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

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

[Disorders of sex differentiation: genes responsible for development of genital system and final phenotype]

OBJECTIVE

The study summarizes data on genes responsible for development of gonads and subsequently of additional structures of genital system in humans. It comprises the effect of gene defects on clinical phenotype.

SUBJECT

Review article.

SETTING

Department of Pediatrics, University Hospital Motol and 2nd Faculty of Medicine, Charles University in Prague.

SUBJECT AND METHOD

We present the overview of genes that contribute to development of genital system. Special emphasis is given on patient's phenotype related with various genetic disorders. Data were mainly found on Pubmed or OMIM web-sites according to key words "sex development" and "sex determination". We focused on ten genes with known relation to gonadal development--SRY, SOX9, SF1, DAX1, WNT4, WT1, DMRT1, DHH, RSPO1, ATRX.

CONCLUSION

Sex development is a complex process orchestrated by numerous genes. Here we collect information on gene defect (gene mutations or defective number of gene copies) that cause gonadal maldevelopment with effects on final phenotype. Currently, genetic background of numerous disorders can be detected. That allows not only to verify the diagnosis but also to predict the future sexual development and genetic risk for other family members.

Prenatal sonographic findings in a fetus with splenogonadal fusion limb defect syndrome

Splenogonadal fusion limb defect syndrome (SGFLD) is a very rare abnormality. We report on a case with prenatal sonographic findings of a fetus with postnatally diagnosed SGFLD syndrome. This is also the second case of prenatal ultrasonographic diagnosis of gastrointestinal malrotation associated with SGFLD. A 26-year-old primigravid woman was referred to our clinic because of nonvisualization of both fetal femoral bones at 20 weeks of gestation. A detailed sonographic examination showed complete bilateral absence of lower limbs, micrognathia, single umbilical artery and a right-sided stomach. Autopsy confirmed prenatal sonographic findings and additionally showed that the spleen was abnormally connected to the left gonad by a fibrous band. In conclusion, although all limbs and both sides were equally affected in most of the reported cases, SGFLD syndrome should be considered in cases with terminal limb defects of lower limbs.

Germ cell sex determination in mammals

One of the major decisions that germ cells make during their development is whether to differentiate into oocytes or sperm. In mice, the germ cells' decision to develop as male or female depends on sex-determining signalling molecules in the embryonic gonadal environment rather than the sex chromosome constitution of the germ cells themselves. In response to these sex-determining cues, germ cells in female embryos initiate oogenesis and enter meiosis, whereas germ cells in male embryos initiate spermatogenesis and inhibit meiosis until after birth. However, it is not clear whether the signalling molecules that mediate germ cell sex determination act in the developing testis or the developing ovary, or what these signalling molecules might be. Here, we review the evidence for the existence of meiosis-inducing and meiosis-preventing substances in the developing gonad, and more recent studies aimed at identifying these molecules in mice. In addition, we discuss the possibility that some of the reported effects of these factors on germ cell development may be indirect consequences of impairing sexual differentiation of gonadal somatic cells or germ cell survival. Understanding the molecular mechanisms of germ cell sex determination may provide candidate genes for susceptibility to germ cell tumours and infertility in humans.

Isolation and characterization of sexual dimorphism genes expressed in chicken embryonic gonads

In chicken, the bipotential embryonic gonad differentiates into either a pair of testes or an ovary, but few genes that underlying the gonadal sex differentiation have been identified and the sex-determination gene is still unknown. To identify more genes involved in chicken sex differentiation, we employed suppression subtractive hybridization to isolate differentially expressed genes between sexes from chicken gonads during a period of E3.5-E6. A total of 152 cDNA clones corresponding to 88 genes (41 from F-M library and 47 from M-F library) were screened using dot-blot analysis. These genes are located mainly on the macrochromosomes (1-5) with five in the sex chromosomes (one in W and four in Z), encoding four dominating molecular categories belonging to enzyme, DNA association, RNA association, and structural protein. Comparing the obtained cDNA sequences with those in chicken EST database, it showed that cDNAs of 32 genes from F-M library and 16 from M-F library have homologs in two reported embryonic gonad cDNA libraries. Quantitative real-time PCR analysis of eight genes involved in epigenetic and transcription regulation showed significantly different expression between sexes of CDK2AP1, SMARCE1, SAP18, SUDS3, and PQBP1 appeared at the early stage in gonad development (E4). Based on the functional comparison of sexual differentially expressed genes, the roles of some putatively important genes including ATP5A1W, CDK2AP1, mitochondrial transcripts, etc. have been analyzed. In conclusion, characterization of isolated genes would provide valuable clues to identify potential candidates involved in genetic mechanisms of chicken sex differentiation and gonad development.

