Estrogen inhibition of Mullerian inhibiting substance in the chick embryo

Mini review: Asymmetric Müllerian duct development in the chicken embryo

Müllerian ducts are paired embryonic tubes that give rise to the female reproductive tract. In humans, the Müllerian ducts differentiate into the Fallopian tubes, uterus and upper portion of the vagina. In birds and reptiles, the Müllerian ducts develop into homologous structures, the oviducts. The genetic and hormonal regulation of duct development is a model for understanding sexual differentiation. In males, the ducts typically undergo regression during embryonic life, under the influence of testis-derived Anti-Müllerian Hormone, AMH. In females, a lack of AMH during embryogenesis allows the ducts to differentiate into the female reproductive tract. In the chicken embryo, a long-standing model for development and sexual differentiation, Müllerian duct development in females in asymmetric. Only the left duct forms an oviduct, coincident with ovary formation only on the left side of the body. The right duct, together with the right gonad, becomes vestigial. The mechanism of this avian asymmetry has never been fully resolved, but is thought to involve local interplay between AMH and sex steroid hormones. This mini-review re-visits the topic, highlighting questions in the field and proposing a testable model for asymmetric duct development. We argue that current molecular and imaging techniques will shed new light on this curious asymmetry. Information on asymmetric duct development in the chicken model will inform our understanding of sexual differentiation in vertebrates more broadly.

Overview of Avian Sex Reversal

Sex determination and differentiation are processes by which a bipotential gonad adopts either a testicular or ovarian cell fate, and secondary sexual characteristics adopt either male or female developmental patterns. In birds, although genetic factors control the sex determination program, sex differentiation is sensitive to hormones, which can induce sex reversal when disturbed. Although these sex-reversed birds can form phenotypes opposite to their genotypes, none can experience complete sex reversal or produce offspring under natural conditions. Promising evidence indicates that the incomplete sex reversal is associated with cell autonomous sex identity (CASI) of avian cells, which is controlled by genetic factors. However, studies cannot clearly describe the regulatory mechanism of avian CASI and sex development at present, and these factors require further exploration. In spite of this, the abundant findings of avian sex research have provided theoretical bases for the progress of gender control technologies, which are being improved through interdisciplinary co-operation and will ultimately be employed in poultry production. In this review, we provide an overview of avian sex determination and differentiation and comprehensively summarize the research progress on sex reversal in birds, especially chickens. Importantly, we describe key issues faced by applying gender control systems in poultry production and chronologically summarize the development of avian sex control methods. In conclusion, this review provides unique perspectives for avian sex studies and helps scientists develop more advanced systems for sex regulation in birds.

An evo-devo perspective of the female reproductive tract

The vertebrate female reproductive tract has undergone considerable diversification over evolution, having become physiologically adapted to different reproductive strategies. This review considers the female reproductive tract from the perspective of evolutionary developmental biology (evo-devo). Very little is known about how the evolution of this organ system has been driven at the molecular level. In most vertebrates, the female reproductive tract develops from paired embryonic tubes, the Müllerian ducts. We propose that formation of the Müllerian duct is a conserved process that has involved co-option of genes and molecular pathways involved in tubulogenesis in the adjacent mesonephric kidney and Wolffian duct. Downstream of this conservation, genetic regulatory divergence has occurred, generating diversity in duct structure. Plasticity of the Hox gene code and wnt signaling, in particular, may underlie morphological variation of the uterus in mammals, and evolution of the vagina. This developmental plasticity in Hox and Wnt activity may also apply to other vertebrates, generating the morphological diversity of female reproductive tracts evident today.

Sex-Determining Mechanism in Avians

The sex of birds is determined by inheritance of sex chromosomes at fertilization. The embryo with two Z chromosomes (ZZ) develops into a male; by contrast, the embryo with Z and W chromosomes (ZW) becomes female. Two theories are hypothesized for the mechanisms of avian sex determination that explain how genes carried on sex chromosomes control gonadal differentiation and development during embryogenesis. One proposes that the dosage of genes on the Z chromosome determines the sexual differentiation of undifferentiated gonads, and the other proposes that W-linked genes dominantly determine ovary differentiation or inhibit testis differentiation. Z-linked DMRT1, which is a strong candidate avian sex-determining gene, supports the former hypothesis. Although no candidate W-linked gene has been identified, extensive evidence for spontaneous sex reversal in birds and aneuploid chimeric chickens with an abnormal sex chromosome constitution strongly supports the latter hypothesis. After the sex of gonad is determined by a gene(s) located on the sex chromosomes, gonadal differentiation is subsequently progressed by several genes. Developed gonads secrete sex hormones to masculinize or feminize the whole body of the embryo. In this section, the sex-determining mechanism as well as the genes and sex hormones mainly involved in gonadal differentiation and development of chicken are introduced.

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.

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.

