Male specific expression suggests role of DMRT1 in human sex determination

Genome-wide identification, phylogeny and expressional profile of the Dmrt gene family in Chinese sturgeon (Acipenser sinensis)

Chinese sturgeon Dmrt gene family was identified and characterized for the first time. A total of 5 putative Dmrt genes were identified. The gene structure, conserved protein domain and the phylogenetic relationship of Dmrt gene family were systematically analyzed. The expressed profile of Chinese sturgeon Dmrt genes in gonad, pituitary and hypothalamus in the male and female were investigated. The results indicated that the accumulation of Dmrt genes was involved in different tissues, and the expression profile also differed among each Dmrt genes. ASDmrt1A, ASDmrt2, ASDmrt3, and ASDmrtA1 were highly expressed in the testis in comparison with other tissue. This result showed that ASDmrt1A, ASDmrt2, ASDmrt3, and ASDmrtA1 played an important role in the development of testicle, and may be useful tool in distinguishing between male and female of Chinese sturgeon. Our study will provide a basis for additional analyses of Chinese sturgeon Dmrt genes. This systematic analysis provided a foundation for further functional characterization of Dmrt genes with an aim of study of Chinese sturgeon Dmrt gene family.

Application of CRISPR/Cas Technology in Spermatogenesis Research and Male Infertility Treatment

As the basis of animal reproductive activity, normal spermatogenesis directly determines the efficiency of livestock production. An in-depth understanding of spermatogenesis will greatly facilitate animal breeding efforts and male infertility treatment. With the continuous development and application of gene editing technologies, they have become valuable tools to study the mechanism of spermatogenesis. Gene editing technologies have provided us with a better understanding of the functions and potential mechanisms of action of factors that regulate spermatogenesis. This review summarizes the applications of gene editing technologies, especially CRISPR/Cas9, in deepening our understanding of the function of spermatogenesis-related genes and disease treatment. The problems of gene editing technologies in the field of spermatogenesis research are also discussed.

DMRT1 gene disruption alone induces incomplete gonad feminization in chicken

Compared with the well-described XY sex determination system in mammals, the avian ZW sex determination system is poorly understood. Knockdown and overexpression studies identified doublesex and mab-3-related transcription factor 1 (DMRT1) as the testis-determining gene in chicken. However, the detailed effects of DMRT1 gene disruption from embryonic to adult development are not clear. Herein, we have generated DMRT1-disrupted chickens using the clustered regularly interspaced short palindromic repeats-associated protein 9 system, followed by an analysis of physiological, hormonal, and molecular changes in the genome-modified chickens. In the early stages of male chicken development, disruption of DMRT1 induced gonad feminization with extensive physiological and molecular changes; however, functional feminine reproductivity could not be implemented with disturbed hormone synthesis. Subsequent RNA-sequencing analysis of the DMRT1-disrupted chicken gonads revealed gene networks, including several novel genes linearly and non-linearly associated with DMRT1, which are involved in gonad feminization. By comparing the gonads of wild type with the genome-modified chickens, a set of genes were identified that is involved in the ZW sex determination system independent of DMRT1. Our results extend beyond the Z-dosage hypothesis to provide further information about the avian ZW sex determination system and epigenetic effects of gonad feminization.

Comparative Genomics Studies on the dmrt Gene Family in Fish

Doublesex and mab-3-related transcription factor (dmrt) genes are widely distributed across various biological groups and play critical roles in sex determination and neural development. Here, we applied bioinformatics methods to exam cross-species changes in the dmrt family members and evolutionary relationships of the dmrt genes based on genomes of 17 fish species. All the examined fish species have dmrt1–5 while only five species contained dmrt6. Most fish harbored two dmrt2 paralogs (dmrt2a and dmrt2b), with dmrt2b being unique to fish. In the phylogenetic tree, 147 DMRT are categorized into eight groups (DMRT1–DMRT8) and then clustered in three main groups. Selective evolutionary pressure analysis indicated purifying selections on dmrt1–3 genes and the dmrt1–3–2(2a) gene cluster. Similar genomic conservation patterns of the dmrt1–dmrt3–dmrt2(2a) gene cluster with 20-kb upstream/downstream regions in fish with various sex-determination systems were observed except for three regions with remarkable diversity. Synteny analysis revealed that dmrt1, dmrt2a, dmrt2b, and dmrt3–5 were relatively conserved in fish during the evolutionary process. While dmrt6 was lost in most species during evolution. The high conservation of the dmrt1–dmrt3–dmrt2(2a) gene cluster in various fish genomes suggests their crucial biological functions while various dmrt family members and sequences across fish species suggest different biological roles during evolution. This study provides a molecular basis for fish dmrt functional analysis and may serve as a reference for in-depth phylogenomics.

Integration and reanalysis of transcriptomics and methylomics data derived from blood and testis tissue of men with 47,XXY Klinefelter syndrome indicates the primary involvement of Sertoli cells in the testicular pathogenesis

Klinefelter syndrome (KS; 47,XXY) is the most common sex chromosomal anomaly and causes a multitude of symptoms. Often the most noticeable symptom is infertility caused by azoospermia with testicular histology showing hyalinization of tubules, germ cells loss, and Leydig cell hyperplasia. The germ cell loss begins early in life leading to partial hyalinization of the testis at puberty, but the mechanistic drivers behind this remain poorly understood. In this systematic review, we summarize the current knowledge on developmental changes in the cellularity of KS gonads supplemented by a comparative analysis of the fetal and adult gonadal transcriptome, and blood transcriptome and methylome of men with KS. We identified a high fraction of upregulated genes that escape X-chromosome inactivation, thus supporting previous hypotheses that these are the main drivers of the testicular phenotype in KS. Enrichment analysis showed overrepresentation of genes from the X- and Y-chromosome and testicular transcription factors. Furthermore, by re-evaluation of recent single cell RNA-sequencing data originating from adult KS testis, we found novel evidence that the Sertoli cell is the most affected cell type. Our results are consistent with disturbed cross-talk between somatic and germ cells in the KS testis, and with X-escapee genes acting as mediators.

Genetic Landscape of Nonobstructive Azoospermia and New Perspectives for the Clinic

Nonobstructive azoospermia (NOA) represents the most severe expression of male infertility, involving around 1% of the male population and 10% of infertile men. This condition is characterised by the inability of the testis to produce sperm cells, and it is considered to have an important genetic component. During the last two decades, different genetic anomalies, including microdeletions of the Y chromosome, karyotype defects, and missense mutations in genes involved in the reproductive function, have been described as the primary cause of NOA in many infertile men. However, these alterations only explain around 25% of azoospermic cases, with the remaining patients showing an idiopathic origin. Recent studies clearly suggest that the so-called idiopathic NOA has a complex aetiology with a polygenic inheritance, which may alter the spermatogenic process. Although we are far from a complete understanding of the molecular mechanisms underlying NOA, the use of the new technologies for genetic analysis has enabled a considerable increase in knowledge during the last years. In this review, we will provide a comprehensive and updated overview of the genetic basis of NOA, with a special focus on the possible application of the recent insights in clinical practice.