[Current status of study on embryonic hematopoietic development in aorta-gonad-mesonephros -- review]

Aorta-gonad-mesonephros (AGM) is well known as a main structure that de novo generates hematopoietic primary stem cells (HSC) in mid-gestation mammalian embryos. Hemogenic endothelium, and recently, subendothelial mesenchyme as well as hemangioblast are shown as contributing to blood formation in AGM region. AGM-HSC displays dynamic changes in surface markers, including CD41, CD45 and several endothelial-specific molecules. The novel finding of interleukin-3 as a potent regulator of AGM-HSC seems very interesting. Moreover, zebra fish model reveals PGE2 as a novel stimulator of HSC in AGM and kidney marrow, which is also the case in mouse hematopoietic tissues. Identification of mesenchymal stem cells with significant hematopoietic supporting capacity in AGM region suggests an alternative pathway to explore new molecules governing embryonic and adult hematopoiesis. In this paper, the hemogenic model in AGM region, surface markers on HSCs in AGM region and regulation of HSCs in AGM region were reviewed.

[Screening of sexual differentially expressed genes in the chicken early embryonic gonads using DNA microarray]

Using Affymetrix's Chicken Genome Array, we used total RNA isolated from the gonads of male and female chicks at embryonic day 9 to identify the genes differentially expressed between male and female. Statistical results show 19 493 genes expressed in male chick's embryonic gonads and 19 368 genes expressed in female. There were 145 genes specificity expressed in male and 189 genes in female. The gene ontology classification (GOC) indicated these differentially expressed genes were mainly involved in cellular component, cell process and molecular banding, a part of genes were involved in organelle component, metabolic process, biologic process, catalytic activity and signal transducer activity. Some genes had reported for sex determination and differentiation in birds, such as avian sex-specific avian sex-specific W-linked, chomodomain-helicase-DNA-binding protein 1 and sex determining region Y-box 9. In addition, we also found several genes or hypothetical proteins were unknown function for the gonad differentiation and development, focus to their biological function and expression pattern in further works would provide a beneficial reference for understand the mechanism of sex differentiation and determination in birds.

Clotrimazole exposure modulates aromatase activity in gonads and brain during gonadal differentiation in Xenopus tropicalis frogs

Clotrimazole is a pharmaceutical used for treatment of fungal infections. It has been found in surface waters outside municipal wastewater treatment plants but data are scarce regarding its effects on aquatic organisms. It is known that clotrimazole and other imidazole fungicides are inhibitors of the enzyme aromatase (CYP 19). Aromatase converts androgens into estrogens and is suggested to be involved in the sex differentiation in amphibians. The aim of the present study was to evaluate effects of larval exposure to clotrimazole on aromatase activity in brain and gonads, and on gonadal differentiation in Xenopus tropicalis frogs. Another purpose was to determine if larval exposure to ethynylestradiol (EE(2)), at a concentration known to cause male-to-female sex reversal, affects aromatase activity in brain and gonads during gonadal differentiation. Tadpoles were exposed from shortly after hatching (Nieuwkoop and Faber developmental stages 47-48) until complete metamorphosis (NF stage 66) to 6, 41, and 375 nM clotrimazole or 100 nM (nominal) EE(2). Aromatase activity was measured in the brain and gonad/kidney complex of tadpoles during gonadal differentiation (NF stage 56) and, in the clotrimazole experiment, also at metamorphosis. In clotrimazole-exposed tadpoles gonadal aromatase activity increased over exposure time in the 41 and 375 nM groups but did not differ significantly from the control group. Gonadal aromatase activity was increased in both sexes exposed to 41 and 375 nM clotrimazole at metamorphosis. Brain aromatase activity was decreased in tadpoles (NF stage 56) exposed to 375 nM clotrimazole, but at metamorphosis no differences were seen between groups or between sexes. No effects of clotrimazole on sex ratio or gonadal histology were noted at completed metamorphosis. EE(2)-exposed tadpoles had a slightly decreased gonadal aromatase activity, though not significantly different from control group, and there was no effect of EE(2) on brain aromatase activity. All EE(2)-exposed tadpoles developed ovaries. These findings indicate that estrogen-induced ovarian differentiation is not paralleled by increased gonadal aromatase activity in X. tropicalis. Further studies are needed, especially on developmental reproductive toxicity, to assess the risk for endocrine disruption in wild amphibians posed by clotrimazole and other imidazole fungicides.