Differential expression of estrogen receptor alpha in the embryonic adrenal-kidney-gonadal complex of the oviparous lizard, Calotes versicolor (Daud.)

Estrogen signalling is critical for ovarian differentiation in reptiles with temperature-dependent sex determination (TSD). To elucidate the involvement of estrogen in this process, adrenal-kidney-gonadal (AKG) expression of estrogen receptor (ERα) was studied at female-producing temperature (FPT) in the developing embryos of the lizard, Calotes versicolor which exhibits a distinct pattern of TSD. The eggs of this lizard were incubated at 31.5±0.5°C (100% FPT). The torso of embryos containing adrenal-kidney-gonadal complex (AKG) was collected during different stages of development and subjected to Western blotting and immunohistochemistry analysis. The ERα antibody recognized two protein bands with apparent molecular weight ∼55 and ∼45kDa in the total protein extracts of embryonic AKG complex of C. versicolor. The observed results suggest the occurrence of isoforms of ERα. The differential expression of two different protein isoforms may reveal their distinct role in cell proliferation during gonadal differentiation. This is the first report to reveal two isoforms of the ERα in a reptile during development. Immunohistochemical studies reveal a weak, but specific, cytoplasmic ERα immunostaining exclusively in the AKG during late thermo-sensitive period suggesting the responsiveness of AKG to estrogens before gonadal differentiation at FPT. Further, cytoplasmic as well as nuclear expression of ERα in the medulla and in oogonia of the cortex (faint activity) at gonadal differentiation stage suggests that the onset of gonadal estrogen activity coincides with sexual differentiation of gonad. Intensity and pattern of the immunoreactions of ERα in the medullary region at FPT suggest endogenous production of estrogen which may act in a paracrine fashion to induce neighboring cells into ovarian differentiation pathway.

Estrogen receptor 1 (ESR1; ERα), not ESR2 (ERβ), modulates estrogen-induced sex reversal in the American alligator, a species with temperature-dependent sex determination

All crocodilians and many turtles exhibit temperature-dependent sex determination where the temperature of the incubated egg, during a thermo-sensitive period (TSP), determines the sex of the offspring. Estrogens play a critical role in sex determination in crocodilians and turtles, as it likely does in most nonmammalian vertebrates. Indeed, administration of estrogens during the TSP induces male to female sex reversal at a male-producing temperature (MPT). However, it is not clear how estrogens override the influence of temperature during sex determination in these species. Most vertebrates have 2 forms of nuclear estrogen receptor (ESR): ESR1 (ERα) and ESR2 (ERβ). However, there is no direct evidence concerning which ESR is involved in sex determination, because a specific agonist or antagonist for each ESR has not been tested in nonmammalian species. We identified specific pharmaceutical agonists for each ESR using an in vitro transactivation assay employing American alligator ESR1 and ESR2; these were 4,4',4''-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT) and 7-bromo-2-(4-hydroxyphenyl)-1,3-benzoxazol-5-ol (WAY 200070), respectively. Alligator eggs were exposed to PPT or WAY 200070 at a MPT just before the TSP, and their sex was examined at the last stage of embryonic development. Estradiol-17β and PPT, but not WAY 200070, induced sex reversal at a MPT. PPT-exposed embryos exposed to the highest dose (5.0 μg/g egg weight) exhibited enlargement and advanced differentiation of the Müllerian duct. These results indicate that ESR1 is likely the principal ESR involved in sex reversal as well as embryonic Müllerian duct survival and growth in American alligators.

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.

Changes in mRNA expression of MMP-2 in the Müllerian duct of chicken embryo

Although asymmetric development of the ovary and the oviduct is a unique characteristic in birds, the mechanism of asymmetric development still remains unclear. Recently, degradation of extracellular matrix has been suggested as an important factor related to the regression of the Müllerian duct in mammals. The present study was conducted to examine a possible role of metalloproteinase-2 (MMP-2) in the regression of the right Müllerian duct in the developing chicken embryo. Morphological changes in the Müllerian ducts were studied on day 15 of incubation and mRNA expresseion of MMP-2 was studied on days 12, 15, and 18 of incubation. Morphological observation demonstrated the disappearance of basement membrane in the right Müllerian duct which undergoes the regression. RT-PCR analysis showed that MMP-2 mRNA expression of the right Müllerian duct increased on days 15 and 18 of incubation coincidently with the time of regression. In the right Müllerian duct, regression was prevented by diethylstilbestrol treatment on day 4 of incubation and a coincident decrease in MMP-2 expression was observed when compared to the control group. These results suggest that MMP-2 may be involved in the regression of the right Müllerian duct in the female embryos of the chicken.

