The effect of cyproterone acetate on the activity of delta 5-3 beta-hydroxysteroid dehydrogenase in tadpole sex transformation

Steroidogenic potential of the gonad during sex differentiation in the rice field frog Hoplobatrachus rugulosus (Anura: Dicroglossidae)

Prior studies demonstrated that gonadal differentiation in the rice field frog, Hoplobatrachus rugulosus, was of an undifferentiated type since all individuals had ovaries at complete metamorphosis. However, the steroidogenic potential of the gonad is still unknown. In this study, H. rugulosus were obtained by stimulating fertilization in the laboratory under natural light and temperature conditions. The gonads were collected and their steroidogenic potential was evaluated by determining the expression level of messenger RNA (mRNA) encoding for cytochrome P450 17-hydroxylase/C17-20 lyase (CYP17) and cytochrome P450 aromatase (CYP19) using quantitative real-time RT-PCR and the localization of CYP17 mRNA in tissues by in situ hybridization. The CYP17 mRNA levels in males at 4-11 weeks postmetamorphosis were higher than in female and intersex gonads. This corresponded to their localization in the gonadal tissues, where CYP17 signals were specifically detected in the Leydig cells of the testis at 5-16 weeks postmetamorphosis but was undetectable in all ovary samples. The CYP19 mRNA levels in females at 4-11 weeks postmetamorphosis was higher than in male and intersex gonads, which corresponded with gonadal development, indicating the potential steroidogenic function of the ovary. Based on the present results, the role of CYP17 and CYP19 mRNA in sex differentiation in H. rugulosus may occur after gonadal sex differentiation and the steroidogenic potential of the gonads exhibited a sexual dimorphic pattern. These results provide a crucial basis for further research on the developmental biology in anuran species.

Gonadal sex differentiation in frogs: how testes become shorter than ovaries

Testis differentiation in anuran amphibians is the result of two opposing processes: degeneration of the distal part, and development of the proximal part, which becomes a functional male gonad. Undifferentiated gonad differentiates directly into a testis without a transition phase. We described the morphology of developing testes in Rana temporaria and Hyla arborea, and made careful histology and ultrastructure in Pelophylax lessonae. The developing testis was divided into 10 stages (I-III, undifferentiated gonad, IV-X, testis). The earliest morphological symptoms of testis differentiation were observed in 4- to 5-week-old tadpoles at Gosner stage 27-28. At that time an undifferentiated gonad, composed of 6-9 metameres, differentiates into a testis. The proximal metameres (2-3 in the right gonad and 3-4 in the left one) differentiate into a functional testis, while the distal ones degenerate. The difference between left and right gonad size is maintained until adulthood (stage X). Degeneration of the distal part progresses along the posterior-anterior gradient and starts at stage IV. It affects first the germ cells with accompanying precursor Sertoli cells, and then the mesenchymal cells and fibroblasts. Finally the external epithelium forms a "sleeve" around the almost empty distal part. The total length of the testes stays the same until stage VIII at Gosner stage 41 (age 74-148 days). Active spermatogenesis starts at stage IX (juveniles after their first hibernation), during which the distal part eventually disappears and the proximal part starts growing considerably due to progressing spermatogenesis.

Agricultural intensity in ovo affects growth, metamorphic development and sexual differentiation in the common toad (Bufo bufo)

