and prevented the release of Cyt-c from the mitochondria into the cytoplasm, which reduces the occurrence of apoptosis. Similarly, the decreased release of Cyt-c from the mitochondria into the cytoplasm and the declined level of apoptosis in Sertoli-germ cells induced by MC-LR were observed after the addition of CsA. These results indicated that the apoptosis of the co-cultured Sertoli-germ cells induced by MC-LR was mediated by the p53-dependent pathway, with the involvement of the opening of mPTP.

Copper-induced apoptosis and autophagy through oxidative stress-mediated mitochondrial dysfunction in male germ cells

Excess copper reduces sperm number and motility but the causes are unclear. We investigated the toxic effects of copper exposure on the immortalized male germ cell line GC-1. Copper addition to cells altered viability and morphology in a dose-dependent manner. Copper addition resulted in increased levels of reactive oxygen species (ROS), malonaldehyde (MDA) and lactate dehydrogenase (LDH) while catalase (CAT) activity and glutathione (GSH) declined. The mitochondrial transmembrane potential and ATP levels decreased in response to copper as did mitochondria fission that led to mitochondrial dysfunction. The apoptosis rate was also proportional to the level of copper in the growth medium. Copper also down-regulated Bcl2 and up-regulated Bax, Casp8 and Casp3 linking the effects of copper to increased apoptosis. The levels of mRNA for the autophagy-related genes (Atg3, Atg5, p62, Lc3b/Lc3a) and proteins (Lc3b/Lc3a, BECN1, Atg5, p62) all increased in copper-treated cells as were levels Lc3 determined by fluorescence microscopy. These results indicated that copper induces apoptosis and autophagy through oxidative stress-mediated mitochondrial dysfunction.

In utero exposure to acetaminophen and ibuprofen leads to intergenerational accelerated reproductive aging in female mice

Nonsteroidal anti-inflammatory drugs (NSAIDs) and analgesic drugs, such as acetaminophen (APAP), are frequently taken during pregnancy, even in combination. However, they can favour genital malformations in newborn boys and reproductive disorders in adults. Conversely, the consequences on postnatal ovarian development and female reproductive health after in utero exposure are unknown. Here, we found that in mice, in utero exposure to therapeutic doses of the APAP-ibuprofen combination during sex determination led to delayed meiosis entry and progression in female F1 embryonic germ cells. Consequently, follicular activation was reduced in postnatal ovaries through the AKT/FOXO3 pathway, leading in F2 animals to subfertility, accelerated ovarian aging with abnormal corpus luteum persistence, due to decreased apoptosis and increased AKT-mediated luteal cell survival. Our study suggests that administration of these drugs during the critical period of sex determination could lead in humans to adverse effects that might be passed to the offspring.

The germline-specific expression of Foxl3a and its paralogous Foxl3b are associated with male gonadal differentiation in the Japanese eel, Anguilla japonica

Unlike its paralog Foxl2, which is well known for its role in ovarian development in vertebrates, the function of Foxl3 is still unclear. Foxl3 is an ancient duplicated copy of Foxl2. It is present as a single copy in ray-finned fish. But, due to repeated losses, it is absent in most tetrapods. Our transcriptomic data, however, show that two Foxl3s (Foxl3a and its paralog Foxl3b) are present in Japanese eel. Foxl3a is predominantly expressed in the pituitary, and Foxl3b is predominantly expressed in the gills. Both Foxl3s show a sex-dimorphic expression, being higher expression in testes than in ovaries. Moreover, Foxl3a and Foxl3b were exclusively expressed during gonadal differentiation in control eels (100% male). Conversely, Foxl3a and Foxl3b significantly decreased after gonadal differentiation in E2-treated eels (100% female). Furthermore, in accordance the difference in adhesive ability between somatic cells and germline cells in testes, Foxl3s showed a high expression in suspension cells (putative germline cells) and low expression in adhesive cells (putative somatic cells). In situ hybridization further showed that Foxl3a and Foxl3b were expressed in the testicular germline cells. In addition, Foxl3s expression was not changed by sex steroids in in vitro testes culture. Taken together, our results suggest that the teleost-specific Foxl3 paralog was repeatedly lost in most fish after the third round of whole genome duplication. The two germline-expressed Foxl3s had higher expression levels in males than in females during gonadal differentiation in Japanese eel. These results demonstrated that Foxl3s might play an important role in germline sexual fate determination from ancient fish to modern fish.

