Gadd45γ and Map3k4 interactions regulate mouse testis determination via p38 MAPK-mediated control of Sry expression

Epigenetic regulation of male fate commitment from an initially bipotential system

A fundamental goal in biology is to understand how distinct cell types containing the same genetic information arise from a single stem cell throughout development. Sex determination is a key developmental process that requires a unidirectional commitment of an initially bipotential gonad towards either the male or female fate. This makes sex determination a unique model to study cell fate commitment and differentiation in vivo. We have focused this review on the accumulating evidence that epigenetic mechanisms contribute to the bipotential state of the fetal gonad and to the regulation of chromatin accessibility during and immediately downstream of the primary sex-determining switch that establishes the male fate.

Loss of p300 and CBP disrupts histone acetylation at the mouse Sry promoter and causes XY gonadal sex reversal

CREB-binding protein (CBP, CREBBP, KAT3A) and its closely related paralogue p300 (EP300, KAT3B), together termed p300/CBP, are histone/lysine acetyl-transferases that control gene expression by modifying chromatin-associated proteins. Here, we report roles for both of these chromatin-modifying enzymes in mouse sex determination, the process by which the embryonic gonad develops into a testis or an ovary. By targeting gene ablation to embryonic gonadal somatic cells using an inducible Cre line, we show that gonads lacking either gene exhibit major abnormalities of XY gonad development at 14.5 dpc, including partial sex reversal. Embryos lacking three out of four functional copies of p300/Cbp exhibit complete XY gonadal sex reversal and have greatly reduced expression of the key testis-determining genes Sry and Sox9. An analysis of histone acetylation at the Sry promoter in mutant gonads at 11.5 dpc shows a reduction in levels of the positive histone mark H3K27Ac. Our data suggest a role for CBP/p300 in testis determination mediated by control of histone acetylation at the Sry locus and reveal a novel element in the epigenetic control of Sry and mammalian sex determination. They also suggest possible novel causes of human disorders of sex development (DSD).

Regulation of Mammary Luminal Cell Fate and Tumorigenesis by p38α

Mammary stem and progenitor cells are essential for mammary gland homeostasis and are also candidates for cells of origin of mammary tumors. Here, we have investigated the function of the protein kinase p38α in the mammary gland using mice that delete this protein in the luminal epithelial cells. We show that p38α regulates the fate of luminal progenitor cells through modulation of the transcription factor RUNX1, an important controller of the estrogen receptor-positive cell lineage. We also provide evidence that the regulation of RUNX1 by p38α probably involves the kinase MSK1, which phosphorylates histone H3 at the RUNX1 promoter. Moreover, using a mouse model for breast cancer initiated by luminal cells, we show that p38α downregulation in mammary epithelial cells reduces tumor burden, which correlates with decreased numbers of tumor-initiating cells. Collectively, our results define a key role for p38α in luminal progenitor cell fate that affects mammary tumor formation.

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Luminal progenitor cell fate in the mammary gland is regulated by p38α

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p38α controls the ER transcriptional program by modulating RUNX1

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p38α regulates H3 phosphorylation at the RUNX1 promoter through the kinase MSK1

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p38α promotes mammary tumorigenesis by maintaining luminal tumor-initiating cells

Biallelic mutations in FLNB cause a skeletal dysplasia with 46,XY gonadal dysgenesis by activating β-catenin

Filamin B (FLNB) functions as a switch that can affect chrondrocyte development and endochondral bone formation through a series of signaling molecules and transcription factors that also affect Sertoli cell development. Here, we report a subject with a novel skeletal dysplasia and co-existing 46,XY gonadal dysgenesis and biallelic mutations in FLNB. Whole exome sequencing was performed to identify mutations. Quantitative polymerase chain reaction (qPCR) and flow variant assays were performed to quantify RNA, proteins and phosphorylated proteins. The TOPFLASH reporter was performed to quantify β-catenin activity. Mutations were identified in the FLNB gene (FLNB:p.F964L, FLNB:p.A1577V). These mutations increased binding of FLNB protein to the MAP3K1 and RAC1 signal transduction complex and activated β-catenin and had different effects on phosphorylation of MAP kinase pathway intermediates and SOX9 expression. Direct activation of β-catenin through the FLNB-MAP3K1-RAC1 complex by FLNB mutations is a novel mechanism for causing 46,XY gonadal dysgenesis. The mechanism of action varies from those reported previously for loss of function mutations in SOX9 and gain-of-function mutations in MAP3K1.

In mammalian foetal testes, SOX9 regulates expression of its target genes by binding to genomic regions with conserved signatures

In mammalian embryonic gonads, SOX9 is required for the determination of Sertoli cells that orchestrate testis morphogenesis. To identify genetic networks directly regulated by SOX9, we combined analysis of SOX9-bound chromatin regions from murine and bovine foetal testes with sequencing of RNA samples from mouse testes lacking Sox9. We found that SOX9 controls a conserved genetic programme that involves most of the sex-determining genes. In foetal testes, SOX9 modulates both transcription and directly or indirectly sex-specific differential splicing of its target genes through binding to genomic regions with sequence motifs that are conserved among mammals and that we called ‘Sertoli Cell Signature’ (SCS). The SCS is characterized by a precise organization of binding motifs for the Sertoli cell reprogramming factors SOX9, GATA4 and DMRT1. As SOX9 biological role in mammalian gonads is to determine Sertoli cells, we correlated this genomic signature with the presence of SOX9 on chromatin in foetal testes, therefore equating this signature to a genomic bar code of the fate of foetal Sertoli cells. Starting from the hypothesis that nuclear factors that bind to genomic regions with SCS could functionally interact with SOX9, we identified TRIM28 as a new SOX9 partner in foetal testes.

Cyp1b1 deletion and retinol deficiency coordinately suppress mouse liver lipogenic genes and hepcidin expression during post-natal development

Cyp1b1 deletion and gestational vitamin A deficiency (GVAD) redirect adult liver gene expression. A matched sufficient pre- and post-natal diet, which has high carbohydrate and normal iron content (LF12), increased inflammatory gene expression markers in adult livers that were suppressed by GVAD and Cyp1b1 deletion. At birth on the LF12 diet, Cyp1b1 deletion and GVAD each suppress liver expression of the iron suppressor, hepcidin (Hepc), while increasing stellate cell activation markers and suppressing post-natal increases in lipogenesis. Hepc was less suppressed in Cyp1b1-/- pups with a standard breeder diet, but was restored by iron supplementation of the LF12 diet.

