Dmrt1 expression is regulated by follicle-stimulating hormone and phorbol esters in postnatal Sertoli cells

Ginsenoside Rg1 promotes neurite growth of retinal ganglion cells through cAMP/PKA/CREB pathways

Background

Mechanisms of synaptic plasticity in retinal ganglion cells (RGCs) are complex and the current knowledge cannot explain. Growth and regeneration of dendrites together with synaptic formation are the most important parameters for evaluating the cellular protective effects of various molecules. The effect of ginsenoside Rg1 (Rg1) on the growth of retinal ganglion cell processes has been poorly understood. Therefore, we investigated the effect of ginsenoside Rg1 on the neurite growth of RGCs.

Methods

Expression of proteins and mRNA were detected by Western blot and qPCR. cAMP levels were determined by ELISA. In vivo effects of Rg1 on RGCs were evaluated by hematoxylin and eosin, and immunohistochemistry staining.

Results

This study found that Rg1 promoted the growth and synaptic plasticity of RGCs neurite by activating the cAMP/PKA/CREB pathways. Meanwhile, Rg1 upregulated the expression of GAP43, Rac1 and PAX6, which are closely related to the growth of neurons. Meantime, H89, an antagonist of PKA, could block this effect of Rg1. In addition, we preliminarily explored the effect of Rg1 on enhancing the glycolysis of RGCs, which could be one of the mechanisms for its neuroprotective effects.

Conclusion

Rg1 promoted neurite growth of RGCs through cAMP/PKA/CREB pathways. This study may lay a foundation for its clinical use of optic nerve diseases in the future.

The transcriptional regulator CBX2 and ovarian function: A whole genome and whole transcriptome approach

The chromobox homolog 2 (CBX2) was found to be important for human testis development, but its role in the human ovary remains elusive. We conducted a genome-wide analysis based on DNA adenine methyltransferase identification (DamID) and RNA sequencing strategies to investigate CBX2 in the human granulosa cells. Functional analysis revealed that CBX2 was upstream of genes contributing to ovarian function like folliculogenesis and steroidogenesis (i.e. ESR1, NRG1, AKR1C1, PTGER2, BMP15, BMP2, FSHR and NTRK1/2). We identified CBX2 regulated genes associated with polycystic ovary syndrome (PCOS) such as TGFβ, MAP3K15 and DKK1, as well as genes implicated in premature ovarian failure (POF) (i.e. POF1B, BMP15 and HOXA13) and the pituitary deficiency (i.e. LHX4 and KISS1). Our study provided an excellent opportunity to identify genes surrounding CBX2 in the ovary and might contribute to the understanding of ovarian physiopathology causing infertility in women.

Estrogen alters gonadal soma-derived factor (Gsdf)/Foxl2 expression levels in the testes associated with testis-ova differentiation in adult medaka, Oryzias latipes

Testis-ova differentiation in sexually mature male medaka (Oryzias latipes) is easily induced by estrogenic chemicals, indicating that spermatogonia persist in sexual bipotentiality, even in mature testes in medaka. By contrast, the effects of estrogen on testicular somatic cells associated with testis-ova differentiation in medaka remain unclear. In this study, we focused on the dynamics of sex-related genes (Gsdf, Dmrt1, and Foxl2) expressed in Sertoli cells in the mature testes of adult medaka during estrogen-induced testis-ova differentiation. When mature male medaka were exposed to estradiol benzoate (EB; 800ng/L), testis-ova first appeared after EB treatment for 14days (observed as the first oocytes of the leptotene-zygotene stage). However, the testis remained structurally unchanged, even after EB treatment for 28days. Although Foxl2 is a female-specific sex gene, EB treatment for 7days induced Foxl2/FOXL2 expression in all Sertoli cell-enclosed spermatogonia before testis-ova first appeared; however, Foxl2 was not detected in somatic cells in control testes. Conversely, Sertoli-cell-specific Gsdf mRNA expression levels significantly decreased after EB treatment for 14days, and no changes were observed in DMRT1 localization following EB treatment, whereas Dmrt1 mRNA levels increased significantly. Furthermore, after EB exposure, FOXl2 and DMRT1 were co-localized in Sertoli cells during testis-ova differentiation, although FOXL2 localization was undetectable in Sertoli-cell-enclosed apoptotic testis-ova, whereas DMRT1 remained localized in Sertoli cells. These results indicated for the first time that based on the expression of female-specific sex genes, feminization of Sertoli cells precedes testis-ova differentiation induced by estrogen in mature testes in medaka; however, complete feminization of Sertoli cells was not induced in this study. Additionally, it is suggested strongly that Foxl2 and Gsdf expression constitute potential molecular markers for evaluating the effects of estrogenic chemicals on testicular somatic cells associated with estrogen-induced testis-ova differentiation in mature male medaka.