Male fertility and strategies for fertility preservation following childhood cancer treatment

Infertility in the male is a potential complication of childhood cancer treatment for long-term survivors. The risk is dependent primarily on the treatment used, but also on the underlying disease. Chemotherapy (especially alkylating agents) and radiotherapy, even in low doses, may damage the seminiferous epithelium and impair spermatogenesis in both children and adults. Leydig cell function and testosterone production are generally preserved after chemotherapy and low dose radiotherapy, whilst larger doses of radiotherapy may result in hypogonadism. Patients treated with potentially gonadotoxic treatments require regular multidisciplinary follow-up including assessment of puberty and gonadal function. Currently the only option available for fertility preservation in young males treated for cancer is semen cryopreservation. For pre-pubertal patients, techniques for fertility preservation remain theoretical and as yet unproven. These include hormonal manipulation of the gonadal environment before treatment, germ cell transplantation and testis xenografting, which have all shown promise in a variety of animal studies. Refinement of these techniques requires investigations in relevant animal models. In the present chapter we include data which suggest that the common marmoset (Callithrix jacchus) monkey, a New World primate, exhibits important parallels with human testicular development and may help us to understand why the pre-pubertal testis is vulnerable to effects of cytotoxic therapy on future fertility.

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

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

Testis development, fertility, and survival in Ethanolamine kinase 2-deficient mice

Ethanolamine kinase 2 (Eki2) was previously isolated from a differential expression screen designed to identify candidate genes involved in testis development and differentiation. In mouse, Eki2 is specifically up-regulated in Sertoli cells of the developing testis at the time of sex determination. Based on this expression profile, Eki2 was considered a good candidate testis-determining gene. To investigate a possible role of Eki2 in testis development, we have generated a mouse with targeted disruption of the Eki2 gene by using an EGFP replacement strategy. No abnormalities were detected in the Eki2-deficient mice with regard to embryonic and adult testis morphology, differentiation, function, or fertility. Furthermore, no significant differences were observed in litter sizes, pup mortality rates, or distribution of the sexes among the offspring. Ethanolamine kinases are involved in the biosynthesis of phosphatidylethanolamine, a major membrane phospholipid. Expression analysis indicates that the absence of an apparent phenotype in the Eki2-deficient mice may be due to compensation by Eki2-family members or the activation of an alternative pathway to generate phosphatidylethanolamine. Expression of EGFP in this mouse model enabled the isolation of gonad cell populations, providing a useful resource from which to obtain relatively pure early steroidogenic cells for further studies.

