Distinct transcriptional mechanisms direct expression of the rat Dmrt1 promoter in sertoli cells and germ cells of transgenic mice

DMRT1 is a testis-determining gene in rabbits and is also essential for female fertility

DMRT1 is the testis-determining factor in several species of vertebrates, but its involvement in mammalian testes differentiation, where SRY is the testis-determining gene, remains ambiguous. So far, DMRT1 loss-of-function has been described in two mammalian species and induces different phenotypes: Disorders of Sex Development (46, XY DSD) in men and male infertility in mice. We thus abolished DMRT1 expression by CRISPR/Cas9 in a third species of mammal, the rabbit. First, we observed that gonads from XY DMRT1-/- rabbit fetuses differentiated like ovaries, highlighting that DMRT1 is involved in testis determination. In addition to SRY, DMRT1 is required in the supporting cells to increase the expression of the SOX9 gene, which heads the testicular genetic cascade. Second, we highlighted another function of DMRT1 in the germline since XX and XY DMRT1-/- ovaries did not undergo meiosis and folliculogenesis. XX DMRT1-/- adult females were sterile, showing that DMRT1 is also crucial for female fertility. To conclude, these phenotypes indicate an evolutionary continuum between non-mammalian vertebrates such as birds and non-rodent mammals. Furthermore, our data support the potential involvement of DMRT1 mutations in different human pathologies, such as 46, XY DSD as well as male and female infertility.

Germline sexual fate is determined by the antagonistic action of dmrt1 and foxl3/foxl2 in tilapia

Germline sexual fate has long been believed to be determined by the somatic environment, but this idea is challenged by recent studies of foxl3 mutants in medaka. Here, we demonstrate that the sexual fate of tilapia germline is determined by the antagonistic interaction of dmrt1 and foxl3, which are transcriptionally repressed in male and female germ cells, respectively. Loss of dmrt1 rescued the germ cell sex reversal in foxl3Δ7/Δ7 XX fish, and loss of foxl3 partially rescued germ cell sex reversal but not somatic cell fate in dmrt1Δ5/Δ5 XY fish. Interestingly, germ cells lost sexual plasticity in dmrt1Δ5/Δ5 XY and foxl3Δ7/Δ7 XX single mutants, as aromatase inhibitor (AI) and estrogen treatment failed to rescue the respective phenotypes. However, recovery of germ cell sexual plasticity was observed in dmrt1/foxl3 double mutants. Importantly, mutation of somatic cell-specific foxl2 resulted in testicular development in foxl3Δ7/Δ7 or dmrt1Δ5/Δ5 mutants. Our findings demonstrate that sexual plasticity of germ cells relies on the presence of both dmrt1 and foxl3. The existence of dmrt1 and foxl3 allows environmental factors to influence the sex fate decision in vertebrates.

Characterization of deoxyribonucleic methylation and transcript abundance of sex-related genes during tempera ture-dependent sex determination in Mauremys reevesii†

A number of genes relevant for sex determination have been found in species with temperature-dependent sex determination. Epigenetics play a key role in sex determination, but characterization of deoxyribonucleic acid methylation of sex-related genes on temperature-dependent sex determination remains unclear. Mauremys reevesii is a typical species with temperature-dependent sex determination. In this study, we analyzed the Cytosine Guanine (CpG) methylation status of the proximal promoters, the messenger ribonucleic acid expression patterns and the correlation between methylation and expression levels of Aromatase, Forkhead box protein L2, Doublesex and mab3-related transcription factor 1, sex-determining region on Y chromosome-box 9, and anti-Müllerian hormone, which are key genes in sex determination in other species. We also analyzed the expression level of genes that encode enzymes involved in methylation and demethylation. The expression levels of Aromatase and Forkhead box protein L2 at the female producing temperature were higher than those at the male producing temperature; the expression levels of Doublesex and mab3-related transcription factor 1, sex-determining region on Y chromosome-box 9, and anti-Müllerian hormone were higher at MPT. The expression of some genes involved in methylation and demethylation is significantly different between male producing temperature and female producing temperature. The expression of messenger ribonucleic acid of genes involved in deoxyribonucleic acid methylation and demethylation affected by temperature, together with other factors, may change the methylation level of the regulatory regions of sex-related genes, which may further lead to temperature-specific expression of sex-related genes, and eventually affect the differentiation of the gonads.

