Different patterns of anti-Müllerian hormone expression, as related to DMRT1, SF-1, WT1, GATA-4, Wnt-4, and Lhx9 expression, in the chick differentiating gonads

Overview of chicken embryo genes related to sex differentiation

Sex determination in chickens at an early embryonic stage has been a longstanding challenge in poultry production due to the unique ZZ:ZW sex chromosome system and various influencing factors. This review has summarized the genes related to the sex differentiation of chicken early embryos (mainly Dmrt1, Sox9, Amh, Cyp19a1, Foxl2, Tle4z1, Jun, Hintw, Ube2i, Spin1z, Hmgcs1, Foxd1, Tox3, Ddx4, cHemgn and Serpinb11 in this article), and has found that these contributions enhance our understanding of the genetic basis of sex determination in chickens, while identifying potential gene targets for future research. This knowledge may inform and guide the development of sex screening technologies for hatching eggs and support advancements in gene-editing approaches for chicken embryos. Moreover, these insights offer hope for enhancing animal welfare and promoting conservation efforts in poultry production.

Expression pattern analysis of anti-Mullerian hormone in testis development of pearlscale angelfish (Centropyge vrolikii)

In vertebrates, anti-Mullerian hormone (Amh) secreted by Sertoli cells (SC) performs a pivotal function in male sex differentiation. Compared with that of higher vertebrates, the expression pattern of Amh is more diversified in fish. In this study, the full-length complementary DNA (cDNA) of Amh in Centropyge vrolikii (Cv-Amh) was cloned and analysed, which was 2,470 bp, including a 238 bp 5'UTR, a 1,602 bp ORF and a 633 bp 3'UTR; the similarity of Amh between Cv-Amh and other fish is relatively high. The quantitative real-time PCR (qRT-PCR) results of healthy tissues and gonads at sex reversal stages in C. vrolikii showed that the expression level of Amh in the testis was significantly higher than that in other tissues (P < 0.05). Amh was weakly expressed in the vitellogenic stage ovary and perinucleolus stage ovary, but its expression significantly increased in the gonads at the hermaphroditic stage, and finally reached the highest in the pure testis after sexual reversal. The results of in situ hybridization indicated that the positive signal of Amh was strongly concentrated in SCs of testis. After Amh knockdown in the gonads, the effect on sex-related genes was tested using qRT-PCR. Among these, the expression of Dmrt1, Cyp11a, Hsd11b2, Sox8 and Sox9 significantly decreased, whereas that of Cyp19a, Sox4, Foxl2 and Sox3 increased. These results suggested that Amh could be the pivotal gene in reproductive regulation in C. vrolikii, and the data will contribute to sex-related research of C. vrolikii in the future.

DMRT1-mediated regulation of TOX3 modulates expansion of the gonadal steroidogenic cell lineage in the chicken embryo

During gonadal sex determination, the supporting cell lineage differentiates into Sertoli cells in males and pre-granulosa cells in females. Recently, single cell RNA-seq data have indicated that chicken steroidogenic cells are derived from differentiated supporting cells. This differentiation process is achieved by a sequential upregulation of steroidogenic genes and downregulation of supporting cell markers. The exact mechanism regulating this differentiation process remains unknown. We have identified TOX3 as a previously unreported transcription factor expressed in embryonic Sertoli cells of the chicken testis. TOX3 knockdown in males resulted in increased CYP17A1-positive Leydig cells. TOX3 overexpression in male and female gonads resulted in a significant decline in CYP17A1-positive steroidogenic cells. In ovo knockdown of the testis determinant DMRT1 in male gonads resulted in a downregulation of TOX3 expression. Conversely, DMRT1 overexpression caused an increase in TOX3 expression. Taken together, these data indicate that DMRT1-mediated regulation of TOX3 modulates expansion of the steroidogenic lineage, either directly, via cell lineage allocation, or indirectly, via signaling from the supporting to steroidogenic cell populations.

Avian Sex Determination: A Chicken and Egg Conundrum

BACKGROUND

Primary sex determination is the developmental process that results in the sexual differentiation of the gonads. Vertebrate sex determination is generally considered to follow the model based on the mammalian system, where a sex-specific master regulatory gene activates one of the two different gene networks that underlie testis and ovary differentiation.

SUMMARY

It is now known that, while many of the molecular components of these pathways are conserved across different vertebrates, a wide variety of different trigger factors are utilized to initiate primary sex determination. In birds, the male is the homogametic sex (ZZ), and significant differences exist between the avian system of sex determination and that of mammals. For example, DMRT1, FOXL2, and estrogen are key factors in gonadogenesis in birds, but none are essential for primary sex determination in mammals.

KEY MESSAGE

Gonadal sex determination in birds is thought to depend on a dosage-based mechanism involving expression of the Z-linked DMRT1 gene, and it may be that this "mechanism" is simply an extension of the cell autonomous sex identity associated with avian tissues, with no sex-specific trigger required.

Amh/Amhr2 Signaling Causes Masculinization by Inhibiting Estrogen Synthesis during Gonadal Sex Differentiation in Japanese Flounder (Paralichthys olivaceus)

The anti-Müllerian hormone (Amh) is a protein belonging to the TGF-β superfamily, the function of which has been considered important for male sex differentiation in vertebrates. The Japanese flounder (Paralichthys olivaceus) is a teleost fish that has an XX/XY sex determination system and temperature-dependent sex determination. In this species, amh expression is up-regulated in genetic males and in temperature-induced masculinization during the sex differentiation period. However, to the best of our knowledge, no reports on the Amh receptor (Amhr2) in flounder have been published, and the details of Amh signaling remain unclear. In this study, we produced amhr2-deficient mutants using the CRISPR/Cas9 system and analyzed the gonadal phenotypes and sex-related genes. The results revealed that the gonads of genetically male amhr2 mutants featured typical ovaries, and the sex differentiation-related genes showed a female expression pattern. Thus, the loss of Amhr2 function causes male-to-female sex reversal in Japanese flounder. Moreover, the treatment of genetically male amhr2 mutants with an aromatase inhibitor fadrozole, which inhibits estrogen synthesis, resulted in testicular formation. These results strongly suggest that Amh/Amhr2 signaling causes masculinization by inhibiting estrogen synthesis during gonadal sex differentiation in the flounder.

Identification of genes related to sexual differentiation and sterility in embryonic gonads of Mule ducks by transcriptome analysis

The key genes of avian gonadal development are of great significance for sex determination. Transcriptome sequencing analysis of Mule duck gonad as potential sterile model is expected to screen candidate genes related to avian gonad development. In this study, the embryonic gonadal tissues of Mule ducks, Jinding ducks, and Muscovy ducks were collected and identified. Six sample groups including female Mule duck (A), male Mule duck (B), female Jinding duck (C), male Jinding duck (D), female Muscovy duck (E), and male Muscovy duck (F) were subjected to RNA sequencing analysis. A total of 9,471 differential genes (DEGs) and 691 protein-protein interaction pairs were obtained. Totally, 12 genes (Dmrt1, Amh, Sox9, Tex14, Trim71, Slc26a8, Spam1, Tdrp, Tsga10, Boc, Cxcl14, and Hsd17b3) were identified to be specifically related to duck testicular development, and 11 genes (Hsd17b1, Cyp19a1, Cyp17a1, Hhipl2, Tdrp, Uts2r, Cdon, Axin2, Nxph1, Brinp2, and Brinp3) were specifically related to duck ovarian development. Seven genes (Stra8, Dmc1, Terb1, Tex14, Tsga10, Spam1, and Plcd4) were screened to be specifically involved in the female sterility of Mule ducks; eight genes (Gtsf1, Nalcn, Tat, Slc26a8, Kmo, Plcd4, Aldh4a1, and Hgd) were specifically involved in male sterility; and five genes (Terb1, Stra8, Tex14 Tsga10 and Spam1) were involved in both female and male sterility. This study provides an insight into the differential development between male and female gonads of ducks and the sterility mechanism of Mule ducks through function, pathway, and protein interaction analyses. Our findings provide theoretical basis for the further research on sex determination and differentiation of birds and the sterility of Mule ducks.