Testis Development

Production of sperm and androgens is the main function of the testis. This depends on normal development of both testicular somatic cells and germ cells. A genetic program initiated from the Y chromosome gene sex-determining region Y (SRY) directs somatic cell specification to Sertoli cells that orchestrate further development. They first guide fetal germ cell differentiation toward spermatogenic destiny and then take care of the full service to spermatogenic cells during spermatogenesis. The number of Sertoli cells sets the limits of sperm production. Leydig cells secrete androgens that determine masculine development. Testis development does not depend on germ cells; that is, testicular somatic cells also develop in the absence of germ cells, and the testis can produce testosterone normally to induce full masculinization in these men. In contrast, spermatogenic cell development is totally dependent on somatic cells. We herein review germ cell differentiation from primordial germ cells to spermatogonia and development of the supporting somatic cells. Testicular descent to scrota is necessary for normal spermatogenesis, and cryptorchidism is the most common male birth defect. This is a mild form of a disorder of sex differentiation. Multiple genetic reasons for more severe forms of disorders of sex differentiation have been revealed during the last decades, and these are described along with the description of molecular regulation of testis development.

Effect of low sperm quality on progeny: a study on zebrafish as model species

Nowadays a decrease tendency in human sperm quality has been reported mainly in developed countries. Reproductive technologies have been very valuable in achieving successful pregnancies with low quality sperm samples. However, considering that spermatozoa molecular contribution is increasingly important in recent studies, it is crucial to study whether fertilization with low sperm quality could leave a molecular mark on progeny. This study explores the consequences that fertilization with low sperm quality may have on progeny, using zebrafish as a model. Good and bad breeders were established attending to sperm quality analyses and were individually tracked. Significant differences in fertilization and malformation rates were obtained in progenies between high and low quality sperm samples. Moreover an altered miR profile was found in the progenies of bad zebrafish breeders (upregulation of miR-141 and miR -122 in 24 hpf embryos) and as a consequence, some of their targets involved in male sex development such as dmrt1, suffered downregulation. Our results indicate that fertilizing with high sperm quality samples becomes relevant from a new perspective: to avoid molecular alterations in the progeny that could remain masked and therefore produce unexpected consequences in it.

Genomic organization and sexually dimorphic expression of the Dmrt1 gene in largemouth bass (Micropterus salmoides)

Doublesex and Mab-3 related transcription factor (Dmrt) genes play important roles in the process of sex determination and differentiation. In this study, a Dmrt1 gene open reading frame sequence was obtained from the gonadal transcriptome data of largemouth bass (Micropterus salmoides), and identified by cloning and sequencing. The ORF of Dmrt1 is 900 bp long, encodes 298 amino acids, and contains the DM region which is characteristic of Dmrt1. Full gDNA sequence of Dmrt1 was composed of five exons and four introns. RT-PCR and Q-PCR analysis of Dmrt1 were conducted in eight tissues and three developmental stages of mature male and female individuals. In situ hybridization was used to locate the expression of Dmrt1 in the testis and ovary of largemouth bass. The results showed that Dmrt1 was highly expressed in the testis of mature fish, but only weakly expressed in other tissues such as heart, liver, and brain, and exhibited gender dimorphism in the gonads of male and female fish at different stages. Furthermore, the expression level in female fish was very low and decreased gradually with ovary maturation. In situ hybridization indicated positive signals were found in early oocytes, but not in mature oocytes, while strong positive signals were found in all types of mature testis cells. The study showed that the sequence and structure of Dmrt1 were highly conserved and exhibited significant gender dimorphism in largemouth bass, as in other fish species. It is suggested that Dmrt1 plays an important role in sex determination and differentiation in largemouth bass.

Diagnostic Application of Targeted Next-Generation Sequencing of 80 Genes Associated with Disorders of Sexual Development

Disorders of sexual development (DSD) are estimated to occur in 1 of 4500 births. Since the genetic etiology of DSD is highly heterogeneous, obtaining a definitive molecular diagnosis by single gene test is challenging. Utilizing a high-throughput sequencing upfront is proposed as an efficient approach to aid in the diagnosis. This study aimed to examine the diagnostic yield of next-generation sequencing in DSD. 32 DSD patients that previously received clinical examinations and single gene tests were selected, with or without a diagnosis. Prior single gene tests were masked, and then samples went through targeted next-generation sequencing of 80 genes from which the diagnostic yield was assessed. A likely diagnosis, with pathogenic or likely pathogenic variants identified, was obtained from nine of the 32 patients (i.e., 28.1%, versus 10% by single gene tests). In another five patients (15.6%), variants of uncertain significance were found. Among 18 variants identified (i.e., 17 single nucleotide variants and one small deletion), eight had not been previously reported. This study supports the notion that next-generation sequencing can be an efficient tool in the clinical diagnosis and variant discovery in DSD.

Evolutionarily conserved, DMRT1, encodes alternatively spliced transcripts and shows dimorphic expression during gonadal differentiation in the lizard, Calotes versicolor

An orthologue of Dmrt1 has been cloned and characterized in the lizard, Calotes versicolor (CvDmrt1). CvDmrt1 encodes alternatively spliced transcripts in genital ridge during gonadal differentiation and in adult testis. Its expression in genital ridge initiates from day 3 and is restricted to mesenchymal cells, which differentiate into the Sertoli cells. Lack of expression in the coelomic epithelium of GR shows that CvDmrt1 expression occurs only in the testicular pathway, and that the Sertoli and granulosa cells in GR may originate from different primordia. From day 25 onwards, the expression shifts majorly towards the germ cells both in testis and ovary. Thus its role in sexual differentiation of C. versicolor, which lacks CSD and TSD, is well documented.

Molecular characterization and expression pattern of dmrt1 in the immature Chinese sturgeon Acipenser sinensis

In this study, the cDNA of dmrt1 gene from the Chinese sturgeon Acipenser sinensis was isolated and its expression pattern was characterized in different tissues of immature A. sinensis. By real-time quantitative PCR (qrtPCR) analysis, the A. sinensis dmrt1 mRNA was detected mainly in gonad and with a higher level in the testis than the ovary, especially in 3 and 4 year-old samples. This indicated that the dmrt1 expression exhibited gradual testis specificity with development. The subcellular localization analysis indicated that the Dmrt1 protein exists only in germ cells and not in somatic cells. These results suggest that A. sinensis dmrt1 might be a highly specific sex differentiation gene for testis development and spermatogenesis.

