Fetal Muse-based therapy prevents lethal radio-induced gastrointestinal syndrome by intestinal regeneration.

BACKGROUND: Human multilineage-differentiating stress enduring (Muse) cells are nontumorigenic endogenous pluripotent-like stem cells that can be easily obtained from various adult or fetal tissues. Regenerative effects of Muse cells have been shown in some disease models. Muse cells specifically home in damaged tissues where they exert pleiotropic effects. Exposition of the small intestine to high doses of irradiation (IR) delivered after radiotherapy or nuclear accident results in a lethal gastrointestinal syndrome (GIS) characterized by acute loss of intestinal stem cells, impaired epithelial regeneration and subsequent loss of the mucosal barrier resulting in sepsis and death. To date, there is no effective medical treatment for GIS. Here, we investigate whether Muse cells can prevent lethal GIS and study how they act on intestinal stem cell microenvironment to promote intestinal regeneration. METHODS: Human Muse cells from Wharton's jelly matrix of umbilical cord (WJ-Muse) were sorted by flow cytometry using the SSEA-3 marker, characterized and compared to bone-marrow derived Muse cells (BM-Muse). Under gas anesthesia, GIS mice were treated or not through an intravenous retro-orbital injection of 50,000 WJ-Muse, freshly isolated or cryopreserved, shortly after an 18 Gy-abdominal IR. No immunosuppressant was delivered to the mice. Mice were euthanized either 24 h post-IR to assess early small intestine tissue response, or 7 days post-IR to assess any regenerative response. Mouse survival, histological stainings, apoptosis and cell proliferation were studied and measurement of cytokines, recruitment of immune cells and barrier functional assay were performed. RESULTS: Injection of WJ-Muse shortly after abdominal IR highly improved mouse survival as a result of a rapid regeneration of intestinal epithelium with the rescue of the impaired epithelial barrier. In small intestine of Muse-treated mice, an early enhanced secretion of IL-6 and MCP-1 cytokines was observed associated with (1) recruitment of monocytes/M2-like macrophages and (2) proliferation of Paneth cells through activation of the IL-6/Stat3 pathway. CONCLUSION: Our findings indicate that a single injection of a small quantity of WJ-Muse may be a new and easy therapeutic strategy for treating lethal GIS.

Foetal exposure to the bisphenols BADGE and BPAF impairs meiosis through DNA oxidation in mouse ovaries.

Many endocrine disruptors have been proven to impair the meiotic process which is required for the production of healthy gametes. Bisphenol A is emblematic of such disruptors, as it impairs meiotic prophase I and causes oocyte aneuploidy following in utero exposure. However, the mechanisms underlying these deleterious effects remain poorly understood. Furthermore, the increasing use of BPA alternatives raises concerns for public health. Here, we investigated the effects of foetal exposure to two BPA alternatives, bisphenol A Diglycidyl Ether (BADGE) and bisphenol AF (BPAF), on oogenesis in mice. These compounds delay meiosis initiation, increase the number of MLH1 foci per cell and induce oocyte aneuploidy. We further demonstrate that these defects are accompanied by changes in gene expression in foetal premeiotic germ cells and aberrant mRNA splicing of meiotic genes. We observed an increase in DNA oxidation after exposure to BPA alternatives. Specific induction of oxidative DNA damage during foetal germ cell differentiation causes similar defects during oogenesis, as observed in 8-oxoguanine DNA Glycosylase (OGG1)-deficient mice or after in utero exposure to potassium bromate (KBrO3), an inducer of oxidative DNA damage. The supplementation of BPA alternatives with N-acetylcysteine (NAC) counteracts the effects of bisphenols on meiosis. Together, our results propose oxidative DNA lesion as an event that negatively impacts female meiosis with major consequences on oocyte quality. This could be a common mechanism of action for numerous environmental pro-oxidant pollutants, and its discovery, could lead to reconsider the adverse effect of bisphenol mixtures that are simultaneously present in our environment.