Insights Into the Roles of GATA Factors in Mammalian Testis Development and the Control of Fetal Testis Gene Expression

Defining how genes get turned on and off in a correct spatiotemporal manner is integral to our understanding of the development, differentiation, and function of different cell types in both health and disease. Testis development and subsequent male sex differentiation of the XY fetus are well-orchestrated processes that require an intricate network of cell-cell communication and hormonal signals that must be properly interpreted at the genomic level. Transcription factors are at the forefront for translating these signals into a coordinated genomic response. The GATA family of transcriptional regulators were first described as essential regulators of hematopoietic cell differentiation and heart morphogenesis but are now known to impact the development and function of a multitude of tissues and cell types. The mammalian testis is no exception where GATA factors play essential roles in directing the expression of genes crucial not only for testis differentiation but also testis function in the developing male fetus and later in adulthood. This minireview provides an overview of the current state of knowledge of GATA factors in the male gonad with a particular emphasis on their mechanisms of action in the control of testis development, gene expression in the fetal testis, testicular disease, and XY sex differentiation in humans.

Genetic Regulation of Avian Testis Development

As in other vertebrates, avian testes are the site of spermatogenesis and androgen production. The paired testes of birds differentiate during embryogenesis, first marked by the development of pre-Sertoli cells in the gonadal primordium and their condensation into seminiferous cords. Germ cells become enclosed in these cords and enter mitotic arrest, while steroidogenic Leydig cells subsequently differentiate around the cords. This review describes our current understanding of avian testis development at the cell biology and genetic levels. Most of this knowledge has come from studies on the chicken embryo, though other species are increasingly being examined. In chicken, testis development is governed by the Z-chromosome-linked DMRT1 gene, which directly or indirectly activates the male factors, HEMGN, SOX9 and AMH. Recent single cell RNA-seq has defined cell lineage specification during chicken testis development, while comparative studies point to deep conservation of avian testis formation. Lastly, we identify areas of future research on the genetics of avian testis development.

LIM Homeodomain (LIM-HD) Genes and Their Co-Regulators in Developing Reproductive System and Disorders of Sex Development

LIM homeodomain (LIM-HD) family genes are transcription factors that play crucial roles in a variety of functions during embryonic development. The activities of the LIM-HD proteins are regulated by the co-regulators LIM only (LMO) and LIM domain-binding (LDB). In the mouse genome, there are 13 LIM-HD genes (Lhx1-Lhx9, Isl1-2, Lmx1a-1b), 4 Lmo genes (Lmo1-4), and 2 Ldb genes (Ldb1-2). Amongst these, Lhx1 is required for the development of the müllerian duct epithelium and the timing of the primordial germ cell migration. Lhx8 is necessary for oocyte differentiation and Lhx9 for somatic cell proliferation in the genital ridges and control of testosterone production in the Leydig cells. Lmo4 is involved in Sertoli cell differentiation. Mutations in LHX1 are associated with müllerian agenesis or Mayer-Rokitansky-Kuster-Hauser (MRKH) syndrome. LHX9 gene variants are reported in cases with disorders of sex development (DSD). Mutations in LHX3 and LHX4 are reported in patients with combined pituitary hormone deficiency having absent or delayed puberty. A transcript map of the Lhx, Lmo, and Ldb genes reveal that multiple LIM-HD genes and their co-regulators are expressed in a sexually dimorphic pattern in the developing mouse gonads. Unraveling the roles of LIM-HD genes during development will aid in our understanding of the causes of DSD.

Effect of aromatase inhibitors on sex differentiation and embryonic development in chicks

Background

Sexual differentiation can occur after exposure to aromatase into the left gonad at 6.5 days of incubation. Aromatase inhibitors work by inhibiting the action of the aromatase, which converts androgens into estrogens by a process called aromatization.

Objectives

The aim of this study was to investigate the effect of in ovo exposure to the aromatase inhibitor from tomato and garlic extract on sexual differentiation and embryonic development in chicken embryos.

Methods

Three hundred eggs divided into five groups: Control 1 (CO; no injection); control 2 distilled water, DW; 0.1 ml/egg); garlic extract (GAR; 0.1 mg/egg); tomato extract (TOM; 0.1 mg/egg); and garlic and tomato extract mixed (ATM, 0.1 ml/egg). The solution was prepared and injected into the albumin from the thin end of the eggs on day five by using a 1 ml syringe with a 23‐gauge needle. The embryonic test (embryo/egg weight) conducted at 7, 14 and 17 days of incubation. After hatching, feather sexing conducted to determine the initial male. Chicks sex was later confirmed on day 42 by an optical microscope lens.

Results

The results revealed that there was a significant increase (p < 0.01) in embryonic growth traits in all experimental treatments as compared to control treatments. There was a significant increase (p < 0.01) in the percentage of hatchability for all experimental treatments compared to control treatments and a significant increase (p < 0.01) in chick quality including one‐day‐old chick length and body weight. All experimental treatments showed a significant increase (p < 0.01) in the male‐to‐female ratio compared to control treatments.

Conclusions

The effect of in ovo exposure to aromatase inhibitors stimulated female‐to‐male sex reversal and improved embryonic development.

The significant sex-biased expression pattern of Sp-Wnt4 provides novel insights into the ovarian development of mud crab (Scylla Paramamosain)

The wingless-type MMTV integration site family member-4 (Wnt4), a member of the wingless-related integration site (Wnt) family, is widely accepted as a key regulator of ovarian development in mammals. In this study, a full-length cDNA of Wnt4 (designated as Sp-Wnt4) was cloned, characterized, and functionally studied in mud crab (Scylla paramamosain). The full-length cDNA of Sp-Wnt4 consists of 2659 bp with an open reading frame (ORF) encoding 359 amino acids, a 907 bp 5'-UTR and a 672 bp 3'-UTR. Sp-Wnt4 contains 25 cysteine (Cys) residues and three potential N-glycosylation sites. Sp-Wnt4 protein shared the highest identity (98.9%) to the Wnt4 protein of Portunus trituberculatus. The phylogenetic tree showed that Sp-Wnt4 and Wnt4 protein of Malacostracan crustaceans clustered together, indicating that they had a close genetic distance. Sp-Wnt4 was expressed at a higher level in the ovary compared to other tissues, with the highest expression level at the third stage (O-III) of the ovarian development (P < 0.05). A downward trend was observed in the expression level of Sp-Wnt4 from the embryo stage to crablet stages (P < 0.05). After unilateral eyestalk ablation, the expression level of Sp-Wnt4 significantly increased in testis (14-fold) and downregulated (3.1-fold) in the gill (P < 0.05) of females. In situ hybridization (ISH) assay revealed that Sp-Wnt4 transcripts were mainly localized in the cytoplasm of oocyte cells. These findings showed that Sp-Wnt4 play crucial roles in the ovarian development of S. paramamosain. In conclusion, our study provides novel insights into the evolution and roles of the Wnt4 gene.

