Analysis of the effect of estrogen/androgen perturbation on penile development in transgenic and diethylstilbestrol-treated mice

Estrogenic endocrine disruptor exposure directly impacts erectile function

Erectile dysfunction (ED) is an extremely prevalent condition which significantly impacts quality of life. The rapid increase of ED in recent decades suggests the existence of unidentified environmental risk factors contributing to this condition. Endocrine Disrupting Chemicals (EDCs) are one likely candidate, given that development and function of the erectile tissues are hormonally dependent. We use the estrogenic-EDC diethylstilbestrol (DES) to model how widespread estrogenic-EDC exposure may impact erectile function in humans. Here we show that male mice chronically exposed to DES exhibit abnormal contractility of the erectile tissue, indicative of ED. The treatment did not affect systemic testosterone production yet significantly increased estrogen receptor α (Esr1) expression in the primary erectile tissue, suggesting EDCs directly impact erectile function. In response, we isolated the erectile tissue from mice and briefly incubated them with the estrogenic-EDCs DES or genistein (a phytoestrogen). These acute-direct exposures similarly caused a significant reduction in erectile tissue contractility, again indicative of ED. Overall, these findings demonstrate a direct link between estrogenic EDCs and erectile dysfunction and show that both chronic and acute estrogenic exposures are likely risk factors for this condition.

Androgenic induction of penile features in postnatal female mouse external genitalia from birth to adulthood: Is the female sexual phenotype ever irreversibly determined?

Female mice were treated for 35 days from birth to 60 days postnatal (P0, [birth], P5, P10, P20 and adult [∼P60]) with dihydrotestosterone (DHT). Such treatment elicited profound masculinization the female external genitalia and development of penile features (penile spines, male urogenital mating protuberance (MUMP) cartilage, corpus cavernosum glandis, corporal body, MUMP-corpora cavernosa, a large preputial space, internal preputial space, os penis). Time course studies demonstrated that DHT elicited canalization of the U-shaped clitoral lamina to create a U-shaped preputial space, preputial lining epithelium and penile epithelium adorned with spines. The effect of DHT was likely due to signaling through androgen receptors normally present postnatally in the clitoral lamina and associated mesenchyme. This study highlights a remarkable male/female difference in specification and determination of urogenital organ identity. Urogenital organ identity in male mice is irreversibly specified and determined prenatally (prostate, penis, and seminal vesicle), whereas many aspects of the female urogenital organogenesis are not irreversibly determined at birth and in the case of external genitalia are not irreversibly determined even into adulthood, the exception being positioning of the female urethra, which is determined prenatally.

One Tool for Many Jobs: Divergent and Conserved Actions of Androgen Signaling in Male Internal Reproductive Tract and External Genitalia

In the 1940s, Alfred Jost demonstrated the necessity of testicular secretions, particularly androgens, for male internal and external genitalia differentiation. Since then, our knowledge of androgen impacts on differentiation of the male internal (Wolffian duct) and external genitalia (penis) has been drastically expanded upon. Between these two morphologically and functionally distinct organs, divergent signals facilitate the establishment of tissue-specific identities. Conversely, conserved actions of androgen signaling are present in both tissues and are largely responsible for the growth and expansion of the organs. In this review we synthesize the existing knowledge of the cell type-specific, organ specific, and conserved signaling mechanisms of androgens. Mechanistic studies on androgen signaling in the Wolffian duct and male external genitalia have largely been conducted in mouse model organisms. Therefore, the majority of the review is focused on mouse model studies.

Cornification and classical versus nonclassical androgen receptor signaling in mouse penile/preputial development

Mouse penile development is androgen-dependent. During development of male and female external genitalia, an internal ectodermal epithelial structure forms called the preputial lamina. At puberty the male preputial lamina canalizes to create the preputial space, effectively splitting into two layers: (a) the epithelial lining of the prepuce and (b) the surface epithelium of the penis. The female preputial lamina does not canalize, and instead remodels into the inverted U-shaped clitoral lamina of the adult female mouse. Androgen-dependent penile development was studied in transgenic mice with pathway-selective AR mutant transgenes through which AR signaling was activated either via the classical (AR-C) or the nonclassical pathway (AR-NC). Penile development and canalization of the preputial lamina was observed in AR-C and wild-type male mice naturally having both AR-C and AR-NC pathways. Conversely, clitoral development occurred in AR null (lacking both AR-C and AR-NC pathways) and AR-NC mice. The process of canalization of the preputial lamina seen in wild-type, AR-C and AR-C/AR-NC male mice involved cornification of the preputial lamina which involved up-regulation of keratin 10 and loricrin. Such up-regulation of these epidermal proteins was absent in the developing and adult clitoral lamina seen in wild-type female mice and AR-NC and AR null male (XY) mice. Thus, signaling through AR-C is sufficient to initiate and promote penile development and canalization of the preputial lamina, a process involving epithelial cornification.