Pollution was cited by the Global Amphibian Assessment to be the second most important cause of amphibian decline worldwide, however, the effects of the agricultural environment on amphibians are not well understood. In this study, spawn from Bufo bufo was taken from four sites in England and Wales with varying intensities of arable agriculture. Spawn was either placed in tanks containing aged tap water (ex-situ, five replicates) or in cages at the native site (caged, five replicates). Hatching success, abnormal tadpoles, and forelimb emergence were recorded during the larval stage. Individuals were also sampled at five time points (TP) during development (5-, 7-, 9-, 12-, 15-weeks post-hatch) and analysed for morphological parameters. The thyroids (TP2) and the gonads (TP3,4,5) were also analysed histologically. With the exception of the thyroid histopathology, all analysed endpoints were significantly different between ex-situ individuals reared under identical conditions from the different sites. In addition, intensity of arable agriculture had a negative effect on growth and development. At one site, despite distinct rearing conditions, a high level of intersex (up to 42%) and similar sex ratios were observed in both ex-situ and caged individuals. Taken together, these data suggest that maternal exposure and/or events in ovo had a much larger effect on growth, metamorphic development, and sexual differentiation in B. bufo than the ambient environment. This could have important implications for traditional exposure scenarios that typically begin at the larval stage. Intersex is reported for the first time in European amphibians in situ, highlighting the potential use of distinct populations of amphibians in fundamental research into the aetiology of specific developmental effects in wild amphibians.

The mechanism of sex determination in vertebrates-are sex steroids the key-factor?

In many vertebrate species, sex is determined at fertilization of zygotes by sex chromosome composition, knows as genotypic sex determination (GSD). But in some species-fish, amphibians and reptiles-sex is determined by environmental factors; in particular by temperature-dependent sex determination (TSD). However, little is known about the mechanisms involved in TSD and GSD. How does TSD differ from GSD? As is well known, genes that activated downstream of sex-determining genes are conserved throughout all classes of vertebrates. What is the main factor that determines sex, then? Sex steroids can reverse sex of several species of vertebrate; estrogens induce the male-to-female sex-reversal, whereas androgens do the female-to-male sex-reversal. For such sex-reversal, a functioning sex-determining gene is not required. However, in R. rugosa CYP19 (P450 aromatase) is expressed at high levels in indifferent gonads before phenotypic sex determination, and the gene is also active in the bipotential gonad of females before sex determination. Thus, we may predict that an unknown factor, a common transcription factor locates on the X and/or W chromosome, intervenes directly or indirectly in the transcriptional up-regulation of the CYP19 gene for feminization in species of vertebrates with both TSD and GSD. Similarly, an unknown factor on the Z and/or Y chromosome probably intervenes directly or indirectly in the regulation of androgen biosynthesis for masculinization. In both cases, a sex-determining gene is not always necessary for sex determination. Taken together, sex steroids may be the key-factor for sex determination in some species of vertebrates.

Sex determination in amphibians

The heterogametic sex is male in all mammals, whereas it is female in almost all birds. By contrast, there are two heterogametic types (XX/XY and ZZ/ZW) for genetic sex determination in amphibians. Though the original heterogametic sex was female in amphibians, the two heterogametic types were probably interchangeable, suggesting that sex chromosomes evolved several times in this lineage. Indeed, the frog Rana rugosa has the XX/XY and ZZ/ZW sex-determining systems within a single species, depending on the local population in Japan. The XY and ZW geographic forms with differentiated sex chromosomes probably have a common origin as undifferentiated sex chromosomes resulted from the hybridization between the primary populations of West Japan and Kanto forms. It is clear that the sex chromosomes are still undergoing evolution in this species group. Regardless of the presence of a sex-determining gene in amphibians, the gonadal sex of some species can be changed by sex steroids. Namely, sex steroids can induce the sex reversal, with estrogens inducing the male-to-female sex reversal, whereas androgens have the opposite effect. In R. rugosa, gonadal activity of CYP19 (P450 aromatase) is correlated with the feminization of gonads. Of particular interest is that high levels of CYP19 expression are observed in indifferent gonads at time before sex determination. Increases in the expression of CYP19 in female gonads and CYP17 (P450 17alpha-hydroxylase/C17-20 lyase) in male gonads suggest that the former plays an important role in phenotypic female determination, whereas the latter is needed for male determination. Thus, steroids could be the key factor for sex determination in R. rugosa. In addition to the role of sex steroids in gonadal sex determination in this species, Foxl2 and Sox3 are capable of promoting CYP19 expression. Since both the genes are autosomal, another factor up-regulating CYP19 expression must be recruited. The factor, which may be located on the X or W chromosome, intervenes directly or indirectly, in the transcriptional regulation of the CYP19 gene for feminization in amphibians. A factor up-regulating CYP17 expression remains to be identified.