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.

Doublesex and mab-3 related transcription factor 1 (DMRT1) is a sex-specific genetic determinant of childhood-onset asthma and is expressed in testis and macrophages

BACKGROUND

Asthma is a disease affecting more boys than girls in childhood and more women than men in adulthood. The mechanisms behind these sex-specific differences are not yet understood.

OBJECTIVE

We analyzed whether and how genetic factors contribute to sex-specific predisposition to childhood-onset asthma.

METHODS

Interactions between sex and polymorphisms on childhood asthma risk were evaluated in the Multicentre Asthma Genetics in Childhood Study (MAGICS)/Phase II International Study of Asthma and Allergies in Childhood (ISAAC II) population on a genome-wide level, and findings were validated in independent populations. Genetic fine mapping of sex-specific asthma association signals was performed, and putatively causal polymorphisms were characterized in vitro by using electrophoretic mobility shift and luciferase activity assays. Gene and protein expression of the identified gene doublesex and mab-3 related transcription factor 1 (DMRT1) were measured in different human tissues by using quantitative real-time PCR and immunohistochemistry.

RESULTS

Polymorphisms in the testis-associated gene DMRT1 displayed interactions with sex on asthma status in a population of primarily clinically defined asthmatic children and nonasthmatic control subjects (lowest P = 5.21 × 10(-6)). Replication of this interaction was successful in 2 childhood populations clinically assessed for asthma but showed heterogeneous results in other population-based samples. Polymorphism rs3812523 located in the putative DMRT1 promoter was associated with allele-specific changes in transcription factor binding and promoter activity in vitro. DMRT1 expression was observed not only in the testis but also in lung macrophages.

CONCLUSION

DMRT1 might influence sex-specific patterns of childhood asthma, and its expression in testis tissue and lung macrophages suggests a potential involvement in hormone or immune cell regulation.

Steroidogenic factor 1 differentially regulates fetal and adult leydig cell development in male mice

The nuclear receptor steroidogenic factor 1 (SF-1, AD4BP, NR5A1) is a key regulator of the endocrine axes and is essential for adrenal and gonad development. Partial rescue of Nr5a1(-/-) mice with an SF-1-expressing transgene caused a hypomorphic phenotype that revealed its roles in Leydig cell development. In contrast to controls, all male rescue mice (Nr5a1(-/-);tg(+/0)) showed varying signs of androgen deficiency, including spermatogenic arrest, cryptorchidism, and poor virilization. Expression of various Leydig cell markers measured by immunohistochemistry, Western blot analysis, and RT-PCR indicated fetal and adult Leydig cell development were differentially impaired. Whereas fetal Leydig cell development was delayed in Nr5a1(-/-);tg(+/0) embryos, it recovered to control levels by birth. In contrast, Sult1e1, Vcam1, and Hsd3b6 transcript levels in adult rescue testes indicated complete blockage in adult Leydig cell development. In addition, between Postnatal Days 8 and 12, peritubular cells expressing PTCH1, SF-1, and CYP11A1 were observed in control testes but not in rescue testes, indicating SF-1 is needed for either survival or differentiation of adult Leydig cell progenitors. Cultured prepubertal rat peritubular cells also expressed SF-1 and PTCH1, but Cyp11a1 was expressed only after treatment with cAMP and retinoic acid. Together, data show SF-1 is needed for proper development of fetal and adult Leydig cells but with distinct primary functions; in fetal Leydig cells, it regulates differentiation, whereas in adult Leydig cells it regulates progenitor cell formation and/or survival.