CONCLUSIONS

The LF12 diet delivered low post-natal iron and attenuated Hepc. Hepc decreases in Cyp1b1-/- and GVAD mice resulted in stellate activation and lipogenesis suppression. Endothelial BMP6, a Hepc stimulant, is a potential coordinator and Cyp1b1 target. These neonatal changes in Cyp1b1-/- mice link to diminished adult obesity and liver inflammation.

Of sex and determination: marking 25 years of Randy, the sex-reversed mouse

On Thursday 9 May 1991, the world awoke to front-page news of a breakthrough in biological research. From Washington to Wollongong, newspapers, radio and TV were abuzz with the story of a transgenic mouse in London called Randy. Why was this mouse so special? The mouse in question was a chromosomal female (XX) made male by the presence of a transgene containing the Y chromosome gene Sry This sex-reversal provided clear experimental proof that Sry was the elusive mammalian sex-determining gene. Twenty-five years on, we reflect on what this discovery meant for our understanding of how males and females arise and what remains to be understood.

Molecular cloning, characterization and functional analysis of a putative mitogen-activated protein kinase kinase kinase 4 (MEKK4) from blood clam Tegillarca granosa

The mitogen-activated protein kinase (MAPK) cascades stand for one of the most important signaling mechanisms in response to environmental stimuli. In the present study, we cloned and identified for the first time the full-length cDNA of MAPK kinase kinase 4 (TgMEKK4) from Blood clam Tegillarca granosa using rapid amplification of cDNA ends method. The full-length cDNA of TgMEKK4 was of 1605 bp in length, encoding a polypeptide of 364 amino acids with a predicted molecular mass of 41.22 kDa and theoretical isoelectric point of 6.29. The conserved MEKK4-domain was identified in TgMEKK4 by SMART program analysis. Homology analysis of the deduced amino acid sequence of TgMEKK4 with other known sequences revealed that TgMEKK4 shared 58%-80% identity to MEKK4s from other species. TgMEKK4 mRNA transcripts could be detected in all tissues examined with the highest expression level in the gill by qRT-PCR. The mRNA expression of TgMEKK4 was up-regulated significantly in hemocytes after Vibrio parahaemolyticus, Vibrio alginolyticus and Lipopolysaccharide (LPS) challenges. Overexpression of TgMEKK4 in HEK 293T cells resulted in the activation of JNK and ERK, but not p38. Consistently, In vivo study indicated that LPS stimulation enhanced JNK, ERK and p38 phosphorylation in blood clams. These results suggest that TgMEKK4 is a powerful factor in the regulation of genes that may be involved in innate immune response of blood clam.

MeDIP-seq and nCpG analyses illuminate sexually dimorphic methylation of gonadal development genes with high historic methylation in turtle hatchlings with temperature-dependent sex determination

Background

DNA methylation alters gene expression but not DNA sequence and mediates some cases of phenotypic plasticity. Temperature-dependent sex determination (TSD) epitomizes phenotypic plasticity where environmental temperature drives embryonic sexual fate, as occurs commonly in turtles. Importantly, the temperature-specific transcription of two genes underlying gonadal differentiation is known to be induced by differential methylation in TSD fish, turtle and alligator. Yet, how extensive is the link between DNA methylation and TSD remains unclear. Here we test for broad differences in genome-wide DNA methylation between male and female hatchling gonads of the TSD painted turtle Chrysemys picta using methyl DNA immunoprecipitation sequencing, to identify differentially methylated candidates for future study. We also examine the genome-wide nCpG distribution (which affects DNA methylation) in painted turtles and test for historic methylation in genes regulating vertebrate gonadogenesis.

Results

Turtle global methylation was consistent with other vertebrates (57% of the genome, 78% of all CpG dinucleotides). Numerous genes predicted to regulate turtle gonadogenesis exhibited sex-specific methylation and were proximal to methylated repeats. nCpG distribution predicted actual turtle DNA methylation and was bimodal in gene promoters (as other vertebrates) and introns (unlike other vertebrates). Differentially methylated genes, including regulators of sexual development, had lower nCpG content indicative of higher historic methylation.

Conclusions

Ours is the first evidence suggesting that sexually dimorphic DNA methylation is pervasive in turtle gonads (perhaps mediated by repeat methylation) and that it targets numerous regulators of gonadal development, consistent with the hypothesis that it may regulate thermosensitive transcription in TSD vertebrates. However, further research during embryogenesis will help test this hypothesis and the alternative that instead, most differential methylation observed in hatchlings is the by-product of sexual differentiation and not its cause.

Electronic supplementary material

The online version of this article (doi:10.1186/s13072-017-0136-2) contains supplementary material, which is available to authorized users.

Transcriptomic responses to environmental temperature by turtles with temperature-dependent and genotypic sex determination assessed by RNAseq inform the genetic architecture of embryonic gonadal development

Vertebrate sexual fate is decided primarily by the individual's genotype (GSD), by the environmental temperature during development (TSD), or both. Turtles exhibit TSD and GSD, making them ideal to study the evolution of sex determination. Here we analyze temperature-specific gonadal transcriptomes (RNA-sequencing validated by qPCR) of painted turtles (Chrysemys picta TSD) before and during the thermosensitive period, and at equivalent stages in soft-shell turtles (Apalone spinifera-GSD), to test whether TSD's and GSD's transcriptional circuitry is identical but deployed differently between mechanisms. Our data show that most elements of the mammalian urogenital network are active during turtle gonadogenesis, but their transcription is generally more thermoresponsive in TSD than GSD, and concordant with their sex-specific function in mammals [e.g., upregulation of Amh, Ar, Esr1, Fog2, Gata4, Igf1r, Insr, and Lhx9 at male-producing temperature, and of β-catenin, Foxl2, Aromatase (Cyp19a1), Fst, Nf-kb, Crabp2 at female-producing temperature in Chrysemys]. Notably, antagonistic elements in gonadogenesis (e.g., β-catenin and Insr) were thermosensitive only in TSD early-embryos. Cirbp showed warm-temperature upregulation in both turtles disputing its purported key TSD role. Genes that may convert thermal inputs into sex-specific development (e.g., signaling and hormonal pathways, RNA-binding and heat-shock) were differentially regulated. Jak-Stat, Nf-κB, retinoic-acid, Wnt, and Mapk-signaling (not Akt and Ras-signaling) potentially mediate TSD thermosensitivity. Numerous species-specific ncRNAs (including Xist) were differentially-expressed, mostly upregulated at colder temperatures, as were unannotated loci that constitute novel TSD candidates. Cirbp showed warm-temperature upregulation in both turtles. Consistent transcription between turtles and alligator revealed putatively-critical reptilian TSD elements for male (Sf1, Amh, Amhr2) and female (Crabp2 and Hspb1) gonadogenesis. In conclusion, while preliminary, our data helps illuminate the regulation and evolution of vertebrate sex determination, and contribute genomic resources to guide further research into this fundamental biological process.