Pregnancy drugs, fetal germline epigenome, and risks for next-generation pathology: A call to action

Drugs taken during pregnancy can affect three generations at once: the gestating woman (F0), her exposed fetus (F1), and the fetal germ cells that confer heritable information for the grandchildren (F2). Unfortunately, despite growing evidence for connections between F0 drug exposures and F2 pathology, current approaches to risk assessment overlook this important dimension of risk. In this commentary, we argue that the unique molecular vulnerabilities of the fetal germline, particularly with regard to global epigenomic reprogramming, combined with empirical evidence for F2 effects of F1 in utero drug and other exposures, should change the way we consider potential long-term consequences of pregnancy drugs and alter toxicology's standard somatic paradigm. Specifically, we (1) suggest that pregnancy drugs common in the postwar decades should be investigated as potential contributors to the "missing heritability" of many pathologies now surging in prevalence; (2) call for inclusion of fetal germline risks in pregnancy drug safety assessment; and (3) highlight the need for intensified research to ascertain generational impacts of diethylstilbestrol, a vanguard question of human germline toxicity. Only by fully addressing this important dimension of transplacental exposure can we responsibly evaluate safety of drug exposures during pregnancy and convey the full scope of risks, while also retrospectively comprehending the generational legacy of recent history's unprecedented glut of evolutionarily novel intrauterine exposures. Environ. Mol. Mutagen. 60:445-454, 2019. © 2019 Wiley Periodicals, Inc.

Transgenerational effects of diesel particulate matter on Caenorhabditis elegans through maternal and multigenerational exposure

Diesel particulate matter (DPM) is a dominant contaminant in fine particulate matters (PM_2.5) and has been proved to induce serious harmful effects to human beings, including lung cancer, allergic, and chronic bronchitis. However, little attention has been paid to understand the transgenerational effects of DPM. In the present study, we focused on the transgenerational effects of DPM in the model organism Caenorhabditis elegans (C. elegans) exposed in either maternal generation (F0) or consecutive generations (F0-F5). In maternal exposure manner, 0.1 and 1.0 µg/mL DPM significantly increased the germ cell apoptosis at F0 generation, while the number of apoptotic germ cells at F1-F5 generation were gradually recovered back to control level. The brood size were significantly reduced by DPM at F2 generation and recovered to control level at F3-F5 generations. In continuous exposure manner, although 0.1 and 1.0 µg/mL DPM induced significant germ cell apoptosis in F0 generation, there was no difference between F0 and other generations. Continuous exposure to DPM at 0.1 and 1.0 µg/mL impaired the brood size in F2 to F5 generations. Using a series of loss-of-function mutant strains, we found that cep-1 (w40), hus-1 (op241), and mitogen-activated protein kinase (MAPK) related signaling pathway genes were involved in DPM-induced apoptosis. Our results clearly demonstrated that the adverse effects of DPM could be passed on through long-term multigenerational exposure and DNA damage checkpoint genes and MAPK signal pathway played an essential role in response to DPM induced development and reproduction toxicity.

Assessing effects of germline exposure to environmental toxicants by high-throughput screening in C. elegans

Chemicals that are highly prevalent in our environment, such as phthalates and pesticides, have been linked to problems associated with reproductive health. However, rapid assessment of their impact on reproductive health and understanding how they cause such deleterious effects, remain challenging due to their fast-growing numbers and the limitations of various current toxicity assessment model systems. Here, we performed a high-throughput screen in C. elegans to identify chemicals inducing aneuploidy as a result of impaired germline function. We screened 46 chemicals that are widely present in our environment, but for which effects in the germline remain poorly understood. These included pesticides, phthalates, and chemicals used in hydraulic fracturing and crude oil processing. Of the 46 chemicals tested, 41% exhibited levels of aneuploidy higher than those detected for bisphenol A (BPA), an endocrine disruptor shown to affect meiosis, at concentrations correlating well with mammalian reproductive endpoints. We further examined three candidates eliciting aneuploidy: dibutyl phthalate (DBP), a likely endocrine disruptor and frequently used plasticizer, and the pesticides 2-(thiocyanomethylthio) benzothiazole (TCMTB) and permethrin. Exposure to these chemicals resulted in increased embryonic lethality, elevated DNA double-strand break (DSB) formation, activation of p53/CEP-1-dependent germ cell apoptosis, chromosomal abnormalities in oocytes at diakinesis, impaired chromosome segregation during early embryogenesis, and germline-specific alterations in gene expression. This study indicates that this high-throughput screening system is highly reliable for the identification of environmental chemicals inducing aneuploidy, and provides new insights into the impact of exposure to three widely used chemicals on meiosis and germline function.