Developmental and sexual dimorphic atlas of the prenatal mouse external genitalia at the single-cell level

Birth defects of the external genitalia are among the most common in the world. Proper formation of the external genitalia requires a highly orchestrated process that involves special cell populations and sexually dimorphic hormone signaling. It is clear what the end result of the sexually dimorphic development is (a penis in the male versus clitoris in the female); however, the cell populations involved in the process remain poorly defined. Here, we used single-cell messenger RNA sequencing in mouse embryos to uncover the dynamic changes in cell populations in the external genitalia during the critical morphogenetic window. We found that overall, male and female external genitalia are largely composed of the same core cellular components. At the bipotential stage of development (embryonic day or E14.5), few differences in cell populational composition exist between male and female. Although similar in cell population composition, genetic differences in key sexual differentiation developmental pathways arise between males and females by the early (E16.5) and late (E18.5) differentiation stages. These differences include discrete cell populations with distinct responsiveness to androgen and estrogen. By late sexual differentiation (E18.5), unique cell populations in both male and female genitalia become apparent and are enriched with androgen- and estrogen-responsive genes, respectively. These data provide insights into the morphogenesis of the external genitalia that could be used to understand diseases associated with defects in the external genitalia.

Estrogens and development of the mouse and human external genitalia

The Jost hypothesis states that androgens are necessary for normal development of the male external genitalia. In this review, we explore the complementary hypothesis that estrogens can elicit abnormal development of male external genitalia. Herein, we review available data in both humans and mice on the deleterious effects of estrogen on external genitalia development, especially during the "window of susceptibility" to exogenous estrogens. The male and female developing external genitalia in both the human and mouse express ESR1 and ESR2, along with the androgen receptor (AR). Human clinical data suggests that exogenous estrogens can adversely affect normal penile and urethral development, resulting in hypospadias. Experimental mouse data also strongly supports the idea that exogenous estrogens cause penile and urethral defects. Despite key differences, estrogen-induced hypospadias in the mouse displays certain morphogenetic homologies to human hypospadias, including disruption of urethral fusion and preputial abnormalities. Timing of estrogenic exposure, or the "window of susceptibility," is an important consideration when examining malformations of the external genitalia in both humans and mice. In addition to a review of normal human and mouse external genital development, this article aims to review the present data on the role of estrogens in normal and abnormal development of the mouse and human internal and external genitalia. Based on the current literature for both species, we conclude that estrogen-dependent processes may play a role in abnormal genital development.

Anatomy of the mouse penis and internal prepuce

This paper addresses a confusing issue of preputial anatomy of the mouse. The term "internal prepuce" was used in 2013 to describe a preputial structure integral to the mouse glans penis. Subsequently in 2015 the same term was applied by another group to describe entirely different morphology, generating confusion in the literature. Because it is inappropriate to use the same term to describe entirely different structures, we take this opportunity to provide further descriptive information on the internal prepuce of the mouse employing gross dissection, analysis of serial histologic section sets, three-dimensional reconstruction, scanning electron microscopy and immunohistochemistry. For this purpose, we review and illustrate the relevant literature and provide some additional new data using standard morphological techniques including immunohistochemistry. The mouse internal prepuce is integral to the glans penis and clearly is involved in sexual function in so far as it contains a major erectile body innervated by penile nerves. The development of the mouse internal prepuce is described for the first time and related to the development of the corpus cavernosum glandis.

Development of the human prepuce and its innervation

Development of the human prepuce was studied over the course of 9-17 weeks of gestation in 30 specimens. Scanning electron microscopy revealed subtle surface features that were associated with preputial development, namely the appearance of epidermal aggregates that appeared to be associated with formation of the preputial fold. Transverse and sagittal sections revealed that the epidermis of the glans is considerably thicker than that of the penile shaft. We described a novel morphogenetic mechanism of formation of the preputial lamina, namely the splitting of the thick epidermis of the glans into the preputial lamina and the epidermis via the intrusion of mesenchyme containing red blood cells and CD31-positive blood vessels. This process begins at 10-11 weeks of gestation in the proximal aspect of the glans and extends distally. The process is likely to be androgen-dependent and mediated via androgen receptors strategically localized to the morphogenetic process, but signaling through estrogen receptor may play a role. Estrogen receptor alpha (ESR1) has a very limited expression in the developing human glans and prepuce, while estrogen receptor beta (ESR2) is expressed more broadly in the developing preputial lamina, epidermis and urethra. Examination of the ontogeny of innervation of the glans penis and prepuce reveals the presence of the dorsal nerve of the penis as early as 9 weeks of gestation. Nerve fibers enter the glans penis proximally and extend distally over several weeks to eventually reach the distal aspect of the glans and prepuce by 14-16 weeks of gestation.

