The development of the male genitourinary system: II. The origin and formation of the urethral plate

An experimental evaluation of the efficacy of perinatal sulforaphane supplementation to decrease the incidence and severity of vinclozolin-induced hypospadias in the mouse model

Determining the mechanisms of toxicity induced by pollutants has long been a research priority in lieu of considering the mechanisms of resilience that prevent deleterious impacts. Protective mechanisms in many taxa can be therapeutically targeted to enhance resilience to synthetic toxicants. For example, the environmental sensor, Nuclear factor (erythroid-derived 2)-like 2 (Nfe2l2 or Nrf2), a transcription factor, facilitates transcription of many protective genes. Hypospadias is a common malformation of the penis. The risk of being born with hypospadias increases with pollutant exposure. We use vinclozolin-induced hypospadias in the mouse as a model to test the hypothesis that pollutant-induced birth defects can be prevented and reduced in severity by augmenting natural mechanisms of resilience. Pregnant mice were exposed to the demasculinizing toxicant, vinclozolin, in combination with increasing doses of the NRF2 activator, sulforaphane. The sulforaphane dose that most effectively increased masculinization (anogenital distance) was identified and used to test the hypothesis that sulforaphane reduces the hypospadias-inducing potency of vinclozolin. Finally, a Nrf2 knockout study was conducted to test whether NRF2 was required for the sulforaphane-induced rescue effects. Sulforaphane supplementation to vinclozolin exposed embryos increased anogenital distance in a nonlinear fashion typical of Nrf2 activators. The most effective dose of sulforaphane (45 mg/kg) reduced the occurrence and severity of vinclozolin-induced hypospadias and corrected penis morphogenesis. The sulforaphane-induced rescue effect was dependent on the presence of Nrf2. Nrf2 plays a critical role in protecting the fetus from vinclozolin and reduces the incidence and severity of hypospadias, the most common birth defect in boys in many countries. This work lays a foundation for developing prenatal supplements that will protect the fetus from pollutant-induced hypospadias. Studying the protective mechanisms that drive resilience to toxicants will facilitate innovation of protective therapies.

Single cell transcriptomic analysis of external genitalia reveals complex and sexually dimorphic cell populations in the early genital tubercle

External genital organs are among the most recognizable sexually dimorphic characters. The penis and clitoris develop from the embryonic genital tubercle, an outgrowth at the anterior margin of the cloaca that undergoes an extensive period of development in male and female embryos prior to the onset of sexual differentiation. In mice, differentiation into the penis and clitoris begins around embryonic day (E)15.5. Current knowledge of cell types that comprise the genital tubercle is limited to a few studies that have fate mapped derivatives of endoderm, mesoderm, and ectoderm. Here we use single cell transcriptomics to characterize the cell populations in the genital tubercles of male and female mouse embryos at E14.5, approximately 24 ​h before the onset of sexual differentiation, and we present the first comprehensive atlas of single-cell gene expression during external genital development. Clustering analyses and annotation using marker genes shows 19 distinct cell populations in E14.5 genital tubercles. Mapping of cell clusters to anatomical locations using in situ gene expression patterns revealed granularity of cellular specializations and positional identities. Although E14.5 precedes sexually dimorphic morphogenesis of the genital tubercle, comparative analysis of males and females identified sexual dimorphisms at the single cell level, including male-specific cell clusters with transcriptional signatures of smooth muscle and bone progenitors, both of which are known to be sexually dimorphic in adult genitalia, as well as immune cells. These results provide a new resource for classification of external genital cell types based on gene expression profiles and reveal sex-specific cellular specializations in the early genital tubercle.