Sex reversal and aromatase in chicken

Aromatase inhibitors administered before sexual differentiation of the gonads can induce sex reversal in female chickens. To analyze the process of sex reversal, we have followed for several months the changes induced by Fadrozole, a nonsteroidal aromatase inhibitor, in gonadal aromatase activity and in morphology and structure of the female genital system. Fadrozole was injected into eggs on day four of incubation, and its effects were examined during the embryonic development and for eight months after hatching. In control females, aromatase activity in the right and the left gonad was high in the middle third of embryonic development, and then decreased up to hatching. After hatching, aromatase activity increased in the left ovary, in particular during folliculogenesis, whereas in the right regressing gonad, it continued to decrease to reach testicular levels at one month. In treated females, masculinization of the genital system was characterized by the maintenance of the right gonad and its differentiation into a testis, and by the differentiation of the left gonad into an ovotestis or a testis; however, in all individuals, the left Müllerian duct and the posterior part of the right Müllerian duct were maintained. In testes and ovotestes, aromatase activity was lower than in gonads of control females (except in the right gonad as of one month after hatching) but remained higher than in testes of control and treated males. Moreover, in ovotestes, aromatase activity was higher in parts displaying follicles than in parts devoid of follicles. The main structural changes in the gonads during sex reversal were partial (in ovotestes) or complete (in testes) degeneration of the cortex in the left gonad, and formation of an albuginea and differentiation of testicular cords/tubes in the two gonads. Testicular cords/tubes transdifferentiated from ovarian medullary cords and lacunae whose epithelium thickened and became Sertolian. Transdifferentiation occurred all along embryonic and postnatal development; thus, new testicular cords/tubes were continuously formed while others degenerated. The sex reversed gonads were also characterized by an abundant fibrous interstitial tissue and abnormal medullary condensations of lymphoid-like cells; in the persisting testicular cords/tubes, spermatogenesis was delayed and impaired. Related to aromatase activity, persistence of too high levels of estrogens can explain the presence of oviducts, gonadal abnormalities and infertility in sex reversed females.

The P450 aromatase (P450 arom) gene is asymmetrically expressed in a critical period for gonadal sexual differentiation in the chick

Steroid hormones appear to play an important role in gonadal sex differentiation of birds. Here we studied the steady-state level of the P450 arom mRNA by reverse transcriptase polymerase chain reaction (RT-PCR) in the left and the right presumptive ovary and testis of developing chicken embryos. The gonads were evaluated every hour during the undifferentiated period, at 144-156 h of incubation (h/i), and every 24 h after sexual differentiation at 168 and 192 h/i. Activity of P450 arom was determined by estrone production from [3H]androstenedione at 144-192 h/i. Moreover, morphological development of the gonad was also examined by light microscopy. Results show that onset of P450 arom mRNA and its protein activity were simultaneously detected in the left and the right ovaries at 147 h/i. Asymmetric function of P450 arom gene expression was observed at 156 h/i when morphological gonadal differentiation is first recognized. Biotransformation of [3H]androstenedione to estrone was also asymmetrically detected between the left and right gonad at 156 h/i and asymmetry was maintained throughout the analyzed stages. It is proposed that there is a gene in birds that is asymmetrically expressed in the undifferentiated stage of the female and the male gonad. In the female this gene could promote P450 arom gene expression, increasing estrogen production, which in turn could induce ovarian cortex proliferation and expression of other structural estrogen-regulated genes involved in ovarian sexual determination.

Temperature-dependent sex determination in the American alligator: AMH precedes SOX9 expression

Gonadal morphogenesis is very similar among mammals, birds, and reptiles. Despite this similarity, each group utilises quite different genetic triggers for sex determination. In mammals, testis development is initiated by action of the Y-chromosome gene SRY. Current evidence suggests that SRY may act together with a related gene, SOX9, to activate another gene(s) in the pathway of testicular differentiation. A downstream candidate for regulation by SRY and SOX9 is AMH. In mouse, Sox9 is expressed in the Sertoli cells of the embryonic testis and it precedes the onset of Amh expression. During mouse gonadogenesis, Amh is confined to the embryonic testis, although it later shows postnatal expression in the ovary. Reptiles such as the American alligator, which exhibit temperature-dependent sex determination (TSD) do not have dimorphic sex chromosomes and apparently no SRY orthologue. SOX9 is expressed during testis differentiation in the alligator; however, it appears to be expressed too late to cause testis determination. Here we describe the cloning and expression of the alligator AMH gene and show that AMH expression precedes SOX9 expression during testis differentiation. This is the opposite to that observed in the mouse where SOX9 precedes AMH expression. The data presented here, as well as findings from recent expression studies in the chick, suggest that AMH expression is not regulated by SOX9 in the non-mammalian vertebrates.