Immunohistochemical detection and biological activities of CYP17 (P450c17) in the indifferent gonad of the frog Rana rugosa

Sex steroids play a crucial role in the gonad differentiation in various species of vertebrates. However, little is known regarding the localization and biological activity of steroid-metabolizing enzymes during gonadal sex differentiation in amphibians. In the present study, we showed by real-time RT-PCR analysis that the expression of CYP17, one of the key steroidogenic enzymes, was higher in the indifferent gonad during sex differentiation in male than in female tadpoles of Rana rugosa but that there was no difference detected in the 3betaHSD mRNA level between the male and female gonads. We next examined the localization of CYP17, 3betaHSD and 17betaHSD in the indifferent and differentiating gonads by using three kinds of antibodies specific for CYP17, 3betaHSD and 17betaHSD, respectively. Positive signals for CYP17, 3betaHSD and 17betaHSD were observed in somatic cells of the indifferent gonad of males and in the interstitial cell of the testis. The enzymatic activity of CYP17 was also examined in the gonad during sex differentiation in this species. [(3)H]Progesterone (Prog) was converted to [(3)H]androstenedione (AE) in the indifferent gonad in males and females, but the rate of its conversion was higher in males than in females. Moreover, fluorescence in situ hybridization (FISH) analysis revealed that the CYP17 gene was located on the q arm of chromosome 9, indicating that CYP17 was autosomal in R. rugosa. Taken together, the results demonstrate that the CYP17 protein is synthesized in somatic cells of the indifferent gonad during gonadal sex differentiation in R. rugosa and that it is more active in converting Prog to AE in males than in females. The data suggest that CYP17 may be involved in testicular formation during sex differentiation in this species.

[Genetic background of sex determination and gonadal development disorders]

Intersexual disorders, the causes of which are frequently difficult to diagnose, usually result from the disruption of sex determination and gonadal development or from impairment in function of endocrine organs such as gonads and adrenal glands. Thus consideration of etiopatogenesis of intersexuality should be based on an analysis of the genetic control of sex determination, gonadal differentiation and first of all molecular regulation of steroidogenic cell differentiation and functioning. These processes take place in the fetal gonads, which explains the small amount of data concerning the development of human gonads. However, numerous investigations of gene expression in murine gonads have revealed a complicated machinery involved in sex determination and gonadal differentiation. Moreover, data obtained from mice have led to a better understanding of the molecular background of sex determination and gonad differentiation in humans. Nevertheless, the interpretation of mouse gene knock-outs does not always reflect mutations of their homologues in man. This article compares data in humans and mice, revealing the existence of many sex-determining genes in both, which should be taken into consideration during the diagnosis of intersexual disorders. Mutations of some genes controlling murine gonad development have not been described in humans so far. This indicates the necessity of conducting extensive genetic analysis of individuals with intersexual disorders.

Having it both ways: Sox protein function between conservation and innovation

Transcription factors of the Sox family arose around the advent of multicellularity in animals, arguing that their ability to regulate the expression of extracellular matrix, cell adhesion and signaling molecules may have been instrumental in the generation of metazoans. In particular, during vertebrate evolution, the Sox family experienced a phase of expansion that led to the appearance of groups of highly homologous Sox proteins and the division of existing Sox protein functions among group members. It furthermore allowed Sox transcription factors to acquire numerous novel functions. These past events of subfunctionalization and neofunctionalization can still be recognized today in all groups of the Sox family. They have led to partial functional redundancies, but also to interesting species-specific variations in the developmental roles of Sox proteins as shown here for the SoxB and the SoxE groups.

Pitx2 deletion in pituitary gonadotropes is compatible with gonadal development, puberty, and fertility

This report introduces a gonadotrope-specific cre transgenic mouse capable of ablating floxed genes in mature pituitary gonadotropes. Initial analysis of this transgenic line, Tg(Lhb-cre)1Sac, reveals that expression is limited to the pituitary cells that produce luteinizing hormone beta, beginning appropriately at e17.5. Cre activity is detectable by a reporter gene in nearly every LHbeta-producing cell, but the remaining hormone-producing cell types and other organs exhibit little to no activity. We used the Tg(Lhb-cre)1Sac strain to assess the role Pitx2 in gonadotrope function. The gonadotrope-specific Pitx2 knockout mice exhibit normal expression of LHbeta, sexual maturation, and fertility, suggesting that Pitx2 is not required for gonadotrope maintenance or for regulated production of gonadotropins.