Sorting and Manipulation of Human PGC-LC Using PDPN and Hanging Drop Cultures.

The generation of oocytes from induced pluripotent stem cells (iPSCs) was proven efficient with mouse cells. However, no human iPSCs have yet been reported to generate cells able to complete oogenesis. Additionally, efficient sorting of human Primordial Germ Cell-like Cells (hPGC-LCs) without genomic integration of fluorescent reporter for their downstream manipulation is still lacking. Here, we aimed to develop a model that allows human germ cell differentiation in vitro in order to study the developing human germline. The hPGC-LCs specified from two iPS cell lines were sorted and manipulated using the PDPN surface marker without genetic modification. hPGC-LCs obtained remain arrested at early stages of maturation and no further differentiation nor meiotic onset occurred when these were cultured with human or mouse fetal ovarian somatic cells. However, when cultured independently of somatic ovarian cells, using BMP4 and the hanging drop-transferred EBs system, early hPGC-LCs further differentiate efficiently and express late PGC (DDX4) and meiotic gene markers, although no SYCP3 protein was detected. Altogether, we characterized a tool to sort hPGC-LCs and an efficient in vitro differentiation system to obtain pre-meiotic germ cell-like cells without using a gonadal niche.

Unexpected Interacting Effects of Physical (Radiation) and Chemical (Bisphenol A) Treatments on Male Reproductive Functions in Mice.

For decades, numerous chemical pollutants have been described to interfere with endogenous hormone metabolism/signaling altering reproductive functions. Among these endocrine disrupting substances, Bisphenol A (BPA), a widely used compound, is known to negatively impact germ and somatic cells in the testis. Physical agents, such as ionizing radiation, were also described to perturb spermatogenesis. Despite the fact that we are constantly exposed to numerous environmental chemical and physical compounds, very few studies explore the impact of combined exposure to chemical and physical pollutants on reproductive health. The aim of this study was to describe the impact of fetal co-exposure to BPA and IR on testicular function in mice. We exposed pregnant mice to 10 µM BPA (corresponding to 0.5 mg/kg/day) in drinking water from 10.5 dpc until birth, and we irradiated mice with 0.2 Gy (γ-ray, RAD) at 12.5 days post-conception. Co-exposure to BPA and γ-ray induces DNA damage in fetal germ cells in an additive manner, leading to a long-lasting decrease in germ cell abundance. We also observed significant alteration of adult steroidogenesis by RAD exposure independently of the BPA exposure. This is illustrated by the downregulation of steroidogenic genes and the decrease of the number of adult Leydig cells. As a consequence, courtship behavior is modified, and male ultrasonic vocalizations associated with courtship decreased. In conclusion, this study provides evidence for the importance of broadening the concept of endocrine disruptors to include physical agents, leading to a reevaluation of risk management and regulatory decisions.

Mouse model of radiation-induced premature ovarian insufficiency reveals compromised oocyte quality: implications for fertility preservation.

RESEARCH QUESTION: What is the impact of radiation exposure on oocyte quality and female fertility? DESIGN: Prepubertal mice underwent whole-body irradiation with a single dose (0.02, 0.1, 0.5, 2, 8 Gy) of gamma- or X-rays. Oocytes were quantified in irradiated (n = 36) and sham-treated (n = 8) mice. After a single exposure to 2 Gy, formation of DNA double-strand breaks (n = 10), activation of checkpoint kinase (Chk2) (n = 10) and dynamics of follicular growth (n = 18) were analysed. Fertility assessment was performed in adult irradiated mice and controls from the number of pups per mouse (n = 28) and the fetal abortion rate (n = 24). Ploidy of mature oocytes (n = 20) was analysed after CREST immunostaining, and uterine sections were examined. RESULTS: Radiation exposure induced a massive loss of primordial follicles with LD50 below 50 mGy for both gamma and X-rays. Growing follicles survived doses up to 8 Gy. This difference in radiosensitivity was not due to a different amount of radio-induced DNA damage, and Chk2 was activated in all oocytes. Exposure to a 2 Gy dose abolished the long-term fertility of females due to depletion of the ovarian reserve. Detailed analysis indicates that surviving oocytes were able to complete folliculogenesis and could be fertilized. This transient fertility allowed irradiated females to produce a single litter albeit with a high rate of fetal abortion (23%, P = 0.0096), related to altered ploidy in the surviving oocytes (25.5%, P = 0.0035). CONCLUSIONS: The effects of radiation on surviving oocyte quality question natural conception as a first-line approach in cancer survivors. Together, the data emphasize the need for fertility preservation before radiation exposure and call for reassessment of the use of cryopreserved oocytes.