Meeting report on the NIDDK/AUA Workshop on Congenital Anomalies of External Genitalia: challenges and opportunities for translational research

Congenital anomalies of the external genitalia (CAEG) are a prevalent and serious public health concern with lifelong impacts on the urinary function, sexual health, fertility, tumor development, and psychosocial wellbeing of affected individuals. Complications of treatment are frequent, and data reflecting long-term outcomes in adulthood are limited. To identify a path forward to improve treatments and realize the possibility of preventing CAEG, the National Institute of Diabetes and Digestive and Kidney Diseases and the American Urological Association convened researchers from a range of disciplines to coordinate research efforts to fully understand the different etiologies of these common conditions, subsequent variation in clinical phenotypes, and best practices for long term surgical success. Meeting participants concluded that a central data hub for clinical evaluations, including collection of DNA samples from patients and their parents, and short interviews to determine familial penetrance (small pedigrees), would accelerate research in this field. Such a centralized datahub will advance efforts to develop detailed multi-dimensional phenotyping and will enable access to genome sequence analyses and associated metadata to define the genetic bases for these conditions. Inclusion of tissue samples and integration of clinical studies with basic research using human cells and animal models will advance efforts to identify the developmental mechanisms that are disrupted during development and will add cellular and molecular granularity to phenotyping CAEG. While the discussion focuses heavily on hypospadias, this can be seen as a potential template for other conditions in the realm of CAEG, including cryptorchidism or the exstrophy-epispadias complex. Taken together with long-term clinical follow-up, these data could inform surgical choices and improve likelihood for long-term success.

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.

Clinical, cytogenetic and molecular genetic characterization of a tandem fusion translocation in a male Holstein cattle with congenital hypospadias and a ventricular septal defect

Hypospadias, disorder of sex development (DSD), is a sporadic congenital abnormality of the genital region in male ruminants, which is characterized by a non-fused urethra during fetal development. Detailed clinical examination classified the hypospadias phenotype of a male Holstein calf studied here as the perineal type. In combined use of cytogenetic analysis and whole genome sequencing, a non-mosaic, pseudo-monosomy 59, XY + tan(18;27) was detected. This chromosomal aberration had its origin in a tandem fusion translocation of the bovine autosomes (BTA) 18 and 27 with an accompanying loss of genomic sequences mainly in the distal end of BTA 18 and the proximal end of BTA 27. The resulting phenotype included hypospadias, growth retardation and ventricular septal defect.

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.

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.

The development of the cloaca in the human embryo

Subdivision of cloaca into urogenital and anorectal passages has remained controversial because of disagreements about the identity and role of the septum developing between both passages. This study aimed to clarify the development of the cloaca using a quantitative 3D morphological approach in human embryos of 4–10 post‐fertilisation weeks. Embryos were visualised with Amira 3D‐reconstruction and Cinema 4D‐remodelling software. Distances between landmarks were computed with Amira3D software. Our main finding was a pronounced difference in growth between rapidly expanding central and ventral parts, and slowly or non‐growing cranial and dorsal parts. The entrance of the Wolffian duct into the cloaca proved a stable landmark that remained linked to the position of vertebra S3. Suppressed growth in the cranial cloaca resulted in an apparent craniodorsal migration of the entrance of the Wolffian duct, while suppressed growth in the dorsal cloaca changed the entrance of the hindgut from cranial to dorsal on the cloaca. Transformation of this ‘end‐to‐end’ into an ‘end‐to‐side’ junction produced temporary ‘lateral (Rathke's) folds’. The persistent difference in dorsoventral growth straightened the embryonic caudal body axis and concomitantly extended the frontally oriented ‘urorectal (Tourneux's) septum’ caudally between the ventral urogenital and dorsal anorectal parts of the cloaca. The dorsoventral growth difference also divided the cloacal membrane into a well‐developed ventral urethral plate and a thin dorsal cloacal membrane proper, which ruptured at 6.5 weeks. The expansion of the pericloacal mesenchyme followed the dorsoventral growth difference and produced the genital tubercle. Dysregulation of dorsal cloacal development is probably an important cause of anorectal malformations: too little regressive development may result in anorectal agenesis, and too much regression in stenosis or atresia of the remaining part of the dorsal cloaca.

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.

Glans wings are separated ventrally by the septum glandis and frenulum penis: MRI documentation and surgical implications

Objective

In the normal human penis, the glans wings are in apposition in the midline ventrally, and are separated by the "septum glandis" and "frenulum" of the prepuce. However, most of the hypospadias repair techniques include dissection of the glans wings and their approximation enclosing the neourethra within the glans.

