SMAD2/3 signaling regulates initiation of mouse Wolffian ducts and proximal differentiation in Müllerian ducts

Male and female reproductive tracts develop from anterior intermediate mesoderm with similar differentiation processes. The anterior intermediate mesoderm develops into the mesonephros, and the Wolffian duct initiates by epithelialization in the mesonephros. The Müllerian duct invaginates from the coelomic epithelium of the cranial mesonephros for ductal formation and is then regionalized into proximal to caudal female reproductive tracts. In this study, we focused on the epithelialization of the Wolffian duct, initiation of the Müllerian duct, and the regionalization step of the Müllerian ducts as a continuous process. By using intermediate mesodermal cells from mouse pluripotent stem cells, we identified that inhibition of SMAD2/3 signaling might be involved in the differentiation into mesenchymal cells, after which mesonephric cells might be then epithelialized during differentiation of the Wolffian duct. Aggregation of coelomic epithelial cells might be related to initiation of the Müllerian duct. Transcriptomic analysis predicted that consensus sequences of SMAD3/4 were enriched among highly expressed genes in the proximal Müllerian duct. SMAD2/3 signaling to regulate differentiation of the Wolffian duct was continuously activated in the proximal Müllerian duct and was involved in proximal and oviductal regionalization. Therefore, SMAD2/3 signaling may be finely tuned to regulate differentiation from initiation to regionalization steps.

Müller cell-derived VEGF is essential for diabetes-induced retinal inflammation and vascular leakage

OBJECTIVE

Vascular endothelial growth factor (VEGF-A or VEGF) is a major pathogenic factor and therapeutic target for diabetic retinopathy (DR). Since VEGF has been proposed as a survival factor for retinal neurons, defining the cellular origin of pathogenic VEGF is necessary for the effectiveness and safety of long-term anti-VEGF therapies for DR. To determine the significance of Müller cell-derived VEGF in DR, we disrupted VEGF in Müller cells with an inducible Cre/lox system and examined diabetes-induced retinal inflammation and vascular leakage in these conditional VEGF knockout (KO) mice.

RESEARCH DESIGN AND METHODS

Leukostasis was determined by counting the number of fluorescently labeled leukocytes inside retinal vasculature. Expression of biomarkers for retinal inflammation was assessed by immunoblotting of TNF-alpha, ICAM-1, and NF-kappaB. Vascular leakage was measured by immunoblotting of retinal albumin and fluorescent microscopic analysis of extravascular albumin. Diabetes-induced vascular alterations were examined by immunoblotting and immunohistochemistry for tight junctions, and by trypsin digestion assays for acellular capillaries. Retinal integrity was analyzed with morphologic and morphometric analyses.

RESULTS

Diabetic conditional VEGF KO mice exhibited significantly reduced leukostasis, expression of inflammatory biomarkers, depletion of tight junction proteins, numbers of acellular capillaries, and vascular leakage compared to diabetic control mice.

CONCLUSIONS

Müller cell-derived VEGF plays an essential and causative role in retinal inflammation, vascular lesions, and vascular leakage in DR. Therefore, Müller cells are a primary cellular target for proinflammatory signals that mediates retinal inflammation and vascular leakage in DR.

Endocrine disruptors in female reproductive tract development and carcinogenesis

Growing concerns over endocrine disrupting chemicals (EDCs) and their effects on human fetal development and adult health have promoted research into the underlying molecular mechanisms of endocrine disruption. Gene targeting technology has allowed insight into the genetic pathways governing reproductive tract development and how exposure to EDCs during a critical developmental window can alter reproductive tract development, potentially forming the basis for adult diseases. This review primarily uses diethylstilbestrol (DES) as a model agent for EDCs and discusses the recent progress elucidating how DES and other EDCs affect murine female reproductive tract development and cancer at the molecular level.

Prenatal Development of the Bovine Oviduct

In this study the development of the bovine Fallopian tube was investigated using light microscopic methods. Formation and differentiation of the Müllerian duct were studied in mesonephroi of 16 embryos and fetuses with a crown-rump lengths (CRL) of 0.9-8.4 cm. The funnel field, the rostral beginning of the Müllerian duct was first observed at a CRL of 0.9 cm. It appears as a thickening of the mesothelium on the craniolateral side of the mesonephros. During later development the Müllerian duct emerges by caudal outgrowth from the funnel field. Formation of a common basal lamina surrounding the caudal tips of Müllerian and Wolffian ducts could be observed at all stages up to CRL of 2.7 cm. The mesothelium and the epithelium of the Wolffian duct adjacent to the Müllerian duct showed a modification of epithelium height in all examined stages. Probably the Wolffian duct influences the growth of Müllerian duct by epithelio-mesenchymal interactions. Fetuses from a CRL of 12.0 to 94.0 cm were used for investigation of the prenatal differentiation of the oviductal mucosa. Folding of the oviductal mucosa started at a CRL of 29.0 cm and continued until birth. Individual primary, secondary and tertiary folds are formed in special proliferation zones and epithelium-folding buds. The cellular differentiation of the oviductal epithelium involves the formation of ciliated and secretory cells during different times of prenatal development. Ciliogenesis was first detected at a CRL of 33.0 cm. Active secretory cells could be observed in the oviductal epithelium from a CRL of 64.0 cm onwards.

[Anti-mullerian hormone and its role in the regulation of ovarian function. Review of the literature]

Anti-mullerian hormone, also called AMH, belongs to the large family of transforming growth factor P. Its role in the sexual differentiation of male fetus is now well known. Recently, AMH has been demonstrated to play an important role in the ovarian function. In fact, AMH seems to regulate the kinetics of follicular development, inhibiting the follicular recruitment and the follicular growth. Thus, this intra-gonadic cybernin could be a decisive determinant of the rapidity of follicular pool exhaustion. Today, some experimental data from the literature suggest that AMH could be a reliable marker of ovarian reserve. This review summarizes the present knowledge about AMH and its role in physiology but also in ovarian pathology.

Müllerian inhibiting substance regulates its receptor/SMAD signaling and causes mesenchymal transition of the coelomic epithelial cells early in Müllerian duct regression

Examination of Müllerian inhibiting substance (MIS) signaling in the rat in vivo and in vitro revealed novel developmental stage- and tissue-specific events that contributed to a window of MIS responsiveness in Müllerian duct regression. The MIS type II receptor (MISRII)-expressing cells are initially present in the coelomic epithelium of both male and female urogenital ridges, and then migrate into the mesenchyme surrounding the male Müllerian duct under the influence of MIS. Expression of the genes encoding MIS type I receptors, Alk2 and Alk3, is also spatiotemporally controlled; Alk2 expression appears earlier and increases predominantly in the coelomic epithelium, whereas Alk3expression appears later and is restricted to the mesenchyme, suggesting sequential roles in Müllerian duct regression. MIS induces expression of Alk2, Alk3 and Smad8, but downregulates Smad5 in the urogenital ridge. Alk2-specific small interfering RNA (siRNA) blocks both the transition of MISRII expression from the coelomic epithelium to the mesenchyme and Müllerian duct regression in organ culture. Müllerian duct regression can also be inhibited or accelerated by siRNA targeting Smad8 and Smad5,respectively. Thus, the early action of MIS is to initiate an epithelial-to-mesenchymal transition of MISRII-expressing cells and to specify the components of the receptor/SMAD signaling pathway by differentially regulating their expression.