A Novel Female-Specific and Sexual Reproduction-Associated Dmrt Gene Discovered in the Stony Coral, Euphyllia ancora

Transcription factors encoded by the Dmrt gene family regulate multiple aspects of animal reproduction. Most studies investigating the Dmrt gene family were conducted in model organisms from bilateral species, with a particular emphasis on gene function in male sex determination. It is still unclear whether the E. ancora Dmrt (EaDmrt) genes found in basal metazoans such as cnidarians share similar characteristics with orthologs in other metazoans. In this study, seven full Dmrt gene transcript sequences for a gonochoric coral, Euphyllia ancora (phylum: Cnidaria; class: Anthozoa), were obtained through transcriptome data mining, RT-PCR analysis, rapid amplification of cDNA ends, and sequencing. These EaDmrts were subjected to quantitative assays measuring temporal and tissue-specific expression. Results demonstrated a unique gene expression pattern for EaDmrtE, which is enriched in female germ cells during the spawning season. Based on the phylogenetic analyses performed across the homologous Dmrt genes in metazoans, we found that the female-specific EaDmrtE gene is not related to the DM1 gene of Acropora spp. coral nor to Dmrt1 of vertebrates, which are involved in sexual reproduction, especially in sex determination (vertebrate Dmrt1). Additionally, high levels of EaDmrtE transcripts detected in unfertilized mature eggs are retained in newly formed zygotes but decrease during embryonic development. We suggest that the newly discovered gene may play a role in oogenesis and early embryogenesis as a maternal factor in corals. Therefore, the sexual reproduction-associated Dmrt gene(s) should have arisen in cnidarians and might have evolved multiple times in metazoans.

Pathogenesis of germ cell neoplasia in testicular dysgenesis and disorders of sex development

Development of human gonads is a sex-dimorphic process which evolved to produce sex-specific types of germ cells. The process of gonadal sex differentiation is directed by the action of the somatic cells and ultimately results in germ cells differentiating to become functional gametes through spermatogenesis or oogenesis. This tightly controlled process depends on the proper sequential expression of many genes and signalling pathways. Disturbances of this process can be manifested as a large spectrum of disorders, ranging from severe disorders of sex development (DSD) to - in the genetic male - mild reproductive problems within the testicular dysgenesis syndrome (TDS), with large overlap between the syndromes. These disorders carry an increased but variable risk of germ cell neoplasia. In this review, we discuss the pathogenesis of germ cell neoplasia associated with gonadal dysgenesis, especially in individuals with 46,XY DSD. We summarise knowledge concerning development and sex differentiation of human gonads, with focus on sex-dimorphic steps of germ cell maturation, including meiosis. We also briefly outline the histopathology of germ cell neoplasia in situ (GCNIS) and gonadoblastoma (GDB), which are essentially the same precursor lesion but with different morphological structure dependent upon the masculinisation of the somatic niche. To assess the risk of germ cell neoplasia in different types of DSD, we have performed a PubMed search and provide here a synthesis of the evidence from studies published since 2006. We present a model for pathogenesis of GCNIS/GDB in TDS/DSD, with the risk of malignancy determined by the presence of the testis-inducing Y chromosome and the degree of masculinisation. The associations between phenotype and the risk of neoplasia are likely further modulated in each individual by the constellation of the gene polymorphisms and environmental factors.

Rare double sex and mab-3-related transcription factor 1 regulatory variants in severe spermatogenic failure

The double sex and mab-3-related transcription factor 1 (DMRT1) gene has long been linked to sex-determining pathways across vertebrates and is known to play an essential role in gonadal development and maintenance of spermatogenesis in mice. In humans, the genomic region harboring the DMRT gene cluster has been implicated in disorders of sex development and recently DMRT1 deletions were shown to be associated with non-obstructive azoospermia (NOA). In this work, we have employed different methods to screen a cohort of Portuguese NOA patients for DMRT1 exonic insertions and deletions [by multiplex ligation probe assay (MLPA); n = 68] and point mutations (by Sanger sequencing; n = 155). We have found three novel patient-specific non-coding variants in heterozygosity that were absent from 357 geographically matched controls. One of these is a complex variant with a putative regulatory role (c.-223_-219CGAAA>T), located in the promoter region within a conserved sequence involved in Dmrt1 repression. Moreover, while DMRT1 domains are highly conserved across vertebrates and show reduced levels of diversity in human populations, two rare synonymous substitutions (rs376518776 and rs34946058) and two rare non-coding variants that potentially affect DMRT1 expression and splicing (rs144122237 and rs200423545) were overrepresented in patients when compared with 376 Portuguese controls (301 fertile and 75 normozoospermic). Overall our previous and present results suggest a role of changes in DMRT1 dosage in NOA potentially also through a process of gene misregulation, even though DMRT1 deleterious variants seem to be rare.

High-density linkage mapping aided by transcriptomics documents ZW sex determination system in the Chinese mitten crab Eriocheir sinensis

The sex determination system in crabs is believed to be XY-XX from karyotypy, but centromeres could not be identified in some chromosomes and their morphology is not completely clear. Using quantitative trait locus mapping of the gender phenotype, we revealed a ZW-ZZ sex determination system in Eriocheir sinensis and presented a high-density linkage map covering ~98.5% of the genome, with 73 linkage groups corresponding to the haploid chromosome number. All sex-linked markers in the family we used were located on a single linkage group, LG60, and sex linkage was confirmed by genome-wide association studies (GWAS). Forty-six markers detected by GWAS were heterozygous and segregated only in the female parent. The female LG60 was thus the putative W chromosome, with the homologous male LG60 as the Z chromosome. The putative Z and W sex chromosomes were identical in size and carried many homologous loci. Sex ratio (5:1) skewing towards females in induced triploids using unrelated animals also supported a ZW-ZZ system. Transcriptome data were used to search for candidate sex-determining loci, but only one LG60 gene was identified as an ankyrin-2 gene. Double sex- and mab3-related transcription factor 1 (Dmrt1), a Z-linked gene in birds, was located on a putative autosome. With complete genome sequencing and transcriptomic data, more genes on putative sex chromosomes will be characterised, thus leading towards a comprehensive understanding of the sex determination and differentiation mechanisms of E. sinensis, and decapod crustaceans in general.

Characterization of the Dmrt1 gene in the black rockfish Sebastes schlegeli revealed a remarkable sex-dimorphic expression

The Dmrt genes encode a large family of transcription factors with a conserved zinc finger-like DNA-binding DM domain. The function of Dmrt1, one of the family members, in sexual development has been well studied in invertebrates and vertebrates. In the present study, the full-length cDNA of Dmrt1 was isolated from the testis of Sebastes schlegeli. The full-length cDNA of S. schlegeli Dmrt1 (SsDmrt1) was 1,587 bp and contained a 189-bp 5' UTR, a 489-bp 3' UTR and a 909-bp open reading frame, which encoded 302 amino acids with a conserved DM domain and an male-specific motif domain. Phylogenetic analysis showed the evolutionary relationships of SsDmrt1 with other known Dmrt genes in fish and tetrapods. Several transcriptional factor-binding sites in the 5' promoter were identified that might regulate SsDmrt1 expression. Quantitative real-time PCR analysis indicated that SsDmrt1 was expressed in all of the inspected larval developmental stages from 1 to 35 days after birth and that the level of expression gradually decreased. The expression of SsDmrt1 in adult gonads was sexually dimorphic with extremely high expression in the testis, but very low expression in the ovary. No expression was detected in other tissues. Using in situ hybridization, we demonstrated that SsDmrt1 was specifically expressed in the germ cells of both the testis and the ovary. Thus, our results suggest that SsDmrt1 may have an important role in the differentiation of both the testis and the ovary of S. schlegeli.

DMRT1 mutations are rarely associated with male infertility

OBJECTIVE

To study a potential association between male infertility and DMRT1 mutations.