Receptors and signaling pathways involved in proliferation and differentiation of Sertoli cells

The identification of the hormones and other factors regulating Sertoli cell survival, proliferation, and maturation in neonatal, peripubertal, and pubertal life remains one of the most critical questions in testicular biology. The regulation of Sertoli cell proliferation and differentiation is thought to be controlled by cell-cell junctions and a set of circulating and local hormones and growth factors. In this review, we will focus on receptors and intracellular signaling pathways activated by androgen, follicle-stimulating hormone, thyroid hormone, activin, retinoids, insulin, insulin-like growth factor, relaxin, and estrogen, with special emphasis on estrogen receptors. Estrogen receptors activate intracellular signaling pathways that converge on cell cycle and transcription factors and play a role in the regulation of Sertoli cell proliferation and differentiation.

Differential role of the estrogen receptors ESR1 and ESR2 on the regulation of proteins involved with proliferation and differentiation of Sertoli cells from 15-day-old rats

The aim of the present study was to investigate the role of each estrogen receptors on the regulation of proteins involved with proliferation and differentiation of Sertoli cells from 15-day-old rats. Activation of ESR1 by 17β-estradiol (E2) and ESR1-selective agonist PPT increased CCND1 expression, and this effect was dependent on NF-kB activation. E2 and the ESR2-selective agonist DPN, but not PPT, increased, in a PI3K and CREB-dependent manner, the expression of CDKN1B and the transcription factors GATA-1 and DMRT1. Analyzing the expression of ESR1 and ESR2 in different stages of development of Sertoli cells, we observed that the ESR1/ESR2 ratio decreased with age, and this ratio seems to be important to determine the end of cell proliferation and the start of cell differentiation. In Sertoli cells from 15-day-old rats, the ESR1/ESR2 ratio favors the effect of ESR1 and the activation of this receptor increased [Methyl-(3)H]thymidine incorporation. We propose that in Sertoli cells from 15-day-old rats E2 modulates Sertoli cell proliferation through ESR1/NF-kB-mediated increase of CCND1, and cell cycle exit and differentiation through ESR2/CREB-mediated increase of CDKN1B, GATA-1 and DMRT1. The present study reinforces the important role of estrogen for normal testis development.

Effects of FSH on testicular mRNA transcript levels in the hypogonadal mouse

FSH acts through the Sertoli cell to ensure normal testicular development and function. To identify transcriptional mechanisms through which FSH acts in the testis, we have treated gonadotrophin-deficient hypogonadal (hpg) mice with recombinant FSH and measured changes in testicular transcript levels using microarrays and real-time PCR 12, 24 and 72 h after the start of treatment. Approximately 400 transcripts were significantly altered at each time point by FSH treatment. At 12 h, there was a clear increase in the levels of a number of known Sertoli cell transcripts (e.g. Fabp5, Lgals1, Tesc, Scara5, Aqp5). Additionally, levels of Leydig cell transcripts were also markedly increased (e.g. Ren1, Cyp17a1, Akr1b7, Star, Nr4a1). This was associated with a small but significant rise in testosterone at 24 and 72 h. At 24 h, androgen-dependent Sertoli cell transcripts were up-regulated (e.g. Rhox5, Drd4, Spinlw1, Tubb3 and Tsx) and this trend continued up to 72 h. By contrast with the somatic cells, only five germ cell transcripts (Dkkl1, Hdc, Pou5f1, Zfp541 and 1700021K02Rik) were altered by FSH within the time-course of the experiment. Analysis of canonical pathways showed that FSH induced a general decline in transcripts related to formation and regulation of tight junctions. Results show that FSH acts directly and indirectly to induce rapid changes in Sertoli cell and Leydig cell transcript levels in the hpg mouse but that effects on germ cell development must occur over a longer time-span.

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.