Two populations of self-maintaining monocyte-independent macrophages exist in adult epididymis and testis.

Macrophages are the principal immune cells of the epididymis and testis, but their origins, heterogeneity, development, and maintenance are not well understood. Here, we describe distinct populations of epididymal and testicular macrophages that display an organ-specific cellular identity. Combining in vivo fate-mapping, chimeric and parabiotic mouse models with in-depth cellular analyses, we found that CD64hiMHCIIlo and CD64loMHCIIhi macrophage populations of epididymis and testis arise sequentially from yolk sac erythro-myeloid progenitors, embryonic hematopoiesis, and nascent neonatal monocytes. While monocytes were the major developmental source of both epididymal and testicular macrophages, both populations self-maintain in the steady-state independent of bone marrow hematopoietic precursors. However, after radiation-induced macrophage ablation or during infection, bone marrow-derived circulating monocytes are recruited to the epididymis and testis, giving rise to inflammatory macrophages that promote tissue damage. These results define the layered ontogeny, maintenance and inflammatory response of macrophage populations in the male reproductive organs.

CEP250 is Required for Maintaining Centrosome Cohesion in the Germline and Fertility in Male Mice.

Male gametogenesis involves both mitotic divisions to amplify germ cell progenitors that gradually differentiate and meiotic divisions. Centrosomal regulation is essential for both types of divisions, with centrioles remaining tightly paired during the interphase. Here, we generated and characterized the phenotype of mutant mice devoid of Cep250/C-Nap1, a gene encoding for a docking protein for fibers linking centrioles, and characterized their phenotype. The Cep250 -/- mice presented with no major defects, apart from male infertility due to a reduction in the spermatogonial pool and the meiotic blockade. Spermatogonial stem cells expressing Zbtb16 were not affected, whereas the differentiating spermatogonia were vastly lost. These cells displayed abnormal γH2AX-staining, accompanied by an increase in the apoptotic rate. The few germ cells that survived at this stage, entered the meiotic prophase I and were arrested at a pachytene-like stage, likely due to synapsis defects and the unrepaired DNA double-strand breaks. In these cells, centrosomes split up precociously, with γ-tubulin foci being separated whereas these were closely associated in wild-type cells. Interestingly, this lack of cohesion was also observed in wild-type female meiocytes, likely explaining the normal fertility of Cep250 -/- female mice. Taken together, this study proposes a specific requirement of centrosome cohesion in the male germline, with a crucial role of CEP250 in both differentiating spermatogonia and meiotic spermatocytes.

Homozygous hypomorphic BRCA2 variant in primary ovarian insufficiency without cancer or Fanconi anaemia trait.