Two transcriptionally distinct pathways drive female development in a reptile with both genetic and temperature dependent sex determination

How temperature determines sex remains unknown. A recent hypothesis proposes that conserved cellular mechanisms (calcium and redox; 'CaRe' status) sense temperature and identify genes and regulatory pathways likely to be involved in driving sexual development. We take advantage of the unique sex determining system of the model organism, Pogona vitticeps, to assess predictions of this hypothesis. P. vitticeps has ZZ male: ZW female sex chromosomes whose influence can be overridden in genetic males by high temperatures, causing male-to-female sex reversal. We compare a developmental transcriptome series of ZWf females and temperature sex reversed ZZf females. We demonstrate that early developmental cascades differ dramatically between genetically driven and thermally driven females, later converging to produce a common outcome (ovaries). We show that genes proposed as regulators of thermosensitive sex determination play a role in temperature sex reversal. Our study greatly advances the search for the mechanisms by which temperature determines sex.

Human Umbilical Cord: Information Mine in Sex-Specific Medicine

Biological differences between sexes should be considered in all stages of research, as sexual dimorphism starts in utero leading to sex-specific fetal programming. In numerous biomedical fields, there is still a lack of stratification by sex despite primary cultured cells retaining memory of the sex and of the donor. The sex of donors in biological research must be known because variations in cells and cellular components can be used as endpoints, biomarkers and/or targets of pharmacological studies. This selective review focuses on the current findings regarding sex differences observed in the umbilical cord, a widely used source of research samples, both in the blood and in the circulating cells, as well as in the different cellular models obtainable from it. Moreover, an overview on sex differences in fetal programming is reported. As it emerges that the sex variable is still often forgotten in experimental models, we suggest that it should be mandatory to adopt sex-oriented research, because only awareness of these issues can lead to innovative research.

Sex determination, gonadal sex differentiation, and plasticity in vertebrate species

A diverse array of sex determination (SD) mechanisms, encompassing environmental to genetic, have been found to exist among vertebrates, covering a spectrum from fixed SD mechanisms (mammals) to functional sex change in fishes (sequential hermaphroditic fishes). A major landmark in vertebrate SD was the discovery of the SRY gene in 1990. Since that time, many attempts to clone an SRY ortholog from nonmammalian vertebrates remained unsuccessful, until 2002, when DMY/dmrt1by was discovered as the SD gene of a small fish, medaka. Surprisingly, however, DMY/dmrt1by was found in only 2 species among more than 20 species of medaka, suggesting a large diversity of SD genes among vertebrates. Considerable progress has been made over the last 3 decades, such that it is now possible to formulate reasonable paradigms of how SD and gonadal sex differentiation may work in some model vertebrate species. This review outlines our current understanding of vertebrate SD and gonadal sex differentiation, with a focus on the molecular and cellular mechanisms involved. An impressive number of genes and factors have been discovered that play important roles in testicular and ovarian differentiation. An antagonism between the male and female pathway genes exists in gonads during both sex differentiation and, surprisingly, even as adults, suggesting that, in addition to sex-changing fishes, gonochoristic vertebrates including mice maintain some degree of gonadal sexual plasticity into adulthood. Importantly, a review of various SD mechanisms among vertebrates suggests that this is the ideal biological event that can make us understand the evolutionary conundrums underlying speciation and species diversity.

Dynamics of the Transcriptome and Accessible Chromatin Landscapes During Early Goose Ovarian Development

In contrast to the situation in mammals, very little is known about the molecular mechanisms regulating early avian ovarian development. This study aimed to investigate the dynamic changes in the histomorphology as well as the genome-wide transcriptome and chromatin accessibility landscapes of the goose ovary during late embryonic and early post-hatching stages. Results from hematoxylin-eosin, periodic acid-Schiff, and anti-CVH immunohistochemical stainings demonstrated that programmed oocyte loss, oocyte nest breakdown and primordial follicle formation, and the primordial-to-secondary follicle transition occur during the periods from embryonic day 15 (E15) to post-hatching day 0 (P0), from P0 to P4, and from P4 to P28, respectively. RNA-seq and ATAC-seq analyses revealed dynamic changes in both the ovarian transcriptome and accessible chromatin landscapes during early ovarian development, exhibiting the most extensive changes during peri-hatching oocyte loss, and moreover, differences were also identified in the genomic distribution of the differential ATAC-seq peaks between different developmental stages, suggesting that chromatin-level regulation of gene expression is facilitated by modulating the accessibility of different functional genomic regions to transcription factors. Motif analysis of developmental stage-selective peak regions identified hundreds of potential cis-regulatory elements that contain binding sites for many transcription factors, including SF1, NR5A2, ESRRβ, NF1, and THRβ, as well as members of the GATA, SMAD, and LHX families, whose expression fluctuated throughout early goose ovarian development. Integrated ATAC-seq and RNA-seq analysis suggested that the number and genomic distribution of the newly appeared and disappeared peaks differed according to developmental stage, and in combination with qRT-PCR validation potentiated the critical actions of the DEGs enriched in cell cycle, MAPK signaling, and FoxO signaling pathways during peri-hatching oocyte loss and those in ligand-receptor interaction, tissue remodeling, lipid metabolism, and Wnt signaling during primordial follicle formation and development. In conclusion, our study provides a framework for understanding the transcriptome and accessible chromatin dynamics during early avian ovarian development and a new avenue to unravel the transcriptional regulatory mechanisms that facilitate the occurrence of relevant molecular events.

Cloning and characterization of wnt4a gene in a natural triploid teleost, Qi river crucian carp (Carassius auratus)

WNT4 (wingless-type MMTV integration site family, member 4) plays a key role in the ovarian differentiation and development in mammals. However, the possible roles of Wnt4 during gonadal differentiation and development need further clarification in teleosts. In this study, we cloned and characterized the full-length cDNA of Qi river crucian carp (Carassius auratus) wnt4a gene (CA-wnt4a). The cDNA of CA-wnt4a is 2337 bp, including the ORF of 1059 bp, encoding a putative protein with a transmembrane domain and a WNT family domain. Sequence and phylogenetic analyses revealed that the CA-Wnt4a identified is a genuine Wnt4a. Tissue distribution analysis showed that CA-wnt4a is expressed in all the tissues examined, including ovary. CA-wnt4a undergoes a stepwise increase in the embryonic stages, suggesting that CA-wnt4a might be involved in the early developmental stage. Ontogenic analysis demonstrated that CA-wnt4a expression is upregulated in the ovaries at 30-50 days after hatching (dah), the critical period of sex determination/differentiation in Qi river crucian carp. From 90 dah, the expression of CA-wnt4a was gradually downregulated in the developing ovaries. Immunohistochemistry demonstrated that CA-Wnt4a was expressed in the somatic and germ cells of the ovary by 30 dah, thereafter, positive signals of Wnt4a were detected in the somatic cells, oogonia and primary growth oocytes from 60 dah. In the sex-reversed testis induced by letrozole treatment, the expression level of CA-wnt4a was significantly downregulated. When CA-wnt4a expression was inhibited by injection of FH535 (an inhibitor of canonical Wnt/β-catenin signal pathway) in the ovaries, levels of cyp19a1a, foxl2 mRNA were significantly downregulated, while sox9b and cyp11c1 were upregulated, which suggested that together with Foxl2-leading estrogen pathway, CA-wnt4a signaling pathway might be involved in ovarian differentiation and repression of the male pathway gene expression in Qi river crucian carp.