Androgen and estrogen receptor expression in the developing human penis and clitoris

To better understand how the human fetal penis and clitoris grows and remodels, we undertook an investigation to define active areas of cellular proliferation and programmed cell death spatially and temporally during development of human fetal external genitalia from the indifferent stage (8 weeks) to 18 weeks of gestation. Fifty normal human fetal penile and clitoral specimens were examined using macroscopic imaging, scanning electron microscopy and immunohistochemical localization for the cellular proliferation and apoptotic markers, Ki67 and Caspase-3. A number of hot spots of cellular proliferation characterized by Ki67 localization are present in the penis and clitoris especially early in development, most notably in the corporal body, glans, remodeling glanular urethra, the urethral plate, the roof of the urethral groove and the fully formed penile urethra. The 12-fold increase in penile length over 10 weeks of growth from 8 to 18 weeks of gestation based on Ki67 labelling appears to be driven by cellular proliferation in the corporal body and glans. Throughout all ages in both the developing penis and clitoris Ki67 labeling was consistently elevated in the ventral epidermis and ventral mesenchyme relative to the dorsal counterparts. This finding is consistent with the intense morphogenetic activity/remodeling in the ventral half of the genital tubercle in both sexes involving formation of the urethral/vestibular plates, canalization of the urethral/vestibular plates and fusion of the urethral folds to form the penile urethra. Areas of reduced or absent Ki67 staining include the urethral fold epithelium that fuses to form the penile tubular urethra. In contrast, the urethral fold mesenchyme is positive for Ki67. Apoptosis was rarely noted in the developing penis and clitoris; the only area of minimal Caspase-3 localization was in the epithelium of the ventral epithelial glanular channel remodeling.

Reproductive tract biology: Of mice and men

The study of male and female reproductive tract development requires expertise in two separate disciplines, developmental biology and endocrinology. For ease of experimentation and economy, the mouse has been used extensively as a model for human development and pathogenesis, and for the most part similarities in developmental processes and hormone action provide ample justification for the relevance of mouse models for human reproductive tract development. Indeed, there are many examples describing the phenotype of human genetic disorders that have a reasonably comparable phenotype in mice, attesting to the congruence between mouse and human development. However, anatomic, developmental and endocrinologic differences exist between mice and humans that (1) must be appreciated and (2) considered with caution when extrapolating information between all animal models and humans. It is critical that the investigator be aware of both the similarities and differences in organogenesis and hormone action within male and female reproductive tracts so as to focus on those features of mouse models with clear relevance to human development/pathology. This review, written by a team with extensive expertise in the anatomy, developmental biology and endocrinology of both mouse and human urogenital tracts, focusses upon the significant human/mouse differences, and when appropriate voices a cautionary note regarding extrapolation of mouse models for understanding development of human male and female reproductive tracts.

Regulatory roles of epithelial-mesenchymal interaction (EMI) during early and androgen dependent external genitalia development

Development of external genitalia (ExG) has been a topic of long mystery in the field of organogenesis research. Early stage male and female of mouse embryos develop a common genital tubercle (GT) in the perineum whose outgrowth extends distally from the posterior cloacal regions. Concomitant with GT outgrowth, the cloaca is divided into urogenital sinus and anorectum by urorectal septum (URS) internally. The outgrowth of the GT is associated with the formation of endodermal epithelial urethral plate (UP) attached to the ventral epidermis of the GT. Such a common developmental phase is observed until around embryonic day 15.5 (E15.5) morphologically in mouse embryogenesis. Various growth factor genes, such as Fibroblast growth factor (Fgf) and Wnt genes are expressed and function during GT formation. Since the discovery of key growth factor signals and several regulatory molecules, elucidation of their functions has been achieved utilizing mouse developmental models, conditional gene knockout mouse and in vitro culture. Analyses on the phenotypes of such mouse models have revealed that several growth factor families play fundamental roles in ExG organogenesis based on the epithelial-mesenchymal interaction (EMI). More recently, EMI between developing urethral epithelia and its bilateral mesenchyme of later stages is also reported during subsequent stage of androgen-dependent male-type urethral formation in the mouse embryo. Mafb, belonging to AP-1 family and a key androgen-responsive mesenchymal gene, is identified and starts to be expressed around E14.5 when masculinization of the urethra is initiated. Mesenchymal cell condensation and migration, which are regulated by nonmuscle myosin, are shown to be essential process for masculinization. Hence, studies on EMI at various embryonic stages are important not only for early but also for subsequent masculinization of the urethra. In this review, a dynamic mode of EMI for both early and late phases of ExG development is discussed.