Serum Müllerian-inhibiting substance levels in adolescent girls with normal menstrual cycles or with polycystic ovary syndrome

OBJECTIVE

To compare serum müllerian-inhibiting substance (MIS) concentrations in adolescent girls with polycystic ovary syndrome (PCOS) or normal menstrual cycles.

DESIGN

Prospective study.

SETTING

University department of obstetrics and gynecology.

PATIENT(S)

Thirty-one girls (12-18 years old) with PCOS and 17 girls (12-19 years old) with normal menstrual cycles.

INTERVENTION(S)

Serum was collected from girls with PCOS or normal cycles during the early follicular phase of the menstrual cycle, stored frozen until assayed.

MAIN OUTCOME MEASURE(S)

Serum levels of MIS, E2, free-T, androstenedione, LH, and FSH.

RESULT(S)

Serum MIS levels in girls with PCOS were significantly higher compared with normal girls (4.1 +/- 2.2 [SD] and 2.4 +/- 1.0 ng/mL, respectively). The subjects were stratified for body mass index (BMI) (< and >25 kg/m2). Serum MIS levels in PCOS girls (4.2 +/- 3.0 ng/mL [BMI <25 kg/m2] and 4.0 +/- 1.6 [BMI >25 kg/m2]) were significantly higher compared with normal girls (2.2 +/- 0.8 and 2.6 +/- 0.7 ng/mL, respectively).

CONCLUSION(S)

Adolescent girls with PCOS have significantly higher serum MIS levels compared with normally cycling girls. Serum MIS levels in PCOS were not influenced by BMI. Increased MIS production may represent an early manifestation of the disease.

Lineage infidelity of epithelial ovarian cancers is controlled by HOX genes that specify regional identity in the reproductive tract

Although epithelial ovarian cancers (EOCs) have been thought to arise from the simple epithelium lining the ovarian surface or inclusion cysts, the major subtypes of EOCs show morphologic features that resemble those of the müllerian duct-derived epithelia of the reproductive tract. We found that HOX genes, which normally regulate mullerian duct differentiation, are not expressed in normal ovarian surface epithelium (OSE), but are expressed in different EOC subtypes according to the pattern of mullerian-like differentiation of these cancers. Ectopic expression of Hoxa9 in tumorigenic mouse OSE cells gave rise to papillary tumors resembling serous EOCs. In contrast, Hoxa10 and Hoxa11 induced morphogenesis of endometrioid-like and mucinous-like EOCs, respectively. Hoxa7 showed no lineage specificity, but promoted the abilities of Hoxa9, Hoxa10 and Hoxa11 to induce differentiation along their respective pathways. Therefore, inappropriate activation of a molecular program that controls patterning of the reproductive tract could explain the morphologic heterogeneity of EOCs and their assumption of müllerian-like features.

Analysis of gene expression induced by diethylstilbestrol (DES) in human primitive Müllerian duct cells using microarray

The Mullerian ducts are strongly influenced by natural estrogen, estradiol (E2) and diethylstilbestrol (DES) in their development. We screened E2 and DES responsive genes using a microarray analysis in human primitive Mullerian duct cell line, EMTOKA cells expressed estrogen receptor (ER) beta. c-myc oncogene and other target genes expression was detected in cells treated by high-dose DES, but ER antagonist ICI 182,780 could not prevent c-myc induction above. Results of our present study suggested the presence of ER independent pathway in oncogenes induction process by high-dose DES treatment in a human primitive Mullerian duct cell line.

Molecular Regulation of Müllerian Development by Hox Genes

HOX genes are a family of regulatory molecules that encode conserved transcription factors controlling aspects of morphogenesis and cell differentiation during normal embryonic development. All metazoans possess a common genetic system for embryonic patterning, and this system is also used in the reproductive tract. Hox genes are also expressed in the adult uterus. Hox genes are essential both for the development of mullerian tract in the embryonic period and adult function. Sex steroids regulate Hox gene expression during embryonic and endometrial development in the menstrual cycle. EMX2 and beta(3)-integrin acting downstream of Hoxa10 gene are likely involved in both these developmental processes. This article reviews the role and molecular regulation of Hox genes in reproductive tract development.

Wnt7a Is a Suppressor of Cell Death in the Female Reproductive Tract and Is Required for Postnatal and Estrogen-Mediated Growth1

The murine female reproductive tract is undifferentiated at birth and undergoes pronounced growth and cytodifferentiation during postnatal life. Postnatal reproductive tract development proceeds in the absence of high levels of circulating estrogens and is disrupted by precocious exposure to estrogens. The WNT gene family is critical in guiding the epithelial-mesenchymal interactions that direct postnatal uterine development. We have previously described a role for Wnt7a in controlling morphogenesis in the uterus. In addition to patterning defects, Wnt7a mutant uteri are atrophic in adults and do not show robust postnatal growth. In the present study, we examine immature female Wnt7a mutant and wild-type uteri to assess the cellular processes that underlie this failure in postnatal uterine growth. Levels of proliferation are higher in wild-type versus Wnt7a mutant uteri. Exposure to the potent estrogen-agonist diethylstilbestrol (DES) leads to an increase in cell proliferation in the uterus in wild-type as well as in mutant uteri, indicating that Wnt7a is not required in mediating cell proliferation. In contrast, we observe that Wnt7a mutant uteri display high levels of cell death in response to DES, whereas wild-type uteri display almost no cell death, revealing that Wnt7a plays a key role as a cell death suppressor. The expression pattern of other key regulatory genes that guide uterine development, including estrogen receptor (alpha), Hox, and other WNT genes, reveals either abnormal spatial distribution of transcripts or abnormal regulation in response to DES exposure. Taken together, the results of the present study demonstrate that Wnt7a coordinates a variety of cell and developmental pathways that guide postnatal uterine growth and hormonal responses and that disruption of these pathways leads to aberrant cell death.

