Using real time RT-PCR analysis to determine multiple gene expression patterns during XX and XY mouse fetal gonad development

Somatic FGFR2 is Required for Germ Cell Maintenance in the Mouse Ovary

During sex determination in the mouse, fibroblast growth factor 9 signals through the fibroblast growth factor receptor 2c isoform (FGFR2c) to trigger Sertoli cell and testis development from 11.5 days post coitum (dpc). In the XX gonad, the FOXL2 and WNT4/RSPO1 pathways drive granulosa cell and ovarian development. The function of FGFR2 in the developing ovary, and whether FGFR2 is required in the testis after sex determination, is not clear. In fetal mouse gonads from 12.5 dpc, FGFR2 shows sexually dimorphic expression. In XX gonads, FGFR2c is coexpressed with FOXL2 in pregranulosa cells, whereas XY gonads show FGFR2b expression in germ cells. Deletion of Fgfr2c in XX mice led to a marked decrease/absence of germ cells by 13.5 dpc in the ovary. This indicates that FGFR2c in the somatic pregranulosa cells is required for the maintenance of germ cells. Surprisingly, on the Fgfr2c-/- background, the germ cell phenotype could be rescued by ablation of Foxl2, suggesting a novel mechanism whereby FGFR2 and FOXL2 act antagonistically during germ cell development. Consistent with low/absent FGFR2 expression in the Sertoli cells of 12.5 and 13.5 dpc XY gonads, XY AMH:Cre; Fgfr2flox/flox mice showed normal testis morphology and structures during fetal development and in adulthood. Thus, FGFR2 is not essential for maintaining Sertoli cell fate after sex determination. Combined, these data show that FGFR2 is not necessary for Sertoli cell function after sex determination but does play an important role in the ovary.

Distinctive functioning of STARD1 in the fetal Leydig cells compared to adult Leydig and adrenal cells. Impact of Hedgehog signaling via the primary cilium

STARD1 stimulates cholesterol transfer to mitochondrial CYP11A1 for conversion to pregnenolone. A cholesterol-binding START domain is guided by an N-terminal domain in a cell selective manner. Fetal and adult Leydig cells (FLC, ALC) show distinct Stard1 regulation. sm- FISH microscopy, which resolves individual molecules of Stard1 mRNA, shows uniformly high basal expression in each FLC. In ALC, in vivo, and cultured MA-10 cells, basal Stard1 expression is minimal. PKA activates loci asynchronously, with delayed splicing/export of 3.5 kb mRNA to mitochondria. After 60 min, ALC transition to an integrated mRNA delivery to mitochondria that is seen in FLC. Sertoli cells cooperate in Stard1 stimulation in FLC by delivering DHH to the primary cilium. There PTCH, SMO and cholesterol cooperate to release GLI3 to activate the Stard1 locus, probably by directing histone changes. ALC lack cilia. PKA then primes locus activation. FLC and ALC share similar SIK/CRTC/CREB regulation characterized for adrenal cells.

Zinc oxide nanoparticles improve testicular steroidogenesis machinery dysfunction in benzo[α]pyrene-challenged rats

Zinc oxide nanoparticles (ZnO NPs) demonstrate potential positive effects on reproduction. However, their protective role against the reproductive toxicity pollutants has not yet been adequately studied at the molecular level. This study was designed to assess this objective using Benzo[α]pyrene B[a]P as reproductive toxic agent . Forty-eight mature male rats were randomly distributed into six groups: Group1 (negative control); Groups 2 and 3 (positive control I and II, wherein the animals were treated with 10 and 30 mg ZnO NPs/kg BW, respectively); Group 4 (B[a]P group; treated with 150 mg B[a]P/kg BW); and Groups 5 and 6 (subjected to B[a]P treatment co-administered with different concentrations of ZnO NPs). We investigated oxidative stress biomarkers; cholesterol side-chain cleavage enzyme (CYP11A1), steroidogenic acute regulatory protein (StAR), and 3β-hydroxysteroid dehydrogenase (3β-HSD) gene expression; testosterone levels; and histopathology of the liver, kidney, and testicles. The B[a]P-treated group showed significant deterioration in all reproductive parameters and displayed induced oxidative stress. ZnO NPs remarkably reduced oxidative stress, effectively upregulated the mRNA levels of CY11A1, StAR, and 3β-HSD, and improved the histological pictures in the examined organs. At their investigated doses and given their NPs properties, ZnO NPs demonstrated a marked ameliorative effect against the reproductive toxic effects of B[a]P. Further studies are needed to thoroughly investigate the molecular mechanisms of ZnO NPs.

Ovarian Follicular Theca Cell Recruitment, Differentiation, and Impact on Fertility: 2017 Update

The major goal of this review is to summarize recent exciting findings that have been published within the past 10 years that, to our knowledge, have not been presented in detail in previous reviews and that may impact altered follicular development in polycystic ovarian syndrome (PCOS) and premature ovarian failure in women. Specifically, we will cover the following: (1) mouse models that have led to discovery of the derivation of two precursor populations of theca cells in the embryonic gonad; (2) the key roles of the oocyte-derived factor growth differentiation factor 9 on the hedgehog (HH) signaling pathway and theca cell functions; and (3) the impact of the HH pathway on both the specification of theca endocrine cells and theca fibroblast and smooth muscle cells in developing follicles. We will also discuss the following: (1) other signaling pathways that impact the differentiation of theca cells, not only luteinizing hormone but also insulinlike 3, bone morphogenic proteins, the circadian clock genes, androgens, and estrogens; and (2) theca-associated vascular, immune, and fibroblast cells, as well as the cytokines and matrix factors that play key roles in follicle growth. Lastly, we will integrate what is known about theca cells from mouse models, human-derived theca cell lines from patients who have PCOS and patients who do not have PCOS, and microarray analyses of human and bovine theca to understand what pathways and factors contribute to follicle growth as well as to the abnormal function of theca.

Leveraging Online Resources to Prioritize Candidate Genes for Functional Analyses: Using the Fetal Testis as a Test Case

With each new microarray or RNA-seq experiment, massive quantities of transcriptomic information are generated with the purpose to produce a list of candidate genes for functional analyses. Yet an effective strategy remains elusive to prioritize the genes on these candidate lists. In this review, we outline a prioritizing strategy by taking a step back from the bench and leveraging the rich range of public databases. This in silico approach provides an economical, less biased, and more effective solution. We discuss the publicly available online resources that can be used to answer a range of questions about a gene. Is the gene of interest expressed in the system of interest (using expression databases)? Where else is this gene expressed (using added-value transcriptomic resources)? What pathways and processes is the gene involved in (using enriched gene pathway analysis and mouse knockout databases)? Is this gene correlated with human diseases (using human disease variant databases)? Using mouse fetal testis as an example, our strategies identified 298 genes annotated as expressed in the fetal testis. We cross-referenced these genes to existing microarray data and narrowed the list down to cell-type-specific candidates (35 for Sertoli cells, 11 for Leydig cells, and 25 for germ cells). Our strategies can be customized so that they allow researchers to effectively and confidently prioritize genes for functional analysis.