DESIGN

Retrospective sequencing study.

SETTING

University hospital.

PATIENT(S)

171 patients with cryptozoospermia (sperm concentration<0.1 million/mL, n=40) or nonobstructive azoospermia (n=131), and 215 normozoospermic controls.

INTERVENTION(S)

Sequence analysis of DMRT1.

MAIN OUTCOME MEASURE(S)

Identification of rare variants in DMRT1 that are associated with male infertility.

RESULT(S)

In total, we detected four putative pathogenic mutations in six patients (3.5%) and less frequently in two controls (0.9%).

CONCLUSION(S)

Point mutations of DMRT1 may be rarely associated with male infertility.

Over-expression of DMRT1 induces the male pathway in embryonic chicken gonads

DMRT1 encodes a conserved transcription factor with an essential role in gonadal function. In the chicken, DMRT1 in located on the Z sex chromosome and is currently the best candidate master regulator of avian gonadal sex differentiation. We previously showed that knockdown of DMRT1 expression during the period of sexual differentiation induces feminisation of male embryonic chicken gonads. This gene is therefore necessary for proper testis development in the chicken. However, whether it is sufficient to induce testicular differentiation has remained unresolved. We show here that over-expression of DMRT1 induces male pathway genes and antagonises the female pathway in embryonic chicken gonads. Ectopic DMRT1 expression in female gonads induces localised SOX9 and AMH expression. It also induces expression of the recently identified Z-linked male factor, Hemogen (HEMGN). Masculinised gonads show evidence of cord-like structures and retarded female-type cortical development. Furthermore, expression of the critical feminising enzyme, aromatase, is reduced in the presence of over-expressed DMRT1. These data indicate that DMRT1 is an essential sex-linked regulator of gonadal differentiation in avians, and that it likely acts via a dosage mechanism established through the lack of global Z dosage compensation in birds.

Expanding roles for the evolutionarily conserved Dmrt sex transcriptional regulators during embryogenesis

Dmrt genes encode a large family of transcription factors characterized by the presence of a DM domain, an unusual zinc finger DNA binding domain. While Dmrt genes are well known for their important role in sexual development in arthropodes, nematodes and vertebrates, several new findings indicate emerging functions of this gene family in other developmental processes. Here, we provide an overview of the evolution, structure and mechanisms of action of Dmrt genes. We summarize recent findings on their function in sexual regulation and discuss more extensively the role played by these proteins in somitogenesis and neural development.

A Wt1-Dmrt1 transgene restores DMRT1 to sertoli cells of Dmrt1(-/-) testes: a novel model of DMRT1-deficient germ cells

DMRT1 is an evolutionarily conserved transcriptional factor expressed only in the postnatal testis, where it is produced in Sertoli cells and germ cells. While deletion of Dmrt1 in mice demonstrated it is required for postnatal testis development and fertility, much is still unknown about its temporal- and cell-specific functions. This study characterized a novel mouse model of DMRT1-deficient germ cells that was generated by breeding Dmrt1-null (Dmrt1(-/-)) mice with Wt1-Dmrt1 transgenic (Dmrt1(+/-;tg)) mice, which express a rat Dmrt1 cDNA in gonadal supporting cells by directing it from the Wilms tumor 1 locus in a yeast artificial chromosome transgene. Like Dmrt1(-/-) mice, male Dmrt1(-/-) transgenic mice (Dmrt1(-/-;tg)) were infertile, while female mice were fertile. Immunohistochemistry and Western blot analysis showed transgenic DMRT1 expressed in supporting cells of the newborn gonads of both sex and in Sertoli cells of the testis afterbirth. Sertoli cells were evaluated by electron microscopy, revealing that maturation of Dmrt1(-/-;tg) Sertoli cells was incomplete. Morphological analysis of testes from 42-day-old mice showed that, compared to Dmrt1(-/-) mice, Dmrt1(-/-;tg) mice have improved seminiferous tubule structure, with lumens present in many. Immunohistochemistry of the polarity markers ESPIN and NECTIN-2 showed that DMRT1 in Sertoli cells is required for NECTIN-2 expression and influences organization of ectoplasmic specializations. Further functional analyses of the transgene on a Dmrt1(-/-) background showed that it did not rescue the decrease in Dmrt1(-/-) testis size, but when expressed on a wild-type background, exogenous DMRT1 prevented the normal age-related decline in testis size and enhanced sperm progressive motility. The studies suggest that DMRT1 in Sertoli cells regulates tubule morphology, spermatogenesis, and sperm function via its effects on Sertoli cell maturation and polarity. Furthermore, expression and function of transgenic DMRT1 in Sertoli cells establishes a novel mouse model of DMRT1-deficient germ cells generated by breeding Dmrt1-null mice with Wt1-Dmrt1 transgenic mice (rescue; Dmrt1(-/-;tg)).

Molecular cloning and expression profile of sex-specific genes, Figla and Dmrt1, in the protogynous hermaphroditic fish, Halichoeres poecilopterus

The genes folliculogenesis specific basic helix-loop-helix (facor in the germline alpha, Figla) and doublesex and mab-3 related transcription factor 1 (Dmrt1) are female- and male-specific genes that play key roles in sex differentiation. To obtain a better understanding of the molecular mechanisms underlying female-to-male sex change, we cloned the cDNAs of these genes from an ovary and a testis of the protogynus wrasse, Halichoeres poecilopterus. This fish has two isoforms of Dmrt1, Dmrt1a and Dmrt1b, caused by an alternative splicing. The Dmrt1b has an insertion of three nucleotides (CAG) in the open reading frame. Figla and Dmrt1 displayed gonadal-specific expression and abundant in the ovaries and in the testes, respectively. In particular, levels of Figla expression in the ovaries were higher in the spawning season than in the non-spawning season. Once sex change began, Figla mRNA decreased and Dmrt1 mRNA increased with progression of oocyte degeneration and spermatogenesis. These expression levels were maintained until the completion of the sex change. Low Figla and high Dmrt1 were also observed in testes of primary males, which functioned as a gonochoristic male throughout its life span in this wrasse. The results of this study suggest that these genes may regulate the gonadal transition from ovary to testis by the same mechanism as that of formation and maintenance of the primary testis in H. poecilopterus.