Roles of p63 in the diethylstilbestrol-induced cervicovaginal adenosis

Women exposed to diethylstilbestrol (DES) in utero develop abnormalities, including cervicovaginal adenosis that can lead to cancer. We report that transient disruption of developmental signals by DES permanently changes expression of p63, thereby altering the developmental fate of Müllerian duct epithelium. The cell fate of Müllerian epithelium to be columnar (uterine) or squamous (cervicovaginal) is determined by mesenchymal induction during the perinatal period. Cervicovaginal mesenchyme induced p63 in Müllerian duct epithelium and subsequent squamous differentiation. In p63(-/-) mice, cervicovaginal epithelium differentiated into uterine epithelium. Thus, p63 is an identity switch for Müllerian duct epithelium to be cervicovaginal versus uterine. P63 was also essential for uterine squamous metaplasia induced by DES-exposure. DES-exposure from postnatal day 1 to 5 inhibited induction of p63 in cervicovaginal epithelium via epithelial ERalpha. The inhibitory effect of DES was transient, and most cervicovaginal epithelial cells recovered expression of p63 by 2 days after discontinuation of DES-treatment. However, some cervicovaginal epithelial cells failed to express p63, remained columnar and persisted into adulthood as adenosis.

AMH signaling: from receptor to target gene

Anti-Müllerian hormone (AMH), also known as Müllerian inhibiting substance (MIS), is a member of the transforming growth factor beta (TGFbeta) superfamily and plays a crucial role during male sexual differentiation. Although the AMH type II receptor has been identified, the identity of the other signaling components has remained unknown. This review describes the identification of candidate AMH type I receptors and an AMH-target gene involved in Müllerian duct regression.

Anti-Müllerian hormone, beta-catenin and Müllerian duct regression

The embryo is initially sexually indifferent, and correct sexual development is dependent on gonadal hormone production. Thus, in the male embryo, anti-Müllerian hormone (AMH), secreted by the Sertoli cells of the testis, induces regression of the Müllerian duct, the anlagen of female reproductive tract. This hormone causes ductal epithelial regression through a paracrine mechanism originating in periductal mesenchyme and the cross-talk between the mesenchymal and epithelial layers accounts for the cranial-to-caudal pattern of Müllerian regression. Here, we review and discuss recent developments concerning the relationship of apoptosis of Müllerian duct to tissue remodeling, mesenchymal-epithelial interactions, and involvement of beta-catenin in AMH signaling in periductal mesenchyme. Determining the role of beta-catenin/LEF-1 signaling is critical for understanding AMH action during Müllerian duct regression.

Development of the human Müllerian duct in the sexually undifferentiated stage

An embryological explanation for the development of the Müllerian duct still poses a major challenge. The development of this duct was investigated systematically in human embryos. Seven embryos (Carnegie stages 18-23) were serially sectioned in the frontal, sagittal, and transversal planes at a thickness of 10 microm and stained with hematoxylin and eosin (H&E) for histological analysis. In all observed embryos, the caudal end of the Müllerian duct was found to be intimately connected to the Wolffian duct. The opening of the Müllerian duct to the coelomic cavity was formed as the result of an invagination of the coelomic epithelium at Carnegie stage 18. The duct grew independently from the invagination during stages 19-23. The fused duct (uterovaginal canal) bifurcated at the caudal portion at Carnegie stages 22 and 23. This is the first description of the caudal portion of the fused Müllerian ducts separating again and returning to each of the Wolffian ducts in human embryos.

Requirement of Bmpr1a for Müllerian duct regression during male sexual development

Elimination of the developing female reproductive tract in male fetuses is an essential step in mammalian sexual differentiation. In males, the fetal testis produces the transforming growth factor beta (TGF-beta) family member anti-Müllerian hormone (Amh, also known as Müllerian-inhibiting substance (Mis)), which causes regression of the Müllerian ducts, the primordia of the oviducts, uterus and upper vagina. Amh induces regression by binding to a specific type II receptor (Amhr2) expressed in the mesenchyme surrounding the ductal epithelium. Mutations in AMH or AMHR2 in humans and mice disrupt signaling, producing male pseudohermaphrodites that possess oviducts and uteri. The type I receptor and Smad proteins that are required in vivo for Müllerian duct regression have not yet been identified. Here we show that targeted disruption of the widely expressed type I bone morphogenetic protein (BMP) receptor Bmpr1a (also known as Alk3) in the mesenchymal cells of the Müllerian ducts leads to retention of oviducts and uteri in males. These results identify Bmpr1a as a type I receptor for Amh-induced regression of Müllerian ducts. Because Bmpr1a is evolutionarily conserved, these findings indicate that a component of the BMP signaling pathway has been co-opted during evolution for male sexual development in amniotes.

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

In mammals, anti-Müllerian hormone (AMH) is produced by Sertoli cells from the onset of testicular differentiation and by granulosa cells after birth. In birds, AMH starts to be expressed in indifferent gonads of both sexes at a similar level and is later up-regulated in males. We previously demonstrated that, unlike in mammals, the onset of AMH expression occurs in chick embryo in the absence of SOX9. We looked for potential factors that might be involved in regulating AMH expression at different stages of chick gonad differentiation by comparing its expression pattern in embryos and young chicken with that of DMRT1, SF-1, WT1, GATA-4, Wnt-4, and Lhx9, by in situ hybridization. The results allowed us to distinguish different phases. (1) In indifferent gonads of both sexes, AMH is expressed in dispersed medullar cells. SF-1, WT1, GATA-4, Wnt-4, and DMRT1 are transcribed in the same region of the gonads, but none of these factors has an expression strictly coincident with that of AMH. Lhx9 is present only in the cortical area. (2) After this period, AMH is up-regulated in male gonads. The up-regulation is concomitant with the beginning of SOX9 expression and a sex dimorphic level of DMRT1 transcripts. It is followed by the aggregation of the AMH-positive cells (Sertoli cells) into testicular cords in which AMH is coexpressed with DMRT1, SF-1, WT1, GATA-4, and SOX9. (3) In the females, the low level of dispersed medullar AMH expression is conserved. With development of the cortex in the left ovary, cells expressing AMH accumulate in the juxtacortical part of the medulla, whereas they remain dispersed in the right ovary. At this stage, AMH expression is not strictly correlated with any of the studied factors. (4) After hatching, the organization of left ovarian cortex is characterized by the formation of follicles. Follicular cells express AMH in conjunction with SF-1, WT1, and GATA-4 and in the absence of SOX9, as in mammals. In addition, they express Lhx9 and Wnt-4, the latter being also found in the oocytes. (5) Moreover, unlike in mammals, the chicken ovary retains a dispersed AMH expression in cortical interstitial cells between the follicles, with no obvious correlation with any of the factors studied. Thus, the dispersed type of AMH expression in indifferent and female gonads appears to be bird-specific and not controlled by the same factors as testicular or follicular AMH transcription.