Methods for the Study of Gonadal Development

Current knowledge on gonadal development and sex determination is the product of many decades of research involving a variety of scientific methods from different biological disciplines such as histology, genetics, biochemistry, and molecular biology. The earliest embryological investigations, followed by the invention of microscopy and staining methods, were based on histological examinations. The most robust development of histological staining techniques occurred in the second half of the nineteenth century and resulted in structural descriptions of gonadogenesis. These first studies on gonadal development were conducted on domesticated animals; however, currently the mouse is the most extensively studied species. The next key point in the study of gonadogenesis was the advancement of methods allowing for the in vitro culture of fetal gonads. For instance, this led to the description of the origin of cell lines forming the gonads. Protein detection using antibodies and immunolabeling methods and the use of reporter genes were also invaluable for developmental studies, enabling the visualization of the formation of gonadal structure. Recently, genetic and molecular biology techniques, especially gene expression analysis, have revolutionized studies on gonadogenesis and have provided insight into the molecular mechanisms that govern this process. The successive invention of new methods is reflected in the progress of research on gonadal development.

Real-Time PCR Quantification of Heteroplasmy in a Mouse Model with Mitochondrial DNA of C57BL/6 and NZB/BINJ Strains

Mouse models are widely employed to study mitochondrial inheritance, which have implications to several human diseases caused by mutations in the mitochondrial genome (mtDNA). These mouse models take advantage of polymorphisms between the mtDNA of the NZB/BINJ and the mtDNA of common inbred laboratory (i.e., C57BL/6) strains to generate mice with two mtDNA haplotypes (heteroplasmy). Based on PCR followed by restriction fragment length polymorphism (PCR-RFLP), these studies determine the level of heteroplasmy across generations and in different cell types aiming to understand the mechanisms underlying mitochondrial inheritance. However, PCR-RFLP is a time-consuming method of low sensitivity and accuracy that dependents on the use of restriction enzyme digestions. A more robust method to measure heteroplasmy has been provided by the use of real-time quantitative PCR (qPCR) based on allelic refractory mutation detection system (ARMS-qPCR). Herein, we report an ARMS-qPCR assay for quantification of heteroplasmy using heteroplasmic mice with mtDNA of NZB/BINJ and C57BL/6 origin. Heteroplasmy and mtDNA copy number were estimated in germline and somatic tissues, providing evidence of the reliability of the approach. Furthermore, it enabled single-step quantification of heteroplasmy, with sensitivity to detect as low as 0.1% of either NZB/BINJ or C57BL/6 mtDNA. These findings are relevant as the ARMS-qPCR assay reported here is fully compatible with similar heteroplasmic mouse models used to study mitochondrial inheritance in mammals.

Next generation sequencing in women affected by nonsyndromic premature ovarian failure displays new potential causative genes and mutations

OBJECTIVE

To identify new molecular actors involved in nonsyndromic premature ovarian failure (POF) etiology.

DESIGN

This is a retrospective case-control cohort study.

SETTING

University research group and IVF medical center.

PATIENT(S)

Twelve women affected by nonsyndromic POF. The control group included 176 women whose menopause had occurred after age 50 and had no antecedents regarding gynecological disease. A further 345 women from the same ethnic origin (general population group) were also recruited to assess allele frequency for potentially deleterious sequence variants.

INTERVENTION(S)

Next generation sequencing (NGS), Sanger sequencing, and bioinformatics analysis.

MAIN OUTCOME MEASURE(S)

The complete coding regions of 70 candidate genes were massively sequenced, via NGS, in POF patients. Bioinformatics and genetics were used to confirm NGS results and to identify potential sequence variants related to the disease pathogenesis.

RESULT(S)

We have identified mutations in two novel genes, ADAMTS19 and BMPR2, that are potentially related to POF origin. LHCGR mutations, which might have contributed to the phenotype, were also detected.

CONCLUSION(S)

We thus recommend NGS as a powerful tool for identifying new molecular actors in POF and for future diagnostic/prognostic purposes.

R-spondin 1/dickkopf-1/beta-catenin machinery is involved in testicular embryonic angiogenesis

Testicular vasculogenesis is one of the key processes regulating male gonad morphogenesis. The knowledge of the molecular cues underlining this phenomenon is one of today’s most challenging issues and could represent a major contribution toward a better understanding of the onset of testicular morphogenetic disorders. R-spondin 1 has been clearly established as a candidate for mammalian ovary determination. Conversely, very little information is available on the expression and role of R-spondin 1 during testicular morphogenesis. This study aims to clarify the distribution pattern of R-spondin 1 and other partners of its machinery during the entire period of testicular morphogenesis and to indicate the role of this system in testicular development. Our whole mount immunofluorescence results clearly demonstrate that R-spondin 1 is always detectable in the testicular coelomic partition, where testicular vasculature is organized, while Dickkopf-1 is never detectable in this area. Moreover, organ culture experiments of embryonic male UGRs demonstrated that Dickkopf-1 acted as an inhibitor of testis vasculature formation. Consistent with this observation, real-time PCR analyses demonstrated that DKK1 is able to slightly but significantly decrease the expression level of the endothelial marker Pecam1. The latter experiments allowed us to observe that DKK1 administration also perturbs the expression level of the Pdgf-b chain, which is consistent with some authors’ observations relating this factor with prenatal testicular patterning and angiogenesis. Interestingly, the DKK1 induced inhibition of testicular angiogenesis was rescued by the co-administration of R-spondin 1. In addition, R-spondin 1 alone was sufficient to enhance, in culture, testicular angiogenesis.

A site-specific, single-copy transgenesis strategy to identify 5' regulatory sequences of the mouse testis-determining gene Sry

The Y-chromosomal gene SRY acts as the primary trigger for male sex determination in mammalian embryos. Correct regulation of SRY is critical: aberrant timing or level of Sry expression is known to disrupt testis development in mice and we hypothesize that mutations that affect regulation of human SRY may account for some of the many cases of XY gonadal dysgenesis that currently remain unexplained. However, the cis-sequences involved in regulation of Sry have not been identified, precluding a test of this hypothesis. Here, we used a transgenic mouse approach aimed at identifying mouse Sry 5' flanking regulatory sequences within 8 kb of the Sry transcription start site (TSS). To avoid problems associated with conventional pronuclear injection of transgenes, we used a published strategy designed to yield single-copy transgene integration at a defined, transcriptionally open, autosomal locus, Col1a1. None of the Sry transgenes tested was expressed at levels compatible with activation of Sox9 or XX sex reversal. Our findings indicate either that the Col1a1 locus does not provide an appropriate context for the correct expression of Sry transgenes, or that the cis-sequences required for Sry expression in the developing gonads lie beyond 8 kb 5' of the TSS.

Opioid receptor expression in human brain and peripheral tissues using absolute quantitative real-time RT-PCR

BACKGROUND

The actions of endogenous opioid peptides are mediated by 3 main classes of opioid receptors; mu (MOR), kappa (KOR), and delta (DOR).

METHODS

We developed an absolute quantitative real-time reverse transcriptase PCR (AQ-rt-RT-PCR) assay to quantify MOR, DOR, and KOR mRNA in 22 human tissues.