BACKGROUND: Primary ovarian insufficiency (POI) affects 1% of women under 40 years and is a public health problem. The genetic causes of POI are highly heterogeneous with isolated or syndromic forms. Recently, variants in genes involved in DNA repair have been shown to cause POI. Notably, syndromic POI with Fanconi anaemia (FA) traits related to biallelic BRCA2 truncated variants has been reported. Here, we report a novel phenotype of isolated POI with a BRCA2 variant in a consanguineous Turkish family. METHODS: Exome sequencing (ES) was performed in the patient. We also performed functional studies, including a homologous recombination (HR) test, cell proliferation, radiation-induced RAD51 foci formation assays and chromosome breakage studies in primary and lymphoblastoid immortalised cells. The expression of BRCA2 in human foetal ovaries was studied. RESULTS: ES identified a homozygous missense c.8524C>T/p.R2842C-BRCA2 variant. BRCA2 defects induce cancer predisposition and FA. Remarkably, neither the patient nor her family exhibited somatic pathologies. The patient's cells showed intermediate levels of chromosomal breaks, cell proliferation and radiation-induced RAD51 foci formation compared with controls and FA cells. R2842C-BRCA2 only partially complemented HR efficiency compared with wild type-BRCA2. BRCA2 is expressed in human foetal ovaries in pachytene stage oocytes, when meiotic HR occurs. CONCLUSION: We describe the functional assessment of a homozygous hypomorphic BRCA2 variant in a patient with POI without cancer or FA trait. Our findings extend the phenotype of BRCA2 biallelic alterations to fully isolated POI. This study has a major impact on the management and genetic counselling of patients with POI.

Divergent Roles of CYP26B1 and Endogenous Retinoic Acid in Mouse Fetal Gonads.

In female mammals, germ cells enter meiosis in the fetal ovaries, while in males, meiosis is prevented until postnatal development. Retinoic acid (RA) is considered the main inducer of meiotic entry, as it stimulates Stra8 which is required for the mitotic/meiotic switch. In fetal testes, the RA-degrading enzyme CYP26B1 prevents meiosis initiation. However, the role of endogenous RA in female meiosis entry has never been demonstrated in vivo. In this study, we demonstrate that some effects of RA in mouse fetal gonads are not recapitulated by the invalidation or up-regulation of CYP26B1. In organ culture of fetal testes, RA stimulates testosterone production and inhibits Sertoli cell proliferation. In the ovaries, short-term inhibition of RA-signaling does not decrease Stra8 expression. We develop a gain-of-function model to express CYP26A1 or CYP26B1. Only CYP26B1 fully prevents STRA8 induction in female germ cells, confirming its role as part of the meiotic prevention machinery. CYP26A1, a very potent RA degrading enzyme, does not impair the formation of STRA8-positive cells, but decreases Stra8 transcription. Collectively, our data reveal that CYP26B1 has other activities apart from metabolizing RA in fetal gonads and suggest a role of endogenous RA in amplifying Stra8, rather than being the initial inducer of Stra8. These findings should reactivate the quest to identify meiotic preventing or inducing substances.

Effects of environmental Bisphenol A exposures on germ cell development and Leydig cell function in the human fetal testis.

BACKGROUND: Using an organotypic culture system termed human Fetal Testis Assay (hFeTA) we previously showed that 0.01 µM BPA decreases basal, but not LH-stimulated, testosterone secreted by the first trimester human fetal testis. The present study was conducted to determine the potential for a long-term antiandrogenic effect of BPA using a xenograft model, and also to study the effect of BPA on germ cell development using both the hFETA and xenograft models. METHODS: Using the hFeTA system, first trimester testes were cultured for 3 days with 0.01 to 10 µM BPA. For xenografts, adult castrate male nude mice were injected with hCG and grafted with first trimester testes. Host mice received 10 µM BPA (~ 500 µg/kg/day) in their drinking water for 5 weeks. Plasma levels of total and unconjugated BPA were 0.10 µM and 0.038 µM respectively. Mice grafted with second trimester testes received 0.5 and 50 µg/kg/day BPA by oral gavage for 5 weeks. RESULTS: With first trimester human testes, using the hFeTA model, 10 µM BPA increased germ cell apoptosis. In xenografts, germ cell density was also reduced by BPA exposure. Importantly, BPA exposure significantly decreased the percentage of germ cells expressing the pluripotency marker AP-2γ, whilst the percentage of those expressing the pre-spermatogonial marker MAGE-A4 significantly increased. BPA exposure did not affect hCG-stimulated androgen production in first and second trimester xenografts as evaluated by both plasma testosterone level and seminal vesicle weight in host mice. CONCLUSIONS: Exposure to BPA at environmentally relevant concentrations impairs germ cell development in first trimester human fetal testis, whilst gonadotrophin-stimulated testosterone production was unaffected in both first and second trimester testis. Studies using first trimester human fetal testis demonstrate the complementarity of the FeTA and xenograft models for determining the respective short-term and long term effects of environmental exposures.