High-throughput sequencing analyses of XX genital ridges lacking FOXL2 reveal DMRT1 up-regulation before SOX9 expression during the sex-reversal process in goats

FOXL2 loss of function in goats leads to the early transdifferentiation of ovaries into testes, then to the full sex reversal of XX homozygous mutants. By contrast, Foxl2 loss of function in mice induces an arrest of follicle formation after birth, followed by complete female sterility. In order to understand the molecular role of FOXL2 during ovarian differentiation in the goat species, putative FOXL2 target genes were determined at the earliest stage of gonadal sex-specific differentiation by comparing the mRNA profiles of XX gonads expressing the FOXL2 protein or not. Of these 163 deregulated genes, around two-thirds corresponded to testicular genes that were up-regulated when FOXL2 was absent, and only 19 represented female-associated genes, down-regulated in the absence of FOXL2. FOXL2 should therefore be viewed as an antitestis gene rather than as a female-promoting gene. In particular, the key testis-determining gene DMRT1 was found to be up-regulated ahead of SOX9, thus suggesting in goats that SOX9 primary up-regulation may require DMRT1. Overall, our results equated to FOXL2 being an antitestis gene, allowing us to propose an alternative model for the sex-determination process in goats that differs slightly from that demonstrated in mice.

Identification and characterization of germ cell genes expressed in the F9 testicular teratoma stem cell line

The F9 cell line, which was derived from a mouse testicular teratoma that originated from pluripotent germ cells, has been used as a model for differentiation. However, it is largely unknown whether F9 cells possess the characteristics of male germ cells. In the present study, we investigated spermatogenic stage- and cell type-specific gene expression in F9 cells. Analysis of previous microarray data showed that a large number of stage-regulated germ cell genes are expressed in F9 cells. Specifically, genes that are prominently expressed in spermatogonia and have transcriptional regulatory functions appear to be enriched in F9 cells. Our in silico and in vitro analyses identified several germ cell-specific or -predominant genes that are expressed in F9 cells. Among them, strong promoter activities were observed in the regions upstream of the spermatogonial genes, Dmrt1 (doublesex and mab-3 related transcription factor 1), Stra8 (stimulated by retinoic acid gene 8) and Tex13 (testis expressed gene 13), in F9 cells. A detailed analysis of the Tex13 promoter allowed us to identify an enhancer and a region that is implicated in germ cell-specificity. We also found that Tex13 expression is regulated by DNA methylation. Finally, analysis of GFP (green fluorescent protein) TEX13 localization revealed that the protein distributes heterogeneously in the cytoplasm and nucleus, suggesting that TEX13 shuttles between these two compartments. Taken together, our results demonstrate that F9 cells express numerous spermatogonial genes and could be used for transcriptional studies focusing on such genes. As an example of this, we use F9 cells to provide comprehensive expressional information about Tex13, and report that this gene appears to encode a germ cell-specific protein that functions in the nucleus during early spermatogenesis.

Transgenic mouse models in the study of reproduction: insights into GATA protein function

For the past 2 decades, transgenic technology in mice has allowed for an unprecedented insight into the transcriptional control of reproductive development and function. The key factor among the mouse genetic tools that made this rapid advance possible is a conditional transgenic approach, a particularly versatile method of creating gene deletions and substitutions in the mouse genome. A centerpiece of this strategy is an enzyme, Cre recombinase, which is expressed from defined DNA regulatory elements that are active in the tissue of choice. The regulatory DNA element (either genetically engineered or natural) assures Cre expression only in predetermined cell types, leading to the guided deletion of genetically modified (flanked by loxP or ‘floxed’ byloxP) gene loci. This review summarizes and compares the studies in which genes encoding GATA family transcription factors were targeted either globally or by Cre recombinases active in the somatic cells of ovaries and testes. The conditional gene loss experiments require detailed knowledge of the spatial and temporal expression of Cre activity, and the challenges in interpreting the outcomes are highlighted. These studies also expose the complexity of GATA-dependent regulation of gonadal gene expression and suggest that gene function is highly context dependent.