Cotreatment of IGF1 and Fadrozole Upregulates the Expression of RSPO1, SOX9, and AMH in Chicken Embryos

Insulin-like growth factor-1 (IGF1) and anti-aromatase synergistically increase the rate and stability of female-to-male sex reversal as well as pre- and postnatal weight gains in hatched chickens. This study aimed at assessing gene expression profiles of chicken embryos treated with IGF1 and fadrozole. Day 3.5 fertile eggs were in ovo injected with one of IGF1, fadrozole anti-aromatase, combined IGF1 and fadrozole, or sham injection. The expression profile was studied on day 6 and day 11 of the embryonic development following gonadal differentiation. On day 6 of embryonic development, simultaneous injection of IGF1 and fadrozole significantly upregulated the expression of RSPO1, AMH, and SOX9 in genetically female embryos compared to single injections and control groups. Also, a higher expression of ESR1 and BMP4 was observed in genetically male embryos on day 6 compared to the control group. In day 11 embryos, a higher expression of BMP4 was detected in both males and females of the IGF1 and fadrozole-administered group compared to the sham injection cohort. In conclusion, the results of this study indicate that combined effects of IGF1 and fadrozole induce female-to-male sex reversal by increasing the expression of testis developmental factors rather than attenuating ovary developmental factors.

Is interstitial 8p23 microdeletion responsible of 46,XY gonadal dysgenesis? One case report from birth to puberty

BACKGROUND

Chromosome 8p deletions are associated with a variety of conditions, including cardiac abnormalities, mental, behavioral problems with variable morphotype and genitourinary anomalies in boys.

METHODS

We describe the follow-up over almost 15 years of a boy who initially presented with perineal hypospadias with a micropenis and cryptorchidism with 46,XY DSD.

RESULTS

Imaging, pathology, and hormonal exploration suggested gonadal dysgenesis. Further genetic studies were deemed necessary during follow-up. The child's further development recommended further genetic analyses. High-resolution analysis showed an interstitial deletion on the short arm of a chromosome 8: 46,XY,del(8)(p23.1p23.1). We reviewed the literature and found 102 cases including 54 boys: 62.7% had mental problems, 50.9% a dysmorphic disorder, 55.9% cardiac anomalies, and 46.3% of the boys had genitourinary anomalies. Our patient's genital abnormalities can be explained by the haploinsufficiency of the genes, such as GATA4 (OMIM 600576) that are included in the deleted area.

CONCLUSION

This case of severe 46,XY DSD raises the question of the role played by 8p23 microdeletion in gonadal dysgenesis. Clinicians are encouraged to look for this anomaly on chromosome 8 in cases of unexplained gonadal dysgenesis even when few signs suggestive of this anomaly are present.

Cloning, tissue distribution and methylation analyses of Lhx9 in Chinese tongue sole (Cynoglossus semilaevis)

Lhx9 is a LIM-homeodomain protein related to gonad development and sex reversal. In this study, we cloned and characterized CS-Lhx9 in the gonads of the Chinese tongue sole (Cynoglossus semilaevis). The full-length cDNA of CS-Lhx9 was 3123 bp, including an ORF of 1149 bp encoding 383 amino acids which contains two LIM domains and a homeobox domain. CS-Lhx9 transcripts were primarily observed in the testis of male and neomale at 1 yah, but nearly undetectable in the ovary. During the development of gonad, CS-Lhx9 exhibited an increasing trend and appeared to reach its peak value of expression in testis at 1 yah. In situ hybridization was performed in male and neomale gonads at 210 dah and 1 yah. The results showed strong CS-Lhx9 signals in the spermatids and spermatozoa (germ cells). Methylation level of CS-Lhx9 promoter was higher in female and lower in male and neomale gonads, showing a negative correlation with CS-Lhx9 expression.

Ovarian activity regulation by anti-Müllerian hormone in early stages of human female life, an overview

The present study aimed at describing the anti-Müllerian hormone (AMH), with special focus on molecular background for ovarian activity, in particular the role AMH plays in sex determination and gonadogenesis process in early stages of prenatal life and folliculogenesis in postnatal life. It is a review of the literature currently indexed and abstracted in MEDLINE, SCOPUS and Google Scholars. The process of sex determination and gonad differentiation occurring during embryogenesis was discussed along with underlying molecular mechanisms. In the postnatal life the impact of AMH on the process of folliculogenesis was described. Clinical use of recent findings was shown as well. Genetic studies and molecular analyses have demonstrated that AMH is highly conservative, indicating its significance in reproductive process on the background of evolutionary processes.

Dose-response effects of light at night on the reproductive physiology of great tits (Parus major): Integrating morphological analyses with candidate gene expression

Artificial light at night (ALAN) is increasingly recognized as a potential threat to wildlife and ecosystem health. Among the ecological effects of ALAN, changes in reproductive timing are frequently reported, but the mechanisms underlying this relationship are still poorly understood. Here, we experimentally investigated these mechanisms by assessing dose‐dependent photoperiodic responses to ALAN in the great tit (Parus major). We individually exposed photosensitive male birds to one of three nocturnal light levels (0.5, 1.5, and 5 lux), or to a dark control. Subsequent histological and molecular analyses on their testes indicated a dose‐dependent reproductive response to ALAN. Specifically, different stages of gonadal growth were activated after exposure to different levels of light at night. mRNA transcript levels of genes linked to the development of germ cells (stra8 and spo11) were increased under 0.5 lux compared to the dark control. The 0.5 and 1.5 lux groups showed slight increases in testis size and transcript levels associated with steroid synthesis (lhr and hsd3b1) and spermatogenesis (fshr, wt1, sox9, and cldn11), although spermatogenesis was not detected in histological analysis. In contrast, all birds under 5 lux had 10 to 30 times larger testes than birds in all other groups, with a parallel strong increase in mRNA transcript levels and clear signs of spermatogenesis. Across treatments, the volume of the testes was generally a good predictor of testicular transcript levels. Overall, our findings indicate that even small changes in nocturnal light intensity can increase, or decrease, effects on the reproductive physiology of wild organisms.

GATA4 is a transcriptional regulator of R-spondin1 in Japanese flounder (Paralichthys olivaceus)

GATA4 is a well-known transcription factor of the GATA family implicated in regulation of sex determination and gonadal development in mammals. In this study, we cloned the full-length cDNA of Paralichthys olivaceus gata4 (Po-gata4). Phylogenetic, gene structure, and synteny analysis showed that Po-GATA4 is homologous to GATA4 of teleost and tetrapod. Po-gata4 transcripts were detected in Sertoli cells, spermatogonia, oogonia and oocytes, with higher transcript levels overall in the testis than the ovary. The promoter region of P. olivaceus R-spondin1was found to contain a GATA4-binding motif. Results of CBA (cleaved amplified polymorphic sequence-based binding assay) indicated that GATA4 could indeed bind to the promoter sequence of R-spondin1. Moreover, human GATA4 recombinant protein could upregulate R-spondin1 in P. olivaceus ovary cells and FBCs (flounder brain cell line). In FBCs, overexpression of Po-gata4 resulted in elevated transcript levels of R-spondin1. Taken together, our results indicate that Po-GATA4 is involved in gonadal development by regulating R-spondin1 expression.