Human foetal ovary shares meiotic preventing factors with the developing testis.

STUDY QUESTION: How can pre-meiotic germ cells persist in the human foetal ovary? SUMMARY ANSWER: Numerous oogonia escaping meiotic entry were retrieved throughout human ovarian development simultaneously with the expression of signalling pathways preventing meiosis, typically described in the rodent embryonic testis. WHAT IS KNOWN ALREADY: The transition from mitosis to meiosis is a key event in female germ cells that remains poorly documented in research on the human ovary. Previous reports described a strikingly asynchronous differentiation in the human female germ line during development, with the persistence of oogonia among oocytes and follicles during the second and third trimesters. The possible mechanisms allowing some cells to escape meiosis remain elusive. STUDY DESIGN SIZE, DURATION: In order to document the extent of this phenomenon, we detailed the expression profile of germ cell differentiation markers using 73 ovaries ranging from 6.4 to 35 weeks post-fertilization. PARTICIPANTS/MATERIALS SETTING, METHODS: Pre-meiotic markers were detected by immunohistochemistry or qRT-PCR. The expression of the main meiosis-preventing factors identified in mice was analysed, and their functionality assessed using organ cultures. MAIN RESULTS AND THE ROLE OF CHANCE: Oogonia stained for AP2γ could be traced from the first trimester until the end of the third trimester. Female germ cell differentiation is organized both in time and space in a centripetal manner in the foetal human ovary. Unexpectedly, some features usually ascribed to rodent pre-spermatogonia could be observed in human foetal ovaries, such as NANOS2 expression and quiescence in some germ cells. The two main somatic signals known to inhibit meiosis in the mouse embryonic testis, CYP26B1 and FGF9, were detected in the human ovary and act simultaneously to repress STRA8 and meiosis in human foetal female germ cells. LARGE SCALE DATA: N/A. LIMITATIONS REASON FOR CAUTION: Our conclusions relied partly on in vitro experiments. Germ cells were not systematically identified with immunostaining and some may have thus escaped analysis. WIDER IMPLICATIONS OF THE FINDINGS: We found evidence that a robust repression of meiotic entry is taking place in the human foetal ovary, possibly explaining the exceptional long-lasting presence of pre-meiotic germ cells until late gestational age. This result calls for a redefinition of the markers known as classical male markers, which may in fact characterize mammalian developing gonads irrespectively of their sex. STUDY FUNDING/COMPETING INTEREST(S): This research was supported by the Université Paris Diderot-Paris 7 and Université Paris-Sud, CEA, INSERM, and Agence de la Biomédecine. The authors declare no conflict of interest.

Implementation of meiosis prophase I programme requires a conserved retinoid-independent stabilizer of meiotic transcripts.

Sexual reproduction is crucially dependent on meiosis, a conserved, specialized cell division programme that is essential for the production of haploid gametes. Here we demonstrate that fertility and the implementation of the meiotic programme require a previously uncharacterized meiosis-specific protein, MEIOC. Meioc invalidation in mice induces early and pleiotropic meiotic defects in males and females. MEIOC prevents meiotic transcript degradation and interacts with an RNA helicase that binds numerous meiotic mRNAs. Our results indicate that proper engagement into meiosis necessitates the specific stabilization of meiotic transcripts, a previously little-appreciated feature in mammals. Remarkably, the upregulation of MEIOC at the onset of meiosis does not require retinoic acid and STRA8 signalling. Thus, we propose that the complete induction of the meiotic programme requires both retinoic acid-dependent and -independent mechanisms. The latter process involving post-transcriptional regulation likely represents an ancestral mechanism, given that MEIOC homologues are conserved throughout multicellular animals.