Analysis of meiosis regulators in human gonads: a sexually dimorphic spatio-temporal expression pattern suggests involvement of DMRT1 in meiotic entry

The mitosis-meiosis switch is a key event in the differentiation of germ cells. In humans, meiosis is initiated in fetal ovaries, whereas in testes meiotic entry is inhibited until puberty. The purpose of this study was to examine the expression pattern of meiosis regulators in human gonads and to investigate a possible role of DMRT1 in the regulation of meiotic entry. The expression pattern of DMRT1, STRA8, SCP3, DMC1, NANOS3, CYP26B1 and NANOS2 was investigated by RT-PCR and immunohistochemistry in a series of human testis samples from fetal life to adulthood, and in fetal ovaries. DMRT1 was expressed in testes throughout development but with marked spatio-temporal changes. At the early fetal period of 8-20 gestational weeks (GW) and at infantile mini-puberty, DMRT1 was predominantly expressed in Sertoli cells, whereas at later stages of gestation (22-40 GW), during childhood and in post-pubertal testes, DMRT1 was most abundant in spermatogonia, except in the A-dark type. In fetal ovaries, DMRT1 was detected in oogonia and oocytes until 20 GW, but was completely down-regulated following meiotic entry. STRA8, SCP3 and DMC1 were expressed mainly in oocytes and spermatogonia in accordance with their role in initiation and progression of meiosis. The putative meiosis inhibitors, CYP26B1 and NANOS2, were primarily expressed in Leydig cells and spermatocytes, respectively. In conclusion, the expression pattern of the investigated meiotic regulators is largely conserved in the human gonads compared with rodents, but with some minor differences, such as a stable expression of CYP26B1 in human fetal ovaries. The sexually dimorphic expression pattern of DMRT1 indicates a similar role in the mitosis-meiosis switch in human gonads as previously demonstrated in mice. The biological importance of the changes in expression of DMRT1 in Sertoli cells remains to be established, but it is consistent with DMRT1 reinforcing the inhibition of meiosis in the testis.

Mammalian sex determination—insights from humans and mice

Disorders of sex development (DSD) are congenital conditions in which the development of chromosomal, gonadal, or anatomical sex is atypical. Many of the genes required for gonad development have been identified by analysis of DSD patients. However, the use of knockout and transgenic mouse strains have contributed enormously to the study of gonad gene function and interactions within the development network. Although the genetic basis of mammalian sex determination and differentiation has advanced considerably in recent years, a majority of 46,XY gonadal dysgenesis patients still cannot be provided with an accurate diagnosis. Some of these unexplained DSD cases may be due to mutations in novel DSD genes or genomic rearrangements affecting regulatory regions that lead to atypical gene expression. Here, we review our current knowledge of mammalian sex determination drawing on insights from human DSD patients and mouse models.

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 differences in behavioral decision-making and the modulation of shared neural circuits

Animals prioritize behaviors according to their physiological needs and reproductive goals, selecting a single behavioral strategy from a repertoire of possible responses to any given stimulus. Biological sex influences this decision-making process in significant ways, differentiating the responses animals choose when faced with stimuli ranging from food to conspecifics. We review here recent work in invertebrate models, including C. elegans, Drosophila, and a variety of insects, mollusks and crustaceans, that has begun to offer intriguing insights into the neural mechanisms underlying the sexual modulation of behavioral decision-making. These findings show that an animal's sex can modulate neural function in surprisingly diverse ways, much like internal physiological variables such as hunger or thirst. In the context of homeostatic behaviors such as feeding, an animal's sex and nutritional status may converge on a common physiological mechanism, the functional modulation of shared sensory circuitry, to influence decision-making. Similarly, considerable evidence suggests that decisions on whether to mate or fight with conspecifics are also mediated through sex-specific neuromodulatory control of nominally shared neural circuits. This work offers a new perspective on how sex differences in behavior emerge, in which the regulated function of shared neural circuitry plays a crucial role. Emerging evidence from vertebrates indicates that this paradigm is likely to extend to more complex nervous systems as well. As men and women differ in their susceptibility to a variety of neuropsychiatric disorders affecting shared behaviors, these findings may ultimately have important implications for human health.

Dimorphic expression of various transcription factor and steroidogenic enzyme genes during gonadal ontogeny in the air-breathing catfish, Clarias gariepinus

In the present study the expression of 13 genes known to be involved in sex differentiation and steroidogenesis in catfish was analyzed during gonadal ontogeny by quantitative real-time RT-PCR. Dmrt1 and sox9a showed exclusive expression in male gonads while ovarian aromatase (cyp19a1) and foxl2 were abundant in differentiating female gonads. Most of the genes related to steroidogenesis were expressed only after gonadal differentiation. However, genes coding for 3β-hydroxysteroid dehydrogenase (3β-hsd), 17α-hydroxylase/C17-20 lyase type 1 (cyp17) and steroidogenic acute regulatory protein (star) were barely detectable during gonadal differentiation. Ovarian aromatase, cyp19a1, which is responsible for estradiol-17β biosynthesis in females, was expressed very early in the undifferentiated gonads of catfish, around 30-40 days post hatch (dph). The steroidogenic enzyme, 11β-hydroxylase (cyp11b1) required for the production of 11-ketotestosterone (11-KT) was expressed only after differentiation of testis. These results suggest that estradiol-17β has a critical role in ovarian differentiation, while the role of 11-KT in testicular differentiation is doubtful. In conclusion, dimorphic expression of dmrt1 and sox9a in gonads during early development is required for testicular differentiation, and sex-specific expression of cyp19a1 and foxl2 in females plays a critical role in ovarian development. Our study reveals that the critical period of gonadal differentiation in catfish starts around 30-40 dph when sex-specific genes showed differential expression.

Aromatase is a direct target of FOXL2: C134W in granulosa cell tumors via a single highly conserved binding site in the ovarian specific promoter

Background

Granulosa cell tumors (GCT) of the ovary often express aromatase and synthesize estrogen, which in turn may influence their progression. Recently a specific point mutation (C134W) in the FOXL2 protein was identified in >94% of adult-type GCT and it is likely to contribute to their development. A number of genes are known to be regulated by FOXL2, including aromatase/CYP19A1, but it is unclear which are direct targets and whether the C134W mutation alters their regulation. Recently, it has been reported that FOXL2 forms a complex with steroidogenic factor 1 (SF-1) which is a known regulator of aromatase in granulosa cells.

Methodology/Principal Findings

In this work, the human GCT-derived cell lines KGN and COV434 were heterozygous and wildtype for the FOXL2:C134W mutation, respectively. KGN had abundant FOXL2 mRNA expression but it was not expressed in COV434. Expression of exogenous FOXL2:C134W in COV434 cells induced higher expression of a luciferase reporter for the ovarian specific aromatase promoter, promoter II (PII) (−516bp) than expression of wildtype FOXL2, but did not alter induction of a similar reporter for the steroidogenic acute regulatory protein (StAR) promoter (−1300bp). Co-immunoprecipitation confirmed that FOXL2 bound SF-1 and that it also bound its homologue, liver receptor homologue 1 (LRH-1), however, the C134W mutation did not alter these interactions or induce a selective binding of the proteins. A highly conserved putative binding site for FOXL2 was identified in PII. FOXL2 was demonstrated to bind the site by electrophoretic mobility shift assays (EMSA) and site-directed mutagenesis of this element blocked its differential induction by wildtype FOXL2 and FOXL2:C134W.

Conclusions/Significance

These findings suggest that aromatase is a direct target of FOXL2:C134W in adult-type GCT via a single distinctive and highly conserved binding site in PII and therefore provide insight into the pathogenic mechanism of this mutation.