Material and methods

In order to obtain detailed information about the normal anatomy of glans penis, magnetic resonance imaging (MRI) findings of the penis were studied in three adults. Transverse, and sagittal sections of the penis were performed with a 1.5-T MRI scanner.

Results

The present MRI study has confirmed that the glans wings do not fuse at the ventral midline and they are seperated by a fibrous tissue (septum glandis). This fibrous tissue is connected to the frenulum, traversing the wings of the glans penis. The glanular urethra forming the fossa navicularis has a wider caliber than the proximal urethra, and its walls are radiologically seen as the extension of that fibrous tissue.

Conclusion

The male urethra is not a uniform tubular structure and has distinct attachments in glans penis. The glans wings are separated ventrally by the septum glandis and frenulum. In hypospadias, the septum glandis and frenulum are entirely missing structures. Therefore, in hypospadias surgery, the anatomical features of the glanular urethra must be taken into consideration.

Hypospadias repair with the glanular-frenular collar (GFC) technique

BACKGROUND

In the normal human penis, the glans wings merge in the midline ventrally, but are separated by the 'septum glandis' in conjunction with the frenulum. The frenulum is also included in the formation of the distal (glanular and subcoronal) urethra, which has a special part known as the 'fossa navicularis'. This has inspired a hypospadias repair technique that simulates the development of the glanular and subcoronal urethra, which can be incorporated into the repair of all cases of hypospadias.

MATERIAL AND METHOD

A total of 121 patients with varying degrees of hypospadias underwent surgery with the described technique: a Y-V plasty was used to dissect the inner foreskin, in a fashion that allowed for its ventral mobilization as a frenular mucosal collar. After tubularization of the proximal urethra, a partial spongioplasty was performed that extended up to the subcoronal level. The glans wings were approximated only at their outermost convexities, with a couple of subepithelial sutures, leaving a slit for the meatus. The cleft-like area between the split wings of the glans penis was filled with the terminal ends of the spongiosum and the dartos of the mucosal collar, which converged to form a septum and a neo-frenulum (glanular-frenular collar, GFC). The midline skin closure of the ventral collar and the circumferential foreskin closure was completed as usual.

RESULTS

At a mean follow-up of 10 months, two patients developed urethral fistula (2%), six had meatal stenosis (5%), and two had glans dehiscence (2%) that resulted in meatal retraction. Overall, patients had a cosmetically satisfying appearance (Figure). Forty-one received secondary circumcision; the parents of 80 (66%) patients were satisfied with the final foreskin appearance obtained with this method.

DISCUSSION

The split wings of the glans penis or so-called ventral cleft between the glans wings that accommodate the frenulum is part of normal anatomy. Hence, in hypospadias surgery, the approximated glans wings should allow for ventral support of the glanular and subcoronal urethra through a reconstructed neo-frenulum. Neither glanular surface enhancement nor extensive dissection of the glans wings and their full-length approximation are necessary, and may in fact be counter-productive.

CONCLUSIONS

The employment of a GFC provided: 1) an anatomical restoration of the distal (glanular and subcoronal) urethra, supported by a frenulum; 2) a protective (undissected) dartos layer over the distal part of the tubularized neourethra; and 3) a space for the re-formation of the fossa navicularis.

Systematic Review to Compare Urothelium Differentiation with Urethral Epithelium Differentiation in Fetal Development, as a Basis for Tissue Engineering of the Male Urethra

BACKGROUND

Tissue-engineered (TE) urethra is desirable in men with urethral disease (stricture or hypospadias) and shortage of local tissue. Although ideally a TE graft would contain urethral epithelium cells, currently, bladder epithelium (urothelium) is widely used, but morphologically different. Understanding the differences and similarities of urothelium and urethral epithelium could help design a protocol for in vitro generation of urethral epithelium to be used in TE grafts for the urethra.

PURPOSE

To understand the development toward urethral epithelium or urothelium to improve TE of the urethra.

METHODS

A literature search was done following PRISMA guidelines. Articles describing urethral epithelium and bladder urothelium development in laboratory animals and humans were selected.