Involvement of a matrix metalloproteinase in MIS-induced cell death during urogenital development

Programmed cell death of the Müllerian duct eliminates the primitive female reproductive tract during normal male sexual differentiation. Müllerian inhibiting substance (MIS or AMH) triggers regression by propagating a BMP-like signaling pathway in the Müllerian mesenchyme that culminates in apoptosis of the Müllerian duct epithelium. Presently, the paracrine signal(s) used in this developmental event are undefined. We have identified a member of the matrix metalloproteinase gene family, Mmp2, as one of the first candidate target genes downstream of the MIS cascade to function as a paracrine death factor in Müllerian duct regression. Consistent with a role in regression, Mmp2 expression was significantly elevated in male but not female Müllerian duct mesenchyme. Furthermore, this sexually dimorphic expression of Mmp2 was extinguished in mice lacking the MIS ligand, suggesting strongly that Mmp2 expression is regulated by MIS signaling. Using rat organ genital ridge organ cultures, we found that inhibition of MMP2 activity prevented MIS-induced regression, whereas activation of MMP2 promoted ligand-independent Müllerian duct regression. Finally, MMP2 antisense experiments resulted in partial blockage of Müllerian duct regression. Based on our findings, we propose that similar to other developmental programs where selective elimination or remodeling of tissues occurs, localized induction of extracellular proteinases is critical for normal male urogenital development.

Roles of p63 in differentiation of Müllerian duct epithelial cells

In the mouse female reproductive tract, p63, a homologue of the p53 tumor suppressor gene, is highly expressed in basal cells of the vaginal and cervical epithelium, but not in the uterine epithelium. P63 is undetectable in the undifferentiated epithelium of the embryonic Müllerian duct. The Mullerian vaginal epithelium becomes p63 positive and stratified during the first week of postnatal development. P63 expression in the Müllerian vaginal epithelium is induced by vaginal mesenchyme. When vaginal mesenchyme was combined with uterine epithelium from newborn mouse, the uterine epithelium was induced to undergo vaginal differentiation and to express p63. Conversely, when the vaginal epithelium from the newborn mouse was recombined with uterine mesenchyme, it underwent uterine differentiation and failed to express p63. After the uterine epithelium or vaginal epithelium differentiates, the expression status of p63 in uterine (negative) and vaginal (positive) epithelia is not altered by heterotypic mesenchyme. Studies with p63-null mice demonstrate that p63 is essential for vaginal epithelial differentiation, because p63-null Müllerian vaginal epithelium developed as uterine epithelium. Thus, p63 determines whether Müllerian duct epithelial cells become uterine or vaginal. Misexpression of p63 in uterine and vaginal epithelial lesions induced by neonatal diethylstilbestrol (DES) exposure induces pathological changes. Irregularities in p63 expression (and thus epithelial differentiation) are observed in the uterine and vaginal epithelia of neonatally DES-exposed mice during the first week of postnatal development. Thus, neonatal DES exposure abnormally transforms uterine and vaginal epithelial differentiation by perturbing epithelial expression of p63 during development.

Autosomal recessive segregation of a truncating mutation of anti-Müllerian type II receptor in a family affected by the persistent Müllerian duct syndrome contrasts with its dominant negative activity in vitro

Anti-Müllerian hormone belongs to the TGFbeta family whose members exert their effects by signaling through two related serine/threonine kinase receptors. Mutations of the anti-Müllerian hormone type II receptor occur naturally, causing the persistent Müllerian duct syndrome. In a family with two members with persistent Müllerian duct syndrome and one normal sibling, we detected two novel mutations of the anti-Müllerian hormone type II receptor gene. One, transmitted by the mother to her three sons, is a deletion of a single base leading to a stop codon, causing receptor truncation after the transmembrane domain. The other, a missense mutation in the substrate-binding site of the kinase domain, is transmitted by the father to the two sons affected by persistent Müllerian duct syndrome, indicating a recessive autosomal transmission as in other cases of persistent Müllerian duct syndrome. Truncating mutations in receptors of the TGFbeta family exert dominant negative activity, which was seen only when each of the mutant anti-Müllerian hormone receptors was overexpressed in an anti-Müllerian hormone-responsive cell line. We conclude that assessment of dominant activity in vitro, which usually involves overexpression of mutant genes, does not necessarily produce information applicable to clinical conditions, in which mutant and endogenous genes are expressed on a one to one basis.

Autocrine and paracrine Müllerian inhibiting substance hormone signaling in reproduction

Members of the transforming growth factor beta (TGFbeta) superfamily are polypeptide growth factors that exhibit diverse effects on normal cell growth, adhesion, mesenchymal-epithelial interactions, cell differentiation, and programmed cell death. This chapter will discuss the work of ourselves and others on one member of this large superfamily, Müllerian inhibiting substance (MIS, or anti-Müllerian hormone, AMH) and its role in reproductive tract development and the adult gonad. Using recombinant MIS protein, it is possible to begin unraveling the molecular mechanism of duct involution in the embryo. Our recent results suggest that MIS triggers cell death by altering mesenchymal-epithelial interactions. In addition to the developmental effects of MIS in secondary sexual differentiation, expression studies of the MIS ligand and the MIS type II receptor (MISIIR) suggest a potential regulatory role for MIS in adult germ cell maturation and gonadal function. Recent data from others suggest that MIS may act in a paracrine manner to block differentiation of interstitial cells of the adult gonad by repressing all or some steps of steroidogenesis. Our studies are highly suggestive of direct repression of steroidogenic enzyme gene expression by activation of the MIS signaling pathway. Thus, for the first time, an opportunity to define fully target genes and components of the MIS signaling pathway may be possible.

Targeted mutagenesis of the endogenous mouse Mis gene promoter: in vivo definition of genetic pathways of vertebrate sexual development

Mutations were introduced into conserved steroidogenic factor 1 (SF1)- and SOX9-binding sites within the endogenous mouse Mullerian inhibiting substance (Mis) promoter. Male mice homozygous for the mutant SF1-binding site correctly initiated Mis transcription in fetal testes, although at significantly reduced levels. Surprisingly, sufficient MIS was produced to eliminate the MUllerian ducts. In contrast, males homozygous for the mutant SOX9-binding site did not initiate Mis transcription, resulting in pseudohermaphrodites. These studies suggest an essential role for SOX9 in the initiation of Mis transcription, whereas SF1 appears to act as a quantitative regulator of Mis transcript levels, perhaps for influencing non-Mullerian duct tissues. Comparative studies of Mis expression in vertebrates indicate that the Mis promoter receives transcriptional inputs that vary between species but result in the same functional readout.