Genome-wide identification of regulatory elements in Sertoli cells

A current goal of molecular biology is to identify transcriptional networks that regulate cell differentiation. However, identifying functional gene regulatory elements has been challenging in the context of developing tissues where material is limited and cell types are mixed. To identify regulatory sites during sex determination, we subjected Sertoli cells from mouse fetal testes to DNaseI-seq and ChIP-seq for H3K27ac. DNaseI-seq identified putative regulatory sites around genes enriched in Sertoli and pregranulosa cells; however, active enhancers marked by H3K27ac were enriched proximal to only Sertoli-enriched genes. Sequence analysis identified putative binding sites of known and novel transcription factors likely controlling Sertoli cell differentiation. As a validation of this approach, we identified a novel Sertoli cell enhancer upstream of Wt1, and used it to drive expression of a transgenic reporter in Sertoli cells. This work furthers our understanding of the complex genetic network that underlies sex determination and identifies regions that potentially harbor non-coding mutations underlying disorders of sexual development.

Redundancy in the World of MAP Kinases: All for One

The protein kinases ERK1 and ERK2 are the effector components of the prototypical ERK1/2 mitogen-activated protein (MAP) kinase pathway. This signaling pathway regulates cell proliferation, differentiation and survival, and is essential for embryonic development and cellular homeostasis. ERK1 and ERK2 homologs share similar biochemical properties but whether they exert specific physiological functions or act redundantly has been a matter of controversy. However, recent studies now provide compelling evidence in support of functionally redundant roles of ERK1 and ERK2 in embryonic development and physiology. In this review, we present a critical assessment of the evidence for the functional specificity or redundancy of MAP kinase isoforms. We focus on the ERK1/ERK2 pathway but also discuss the case of JNK and p38 isoforms.

Genetic Analyses Reveal Functions for MAP2K3 and MAP2K6 in Mouse Testis Determination

Testis determination in mammals is initiated by expression of SRY in somatic cells of the embryonic gonad. Genetic analyses in the mouse have revealed a requirement for mitogen-activated protein kinase (MAPK) signaling in testis determination: targeted loss of the kinases MAP3K4 and p38 MAPK causes complete XY embryonic gonadal sex reversal. These kinases occupy positions at the top and bottom level, respectively, in the canonical threetier MAPK-signaling cascade: MAP3K, MAP2K, MAPK. To date, no role in sex determination has been attributed to a MAP2K, although such a function is predicted to exist. Here, we report roles for the kinases MAP2K3 and MAP2K6 in testis determination. C57BL/6J (B6) embryos lacking MAP2K3 exhibited no significant abnormalities of testis development, whilst those lacking MAP2K6 exhibited a minor delay in testis determination. Compound mutants lacking three out of four functional alleles at the two loci also exhibited delayed testis determination and transient ovotestis formation as a consequence, suggestive of partially redundant roles for these kinases in testis determination. Early lethality of double-knockout embryos precludes analysis of sexual development. To reveal their roles in testis determination more clearly, we generated Map2k mutant B6 embryos using a weaker Sry allele (Sry^AKR). Loss of Map2k3 on this highly sensitized background exacerbates ovotestis development, whilst loss of Map2k6 results in complete XY gonadal sex reversal associated with reduction of Sry expression at 11.25 days postcoitum. Our data suggest that MAP2K6 functions in mouse testis determination, via positive effects on Sry, and also indicate a minor role for MAP2K3.

Signaling Pathways Involved in Mammalian Sex Determination and Gonad Development

The development of any organ system requires a complex interplay of cellular signals to initiate the differentiation and development of the heterogeneous cell and tissue types required to carry out the organs' functions. In this way, an extracellular stimulus is transmitted to an intracellular target through an array of interacting protein intermediaries, ultimately enabling the target cell to elicit a response. Surprisingly, only a small number of signaling pathways are implicated throughout embryogenesis and are used over and over again. Gonadogenesis is a unique process in that 2 morphologically distinct organs, the testes and ovaries, arise from a common precursor, the bipotential genital ridge. Accordingly, most of the signaling pathways observed throughout embryogenesis also have been shown to be important for mammalian sex determination and gonad development. Here, we review the mechanisms of signal transduction within these pathways and the importance of these pathways throughout mammalian gonad development, mainly concentrating on data obtained in mouse but including other species where appropriate.

Molecular mechanisms associated with 46,XX disorders of sex development

In the female gonad, distinct signalling pathways activate ovarian differentiation while repressing the formation of testes. Human disorders of sex development (DSDs), such as 46,XX DSDs, can arise when this signalling is aberrant. Here we review the current understanding of the genetic mechanisms that control gonadal development, with particular emphasis on those that drive or inhibit ovarian differentiation. We discuss how disruption to these molecular pathways can lead to 46,XX disorders of ovarian development. Finally, we look at recently characterized novel genes and pathways that contribute and speculate how advances in technology will aid in further characterization of normal and disrupted human ovarian development.

The Gonadal Supporting Cell Lineage and Mammalian Sex Determination: The Differentiation of Sertoli and Granulosa Cells

The supporting cell lineage plays a crucial role in nurturing the development of germ cells in the adult gonad. Sertoli cells in the testis support the progression of spermatogonial stem cells through meiosis to the production of motile spermatozoa. Granulosa cells, meanwhile, are a critical component of the ovarian follicle that produces the mature oocyte. It is a distinctive feature of the embryonic gonad that at least some of the supporting cells are derived from a single sexually bipotential precursor lineage. It is the commitment of this somatic lineage to either the Sertoli or granulosa cell fate that defines sex determination. In this chapter we review what is known about the key molecules responsible for this lineage decision in the developing mammalian gonads, relying primarily on data from studies of mice and humans. We focus on recent advances in our understanding of the mutually antagonistic interactions of testis- and ovary-determining pathways and their complexity as revealed by genetic analyses. For the sake of simplicity, we will deal with supporting cells in testis and ovary development in separate sections, but numerous points of contact exist between these accounts of gonadogenesis in male and female embryos, primarily due to the aforementioned mutual antagonisms. The final section will offer a brief synthesis of these organ-specific overviews and a summary of the key themes that emerge in this review of supporting cell differentiation in mammalian sex determination.