In vivo regulation of follicle-stimulating hormone receptor by the transcription factors upstream stimulatory factor 1 and upstream stimulatory factor 2 is cell specific

Pituitary FSH promotes pubertal timing and normal gametogenesis by binding its receptor (FSHR) located on Sertoli and granulosa cells of the testis and ovary, respectively. Studies on Fshr transcription provide substantial evidence that upstream stimulatory factor (USF) 1 and USF2, basic helix-loop-helix leucine zipper proteins, regulate Fshr through an E-box within its promoter. However, despite the strong in vitro support for USF1 and USF2 in Fshr regulation, there is currently no in vivo corroborating evidence. In the present study, chromatin immunoprecipitation demonstrated specific binding of USF1 and USF2 to the Fshr promoter in both Sertoli and granulosa cells, in vivo. Control cells lacking Fshr expression showed no USF-Fshr promoter binding, thus correlating USF-promoter binding to gene activity. Evaluation of Fshr expression in Usf1 and Usf2 null mice further explored USF's role in Fshr transcription. Loss of either gene significantly reduced ovarian Fshr levels, whereas testis levels were unaltered. Chromatin immunoprecipitation analysis of USF-Fshr promoter binding in Usf-null mice indicated differences in the composition of promoter-bound USF dimers in granulosa and Sertoli cells. Promoter-bound USF dimer levels declined in granulosa cells from both null mice, despite increased USF2 levels in Usf1-null ovaries. However, compensatory increases in promoter-bound USF homodimers were evident in Usf-null Sertoli cells. In summary, this study provides the first in vivo evidence that USF1 and USF2 bind the Fshr promoter and revealed differences between Sertoli and granulosa cells in compensatory responses to USF loss and the USF dimeric composition required for Fshr transcription.

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.

Transgenic rescue of SF-1-null mice

Steroidogenic factor 1 (SF-1, Nr5a1, and Ad4bp) is an orphan nuclear receptor required for adrenal and gonad development and endocrine regulation. To extend our understanding of SF-1 function and the mechanisms controlling its expression, a transgenic rescue strategy was employed to locate important transcriptional control regions and to reveal functional roles of the protein. A rat yeast artificial chromosome containing Ftz-F1, the gene encoding SF-1, was used to generate mice with different transgenes that varied in size. Rat SF-1 mRNA expression was assayed to assess each transgene's targeting ability. SF-1-deficient/transgene-positive (SF-1(-/-); tg/+) "rescue" mice were then generated and the animals' developmental and reproductive status was evaluated. The results identified differences in expression patterns and rescue abilities that provided insight into SF-1 transcriptional control and function. Comparing transgene maps and mRNA profiles placed critical transcriptional elements for pituitary and hypothalamic expression to a region 3' to intron 4, whereas examination of rescued mice revealed that an approximately 153-kb region of the Ftz-F1 locus recapitulates most or all activity ascribed to the endogenous allele. A second line of rescued mice was hypomorphic, with males showing defects in androgen-dependent tissues due to abnormal Leydig cell differentiation. Histological analysis of embryonic (e14.5) and adult testes from these mice implicated SF-1 in roles that are distinct in fetal and adult Leydig cells.

Multiple Alternative Splicing and Differential Expression of dmrt1 During Gonad Transformation of the Rice Field Eel1

Morphologically distinct males and females are observed throughout the animal kingdom. Why and how sex evolved and is maintained in most living organisms remains a key question in cellular and evolutionary biology. Here we report that four isoforms of dmrt1 (dsx- and mab3-related transcription factor 1) are generated in testis, ovotestis, and ovary by alternative splicing in the rice field eel, a fresh water fish that undergoes natural sex reversal from female to male during its life cycle. These transcripts encode four different size proteins with 301, 196, 300, and 205 amino acids. Like fly doublesex splicing, the dmrt1 of the rice field eel is also alternatively spliced at the 3' region, which generates diverse isoforms in gonads by alternative use of 3' sequences. Not only is dmrt1 expressed specifically in gonads, but its multiple isoforms are differentially coexpressed in gonadal epithelium during gonad transformation. Expression levels of a and b isoforms of dmrt1 ranged from low to high (ovary < ovotestis I < ovotestis II < ovotestis III < testis), based on comparisons of mean values from real-time fluorescent quantitative reverse transcription-polymerase chain reaction analysis. The overall expression level of dmrt1 b was much lower than that of dmrt1 a. Expression of dmrt1 d was not only low, but it also did not change significantly during sex transformation. The differential expression of dmrt1 isoforms may also be regulated by their 3' untranslated regions (UTRs), although these 3' UTRs do not contribute to intracellular localization of the Dmrt1 protein. These results provide new insight into roles of regulation at the level of splicing of dmrt1 in governing the sex differentiation cascade.