Clitoral development in the mouse and human

The goal of this report is (a) to provide the first detailed description of mouse clitoral development, and (b) to compare mouse and human clitoral development. For this purpose, external genitalia of female mice were examined by wholemount microscopy, histology and immunohistochemistry from 14 days of gestation to 10 days postnatal. Human clitoral development was examined by these techniques as well as by scanning electron microscopy and optical projection tomography from 8 to 19 weeks of gestation. The adult mouse clitoris is an internal organ defined by a U-shaped clitoral lamina whose development is associated with the prenatal medial and distal growth of the female preputial swellings along the sides of the genital tubercle to form the circumferential preputial lamina. Regression of the ventral aspect of the preputial lamina leads to formation of the U-shaped clitoral lamina recognized as early as 17 days of gestation. While the adult U-shaped mouse clitoral lamina is closely associated with the vagina, and it appears to be completely non-responsive to estrogen as opposed to the highly estrogen-responsive vaginal epithelium. The prominent perineal appendage in adult females is prepuce, formed via fusion of the embryonic preputial swellings and is not the clitoris. The human clitoris is in many respects a smaller anatomic version of the human penis having all of the external and internal elements except the urethra. The human clitoris (like the human penis) is derived from the genital tubercle with the clitoral glans projecting into the vaginal vestibule. Adult morphology and developmental processes are virtually non-comparable in the mouse and human clitoris.

Atrazine induces penis abnormalities including hypospadias in mice

Use of the herbicide atrazine (ATR) is banned in the European Union; yet, it is still widely used in the USA and Australia. ATR is known to alter testosterone and oestrogen production and thus reproductive characteristics in numerous species. In this proof of concept study, we examined the effect of ATR exposure, at a supra-environmental dose (5 mg/kg bw/day), beginning on E9.5 in utero, prior to sexual differentiation of the reproductive tissues, until 26 weeks of age, on the development of the mouse penis. Notably, this is the first study to specifically investigate whether ATR can affect penis characteristics. We show that ATR exposure, beginning in utero, causes a shortening (demasculinisation) of penis structures and increases the incidence of hypospadias in mice. These data indicate the need for further studies of ATR on human reproductive development and fertility, especially considering its continued and widespread use.

A critical role for estrogen signaling in penis development

Hypospadias, a developmental defect of the penis, is one of the most common congenital malformations in humans. Its incidence has rapidly increased over recent decades, and this has been largely attributed to our increased exposure to endocrine-disrupting chemicals. Penis development is primarily an androgen-driven process; however, estrogen and xenoestrogens are known to affect penis development in both humans and mice. Here, we investigated the role of estrogen in the developing penis. Using a novel penis culture system, we showed that exogenous estrogen directly targets the developing penis in utero to cause hypospadias. In addition, we also uncovered an unexpected endogenous role for estrogen in normal postnatal penis development and showed that a loss of estrogen signaling results in a mild hypospadias phenotype, the most common manifestation of this disease in humans. Our findings demonstrated that both androgen and estrogen signaling are intrinsically required for normal urethral closure. These findings confirmed that penis development is not an entirely androgen-driven process but one in which endogenous estrogen signaling also plays a critical role.-Govers, L. C., Phillips, T. R., Mattiske, D. M., Rashoo, N., Black, J. R., Sinclair, A., Baskin, L. S., Risbridger, G. P., Pask, A. J. A critical role for estrogen signaling in penis development.

Prenatal masculinization of the auditory system in infants: The MIREC-ID study

Sex differences in inner-ear function are detectable in infants, notably through the measurement of otoacoustic emissions (OAEs). Prevailing theories posit that prenatal exposure to high levels of androgens in boys may weaken OAEs, and that this phenomenon may predominantly affect the right ear/left hemisphere (Geschwind-Galaburda (GG) hypothesis). Yet, actual tests of these models have been difficult to implement in humans. Here we examined the relationship between markers of fetal androgen exposure collected at birth (anogenital distances (AGD); penile length/width, areolar/scrotal/vulvar pigmentation) and at 6 months of age (2^nd to 4^th digit ratio (2D:4D)) with two types of OAEs, click-evoked OAEs (CEOAEs) and distortion-product OAEs (DPOAEs) (n = 49; 25 boys; 24 girls). We found that, in boys, scrotal pigmentation was inversely associated with the amplitude and reproducibility of CEOAEs in the right ear at 4 kHz, with trends also present in the same ear for mean CEOAE amplitude and CEOAE amplitude at 2 kHz. Penile length was inversely associated with the mean amplitude of DPOAEs in both the right and left ears, as well as with DPOAE amplitude in the right ear at 2 kHz and the reproducibility of CEOAEs in the left ear at 2.8 kHz. Finally, AGD-scrotum in boys was positively associated in boys with the amplitude of DPOAEs in the left ear at 2.8 kHz. Unexpectedly, there were no sex differences in the amplitude or reproducibility of OAEs, nor, in girls, any associations between androgenic markers and auditory function. Nonetheless, these findings, reported for the first time in a sample of human infants, support both the prenatal-androgen-exposure and GG models as explanations for the masculinization of auditory function in male infants.