GATA Regulation and Function During the Ovarian Life Cycle

GATA4 and GATA6 are the sole GATA factors expressed in the ovary during embryonic development and adulthood. Up today, GATA4 and GATA6 are the only transcription factors that have been conditionally deleted during ovarian development and at each major stage of follicle maturation. The evidence from these transgenic mice revealed that GATA4 and GATA6 are crucial for follicles assembly, granulosa cell differentiation, postnatal follicle growth, and luteinization. Thus, conditional knockdown of both factors in the granulosa cells at any stage of development leads to female infertility. GATA targets impacting female reproduction include genes involved in steroidogenesis, hormone signaling, ovarian hormones, extracellular matrix organization, and apoptosis/cell division.

Morphogenesis-related gene-expression profile in porcine oocytes before and after in vitro maturation

Mammalian oocyte maturation is achieved when oocytes reach metaphase II (MII) stage, and accumulate mRNA and proteins in the cytoplasm following fertilization. It has been shown that oocytes investigated before and after in vitro maturation (IVM) differ significantly in transcriptomic and proteomic profiles. Additionally, folliculogenesis and oogenesis is accompanied by morphogenetic changes, which significantly influence further zygote formation and embryo growth. This study aimed to determine new transcriptomic markers of porcine oocyte morphogenesis that are associated with cell maturation competence. An Affymetrix microarray assay was performed on an RNA template isolated from porcine oocytes before (n = 150) and after (n = 150) IVM. The brilliant cresyl blue (BCB) staining test was used for identification of cells with the highest developmental capacity. DAVID (Database for Annotation, Visualization, and Integrated Discovery) software was used for the extraction of the genes belonging to a cell morphogenesis Gene Ontology group. The control group consisted of freshly isolated oocytes. In total, 12,000 different transcripts were analysed, from which 379 genes were downregulated and 40 were upregulated in oocytes following IVM. We found five genes, SOX9, MAP1B, DAB2, FN1, and CXCL12, that were significantly upregulated in oocytes after IVM (in vitro group) compared with oocytes analysed before IVM (in vivo group). In conclusion, we found new transcriptomic markers of oocyte morphogenesis, which may be also recognized as significant mediators of cellular maturation capacity in pigs. Genes SOX9, MAP1B, DAB2, FN1, and CXCL12 may be involved in the regulation of the MII stage oocyte formation and several other processes that are crucial for porcine reproductive competence.

Gene Expression Profiling Reveals Potential Players of Left-Right Asymmetry in Female Chicken Gonads

Most female birds develop only a left ovary, whereas males develop bilateral testes. The mechanism underlying this process is still not completely understood. Here, we provide a comprehensive transcriptional analysis of female chicken gonads and identify novel candidate side-biased genes. RNA-Seq analysis was carried out on total RNA harvested from the left and right gonads on embryonic day 6 (E6), E12, and post-hatching day 1 (D1). By comparing the gene expression profiles between the left and right gonads, 347 differentially expressed genes (DEGs) were obtained on E6, 3730 were obtained on E12, and 2787 were obtained on D1. Side-specific genes were primarily derived from the autosome rather than the sex chromosome. Gene ontology and pathway analysis showed that the DEGs were most enriched in the Piwi-interactiing RNA (piRNA) metabolic process, germ plasm, chromatoid body, P granule, neuroactive ligand-receptor interaction, microbial metabolism in diverse environments, and methane metabolism. A total of 111 DEGs, five gene ontology (GO) terms, and three pathways were significantly different between the left and right gonads among all the development stages. We also present the gene number and the percentage within eight development-dependent expression patterns of DEGs in the left and right gonads of female chicken.

Male-biased miR-92 from early chicken embryonic gonads directly targets ATRX and DDX3X

MiR-17-92 cluster consists of multifunctional miRNAs related to gonadal development in mammals. Our preliminary data showed that gga-miR-92 was male-biased in chicken embryonic gonads at E5.5 and E6.5. MiR-92(a-2) and two putative targets (ATRX and DDX3X) were highly conserved and located on mammalian Chromosome X but on autosomes in chicken. Here, we studied the expression and interaction of miR-92 and the targets (ATRX and DDX3X) in chicken embryonic gonads. What's more, male-biased miR-92 shows an opposite expression tendency with ATRX and DDX3X in eight embryonic stages and different tissues at E10.5 by qRT-PCR. To verify the regulation relationship between miR-92 and two targets, we performed dual-luciferase reporter assay in DF1, overexpression and inhibition of miR-92 in chicken embryonic fibroblasts (CEFs). The results show that miR-92 directly targets ATRX and DDX3X by binding the 3' un-translated region (3'-UTR), and the over-expression and inhibition of miR-92 negatively regulates ATRX and DDX3X. After the identification of the expression of their downstream genes (AMH and WNT4) in mRNA level, we found that there is no regulatory relationship between ATRX and DDX3X. The overall results indicate that miR-92 may perform roles in early chicken gonadogenesis by regulating the expressions of ATRX and DDX3X, respectively.

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.

Expression of wnt4/5 during reproductive cycle of catfish and wnt5 promoter analysis

Signaling molecules, Wnt4 and Wnt5, are essential for ovarian growth during developmental stages in mammals. Although these molecules were identified in several teleosts, their precise expression and role in reproductive processes have not yet been explored in any lower vertebrates. In view of this, using catfish, Clarias batrachus as an animal model, cloning and expression analysis of wnt4 and wnt5 were analyzed in different tissues, at various developmental stages, during ovarian reproductive cycle and after gonadotropin induction. These studies indicate a plausible influence of Wnts in ovarian development and recrudescence. Transcript and protein localization revealed their presence in peri-nucleolar, pre-vitellogenic, vitellogenic and follicular layer of post-vitellogenic oocytes. Synchronous expression of pax2 and wnt5 during the ovarian development and recrudescence of catfish led us to analyze the importance of putative binding element of Pax2 in the 5'-promoter motif of wnt5 Promoter activity of wnt5 was analyzed by luciferase assays after transfecting progressive deletion constructs in pGL3 basic vector into the mammalian cell lines (HEK 293 and CHO). The constructs having putative Pax2 motif showed high promoter activity compared with controls. Likewise, the constructs with site-directed mutagenesis showed increased activity after supplementing recombinant Pax2 indicating the prominence of this motif in wnt5 promoter, in vitro Electrophoretic gel mobility shift, supershift and chromatin immunoprecipitation assays confirmed the binding of Pax2 to its corresponding cis-acting element in the upstream of wnt5 This study is the first of its kind to report the critical transcriptional interaction of Pax2 on wnt5 vis-à-vis ovarian development in teleosts.