RESULTS

Twenty-nine studies on development of urethral epithelium and 29 studies on development of urothelium were included. Both tissue linings derive from endoderm and although adult urothelium and urethral epithelium are characterized by different gene expression profiles, the signaling pathways underlying their development are similar, including Shh, BMP, Wnt, and FGF. The progenitor of the urothelium and the urethral epithelium is the early fetal urogenital sinus (UGS). The urethral plate and the urothelium are both formed from the p63+ cells of the UGS. Keratin 20 and uroplakins are exclusively expressed in urothelium, not in the urethral epithelium. Further research has to be done on unique markers for the urethral epithelium.

CONCLUSION

This review has summarized the current knowledge about embryonic development of urothelium versus urethral epithelium and especially focuses on the influencing factors that are potentially specific for the eventual morphological differences of both cell linings, to be a basis for developmental or tissue engineering of urethral tissue.

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.

Molecular Characterization of the Genital Organizer: Gene Expression Profile of the Mouse Urethral Plate Epithelium

PURPOSE

Lower urinary tract malformations are among the most common congenital anomalies in humans. Molecular genetic studies of mouse external genital development have begun to identify mechanisms that pattern the genital tubercle and orchestrate urethral tubulogenesis. The urethral plate epithelium is an endodermal signaling region that has an essential role in external genital development. However, little is known about the molecular identity of this cell population or the genes that regulate its activity.

MATERIALS AND METHODS

We used microarray analysis to characterize differences in gene expression between urethral plate epithelium and surrounding tissue in mouse genital tubercles. In situ hybridizations were performed to map gene expression patterns and ToppCluster (https://toppcluster.cchmc.org/) was used to analyze gene associations.

RESULTS

A total of 84 genes were enriched at least 20-fold in urethral plate epithelium relative to surrounding tissue. The majority of these genes were expressed throughout the urethral plate in males and females at embryonic day 12.5 when the urethral plate is known to signal. Functional analysis using ToppCluster revealed genetic pathways with known functions in other organ systems but unknown roles in external genital development. Additionally, a 3-dimensional molecular atlas of genes enriched in urethral plate epithelium was generated and deposited at the GUDMAP (GenitoUrinary Development Molecular Anatomy Project) website (http://gudmap.org/).

CONCLUSIONS

We identified dozens of genes previously unknown to be expressed in urethral plate epithelium at a crucial developmental period. It provides a novel panel of genes for analysis in animal models and in humans with external genital anomalies.

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.

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.

Tissue-specific roles of Fgfr2 in development of the external genitalia

Congenital anomalies frequently occur in organs that undergo tubulogenesis. Hypospadias is a urethral tube defect defined by mislocalized, oversized, or multiple openings of the penile urethra. Deletion of Fgfr2 or its ligand Fgf10 results in severe hypospadias in mice, in which the entire urethral plate is open along the ventral side of the penis. In the genital tubercle, the embryonic precursor of the penis and clitoris, Fgfr2 is expressed in two epithelial populations: the endodermally derived urethral epithelium and the ectodermally derived surface epithelium. Here, we investigate the tissue-specific roles of Fgfr2 in external genital development by generating conditional deletions of Fgfr2 in each of these cell types. Conditional deletion of Fgfr2 results in two distinct phenotypes: endodermal Fgfr2 deletion causes mild hypospadias and inhibits maturation of a complex urethral epithelium, whereas loss of ectodermal Fgfr2 results in severe hypospadias and absence of the ventral prepuce. Although these cell type-specific mutants exhibit distinctive genital anomalies, cellular analysis reveals that Fgfr2 regulates epithelial maturation and cell cycle progression in the urethral endoderm and in the surface ectoderm. The unexpected finding that ectodermal deletion of Fgfr2 results in the most severe hypospadias highlights a major role for Fgfr2 in the developing genital surface epithelium, where epithelial maturation is required for maintenance of a closed urethral tube. These results demonstrate that urethral tubulogenesis, prepuce morphogenesis, and sexually dimorphic patterning of the lower urethra are controlled by discrete regions of Fgfr2 activity.

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.