Nuclear receptors and endocrine disruptors in fetal and neonatal testes: a gapped landscape.

During the last decades, many studies reported that male reproductive disorders are increasing among humans. It is currently acknowledged that these abnormalities can result from fetal exposure to environmental chemicals that are progressively becoming more concentrated and widespread in our environment. Among the chemicals present in the environment (air, water, food, and many consumer products), several can act as endocrine disrupting compounds (EDCs), thus interfering with the endocrine system. Phthalates, bisphenol A (BPA), and diethylstilbestrol (DES) have been largely incriminated, particularly during the fetal and neonatal period, due to their estrogenic and/or anti-androgenic properties. Indeed, many epidemiological and experimental studies have highlighted their deleterious impact on fetal and neonatal testis development. As EDCs can affect many different genomic and non-genomic pathways, the mechanisms underlying the adverse effects of EDC exposure are difficult to elucidate. Using literature data and results from our laboratory, in the present review, we discuss the role of classical nuclear receptors (genomic pathway) in the fetal and neonatal testis response to EDC exposure, particularly to phthalates, BPA, and DES. Among the nuclear receptors, we focused on some of the most likely candidates, such as peroxisome-proliferator activated receptor (PPAR), androgen receptor (AR), estrogen receptors (ERα and ß), liver X receptors (LXR), and small heterodimer partner (SHP). First, we describe the expression and potential functions (based on data from studies using receptor agonists and mouse knockout models) of these nuclear receptors in the developing testis. Then, for each EDC studied, we summarize the main evidences indicating that the reprotoxic effect of each EDC under study is mediated through a specific nuclear receptor(s). We also point-out the involvement of other receptors and nuclear receptor-independent pathways.

The zinc-finger protein basonuclin 2 is required for proper mitotic arrest, prevention of premature meiotic initiation and meiotic progression in mouse male germ cells.

Absence of mitosis and meiosis are distinguishing properties of male germ cells during late fetal and early neonatal periods. Repressors of male germ cell meiosis have been identified, but mitotic repressors are largely unknown, and no protein repressing both meiosis and mitosis is known. We demonstrate here that the zinc-finger protein BNC2 is present in male but not in female germ cells. In testis, BNC2 exists as several spliced isoforms and presumably binds to DNA. Within the male germ cell lineage, BNC2 is restricted to prospermatogonia and undifferentiated spermatogonia. Fetal prospermatogonia that lack BNC2 multiply excessively on embryonic day (E)14.5 and reenter the cell cycle prematurely. Mutant prospermatogonia also engage in abnormal meiosis; on E17.5, Bnc2(-/-) prospermatogonia start synthesizing the synaptonemal protein SYCP3, and by the time of birth, many Bnc2(-/-) prospermatogonia have accumulated large amounts of nonfilamentous SYCP3, thus appearing to be blocked at leptonema. Bnc2(-/-) prospermatogonia do not undergo proper male differentiation, as they lack almost all the mRNA for the male-specific methylation protein DNMT3L and have increased levels of mRNAs that encode meiotic proteins, including STRA8. Bnc2(-/-) prospermatogonia can produce spermatogonia, but these enter meiosis prematurely and undergo massive apoptotic death during meiotic prophase. This study identifies BNC2 as a major regulator of male germ stem cells, which is required for repression of meiosis and mitosis in prospermatogonia, and for meiosis progression during spermatogenesis. In view of the extreme evolutionary conservation of BNC2, the findings described here are likely to apply to many species.

Concerns about the widespread use of rodent models for human risk assessments of endocrine disruptors.