RESULTS

MOR mRNA was greatly enriched (12-20×10(6)copies/μg) in the cerebellum, nucleus accumbens, and caudate nucleus; moderate (6×10(6)copies/μg) in the dorsal root ganglion, spinal cord, and adrenal gland; low (2×10(4)copies/μg) in the pancreas and small intestine; and absent in the lung, spleen, kidney, heart, skeletal muscle, liver, and thymus. High levels (>8.8×10(6)copies/μg) of DOR mRNA were expressed in the brain and dorsal root ganglion; moderate (1.5×10(6)copies/μg) in the adrenal gland and pancreas; low (2×10(4)-6.5×10(5)copies/μg in the cerebellum, spinal cord, small intestine, skeletal muscle, thymus, lung, and kidney); and very low (3.8×10(3)copies/μg) in the heart. DOR mRNA was not detected in the spleen or liver. KOR mRNA was moderate (1×10(6)copies/μg) in brain regions and dorsal root ganglion, but low (1.6-7×10(5)copies/μg) in the cerebellum, temporal lobe and all other peripheral tissues.

CONCLUSIONS

Our data demonstrate that the AQ-rt-RT-PCR is a highly reproducible and precise method to study the expression of opioid receptors in various tissues and under different disease conditions.

A genome-wide expression profile of adrenocortical cells in knockout mice lacking steroidogenic acute regulatory protein

Steroidogenic acute regulatory protein (StAR) facilitates cholesterol transfer into the inner mitochondrial membrane in the acute phase of steroidogenesis. Mice lacking StAR (Star(-/-)) share phenotypes with human individuals having congenital lipoid adrenal hyperplasia including compromised production of steroid hormones and florid accumulation of cholesterol esters in adrenal glands and gonads. To define a specific pattern of molecular changes with StAR deficiency, we performed transcriptome analysis of adrenal cells selectively isolated by fluorescent-activated cell sorting at embryonic d 17.5 or 18.5 in seven wild-type (Star(+/+)) or four Star(-/-) mice having the transgene targeting the enhanced green fluorescent protein to cell lineages that express StAR. A gene expression profile was obtained by whole-mouse genome microarray and confirmed by quantitative real-time PCR, identifying 1206 and 767 significantly up-regulated and down-regulated genes, respectively, in Star(-/-) mice compared with Star(+/+) mice (fold difference ≥ 2 and P value < 0.05 with false discovery rate < 0.2). In Star(-/-) mice, expression levels of genes involved in cholesterol efflux and the inflammatory response were significantly up-regulated, whereas those related to steroid hormone biosynthesis or cholesterol biosynthesis and influx were not significantly changed. Immunoreactive Iba1 or F4/80 (macrophage marker) in adrenal glands of Star(-/-) mice was detected not only in an increased number of resident macrophages but also in most adrenocortical cells. These findings expand our understanding of the pathophysiology of adrenal glands with the disruption of StAR and propose a reciprocal interaction between adrenocortical cells and resident macrophages inside adrenal glands of Star(-/-) mice.

Different levels of testicular organization during gonadal differentiation in B6.Y(Tir) mice manifesting sex reversal

B6.Y(Tir) (mice with Y chromosome from a strain in Tirano, Italy, and autosomes and X-chromosomes from the B6 strain) mice provide an excellent model for analysing sex development that occurs during gonadal differentiation; however, the molecular mechanisms that contribute to sex reversal are unclear. Our aim has been to establish which molecular events participate in this sex reversal. The pattern of gene expression related to testicular [Sry (sex-determining region of the Y chromosome), Sox9 (Sry-related high-mobility group box gene 9) and Mis (Müllerian-inhibiting substance)] and ovarian [Wnt4 (Wingless-type MMTV (murine-mammary-tumour virus) integration site family, member 4), Rspo1 (cysteine-rich secretory protein containing a thrombospondin type 1 repeat) and Stra8 (stimulated by retinoic acid gene 8)] differentiation was analysed by applying immunofluorescence and real-time RT-PCR (reverse transcription-PCR), focusing on XY gonads from the B6.Y(Tir) mouse, but also analysing the normal strains CD-1 and C57BL/6J (B6). The expression of genes related to the process of sexual differentiation was altered in the case of the B6.Y(Tir) strain, both at the transcript and protein level, inducing differentiation of ovaries and ovotestes, but not the formation of the testes, which were normal. Our results indicate that the expression of testicular genes is inhibited at various levels, permitting the expression of ovarian genes such as Wnt4, Stra8 and Rspo1. However, their activity was not clear when the data were averaged. Correlation analysis indicated that an ovary differentiation pathway is activated when the testicular differentiation pathway is inhibited.

Sex reversal in C57BL/6J XY mice caused by increased expression of ovarian genes and insufficient activation of the testis determining pathway

Sex reversal can occur in XY humans with only a single functional WT1 or SF1 allele or a duplication of the chromosome region containing WNT4. In contrast, XY mice with only a single functional Wt1, Sf1, or Wnt4 allele, or mice that over-express Wnt4 from a transgene, reportedly are not sex-reversed. Because genetic background plays a critical role in testis differentiation, particularly in C57BL/6J (B6) mice, we tested the hypothesis that Wt1, Sf1, and Wnt4 are dosage sensitive in B6 XY mice. We found that reduced Wt1 or Sf1 dosage in B6 XY(B6) mice impaired testis differentiation, but no ovarian tissue developed. If, however, a Y(AKR) chromosome replaced the Y(B6) chromosome, these otherwise genetically identical B6 XY mice developed ovarian tissue. In contrast, reduced Wnt4 dosage increased the amount of testicular tissue present in Sf1+/- B6 XY(AKR), Wt1+/- B6 XY(AKR), B6 XY(POS), and B6 XY(AKR) fetuses. We propose that Wt1(B6) and Sf1(B6) are hypomorphic alleles of testis-determining pathway genes and that Wnt4(B6) is a hypermorphic allele of an ovary-determining pathway gene. The latter hypothesis is supported by the finding that expression of Wnt4 and four other genes in the ovary-determining pathway are elevated in normal B6 XX E12.5 ovaries. We propose that B6 mice are sensitive to XY sex reversal, at least in part, because they carry Wt1(B6) and/or Sf1(B6) alleles that compromise testis differentiation and a Wnt4(B6) allele that promotes ovary differentiation and thereby antagonizes testis differentiation. Addition of a "weak" Sry allele, such as the one on the Y(POS) chromosome, to the sensitized B6 background results in inappropriate development of ovarian tissue. We conclude that Wt1, Sf1, and Wnt4 are dosage-sensitive in mice, this dosage-sensitivity is genetic background-dependant, and the mouse strains described here are good models for the investigation of human dosage-sensitive XY sex reversal.

Wnt signaling in ovarian development inhibits Sf1 activation of Sox9 via the Tesco enhancer

Genome analysis of patients with disorders of sex development, and gain- and loss-of-function studies in mice indicate that gonadal development is regulated by opposing signals. In females, the Wnt/β-catenin canonical pathway blocks testicular differentiation by repressing the expression of the Sertoli cell-specific gene Sox9 by an unknown mechanism. Using cell and embryonic gonad culture models, we show that activation of the Wnt/β-catenin pathway inhibits the expression of Sox9 and Amh, whereas mRNA and protein levels of Sry and steroidogenic factor 1 (Sf1), two key transcriptional regulators of Sox9, are not altered. Ectopic activation of Wnt/β-catenin signaling in male gonads led to a loss of Sf1 binding to the Tesco enhancer and absent Sox9 expression that we also observed in wild-type ovaries. Moreover, ectopic Wnt/β-catenin signaling induced the expression of the female somatic cell markers, Bmp2 and Rspo1, as a likely consequence of Sox9 loss. Wnt/β-catenin signaling in XY gonads did not, however, affect gene expression of the steroidogenic Leydig cell Sf1 target gene, Cyp11a1, or Sf1 binding to the Cyp11a1 promoter. Our data support a model in ovary development whereby activation of β-catenin prevents Sf1 binding to the Sox9 enhancer, thereby inhibiting Sox9 expression and Sertoli cell differentiation.