Effect of prenatal exposure to diethylstilbestrol on Müllerian duct development in fetal male mice

The clinical use of diethylstilbestrol (DES) by pregnant women has resulted in an increased incidence of genital carcinoma in the daughters born from these pregnancies. Also, in the so-called DES-sons abnormalities were found, mainly, the presence of Müllerian duct remnants, which indicates that fetal exposure to DES may have an effect on male sex differentiation. Fetal regression of the Müllerian ducts is under testicular control through anti-Müllerian hormone (AMH). In male mice, treated in utero with DES, the Müllerian ducts do not regress completely, although DES-exposed testes do produce AMH. We hypothesized that incomplete regression in DES-exposed males is caused by a diminished sensitivity of the Müllerian ducts to AMH. Therefore, the effect of DES on temporal aspects of Müllerian duct regression and AMH type II receptor (AMHRII) messenger RNA (mRNA) expression in male mouse fetuses was studied. It was observed that Müllerian duct regression was incomplete at E19 (19 days post coitum), upon DES administration during pregnancy from E9 through E16. Furthermore, analysis of earlier time points of fetal development revealed that the DES treatment had clearly delayed the onset of Müllerian duct formation by approximately 2 days; in untreated fetuses, Müllerian duct formation was complete by E13, whereas fully formed Müllerian ducts were not observed in DES-treated male fetuses until E15. Using in situ hybridization, no change in the localization of AMH and AMHRII mRNA expression was observed in DES-exposed male fetuses. The mRNA expression was quantified using ribonuclease protection assay, showing an increased expression level of AMH and AMHRII mRNAs at E 13 in DES-exposed male fetuses. Furthermore, the mRNA expression levels of Hoxa 11 and steroidogenic factor-1 (SF-1) were determined as a marker for fetal development. Prenatal DES exposure had no effect on Hoxa 11 mRNA expression, indicating that DES did not exert an overall effect on the rate of fetal development. In DES-exposed male fetuses, SF-1 showed a similar increase in mRNA expression as AMH, in agreement with the observations that the AMH gene promoter requires an intact SF-1 DNA binding site for time- and cell-specific expression, although an effect of DES on SF-1 expression in other tissues, such as the adrenal and pituitary gland, cannot be excluded. However, the increased expression levels of AMH and AMHRII mRNAs do not directly explain the decreased sensitivity of the Müllerian ducts to AMH. Therefore, it is concluded that prenatal DES exposure of male mice delays the onset of Müllerian duct development, which may result in an asynchrony in the timing of Müllerian duct formation, with respect to the critical period of Müllerian duct regression, leading to persistence of Müllerian duct remnants in male mice.

Regulation of sexual dimorphism in mammals

Sexual dimorphism in humans has been the subject of wonder for centuries. In 355 BC, Aristotle postulated that sexual dimorphism arose from differences in the heat of semen at the time of copulation. In his scheme, hot semen generated males, whereas cold semen made females (Jacquart, D., and C. Thomasset. Sexuality and Medicine in the Middle Ages, 1988). In medieval times, there was great controversy about the existence of a female pope, who may have in fact had an intersex phenotype (New, M. I., and E. S. Kitzinger. J. Clin. Endocrinol. Metab. 76: 3-13, 1993.). Recent years have seen a resurgence of interest in mechanisms controlling sexual differentiation in mammals. Sex differentiation relies on establishment of chromosomal sex at fertilization, followed by the differentiation of gonads, and ultimately the establishment of phenotypic sex in its final form at puberty. Each event in sex determination depends on the preceding event, and normally, chromosomal, gonadal, and somatic sex all agree. There are, however, instances where chromosomal, gonadal, or somatic sex do not agree, and sexual differentiation is ambiguous, with male and female characteristics combined in a single individual. In humans, well-characterized patients are 46, XY women who have the syndrome of pure gonadal dysgenesis, and a subset of true hermaphrodites are phenotypic men with a 46, XX karyotype. Analysis of such individuals has permitted identification of some of the molecules involved in sex determination, including SRY (sex-determining region Y gene), which is a Y chromosomal gene fulfilling the genetic and conceptual requirements of a testis-determining factor. The purpose of this review is to summarize the molecular basis for syndromes of sexual ambiguity seen in human patients and to identify areas where further research is needed. Understanding how sex-specific gene activity is orchestrated may provide insight into the molecular basis of other cell fate decisions during development which, in turn, may lead to an understanding of aberrant cell fate decisions made in patients with birth defects and during neoplastic change.

Sites of estrogen receptor and aromatase expression in the chicken embryo

Estrogens have been implicated in sexual differentiation of both the gonads and the genitalia of birds. In chicken embryos, the gonads are steroidogenically active from an early age, and the aromatase gene, (cAROM), necessary for estrogen synthesis, is expressed only in females at the time of gonadal sex differentiation. However, no studies have directly demonstrated the distribution of estrogen receptor (cER) transcripts or proteins in the embryonic avian reproductive system. Whole-mount in situ hybridization and immunohistochemistry were used here to identify sites of estrogen receptor expression in the embryonic chicken urogenital system. Estrogen receptor mRNA was observed in both male and female gonads prior to morphological differentiation, at Stage 26 (4.5 days of incubation), and continued until after sexual dimorphism at Stage 32 (7.5 days). Transcripts of cER were also detected in the Müllerian ducts and developing external genitalia of both sexes. Estrogen receptor protein was analysed in the embryonic gonads by immunohistochemistry and found to be most abundant in the cortex of the left ovary, although it was also present in the medulla of both female gonads. No significant cER protein expression was detected in the male gonad by immunohistochemistry. In contrast, the aromatase gene was expressed in the gonads of female embryos from the onset of sexual dimorphism but was not detectable in male gonads at any stage examined. These findings suggest that estrogen involvement in both gonadogenesis and genital development in chickens is mediated by the estrogen receptor.