Biology of the Sertoli Cell in the Fetal, Pubertal, and Adult Mammalian Testis

A healthy man typically produces between 50 × 10(6) and 200 × 10(6) spermatozoa per day by spermatogenesis; in the absence of Sertoli cells in the male gonad, this individual would be infertile. In the adult testis, Sertoli cells are sustentacular cells that support germ cell development by secreting proteins and other important biomolecules that are essential for germ cell survival and maturation, establishing the blood-testis barrier, and facilitating spermatozoa detachment at spermiation. In the fetal testis, on the other hand, pre-Sertoli cells form the testis cords, the future seminiferous tubules. However, the role of pre-Sertoli cells in this process is much less clear than the function of Sertoli cells in the adult testis. Within this framework, we provide an overview of the biology of the fetal, pubertal, and adult Sertoli cell, highlighting relevant cell biology studies that have expanded our understanding of mammalian spermatogenesis.

Functional microarray analysis of differentially expressed genes in granulosa cells from women with polycystic ovary syndrome related to MAPK/ERK signaling

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age. Although its aetiology and pathogenesis remain unclear, recent studies suggest that the dysfunction of granulosa cells may partly be responsible. This study aimed to use cDNA microarray technology to compare granulosa cell gene expression profiles in women with and without PCOS to identify genes that may be aetiologically implicated in the pathogenesis of PCOS. The study cohort included 12 women undergoing in vitro fertilization, six with PCOS and six without PCOS. Differential gene expression profiles were classified by post-analyses of microarray data, followed by western blot analyses to confirm the microarray data of selected genes. In total, 243 genes were differentially expressed (125 upregulated and 118 downregulated) between the PCOS and non-PCOS granulosa cells. These genes are involved in reproductive system development, amino acid metabolism and cellular development and proliferation. Comparative analysis revealed genes involved in the mitogen-activated protein kinase/extracellular regulated kinase (MAPK/ERK) signaling pathways. Western blot analyses confirmed that mitogen-activated protein kinase kinase kinase 4 and phospho-ERK1/2 were decreased in PCOS granulosa cells. This study identified candidate genes involved in MAPK/ERK signaling pathways that may influence the function of granulosa cells in PCOS.

Epigenetics of sex determination in mammals

Epigenetics is the study of changes in gene function that cannot be explained by changes in DNA sequence. A mammalian body contains more than two hundred types of cells. Since all of them are derived from a single fertilized egg, their genotypes are identical. However, the gene expression patterns are different between the cell types, indicating that each cell type has unique own "epigenotype". Epigenetic gene regulation mechanisms essentially contribute to various processes of mammalian development. The essence of epigenetic regulation is the structural change of chromatin to modulate gene activity in a spatiotemporal manner. DNA methylation and histone modifications are the major epigenetic mechanisms. Sex determination is the process for gender establishment. There are two types of sex-determining mechanisms in animals, environmental sex determination (ESD) and genotypic sex determination (GSD). Recent studies have provided some evidence that epigenetic mechanisms play indispensable roles in ESD and GSD. Some fishes undergo ESD, in which DNA methylation is essentially involved. GSD is employed in therian mammals, where Sry (sex-determining region on the Y chromosome) triggers testis differentiation from undifferentiated gonads. Sry expression is tightly regulated in a spatiotemporal manner. A recent study demonstrated that histone modification is involved in Sry regulation. In this review, we discuss the role of epigenetic mechanisms for sex determination in mammals and other vertebrates.

Identification of candidate gonadal sex differentiation genes in the chicken embryo using RNA-seq

BACKGROUND

Despite some advances in recent years, the genetic control of gonadal sex differentiation during embryogenesis is still not completely understood. To identify new candidate genes involved in ovary and testis development, RNA-seq was used to define the transcriptome of embryonic chicken gonads at the onset of sexual differentiation (day 6.0/stage 29).

RESULTS

RNA-seq revealed more than 1000 genes that were transcribed in a sex-biased manner at this early stage of gonadal differentiation. Comparison with undifferentiated gonads revealed that sex biased expression was derived primarily from autosomal rather than sex-linked genes. Gene ontology and pathway analysis indicated that many of these genes encoded proteins involved in extracellular matrix function and cytoskeletal remodelling, as well as tubulogenesis. Several of these genes are novel candidate regulators of gonadal sex differentiation, based on sex-biased expression profiles that are altered following experimental sex reversal. We further characterised three female-biased (ovarian) genes; calpain-5 (CAPN5), G-protein coupled receptor 56 (GPR56), and FGFR3 (fibroblast growth factor receptor 3). Protein expression of these candidates in the developing ovaries suggests that they play an important role in this tissue.

CONCLUSIONS

This study provides insight into the earliest steps of vertebrate gonad sex differentiation, and identifies novel candidate genes for ovarian and testicular development.

Biological factors underlying sex differences in neurological disorders

The prevalence, age of onset, pathophysiology, and symptomatology of many neurological and neuropsychiatric conditions differ significantly between males and females. Females suffer more from mood disorders such as depression and anxiety, whereas males are more susceptible to deficits in the dopamine system including Parkinson's disease (PD), attention-deficit hyperactivity disorder (ADHD), schizophrenia, and autism spectrum disorders (ASD). Until recently, these sex differences have been explained solely by the neuroprotective actions of sex hormones in females. Emerging evidence however indicates that the sex chromosome genes (i.e. X- and Y-linked genes) also contribute to brain sex differences. In particular, the Y-chromosome gene, SRY (Sex-determining Region on the Y chromosome) is an interesting candidate as it is expressed in dopamine-abundant brain regions, where it regulates dopamine biosynthesis and dopamine-mediated functions such as voluntary movement in males. Furthermore, SRY expression is dysregulated in a toxin-induced model of PD, suggesting a role for SRY in the pathogenesis of dopamine cells. Taken together, these studies highlight the importance of understanding the interplay between sex-specific hormones and sex-specific genes in healthy and diseased brain. In particular, better understanding of regulation and function of SRY in the male brain could provide entirely novel and important insights into genetic factors involved in the susceptibility of men to neurological disorders, as well as development of novel sex-specific therapies.