Characterization and tissue distribution of Lhx9 and Lhx9α in Chinese giant salamander Andrias davidianus

Lhx9 is an LIM (named for the first three proteins in which the domain was found, Lin-11, Isl1 and Mec-3) homeodomain protein involved in development and differentiation of the gonad. In this study, we isolated the full-length Lhx9 and Lhx9α from Andrias davidianus, detected the tissue distribution and analysed the methylation of the promoters. We identified Lhx9 of 1411 bp and Lhx9α of 1153-bp length, differing in the 3'-flanking region, encoding 399 and 330 amino acids, respectively. The Lhx9 gene was detected primarily in liver, ovary and heart with moderate expression in brain, pituitary, intestine and spleen, and low expression in the remaining examined tissues, while Lhx9α expression was high in heart, pituitary and liver, and low in spleen and stomach. Significantly higher Lhx9 expression was observed in ovary than in testis, with no differences in Lhx9α expression between testis and ovary observed. Bisulphite sequencing revealed significantly higher methylation in testis compared to ovary. The methylation level of CpG sites -733, -673, -615 and -594 exhibited significantly higher levels in testis than in ovary, which was negatively correlated with Lhx9 expression. The methylation and expression patterns suggested that promoter methylation suppressed expression of Lhx9 in A. davidianus.

Foxl2 and Its Relatives Are Evolutionary Conserved Players in Gonadal Sex Differentiation

Foxl2 is a member of the large family of Forkhead Box (Fox) domain transcription factors. It emerged during the last 15 years as a key player in ovarian differentiation and oogenesis in vertebrates and especially mammals. This review focuses on Foxl2 genes in light of recent findings on their evolution, expression, and implication in sex differentiation in animals in general. Homologs of Foxl2 and its paralog Foxl3 are found in all metazoans, but their gene evolution is complex, with multiple gains and losses following successive whole genome duplication events in vertebrates. This review aims to decipher the evolutionary forces that drove Foxl2/3 gene specialization through sub- and neo-functionalization during evolution. Expression data in metazoans suggests that Foxl2/3 progressively acquired a role in both somatic and germ cell gonad differentiation and that a certain degree of sub-functionalization occurred after its duplication in vertebrates. This generated a scenario where Foxl2 is predominantly expressed in ovarian somatic cells and Foxl3 in male germ cells. To support this hypothesis, we provide original results showing that in the pea aphid (insects) foxl2/3 is predominantly expressed in sexual females and showing that in bovine ovaries FOXL2 is specifically expressed in granulosa cells. Overall, current results suggest that Foxl2 and Foxl3 are evolutionarily conserved players involved in somatic and germinal differentiation of gonadal sex.

Sertoli cells are capable of proliferation into adulthood in the transition region between the seminiferous tubules and the rete testis in Wistar rats

Sertoli cells (SCs) play a crucial role in testis differentiation, development and function, determining the magnitude of sperm production in sexually mature animals. For over 40 years, it has been considered that these key testis somatic cells stop dividing during early pre-pubertal phase, between around 10 to 20 days after birth respectively in mice and rats, being after that under physiological conditions a stable and terminally differentiated population. However, evidences from the literature are challenging this dogma. In the present study, using several important functional markers (Ki-67, BrdU, p27, GATA-4, Androgen Receptor), we investigated the SC differentiation status in 36 days old and adult Wistar rats, focusing mainly in the transition region (TR) between the seminiferous tubules (ST) and the rete testis. Our results showed that SCs in TR remain undifferentiated for a longer period and, although at a lesser degree, even in adult rats proliferating SCs were observed in this region. Therefore, these findings suggest that, different from the other ST regions investigated, SCs residing in the TR exhibit a distinct functional phenotype. These undifferentiated SCs may compose a subpopulation of SC progenitors that reside in a specific microenvironment capable of growing the ST length if needed from this particular testis region. Moreover, our findings demonstrate an important aspect of testis function in mammals and opens new venues for other experimental approaches to the investigation of SC physiology, spermatogenesis progression and testis growth. Besides that, the TR may represent an important site for pathophysiological investigations and cellular interactions in the testis.

GATA4 Regulates Blood-Testis Barrier Function and Lactate Metabolism in Mouse Sertoli Cells

Conditional deletion of Gata4 in Sertoli cells (SCs) of adult mice has been shown to increase permeability of the blood-testis barrier (BTB) and disrupt spermatogenesis. To gain insight into the molecular underpinnings of these phenotypic abnormalities, we assessed the impact of Gata4 gene silencing in cell culture models. Microarray hybridization identified genes dysregulated by siRNA-mediated inhibition of Gata4 in TM4 cells, an immortalized mouse SC line. Differentially expressed genes were validated by quantitative RT-PCR analysis of primary cultures of Gata4(flox/flox) mouse SCs that had been subjected to cre-mediated recombination in vitro. Depletion of GATA4 in TM4 cells and primary SCs was associated with altered expression of genes involved in key facets of BTB maintenance, including tight/adherens junction formation (Tjp1, Cldn12, Vcl, Tnc, Csk) and extracellular matrix reorganization (Lamc1, Col4a1, Col4a5, Mmp10, Mmp23, Timp2). Western blotting and immunocytochemistry demonstrated reduced levels of tight junction protein-1, a prototypical tight junction protein, in GATA4-depleted cells. These changes were accompanied by a loss of morphologically recognizable junctional complexes and a decline in epithelial membrane resistance. Furthermore, Gata4 gene silencing was associated with altered expression of Hk1, Gpi1, Pfkp, Pgam1, Gls2, Pdk3, Pkd4, and Ldhb, genes regulating the production of lactate, a key nutrient that SCs provide to developing germ cells. Comprehensive metabolomic profiling demonstrated impaired lactate production in GATA4-deficient SCs. We conclude that GATA4 plays a pivotal role in the regulation of BTB function and lactate metabolism in mouse SCs.

Overexpression of Anti-Müllerian Hormone Disrupts Gonadal Sex Differentiation, Blocks Sex Hormone Synthesis, and Supports Cell Autonomous Sex Development in the Chicken

The primary role of Anti-Müllerian hormone (AMH) during mammalian development is the regression of Müllerian ducts in males. This highly conserved function is retained in birds and is supported by the high levels of AMH expression in developing testes. Mammalian AMH expression is regulated by a combination of transcription factors, the most important being Sry-type high-mobility-group box transcription factor-9 (SOX9). In the chicken embryo, however, AMH mRNA expression precedes that of SOX9, leading to the view that AMH may play a more central role in avian testicular development. To define its role in chicken gonadal development, AMH was overexpressed using the RCASBP viral vector. AMH caused the gonads of both sexes to develop as small and undeveloped structures at both embryonic and adult stages. Molecular analysis revealed that although female gonads developed testis-like cords, gonads lacked Sertoli cells and were incapable of steroidogenesis. A similar gonadal phenotype was also observed in males, with a complete loss of both Sertoli cells, disrupted SOX9 expression and gonadal steroidogenesis. At sexual maturity both sexes showed a female external phenotype but retained sexually dimorphic body weights that matched their genetic sexes. These data suggest that AMH does not operate as an early testis activator in the chicken but can affect downstream events, such as sex steroid hormone production. In addition, this study provides a unique opportunity to assess chicken sexual development in an environment of sex hormone deficiency, demonstrating the importance of both hormonal signaling and direct cell autonomous factors for somatic sex identity in birds.