The ever-increasing number of new chemicals introduced into our environment poses a significant problem for risk assessment. In addition, assessing the direct impact of toxicants on human meiosis remains challenging. We successfully utilized a high-throughput platform in the nematode C. elegans, a genetically tractable model organism which shares a high degree of gene conservation with humans, to identify chemicals that affect the germline leading to aneuploidy. We assessed chemicals that are highly prevalent in the environment in worms carrying a fluorescent reporter construct allowing for the identification of X chromosome nondisjunction combined with a mutation increasing cuticle permeability for analysis of low doses of exposure. Follow up analysis of three chemicals: DBP, permethrin and TCMTB, further validated the use of this strategy. Exposure to these chemicals resulted in elevated levels of DNA double-strand breaks, activation of a DNA damage checkpoint, chromosome morphology defects in late meiotic prophase I as well as impaired early embryogenesis and germline-specific changes in gene expression. Our results support the use of this high-throughput screening system to identify environmental chemicals inducing aneuploidy, and provide new insights into the effects of exposure to DBP, permethrin, and TCMTB on meiosis and germline function.

Endocrine-disrupting chemicals in aquatic environment: what are the risks for fish gametes?

Over the past 25 years, extensive research in vertebrate species has identified several genomic pathways altered by exposures to anthropogenic chemicals with hormone-like activity mediated by their interaction with nuclear receptors. In addition, many pollutants have been shown to interfere with non-genomic (non-classical) pathways, but this mechanism of endocrine disruption is still poorly understood. Recently, the number of publications describing the effects of Endocrine disrupting chemicals (EDCs) on fish reproduction, focusing on the deregulation of the hypothalamus-pituitary-gonadal axis as well as on gamete quality, significantly increased. Depending on their ability to mimic endogenous hormones, the may differently affect male or female reproductive physiology. Inhibition of gametogenesis, development of intersex gonads, alteration of the gonadosomatic index, and decreased fertility rate have been largely documented. In males, alterations of sperm density, motility, and fertility have been observed in several wild species. Similar detrimental effects were described in females, including negative outcomes on oocyte growth and maturation plus the occurrence of apoptotic/autophagic processes. These pathways may affect gamete viability considered as one of the major indicators of reproductive endocrine disruption. Pollutants act also at DNA level producing DNA mutations and changes in epigenetic pathways inducing specific mechanisms of toxicity and/or aberrant cellular responses that may affect subsequent generation(s) through the germline. In conclusion, this review summarizes the effects caused by EDC exposure on fish reproduction, focusing on gametogenesis, giving a general overview of the different aspects dealing with this issue, from morphological alteration, deregulation of steroidogenesis, hormonal synthesis, and occurrence of epigenetic process.

Nanoplastics impaired oyster free living stages, gametes and embryos

In the marine environment, most bivalve species base their reproduction on external fertilization. Hence, gametes and young stages face many threats, including exposure to plastic wastes which represent more than 80% of the debris in the oceans. Recently, evidence has been produced on the presence of nanoplastics in oceans, thus motivating new studies of their impacts on marine life. Because no information is available about their environmental concentrations, we performed dose-response exposure experiments with polystyrene particles to assess the extent of micro/nanoplastic toxicity. Effects of polystyrene with different sizes and functionalizations (plain 2-μm, 500-nm and 50-nm; COOH-50 nm and NH₂-50 nm) were assessed on three key reproductive steps (fertilization, embryogenesis and metamorphosis) of Pacific oysters (Crassostrea gigas). Nanoplastics induced a significant decrease in fertilization success and in embryo-larval development with numerous malformations up to total developmental arrest. The NH₂-50 beads had the strongest toxicity to both gametes (EC₅₀ = 4.9 μg/mL) and embryos (EC₅₀ = 0.15 μg/mL), showing functionalization-dependent toxicity. No effects of plain microplastics were recorded. These results highlight that exposures to nanoplastics may have deleterious effects on planktonic stages of oysters, presumably interacting with biological membranes and causing cyto/genotoxicity with potentially drastic consequences for their reproductive success.