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

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

Expression profiles for six zebrafish genes during gonadal sex differentiation

BACKGROUND

The mechanism of sex determination in zebrafish is largely unknown and neither sex chromosomes nor a sex-determining gene have been identified. This indicates that sex determination in zebrafish is mediated by genetic signals from autosomal genes. The aim of this study was to determine the precise timing of expression of six genes previously suggested to be associated with sex differentiation in zebrafish. The current study investigates the expression of all six genes in the same individual fish with extensive sampling dates during sex determination and -differentiation.

RESULTS

In the present study, we have used quantitative real-time PCR to investigate the expression of ar, sox9a, dmrt1, fig alpha, cyp19a1a and cyp19a1b during the expected sex determination and gonadal sex differentiation period. The expression of the genes expected to be high in males (ar, sox9a and dmrt1a) and high in females (fig alpha and cyp19a1a) was segregated in two groups with more than 10 times difference in expression levels. All of the investigated genes showed peaks in expression levels during the time of sex determination and gonadal sex differentiation. Expression of all genes was investigated on cDNA from the same fish allowing comparison of the high and low expressers of genes that are expected to be highest expressed in either males or females. There were 78% high or low expressers of all three "male" genes (ar, sox9a and dmrt1) in the investigated period and 81% were high or low expressers of both "female" genes (fig alpha and cyp19a1a). When comparing all five genes with expected sex related expression 56% show expression expected for either male or female. Furthermore, the expression of all genes was investigated in different tissue of adult male and female zebrafish.

CONCLUSION

In zebrafish, the first significant peak in gene expression during the investigated period (2-40 dph) was dmrt1 at 10 dph which indicates involvement of this gene in the early gonadal sex differentiation of males.

Steroid receptor expression in the developing copulatory system of the green anole lizard (Anolis carolinensis)

In adulthood, the copulatory system in male green anole lizards is characterized by the presence of two hemipenes, each controlled by ipsilateral muscles. These structures are present in both sexes early in development, but prior to hatching regress completely in females. Embryonic treatment with steroid hormones alters the morphology of the copulatory system, suggesting active roles for both androgens and estrogens in sexual differentiation. To elucidate the timing and sites of steroid hormone action in the embryonic copulatory system, the distributions of androgen receptor (AR) and estrogen receptor-alpha (ER alpha) mRNA expression were examined. In situ hybridization was conducted on the rostral tail of anoles at three stages spanning differentiation of the copulatory structures: embryonic days (E) 13, 18, and 24 (hatching occurs at approximately E34). At E13, males expressed significantly higher levels of AR mRNA in both hemipenes and muscles than did females, while females at the same age tended to express higher levels of ER alpha mRNA in these structures. By E18, hemipenes and copulatory muscles were regressed in most females, and were not present in any females at E24. In males, no effect of age was detected on the expression of either AR or ER alpha. These data suggest that peripheral copulatory structures in the embryonic anole are direct targets for the actions of both androgens and estrogens in sexual differentiation, consistent with the idea that estradiol facilitates regression in females and androgen promotes survival in males. However, the issue of whether or not a critical period exists remains open.

Identification and gene expression profiling of the Pum1 and Pum2 members of the Pumilio family in the chicken

Members of the Pumilio (Pum) family of RNA-binding proteins act as translational repressors and are required for germ cell development and asymmetric division. We identified the chicken Pum1 and Pum2 genes and analyzed their expression patterns in various tissues. Comparative sequence analysis of the Pum1 and Pum2 proteins from the drosophila, chicken, mouse, and human revealed a high degree of evolutionary conservation in terms of the levels of homology of the peptide sequences and the structure of Pumilio homology domain (PUM-HD), C-terminal RNA-binding domain, with similar spacing between the adjacent Pum eight tandem repeats. In addition, phylogenetic patterns of pumilio family showed that Pum 1 and 2 of chicken are more closely related to those of mouse and human than other species and Pum1 is more conserved than Pum2. Using real-time RT-PCR, the expression levels of the Pum1 and Pum2 genes were found to be highest in hatched female gonads, and high-level expression of Pum2 was detected in 12-day and hatched gonads among the various chicken embryonic tissues tested. In adult tissues, the expression levels of Pum1 and Pum2 were expressed at higher levels in the testis and muscle than in any other tissue. The characteristics of the tissue-specific expression of Pum genes suggest that Pum1 and Pum2 have effects crucially in particular stage during development of chicken gonads depending on sexual maturation.