In search of determinants: gene expression during gonadal sex differentiation

The diversity of inputs that guide sexual fate during development is both intriguing and daunting. In the field of fish biology, the study of sex determination is of great importance. For example, in aquaculture, sexually dimorphic growth rates and overall size leads to one sex being more marketable than the other. Moreover, for breeding purposes it is important to maintain balanced sex ratios. Furthermore, sex determination is sensitive to environmental factors, such as temperature and contaminants, which can lead to skewed sex ratios, intersexes and sterility in wild or farmed fish. The gonad is typically the first organ to exhibit morphological signs of sexual dimorphism and therefore is likely to be the primary organ system whose fate is controlled by the sex determination cues in many fish species. Additionally, the sexual fate of the gonad has been shown to fully or partially control organismal sex differentiation. Thus, understanding the genetic regulation of gonadal sex differentiation is critical in studies of fish sex determination. This review summarizes recent knowledge of genes expressed during gonadal sex differentiation in gonochoristic teleost fish. Three species are discussed, which serve as excellent model systems for probing teleost sex differentiation: the Oreochromis niloticus, Oryzias latipes and Danio rerio. The similarities and differences between gonadal gene expression in these three species and in comparison to mammals suggest conserved roles during vertebrate gonadal sex differentiation. In the future, it will be essential to develop tools to assay the function of genes expressed during gonadal sex differentiation in fish.

Genetic mechanisms underlying male sex determination in mammals

Genetic control of gonadal development proceeds through either the male or female molecular pathways, driving bipotential gonadal anlage differentiation into a testis or ovary. Antagonistic interactions between the 2 pathways determine the gonadal sex. Essentially sex determination is the enhancement of one of the 2 pathways according to genetic sex. Initially, Sry with other factors upregulates Sox9 expression in XY individuals. Afterwards the expression of Sox9 is maintained by a positive feedback loop with Fgf9 and prostaglandin D2 as well as by autoregulative ability of Sox9. If these factors reach high concentrations, then Sox9 and/or Fgf9 may inhibit the female pathway. Surprisingly, splicing, nuclear transport, and extramatrix proteins may be involved in sex determination. The male sex determination pathway switches on the expression of genes driving Sertoli cell differentiation. Sertoli cells orchestrate testicular differentiation. In the absence of Sry, the predomination of the female pathway results in the realization of a robust genetic program that drives ovarian differentiation.

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.

Expression pattern of dmrt4 from olive flounder (Paralichthys olivaceus) in adult gonads and during embryogenesis

The dmrt (doublesex and mab-3 related transcription factor) gene family comprises several transcription factors that share a conserved DM domain. Dmrt1 is considered to be involved in sexual development, but the precise function of other family members is unclear. In this study, we isolated genomic DNA and cDNA sequences of dmrt4, a member of the dmrt gene family, from olive flounder, Paralichthys olivaceus, through genome walking and real-time reverse transcriptase (RT)-PCR. Sequence analysis indicated that its genomic DNA contains two exons and one intron. A transcriptional factor binding sites prediction program identified a sexual development-related protein, Sox9 (Sry-like HMG box containing 9) in its 5' promoter. Protein alignment and phylogenetic analysis suggested that flounder Dmrt4 is closely related to tilapia Dmo (DM domain gene in ovary). The expression of dmrt4 in adult flounder was sexually dimorphic, as shown by real-time RT-PCR analysis, with strong expression in the testis but very weak expression in the ovary. Its expression was also strong in the brain and gill, but there was only weak or no expression at all in some of the other tissues tested of both sexes. During embryogenesis, its expression was detected in most developmental stages, although the level of expression was distinctive of the various stages. Whole mount in situ hybridization revealed that the dmrt4 was expressed in the otic placodes, forebrain, telencephalon and olfactory placodes of embryos at different developmental stages. These results will improve our understanding of the possible role of flounder dmrt4 in the development of the gonads, nervous system and sense organs.

Generation of antibodies against DMRT1 and DMRT4 of Oreochromis aurea and analysis of their expression profile in Oreochromis aurea tissues

Sex determination is composed of somatic and germ-line sex differentiation hierarchies whose interaction is poorly understood. A single gene known to control somatic sex determination, the DM-domain containing (Doublesex/Mab-3 DNA-binding motif) gene, is highly conserved across species. Vertebrate DMRT1 (DM-related transcription factor 1) expression occurs predominantly in the testis. Here, however, isolated two distinct DM-domain cDNA from Oreochromis aurea ovary and testis have been named DMRT4 (DM-related transcription factor 4) and DMRT1 by BLAST, respectively. Despite high homology in the DM-domain, there is little similarity outside the DM-domain. To better understand the structure, function, and possible roles of DMRT4 and DMRT1 as potential candidates for sex differentiation and sex determination, the intact regions encoding DMRT4 and DMRT1 obtained by PCR were sub-cloned into the vector pMAL-c2x and introduced into the Escherichia coli TB1 cell for efficient fusion expression. After purification and cleavage, DMRT4 and DMRT1 proteins were used to immunize adult rabbits following standard protocols. Consequently, it was found by using Western blot analysis that polyclonal antibodies against DMRT4 and DMRT1 had high specificity. The relative expression levels of DMRT4 and DMRT1 mRNA were determined by fluorescent Real-time RT-PCR in female and male Oreochromis aurea with beta-actin as the internal standard. DMRT1 was expressed only in testis, whereas DMRT4 was over expressed in the ovary, but in both female and male, a slight expression in the brain was also detected. Statistical analysis showed that in the brain, mean DMRT4 mRNA levels in female were significantly higher than in male. Meanwhile, the expression of DMRT4 and DMRT1 protein was also analyzed using the purified antibodies through Western blot and immunohistochemistry. It was found that DMRT4 was exclusively expressed in the ovary and DMRT1 in the testis. Study on DMRT4 and DMRT1 expression facilitated the elucidation of their roles and the understanding of sex differentiation of fish.

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

DMRT1 is a transcription factor expressed only in Sertoli cells and undifferentiated spermatogonia of the postnatal testis, where it is required for proper cellular differentiation and fertility. To elucidate the transcriptional regulatory regions that provide DMRT1's cell-specific expression, transgenic mice containing a LacZ reporter gene driven by variable amounts of rat Dmrt1 5' flanking sequence, 9 kb and smaller, were evaluated. Examination of transgene expression by RT-PCR indicated that multiple promoter regions direct Dmrt1 to the testis and that sequences upstream of 2.8 kb are needed for both Sertoli cell expression and limiting transcriptional influence imposed by surrounding chromatin. Thus, whereas many of the transgenes were expressed in the testis, the ones with smaller promoters were significantly more prone to expression at ectopic sites or to complete silencing. Transgene expression in Sertoli cells and germ cells was assessed by immunohistochemistry and RT-PCR following busulfan treatment to remove germ cells. Both evaluations indicated expression of the 9- and 3.2-kb promoters in Sertoli cells and germ cells, whereas activity of smaller promoters was largely restricted to germ cells. In all, the present study provides in vivo evidence that distinct promoter sequences participate in Dmrt1 regulation in somatic cells and germ cells, with the -3.2 kb/-2.8 kb region directing expression in Sertoli cells and downstream sequences (< or =1.3 kb) directing it in germ cells. Further exploration of the mechanisms restricting Dmrt1 expression to the testis revealed that FOXL2, a transcription factor required for differentiation of the ovary, repressed Dmrt1 promoter through the -3.2 kb/-2.8 kb regulatory region, offering a potential mechanism for Dmrt1 transcriptional silencing in granulosa cells.