SMAD2 and p38 signaling pathways act in concert to determine XY primordial germ cell fate in mice

The sex of primordial germ cells (PGCs) is determined in developing gonads on the basis of cues from somatic cells. In XY gonads, sex-determining region Y (SRY) triggers fibroblast growth factor 9 (FGF9) expression in somatic cells. FGF signaling, together with downstream nodal/activin signaling, promotes male differentiation in XY germ cells by suppressing retinoic acid (RA)-dependent meiotic entry and inducing male-specific genes. However, the mechanism by which nodal/activin signaling regulates XY PGC fate is unknown. We uncovered the roles of SMAD2/3 and p38 MAPK, the putative downstream factors of nodal/activin signaling, in PGC sexual fate decision. We found that conditional deletion of Smad2, but not Smad3, from XY PGCs led to a loss of male-specific gene expression. Moreover, suppression of RA signaling did not rescue male-specific gene expression in Smad2-mutant testes, indicating that SMAD2 signaling promotes male differentiation in a RA-independent manner. By contrast, we found that p38 signaling has an important role in the suppression of RA signaling. The Smad2 deletion did not disrupt the p38 signaling pathway even though Nodal expression was significantly reduced, suggesting that p38 was not regulated by nodal signaling in XY PGCs. Additionally, the inhibition of p38 signaling in the Smad2-mutant testes severely impeded XY PGC differentiation and induced meiosis. In conclusion, we propose a model in which p38 and SMAD2 signaling coordinate to determine the sexual fate of XY PGCs.

Comparative analysis of developmentally regulated expressions of Gadd45a, Gadd45b, and Gadd45g in the mouse and marmoset cerebral cortex

The cerebral cortex is an indispensable region that is involved in higher cognitive function in the mammalian brain, and is particularly evolved in the primate brain. It has been demonstrated that cortical areas are formed by both innate and activity-dependent mechanisms. However, it remains unknown what molecular changes induce cortical expansion and complexity during primate evolution. Active DNA methylation/demethylation is one of the epigenetic mechanisms that can modify gene expression via the methylation/demethylation of promoter regions. Three growth arrest and DNA damage-inducible small nuclear proteins, Gadd45 alpha, beta, and gamma, have been identified as regulators of methylation status. To understand the involvement of epigenetic factors in primate cortical evolution, we started by analyzing expression of these demethylation genes in the developing common marmoset (Callithrix jacchus) and mouse (Mus musculus) brain. In the marmoset brain, we found that cortical expression levels of Gadd45 alpha and gamma were reduced during development, whereas there was high expression of Gadd45 beta in some areas of the adult brain, including the prefrontal, temporal, posterior parietal and insula cortices, which are particularly expanded in greater primates and humans. Compared to the marmoset brain, there were no clear regional differences and constant or reduced Gadd45 expression was seen between juvenile and adult mouse brain. Double staining with a neuronal marker revealed that most Gadd45-expressing cells were NeuN-positive neurons. Thus, these results suggest the possibility that differential Gadd45 expression affects neurons, contributing cortical evolution and diversity.

Epigenetic regulation of mammalian sex determination

Epigenetics is the study of changes in gene function that cannot be explained by changes in DNA sequence. A mammalian body contains more than two-hundred different types of cells, all derived from a single fertilized egg. Epigenetic gene regulation mechanisms essentially contribute to various processes of mammalian development. The essence of epigenetic regulation is the modulation of gene activity through changes in chromatin structure. DNA methylation and histone modifications are the major epigenetic mechanisms. Sex determination is the process of establishing a gender. Sry, the sex-determining gene in therian mammals, initiates testis differentiation. Recent studies have provided evidence that epigenetic mechanisms contribute to Sry regulation.

Molecular Characterization, Polymorphism, and Association of Porcine GADD45G Gene

Growth arrest and DNA-damage-inducible gamma (GADD45G) is a reproduction related gene. In this study, the full-length cDNA sequence of porcine GADD45G gene was cloned through rapid amplification of cDNA ends (RACE) method. The porcine GADD45G gene encodes a protein of 159 amino acids that shares high homology with the GADD45G of nine species: chimpanzee (97%), sumatran orangutan (97%), white-tufted-ear marmoset (97%), northern white-cheeked gibbon (97%), cattle (97%), human (97%), rhesus monkey (97%), rat (96%), and mouse (95%). This novel porcine gene was assigned to GeneID: 100152997. Phylogenetic analysis revealed that the porcine GADD45G gene has a closer genetic relationship with the GADD45G gene of cattle. Computer-assisted analysis indicated that porcine GADD45G gene is structured in four exons and three introns. PCR-Rsa I-RFLP was established to detect an A/G mutation on the position of 294-bp of coding sequence and eight pig breeds display obvious genotype and allele frequency differences at this mutation locus. Association of this SNP with litter size traits was assessed in Large White (n = 100) and Landrace (n = 100) pig populations, and result demonstrated that this polymorphic locus was significantly associated with the litter size of all parities in Large White and Landrace sows (P < 0.01). Therefore, porcine GADD45G gene could be a useful candidate gene in selection for increasing the litter size. These data serve as a foundation for further insight into this novel porcine gene.

MicroRNA-383 regulates the apoptosis of tumor cells through targeting Gadd45g

Background

MicroRNAs (miRNAs) are a class of small non-coding single-stranded RNA molecules that inhibit gene expression at post-transcriptional level. Gadd45g (growth arrest and DNA-damage-inducible 45 gamma) is a stress-response protein, which has been implicated in several biological processes, including DNA repair, the cell cycle and cell differentiation.

Results

In this work, we found that miR-383 is a negative regulator of Gadd45g. Forced expression of miR-383 decreased the expression of Gadd45g through binding to the 3′ untranslated region (3′-UTR), whereas inhibition of miR-383 increased Gadd45g expression. The presence of miR-383 increased the cellular sensitivity to DNA damage in breast cancer cells, which was rescued by ectopic expression of Gadd45g without the 3′-UTR. miR-383 also regulates the expression of Gadd45g in embryonic stem (ES) cells, but not their apoptosis under genotoxic stress. miR-383 was further showed to negatively regulate ES cell differentiation via targeting Gadd45g, which subsequently modulates the pluripotency-associated genes. Taken together, our study demonstrates that miR-383 is a negative regulator of Gadd45g in both tumor cells and ES cells, however, has distinct function in regulating cell apoptosis. miR-383 may be used as antineoplastic agents in cancer chemotherapy.