Bone morphogenetic protein 4 modulates c-Kit expression and differentiation potential in murine embryonic aorta-gonad-mesonephros haematopoiesis in vitro

The transforming growth factor-β-related factor bone morphogenetic protein 4 (BMP4) is expressed in the human embryonic aorta-gonad-mesonephros (AGM) coincident with the emergence of haematopoietic cells and influences postnatal mammalian haematopoietic stem cells in vitro. To investigate the role of BMP4 in mammalian embryonic haematopoiesis, cells were isolated from murine AGM and two populations of CD34⁺ cells with different levels of c-Kit expression and multipotency were identified. CD34⁺/c-Kit^high cells express CD45 and are haematopoietic-restricted progenitors. In contrast, CD34⁺/c-Kit^low cells are Flk1+/CD45^neg and generate adherent colonies in ex vivo culture that resemble haemangioblast colonies identified in other systems. The addition of BMP4 to AGM cells resulted in expansion of the CD34⁺/c-Kit^low cell pool within 48 h, via a combination of down modulation of the c-Kit receptor in CD34⁺/c-Kit^high cells and proliferation. In long-term culture, BMP4 increased the growth/survival of CD34⁺/c-Kit^high haematopoietic progenitors, effects that were blocked by BMP inhibitors. CD34⁺/c-Kit^high progenitors cultured with BMP4 also generated adherent colonies typical of c-Kit^low cells. These results suggest that BMP4 regulates c-Kit expression and differentiation potential in CD34⁺ AGM cells and supports a role for BMP signalling in the maintenance of multipotency during embryonic haematopoiesis, providing an insight into stem cell homeostasis within the mammalian haematopoietic niche.

Proceedings of the Summit on Environmental Challenges to Reproductive Health and Fertility: executive summary

The 2007 Summit on Environmental Challenges to Reproductive Health and Fertility convened scientists, health care professionals, community groups, political representatives, and the media to hear presentations on the impact of environmental contaminants on reproductive health and fertility, and to discuss opportunities to improve health through research, education, communication, and policy. Environmental reproductive health focuses on exposures to environmental contaminants, particularly during critical periods of development, and their potential effects on future reproductive health, including conception, fertility, pregnancy, adolescent development, and adult health. Approximately 87,000 chemical substances are registered for commercial use in the United States, with ubiquitous human exposures to environmental contaminants in air, water, food, and consumer products. Exposures during critical windows of susceptibility may result in adverse effects with lifelong and even intergenerational health impacts. Effects can include impaired development and function of the reproductive tract and permanently altered gene expression, leading to metabolic and hormonal disorders, reduced fertility and fecundity, and illnesses such as testicular, prostate, uterine, and cervical cancers later in life. This executive summary reviews effects of pre- and postnatal exposures on male and female reproductive health, and provides a series of recommendations for advancing the field in the areas of research, policy, health care, and community action.

Control of receptor internalization, signaling level, and precise arrival at the target in guided cell migration

Activation of the chemokine receptor CXCR4 by SDF1 controls a variety of biological processes in development, immune response, and disease [1-5]. The carboxyl-terminal region of CXCR4 is subject to phosphorylation that allows binding of regulatory proteins [5]; this results in downregulation of CXCR4 signaling and receptor internalization [6]. Notably, truncations of this part of CXCR4 have been implicated in WHIM syndrome, a dominantly inherited immunodeficiency disorder [7, 8]. Despite its importance in receptor signaling and the clinical relevance of its regulation, the precise function of regulating signaling level and internalization in controlling cell behavior is not known. Whereas a number of in vitro studies suggested that the carboxyl terminus of CXCR4 positively regulates chemotaxis (e.g., [9]), others reached the opposite conclusion [8, 10, 11]. These conflicting results highlight the importance of investigating this process under physiological conditions in the live animal. In this study, we demonstrate the significance of internalization and of controlling receptor signaling level for SDF-1-guided migration. We found that whereas internalization and the control over signaling intensity are dispensable for cell motility and directional sensing, they are essential for fine-tuning of migration in vivo, allowing precise arrival of zebrafish PGCs at their target, the region where the gonad develops.