Effects of embryonic estrogen on differentiation of the gonads and secondary sexual characteristics of male zebra finches

Male zebra finches sing to court females, whereas females do not normally sing. In parallel, the telencephalic brain regions that control song are larger in volume and contain larger cells in males than in females. The vocal control organ (syrinx) is also larger in males. Some evidence suggests that the sexual differentiation of both anatomy and behavior is under the regulation of gonadal hormones during early development, yet recent data conflict with the idea that the sole source of masculinization of the neural song system is the testes. In the present experiment, we treated genetic males with estradiol benzoate on embryonic day 5 and measured the volume of and neuron soma size in robust nucleus of the archistriatum (RA) and the high vocal center (HVC), two telencephalic song control nuclei. We also weighed the syrinx, the muscles of which are the target of the motor pathway containing the two brain regions. The estrogen treatment disrupted testicular morphology, and induced an oviduct in six of seven animals, but it had no effect on any of four measures of masculinization of the neural song system. These results suggest that normal testicular tissue is not required for masculine development of the neural song system.

Characterization of mullerian inhibiting substance binding on cervical carcinoma cells demonstrated by immunocytochemistry

Müllerian inhibiting substance (MIS) is a glycoprotein released from Sertoli cells or follicular cells of gonads, responsible for the regression of Müllerian ducts and/or Müllerian-derived tumor cells. Binding of MIS to target cells is essential for initiating regression. A human cervical carcinoma CaSki cell was examined by quantitative immunocytochemistry detected by anti-avian MIS antibody for MIS binding ability. Various treatments of WGA-peroxidase conjugate, enzyme digestion, sodium periodate or exogenous estrogen before antibody recognition were performed. It was found that the WGA partially blocked MIS binding to CaSki cell surfaces. Protease digestion of CaSki cell surfaces prior to addition of MIS or an anticervical carcinoma monoclonal antibody 1H10 (MAb 1H10), blocked the binding of MIS but not MAb 1H10 to cell surfaces. Sodium periodate and overnight exposure of CaSki cells to estrogen or diethylstilbestrol before or after fixation of the cells, did not influence MIS binding ability in vitro. MIS binding was higher on avian Müllerian duct compared with MIS binding to CaSki cells by quantitative immuno-gold labeling analysis. MAb 1H10 immuno-gold complexes binding to CaSki cells was also obtained and compared with MIS immuno-gold bindings. MIS binding site could be a polypeptide which survived sodium periodate treatment. The 'critical window' period, in which developing Müllerian ducts respond to exogenous estrogen protection from MIS regression, is possibly lost in CaSki cell.

The effects of norethindrone on the mullerian ducts of the American alligator

Norethindrone, a reported aromatase inhibitor, has been used to examine the role of estrogens in the unilateral regression of the mullerian ducts that occurs in female chick embryos. The mullerian ducts are embryonic oviducts that regress in most male vertebrates under the influence of the testicular hormone, mullerian inhibiting substance (MIS). The ovaries of the chick also produce MIS during early development, but only the right duct regresses. Based on the finding that the left duct contains significantly more estradiol binding sites than the right duct, it has been proposed that the left duct is protected from the effects of MIS by preferentially binding estradiol from the ovaries. In support of this theory, norethindrone (0.1 and 0.5 mg) injected into the airsac of chick eggs results in regression of the left mullerian duct of female embryos, presumably by blocking the synthesis of estradiol. In the present study, it was hypothesized that crocodilians, because of the common ancestry they share with birds, would respond in a similar manner by exhibiting regression of both mullerian ducts in response to norethindrone. However, the application of norethindrone (0.5 mg) to the chorioallantoic membrane of female alligator embryos in ovo resulted in significant hypertrophy of the ducts, indicating that norethindrone had an estrogenic effect in the alligator rather than acting as an aromatase inhibitor. There was no effect of norethindrone on the gonads.