Development of the human penis and clitoris

The human penis and clitoris develop from the ambisexual genital tubercle. To compare and contrast the development of human penis and clitoris, we used macroscopic photography, optical projection tomography, light sheet microscopy, scanning electron microscopy, histology and immunohistochemistry. The human genital tubercle differentiates into a penis under the influence of androgens forming a tubular urethra that develops by canalization of the urethral plate to form a wide diamond-shaped urethral groove (opening zipper) whose edges (urethral folds) fuse in the midline (closing zipper). In contrast, in females, without the influence of androgens, the vestibular plate (homologue of the urethral plate) undergoes canalization to form a wide vestibular groove whose edges (vestibular folds) remain unfused, ultimately forming the labia minora defining the vaginal vestibule. The neurovascular anatomy is similar in both the developing human penis and clitoris and is the key to successful surgical reconstructions.

Contrasting mechanisms of penile urethral formation in mouse and human

This paper addresses the developmental mechanisms of formation of the mouse and human penile urethra and the possibility that two disparate mechanisms are at play. It has been suggested that the entire penile urethra of the mouse forms via direct canalization of the endodermal urethral plate. While this mechanism surely accounts for development of the proximal portion of the mouse penile urethra, we suggest that the distal portion of the mouse penile urethra forms via a series of epithelial fusion events. Through review of the recent literature in combination with new data, it is unlikely that the entire mouse urethra is formed from the endodermal urethral plate due in part to the fact that from E14 onward the urethral plate is not present in the distal aspect of the genital tubercle. Formation of the distal portion of the mouse urethra receives substantial contribution from the preputial swellings that form the preputial-urethral groove and subsequently the preputial-urethral canal, the later of which is subdivided by a fusion event to form the distal portion of the mouse penile urethra. Examination of human penile development also reveals comparable dual morphogenetic mechanisms. However, in the case of human, direct canalization of the urethral plate occurs in the glans, while fusion events are involved in formation of the urethra within the penile shaft, a pattern exactly opposite to that of the mouse. The highest incidence of hypospadias in humans occurs at the junction of these two different developmental mechanisms. The relevance of the mouse as a model of human hypospadias is discussed.

Renal Subcapsular xenografing of human fetal external genital tissue - A new model for investigating urethral development

In this paper, we introduce our novel renal subcapsular xenograft model for the study of human penile urethral and clitoral development. We grafted fifteen intact fetal penes and clitorides 8-11 weeks fetal age under the renal capsules of gonadectomized athymic mice. The mice were treated with a subcutaneous pellet of dihydrotestosterone (DHT), diethylstilbestrol (DES) or untreated with hormones. Xenografts were harvested after fourteen days of growth and analyzed via serial histologic sectioning and immunostaining for Ki-67, cytokeratins 6, 7 and 10, uroplakin and the androgen receptor. Non-grafted specimens of similar fetal age were sectioned and immunostained for the same antigenic markers. 14/15 (93.3%) grafts were successfully propagated and harvested. The developing urethral plate, urethral groove, tubular urethra, corporal bodies and preputial lamina were easily identifiable. These structures demonstrated robust cellularity, appropriate architecture and abundant Ki-67 expression. Expression patterns of cytokeratins 6, 7 and 10, uroplakin and the androgen receptor in xenografted specimens demonstrated characteristic male/female differences analogous to non-grafted specimens. DHT treatment reliably produced tubularization of nascent urethral and vestibular structures and male patterns of androgen receptor expression in grafts of both genetic sexes while estrogenic or hormonally absent conditions reliably resulted in a persistent open urethral/vestibular groove and female patterns of androgen receptor expression. This model's success enables further study into causal pathways by which endocrine-disrupting and endocrine-mimicking substances may directly cause disruption of normal human urethral development or hypospadias.

Comparative Morphology of the Penis and Clitoris in Four Species of Moles (Talpidae)

The penile and clitoral anatomy of four species of Talpid moles (broad-footed, star-nosed, hairy-tailed, and Japanese shrew moles) were investigated to define penile and clitoral anatomy and to examine the relationship of the clitoral anatomy with the presence or absence of ovotestes. The ovotestis contains ovarian tissue and glandular tissue resembling fetal testicular tissue and can produce androgens. The ovotestis is present in star-nosed and hairy-tailed moles, but not in broad-footed and Japanese shrew moles. Using histology, three-dimensional reconstruction, and morphometric analysis, sexual dimorphism was examined with regard to a nine feature masculine trait score that included perineal appendage length (prepuce), anogenital distance, and presence/absence of bone. The presence/absence of ovotestes was discordant in all four mole species for sex differentiation features. For many sex differentiation features, discordance with ovotestes was observed in at least one mole species. The degree of concordance with ovotestes was highest for hairy-tailed moles and lowest for broad-footed moles. In relationship to phylogenetic clade, sex differentiation features also did not correlate with the similarity/divergence of the features and presence/absence of ovotestes. Hairy-tailed and Japanese shrew moles reside in separated clades, but they exhibit a high degree of congruence. Broad-footed and hairy-tailed moles reside within the same clade but had one of the lowest correlations in features and presence/absence of ovotestes. Thus, phylogenetic affinity and the presence/absence of ovotestes are poor predictors for most sex differentiation features within mole external genitalia.