Modulation of brain β-endorphin concentration by the specific part of the Y chromosome in mice

BACKGROUND

Several studies in animal models suggest a possible effect of the specific part of the Y-chromosome (Y(NPAR)) on brain opioid, and more specifically on brain β-endorphin (BE). In humans, male prevalence is found in autistic disorder in which observation of abnormal peripheral or central BE levels are also reported. This suggests gender differences in BE associated with genetic factors and more precisely with Y(NPAR).

METHODOLOGY/PRINCIPAL FINDINGS

Brain BE levels and plasma testosterone concentrations were measured in two highly inbred strains of mice, NZB/BlNJ (N) and CBA/HGnc (H), and their consomic strains for the Y(NPAR). An indirect effect of the Y(NPAR) on brain BE level via plasma testosterone was also tested by studying the correlation between brain BE concentration and plasma testosterone concentration in eleven highly inbred strains. There was a significant and major effect (P<0.0001) of the Y(NPAR) in interaction with the genetic background on brain BE levels. Effect size calculated using Cohen's procedure was large (56% of the total variance). The variations of BE levels were not correlated with plasma testosterone which was also dependent of the Y(NPAR).

CONCLUSIONS/SIGNIFICANCE

The contribution of Y(NPAR) on brain BE concentration in interaction with the genetic background is the first demonstration of Y-chromosome mediated control of brain opioid. Given that none of the genes encompassed by the Y(NPAR) encodes for BE or its precursor, our results suggest a contribution of the sex-determining region (Sry, carried by Y(NPAR)) to brain BE concentration. Indeed, the transcription of the Melanocortin 2 receptor gene (Mc2R gene, identified as the proopiomelanocortin receptor gene) depends on the presence of Sry and BE is derived directly from proopiomelanocortin. The results shed light on the sex dependent differences in brain functioning and the role of Sry in the BE system might be related to the higher frequency of autistic disorder in males.

Expression of miRNAs in ovine fetal gonads: potential role in gonadal differentiation

BACKGROUND

Gonadal differentiation in the mammalian fetus involves a complex dose-dependent genetic network. Initiation and progression of fetal ovarian and testicular pathways are accompanied by dynamic expression patterns of thousands of genes. We postulate these expression patterns are regulated by small non-coding RNAs called microRNAs (miRNAs). The aim of this study was to identify the expression of miRNAs in mammalian fetal gonads using sheep as a model.

METHODS

We determined the expression of 128 miRNAs by real time PCR in early-gestational (gestational day (GD) 42) and mid-gestational (GD75) sheep ovaries and testes. Expression data were further examined and validated by bioinformatic analysis.

RESULTS

Expression analysis revealed significant differences between ovaries and testes among 24 miRNAs at GD42, and 43 miRNAs at GD75. Bioinformatic analysis revealed that a number of differentially expressed miRNAs are predicted to target genes known to be important in mammalian gonadal development, including ESR1, CYP19A1, and SOX9. In situ hybridization revealed miR-22 localization within fetal testicular cords. As estrogen signaling is important in human and sheep ovarian development, these data indicate that miR-22 is involved in repressing estrogen signaling within fetal testes.

CONCLUSIONS

Based on our results we postulate that gene expression networks underlying fetal gonadal development are regulated by miRNAs.

Expression of sex and reproduction-related genes in Marsupenaeus japonicus

Expressed sequence tags (ESTs) were identified from reciprocal suppression subtractive hybridization cDNA libraries from Marsupenaeus japonicus (Kuruma shrimp) female and male gonads. The expression profiles of 24 of these ESTs were determined in female and male gonads and developing postlarvae by real-time quantitative reverse transcription-polymerase chain reaction. When expression was determined in gonads, six of the ESTs were expressed in ovaries only, and five of the ESTs were expressed in testes only. When expression was determined in whole individuals during postlarval development, expression of the ESTs was low and inconsistent until stage PL110 (110 days since metamorphosis from mysis stage to the first postlarval stage). At PL110, seven of the ESTs were detected in females only, and seven ESTs were detected in males only. Sex-specific expression at this developmental stage indicates that these ESTs act as important gonadal development markers and may have a role in gametogenesis.

Developmental expression of Smoc1 and Smoc2 suggests potential roles in fetal gonad and reproductive tract differentiation

SMOC1 and SMOC2 are matricellular proteins thought to influence growth factor signaling, migration, proliferation, and angiogenesis. We examined the expression and regulation of Smoc1 and Smoc2 in fetal gonad/mesonephros complexes to discover possible roles for these genes in gonad and mesonephros development. Smoc1 was upregulated at approximately E10.75 in a center-to-poles wave in pre-Sertoli and pre-granulosa cells and its expression was greatly reduced in Wt1, Sf1, and Fog2 mutants. After E13.5, Smoc1 was downregulated in an anterior-to-posterior wave in granulosa cells but persisted in Sertoli cells, suggesting a sexually dimorphic requirement in supporting cell lineage differentiation. Smoc2 was expressed in Leydig cells, mesonephroi, and Wnt4 mutant ovaries, but not wildtype ovaries. Using organ culture, we determined that Smoc2 expression was dependent on Hedgehog signaling in testes, mesonephroi, and kidneys. Overall, these results demonstrate that SMOC1 and SMOC2 may mediate intercellular signaling and cell type-specific differentiation during gonad and reproductive tract development.

New candidate genes identified for controlling mouse gonadal sex determination and the early stages of granulosa and Sertoli cell differentiation

Mammalian gonadal sex-determining (GSD) genes are expressed in a unique population of somatic cells that differentiate into granulosa cells in XX gonads or Sertoli cells in XY gonads. The ability to efficiently isolate these somatic support cells (SSCs) during the earliest stages of gonad development would facilitate identifying 1) new candidate GSD genes that may be involved in cases of unexplained abnormal gonad development and 2) genes involved in the earliest stages of granulosa and Sertoli cell differentiation. We report the development of a unique mouse carrying two transgenes that allow XX and XY mice to be distinguished as early as Embryonic Day 11.5 (E11.5) and allow SSCs to be isolated from undifferentiated (E11.5) and early differentiated (E12.5) fetal gonads. The Mouse Genome 430v2.0 GeneChip (Affymetrix) was used to identify transcripts exhibiting a sexual dimorphic expression pattern in XX and XY isolated SSCs. The analysis revealed previously unidentified sexually dimorphic transcripts, including low-level expressed genes such as Sry, a gene not identified in other microarray studies. Multigene real-time PCR analysis of 57 genes verified that 53 were expressed in fetal gonads in a sexually dimorphic pattern, and whole-mount in situ hybridization analysis verified 4930563E18Rik, Pld1, and Sprr2d are expressed in XX gonads, and Fbln2, Ppargc1a, and Scrn1 are expressed in XY gonads. Taken together, the data provide a comprehensive resource for the spatial-temporal expression pattern of genes that are part of the genetic network underlying the early stages of mammalian fetal gonadal development, including the development of granulosa and Sertoli cells.