Conclusion

We demonstrate for the first time that miR-383 can specifically regulates the expression of Gadd45g by directly targeting to the 3-UTR region of Gadd45g mRNA, a regulatory process conserved in human tumor cells and mouse embryonic stem cells. These two compotents can be potentially used as antineoplastic agents in cancer chemotherapy.

Molecular characterization and functional divergence of two Gadd45g homologs in sex determination in half-smooth tongue sole (Cynoglossus semilaevis)

The growth arrest and DNA-damage-inducible protein 45 gamma (Gadd45g) is known to play a major role in embryonic development and sex determination. In this study, two Gadd45g genes were isolated from half-smooth tongue sole (Cynoglossus semilaevis). Using chromosomal fluorescence in situ hybridization (FISH), Gadd45g1 and Gadd45g2 were located on the W and Z chromosomes, respectively. The full-length cDNA sequences of Gadd45g1 (1270bp) and Gadd45g2 (1181bp) were predicted to contain a 480-bp coding sequence that could encode a protein of 159 amino acids residues. A phylogenetic tree showed that the predicted Gadd45g1 and Gadd45g2 amino acid sequences clustered closely in one branch. It is proposed that Gadd45g1 and Gadd45g2 are paralogous genes derived from the divergence of the sex chromosome. Ka/Ks ratios indicated that Gadd45g1 and Gadd45g2 may have undergone a high number of mutations and have a divergence time of only about 68,000years, although Gadd45g homologs are highly conserved. The qRT-PCR demonstrated that Gadd45g1 and Gadd45g2 were highly expressed in ovary, and negligibly expressed in testis of male and neo-male. During development of the ovary (from 80 to 150days), the expression levels of both genes reached high levels. Gadd45g1 was also highly expressed at 50days, the stage just before gonad differentiation in C. semilaevis. All these findings imply functional divergence of the two Gadd45g homologs; Gadd45g1 may be necessary for sex differentiation in the early stage of gonad development, and then Gadd45g1 and Gadd45g2 maintain ovary development and the female character of half-smooth tongue sole.

Genetic regulation of mammalian gonad development

Sex-specific gonadal development starts with formation of the bipotential gonad, which then differentiates into either a mature testis or an ovary. This process is dependent on activation of either the testis-specific or the ovary-specific pathway while the opposite pathway is continuously repressed. A network of transcription factors tightly regulates initiation and maintenance of these distinct pathways; disruption of these networks can lead to disorders of sex development in humans and male-to-female or female-to-male sex reversal in mice. Sry is the Y-linked master switch that is both required and sufficient to drive the testis-determining pathway. Another key component of the testis pathway is Sox9, which acts immediately downstream of Sry. In contrast to the testis pathway, no single sex-determining factor has been identified in the ovary pathway; however, multiple genes, such as Foxl2, Rspo1, Ctnnb1, and Wnt4, seem to work synergistically and in parallel to ensure proper ovary development. Our understanding of the regulatory networks that underpin testis and ovary development has grown substantially over the past two decades.

DSDs: genetics, underlying pathologies and psychosexual differentiation

Mammalian sex determination is the unique process whereby a single organ, the bipotential gonad, undergoes a developmental switch that promotes its differentiation into either a testis or an ovary. Disruptions of this complex genetic process during human development can manifest as disorders of sex development (DSDs). Sex development can be divided into two distinct processes: sex determination, in which the bipotential gonads form either testes or ovaries, and sex differentiation, in which the fully formed testes or ovaries secrete local and hormonal factors to drive differentiation of internal and external genitals, as well as extragonadal tissues such as the brain. DSDs can arise from a number of genetic lesions, which manifest as a spectrum of gonadal (gonadal dysgenesis to ovotestis) and genital (mild hypospadias or clitoromegaly to ambiguous genitalia) phenotypes. The physical attributes and medical implications associated with DSDs confront families of affected newborns with decisions, such as gender of rearing or genital surgery, and additional concerns, such as uncertainty over the child's psychosexual development and personal wishes later in life. In this Review, we discuss the underlying genetics of human sex determination and focus on emerging data, genetic classification of DSDs and other considerations that surround gender development and identity in individuals with DSDs.

R-spondin1, WNT4, and the CTNNB1 signaling pathway: strict control over ovarian differentiation

Sex differentiation is a unique developmental process. Starting from a bipotential gonad, it gives rise to the ovary and the testis, two highly specialized organs that differ morphologically and physiologically despite sharing common reproductive and endocrine functions. This highlights the specific plasticity of the gonadal precursors and the existence of complex antagonistic genetic regulation. Mammalian sex determination is controlled by paternal transmission of the Y-linked gene, sex-determining region Y (SRY). Using mouse models, it has been shown that the main role of Sry is to activate the expression of the transcription factor Sox9; either one of these two genes is necessary and sufficient to allow testicular development through Sertoli cell differentiation. Thus, defects in SRY/Sry and/or SOX9/Sox9 expression result in male-to-female sex reversal of XY individuals. Molecular mechanisms governing ovarian differentiation remained unknown for a long time, until the discovery of the roles of R-spondin1 (RSPO1) and WNT4. In XX individuals, activation of the β-catenin signaling pathway by the secreted proteins RSPO1 and WNT4 is required to allow granulosa cell differentiation and, in turn, ovarian differentiation. Thus, mutations in RSPO1 result in female-to-male sex reversal of XX patients, and mouse models have allowed the identification of genetic cascades activated by RSPO1 and WNT4 to regulate ovarian development. In this review, we will discuss the respective roles of RSPO1, WNT4, and the β-catenin signaling pathway during ovarian differentiation in mice.

Regulation of male sex determination: genital ridge formation and Sry activation in mice

Sex determination is essential for the sexual reproduction to generate the next generation by the formation of functional male or female gametes. In mammals, primary sex determination is commenced by the presence or absence of the Y chromosome, which controls the fate of the gonadal primordium. The somatic precursor of gonads, the genital ridge is formed at the mid-gestation stage and gives rise to one of two organs, a testis or an ovary. The fate of the genital ridge, which is governed by the differentiation of somatic cells into Sertoli cells in the testes or granulosa cells in the ovaries, further determines the sex of an individual and their germ cells. Mutation studies in human patients with disorders of sex development and mouse models have revealed factors that are involved in mammalian sex determination. In most of mammals, a single genetic trigger, the Y-linked gene Sry (sex determination region on Y chromosome), regulates testicular differentiation. Despite identification of Sry in 1990, precise mechanisms underlying the sex determination of bipotential genital ridges are still largely unknown. Here, we review the recent progress that has provided new insights into the mechanisms underlying genital ridge formation as well as the regulation of Sry expression and its functions in male sex determination of mice.