Fetal testis is a major target of endocrine disruptors (EDs). During the last 20 years, we have developed an organotypic culture system that maintains the function of the different fetal testis cell types and have used this approach as a toxicological test to evaluate the effects of various compounds on gametogenesis and steroidogenesis in rat, mouse and human testes. We named this test rat, mouse and human fetal testis assay. With this approach, we compared the effects of six potential EDs ((mono-(2-ethylhexyl) phthalate (MEHP), cadmium, depleted uranium, diethylstilboestrol (DES), bisphenol A (BPA) and metformin) and one signalling molecule (retinoic acid (RA)) on the function of rat, mouse and human fetal testis at a comparable developmental stage. We found that the response is similar in humans and rodents for only one third of our analyses. For instance, RA and MEHP have similar negative effects on gametogenesis in the three species. For another third of our analyses, the threshold efficient concentrations that disturb gametogenesis and/or steroidogenesis differ as a function of the species. For instance, BPA and metformin have similar negative effects on steroidogenesis in human and rodents, but at different threshold doses. For the last third of our analyses, the qualitative response is species specific. For instance, MEHP and DES affect steroidogenesis in rodents, but not in human fetal testis. These species differences raise concerns about the extrapolation of data obtained in rodents to human health risk assessment and highlight the need of rigorous comparisons of the effects in human and rodent models, when assessing ED risk.

MEIOB targets single-strand DNA and is necessary for meiotic recombination.

Meiotic recombination is a mandatory process for sexual reproduction. We identified a protein specifically implicated in meiotic homologous recombination that we named: meiosis specific with OB domain (MEIOB). This protein is conserved among metazoan species and contains single-strand DNA binding sites similar to those of RPA1. Our studies in vitro revealed that both recombinant and endogenous MEIOB can be retained on single-strand DNA. Those in vivo demonstrated the specific expression of Meiob in early meiotic germ cells and the co-localization of MEIOB protein with RPA on chromosome axes. MEIOB localization in Dmc1 (-/-) spermatocytes indicated that it accumulates on resected DNA. Homologous Meiob deletion in mice caused infertility in both sexes, due to a meiotic arrest at a zygotene/pachytene-like stage. DNA double strand break repair and homologous chromosome synapsis were impaired in Meiob (-/-) meiocytes. Interestingly MEIOB appeared to be dispensable for the initial loading of recombinases but was required to maintain a proper number of RAD51 and DMC1 foci beyond the zygotene stage. In light of these findings, we propose that RPA and this new single-strand DNA binding protein MEIOB, are essential to ensure the proper stabilization of recombinases which is required for successful homology search and meiotic recombination.

Cellular and molecular effect of MEHP Involving LXRα in human fetal testis and ovary.

BACKGROUND: Phthalates have been shown to have reprotoxic effects in rodents and human during fetal life. Previous studies indicate that some members of the nuclear receptor (NR) superfamilly potentially mediate phthalate effects. This study aimed to assess if expression of these nuclear receptors are modulated in the response to MEHP exposure on the human fetal gonads in vitro. METHODOLOGY/PRINCIPAL FINDINGS: Testes and ovaries from 7 to 12 gestational weeks human fetuses were exposed to 10(-4)M MEHP for 72 h in vitro. Transcriptional level of NRs and of downstream genes was then investigated using TLDA (TaqMan Low Density Array) and qPCR approaches. To determine whether somatic or germ cells of the testis are involved in the response to MEHP exposure, we developed a highly efficient cytometric germ cell sorting approach. In vitro exposure of fetal testes and ovaries to MEHP up-regulated the expression of LXRα, SREBP members and of downstream genes involved in the lipid and cholesterol synthesis in the whole gonad. In sorted testicular cells, this effect is only observable in somatic cells but not in the gonocytes. Moreover, the germ cell loss induced by MEHP exposure, that we previously described, is restricted to the male gonad as oogonia density is not affected in vitro. CONCLUSIONS/SIGNIFICANCE: We evidenced for the first time that phthalate increases the levels of mRNA for LXRα, and SREBP members potentially deregulating lipids/cholesterol synthesis in human fetal gonads. Interestingly, this novel effect is observable in both male and female whereas the germ cell apoptosis is restricted to the male gonad. Furthermore, we presented here a novel and potentially very useful flow cytometric cell sorting method to analyse molecular changes in germ cells versus somatic cells.