Characterization of wise protein and its molecular mechanism to interact with both Wnt and BMP signals

Cross-talk of BMP and Wnt signaling pathways has been implicated in many aspects of biological events during embryogenesis and in adulthood. A secreted protein Wise and its orthologs (Sostdc1, USAG-1, and Ectodin) have been shown to modulate Wnt signaling and also inhibit BMP signals. Modulation of Wnt signaling activity by Wise is brought about by an interaction with the Wnt co-receptor LRP6, whereas BMP inhibition is by binding to BMP ligands. Here we have investigated the mode of action of Wise on Wnt and BMP signals. It was found that Wise binds LRP6 through one of three loops formed by the cystine knot. The Wise deletion construct lacking the LRP6-interacting loop domain nevertheless binds BMP4 and inhibits BMP signals. Moreover, BMP4 does not interfere with Wise-LRP6 binding, suggesting separate domains for the physical interaction. Functional assays also show that the ability of Wise to block Wnt1 activity through LRP6 is not impeded by BMP4. In contrast, the ability of Wise to inhibit BMP4 is prevented by additional LRP6, implying a preference of Wise in binding LRP6 over BMP4. In addition to the interaction of Wise with BMP4 and LRP6, the molecular characteristics of Wise, such as glycosylation and association with heparan sulfate proteoglycans on the cell surface, are suggested. This study helps to understand the multiple functions of Wise at the molecular level and suggests a possible role for Wise in balancing Wnt and BMP signals.

Fetal testis dysgenesis and compromised Leydig cell function in Tgfbr3 (beta glycan) knockout mice

Betaglycan (Tgfbr3) is a coreceptor for transforming growth factor-beta (TGFB) superfamily ligands. In the current study, a defect in seminiferous cord formation was detected in 12.5-13.5 days postcoitum (dpc) beta glycan null murine testis. Immunohistochemistry with antibodies against cell-specific markers revealed defects in somatic cell populations. To confirm these data, quantitative real-time PCR was performed to determine changes in the expression levels of genes involved in fetal testis cell differentiation and function. The expression levels of the Leydig cell markers Insl3, Cyp17a1, Cyp11a1, Star, and Hsd3b1 were reduced in knockout testis compared to wild-type testis, beginning at 12.5 dpc. Whole mount in situ hybridization confirmed that Cyp11a1 expression was reduced in the null testis, but its distribution pattern was unchanged. Apoptosis was not affected by the loss of beta glycan, but proliferation within the interstitium was reduced at 14.5 dpc. However, morphometric analysis showed no changes in Leydig cell counts between the wild-type and the knockout testes at 14.5 dpc, indicating that fetal Leydig function, rather than number, was affected by the loss of beta glycan. The expression levels of Sertoli cell markers Dhh, Sox9, and Amh were also reduced in the knockout testis at 14.5 dpc. However, the expression of fetal germ cell markers Pou5f1 and DDX4 were not changed across the genotypes at any age examined. Our data show that the presence of beta glycan is required for normal cord formation, normal fetal Leydig cell development, and the establishment of fetal testis endocrine function, thus implicating TGFB superfamily members as regulators of early fetal testis structure and function.

Developmental staging of male murine embryonic gonad by SAGE analysis

Despite the identification of key genes such as Sry integral to embryonic gonadal development, the genomic classification and identification of chromosomal activation of this process is still poorly understood. To better understand the genetic regulation of gonadal development, we performed Serial Analysis of Gene Expression (SAGE) to profile the genes and novel transcripts, and an average of 152,000 tags from male embryonic gonads at E10.5 (embryonic day 10.5), E11.5, E12.5, E13.5, E15.5 and E17.5 were analyzed. A total of 275,583 non-singleton tags that do not map to any annotated sequence were identified in the six gonad libraries, and 47,255 tags were mapped to 24,975 annotated sequences, among which 987 sequences were uncharacterized. Utilizing an unsupervised pattern identification technique, we established molecular staging of male gonadal development. Rather than providing a static descriptive analysis, we developed algorithms to cluster the SAGE data and assign SAGE tags to a corresponding chromosomal position; these data are displayed in chromosome graphic format. A prominent increase in global genomic activity from E10.5 to E17.5 was observed. Important chromosomal regions related to the developmental processes were identified and validated based on established mouse models with developmental disorders. These regions may represent markers for early diagnosis for disorders of male gonad development as well as potential treatment targets.

Novel markers of early ovarian pre-granulosa cells are expressed in an Sry-like pattern

Mammalian gonad differentiation involves sexually dimorphic cell-fate decisions within the bipotential gonadal primordia. Testis differentiation is initiated by a center-to-poles wave of Sry expression that induces supporting cell precursors (SCPs) to become Sertoli rather than granulosa cells. The initiation of ovary differentiation is less well understood. We identified two novel SCP markers, 1700106J16Rik and Sprr2d, whose expression is ovary-biased during early gonad development, and altered in Wnt4, Sf1, Wt1, and Fog2 mutant gonads. In XX and XY gonads, both genes were up-regulated at approximately E11 in a center-to-poles wave, and then rapidly down-regulated in XY gonads in a center-to-poles wave, which is reminiscent of Sry expression in XY gonads. Our data suggest that 1700106J16Rik and Sprr2d may have important roles in early gonad development, and are consistent with the hypothesis that ovarian SCP differentiation occurs in a center-to-poles wave with similar timing to that of testicular SCP differentiation.

The Maestro (Mro) gene is dispensable for normal sexual development and fertility in mice

The mammalian gonad arises as a bipotential primordium from which a testis or ovary develops depending on the chromosomal sex of the individual. We have previously used DNA microarrays to screen for novel genes controlling the developmental fate of the indifferent embryonic mouse gonad. Maestro (Mro), which encodes a HEAT-repeat protein, was originally identified as a gene exhibiting sexually dimorphic expression during mouse gonad development. Wholemount in situ hybridisation analysis revealed Mro to be expressed in the embryonic male gonad from approximately 11.5 days post coitum, prior to overt sexual differentiation. No significant expression was detected in female gonads at the same developmental stage. In order to address its physiological function, we have generated mice lacking Maestro using gene targeting. Male and female mice homozygous for a Mro null allele are viable and fertile. We examined gonad development in homozygous male embryos in detail and observed no differences when compared to wild-type controls. Immunohistochemical analysis of homozygous mutant testes of adult mice revealed no overt abnormalities. Expression profiling using DNA microarrays also indicated no significant differences between homozygote embryonic male gonads and controls. We conclude that Maestro is dispensable for normal male sexual development and fertility in laboratory mice; however, the Mro locus itself does have utility as a site for insertion of transgenes for future studies in the fields of sexual development and Sertoli cell function.

Inhibition of HMG CoA reductase reveals an unexpected role for cholesterol during PGC migration in the mouse

BACKGROUND

Primordial germ cells (PGCs) are the embryonic precursors of the sperm and eggs. Environmental or genetic defects that alter PGC development can impair fertility or cause formation of germ cell tumors.