Epigenetic control of gonadal aromatase (cyp19a1) in temperature-dependent sex determination of red-eared slider turtles

In the red-eared slider turtle (Trachemys scripta), a species with temperature-dependent sex determination (TSD), the expression of the aromatase gene during gonad development is strictly limited to the female-producing temperature. The underlying mechanism remains unknown. In this study, we identified the upstream 5'-flanking region of the aromatase gene, gonad-specific promoter, and the temperature-dependent DNA methylation signatures during gonad development in the red-eared slider turtle. The 5'-flanking region of the slider aromatase exhibited sequence similarities to the aromatase genes of the American alligator, chicken, quail, and zebra finch. A putative TATA box was located 31 bp upstream of the gonad-specific transcription start site. DNA methylation at the CpG sites between the putative binding sites of the fork head domain factor (FOX) and vertebrate steroidogenic factor 1 (SF1) and adjacent TATA box in the promoter region were significantly lower in embryonic gonads at the female-producing temperature compared the male-producing temperature. A shift from male- to female-, but not from female- to male-, producing temperature changed the level of DNA methylation in gonads. Taken together these results indicate that the temperature, particularly female-producing temperature, allows demethylation at the specific CpG sites of the promoter region which leads the temperature-specific expression of aromatase during gonad development.

Molecular evolution of vertebrate sex-determining genes

Y-linked Dmy (also called dmrt1bY) in the teleost fish medaka, W-linked Dm-W in the African clawed frog (Xenopus laevis), and Z-linked Dmrt1 in the chicken are all sex chromosome-linked Dmrt1 homologues required for sex determination. Dmy and Dm-W both are Dmrt1 palalogues evolved through Dmrt1 duplication, while chicken Dmrt1 is a Z-linked orthologue. The eutherian sex-determining gene, Sry, evolved from an allelic gene, Sox3. Here we analyzed the exon–intron structures of the Dmrt1 homologues of several vertebrate species through information from databases and by determining the transcription initiation sites in medaka, chicken, Xenopus, and mouse. Interestingly, medaka Dmrt1 and Dmy and Xenopus Dm-W and Dmrt1 have a noncoding-type first exon, while mouse and chicken Dmrt1 do not. We next compared the 5′-flanking sequences of the Dmrt1 noncoding and coding exons 1 of several vertebrate species and found conservation of the presumptive binding sites for some transcription factors. Importantly, based on the phylogenetic trees for Dmrt1 and Sox3 homologues, it was implied that the sex-determining gene Dmy, Dm-W, and Sry have a higher substitution rate than thier prototype genes. Finally, we discuss the evolutionary relationships between vertebrate sex chromosomes and the sex-determining genes Dmy/Dm-W and Sry, which evolved by neofunctionalization of Dmrt1 and Sox3, respectively, for sex determining function. We propose a coevolution model of sex determining gene and sex chromosome, in which undifferentiated sex chromosomes easily allow replacement of a sex-determining gene with another new one, while specialized sex chromosomes are restricted a particular sex-determining gene.