A highly conserved cis-regulatory motif directs differential gonadal synexpression of Dmrt1 transcripts during gonad development

Differential gene expression largely accounts for the coordinated manifestation of the genetic programme underlying embryonic development and cell differentiation. The 3′ untranslated region (3′-UTR) of eukaryotic genes can contain motifs involved in regulation of gene expression at the post-transcriptional level. In the 3′-UTR of dmrt1, a key gene that functions in gonad development and differentiation, an 11-bp protein-binding motif was identified that mediates gonad-specific mRNA localization during embryonic and larval development of fish. Mutations that disrupt the 11-bp motif leading to in vitro protein-binding loss and selective transcript stabilization failure indicate a role for this motif in RNA stabilization through protein binding. The sequence motif was found to be conserved in most of the dmrt1 homologous genes from flies to humans suggesting a widespread conservation of this specific mechanism.

Sexual dimorphic expression of DMRT1 and Sox9a during gonadal differentiation and hormone-induced sex reversal in the teleost fish Nile tilapia (Oreochromis niloticus)

We examined the expression profiles of tDMRT1 and Sox9a during gonadal sex differentiation and hormone-induced sex reversal. tDMRT1 was detected in the gonial germ-cell-surrounding cells in XY fry specifically before the appearance of any signs of morphological sex differentiation, that is, sex differences in germ cell number and histogenesis, such as differentiation into intratesticular efferent duct or ovarian cavity. The signals became localized in the Sertoli and epithelial cells comprising the efferent duct during gonadal differentiation. After the induction of XY sex reversal with estrogen, tDMRT1 decreased and then disappeared completely. In contrast, tDMRT1 was expressed in the germ-cell-surrounding cells in XX sex reversal with androgen. On the other hand, Sox9a did not show sexual dimorphism before the appearance of sex differences in histogenesis and was not expressed in the efferent duct in the testis. These results suggest that tDMRT1 is a superior testicular differentiation marker in tilapia.

The creation of sexual dimorphism in the Drosophila soma

Animals have evolved a fascinating array of mechanisms for conducting sexual reproduction. These include producing the sex-specific gametes, as well as mechanisms for attracting a mate, courting a mate, and getting the gametes together. These processes require that males and females take on dramatically different forms (sexual dimorphism). Here, we will explore the problem of how sex is determined in Drosophila, and pay particular attention to how information about sexual identity is used to instruct males and females to develop differently. Along the way, we will highlight new work that challenges some of the traditional views about sex determination. In Drosophila, it is commonly thought that every cell decides its own sex based on its sex chromosome constitution (XX vs. XY). However, we now know that many cell types undergo nonautonomous sex determination, where they are told what sex to be through signals from surrounding cells, independent of their own chromosomal content. Further, it now appears that not all cells even "know" their sex, since key members of the sex determination pathway are not expressed in all cells. Thus, our understanding of how sex is determined, and how sexual identity is used to create sexual dimorphism, has changed considerably.

The function of Dmrt genes in vertebrate development: It is not just about sex

The Dmrt genes encode a large family of transcription factors whose function in sexual development has been well studied in invertebrates and vertebrates. Their expression pattern is not restricted to the developing gonads, indicating that Dmrt genes might regulate other developmental processes. Here we review the expression pattern of several members of this family across species and summarize recent findings on the function of a subset of these genes in non-gonadal tissues.

Sex-specific differences in mouse DMRT1 expression are both cell type- and stage-dependent during gonad development

Immunohistochemistry was used to examine GCNA1, a germ cell-specific protein, together with DMRT1 (Doublesex and Mab-3-related transcription factor-1), a transcription factor implicated in Sertoli cell and germ cell function, in order to resolve DMRT1's cellular profile during pre- and postnatal gonad development in the mouse. In the indifferent gonad (10.5-11.5 days postcoitus [dpc]), DMRT1 localized to somatic cells and GCNA1(+) germ cells and was indistinguishable in males and females. By 12.5 dpc, a clear sexual preference for DMRT1 in male somatic cells was observed, with male DMRT1 localized to testicular cords and more abundant in Sertoli cells than in germ cells and female DMRT1 diffusely labeled and markedly lower in somatic cells than in germ cells. A male somatic preference continued throughout development, with DMRT1 evident in Sertoli cells at all ages examined and absent in ovarian somatic cells from 13.5 dpc onward. In contrast, expression in primordial germ cells was not sexually distinct, and both sexes showed DMRT1 increasing through 13.5 dpc and absent by 15.5 dpc. Notably, sexual differences in germ cell DMRT1 were detected after birth, when it was detected only in spermatogonia of the testis. Colocalization of DMRT1 with proliferation markers KI67 and proliferating cell nuclear antigen (PCNA) and stem cell markers OCT4 (also known as POU5F1) and NGN3 indicated that, in postnatal testes, DMRT1 was present in both stem and proliferating spermatogonia. Together, the findings implicate opposite functions for DMRT1 in somatic and germ cells of the testis. In Sertoli cells, DMRT1 expression correlated with differentiation, whereas in germ cells, it suggested a role in expansion and maintenance of undifferentiated spermatogonia.

Cell type-autonomous and non-autonomous requirements for Dmrt1 in postnatal testis differentiation

Genes containing the DM domain, a conserved DNA binding motif first found in Doublesex of Drosophila and mab-3 of Caenorhabditis elegans, regulate sexual differentiation in multiple phyla. The DM domain gene Dmrt1 is essential for testicular differentiation in vertebrates. In the mouse, Dmrt1 is expressed in pre-meiotic germ cells and in Sertoli cells, which provide essential support for spermatogenesis. Dmrt1 null mutant mice have severely dysgenic testes in which Sertoli cells and germ cells both fail to differentiate properly after birth. Here we use conditional gene targeting to identify the functions of Dmrt1 in each cell type. We find that Dmrt1 is required in Sertoli cells for their postnatal differentiation, and for germ line maintenance and for meiotic progression. Dmrt1 is required in germ cells for their radial migration to the periphery of the seminiferous tubule where the spermatogenic niche will form, for mitotic reactivation and for survival beyond the first postnatal week. Thus Dmrt1 activity is required autonomously in the Sertoli and germ cell lineages, and Dmrt1 activity in Sertoli cells is also required non-autonomously to maintain the germ line. These results demonstrate that Dmrt1 plays multiple roles in controlling the remodeling and differentiation of the juvenile testis.

Sex determination and gonadal development in mammals

Arguably the most defining moment in our lives is fertilization, the point at which we inherit either an X or a Y chromosome from our father. The profoundly different journeys of male and female life are thus decided by a genetic coin toss. These differences begin to unfold during fetal development, when the Y-chromosomal Sry ("sex-determining region Y") gene is activated in males and acts as a switch that diverts the fate of the undifferentiated gonadal primordia, the genital ridges, towards testis development. This sex-determining event sets in train a cascade of morphological changes, gene regulation, and molecular interactions that directs the differentiation of male characteristics. If this does not occur, alternative molecular cascades and cellular events drive the genital ridges toward ovary development. Once testis or ovary differentiation has occurred, our sexual fate is further sealed through the action of sex-specific gonadal hormones. We review here the molecular and cellular events (differentiation, migration, proliferation, and communication) that distinguish testis and ovary during fetal development, and the changes in gene regulation that underpin these two alternate pathways. The growing body of knowledge relating to testis development, and the beginnings of a picture of ovary development, together illustrate the complex mechanisms by which these organ systems develop, inform the etiology, diagnosis, and management of disorders of sexual development, and help define what it is to be male or female.