RESULTS

We demonstrate a novel role for cholesterol during germ cell migration in mice. Cholesterol was measured in living tissue dissected from mouse embryos and was found to accumulate within the developing gonads as germ cells migrate to colonize these structures. Cholesterol synthesis was blocked in culture by inhibiting the activity of HMG CoA reductase (HMGCR) resulting in germ cell survival and migration defects. These defects were rescued by co-addition of isoprenoids and cholesterol, but neither compound alone was sufficient. In contrast, loss of the last or penultimate enzyme in cholesterol biosynthesis did not alter PGC numbers or position in vivo. However embryos that lack these enzymes do not exhibit cholesterol defects at the stage at which PGCs are migrating. This demonstrates that during gestation, the cholesterol required for PGC migration can be supplied maternally.

CONCLUSION

In the mouse, cholesterol is required for PGC survival and motility. It may act cell-autonomously by regulating clustering of growth factor receptors within PGCs or non cell-autonomously by controlling release of growth factors required for PGC guidance and survival.

The developmentally-regulated Smoc2 gene is repressed by Aryl-hydrocarbon receptor (Ahr) signaling

SPARC-Related Modular Calcium Binding Protein-2 (Smoc-2) is a broadly-expressed matricellular protein which contributes to mitogenesis via activation of Integrin-Linked Kinase (ILK). Here we show that expression of Smoc2 is repressed in cultured cells following treatment with Aryl-hydrocarbon receptor (Ahr) ligands including the ubiquitous environmental pollutants Benzo[a]pyrene (B[a]P) and 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD). The Smoc2 promoter contains two consensus putative Ahr-binding sites and Smoc2 promoter-driven reporter genes are repressed in response to B[a]P in an Ahr-dependent manner in cultured cells. Using organ culture experiments we show that TCDD also represses Smoc2 mRNA expression in testes from Ahr(+/+) but not Ahr(-/-) mice. Therefore, exposure to Ahr ligands is likely to affect Smoc2 expression in vivo. Taken together our results indicate that Smoc2 is a novel transcriptional target of activated Ahr. Perturbation of Smoc2 expression may mediate the adverse developmental effects of environmental aryl-hydrocarbon exposure.

Sex-specific roles of beta-catenin in mouse gonadal development

Sexually dimorphic development of the gonads is controlled by positive and negative regulators produced by somatic cells. Many Wnt ligands, including ones that signal via the canonical beta-catenin pathway, are expressed in fetal gonads. beta-catenin, a key transcriptional regulator of the canonical Wnt pathway and an element of the cell adhesion complex, is essential for various aspects of embryogenesis. To study the involvement of beta-catenin in sex determination, we ablated beta-catenin specifically in the SF1-positive population of somatic cells. Although beta-catenin was present in gonads of both sexes, it was necessary only for ovarian differentiation but dispensable for testis development. Loss of beta-catenin in fetal testes did not affect Sertoli cell differentiation, testis morphogenesis or masculinization of the embryos. However, we observed molecular and morphological defects in ovaries lacking beta-catenin, including formation of testis-specific coelomic vessel, appearance of androgen-producing adrenal-like cells and loss of female germ cells. These phenotypes were strikingly similar to those found in the R-spondin1 (Rspo1) and Wnt4 knockout ovaries. In the absence of beta-catenin, expression of Wnt4 was down-regulated while that of Rspo1 was not affected, placing beta-catenin as a component in between Rspo1 and Wnt4. Our results demonstrate that beta-catenin is responsible for transducing sex-specific signals in the SF1-positive somatic cell population during mouse gonadal development.

Effects of gestational diethylstilbestrol treatment on male and female gonads during early embryonic development

To study the effects of gestational exposure to estrogen on early gonadal differentiation, pregnant mice were treated by sc injection of diethylstilbestrol (DES) or vehicle from embryonic day (E) 8.5 to E14.5, and gonads at E11.5, E12.5, and E14.5 were examined. Quantitative real-time RT-PCR and in situ hybridization revealed that mRNA levels of steroidogenic factor 1 (SF-1), a key regulator of gonadal differentiation, and several male gonad-specific genes, including Müllerian-inhibiting substance (MIS), steroidogenic acute regulatory protein, cholesterol side-chain cleavage cytochrome P450, and Cerebellin 1 precursor protein, were significantly decreased in the DES-treated testis, compared with the control testis at E12.5 and/or E14.5. Immunohistochemistry demonstrated that the staining intensities for SF-1 and MIS in Sertoli cells were apparently reduced in the DES-treated testis, compared with those of the controls, at E12.5 and E14.5. Because MIS, steroidogenic acute regulatory protein, cholesterol side-chain cleavage cytochrome P450, and Cerebellin 1 precursor protein are activated under the regulation of SF-1, the down-regulation of these factors may be due to reduced SF-1 expression. Immunohistochemistry for laminin-1 demonstrated that ovigerous cords in the DES-treated ovary were smaller than those in controls at E14.5. Moreover, the number of 5-bromo-2'deoxyuridine-5-monophosphate-labeled cells in the DES-treated testis was significantly reduced at E12.5 and E14.5, compared with controls, and that in the DES-treated ovary remained higher than that in the control ovary at E14.5. The results suggest that exogenous estrogens can alter sex-specific genetic pathways governing early differentiation and cell proliferation of both male and female gonads.

Ectopic expression of mouse Sry interferes with Wnt/beta-catenin signaling in mouse embryonal carcinoma cell lines

In mammals, Sry is the master regulator of male sex determination, although how it functions is still unclear. By contrast, female sex determination depends on the action of Rspo1 and Wnt4, the regulators of Wnt/beta-catenin signaling. To seek a possible interaction between male and female sex determination mechanisms, we examined whether Sry affects Wnt/beta-catenin signaling. Using the TOPFLASH reporter system to measure Lef/Tcf-dependent transcriptional activity, we showed that ectopic expression of mouse Sry strongly suppressed Wnt/beta-catenin signaling in mouse embryonal carcinoma and human embryonic kidney cell lines. This inhibition occurred downstream of beta-catenin but upstream of Lef/Tcf, and depended on both the HMG-box and the C-terminal transcriptional activation domain. By contrast, TOPFLASH was not inhibited by human SRY, which apparently lacks a transcriptional activation domain. However, a fusion construct consisting of human SRY attached to the C-terminal domain of mouse Sry was able to inhibit TOPFLASH effectively. Furthermore, Sry constructs carrying point mutations equivalent to those in human sex reversal mutations were less effective in inhibiting Wnt/beta-catenin signaling. Also, we showed that the action of Sry as a transcriptional activator was both necessary and sufficient to inhibit Wnt/beta-catenin signaling, suggesting that the transcriptional targets of Sry are responsible for the inhibition of signaling. Sox9 is a potential transcriptional target of Sry, although quantitative RT-PCR analysis indicates that the expression of Sox9 was not up-regulated by the ectopic expression of mouse Sry in mouse embryonal carcinoma cells. While the present study demonstrates an impact of mouse Sry on Wnt/beta-catenin signaling at an in vitro level, it requires further investigations to assess whether such action also takes place in vivo to regulate male sex determination.

Expression of the Ladybird-like homeobox 2 transcription factor in the developing mouse testis and epididymis

BACKGROUND

Homeoproteins are a class of transcription factors that are well-known regulators of organogenesis and cell differentiation in numerous tissues, including the male reproductive system. Indeed, a handful of homeoproteins have so far been identified in the testis and epididymis where a few were shown to play important developmental roles. Through a degenerate PCR approach aimed at identifying novel homeoproteins expressed in the male reproductive system, we have detected several homeoproteins most of which had never been described before in this tissue. One of these homeoproteins is Ladybird-like homeobox 2 (Lbx2), a homeobox factor mostly known to be expressed in the nervous system.