Molecular mechanisms of temperature-dependent sex determination in the context of ecological developmental biology

Temperature-dependent sex determination (TSD) is a prime example of phenotypic plasticity in that gonadal sex is determined by the temperature of the incubating egg. In the red-eared slider turtle (Trachemys scripta), the effect of temperature can be overridden by exogenous ligands, i.e., sex steroid hormones and steroid metabolism enzyme inhibitors, during the temperature-sensitive period (TSP) of development. Precisely how the physical signal of temperature is transduced into a biological signal that ultimately results in sex determination remains unknown. In this review, we discuss the sex determining pathway underlying TSD by focusing on two candidate sex determining genes, Forkhead box protein L2 (FoxL2) and Doublesex mab3- related transcription factor 1 (Dmrt1). They appear to be involved in transducing the environmental temperature signal into a biological signal that subsequently determines gonadal sex. FoxL2 and Dmrt1 exhibit gonad-typical patterns of expression in response to temperature during the TSP in the red-eared slider turtle. Further, the biologically active ligands regulate the expression of FoxL2 and Dmrt1 during development to modify gonad trajectory. The precise regulatory mechanisms of expression of these genes by temperature or exogenous ligands are not clear. However, the environment often influences developmental gene expression by altering the epigenetic status in regulatory regions. Here, we will discuss if the regulation of FoxL2 and Dmrt1 expression by environment is mediated through epigenetic mechanisms during development in species with TSD.

Sex and the singular DM domain: insights into sexual regulation, evolution and plasticity

Most animals reproduce sexually, but the genetic and molecular mechanisms that determine the eventual sex of each embryo vary remarkably. DM domain genes, which are related to the insect gene doublesex, are integral to sexual development and its evolution in many metazoans. Recent studies of DM domain genes reveal mechanisms by which new sexual dimorphisms have evolved in invertebrates and show that one gene, Dmrt1, was central to multiple evolutionary transitions between sex-determining mechanisms in vertebrates. In addition, Dmrt1 coordinates a surprising array of distinct cell fate decisions in the mammalian gonad and even guards against transdifferentiation of male cells into female cells in the adult testis.

Differential marker protein expression specifies rarefaction zone-containing human Adark spermatogonia

It is unclear whether the distinct nuclear morphologies of human Adark(Ad) and Apale(Ap) spermatogonia are manifestations of different stages of germ cell development or phases of the mitotic cycle, or whether they may reflect still unknown molecular differences. According to the classical description by Clermont, human dark type A spermatogonium (Ad) may contain one, sometimes two or three nuclear ‘vacuolar spaces’ representing chromatin rarefaction zones. These structures were readily discerned in paraffin sections of human testis tissue during immunohistochemical and immunofluorescence analyses and thus represented robust morphological markers for our study. While a majority of the marker proteins tested did not discriminate between spermatogonia with and without chromatin rarefaction zones, doublesex- and mab-3-related transcription factor (DMRT1), tyrosine kinase receptor c-Kit/CD117 (KIT) and proliferation-associated antigen Ki-67 (KI-67) appeared to be restricted to subtypes which lacked the rarefaction zones. Conversely, exosome component 10 (EXOSC10) was found to accumulate within the rarefaction zones, which points to a possible role of this nuclear domain in RNA processing.

Conditional ablation of Gata4 and Fog2 genes in mice reveals their distinct roles in mammalian sexual differentiation

Assembly of functioning testis and ovary requires a GATA4-FOG2 transcriptional complex. To define the separate roles for GATA4 and FOG2 proteins in sexual development of the testis we have ablated the corresponding genes in somatic gonadal cells. We have established that GATA4 is required for testis differentiation, for the expression of Dmrt1 gene, and for testis cord morphogenesis. While Sf1Cre-mediated excision of Gata4 permitted normal expression of most genes associated with embryonic testis development, gonadal loss of Fog2 resulted in an early partial block in male pathway and sex reversal. We have also determined that testis sexual differentiation is sensitive to the timing of GATA4 loss during embryogenesis. Our results now demonstrate that these two genes also have non-overlapping essential functions in testis development.