Computational modeling and simulation of genital tubercle development

Hypospadias is a developmental defect of urethral tube closure that has a complex etiology involving genetic and environmental factors, including anti-androgenic and estrogenic disrupting chemicals; however, little is known about the morphoregulatory consequences of androgen/estrogen balance during genital tubercle (GT) development. Computer models that predictively model sexual dimorphism of the GT may provide a useful resource to translate chemical-target bipartite networks and their developmental consequences across the human-relevant chemical universe. Here, we describe a multicellular agent-based model of genital tubercle (GT) development that simulates urethrogenesis from the sexually-indifferent urethral plate stage to urethral tube closure. The prototype model, constructed in CompuCell3D, recapitulates key aspects of GT morphogenesis controlled by SHH, FGF10, and androgen pathways through modulation of stochastic cell behaviors, including differential adhesion, motility, proliferation, and apoptosis. Proper urethral tube closure in the model was shown to depend quantitatively on SHH- and FGF10-induced effects on mesenchymal proliferation and epithelial apoptosis-both ultimately linked to androgen signaling. In the absence of androgen, GT development was feminized and with partial androgen deficiency, the model resolved with incomplete urethral tube closure, thereby providing an in silico platform for probabilistic prediction of hypospadias risk across combinations of minor perturbations to the GT system at various stages of embryonic development.

Mouse hypospadias: A critical examination and definition

Hypospadias is a common malformation whose etiology is based upon perturbation of normal penile development. The mouse has been previously used as a model of hypospadias, despite an unacceptably wide range of definitions for this malformation. The current paper presents objective criteria and a definition of mouse hypospadias. Accordingly, diethylstilbestrol (DES) induced penile malformations were examined at 60 days postnatal (P60) in mice treated with DES over the age range of 12 days embryonic to 20 days postnatal (E12-P20). DES-induced hypospadias involves malformation of the urethral meatus, which is most severe in DES E12-P10, DES P0-P10 and DES P5-P15 groups, and less so or absent in the other treatment groups. A frenulum-like ventral tether between the penis and the prepuce was seen in the most severely affected DES-treated mice. Internal penile morphology was also altered in the DES E12-P10, DES P0-P10 and DES P5-P15 groups (with little effect in the other DES treatment groups). Thus, adverse effects of DES are a function of the period of DES treatment and most severe in the P0-P10 period. In "estrogen mutant mice" (NERKI, βERKO, αERKO and AROM+) hypospadias was only seen in AROM+ male mice having genetically-engineered elevation is serum estrogen. Significantly, mouse hypospadias was only seen distally at and near the urethral meatus where epithelial fusion events are known to take place and never in the penile midshaft, where urethral formation occurs via an entirely different morphogenetic process.

Anatomy of mole external genitalia: Setting the record straight

Anatomy of male and female external genitalia of adult mice (Mus musculus) and broad-footed moles (Scapanus latimanus) was re-examined to provide more meaningful anatomical terminology. In the past the perineal appendage of male broad-footed moles has been called the penis, while the female perineal appendage has been given several terms (e.g. clitoris, penile clitoris, peniform clitoris and others). Histological examination demonstrates that perineal appendages of male and female broad-footed moles are the prepuce, which in both sexes are covered externally with a hair-bearing epidermis and lacks erectile bodies. The inner preputial epithelium is non-hair-bearing and defines the preputial space in both sexes. The penis of broad-footed moles lies deep within the preputial space, is an "internal organ" in the resting state and contains the penile urethra, os penis, and erectile bodies. The clitoris of broad-footed moles is defined by a U-shaped clitoral epithelial lamina. Residing within clitoral stroma encompassed by the clitoral epithelial lamina is the corpus cavernosum, blood-filled spaces and the urethra. External genitalia of male and female mice are anatomically similar to that of broad-footed moles with the exception that in female mice the clitoris contains a small os clitoridis and lacks defined erectile bodies, while male mice have an os penis and a prominent distal cartilaginous structure within the male urogenital mating protuberance (MUMP). Clitori of female broad-footed moles lack an os clitoridis but contain defined erectile bodies, while male moles have an os penis similar to the mouse but lack the distal cartilaginous structure.