Early expression of AMH in chicken embryonic gonads precedes testicular SOX9 expression

In mammals, anti-Müllerian hormone (AMH) is produced by Sertoli cells from the onset of testicular differentiation and by granulosa cells only after birth. SOX9, a transcription factor related to the testis-determining factor SRY, is expressed in mouse testis 1 day before AMH. To determine the relationship between AMH and SOX9 in birds, we cloned the AMH promoter in search of SOX9 response elements, and we compared the expression of AMH and SOX9 in the gonads of chick embryos using in situ hybridization. Potential SOX response elements were found in the AMH promoter; however, AMH is expressed in both sexes at stage 25, 1 day before the first SOX9 transcripts appear in the male gonads. SOX9 is never expressed in the female. These results do not support the hypothesis that SOX9 could trigger the expression of testicular AMH in the chick but does not exclude a later role in testis development.

New insights into mullerian inhibiting substance and its mechanism of action

The primary function of MIS in mammals is to initiate regression of Mullerian structures in males as part of normal sexual development. As we learn more about its other roles, particularly its influence on the growth and differentiation of cell types within the gonad, a more thorough understanding of the receptors that MIS stimulates and the downstream signaling cascade with which it interacts will help in the development of diagnostic and therapeutic uses of MIS.

Embryology and endocrinology of genital development

In the human male fetus, testes develop by the 7th week and begin to secrete two hormones: anti-müllerian hormone (AMH) induces the regression of müllerian ducts, the anlagen of the uterus, fallopian tubes and upper vagina, upon binding to a specific membrane receptor, whereas testosterone induces the differentiation of the wolffian ducts into the epididymes, vasa deferentia and seminal vesicles. In some target tissues, testosterone is converted to dihydrotestosterone, which is responsible for masculinization of the urogenital sinus and external genitalia. Both androgens act upon binding to the same nuclear receptor. In the absence of AMH and androgen action, or example in the female or in abnormal male differentiation, the internal and external genital primordia differentiate following the female pathway, even in the absence of ovaries. In males, an impaired function of the AMH-dependent pathway results in the persistent müllerian duct syndrome, a disorder characterized by the presence of uterus and fallopian tubes in otherwise normally virilized boys. Several mutations found in the AMH and AMH-receptor genes explain the pathophysiology of this syndrome.

Why do women menstruate? Historical and evolutionary review

Theories regarding the significance of menstruation from the time of Aristotle to the present are reviewed, followed by a brief description of the evolutionary changes in the uterus. A specific duct for the transport of ova first appears in jawed fishes. Its important role in the evolution of internal fertilisation and the protection and nourishment of the embryo is followed through the vertebrate orders, amphibia, reptiles and mammals. The problems associated with the presence of a gamete or zygote of different genetic make up inside the maternal tract is stressed, and the mechanisms to overcome or modify the maternal inflammation reaction discussed. In egg laying reptiles and birds, the secretion of coverings around the embryo presumably shields the foreignness of the tissue, while in viviparous animals, the secretion of progesterone plays a major role in controlling the inflammatory reaction. In some mammals, for example the mouse, the invasiveness of the trophoblast is such that the blastocyst penetrates inside the wall of the endometrium. The stroma responds under the influence of progesterone, to undergo an implantation/decidual reaction which bears considerable resemblance to an inflammatory/granulation tissue reaction. A similar reaction occurs in women during the luteal phase in anticipation of a very invasive blastocyst. When there is no fertilisation the progesterone drops and the differentiated stromal tissue is shed with bleeding; menstruation.

Regulation of testicular anti-M ullerian hormone secretion

Anti-Müllerian hormone (AMH) is a glycoprotein secreted by Sertoli cells from the time of testicular differentiation and is responsible for the regression of Müllerian ducts in the male fetus. The chronology of AMH expression is very important because Müllerian ducts lose their responsiveness a few days after AMH secretion begins, which suggests that the AMH gene is under precise transcriptional control. Steroidogenic factor 1 (SF-1) is the only transcriptional regulator with demonstrated action on AMH expression. Although necessary for AMH expression, SF-1 alone is not sufficient to induce AMH transcription. SRY expression is turned on in Sertoli cells just before AMH expression is initiated, but the effective implication of SRY in AMH regulation remains unclear. During puberty, AMH expression is regulated negatively by androgens and declines dramatically in seminiferous tubules with meiotic development. Low serum AMH levels are observed in both central and gonadotropin-independent precocious puberty, which suggests that gonadotropins do not down-regulate AMH at puberty. Serum AMH returns to normal infantile values 3-6 months after treatment. The absence of androgen response elements on the AMH promoter and the slow response to androgen withdrawal suggest that androgen regulation of AMH secretion is indirect. In patients with defects of androgen production or action, serum AMH reaches abnormally high levels in the neonatal and pubertal periods, which suggests a possible stimulatory role for gonadotropins that could be observed only in the absence of suppressive effects of androgens.

Bioactivation of Müllerian inhibiting substance during gonadal development by a kex2/subtilisin-like endoprotease

During male gonadal development Müllerian duct regression is mediated by the actions of the hormone Müllerian inhibiting substance (MIS), a member of the transforming growth factor beta superfamily. MIS is considered to be unique among members of this superfamily because bioactivation of MIS via proteolytic processing is hypothesized to occur at its target organ, the Müllerian duct. We find instead that the majority of MIS is processed and secreted from the embryonic testes as a complex in which the mature region remains noncovalently associated with the prodomain. In addition, we have identified two candidate endoproteases that are expressed in the testes and that may be capable of processing MIS in vivo. These kex2/subtilisin-like enzymes, PC5 and furin, are members of the proprotein convertase family that have been implicated in hormone bioactivation via proteolytic processing after dibasic amino acid cleavage recognition sites. Coexpression of PC5 and MIS in transfected mammalian cells results in efficient processing and bioactivation of MIS. Our results suggest that MIS is a natural substrate for PC5, thereby supporting a role for prohormone convertases in the activation of transforming growth factor beta-related hormones during development.

Molecular biology of MIS and its receptors

It is important, given the potential use of MIS as an anticancer agent against tumors of Müllerian duct origin, that the search continue to identify binding isoforms of the MIS type II receptor or to identify other factors in the heteromeric complex that might be required for specific binding of this ligand to be observed. With confidence in binding one can use receptor probes to screen patients with ovarian cancer and to identify those that express receptor. This subgroup can then be examined for binding of the MIS ligand and subsequently for antiproliferative response to MIS, in order to preselect candidate patients for receptor-directed MIS treatment. Thus, a once obscure phenomenon observed in the Freemartin has led to the purification and cloning of MIS and the identification of its receptor components, as well as an understanding of their regulation and expression. Elucidation of these molecular events brings us closer to the use of molecules such as MIS in the clinical setting.