Development of germ cells in the mouse

In mammals, germ cells are induced from a population of cells at the base of the allantois. This regulative mechanism of germ line induction depends on Bmp signals and a combination of epigenetic changes that silence somatic differentiation genes and activate pluripotency genes. RNA binding proteins are a conserved feature of germ cell development in mammals, and play critical roles in the establishment and maintenance of pluripotency. After their specification, germ cells move through the gut to the gonads under the influence of migratory and attractive cues. In the gonad, germ cells initiate sex-specific differentiation. Germ cells that arrive in the ovary enter meiosis, whereas germ cells that arrive in the testis undergo mitotic arrest. Entry into meiosis is controlled by retinoic acid signals that are blocked in the testis. The signals regulating mitotic arrest in the testis are still not completely understood, but likely involve RNA-binding proteins. Epigenetic reprograming occurs during specification, migratory stages, and sex-specific stages, when maternal and paternal imprints are established. The facility of transitions between germ cells and stem cells suggests a close relationship among their genomic programs.

Embryonic stromal clones reveal developmental regulators of definitive hematopoietic stem cells

Hematopoietic stem cell (HSC) self-renewal and differentiation is regulated by cellular and molecular interactions with the surrounding microenvironment. During ontogeny, the aorta-gonad-mesonephros (AGM) region autonomously generates the first HSCs and serves as the first HSC-supportive microenvironment. Because the molecular identity of the AGM microenvironment is as yet unclear, we examined two closely related AGM stromal clones that differentially support HSCs. Expression analyses identified three putative HSC regulatory factors, beta-NGF (a neurotrophic factor), MIP-1gamma (a C-C chemokine family member) and Bmp4 (a TGF-beta family member). We show here that these three factors, when added to AGM explant cultures, enhance the in vivo repopulating ability of AGM HSCs. The effects of Bmp4 on AGM HSCs were further studied because this factor acts at the mesodermal and primitive erythropoietic stages in the mouse embryo. In this report, we show that enriched E11 AGM HSCs express Bmp receptors and can be inhibited in their activity by gremlin, a Bmp antagonist. Moreover, our results reveal a focal point of Bmp4 expression in the mesenchyme underlying HSC containing aortic clusters at E11. We suggest that Bmp4 plays a relatively late role in the regulation of HSCs as they emerge in the midgestation AGM.

Inhibition of primordial germ cell proliferation by the medaka male determining gene Dmrt I bY

Background

Dmrt1 is a highly conserved gene involved in the determination and early differentiation phase of the primordial gonad in vertebrates. In the fish medaka dmrt1bY, a functional duplicate of the autosomal dmrt1a gene on the Y-chromosome, has been shown to be the master regulator of male gonadal development, comparable to Sry in mammals. In males mRNA and protein expression was observed before morphological sex differentiation in the somatic cells surrounding primordial germ cells (PGCs) of the gonadal anlage and later on exclusively in Sertoli cells. This suggested a role for dmrt1bY during male gonad and germ cell development.

Results

We provide functional evidence that expression of dmrt1bY leads to negative regulation of PGC proliferation. Flow cytometric measurements revealed a G2 arrest of dmrt1bY expressing cells. Interestingly, also non-transfected cells displayed a significantly lower fraction of proliferating cells, pointing to a possible non-cell autonomous action of dmrt1bY. Injection of antisense morpholinos led to an increase of PGCs in genetically male embryos due to loss of proliferation inhibition.

Conclusion

In medaka, dmrt1bY mediates a mitotic arrest of PGCs in males prior to testes differentiation at the sex determination stage. This occurs possibly via a cross-talk of Sertoli cells and PGCs.