RESULTS

To better define the expression profile of Lbx2 in the male reproductive system, we have performed in situ hybridization throughout testicular and epididymal development and into adulthood. Lbx2 expression was also confirmed by real time RT-PCR in those tissues and in several testicular and epididymal cell lines. In the epididymis, a highly segmented tissue, Lbx2 shows a regionalized expression profile, being more expressed in proximal segments of the caput epididymis than any other segment. In the testis, we found that Lbx2 is constitutively expressed at high levels in Sertoli cells. In interstitial cells, Lbx2 is weakly expressed during fetal and early postnatal life, highly expressed around P32-P36, and absent in adult animals. Finally, Lbx2 can also be detected in a population of germ cells in adults.

CONCLUSION

Altogether, our data suggest that the homeoprotein Lbx2 might be involved in the regulation of male reproductive system development and cell differentiation as well as in male epididymal segmentation.

Microarray analysis of thapsigargin-induced stress to the endoplasmic reticulum of mouse osteoblasts

Activating transcription factor 4 (ATF4) protein has a dual role in osteoblasts. It functions as a responder to stress to the endoplasmic reticulum (ER) as well as a transcription factor for bone formation. Little is known about molecular pathways that can potentially lead to stress-induced apoptosis or homeostasis of extracellular matrix (ECM) molecules. Based on microarray-derived mRNA expression data for mouse osteoblasts (MC3T3 E1 cells, clone 4), we analyzed the ER-stress responses in the presence of 10 nM Thapsigargin using two computational approaches: "Gene Set Enrichment Analysis (GSEA)" and "Ingenuity Pathways Analysis (IPA)." GSEA presented a strong linkage to an expression pattern observed in the responses to hypoxia, and IPA identified two molecular pathways: ATF4-unlinked connective tissue development and ATF4-linked organ morphology. Real-time polymerase chain reaction (PCR) and Western blot analyses validated eIF2alpha-driven translational regulation as well as ATF4-linked transcriptional activation of transcription factors and growth factors including FOS, FGF-9, and BMP-2. Consistent with the role of p38 MAPK in hypoxia, phosphorylation of p38 MAPK was activated in nonapoptotic osteoblasts under surviving ER stress. Furthermore, the level of phosphorylated PERK was elevated. These results support cross-talk between p38 MAPK and ER kinase, presenting a similarity to the responses to hypoxia as well as a pathway toward connective tissue development and organ morphology.

Correct dosage of Fog2 and Gata4 transcription factors is critical for fetal testis development in mice

Previous reports suggested that humans and mice differ in their sensitivity to the genetic dosage of transcription factors that play a role in early testicular development. This difference implies that testis determination might be somewhat different in these two species. We report that the Fog2 and Gata4 transcription factors are haploinsufficient for testis determination in mice. Whether gonadal sex reversal occurs depends on genetic background (i.e., modifier genes). For example, C57BL/6J (B6) XY mice develop testes if they are heterozygous for a mutant Fog2 (Fog2-) or Gata4 (Gata4(ki)) allele. However, if the B6 Y chromosome (Y(B6)) is replaced by the AKR Y chromosome (Y(AKR)), B6 Fog2-/+ XY(AKR) mice develop ovaries, and B6 Gata4(ki)/+ XY(AKR) mice develop ovaries and ovotestes (gonads containing both ovarian and testicular tissue). Furthermore, DBA/2J (D2) Fog2-/+ XY(AKR) mice and (B6 x D2)F1 hybrid Gata4(ki)/+ XY(AKR) mice develop testes. Sry is expressed in the mutant XY gonads, indicating that the lack of Sry expression is not the cause of ovarian tissue development in B6 Fog2-/+ or Gata4(ki)/+ XY(AKR) mice. However, up-regulation of Sox9 expression, which is critical for normal testicular development, does not occur in mutant XY gonads that develop as ovaries. We conclude that under certain genetic conditions, Sox9 up-regulation depends on the proper dosage of Fog2 and Gata4. We propose that in humans the FOG2 and/or GATA4 genes might be haploinsufficient for normal testis determination and thus could be the cause of some previously unassigned cases of XY gonadal sex reversal.

Bmp2 transcription in osteoblast progenitors is regulated by a distant 3' enhancer located 156.3 kilobases from the promoter

Bone morphogenetic protein 2 (encoded by Bmp2) has been implicated as an important signaling ligand for osteoblast differentiation and bone formation and as a genetic risk factor for osteoporosis. To initially survey a large genomic region flanking the mouse Bmp2 gene for cis-regulatory function, two bacterial artificial chromosome (BAC) clones that extend far upstream and downstream of the gene were engineered to contain a lacZ reporter cassette and tested in transgenic mice. Each BAC clone directs a distinct subset of normal Bmp2 expression patterns, suggesting a modular arrangement of distant Bmp2 regulatory elements. Strikingly, regulatory sequences required for Bmp2 expression in differentiating osteoblasts, as well as tooth buds, hair placodes, kidney, and other tissues, are located more than 53 kilobases 3' to the promoter. By testing BACs with engineered deletions across this distant 3' region, we parsed these regulatory elements into separate locations and more closely refined the location of the osteoblast progenitor element. Finally, a conserved osteoblast progenitor enhancer was identified within a 656-bp sequence located 156.3 kilobases 3' from the promoter. The identification of this enhancer should permit further investigation of upstream regulatory mechanisms that control Bmp2 transcription during osteoblast differentiation and are relevant to further studies of Bmp2 as a candidate risk factor gene for osteoporosis.

Male fetal germ cells are targets for androgens that physiologically inhibit their proliferation

In adulthood, the action of androgens on seminiferous tubules is essential for full quantitatively normal spermatogenesis and fertility. In contrast, their role in the fetal testis, and particularly in fetal germ cell development, remains largely unknown. Using testicular feminized (Tfm) mice, we investigated the effects of a lack of functional androgen receptor (AR) on fetal germ cells, also named gonocytes. We demonstrated that endogenous androgens/AR physiologically control normal gonocyte proliferation. We observed an increase in the number of gonocytes at 17.5 days postconception resulting from an increase in proliferative activity in Tfm mice. In a reciprocal manner, gonocyte proliferation is decreased by the addition of DHT in fetal testis organotypic culture. Furthermore, the AR coregulator Hsp90alpha (mRNA and protein) specifically expressed in gonocytes was down-regulated in Tfm mice at 15.5 days postconception. To investigate whether these effects could result from direct action of androgens on gonocytes, we collected pure gonocyte preparations and detected AR transcripts therein. We used an original model harboring a reporter gene that specifically reflects AR activity by androgens and clearly demonstrated the presence of a functional AR protein in fetal germ cells. These data provide in vivo and in vitro evidence of a new control of endogenous androgens on gonocytes identified as direct target cells for androgens. Finally, our results focus on a new pathway in the fetal testis during the embryonic period, which is the most sensitive to antiandrogenic endocrine disruptors.