Cloning and expression of the chick anti-Müllerian hormone gene

Müllerian duct regression in male embryos is due to early production by fetal Sertoli cells of anti-Müllerian hormone, a homodimeric protein of the transforming growth factor- beta superfamily. In mammals, both female Müllerian ducts develop into the uterus and Fallopian tubes, whereas in birds, the right oviduct does not develop. To gain insight into sex differentiation in birds, we have cloned the cDNA for chick anti-Müllerian hormone using antibodies raised against the partially purified protein. Expression cloning was required because of the lack of cross-hybridization between mammalian and chick anti-Müllerian hormone DNA. The chick DNA and protein are significantly longer, due to insertions that abolish nucleotide homology, except in the cDNA coding for the C-terminal, bioactive part of the protein. Nevertheless, the general structure of the gene, sequenced from the transcription initiation to the polyadenylation site, and the main features of the protein are conserved between the chick and mammals. The chick anti-Müllerian hormone gene is expressed at high levels in Sertoli cells of the embryonic testes and in lower amounts in both ovaries, higher levels being reached on the left side after 10 days of incubation.

Reduction of epidermal growth factor receptor phosphorylation by activated Mullerian inhibiting substance is vanadate-sensitive

The carboxy-terminal domain of recombinant human Mullerian inhibiting substance (MIS) inhibits cellular proliferation in vitro and decreases epidermal growth factor (EGF)-dependent phosphorylation of the EGF receptor. Proteolytically cleaved and undissociated MIS is more potent than carboxy-terminal MIS alone, supporting a functional role for the amino-terminal region of the molecule. MIS does not block EGF binding to the EGF receptor, thus, MIS reduction of EGF receptor phosphorylation must occur distal to receptor ligand binding. The effect of proteolytically cleaved MIS on reduction of EGF receptor phosphorylation in membrane preparations is decreased by a specific phosphatase inhibitor, vanadate, thus implicating a membrane phosphatase in this MIS action at the EGF receptor.

Pax-2 controls multiple steps of urogenital development

Urogenital system development in mammals requires the coordinated differentiation of two distinct tissues, the ductal epithelium and the nephrogenic mesenchyme, both derived from the intermediate mesoderm of the early embryo. The former give rise to the genital tracts, ureters and kidney collecting duct system, whereas mesenchymal components undergo epithelial transformation to form nephrons in both the mesonephric (embryonic) and metanephric (definitive) kidney. Pax-2 is a transcriptional regulator of the paired-box family and is widely expressed during the development of both ductal and mesenchymal components of the urogenital system. We report here that Pax-2 homozygous mutant newborn mice lack kidneys, ureters and genital tracts. We attribute these defects to dysgenesis of both ductal and mesenchymal components of the developing urogenital system. The Wolffian and Mullerian ducts, precursors of male and female genital tracts, respectively, develop only partially and degenerate during embryogenesis. The ureters, inducers of the metanephros are absent and therefore kidney development does not take place. Mesenchyme of the nephrogenic cord fails to undergo epithelial transformation and is not able to form tubules in the mesonephros. In addition, we show that the expression of specific markers for each of these components is de-regulated in Pax-2 mutants. These data show that Pax-2 is required for multiple steps during the differentiation of intermediate mesoderm. In addition, Pax-2 mouse mutants provide an animal model for human hereditary kidney diseases.

The marsupial male: a role model for sexual development

Sexual differentiation in male marsupials has many similarities with that of eutherians. Marsupials have an XX-XY sex determining mechanism, and have a homologue of the testis-determining SRY gene on their Y-chromosome. However, the development pattern of SRY gene expression is different from the mouse in that it is expressed for a much longer period. SRY is expressed in a range of non-gonadal tissues in male pouch young and adults which is similar to the human pattern, and raises questions as to its particular role(s) in sexual differentiation. Similarly Müllerian inhibiting substance (MIS) is produced in the developing testis over a longer period than in the mouse. Since ovaries cultured with MIS or transplanted into male recipient pouch young develop tubular structures, MIS may induce Sertoli cell formation. Testosterone is produced by the neonatal testis, and this stimulates Wolffian duct development to form the vas deferens and epididymis. Virilization of urogenital sinus is also androgen-dependent. However, virilization of the prostate and phallus occurs more than three weeks after the onset of testosterone production, suggesting that the timing of this may be regulated by delayed activation of the androgen receptor pathway. Unlike in eutherians, differentiation of the scrotum and mammary glands is not dependent on testicular hormones, but is independently regulated by an X-linked genetic mechanism. Clearly marsupials provide a unique perspective to help us clarify the mechanisms underlying sexual development in all mammals.

The müllerian inhibitor and mammalian sexual development

The elegant embryological experiments of Jost demonstrated the existence of a foetal testicular factor that is required to cause the regression of the müllerian duct system, the anlagen of the uterus, oviducts and upper portion of the vagina, during male sexual development. The müllerian inhibitor currently known as müllerian-inhibiting substance (MIS) or anti-müllerian hormone (AMH), is a member of the transforming growth factor-beta (TGF-beta) family of growth and differentiation factors. The genetic manipulation of the mouse germline has lead to the generation of animal models for MIS function. Female transgenic mice that chronically express MIS during embryogenesis are born without a uterus or oviducts and their ovaries lose germ cells and degenerate, recapitulating the phenotype of the bovine freemartin. Some male transgenic mice from very high MIS-expressing lines are feminized, suggesting alterations in androgen biosynthesis. Male mice homozygous for a targeted mutation of the MIS gene develop as male pseudohermaphrodites with both male (testes and Wolffian duct-derived) and female (müllerian duct-derived) reproductive organs. Most are infertile because the development of two reproductive systems physically blocks the exit of sperm from these males. In addition, Leydig cell hyperplasia is detected in a proportion of these males and in one case a Leydig cell tumour was found. Recently, a gene encoding a TGF-beta family type II Ser/Thr kinase membrane-bound receptor has been isolated that is expressed in both male and female gonads and in the mesenchyme surrounding the müllerian ducts during embryogenesis. These findings suggest that MIS-mediated müllerian duct regression occurs indirectly through mesenchymal tissue. A targeted mutation of this receptor has been established in the mouse germline. Mice homozygous for this receptor mutation should be useful in understanding the MIS signalling pathway for müllerian duct regression and gonadal function.