Effects of the antiandrogens, vinclozolin and cyproterone acetate on gonadal development in the Japanese medaka (Oryzias latipes)

This study was focused on determining the effects of exposure to antiandrogens on the gonadal development of Japanese medaka (Oryzias latipes). Test compounds included the fungicide, vinclozolin and the clinical antiandrogen, cyproterone acetate. Newly hatched medaka were exposed to aqueous solutions of vinclozolin (2500 microg/l) and the vinclozolin fungicide formulation, Ronilan (1000 and 5000 microg/l) and cyproterone acetate (1 and 10 microg/l), for 3 months. Histological evaluation of the gonadal tissues of exposed fish indicated that the 5000 microg/l concentration of the vinclozolin formulation (Ronilan) induced a low incidence of intersex (i.e. testis-ova) and the 2500 microg/l concentration of vinclozolin-affected spermatogenesis in males. Also, the vinclozolin treatments induced moderate ovarian atresia. Cyproterone acetate also induced a low incidence of testis-ova, but in contrast to the vinclozolin treatment the amount of ovarian tissue in the testis-ova was equal to or greater than the amount of testicular tissue. In the cyproterone acetate treatments, both oogenesis and spermatogenesis were moderately inhibited at all test concentrations. The results of this study indicate that antiandrogens have the potential to alter testicular development and gametogenesis in fish. However, research is needed to determine the mechanisms by which antiandrogens affect fish.

Effects of androgens on sex differentiation of the urodele Pleurodeles waltl

In nonmammalian vertebrates, steroids have been hypothesized to induce somatic sex differentiation, since manipulations of the steroidal environment of gonads have led to various degrees of sex reversal. Whereas the critical role of estrogens in ovarian differentiation is well documented, studies on androgens have produced a perplexing variety of results depending upon species variations and nature of androgens used. In this way, testosterone induces masculinization of females in some species but provokes paradoxical feminization of males in many other species such as the urodelan Pleurodeles waltl. In reptiles this phenomenon could be interpreted by conversion of exogenous testosterone to estradiol by aromatase. Treatments of Pleurodeles larvae with nonaromatizable androgens bring support to this hypothesis and suggest a role of androgens in sex differentiation. Dihydrotestosterone (DHT) could not induce the paradoxical feminization of ZZ larvae. In addition, DHT as well as 11beta-hydroxy-androstenedione could drive a functional male differentiation of ZW larvae. Moreover, other 5alpha reduced androgens also induced sex reversal of female larvae. Yet, the 5alpha reductase inhibitor CGP 53133 and antiandrogens such as flutamide or cyproterone acetate did not exert any effect on male sex differentiation of ZZ larvae. Though the precise role of androgens is still unknown, especially for 11-oxygenated androgens, our results suggest an implication in male sex differentiation. In this way, testosterone could play a pivotal role in being metabolized either into other androgens during testis differentiation or into estradiol during ovarian differentiation.

The effects of aromatase and 5 alpha-reductase inhibitors, antiandrogen, and sex steroids on Bidder's organs development and gonadal differentiation in Bufo bufo tadpoles

Embryos of toads (Bufo bufo) were treated with aromatase (4-OHA) and 5 alpha-reductase (17 beta C) inhibitors, antiandrogen (CPA), estradiol-17 beta, testosterone, and 5 alpha-dihydrotestosterone in order to study the role played by sex steroids in the development and sex differentiation of gonads. Test compounds were administered to tadpoles in water and morphometric and cytometric analyses were carried out on histological sections of the cephalic Bidder's organ (a rudimentary ovary) and of the gonadal region. In Bidder's organs, the number and size of oogonia and oocytes were modified by the treatments. However, the female commitment of the Bidder's organ occurs independently from steroid treatments that lead to an acceleration or slackening of the processes of proliferation and differentiation of oogonia. 4-OHA and androgens caused various degrees of inhibition of ovarian differentiation, with gonads maintaining an undifferentiated condition. Estrogen provoked a shift of the sex ratio towards the female sex, yet slackened gonadal growth. 17 beta C accelerated ovarian differentiation in females while CPA enhanced gonadal differentiation in both sexes by promoting the germ and somatic cell proliferation. We suggest that sex hormones may have a local regulatory role in gonadal differentiation during early developmental stages. Furthermore, the strong tendency of Bidderian germ cells to develop in the oogenetic way regardless of sex genotype and steroid treatments, and the quantitative sex differences found in the control Bidder's organs and gonads, suggest that other factors (such as intracellular mechanisms) may be involved in the initial steps of the process of germ cell differentiation.