Transcriptional profile of mouse pre-granulosa and Sertoli cells isolated from early-differentiated fetal gonads

Gonadal sex determining (GSD) genes that initiate fetal ovarian and testicular development and differentiation are expressed in the cells of the urogenital ridge that differentiate as somatic support cells (SSCs), i.e., granulosa cells of the ovary and Sertoli cells of the testis. To identify potential new mammalian GSD genes, we used the Mouse Genome 430v2.0 GeneChip to analyze gene expression differences between XX and XY SSCs cells isolated from the gonads of embryonic day (E) 13 C57BL/6J fetuses carrying an EGFP reporter transgene expressed specifically in SSCs. In addition, genome wide expression differences between XX and XY E13 whole gonads were examined. Analysis revealed that XX and XY E13 SSCs differentially express 647 transcripts (False Discovery Rate cutoff 1%), including transcripts not previously reported to exhibit a sexually dimorphic expression pattern in this unique cell population. Enrichment for genes controlling cell proliferation was noted in XY SSCs, whereas enrichment for genes controlling cell morphology and metabolic status was identified in XX SSCs. Among the newly identified differentially expressed transcripts are potential GSD genes involved in unexplained human sex reversal cases.

Balancing the bipotential gonad between alternative organ fates: a new perspective on an old problem

The embryonic gonads give rise to one of two morphologically and functionally different organs, a testis or an ovary. Sex determination is the embryonic process that determines the developmental fate of the gonad. In mammals, sex determination is regulated by a DNA binding protein encoded on the Y chromosome, Sry, and it's downstream mediator, Sox9, which trigger testis determination in the bipotential gonad. However, evidence suggests that the extracellular signals. Fgf9 and Wnt4, are also required to establish divergent organogenesis of the gonad. In this review, we discuss how these extracellular signals interface with cell-autonomous factors to determine the fate of the mammalian gonad, and we derive a model that could provide a molecular explanation for testis determination in vertebrates where Sry is absent.

Male-biased expression of X-chromosomal DM domain-less Dmrt8 genes in the mouse

The vertebrate DMRT gene family encodes putative transcription factors related to the sexual regulators Doublesex (Drosophila melanogaster) and MAB-3 (Caenorhabditis elegans). They share a highly conserved DNA binding motif, the DM domain. In human and mouse seven DMRT genes (DMRT1-DMRT7) have been analyzed. DMRT8, a gene related to DMRT7, is located on the X chromosome in placental mammals. While DMRT8 is single copy in most mammals, three copies are present in mouse, rat, and rabbit. Despite the loss of the DM domain, DMRT8 genes have been maintained in the mammalian lineage, suggesting a DM domain-independent function. In adult mouse, two Dmrt8 genes are expressed exclusively in testis. Dmrt8.1 mRNA was detected in Sertoli cells by in situ hybridization. In embryos, Dmrt8.2 shows a dynamic expression restricted to male and female gonads and might therefore be involved in sexual development in the mouse.

Developmental and hormonal regulation of meltrin beta (ADAM19) expression in mouse testes during embryonic and postnatal life

More than half of ADAM (a disintegrin and metalloprotease) family members are expressed in mammalian male reproductive organs such as testis and epididymis. The ADAM19 gene identified in mouse is a member of the ADAM family and is highly enriched in testes of a newborn mouse. The present study was performed to determine its expression pattern in whole mouse testes in vivo as well as its in vitro action and regulation in testis cells from 2-day-old mice. Reverse transcriptase polymerase chain reaction (RT-PCR) detected ADAM19 mRNA from 15.5 days postcoitum (dpc) to 21 days postpartum (dpp), with high expression during the perinatal period. Immunohistochemistry demonstrated ADAM19 protein localization to the seminiferous cords at both embryonic and postnatal ages examined (from 15.5-19.5 dpc to 2 dpp). In particular, we obtained new evidence that a neutralizing antibody to ADAM19 had no influence on the proliferation of 2 dpp testis cells cultured in serum-free medium when compared to controls. Interestingly, it inhibited the 2 dpp testis cell proliferation elicited by stimulation with 10% FCS (P<0.01) or FSH (P<0.05). Lastly, using a model of 2 dpp testis cell cultures and RT-PCR procedures, we demonstrated that follicle stimulating-hormone (FSH) reduced the levels of ADAM19 mRNA in a time-dependent manner. Taken together, these results indicate that the expression of ADAM19 may be subject to regulation by FSH during mouse testis development. Furthermore, ADAM19 can act to regulate the proliferation of perinatal testis cells in the perinatal period.

Expression profiling of purified mouse gonadal somatic cells during the critical time window of sex determination reveals novel candidate genes for human sexual dysgenesis syndromes

Despite the identification of SRY as the testis-determining gene in mammals, the genetic interactions controlling the earliest steps of male sex determination remain poorly understood. In particular, the molecular lesions underlying a high proportion of human XY gonadal dysgenesis, XX maleness and XX true hermaphroditism remain undiscovered. A number of screens have identified candidate genes whose expression is modulated during testis or ovary differentiation in mice, but these screens have used whole gonads, consisting of multiple cell types, or stages of gonadal development well beyond the time of sex determination. We describe here a novel reporter mouse line that expresses enhanced green fluorescent protein under the control of an Sf1 promoter fragment, marking Sertoli and granulosa cell precursors during the critical period of sex determination. These cells were purified from gonads of male and female transgenic embryos at 10.5 dpc (shortly after Sry transcription is activated) and 11.5 dpc (when Sox9 transcription begins), and their transcriptomes analysed using Affymetrix genome arrays. We identified 266 genes, including Dhh, Fgf9 and Ptgds, that were upregulated and 50 genes that were downregulated in 11.5 dpc male somatic gonad cells only, and 242 genes, including Fst, that were upregulated in 11.5 dpc female somatic gonad cells only. The majority of these genes are novel genes that lack identifiable homology, and several human orthologues were found to map to chromosomal loci implicated in disorders of sexual development. These genes represent an important resource with which to piece together the earliest steps of sex determination and gonad development, and provide new candidates for mutation searching in human sexual dysgenesis syndromes.

Growth factors sustain primordial germ cell survival, proliferation and entering into meiosis in the absence of somatic cells

It is known that mammalian primordial germ cells (PGCs), the precursors of oocytes and prospermatogonia, depend for survival and proliferation on specific growth factors and other undetermined compounds. Adhesion to neighboring somatic cells is also believed to be crucial for preventing PGC apoptosis occurring when they lose appropriate cell to cell contacts. This explains the current impossibility to maintain isolated mouse PGCs in culture for periods longer than a few hours in the absence of suitable cell feeder layers producing soluble factors and expressing surface molecules necessary for preventing PGTC apoptosis and stimulating their proliferation. In the present paper, we identified a cocktail of soluble growth factors, namely KL, LIF, BMP-4, SDF-1, bFGF and compounds (N-acetyl-L-cysteine, forskolin, retinoic acid) able to sustain the survival and self-renewal of mouse PGCs in the absence of somatic cell support. We show that under culture conditions allowing PGC adhesion to an acellular substrate, such growth factors and compounds were able to prevent the occurrence of significant levels of apoptosis in PGCs for two days, stimulate their proliferation and, when LIF was omitted from the cocktail, allow most of them to enter into and progress through meiotic prophase I. These results consent for the first time to establish culture conditions for purified mammalian PGCs in the absence of somatic cell support and should make easier the molecular dissection of the processes governing the development of such cells crucial for early gametogenesis.