Cleavage of Müllerian inhibiting substance activates antiproliferative effects in vivo

Müllerian inhibiting substance (MIS), an inhibitor of growth and development of the female reproductive ducts in male fetuses, requires precise proteolytic cleavage to yield its biologically active species. Human plasmin is now used to cleave and, thereby, activate immunoaffinity-purified recombinant human MIS at its monobasic arginine-serine site at residues 427-428. To avoid the need for exogenous enzymatic cleavage and to simplify purification, we created an arginine-arginine dibasic cleavage site (MIS RR) using site-directed mutagenesis to change the serine at position 428 (AGC) to an arginine (cGC). The mutant cDNA was then stably transfected into a MIS-responsive ocular melanoma cell line, OM431, followed by cloning for amplified expression to test its biological activity in vitro and in vivo. Media from each clone were assayed for production of MIS RR by a sensitive ELISA for holo-MIS, and high- and low-producing clones were selected for further study. Media from the highest MIS RR producer caused Müllerian duct regression in an organ culture bioassay. Other transfections were done with an empty vector (pcDNAI Neo) or a construct lacking the leader sequence and thus failing to secrete MIS, to serve as controls. The OM431 clones containing the MIS RR mutant were growth inhibited in monolayer culture. The high- and low-producing MIS RR OM431 clones, along with transfected OM431 controls, were injected into the tail veins of immunosuppressed severe combined immunodeficiency mice for in vivo analyses. Four to 6 weeks later, pulmonary metastases were counted in uniformly inflated lungs. OM431 clones containing the more easily cleaved MIS RR displayed a significant dose-dependent reduction in pulmonary metastases when compared to the lungs of animals given injections of OM431 clones containing empty vector, leaderless MIS, or wild-type MIS that requires activation by plasmin cleavage. Since the purification protocol of MIS RR is less complicated than that for wild-type MIS, which requires subsequent enzymatic activation, MIS RR can be used for scale-up production with increased yields for further therapeutic trials against MIS-sensitive tumors.

Extended production of the müllerian duct regressor in the American alligator

Regression of the müllerian ducts in mammals and birds is caused by the testicular hormone, müllerian inhibiting substance (MIS), which is produced for an extended period of time after testicular differentiation. Because it is present long after the ducts regress, it has been proposed to have additional effects other than inducing Mullerian duct regression. A testicular substance also appears to be responsible for müllerian duct regression in the alligator based on studies in which testicular grafts from hatchling males caused regression when implanted into castrated hatchling females. In this study, the approximate ontogeny of the regressor in the alligator was investigated by implanting testicular grafts from both hatchling and yearling males into castrated female hatchlings. Histological quantification of the ducts revealed that regression in both treatment groups was not significantly different indicating that the müllerian duct regressor in the alligator is produced for at least a year after hatching and may have additional nonregressive functions in the alligator as has been proposed for mammals and birds.

Msx1 (Hox-7.1) in the adult mouse uterus: cellular interactions underlying regulation of expression

We report here that Msx1 (formerly Hox-7.1) is expressed at high levels in uterine epithelial cells of the non-pregnant adult. These cells undergo pronounced changes in morphology in response to embryo implantation and show a concomitant decrease in Msx1 levels. While Msx1 is restricted to the uterus in adulthood, we observe Msx1 expression throughout the entire perinatal Mullerian duct epithelium in the prospective uterus, cervix and vagina. Through analysis of tissue recombinants, the expression of Msx1 in the epithelium was shown to be dependent upon an interaction with the underlying mesenchyme of uterine origin. The capacity of uterine mesenchyme to support or induce Msx1 expression in Mullerian epithelium is correlated with mesenchymal expression of Wnt-5a. Whereas Msx1 expression in the epithelium results from interaction with uterine mesenchyme, Wnt-5a expression is an intrinsic property of the uterine mesenchyme and does not depend upon the epithelium. The observation that Msx1 is expressed in the adult uterine epithelium and that conversion of the presumptive vaginal epithelium to uterine epithelium can be elicited only during the first week of postnatal development when Msx1 expression is detected suggests that, in addition to regulating various aspects of uterine epithelial morphology and function (e.g. gestation), this homeobox-containing gene plays a role in maintaining the uterus in a morphogenic and developmentally responsive state prerequisite for its unique function.

Male sex determination: current concepts of male sexual differentiation

In order for an infant to develop as a phenotypically complete male or female, a cascade of complex molecular and morphological events must occur at the appropriate time and in the correct sequence during ontogeny. The male embryo's genetic sex is determined by its chromosomal constituents, the most important of which is the sex-determining gene, or testis-determining factor (TDF), on the Y chromosome. Male gonadal sex, or testis formation, is subsequently thought to be determined by this gene and by other secondary pathways. The male gonad, in turn, normally produces hormones such as testosterone and Mullerian inhibiting substance (MIS) that regulate differentiation of the internal and external genitalia, thus determining phenotypic sex. When an abnormality develops in any of the above three processes, an intersex infant with ambiguous genitalia results from the incongruent genetic, gonadal, and phenotypic sex. Clinically, such 46XY males with intersex abnormalities present challenges for gender assignment, timely surgical intervention, and appropriate hormonal therapy.

A novel member of the transmembrane serine/threonine kinase receptor family is specifically expressed in the gonads and in mesenchymal cells adjacent to the mullerian duct

The activin and TGF-beta type II receptors are members of a separate subfamily of transmembrane receptors with intrinsic protein kinase activity, which also includes the recently cloned TGF-beta type I receptor. We have isolated and characterized a cDNA clone (C14) encoding a new member of this subfamily. The domain structure of the C14-encoded protein corresponds with the structure of the other known transmembrane serine/threonine kinase receptors. It also contains the two inserts in the kinase domain that are characteristic for this subfamily. Using in situ hybridization, C14 mRNA was detected in the mesenchymal cells located adjacent to the mullerian ducts of males and females at day 15 (E15) of embryonic development. Marked C14 mRNA expression was also detected in the female gonads. In female E16 embryos, the C14 mRNA expression pattern remained similar to that in E15 embryos. However, in male E16 embryos C14 mRNA was detected in a circular area that includes the degenerating mullerian duct. The expression of C14 mRNA was also studied using RNase protection assays. At E15 and E16, C14 mRNA is expressed in the female as well as in the male urogenital ridge. However, at E19, a high C14 mRNA level in the female urogenital ridge contrasts with a lack of C14 mRNA in the male urogenital ridge. This correlates with the almost complete degeneration of the mullerian ducts in male embryos at E19. C14 mRNA expression was also detected in embryonic testes at E15, E16 and E19 using RNase protection assays, but at much lower levels than those found in the developing ovaries.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-müllerian hormone and testosterone serum levels are inversely during normal and precocious pubertal development

Anti-Müllerian hormone (AMH), also called Müllerian inhibiting substance or factor, is produced by Sertoli cells from fetal life until puberty. In the present study, AMH, testosterone (T), LH, and FSH were measured by immunochemical methods in the serum of 50 boys with normal or delayed pubertal development, 4 patients with suspected androgen insensitivity, and 11 patients with either central (CPP) or gonadotropin-independent (GIPP) precocious puberty to investigate the hormonal regulatory mechanisms of AMH secretion at puberty. An inverse relationship between AMH and T levels was demonstrated. In boys with normal or delayed puberty with T concentrations below 6.7 nmol/L, AMH values were elevated (mean +/- SEM, 22.4 +/- 3.1 micrograms/L) and widely dispersed. In subjects with T levels over 6.7 nmol/L, AMH levels were uniformly low (3.4 +/- 0.5 micrograms/L), except in patients with suspected androgen insensitivity. No significant relationship was found between AMH and gonadotropin levels. Similar results were obtained in patients with either CPP or GIPP. Longitudinal studies were performed on four boys with CPP and two with GIPP before and after treatment. At the time of diagnosis, the T concentration was high, and AMH levels were usually low in CPP and GIPP patients alike. When appropriate treatment was initiated, the T concentration was normalized within 2-4 weeks, but restoration of prepubertal AMH levels required several months. Mature Sertoli cells were observed in testicular biopsies performed in three patients with untreated GIPP. Our results suggest that gonadotropins are not directly implicated in repression of AMH synthesis at puberty, but, rather, that the decrease in AMH production is the consequence of an androgen-mediated, long term, reversible chain of events leading to morphological and functional maturation of the Sertoli cells. Thus, the fall in serum AMH levels appears to be an excellent marker of Sertoli cell pubertal development.