GATA factors in endocrine neoplasia

GATA transcription factors are structurally-related zinc finger proteins that recognize the consensus DNA sequence WGATAA (the GATA motif), an essential cis-acting element in the promoters and enhancers of many genes. These transcription factors regulate cell fate specification and differentiation in a wide array of tissues. As demonstrated by genetic analyses of mice and humans, GATA factors play pivotal roles in the development, homeostasis, and function of several endocrine organs including the adrenal cortex, ovary, pancreas, parathyroid, pituitary, and testis. Additionally, GATA factors have been shown to be mutated, overexpressed, or underexpressed in a variety of endocrine tumors (e.g., adrenocortical neoplasms, parathyroid tumors, pituitary adenomas, and sex cord stromal tumors). Emerging evidence suggests that GATA factors play a direct role in the initiation, proliferation, or propagation of certain endocrine tumors via modulation of key developmental signaling pathways implicated in oncogenesis, such as the WNT/β-catenin and TGFβ pathways. Altered expression or function of GATA factors can also affect the metabolism, ploidy, and invasiveness of tumor cells. This article provides an overview of the role of GATA factors in endocrine neoplasms. Relevant animal models are highlighted.

Early Development of the Gonads: Origin and Differentiation of the Somatic Cells of the Genital Ridges

The earliest manifestation of gonadogenesis in vertebrates is the formation of the genital ridges. The genital ridges form through the transformation of monolayer coelomic epithelium into a cluster of somatic cells. This process depends on increased proliferation of coelomic epithelium and disintegration of its basement membrane, which is foreshadowed by the expression of series of regulatory genes. The earliest expressed gene is Gata4, followed by Sf1, Lhx9, Emx2, and Cbx2. The early genital ridge is a mass of somatic SF1-positive cells (gonadal precursor cells) that derive from proliferating coelomic epithelium. Primordial germ cells (PGCs) immigrate to the coelomic epithelium even in the absence of genital ridges, e.g., in mouse null mutants for Gata4. And conversely, the PGCs are not required for the formation of the genital ridges. After reaching genital ridges, the PGCs become enclosed by somatic cells derived from coelomic epithelium. Subsequently, the expression of sex-determining genes begins and the bipotential gonads differentiate into either testes or ovaries. Gonadal precursor cells, derived from coelomic epithelium, give rise to the somatic supporting cells such as Sertoli cells, follicular cells, and probably also peritubular myoid and steroidogenic cells.

Anti-Müllerian Hormone Is Required for Chicken Embryonic Urogenital System Growth but Not Sexual Differentiation

In mammals, the primary role of anti-Müllerian hormone (AMH) during development is the regression of Müllerian ducts in males. These structures otherwise develop into fallopian tubes, oviducts, and upper vagina, as in females. This highly conserved function is retained in birds and is supported by the high levels of AMH expression in developing testes. In mammals, AMH expression is controlled partly by the transcription factor, SOX9. However, in the chicken, AMH mRNA expression precedes that of SOX9 , leading to the view that AMH may lie upstream of SOX9 and play a more central role in avian testicular development. To help define the role of AMH in chicken gonad development, we suppressed AMH expression in chicken embryos using RNA interference. In males, AMH knockdown did not affect the expression of key testis pathway genes, and testis cords developed normally. However, a reduction in the size of the mesonephros and gonads was observed, a phenotype that was evident in both sexes. This growth defect occurred as a result of the reduced proliferative capacity of the cells of these tissues, and male gonads also had a significant reduction in germ cell numbers. These data suggest that although AMH does not directly contribute to testicular or ovarian differentiation, it is required in a sex-independent manner for proper cell proliferation and urogenital system growth.

Manipulation of broiler chickens sex differentiation by in ovo injection of aromatase inhibitors, and garlic and tomato extracts

The influence of in ovo administration of aromatase inhibitors, clomiphen citrate, tomoxifen, and garlic and tomato extracts on sex differentiation in broiler chickens were investigated in 2 experiments. Five hundred, and 1,000 fertile eggs from Ross 308 strain were used in experiments 1 and 2, respectively. In both experiments, eggs were divided into 5 groups: control group (DW, 0.1 mL/egg), tomoxifen (0.05 mg/egg), clomiphene citrate (0.05 mg/egg), garlic and tomato extracts (0.1 mL/egg). Eggs were sanitized and prepared for incubation in a regular automatic hatchery. Experimental preparations were injected into eggs at day 5 of the incubation period. Injection sites on the eggs were cleaned with 70% ethylic alcohol, bored by a needle, and aromatase inhibitors were injected into the white from the thin end of the eggs by insulin syringe and then sealed by melted paraffin. In experiment 1, hatched one-day-old chicks (mixed-sex) were raised till 42 days of age in 25 floor pens with a completely randomized design. Experiment 2 was designed to investigate the effects of sex and treatments on the feed-to-gain ratio of broiler chicks. In experiment 2, hatched one-day-old chicks were feather sexed and raised till 42 days of age in 50 floor pens. A completely randomized design with a 2 × 5 factorial arrangement of treatments (sex×treatment) was used. Gonads of the chicks were checked to determine their sex on day 42 by optic microscope to make sure feather sexing was correct. At the end of both experiments, on day 42, one bird from each pen was slaughtered for carcass analysis. In experiment 1, hatchability and the one-day-old weight of chicks showed no significant differences among treatments (P > 0.05). However, in ovo administration of garlic and tomato extracts caused the highest percentage of male chicks (P < 0.05). Also, the percentage of thighs and wings of the males were significantly higher than those of females (P < 0.05). In experiment 2, feed-to-gain ratio of male and female broiler chicks showed no significant differences among treatments (P > 0.05).

Blood-testis barrier and spermatogenesis: lessons from genetically-modified mice

The blood-testis barrier (BTB) is found between adjacent Sertoli cells in the testis where it creates a unique microenvironment for the development and maturation of meiotic and postmeiotic germ cells in seminiferous tubes. It is a compound proteinous structure, composed of several types of cell junctions including tight junctions (TJs), adhesion junctions and gap junctions (GJs). Some of the junctional proteins function as structural proteins of BTB and some have regulatory roles. The deletion or functional silencing of genes encoding these proteins may disrupt the BTB, which may cause immunological or other damages to meiotic and postmeiotic cells and ultimately lead to spermatogenic arrest and infertility. In this review, we will summarize the findings on the BTB structure and function from genetically-modified mouse models and discuss the future perspectives.

In vitro generation and characterization of chicken long-term germ cells from different embryonic origins

Primordial germ cells (PGCs) are the precursors of differentiated germ cells. Located in the epiblast of a stage X (EG&K) embryo, the PGCs translocate anteriorly to the germinal crescent and migrate, within 48 to 56 hours of development, through the blood vascular system to the germinal ridges where they become the gonadal germ cells (GGCs). We aim to generate, compare, and determine the basic characters of the in vitro long-term cultured PGCs derived from (1) the chicken blastodermal cells (at stages IX-XII); (2) the chicken blood of a 2-day old embryo (stages 14-17 Hamburger Hamilton [HH]); and (3) the long-term cultured gonocytes taken from male gonads of a 5- to 6-day-old embryo (stages 29-30 HH). In presence of fibroblast growth factor, chicken blastodermal cells are able to long-term proliferate and generate small, round, alkaline phosphatase-positive cell clusters. Molecular characterization shows that these selected and amplified clusters show a PGC-like cell profile, as they express cPOUV (a pluripotent-associated marker), NR6A1/GCNF and DDX4/CVH (germ cell-specific genes). Both chicken PGCs and GGCs, obtained from embryonic blood and gonads, at 14 to 17 HH and 29 to 30 HH, respectively, generate long-term germ cell cultures and positively react in vitro to periodic acid-Schiff. Immunochemical analyses reveal that these cell lines are specifically recognized by anti-SSEA-1, anti-EMA-1, anti-CVH, anti-β1-integrin, and anti-CEACAM antibodies. The presence of surrounding cells may suggest a stronger dependency toward the niche process for the GGCs. The reactivity of chicken embryonic germ cells obtained from the two different sources to the specific markers used in this study was not altered through the culture. In conclusion, the morphologic analysis specific for chicken PGCs and GGCs will further contribute to quick and reliable characterization of long-term cultured in vitro chicken germ cells.