A FTZ-F1-containing yeast artificial chromosome recapitulates expression of steroidogenic factor 1 in vivo

Steroidogenic factor 1 (SF-1/Nr5a1) is an orphan nuclear receptor encoded by the Ftz-F1 gene and is required for gonad and adrenal development and regulation of hormone production within the reproductive and adrenal axes. To extend our understanding of Ftz-F1 and its role in SF-1 expression, we identified and characterized a yeast artificial chromosome (YAC) containing Ftz-F1. Within this YAC, Ftz-F1 is centrally located and flanked by genes encoding a second orphan nuclear receptor, germ cell nuclear factor, and proteasome (prosome, macropain) subunit beta type 7. Three lines of transgenic mice carrying the YAC were generated and in two lines (lines 7 and 14), RT-PCR and ribonuclease protection analysis showed that expression of transgenic SF-1 mimicked that of endogenous SF-1, both spatially and quantitatively. In the third line (line 15), pituitary and hypothalamic expression were absent. Comparison of the integrated transgenes revealed that line 15 was truncated at the end of intron 4 and revealed a region within the locus that is responsible for SF-1 expression in the pituitary and hypothalamus. The line 14 transgene was introduced into a mouse strain lacking functional SF-1. Examination of SF-1-deficient, transgene-positive mice revealed that the YAC was able to rescue adrenal and gonad development, which normally arrests in the SF-1-null embryos and showed that the 153-kb transgene integrated in line 14 is sufficient to properly direct SF-1 expression and support its biological activity. Thus, the study defines a region of Ftz-F1 that contains the requisite set of regulatory elements to direct SF-1 cell-specific expression and all temporal and quantitative changes need for its biological activity.

Gene structure, multiple alternative splicing, and expression in gonads of zebrafish Dmrt1

Many basic cellular processes are shared across vast phylogenetic distances, whereas sex-determining mechanisms are highly variable between phyla although the existence of two sexes is nearly universal in the animal kingdom. The only molecular similarity in sex determination found so far between phyla is among the fly doublesex, worm mab-3, and vertebrate Dmrt1/DMY, which contain a zinc-finger-like DNA-binding motif, DM domain. Here we report that three isoforms of the zebrafish Dmrt1 were generated in gonads by multiple alternative splicing, which encoded predicted proteins with 267, 246, and 132 amino acids, respectively. By cDNA cloning and genomic structure analysis, we found that there were seven exons of Dmrt1, which were alternatively spliced to generate the Dmrt1 isoforms. Northern blotting analysis revealed that expression of zebrafish Dmrt1 was higher in testis than ovary. Real time fluorescent quantitative RT-PCR indicated that expression of isoform a of Dmrt1 was dominantly higher than those of Dmrt1 b and c. Furthermore, in situ hybridization to gonads sections showed that Dmrt1 was expressed in developing germ cells of both testis and ovary, suggesting that the Dmrt1 gene is not only associated with testis development, but also, may be important in ovary differentiation of zebrafish.

Role of the basic helix-loop-helix transcription factor, scleraxis, in the regulation of Sertoli cell function and differentiation