Action of estradiol on müllerian duct regression induced by treatment with norethindrone of female chick embryos

Treatment of genetically female chick embryos with norethindrone (NET), a progesterone-like steroid chemically related to testosterone, caused two types of Müllerian duct (MD) deficiencies. The first consisted in an absence of the caudal part of the ducts owing to their partial agenesia occurring between Days 5 and 7 of embryonic life. This is nonspecific since it was observed after a treatment with almost all steroidal sex hormones. In particular, this was obtained with estradiol which also increases the frequency and extent of agenesia caused by the NET, as reported here. The second type of deficiency appeared between Days 12 and 14 and was due to a regression destroying the more or less large part of the MDs having escaped agenesia, i.e., for most of the cephalic half. This resulted from the influence of the anti-Müllerian hormone originating from the ovary and normally inhibited by the ovarian estrogens. This protective action of endogenous estrogens was inhibited by the NET, but an additional treatment with estradiol removed this inhibition and prevented duct regression. Our results suggest that estrogen protects the duct from the regression induced indirectly by NET, by acting both at gonad and MD levels.

Quantitative change in fibronectin in cultured müllerian mesenchymal cells in response to diethylstilbestrol and müllerian-inhibiting substance

I report on the synthesis of fibronectin in the developing chick Müllerian duct mesenchymal cells. Before the differentiation of female chick Müllerian duct, the amount of fibronectin in the cells of the right duct is 44% lower than in the left duct. While after differentiation, the amount of fibronectin in the right duct is 29% lower, as compared to the left duct. Estrogenic hormone diethylstilbestrol (DES) treatment was carried out at the 5th day of incubation when both female Müllerian ducts were undifferentiated. Three days after DES treatment, the regression of the right duct was prevented, and the amount of fibronectin was induced by 89%, while induction in the left duct was 11%. Eight days after DES administration, the amount of fibronectin in the right and left Müllerian duct was induced by 150 and 76%, respectively. After DES treatment in the male embryo, both Müllerian ducts were retained, and the capacity for fibronectin synthesis was preserved. Application of the indirect immunocytochemical labeling technique revealed Müllerian-inhibiting substance (MIS) binding sites on the membrane of the Müllerian mesenchymal cells. The addition of chick MIS in the culture medium reduced the amount of detectable fibronectin in the cultured mesenchymal cells. The synthesis of fibronectin in intestinal mesenchymal cells was not affected by DES or MIS.

Lectin bindings and diethylstilbestrol effects on the recognition of mullerian inhibiting substance (MIS) on chick mullerian ducts by MIS-antiserum

A high intensity of lectin bindings was demonstrated on the epithelial cells and serosa cells of the regressing right Mullerian ducts (Mds) in the female chick embryos. The strong lectin bindings occurs on, or in the regressing Md cells along with marked surface MIS bindings at the age of day 13. However, at the age of days 5-7 1/2, bindings of lectins were weak. Neither Wheat-germ agglutinin (WGA) or Concanavalin A (Con-A) labelings before MIS-antiserum (MIS-Ab) incubation can block antibody recognitions to the antigens, including MIS and growth hormone at the age of day 13. Our previous studies indicated that after WGA labeling on the surfaces of Md epithelial cells prior to the incubation of MIS-Ab at day 10 did not prevent the recognition of MIS-Ab (Wang 1989). On the contrary, at day 7 1/2, the specific binding of MIS was eliminated after preincubations with lectins and prenatal diethylstilbestrol (DES) treatment at the age of day 5. It is suggested that DES provides a protection to the Mds from MIS-induced regression by preventing the MIS binding to its specific membrane receptors. An increase of extra- and intracellular glycoproteins or carbohydrates of regressing Md epithelial cells were suggested. Internalization of WGA but not MIS molecules was found in Md epithelial cells. The Golgi saccules were negative of lectin bindings.

The effects of estradiol and testosterone on mullerian-duct regression in the American alligator (Alligator mississippiensis)

Female hatchling alligators were castrated and implanted with a graft of either skeletal muscle tissue or testicular tissue from male hatchlings. Following surgery, each female also received a sustained-release pellet (Innovative Research of America, Rockville, MD) implanted subcutaneously that delivered one of the following treatments: a control substance (0.1 mg), 17 beta-estradiol (0.01 mg), or testosterone propionate (0.1 mg). Treated and final control females were sacrificed 8 weeks after surgery, and the mullerian and wolffian ducts were removed and examined histologically. The testis graft induced regression of the mullerian ducts in both the testosterone- and control-treated females. In the estradiol-treated females, however, no mullerian-duct regression occurred, indicating that estradiol prevented testis-induced regression. In the females that received a muscle graft, the mullerian ducts of placebo-treated females were morphologically similar to those of the intact final control females, but they were smaller in size. On the other hand, estradiol-treated mullerian ducts exhibited significant hypertrophy, but differentiation of muscle tissue in the stroma was not induced. Some of the testosterone-treated ducts were also slightly stimulated, but none showed any signs of regression. This suggests that testosterone does not induce regression in this species. Finally, there was no effect of either graft treatment or steroid treatment on the wolffian ducts. The evolutionary significance of these results is discussed.