GATA4 is a key regulator of steroidogenesis and glycolysis in mouse Leydig cells

Transcription factor GATA4 is expressed in somatic cells of the mammalian testis. Gene targeting studies in mice have shown that GATA4 is essential for proper differentiation and function of Sertoli cells. The role of GATA4 in Leydig cell development, however, remains controversial, because targeted mutagenesis experiments in mice have not shown a consistent phenotype, possibly due to context-dependent effects or compensatory responses. We therefore undertook a reductionist approach to study the function of GATA4 in Leydig cells. Using microarray analysis and quantitative RT-PCR, we identified a set of genes that are down-regulated or up-regulated after small interfering RNA (siRNA)-mediated silencing of Gata4 in the murine Leydig tumor cell line mLTC-1. These same genes were dysregulated when primary cultures of Gata4(flox/flox) adult Leydig cells were subjected to adenovirus-mediated cre-lox recombination in vitro. Among the down-regulated genes were enzymes of the androgen biosynthetic pathway (Cyp11a1, Hsd3b1, Cyp17a1, and Srd5a). Silencing of Gata4 expression in mLTC-1 cells was accompanied by reduced production of sex steroid precursors, as documented by mass spectrometric analysis. Comprehensive metabolomic analysis of GATA4-deficient mLTC-1 cells showed alteration of other metabolic pathways, notably glycolysis. GATA4-depleted mLTC-1 cells had reduced expression of glycolytic genes (Hk1, Gpi1, Pfkp, and Pgam1), lower intracellular levels of ATP, and increased extracellular levels of glucose. Our findings suggest that GATA4 plays a pivotal role in Leydig cell function and provide novel insights into metabolic regulation in this cell type.

Identification of side population cells in chicken embryonic gonads

The side population (SP) phenotype, defined by the ability of a cell to efflux fluorescent dyes such as Hoechst, is common to several stem/progenitor cell types. In avian species, SP phenotype has been identified in pubertal and adult testes, but nothing is known about its expression during prenatal development of a male gonad. In this study, we characterized the Hoechst SP phenotype via the cytofluorimetric analysis of disaggregated testes on different days of chicken embryonic development. Male prenatal gonads contained a fraction of SP cells at each stage analyzed. At least two main SP fractions, named P3 and P4, were identified. The percentage of P3 fraction decreased as development proceeds, whereas P4 cell number was not affected by gonad growth. Functional inhibition of BCRP1 channel membrane using Verapamil and/or Ko143 showed that P3, but not P4 phenotype, was dependent on BCRP1 activity. Molecular analysis of both P3- and P4-sorted fractions revealed a differential RNA expression pattern, indicating that P3 cells mainly contained germinal stem cell markers, whereas P4 was preferentially composed of both Sertoli and Leydig cell progenitor markers. Finally, these findings provided evidence that the SP phenotype is a common feature of both germ and somatic cells detected in chicken developing testis.

Conserved action of β-catenin during female fate determination in the red-eared slider turtle

In reptiles such as the red-eared slider turtle Trachemys scripta, development of an ovary from the bipotential gonad requires a coordinated expansion of the cortical domain and regression of the medulla. While estrogen, which is necessary and sufficient for ovarian development in non-mammalian vertebrates, is thought to feminize both compartments, it remains unclear whether there is a signaling relationship between the two domains that coordinates their fates. We show that aromatase, the estrogen-synthesizing enzyme, is localized to the medulla of the differentiating turtle ovary and that differentiation of the medulla precedes and is independent of cortical expansion. Coordinated feminization of the two domains may therefore rely on an estrogenic signal from the differentiating medulla. In eutherian mammals, where estrogen is dispensable for early ovary development, the canonical Wnt signaling pathway is critical for female fate determination. Whether this function is conserved among vertebrates and how it is potentially integrated with estrogen signaling are uncertain. Using a novel in vitro turtle gonad culture system, we demonstrate that ectopic activation of the canonical Wnt signaling pathway in presumptive male gonads induced a partial sex-reversal of the medulla, but inhibition of the pathway was not sufficient to sex-reverse differentiating ovaries. These patterns are similar to those previously observed in mice. Wnt signaling appears to function downstream of estrogen, as ectopic activation of the pathway rescued female development when estrogen synthesis was inhibited. Our findings therefore suggest that the ovary-promoting effects of the Wnt signaling pathway may be functionally conserved between mammals and reptiles.

Gene expression of chicken gonads is sex- and side-specific

In chicken, the left and right female gonads undergo a completely different program during development. To learn more about the molecular factors underlying side-specific development and to identify potential sex- and side-specific genes in developing gonads, we separately performed next-generation sequencing-based deepSuperSAGE transcription profiling from left and right, female and male gonads of 19-day-old chicken embryos. A total of 836 transcript variants were significantly differentially expressed (p < 10(-5)) between combined male and female gonads. Left-right comparison revealed 1,056 and 822 differentially (p < 10(-5)) expressed transcript variants for male and female gonads, respectively, of which 72 are side-specific in both sexes. At least some of these may represent key players for lateral development in birds. Additionally, several genes with laterally differential expression in the ovaries seem to determine female gonads for growth or regression, whereas right-left differences in testes are mostly limited to the differentially expressed genes present in both sexes. With a few exceptions, side-specific genes are not located on the sex chromosomes. The large differences in lateral gene expression in the ovaries in almost all metabolic pathways suggest that the regressing right gonad might have undergone a change of function during evolution.

Identification, expression, and regulation of anti-Müllerian hormone type-II receptor in the embryonic chicken gonad

Anti-Müllerian hormone (AMH) signaling is required for proper development of the urogenital system in vertebrates. In male mammals, AMH is responsible for regressing the Müllerian ducts, which otherwise develop into the fallopian tubes, oviducts, and upper vagina of the female reproductive tract. This role is highly conserved across higher vertebrates. However, AMH is required for testis development in fish species that lack Müllerian ducts, implying that AMH signaling has broader roles in other vertebrates. AMH signals through two serine/threonine kinase receptors. The primary AMH receptor, AMH receptor type-II (AMHR2), recruits the type I receptor, which transduces the signal intracellularly. To enhance our understanding of AMH signaling and the potential role of AMH in gonadal sex differentiation, we cloned chicken AMHR2 cDNA and examined its expression profile during gonadal sex differentiation. AMHR2 is expressed in the gonads and Müllerian ducts of both sexes but is more strongly expressed in males after the onset of gonadal sex differentiation. In the testes, the AMHR2 protein colocalizes with AMH, within Sertoli cells of the testis cords. AMHR2 protein expression is up-regulated in female embryos treated with the estrogen synthesis inhibitor fadrozole. Conversely, knockdown of the key testis gene DMRT1 leads to disruption of AMHR2 expression in the developing seminiferous cords of males. These results indicate that AMHR2 is developmentally regulated during testicular differentiation in the chicken embryo. AMH signaling may be important for gonadal differentiation in addition to Müllerian duct regression in birds.

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

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