Sertoli cells are a postmitotic terminally differentiated cell population in the adult testis that form the seminiferous tubules and provide the microenvironment and structural support for developing germ cells. The transcription factors that regulate Sertoli cell differentiation remain to be elucidated. The basic helix-loop-helix transcription factors are involved in the differentiation of a variety of cell lineages during development and are expressed in pubertal Sertoli cells. A yeast-two-hybrid procedure was used to screen a Sertoli cell library from 20-d-old pubertal rats to identify dimerization partners with the ubiquitous E47 basic helix-loop-helix transcription factor. Scleraxis was identified as one of the interacting partners. Among the cell types of the testis, scleraxis expression was found to be specific to Sertoli cells. Analysis of the expression pattern of scleraxis mRNA in developing Sertoli cells revealed an increase in scleraxis message at the onset of puberty. Sertoli cells respond to FSH to promote expression of differentiated gene products such as transferrin that aid in proper development of the germ cells. Analysis of the hormonal regulation of scleraxis expression revealed a 4-fold increase in scleraxis mRNA in response to the presence of FSH or dibutryl cAMP in cultured Sertoli cells. An antisense oligonucleotide procedure and overexpression analysis were used to determine whether scleraxis regulates the expression of Sertoli cell differentiated gene products. An antisense oligonucleotide to scleraxis down-regulated transferrin promoter activity in Sertoli cells. A transient overexpression of scleraxis in Sertoli cells stimulated transferrin and androgen binding protein promoter activities and the expression of a number of differentiated genes. Observations suggest scleraxis functions in a number of adult tissues and is involved in the regulation and maintenance of Sertoli cell function and differentiation. This is one of the first adult and nontendon/chondrocyte-associated functions described for scleraxis.

Silencing of Fshr occurs through a conserved, hypersensitive site in the first intron

Expression of the FSH receptor (Fshr) is restricted to testicular Sertoli cells and ovarian granulosa cells, thereby limiting the direct targets of FSH action to these somatic cells of the gonads. Earlier studies indicate that transcription of Fshr in the gonads requires elements outside the gene's immediate 5' flanking sequence. To help uncover candidate regulatory sequences, comparative genomics and deoxyribonuclease I hypersensitivity mapping were employed. A total of 156 evolutionarily conserved sequences were found, and partial deoxyribonuclease I hypersensitivity mapping across 45 kb of 5' flanking sequence and the first intron identified four hypersensitive sites, DHS1-4. Notably, DHS1 and DHS2 localized to conserved sites in the promoter region and exon 1 and correlated with the active state of the gene. DHS3 also corresponded to a conserved site (site 7) but was more pronounced in nonexpressing myoid cells, suggesting a role in gene silencing. Transient transfection analysis of DHS3 confirmed its role in gene silencing, a function that was promoter, cell type, and position dependent. Protein-DNA binding studies on DHS3 revealed that octamer transcription factor 1 (OCT-1) and GATA-4 bound site 7, in vitro, and transient transfection analysis showed that their binding sites were required for silencing activity. Furthermore, chromatin immunoprecipitation revealed that OCT-1 bound to site 7 in the endogenous gene, but only in myoid cells. In contrast, GATA-1 bound site 7 predominantly in Sertoli cells, suggesting that it attenuates silencer activity. The findings reveal that OCT-1 binds within DHS3 to silence Fshr transcription and implicate members of the GATA family in the modulation of this activity.

Gata4 regulates testis expression of Dmrt1

The doublesex and mab-3 related transcription factor 1 (Dmrt1) is a putative transcriptional regulator that is expressed exclusively in the gonads and is required for postnatal testis differentiation. Here we describe the transcriptional mechanisms regulating testis-specific expression of the Dmrt1 gene. Transient-transfection analysis identified a region of the promoter between kb -3.2 and -2.8 that is important for Sertoli cell-specific expression. DNase I footprinting revealed four sites of DNA-protein interaction within this region, three of which were prominent in primary Sertoli cells. Analysis of these sites, using electrophoretic mobility shift assays, revealed that Gata4 and another unknown factor bound within these regions. Further transient-transfection assays of various mutant promoters established the functional relevance of the Gata4-response and unknown factor-response elements, while studies of Dmrt1 expression in 13.5 days postcoitum Fog2 null gonads supported the in vivo importance of Gata4's regulation. As a whole, these studies identify Gata4 as an important regulator in the Dmrt1 transcriptional machinery that is responsible for robust expression of Dmrt1 in the testis.