Gonadal differentiation and secretions of estradiol and testosterone of the ovaries of Rana catesbeiana tadpoles treated with 4-hydroxyandrostenedione

Laparotomized female tadpoles of Rana catesbeiana at TK stages X-XII, about 9 months old, were implanted intraperitoneally with empty capsules or capsules containing 4-hydroxyandrostenedione (4-OHA), known as an aromatase inhibitor in vertebrates. Histology, gonosomatic index, and secretions of estradiol (E2) and testosterone (T) of the ovaries were investigated. Three months after the treatment, histological examination revealed various degrees of sex reversal in the ovaries treated with 4-OHA and 79% (57 in 72) were transformed into testes. The ovaries of control tadpoles, however, displayed normal histological appearance. Radioimmunoassay showed that secretion of E2 was decreased while that of T was increased in 4-OHA treated ovaries. The gonosomatic index displayed a decline tendency from control females through experimental animals to untreated control males. These results indicated that activity of aromatase in the ovaries was inhibited by 4-OHA, resulting in accumulation of T which induced transformation of the ovaries into testes.

In vitro inhibition of estradiol secretion of tadpole ovaries by cyanoketone

We have demonstrated the presence of delta 5-3 beta-hydroxysteroid dehydrogenase (HSD) activity in tadpole ovaries of Rana catesbeiana. In the present study, we wish to determine whether estradiol (E2) secretion of tadpole ovaries could be influenced by cyanoketone (CK), a specific inhibitor of delta 5-3 beta-HSD. R catesbeina tadpoles at the premetamorphic climax were used, and pooled ovaries were incubated, 30 mg/tube, with CK at dosages of 0, 0.001, 0.01, 0.1, 1, and 10 micrograms/ml of Krebs-Ringer bicarbonate buffer for 6 hr. Media were collected for assay of E2 by radioimmunoassay (RIA). Results showed an inhibition of E2 secretion by CK that was positively correlated with CK dosage, but plateaued at doses of 0.1 microgram/ml and higher. This finding was comparable to that of G.F. Young, H. Kagawa, and Y. Nagahama (1982, Gen. Comp. Endocrinol. 47, 357-360) on adult fish ovaries. However, adult vertebrates depend on gonadotropins to regulate secretion of E2 while tadpoles, being immature, might secrete E2 independently of pituitaries. When the histochemical test for delta 5-3 beta-HSD activity was performed on in vitro CK-treated ovaries, there was a decrease of enzyme activity by CK. The RIA and histochemical findings may contribute to the concept of sex transformation in which a disturbance of steroidogenesis may induce sex reversal from females to males, at least in tadpoles.

The correlation of fine structure with endocrine function of ovarian follicle cells in tadpoles

Electron microscopic study of the ovaries of metamorphosing Rana catesbeiana tadpoles stimulated by anterior pituitary implantation revealed striking alterations of several organelles in the follicle cells and oocytes when compared with the controls. Pituitary implantation caused activation of the follicle cells as shown by activation of mitochondria, voluminous Golgi complexes, mobilization of the lipid droplets, increased rough endoplasmic reticulum, and increased numbers of glycogen granules. Activation of oocyte mitochondria was also observed. These findings are discussed with respect to the correlation of the ultrastructure and endocrine function in the tadpole ovaries.