Diethylstilbestrol-induced mouse hypospadias: "window of susceptibility"

This review presents published and novel results that define the programming window for diethylstilbestrol (DES)-induced abnormal development of the mouse penis. These data indicate that DES has its greatest effect during the period of most intense penile morphogenesis, namely postnatal days 0-15 (P0-P15). Pregnant mice and their neonatal pups were injected subcutaneously with 200 ng/gbw DES every other day from embryonic day 12-18 (DES E12-E18), postnatal day 0-10 (DES P0-P10), embryonic day 12 to postnatal day 10 (DES E12-P10), postnatal day 5-15 (DES P5-P15), and postnatal day 10-20 (DES P10-P20). Aged-matched controls received sesame oil vehicle. After euthanasia at 10, 15, 20 and 60 days, penises were analyzed by gross morphology, histology and morphometry. Penises of all 5 groups of DES-treated mice were reduced in size, which was confirmed by morphometric analysis of internal penile structures. The most profound effects were seen in the DES E12-P10, DES P0-P10, and DES P5-P15 groups, thus defining a DES "programming window". For all parameters, DES treatment from P10 to P20 showed the most mild of effects. Adverse effects of DES on the MUMP cartilage and erectile bodies observed shortly after the last DES injection reverted to normality in the DES P5-P15, but not in the E12-P10 and P0-P10 groups, in which MUMP cartilage and erectile body malformations persisted into adulthood, again emphasizing a "window of susceptibility" in the early neonatal period.

Methods for studying human organogenesis

This review details methods for utilizing D & C suction abortus specimens as a source of human fetal organs to study the morphogenetic and molecular mechanisms of human fetal organ development. By this means it is possible to design experiments elucidating the molecular mechanisms of human fetal organ development and to compare and contrast human developmental mechanisms with that of laboratory animals. Finally human fetal organs can be grown in vivo as grafts to athymic mice, thus allowing ethical analysis of potential adverse effects of environmental toxicants.

Male infants with hypospadias and/or cryptorchidism show a lower 2D/4D digit ratio than normal boys

BACKGROUND

In humans the ratio of the index finger to the ring finger is sexually dimorphic, with the mean ratio being larger in women than in men. It has been suggested that this difference is related to prenatal androgen exposure. This has been further demonstrated in children with congenital adrenal hyperplasia. Normal development of the male external genitalia is linked to androgen-mediated events during gestation. We therefore wanted to determine if the 2D:4D digit ratio was normal in boys with cryptorchidism or hypospadias.

METHODS

We prospectively enrolled all prepubertal patients seen in the outpatient clinic for cryptorchidism or hypospadias between September and December 2012. We then compared their 2D:4D digit ratio with two control groups made up of normal boys and normal girls. Interobserver and intraobserver variability was evaluated.

RESULTS

We included 57 boys with hypospadias and/or cryptorchidism, 79 boys without genital abnormalities and 25 girls without genital abnormalities. The mean 2D:4D ratio for both hands was significantly different between the three groups, with the digit ratio for boys with genital anomalies being lower than for normal boys and normal girls (p<0.0001).

CONCLUSIONS

It appears that boys with genital abnormalities (cryptorchidism and/or hypospadias) have a lower 2D:4D digit ratio than boys without genital anomalies.

A Comprehensive Atlas of the Adult Mouse Penis

Mice are routinely used to study the development of the external genitalia and, in particular, the process of male urethral closure. This is because misplacement of the male penile urethra, or hypospadias, is amongst the most common birth defects reported in humans. While mice present a tractable model to study penile development, several structures differ between mice and humans, and there is a lack of consensus in the literature on their annotation and developmental origins. Defining the ontology of the mouse prepuce is especially important for the relevance and interpretation of mouse models of hypospadias to human conditions. We have developed a detailed annotation of the adult mouse penis that addresses these differences and enables an accurate comparison of murine and human hypospadias phenotypes. Through MRI data, gross morphology and section histology, we define the origin of the mouse external and internal prepuces, their relationship to the single human foreskin as well as provide a comprehensive view of the various structures of the mouse penis and their associated muscle attachments within the body. These data are combined to annotate structures in a novel 3D adult penis atlas that can be downloaded, viewed at any angle, and manipulated to examine the relationship of various structures.