Conservation of the function of DMRT1 regulatory sequences in mammalian sex differentiation

Among genes involved in sex determination and differentiation, DMRT1 is the only one characterized to date containing a domain (the DM domain) that is conserved between phyla. To study DMRT1 transcriptional regulation within mammalian phyla, we generated transgenic mice that express green fluorescent protein (GFP) or Cre-recombinase (Cre) under the control of 2.6 kb of pig DMRT1 5' flanking sequences (pDMRT1p-GFP and pDMRT1p-Cre, respectively). Within the pDMRT1p-GFP positive mice, GFP expression was observed in the XY genital ridge by embryonic day 11.5 (e11.5) and remained detectable during testis embryonic development to birth. GFP expression was restricted within testis cords as soon as cords were detectable. No fluorescence was observed in developing ovaries, although more sensitive RT-PCR analysis revealed transgene expression in embryonic ovaries from e13.5 to e15.5. RT-PCR performed on fluorescent activated cell sorter (FACS)-purified GFP cells from e14.5, e17.5, and e19.5 developing testis showed that GFP expression was restricted to cells expressing the endogenous mouse Dmrt1. GFP cells also expressed Mis and Oct4, showing that the transgene is expressed in both Sertoli cell and germ cell compartments. In postnatal testis, transgene expression was detectable by GFP fluorescence from P0 to P21 in mice heterozygous for the transgene and through adulthood in mice homozygous for the transgene. In pDMRT1p-Cre positive mice, Cre expression was detected within the genital ridges of both XY and XX embryos. We conclude that DMRT1 regulatory mechanisms during sexual differentiation are functionally conserved across mammalian evolution. The transgenic mouse lines described should provide useful marker systems for studies involving Dmrt1 gene expression during sex differentiation.

Positive regulation of retinoic acid receptor alpha by protein kinase C and mitogen-activated protein kinase in sertoli cells

Retinoic acid receptor alpha (RARalpha) is required for normal testis function. Similar to other steroid hormone receptors, RARalpha appears to undergo an activation process by which it translocates from the cytoplasm to the nucleus where it acts as a transcription factor. In this report, we demonstrate that RARalpha nuclear trafficking in Sertoli cells is positively regulated by phorbol-12-myristate-13-acetate-activated protein kinase C without the requirement of ligand, retinoic acid. Protein kinase C then stimulates the downstream mitogen-activated protein kinase, and the nuclear localization of RARalpha is dependent on activation of both kinases. The increase in RARalpha nuclear translocation is also coupled with enhanced transcriptional activity of RARalpha. This mechanism of RARalpha positive regulation is unique, different from that of its negative regulation, that has previously been shown to be dependent on cAMP-dependent protein kinase A and more importantly, dependent on its ligand. However, the mechanism by which retinoic acid positively influences the nuclear localization of RARalpha is not due to retinoic acid directly increasing protein kinase C or mitogen-activated protein kinase activities. Nonetheless, the positive influence of retinoic acid is also dependent on these two kinases as determined by inhibitor studies. These results suggest two mechanisms for RARalpha activation in Sertoli cells: one involving only the two kinases, the other involving both the ligand and the two kinases. These regulatory mechanisms for RARalpha activation, both positive and negative, may be critical for the proper function of RARalpha in the testis.

Sp1 and Egr1 regulate transcription of the Dmrt1 gene in Sertoli cells

Dmrt1 is a recently described gene that is specifically expressed in the gonads and is required for postnatal testis differentiation. Here, we describe the transcriptional mechanisms regulating the Dmrt1 proximal promoter in testicular Sertoli cells. A genomic clone containing exon 1 of the rat Dmrt1 gene and more than 9 kilobases of 5' flanking sequence was isolated and characterized. Several prominent transcriptional start sites were identified, with the major site located 102 bases from the translational start. The Dmrt1 5' flanking region from -5000 to +74 was transcriptionally active in primary Sertoli cells, and deletion analysis of this fragment identified 2 major regions needed for full Dmrt1 promoter function. These regions were located between -3200 and -2000 base pairs (bp) and downstream of -150 bp relative to the major transcriptional start site. DNase I footprint analysis of the region downstream of -150 bp revealed 3 regions that are bound by proteins from Sertoli cell nuclear extracts. Site-directed mutagenesis of these regions identified 2 elements that activate the Dmrt1 promoter and 2 that repress it. The positive elements bind the transcription factors Sp1, Sp3, and Egr1, suggesting that these transcription factors play a critical role in Dmrt1 regulation in the testis.