GATA transcription factors in the developing reproductive system

Previous work has firmly established the role for both GATA4 and FOG2 in the initial global commitment to sexual fate, but their (joint or individual) function in subsequent steps remained unknown. Hence, gonad-specific deletions of these genes in mice were required to reveal their roles in sexual development and gene regulation. The development of tissue-specific Cre lines allowed for substantial advances in the understanding of the function of GATA proteins in sex determination, gonadal differentiation and reproductive development in mice. Here we summarize the recent work that examined the requirement of GATA4 and FOG2 proteins at several critical stages in testis and ovarian differentiation. We also discuss the molecular mechanisms involved in this regulation through the control of Dmrt1 gene expression in the testis and the canonical Wnt/ß-catenin pathway in the ovary.

A novel ncRNA gene from mouse chromosome 5 trans-splices with Dmrt1 on chromosome 19

Dmrt1 (Dsx- and Mab3-related transcription factor-1), a conserved transcription factor in different phyla, is a key regulator in sex determination. Here, we report the novel ncRNA gene Dmr (Dmrt1-related gene), from mouse chromosome 5 that trans-splices with Dmrt1 from chromosome 19 to generate a Dmrt1 protein that lacks the C-terminus. Dmr is mouse and rat specific, and the surrounding genes are also conserved in both species. Dmr is alternatively spliced, and three isoforms, Dmr a, b and c, are detected in the testis. Further, Dmr serves mainly as a 3' UTR, promotes trans-splicing and down-regulates the Dmrt1 protein. These results suggest that Dmr might play a negative regulatory role for Dmrt1 in male sexual development.

Ochratoxin A: in utero exposure in mice induces adducts in testicular DNA

Ochratoxin A (OTA) is a nephrotoxin and carcinogen that is associated with Balkan endemic nephropathy and urinary tract tumors. OTA crosses the placenta and causes adducts in the liver and kidney DNA of newborns. Because the testis and kidney develop from the same embryonic tissue, we reasoned that OTA also may cause adducts transplacentally in the testis. We tested the hypothesis that acute exposure to OTA, via food and via exposure in utero , causes adducts in testicular DNA and that these lesions are identical to those that can be produced in the kidney and testis by the consumption of OTA. Adult mice received a single dose of OTA (from 0–1,056 µg/kg) by gavage. Pregnant mice received a single i.p. injection of OTA (2.5 mg/kg) at gestation day 17. DNA adducts were determined by 32P-postlabeling. Gavage-fed animals sacrificed after 48 hours accumulated OTA in kidney and testis and showed DNA adducts in kidney and testis. Some OTA metabolites isolated from the tissues were similar in both organs (kidney and testis). The litters of mice exposed prenatally to OTA showed no signs of overt toxicity. However, newborn and 1-month old males had DNA adducts in kidney and testis that were chromatographically similar to DNA adducts observed in the kidney and testis of gavage-fed adults. One adduct was identified previously as C8-dG-OTA adduct by LC MS/MS. No adducts were observed in males from dams not exposed to OTA. Our findings that in utero exposure to OTA causes adducts in the testicular DNA of male offspring support a possible role for OTA in testicular cancer.

Doublesex- and Mab-3-related transcription factor-1 repression of aromatase transcription, a possible mechanism favoring the male pathway in tilapia

Doublesex- and Mab-3-related transcription factor-1 (Dmrt1) is an important transcription factor implicated in early testicular differentiation in vertebrates, but its target genes are largely unknown. In the Nile tilapia, estrogen is the natural inducer of ovarian differentiation. Our recent studies have shown that Forkhead-l2 up-regulated transcription of the Cyp19a1a gene (aromatase) in the gonads in a female-specific manner. However, the upstream factor(s) down-regulating Cyp19a1a expression during testicular differentiation remains unclear. In the present study, we used in vitro (promoter analysis) and in vivo (transgenesis and in situ hybridization) approaches to examine whether Dmrt1 inhibits Cyp19a1a's transcriptional activity. The in vitro analysis using luciferase assays revealed that Dmrt1 repressed basal as well as Ad4BP/SF-1-activated Cyp19a1a transcription in HEK 293 cells. Luciferase assays with various deletions of Dmrt1 also showed that the Doublesex and Mab-3 domain is essential for the repression. In vitro-translated Dmrt1 and the nuclear extract from tilapia testis could directly bind to the palindrome sequence ACATATGT in the Cyp19a1a promoter, as determined by EMSAs. Transgenic overexpression of Dmrt1 in XX fish resulted in decreased aromatase gene expression, reduced serum estradiol-17beta levels, retardation of the ovarian cavity's development, varying degrees of follicular degeneration, and even a partial to complete sex reversal. Our results indicate that aromatase is one of the targets of Dmrt1. Dmrt1 suppresses the female pathway by repressing aromatase gene transcription and estrogen production in the gonads of tilapia and possibly other vertebrates.