A tortuous proximal urethra in urorectal septum malformation sequence?

We observed a newborn boy with urorectal septum malformation sequence. Anomalies of the genitalia and rectum were present. He expired on the first day of life, due to severe lung hypoplasia. Autopsy showed a colon that ended in a blind sac, an enlarged bladder with no grossly visible urethra, and dysplastic kidneys. A cone-shaped tissue at the usual site of the bladder outlet contained tortuous and slit-like lumina, suggesting an undeveloped proximal urethra. The urethral structure was lined by transitional epithelium with squamous metaplasia. Many small buds-lined with columnar epithelium-branched from the urethral structure. These ductal buds lined with columnar epithelium stained for prostatic acid phosphatase. Basal cells surrounding the ductal buds stained for p63 and high molecular weight cytokeratin-supporting an interpretation that the buds were early prostatic ducts with normal histology. To our knowledge, these are the first histological images of an undeveloped, obstructed urethra associated with the urorectal septum malformation sequence.

Development of the external genitalia and their sexual dimorphic regulation in mice

The study of the external genitalia is divided into 2 developmental stages: the formation and growth of a bipotential genital tubercle (GT) and the sexual differentiation of the male and female GT. The sexually dimorphic processes, which occur during the second part of GT differentiation, are suggested to be governed by androgen signaling and more recently crosstalk with other signaling factors. The process of elucidating the regulatory mechanisms of hormone signaling towards other signaling networks in the GT is still in its early stages. Nevertheless, it is becoming a productive area of research. This review summarizes various studies on the development of the murine GT and the defining characteristics of a masculinized GT and presents the different signaling pathways possibly involved during masculinization.

Embryology of the distal urethra and external genitals

Faulty ventral openings of the urethra constitute a broad spectrum of malformations that are subsumed under the term "hypospadia." The normal development of the urethra and the genitals critically depends on the following events: (a) formation of the external genitalia, (b) fate of the cloacal membrane, and (c) formation of the distal urethra. The purpose of this study was to demonstrate these events using microsurgical techniques and scanning electron microscopy in staged rat embryos.

Bmp7 expression and null phenotype in the urogenital system suggest a role in re-organization of the urethral epithelium

Signaling by Bone morphogenetic proteins (Bmps) has multiple and diverse roles in patterning and morphogenesis of the kidney, eye, limbs and the neural tube. Here, we employed the Bmp7(lacZ) strain to perform a detailed analysis of Bmp7 expression and the null phenotype during development of the mouse urogenital system. The urethral compartment originates in mid-embryogenesis from the ventral part of the cloaca, a transient cavity at the caudal end of the hindgut. At mid-gestation, Bmp7 expression was detected within several specific domains in the cloacal epithelium and mesenchyme. In late embryogenesis, Bmp7 expression was present in the urethra, rectum, the urethral glands, corpus cavernosum, and in the male and female genital ducts. Importantly, loss of Bmp7 resulted in arrest in cloacal septation, and severe defects in morphogenesis of the genital urethra and mesenchyme. Together, our analysis of Bmp7 expression and the null phenotype, indicates that Bmp7 may play an important role in re-organization of the epithelium during cloacal septation and morphogenesis of the genital tubercle.

Cell lineage analysis demonstrates an endodermal origin of the distal urethra and perineum

Congenital malformations of anorectal and genitourinary (collectively, anogenital) organs occur at a high frequency in humans, however the lineage of cells that gives rise to anogenital organs remains poorly understood. The penile urethra has been reported to develop from two cell populations, with the proximal urethra developing from endoderm and the distal urethra forming from an apical ectodermal invagination, however this has never been tested by direct analysis of cell lineage. During gut development, endodermal cells express Sonic hedgehog (Shh), which is required for normal patterning of digestive and genitourinary organs. We have taken advantage of the properties of Shh expression to genetically label and follow the fate of posterior gut endoderm during anogenital development. We report that the entire urethra, including the distal (glandar) region, is derived from endoderm. Cloacal endoderm also gives rise to the epithelial linings of the bladder, rectum and anterior region of the anus. Surprisingly, the lineage map also revealed an endodermal origin of the perineum, which is the first demonstration that endoderm differentiates into skin. In addition, we fate mapped genital tubercle ectoderm and show that it makes no detectable contribution to the urethra. In males, formation of the urethral tube involves septation of the urethral plate by continued growth of the urorectal septum. Analysis of cell lineage following disruption of androgen signaling revealed that the urethral plate of flutamide-treated males does not undergo this septation event. Instead, urethral plate cells persist to the ventral margin of the tubercle, mimicking the pattern seen in females. Based on these spatial and temporal fate maps, we present a new model for anogenital development and suggest that disruptions at specific developmental time points can account for the association between anorectal and genitourinary defects.