Müllerian inhibiting substance: new perspectives and future directions

MIS, as a differentiate and antiproliferative agent, is precisely regulated, for example, at the transcriptional level by such transacting factors as SRY, and posttranslationally by testosterone. Processing of MIS most likely requires an as yet unknown in vivo protease which probably serves to control cleavage of MIS and hence its activation at specific sites wherein a localized program of cell death is initiated via a receptor mediated event. Progress has been made in understanding the molecular domains of MIS; current efforts are focused on characterizing the wild type MIS receptor as well as cloning and expressing the MIS receptor. We need now to understand how to target and efficiently activate MIS at its projected site of action. We must focus, after structural analysis of its receptor, on elucidating the MIS initiated intracellular signals which result in localized cell inhibition. Understanding of these mechanisms will permit design of antitumor agents and therapeutic strategies. Similarly, understanding regulation of MIS expression may lead to therapeutic induction of expression in those states where depressed expression is associated with tumorigenesis, sexual ambiguity, or infertility.

Effect of human recombinant mullerian inhibiting substance on isolated epithelial and mesenchymal cells during mullerian duct regression in the rat

The effect of human recombinant Mullerian Inhibiting Substance (MIS) on the regression of the Mullerian duct (MD) of female rat fetuses was examined in vitro to determine whether MIS acts on MD epithelium and/or mesenchyme at the critical periods of sexual differentiation. Urogenital ridges (URs) of female rat fetuses at 14.5- to 18.5-days of gestation (plug day = 0) were cultured for 3 days with or without recombinant human MIS in CMRL 1066 medium with 10% female fetal calf serum. In URs from 14.5- and 15.5-day-old fetuses, the cranial portion of the MD regressed almost completely during the 3-day culture period in the presence of MIS, whereas the caudal half to third of the MD remained intact but tapered to a fine point cranially. MDs survived in URs from 16.5-day-old fetuses cultured in the presence of MIS except that the cranial portion of the MDs was deformed. MIS did not elicit regression of MDs in URs obtained from 17.5- and 18.5-day-old fetuses, but instead caused the MD epithelium to form bulges projecting into the mesenchyme. MD epithelium at 15.5-days of gestation was separated from the surrounding UR mesenchyme, and both components (MD epithelium and mesenchyme) were cultured separately for 3 days in the presence or absence of MIS. Both epithelial and mesenchymal cells survived in the presence or absence of MIS. MD epithelium formed typical epithelial colonies, whereas UR mesenchyme spread as fibroblastic cells. Analysis of labeling index after incorporation of [3H] thymidine demonstrated that MD epithelial DNA synthesis was not influenced by MIS. In contrast, mesenchymal labeling index was reduced significantly by MIS. This effect of MIS on UR mesenchyme in conjunction with earlier histological observations of mesenchymal condensation during MD regression and an absence of direct effects of MIS on the epithelium suggests that MIS elicits its effect on the MD epithelium via the surrounding mesenchyme.

Mullerian inhibiting substance messenger ribonucleic acid expression in granulosa and Sertoli cells coincides with their mitotic activity

In males, Mullerian inhibiting substance (MIS) mRNA was first detected on the medial aspect of the urogenital ridge early on the morning of day 13 of gestation before testicular differentiation was evident, and localized to the more obvious Sertoli cells later on embryonic day 13. MIS transcripts remained at maximal levels between 14.5 and 17.5 days gestation, while the Mullerian duct involutes, and remained high until birth. MIS gene expression decreased progressively after birth and, as germ cell meiosis increased, became barely detectable in the Sertoli cells of the seminiferous tubules. In female rats, MIS mRNA was first detected in the single layer of cuboidal granulosa cells surrounding larger primary follicles 3 days after birth, coincident with the initiation of follicular growth. As follicular growth progressed, MIS mRNA expression was high in preantral and small antral follicles, especially in those granulosa cells closest to the oocyte. MIS mRNA expression decreased gradually in larger antral follicles, remaining prominent only in the cumulus cells and the dividing population of granulosa cells closest to the lumen. MIS gene expression was absent in follicles with features of atresia and in the larger antral follicles. The expression of MIS mRNA in actively dividing Sertoli and granulosa cells correlates with the stages of germ cell division. These findings are suggestive of a role for MIS in the control of germ cell maturation.

Mullerian duct regression and antiproliferative bioactivities of mullerian inhibiting substance reside in its carboxy-terminal domain

A 25-kilodalton dimeric carboxy-terminal fragment of the recombinant human Mullerian inhibiting substance protein (rhMIS) was produced by proteolytic cleavage with plasmin and purified by size-exclusion chromatography. The identity of the isolated dimer as the carboxy-terminal fragment was confirmed by gel electrophoresis and Western analysis. As was true of every sample of the holo molecule, all preparations of the carboxy-terminal domain of rhMIS (n = 10), when added in the 0.5-5.0 micrograms/ml range, exhibited a dose-dependent partial to complete regression of the 14.5-day fetal rat Mullerian duct in an organ culture assay. The carboxy-terminal dimer also inhibited, in a dose-dependent manner, the growth of A431 cells in monolayer cultures. Daily addition of 5, 10, or 20 micrograms carboxy-terminus for 3 days resulted in 0%, 25%, and 100% inhibition of cell proliferation, respectively. Similar and higher doses of holo rhMIS had no or inconsistent antiproliferative activity (0-34% inhibition), even though the preparations caused Mullerian duct regression. All amino-terminal fragments prepared using this separation protocol were found to be inactive in these assays. These findings suggest that the bioactivity of rhMIS as a regressor of fetal Mullerian ducts and an inhibitor of A431 cell growth resides in its carboxy-terminal domain. These results indicate that the urogenital ridge tissue, but not A431 cells in culture, may be capable of cleaving intact MIS to a biologically active conformation.