Generation of fertile and fecund F0 XY female mice from XY ES cells

Known examples of male to female sex reversal in mice are caused by either strain incompatibilities or mutations in genes required for male sex determination. The resultant XY females are often sterile or exhibit very poor fertility. We describe here embryonic stem (ES) cell growth conditions that promote the production of healthy, anatomically normal fertile and fecund female F0 generation mice completely derived from gene-targeted XY male ES cells. The sex reversal is a transient trait that is not transmitted to the F1 progeny. Growth media with low osmolality and reduced sodium bicarbonate, maintained throughout the gene targeting process, enhance the yield of XY females. As a practical application of the induced sex reversal, we demonstrate the generation of homozygous mutant mice ready for phenotypic studies by the breeding of F0 XY females with their isogenic XY male clonal siblings, thereby eliminating one generation of breeding and the associated costs.

Molecular mechanisms involved in mammalian primary sex determination

Sex determination refers to the developmental decision that directs the bipotential genital ridge to develop as a testis or an ovary. Genetic studies on mice and humans have led to crucial advances in understanding the molecular fundamentals of sex determination and the mutually antagonistic signaling pathway. In this review, we summarize the current molecular mechanisms of sex determination by focusing on the known critical sex determining genes and their related signaling pathways in mammalian vertebrates from mice to humans. We also discuss the underlying delicate balance between testis and ovary sex determination pathways, concentrating on the antagonisms between major sex determining genes.

GADD45γ regulates the thermogenic capacity of brown adipose tissue

The coactivator peroxisome proliferator-activated receptor-gamma coactivator 1 α (PGC-1α) is widely considered a central transcriptional regulator of adaptive thermogenesis in brown adipose tissue (BAT). However, mice lacking PGC-1α specifically in adipose tissue have only mild thermogenic defects, suggesting the presence of additional regulators. Using the activity of estrogen-related receptors (ERRs), downstream effectors of PGC-1α, as read-out in a high-throughput genome-wide cDNA screen, we identify here growth arrest and DNA-damage-inducible protein 45 γ (GADD45γ) as a cold-induced activator of uncoupling protein 1 (UCP1) and oxidative capacity in BAT. Mice lacking Gadd45γ have defects in Ucp1 induction and the thermogenic response to cold. GADD45γ works by activating MAPK p38, which is a potent activator of ERRβ and ERRγ transcriptional function. GADD45γ activates ERRγ independently of PGC-1 coactivators, yet synergizes with PGC-1α to induce the thermogenic program. Our findings elucidate a previously unidentified GADD45γ/p38/ERRγ pathway that regulates BAT thermogenesis and may enable new approaches for the stimulation of energy expenditure. Our study also implicates GADD45 proteins as general metabolic regulators.

Switching on sex: transcriptional regulation of the testis-determining gene Sry

Mammalian sex determination hinges on the development of ovaries or testes, with testis fate being triggered by the expression of the transcription factor sex-determining region Y (Sry). Reduced or delayed Sry expression impairs testis development, highlighting the importance of its accurate spatiotemporal regulation and implying a potential role for SRY dysregulation in human intersex disorders. Several epigenetic modifiers, transcription factors and kinases are implicated in regulating Sry transcription, but it remains unclear whether or how this farrago of factors acts co-ordinately. Here we review our current understanding of Sry regulation and provide a model that assembles all known regulators into three modules, each converging on a single transcription factor that binds to the Sry promoter. We also discuss potential future avenues for discovering the cis-elements and trans-factors required for Sry regulation.

Transient neuroprotection by SRY upregulation in dopamine cells following injury in males

Emerging evidence suggest sex-specific regulation of dopamine neurons may underlie susceptibility of males to disorders such as Parkinson's disease (PD). In healthy male dopamine neurons, the Y-chromosome gene product, the sex-determining region on the Y chromosome (SRY) modulates dopamine biosynthesis and motor function. We investigated the regulation and function of SRY in a model of dopamine cell injury. Treatment with the dopaminergic toxin, 6-hydroxydopamine (6-OHDA), significantly elevated SRY mRNA expression (9-fold) in human male dopamine M17 cells. SRY up-regulation occurred via the p-quinone pathway, associated with a 3.5-fold increase in expression of GADD45γ, a DNA damage inducible factor gene and known SRY regulator. In turn, a signaling cascade involving GADD45γ/p38-MAPK/GATA activated the SRY promoter. Knockdown of SRY mRNA in 6-OHDA-treated M17 cells was deleterious, increasing levels of reactive oxygen species (ROS), pro-apoptotic marker PUMA mRNA, and cell injury (+25%, +32% and +34%, respectively). Conversely, ectopic over-expression of SRY in 6-OHDA-treated female SH-SY5Y cells was protective, decreasing ROS, PUMA, and cell injury (-40%, -46%, and -30%, respectively). However, the 6-OHDA-induced increase in SRY expression was diminished with higher concentrations of toxins or with chronic exposure to 6-OHDA. We conclude that SRY upregulation after dopamine cell injury is initially a protective response in males, but diminishes with gradual loss in dopamine cells. We speculate that dysregulation of SRY may contribute the susceptibility of males to PD.

A novel mouse Fgfr2 mutant, hobbyhorse (hob), exhibits complete XY gonadal sex reversal

The secreted molecule fibroblast growth factor 9 (FGF9) plays a critical role in testis determination in the mouse. In embryonic gonadal somatic cells it is required for maintenance of SOX9 expression, a key determinant of Sertoli cell fate. Conditional gene targeting studies have identified FGFR2 as the main gonadal receptor for FGF9 during sex determination. However, such studies can be complicated by inefficient and variable deletion of floxed alleles, depending on the choice of Cre deleter strain. Here, we report a novel, constitutive allele of Fgfr2, hobbyhorse (hob), which was identified in an ENU-based forward genetic screen for novel testis-determining loci. Fgr2^hob is caused by a C to T mutation in the invariant exon 7, resulting in a polypeptide with a mis-sense mutation at position 263 (Pro263Ser) in the third extracellular immunoglobulin-like domain of FGFR2. Mutant homozygous embryos show severe limb and lung defects and, when on the sensitised C57BL/6J (B6) genetic background, undergo complete XY gonadal sex reversal associated with failure to maintain expression of Sox9. Genetic crosses employing a null mutant of Fgfr2 suggest that Fgr2^hob is a hypomorphic allele, affecting both the FGFR2b and FGFR2c splice isoforms of the receptor. We exploited the consistent phenotype of this constitutive mutant by analysing MAPK signalling at the sex-determining stage of gonad development, but no significant abnormalities in mutant embryos were detected.