Quantification of müllerian inhibiting substance in developing chick gonads by a competitive enzyme-linked immunosorbent assay

An immunoblotting method was used to purify a Müllerian-inhibiting substance (MIS)-specific antiserum. The serum was used to quantify the content of MIS in developing chick gonads by competitive enzyme-linked immunosorbent assay. From embryonic stages to the eleventh week after hatching, male chicken testes have a high content of MIS in the following two stages: (1) from the sixth to the eighth day and from the fourteenth to the twentieth day of incubation, and (2) from the second to the eighth week after hatching. The high content of MIS in the early embryonic stage is closely correlated with the natural pattern of Müllerian duct regression observed in the male embryo. From the sixth to the twelfth day of incubation, the female right ovary contains a higher content of MIS than that of the left ovary. Up to the fourteenth day of incubation, the content of MIS in the left ovary reaches maximum levels and then declines. The combination of MIS from right and left ovaries was found to be highest in the ninth to the fourteenth day of incubation, when the regression of the right Müllerian duct reached its highest peak. However, the question of the inability of MIS to cause regression of the female left Müllerian duct and the caudal part of the right duct is raised and discussed. The hypothesis that prenatal estrogenic hormone (diethylstilbestrol) protects the Müllerian duct has been reevaluated. It was found that estrogen does not reduce the MIS content in prenatally treated gonads.

Müllerian inhibiting substance as oocyte meiosis inhibitor

Müllerian inhibiting substance (MIS) inhibited the resumption of meiosis in both denuded and cumulus cell-enclosed rat oocytes in vitro. Spontaneous germinal vesicle breakdown was prevented in both types of oocytes treated by a purified MIS preparation at protein concentrations of 15 micrograms to 150 pg/ml. The inhibiting effect of MIS on the resumption of meiosis was dose dependent, reversible and cyclic AMP independent. Neither follicular-stimulating hormone, luteinizing hormone, progesterone, estradiol, nor testosterone acted significantly to influence MIS-mediated inhibition of rat oocyte maturation. In contrast, MIS had no influence on meiosis in the mouse, where other protein has been reported to inhibit the cumulus cell-enclosed oocyte in a cyclic AMP-dependent fashion. Thus MIS may be yet another inhibitor of oocyte meiosis, acting in the rat by a mechanism different from those inhibitors known, in the mouse ovary, to exert their effect in a cyclic AMP-dependent manner.

Sertoli cell production of müllerian inhibiting substance in vitro

Sertoli cell cultures were monitored for müllerian inhibiting substance with a solid phase radioimmunoassay. Sertoli cells from newborn calf testes were placed in defined media free of serum in monolayer culture after treatment with trypsin-collagenase followed by gravity separation. Immunoreactive müllerian inhibiting substance was detected in the culture media of Sertoli cells but not National Institutes of Health 3T3 cells. To verify that the Sertoli cells were intact, cyclic adenosine monophosphate levels were determined after follicle-stimulating hormone stimulation. Cyclic adenosine monophosphate levels were elevated in Sertoli cells but not National Institutes of Health 3T3 cells. The newborn calf Sertoli cell culture provides a useful system in which to study factors affecting müllerian inhibiting substance production and release, and documents this substance as another reliable marker for the Sertoli cell. Müllerian inhibiting substance levels also could be measured in media beneath testicular fragments in organ culture, and were increased and prolonged in comparison to müllerian inhibiting substance release from Sertoli cell monolayer cultures. Modulation of müllerian inhibiting substance release from monolayer and organ cultures then was attempted. Neither gonadotropin nor steroid additions affected the release of müllerian inhibiting substance during 24 to 72 hours in organ or tissue culture. We are using the müllerian inhibiting substance radioimmunoassay to monitor attempts to immortalize a Sertoli cell line capable of continuous müllerian inhibiting substance production using viral deoxyribonucleic acid transfection techniques.

Mullerian inhibiting substance: a fetal hormone with surgical implications

Mullerian Inhibiting Substance (MIS) is secreted from the fetal (and postnatal) testis and is known to cause regression of the Mullerian ducts, the anlage of the fallopian tubes, uterus and upper vagina. It is a large glycoprotein hormone, the action of which appears to be modulated by sex steroids: mainly testosterone in mammals and oestrogen in birds. Recent evidence has raised the possibility that its action may be to diminish cell surface phosphorylation and thereby change the direction of differentiation of the Mullerian duct towards regression. Other suspected functions for MIS include control of testicular descent and inhibition of malignant tumours of the female genital tract.