Gender-dependent differences in the incidence of ochratoxin A-induced neural tube defects in the Pdn/Pdn mouse

Genetic polydactyly/arhinencephaly mouse embryo, Pdn/Pdn, exhibits suppression of Gli3 gene expression. Ochratoxin A (OTA) is a teratogen that causes neural tube defects (NTD) in mice. We investigated gender-dependent differences in the incidence of NTD induced by OTA in the Pdn/Pdn mouse. After administering 2 mg/kg OTA to Pdn/+ female mice, mated with Pdn/+ males, on day 7.5 of gestation, we examined the genotypes, sex and NTD of fetuses on day 18. Non-treated Pdn/Pdn had a 15.8% risk of NTD, and all NTD fetuses were female. When Pdn/Pdn embryos were exposed to OTA, the incidence of NTD increased to 16 (51.6%) of 31 Pdn/Pdn fetuses, and 10 (71.4%) of 14 male Pdn/Pdn fetuses exhibited NTD. From these results, it was speculated that NTD in OTA-treated male Pdn/Pdn were due to the synergistic effect between depressed Gli3 and altered sex-correlated gene expression from OTA treatment. After treatment with OTA, the embryos were recovered on day 9 and gene expressions, which were correlated with Gli3, telencephalic morphogenesis, formation of gonadal anlage, and gender-dependent differentiation were investigated. From real-time polymerase chain reaction analysis results, it was suggested that the manifestation of NTD in the male OTA-treated Pdn/Pdn might be due to the complicated altered gene expressions among Gli3, Wnt7b, Wnt8b, Fez1, Barx1, Lim1, Dmrt1, Igf1, Fog2, Dax1 and Sox9, and in particular, upregulation and gender-dependent difference in Barx1 and gender-dependent difference in Sox9 gene expressions might be noteworthy findings.

Characterisation of ATRX, DMRT1, DMRT7 and WT1 in the platypus (Ornithorhynchus anatinus)

One of the most puzzling aspects of monotreme reproductive biology is how they determine sex in the absence of the SRY gene that triggers testis development in most other mammals. Although monotremes share a XX female/XY male sex chromosome system with other mammals, their sex chromosomes show homology to the chicken Z chromosome, including the DMRT1 gene, which is a dosage-dependent sex determination gene in birds. In addition, monotremes feature an extraordinary multiple sex chromosome system. However, no sex determination gene has been identified as yet on any of the five X or five Y chromosomes and there is very little knowledge about the conservation and function of other known genes in the monotreme sex determination and differentiation pathway. We have analysed the expression pattern of four evolutionarily conserved genes that are important at different stages of sexual development in therian mammals. DMRT1 is a conserved sex-determination gene that is upregulated in the male developing gonad in vertebrates, while DMRT7 is a mammal-specific spermatogenesis gene. ATRX, a chromatin remodelling protein, lies on the therian X but there is a testis-expressed Y-copy in marsupials. However, in monotremes, the ATRX orthologue is autosomal. WT1 is an evolutionarily conserved gene essential for early gonadal formation in both sexes and later in testis development. We show that these four genes in the adult platypus have the same expression pattern as in other mammals, suggesting that they have a conserved role in sexual development independent of genomic location.