Nodal signaling regulates the entry into meiosis in fetal germ cells.

The mechanisms regulating the entry into meiosis in mammalian germ cells remain incompletely understood. We investigated the involvement of the TGF-ß family members in fetal germ cell meiosis initiation. Nodal, a member of the TGF-ß family, and its target genes are precociously expressed in embryonic gonads and show sexual dimorphism in favor of the developing testis. Nodal receptor genes, Acvr2a and Acvr2b, Alk4, and Tdgf1/Cripto, were identified in male germ cells. Nodal itself, Tdgf1, and Lefty1 and Lefty2 are targets of Nodal signaling and were all found specifically expressed in male germ cells. To elucidate the role of this signaling pathway, activin-like kinases that mediate TGF-ß/Nodal/activin signaling were inhibited in 11.5 d postconception testis in organotypic culture. Activin-like kinases inhibition disrupted normal male germ cell development and induced germ cell entry into meiosis such as that observed in female germ cells at the equivalent stage. Interestingly Stra8, the gatekeeper of the mitotic/meiotic switch, was induced independently of any change of either Cyp26b1 or Fgf9 expression, the two genes currently identified as testicular meiotic inhibitors. On the other hand, recombinant Nodal significantly dampened Stra8 expression and germ cell meiosis in cultured 11.5 d postconception ovaries. Our results allowed us to propose for the first time an autocrine role of Nodal during the development of germ cells and indicate that members of the TGB-ß family may reinforce the male fate and prevent meiosis in embryonic germ cells.

Antagonistic effects of gestational dietary exposure to low-dose vinclozolin and genistein on rat fetal germ cell development.

Continuous, low-dose exposure to a phytoestrogen (1 mg/kg/day genistein) and/or to an antiandrogenic food contaminant (1 mg/kg/day vinclozolin) has been recently reported to affect male reproductive tract and fertility [1] in adults. We investigated whether alterations of the testis are already present at the end of in utero exposure using the same rat model and doses following exposure from conception to delivery. After vinclozolin exposure, we observed in the neonate a slight but significant alteration of steroidogenesis and gametogenesis with a reduction of testosterone secretion and of the number of gonocytes. In contrast, genistein exposure had no effect. While the vinclozolin-genistein mixture acts in a synergistic manner to induce the most significant alterations in the adult, interestingly, genistein antagonized the deleterious effect of vinclozolin on germ cells in the neonate. This difference emphasizes the importance of studying the effects of endocrine disruptors during various developmental stages to understand their effects.

TGFbeta signaling in male germ cells regulates gonocyte quiescence and fertility in mice.

During testis development, proliferation and death of gonocytes are highly regulated to establish a standard population of adult stem spermatogonia that maintain normal spermatogenesis. As Transforming Growth Factor beta (TGFbeta) can regulate proliferation and apoptosis, we investigated its expression and functions during testis development. We show that TGFbeta2 is only expressed in quiescent gonocytes and decreases gonocyte proliferation in vitro. To study the functions of TGFbeta2, we developed conditional mice that invalidate the TGFbeta receptor type II in germ cells. Most of the knock-out animals die during fetal life, but the surviving adults show a reduced pool of spermatogonial stem/progenitor cells and become sterile with time. Using an organ culture system mimicking in vivo development, we show higher proportions of proliferating and apoptotic gonocytes from 13.5 dpc until 1 dpp, suggesting a reduction of germinal quiescence in these animals. Conversely, a 24-hour TGFbeta2-treatment of explanted wild-type testes, isolated every day from 13.5 dpc until 1 dpp, increased the duration of quiescence. These data show that the TGFbeta signaling pathway plays a physiological role during testis development by acting directly as a negative regulator of the fetal and neonatal germ cell proliferation, and indicate that the TGFbeta signaling pathway might regulate the duration of germ cell quiescence and is necessary to maintain adult spermatogenesis.