Prenatal diethylstilbestrol induces malformation of the external genitalia of male and female mice and persistent second-generation developmental abnormalities of the external genitalia in two mouse strains

Potential trans-generational influence of diethylstilbestrol (DES) exposure emerged with reports of effects in grandchildren of DES-treated pregnant women and of reproductive tract tumors in offspring of mice exposed in utero to DES. Accordingly, we examined the trans-generational influence of DES on development of external genitalia (ExG) and compared effects of in utero DES exposure in CD-1 and C57BL/6 mice injected with oil or DES every other day from gestational days 12 to 18. Mice were examined at birth, and on 5-120 days postnatal to evaluate ExG malformations. Of 23 adult (>60 days) prenatally DES-exposed males, features indicative of urethral meatal hypospadias (see text for definitions) ranged from 18% to 100% in prenatally DES-exposed CD-1 males and 31% to 100% in prenatally DES-exposed C57BL/6 males. Thus, the strains differed only slightly in the incidence of male urethral hypospadias. Ninety-one percent of DES-exposed CD-1 females and 100% of DES-exposed C57BL/6 females had urethral-vaginal fistula. All DES-exposed CD-1 and C57BL/6 females lacked an os clitoris. None of the prenatally oil-treated CD-1 and C57BL/6 male and female mice had ExG malformations. For the second-generation study, 10 adult CD-1 males and females, from oil- and DES-exposed groups, respectively, were paired with untreated CD-1 mice for 30 days, and their offspring evaluated for ExG malformations. None of the F1 DES-treated females were fertile. Nine of 10 prenatally DES-exposed CD-1 males sired offspring with untreated females, producing 55 male and 42 female pups. Of the F2 DES-lineage adult males, 20% had exposed urethral flaps, a criterion of urethral meatal hypospadias. Five of 42 (11.9%) F2 DES lineage females had urethral-vaginal fistula. In contrast, all F2 oil-lineage males and all oil-lineage females were normal. Thus, prenatal DES exposure induces malformations of ExG in both sexes and strains of mice, and certain malformations are transmitted to the second-generation.

Comparative effects of neonatal diethylstilbestrol on external genitalia development in adult males of two mouse strains with differential estrogen sensitivity

The effect of neonatal exposure to diethylstilbestrol (DES), a potent synthetic estrogen, was examined to evaluate whether the CD-1 (estrogen insensitive, outbred) and C57 (estrogen sensitive, inbred) mouse strains differ in their response to estrogen disruption of male ExG differentiation. CD-1 and C57BL/6 litters were injected with sesame oil or DES (200 ng/g/5 μl in sesame oil vehicle) every other day from birth to day 10. Animals were sacrificed at the following time points: birth, 5, 10 and 60 days postnatal. Neonatally DES-treated mice from both strains had many ExG abnormalities that included the following: (a) severe truncation of the prepuce and glans penis, (b) an abnormal urethral meatus, (c) ventral tethering of the penis, (d) reduced os penis length and glans width, (e) impaired differentiation of cartilage, (f) absence of urethral flaps, and (g) impaired differentiation of erectile bodies. Adverse effects of DES correlated with the expression of estrogen receptors within the affected tissues. While the effects of DES were similar in the more estrogen-sensitive C57BL/6 mice versus the less estrogen-sensitive CD-1 mice, the severity of DES effects was consistently greater in C57BL/6 mice. We suggest that many of the effects of DES, including the induction of hypospadias, are due to impaired growth and tissue fusion events during development.

The power and perils of animal models with urogenital anomalies: handle with care

Congenital abnormalities of the urogenital tracts form a major part of clinical practice for paediatric urologists, but their knowledge of normal and abnormal development is often limited. Advances in understanding frequently come from studying experimental findings from animal models, however, most clinicians underestimate both the power and perils of extrapolating scientific knowledge from animals. In this review, the key issues that urologists need to understand in order to link animal studies to clinical practice are discussed. Urologists must avoid the traps of anthropomorphism (assuming humans are always the same as animal models) or anthropocentrism (assuming humans are too different from animal models). This review used two common disorders: hypospadias and undescended testes.

Development of the external genitalia: perspectives from the spotted hyena (Crocuta crocuta)

This review/research paper summarizes data on development of the external genitalia of the spotted hyena, a fascinating mammal noted for extreme masculinization of the female external genitalia. The female spotted hyena is the only extant mammal that mates and gives birth through a pendulous penis-like clitoris. Our studies indicate that early formation of the phallus in both males and females is independent of androgens; indeed the phallus forms before the fetal testes or ovaries are capable of synthesizing androgens. Likewise, pre- and postnatal growth in length of the penis and clitoris is minimally affected by "androgen status". Nonetheless, several internal morphologies, as well as external surface features of the phallus, are androgen-dependent and thus account for dimorphism between the penis and clitoris. Finally, estrogens play a critical role in penile and clitoral development, specifying the position of the urethral orifice, determining elasticity of the urethral meatus, and facilitating epithelial-epithelial fusion events required for proper formation of the distal urethra/urogenital sinus and prepuce. Accordingly, prenatal inhibition of estrogen synthesis via administration of letrozole (an aromatase inhibitor) leads to malformations of the glans as well as the prepuce (hypospadias). The effects of prenatal androgens, anti-androgens and impaired estrogen synthesis correlated with the tissue expression of androgen and estrogen receptors.