Differential and spermatogenic cell-specific expression of DMRT1 during sex reversal in protogynous hermaphroditic groupers

DMRT1 has been suggested to play different roles in sex determination and gonad differentiation, because different expression patterns have been reported among different vertebrates. The groupers, since their gonads first develop as ovary and then reverse into testis, have been thought as good models to study sex differentiation and determination. In this study, we cloned the full-length cDNAs of DMRT1 gene from orange-spotted grouper (Epinephelus coioides), and prepared corresponding anti-EcDMRT1 antiserum to study the relationship of DMRT1 to sex reversal. One important finding is that the grouper DMRT1 is not only differentially expressed in different stage gonads, but also restricted to specific stages and specific cells of spermatogenesis. Grouper DMRT1 protein exists only in spermatogonia, primary spermatocytes and secondary spermatocytes, but not in the supporting Sertoli cells. Moreover, we confirmed that EcSox3 is expressed not only in oogonia and different stage oocytes, but also in Sertoli cells and spermatogonia, and EcSox9 is expressed only in Sertoli cells. The data suggested that grouper DMRT1 might be a more specific sex differentiation gene for spermatogenesis, and play its role at the specific stages from spermatogonia to spermatocytes. In addition, no introns were found in the grouper DMRT1, and no duplicated DMRT1 genes were detected. The finding implicates that the intronless DMRT1 that is able to undergo rapid transcriptional turnover might be a significant gene for stimulating spermatogenesis in the protogynous hermaphroditic gonad.

Multiple alternative splicing of mouse Dmrt1 during gonadal differentiation

Evolutionarily conserved Dmrt1 encodes a transcriptional regulator that is expressed exclusively in the gonads and is required for testis differentiation. Here we report that four transcripts of the mouse Dmrt1 were generated in developing gonads and adult testis by alternative splicing. Dmrt1 a encodes the known protein with 374 amino acids. Dmrt1 b, Dmrt1 c, and Dmrt1 d encode predicted proteins with 212, 257, and 194 amino acids, respectively. Dmrt1 a2 and Dmrt1 a3 have anterior alternative polyadenylation signals in 3'UTR than the known Dmrt1 transcript (Dmrt1 a1). Dmrt1 a2 lacks 18 nucleic acids in 3'UTR. Interestingly, Dmrt1 b lacks exon5, Dmrt1 c lacks exon3, and Dmrt1 d lacks both exon1 and exon2 which encode DM domain. RT-PCR showed that all of Dmrt1 transcripts were only detectable in adult testis. However, during gonadogenesis, the multiple alternatively spliced transcripts all had gonad-specific and sexually dimorphic expression profiles. Northern blot and real time fluorescent quantitative RT-PCR further indicated that the expression of Dmrt1 a was dominantly higher than those of Dmrt1 b, c, and d, although they showed a similar up and down pattern of expression during embryo development. The expression of Dmrt1 transcripts climbed up to a climax at 13.5dpc in both male and female gonad. Afterwards, expression in male gonad decreased to a low level and maintained, whereas female one reduced rapidly until undetectable in adult ovary. These results provide new insight into roles of regulation at level of splicing of the Dmrt1 in governing sex differentiation.

Dmrt1 expression in response to estrogen treatment in a reptile with temperature-dependent sex determination

Dmrt1 has been implicated as an important factor in sex determination in all classes of vertebrates, including reptiles with temperature-dependent sex determination (TSD). Specifically, early embryonic expression of Dmrt1 appears to be an integral part of normal testicular development in vertebrates. Recently, a number of TSD studies have placed Dmrt1 expression at the top of a short list of putative temperature-sensitive events for TSD. Dmrt1 expression has been shown to be up-regulated at male-producing temperatures during the thermosensitive period (TSP) of several TSD reptile species. An interesting finding in Dmrt1 studies of fish and amphibians has been that in species where exogenous steroids can stimulate sex reversal, Dmrt1 expression can also be manipulated by these steroid treatments. In the current study, we examine the effects of exogenous 17beta-estradiol treatment on Dmrt1 expression at male-producing temperature (26 degrees C) in a reptile with TSD, the red-eared slider turtle, Trachemys scripta. Previous studies have demonstrated that exogenous estrogens can stimulate sex reversal (at male-producing temperatures) in this species of turtle. In the current study, T. scripta embryos that received estradiol treatment displayed a significant decrease in Dmrt1 expression during the TSP, while embryos in the control group (no estradiol treatment) showed significant increases in Dmrt1 expression during the TSP. Furthermore, the pattern of Dmrt1 expression for the estradiol-treated group was similar to the pattern we previously reported for Dmrt1 at female-producing temperature (31 degrees C). These findings indicate that exogenous estrogen is acting at or before the Dmrt1 event in the sex determination/sex differentiation cascade of T. scripta. Further, the results are consistent with the hypothesis that exogenous estrogen could be exerting its feminizing effect by down-regulating the expression of Dmrt1.

DMRT gene cluster analysis in the platypus: new insights into genomic organization and regulatory regions

We isolated and characterized a cluster of platypus DMRT genes and compared their arrangement, location, and sequence across vertebrates. The DMRT gene cluster on human 9p24.3 harbors, in order, DMRT1, DMRT3, and DMRT2, which share a DM domain. DMRT1 is highly conserved and involved in sexual development in vertebrates, and deletions in this region cause sex reversal in humans. Sequence comparisons of DMRT genes between species have been valuable in identifying exons, control regions, and conserved nongenic regions (CNGs). The addition of platypus sequences is expected to be particularly valuable, since monotremes fill a gap in the vertebrate genome coverage. We therefore isolated and fully sequenced platypus BAC clones containing DMRT3 and DMRT2 as well as DMRT1 and then generated multispecies alignments and ran prediction programs followed by experimental verification to annotate this gene cluster. We found that the three genes have 58-66% identity to their human orthologues, lie in the same order as in other vertebrates, and colocate on 1 of the 10 platypus sex chromosomes, X5. We also predict that optimal annotation of the newly sequenced platypus genome will be challenging. The analysis of platypus sequence revealed differences in structure and sequence of the DMRT gene cluster. Multispecies comparison was particularly effective for detecting CNGs, revealing several novel potential regulatory regions within DMRT3 and DMRT2 as well as DMRT1. RT-PCR indicated that platypus DMRT1 and DMRT3 are expressed specifically in the adult testis (and not ovary), but DMRT2 has a wider expression profile, as it does for other mammals. The platypus DMRT1 expression pattern, and its location on an X chromosome, suggests an involvement in monotreme sexual development.