Regulation of sex determination in mice by a non-coding genomic region

To identify novel genomic regions that regulate sex determination, we utilized the powerful C57BL/6J-Y(POS) (B6-Y(POS)) model of XY sex reversal where mice with autosomes from the B6 strain and a Y chromosome from a wild-derived strain, Mus domesticus poschiavinus (Y(POS)), show complete sex reversal. In B6-Y(POS), the presence of a 55-Mb congenic region on chromosome 11 protects from sex reversal in a dose-dependent manner. Using mouse genetic backcross designs and high-density SNP arrays, we narrowed the congenic region to a 1.62-Mb genomic region on chromosome 11 that confers 80% protection from B6-Y(POS) sex reversal when one copy is present and complete protection when two copies are present. It was previously believed that the protective congenic region originated from the 129S1/SviMJ (129) strain. However, genomic analysis revealed that this region is not derived from 129 and most likely is derived from the semi-inbred strain POSA. We show that the small 1.62-Mb congenic region that protects against B6-Y(POS) sex reversal is located within the Sox9 promoter and promotes the expression of Sox9, thereby driving testis development within the B6-Y(POS) background. Through 30 years of backcrossing, this congenic region was maintained, as it promoted male sex determination and fertility despite the female-promoting B6-Y(POS) genetic background. Our findings demonstrate that long-range enhancer regions are critical to developmental processes and can be used to identify the complex interplay between genome variants, epigenetics, and developmental gene regulation.

Disorders of sex development (DSDs): an update

CONTEXT

Disorders of sex development (DSDs) may arise from genetic defects in testis or ovary determination. Current analytical technologies and improved understanding of major regulatory pathways have cast new insight into the genetic basis for these disorders.

EVIDENCE ACQUISITION

A PubMed search was performed for the years 2011-13 using the terms "disorder of sex development," "gonadal dysgenesis," "ovarian dysgenesis," "array CGH," and "whole exome sequencing." Only articles from peer-reviewed journals were included.

EVIDENCE SYNTHESIS

Key themes that emerged included aberrant regulation of SOX9 via the hTES promoter in 46,XY gonadal DSDs, the role of the MAPK pathway in normal and aberrant gonadal development, and the role of new technologies in identification of gonadal DSDs.

CONCLUSIONS

With the advent of the robust new technologies of array comparative genomic hybridization and genomic sequencing in recent years, many new sex-determining genes have been identified. These genes have been organized into ovarian- and testicular-determining pathways that can block each other's activities. Identification of a mutation in a sex-determining gene in an individual affected with a DSD may warrant more extensive investigation for other phenotypic effects as well as genetic testing of other family members.

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

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

Gadd45 in stress signaling, cell cycle control, and apoptosis

The first identified Gadd45 gene, Gadd45a, encodes a ubiquitously expressed protein that is often induced by DNA damage and other stress signals associated with growth arrest and apoptosis. This protein and the other two members of this small gene family, Gadd45b and Gadd45g, have been implicated in a variety of the responses to cell injury including cell cycle checkpoints, apoptosis, and DNA repair. In vivo, many of the prominent roles for the Gadd45 proteins are associated with signaling mediated by p38 mitogen-activated protein kinases (MAPK). Gadd45 proteins can contribute to p38 activation either by activation of upstream kinase(s) or by direct interaction. In vivo, there are important tissue and cell-type-specific differences in the roles for Gadd45 in MAPK signaling. In addition to being p53-regulated, Gadd45a has been found to contribute to p53 activation via p38. Like other stress and signaling proteins, Gadd45 proteins show complex regulation and numerous effectors.

The genetics of disorders of sex development in humans

One of the defining events during human embryonic development with the most far-reaching effects for the individual is whether the embryo develops as male or female. The crucial step in this process is the differentiation of the bipotential embryonic gonads into either testes or ovaries. If the embryo inherits X and Y sex chromosomes, the Y-linked SRY (sex determining region in Y) gene initiates a network of genes that results in a functional testis and ultimately a male phenotype. By contrast, in an embryo with 2 X chromosomes, the undifferentiated gonad develops as an ovary resulting in a female phenotype. Perturbation of any of the genes in either the testicular or ovarian developmental pathway can result in individuals with disorders of sex development. In this review, we provide a summary of known components of testicular or ovarian pathways and their antagonistic actions and give a brief overview of new technologies currently used to identify the missing pieces of the sex development network.

Transgenic expression of Map3k4 rescues T-associated sex reversal (Tas) in mice

Disorders of sex development in the human population range in severity from mild genital defects to gonadal sex reversal. XY female development has been associated with heterozygous mutations in several genes, including SOX9, WT1 and MAP3K1. In contrast, XY sex reversal in mice usually requires complete absence of testis-determining gene products. One exception to this involves T-associated sex reversal (Tas), a phenomenon characterized by the formation of ovotestes or ovaries in XY mice hemizygous for the hairpin-tail (T(hp)) or T-Orleans (T(Orl)) deletions on proximal mouse chromosome 17. We recently reported that mice heterozygous for a null allele of Map3k4, which resides in the T(hp) deletion, exhibit XY ovotestis development and occasional gonadal sex reversal on the sensitized C57BL/6J-Y(AKR) (B6-Y(AKR)) genetic background, reminiscent of the Tas phenotype. However, these experiments did not exclude the possibility that loss of other loci in the T(hp) deletion, or other effects of the deletion itself, might contribute to Tas. Here, we show that disruption to Sry expression underlies XY gonadal defects in B6-Y(AKR) embryos harbouring the T(hp) deletion and that a functional Map3k4 bacterial artificial chromosome rescues these abnormalities by re-establishing a normal Sry expression profile. These data demonstrate that Map3k4 haploinsufficiency is the cause of T-associated sex reversal and that levels of this signalling molecule are a major determinant of the expression profile of Sry.