Early sex differences in hormonal potentialities of gonads from quail embryos with a sex-linked pigmentation marker: an in vitro radioimmunoassay study

Quail embryos with a sex-linked eye pigmentation marker allowing sex identification at autopsy provided a biological model for radioimmunoassay of sex steroids in embryonic quail gonads at a very early stage (51/2 and 61/2 days). The purpose was to demonstrate a sex difference in hormonal potentialities of the gonads before any morphological indication of sexual differentiation. Evidence of early steroidogenesis by undifferentiated gonads could be obtained: estrogen synthesis characterized female gonads, while testosterone was produced by the gonads of both sexes. The sex hormonal production was concomitant with, or even preceded, the apparent beginning of sex differentiation of gonads.

Steroid modulation of Mullerian duct regression in the chick embryo

The recent demonstrations that Mullerian inhibiting substance (MIS) is present in embryonic chick ovaries (P. K. Hutson, H. Ikawa, and P. K. Donahoe (1981). J. Pediatr. Surg. 16, 822-827), and that exogenous diethylstilbestrol does not significantly inhibit MIS secretion from feminized testes (Hutson et al. (1982) J. Pediatr. Surg. 17, 953-959), suggest that ovarian estrogens protect the female left Mullerian duct from MIS-induced regression. The possibility exists, however, that ovarian MIS may be inactive. This study was designed to see if interference with estrogen action in ovo would allow MIS to cause regression of the female left Mullerian duct. The "antiestrogens," tamoxifen and LY117018, had little effect on the female Mullerian ducts unless given in high doses or with added testosterone (greater than 0.1 mg). Two compounds known to inhibit estrogen synthesis, aminoglutethimide and 4-hydroxyandrostenedione, had no effect on their own, even in high doses (less than 1.0 mg/egg). However, when administered together (0.5 mg each) there was significant disappearance of the lower ends of both Mullerian ducts. Norethindrone, which has been described recently as an aromatase inhibitor (Y. Osawa, C. Yarborough, and V. Osawa (1982). Science (Washington, D. C.) 215, 1249-1251) caused partial regression of the upper end of the left Mullerian duct as well as complete loss of the lower ends of both ducts in the female. These results suggest that the steroid environment is a critical factor in the response of the Mullerian ducts to MIS, and that estrogen blockage may allow endogenous MIS from the ovary to induce partial regression of the Mullerian ducts in the female chick embryo.

Subrenal capsule assay to test the viability of parenterally delivered müllerian inhibiting substance

Production of bovine müllerian inhibiting substance (MIS) has been increased to allow generation of large quantities of biologically active purified material. The limited MIS previously available allowed only pretreatment of tumors prior to colony inhibition or implanting in nude mice. In preparation for posttransplantation tumor treatment, a subrenal capsule assay, which was first used against human tumors heterotransplanted into nude mice and subsequently against those heterotransplanted into immunocompetent mice, was adapted to determine (1) if MIS preparations could traverse the bloodstream without degradation and (2) the optimal dose required to produce a biologic effect. Urogenital ridges from female 14-day-old rat embryos were transferred atraumatically to small pouches beneath the renal capsule of the immunocompetent male CDF1 mice. The cranial-caudal orientation of the ridge with its müllerian duct was maintained. Over the next 72 hours, the mice were injected via the tail vein with 0.1 mL of an MIS-containing solution over a 100-fold concentration range. After three days, the kidneys were removed and shaved just below the ridge, which was then placed in soft agar for orientation and subsequent serial sectioning. After fixation, dehydration, and paraffin embedding, sections were stained and regression of the müllerian duct was graded and compared according to concentration and number of MIS doses administered. Regression diminished from almost complete (4+) at the highest dose, to minimal (1 to 2+) at 1/100 of that dose. Heat-inactivated and vehicle controls caused no regression of the müllerian ducts.(ABSTRACT TRUNCATED AT 250 WORDS)

The fate of the grafted quail Mullerian duct in the chick embryonic coelom

Recent morphological analyses of Mullerian duct regression suggested that some ductal cells might survive, in contrast to the previous view that regression was an example of "programmed cell death." The present study was designed to demonstrate survival of Mullerian duct cells after regression, and to map migration into local or distant tissues. Seven or eight-day-old chick embryos received intraabdominal grafts of Mullerian ducts from seven- or eight-day-old quails, creating chick-quail chimeras. Three or four days later the abdomen was serially sectioned and examined histologically using a modified Feulgen stain. Sixty-six of the 230 grafted embryos survived (29%). After sectioning, grafts were found in 34 of the 58 embryos in the body wall, peritoneum or mesenephros, with several adherent to the hosts' Mullerian ducts. Twenty female embryos contained grafts, all of which were developing normally. Fourteen male embryos contained grafts in various stages of regression. Regression was more advanced in mesonephric or body wall grafts while free intraperitoneal grafts showed the least regression. Migration of quail cells was striking when seen in grafts placed in the mesonephros or adherent to the host Mullerian duct. In these, regressing quail cells migrated into and became incorporated in adjacent chick mesenephros. Migration patterns were seen also in non-regressing cells in female hosts, where quail cells "homed" to the host chick Mullerian duct structures.