Epithelial and muscular regionalization of the human developing anorectum

In the past, interpretations of anorectal development were mainly based on analysis of serially sectioned embryos of various nonhuman species as well as some human specimens. A four-dimensional view of the developmental situation in the human has never been established nor connected to recent findings obtained from newer molecular techniques. We, therefore, investigated human embryonic and fetal pelves by means of immunohistochemistry and in situ hybridization to elucidate differentiation and interaction of epithelial and mesenchymal layers of the anorectum. To emphasize spatial as well as sequential morphological development, we produced three-dimensional reconstructions of the specimens at hand. Research conducted proved that the decisive steps of epithelial and muscular differentiation occur between the 7th and 9th week after conception. This study elucidates a biphasic epithelial "closure" in the anal canal and interactions between epithelium, smooth musculature, and skeletal musculature. Based on the results presented here, it is possible to describe the pathogenesis of two anorectal malformations: the imperforate anal membrane and the anal membrane stenosis. This study will now provide the basis for further research into developmental processes occurring before the ones examined.

Congenital anomalies of the male urethra

The spectrum of congenital anomalies of the male urethra is presented. The embryologic basis of each anomaly, when known, is discussed. Clinical and imaging features of each entity are presented.

Urethral duplication in males: our experience in ten cases

Urethral duplication is a rare congenital anomaly, affecting mainly boys. Clinical presentation varies because of the different anatomical patterns of this abnormality. We report our experience in ten males affected by urethral duplication. We retrospectively reviewed the records of ten males affected by urethral duplication. Mild cases of distal type I duplications as well as "Y-type" duplication associated to anorectal malformation were excluded. Evaluation included voiding cystourethrography, retrograde urethrography, intravenous urography and urethrocystoscopy. Mean age at diagnosis was 46.7 +/- 32.3 months A blind ending duplicated urethra (type I) was present in three patients, two urethras originating from a common bladder neck (type II A2) in three, an "Y-type" duplication in three and a complete bladder with incomplete urethral duplication in one. Surgical management included excision of the duplicated urethra in four patients while a displacement of the ventral urethra (in "Y-type" duplication) in perineal-scrotal or scrotal position was performed in two patients as first stage of urethral reconstruction. Good cosmetical and functional results were achieved in all six treated boys while surgical management was not required in four. Urethral duplication is often associated with genito-urinary and gastro-intestinal abnormalities. Embryology is unclear and a lot of hypotheses have been proposed. We believe that the same embryological explanation cannot be applied to all subtypes of urethral duplication. Management must be evaluated for each case. The overall prognosis is good, in spite of the presence of other severe associate congenital anomalies.

A case of congenital megalourethra

Congenital megalourethra is a rare anomaly of the penile urethra caused by a mesenchymal defect. We describe a baby boy with scaphoid type megalourethra and review the embryology and management of this condition.

The development of the male genitourinary system: III. The formation of the spongiose and glandar urethra

It is generally agreed that the urethral plate disintegrates, resulting in the urethral groove. This is subsequently transformed into the urethra by fusion of the urethral folds, which flank its sides. Recently, the existence of such a groove and folds has been denied and this challenge to the long accepted existence of such folds is significant since hypospadias is considered to result from failure of their fusion. The present studies indicate that mesodermal fold formation and its subsequent subepithelial fusion across the midline plays an essential role in urethral tube formation. Disruption of this process readily explains common congenital abnormalities of the urethra.