Anatomy of mole external genitalia: Setting the record straight

Standardizing urethral stricture models in rats: a comprehensive study on histomorphologic and molecular approach

PURPOSE

To create a reproducible and standardized urethral stricture model in rats, evaluating both histomorphologic findings and gene expression data. In studies involving experimental animals, more standardization is needed for the creation of a urethral stricture model.

METHODS

Sixteen male rats were randomized into two groups. The Sham group (n:8) underwent only a penoscrotal incision, while the stricture group (n:8) had their urethras exposed through a penoscrotal incision, followed by electrocauterization to the corpus spongiosum. On the 15th day, blood and urethral tissues were harvested for histologic and molecular analyses. Histomorphologic, immunohistochemical, and reverse transcription polymerase chain reaction analyses were performed.

RESULTS

The stricture group exhibited more severe and intense spongiofibrosis, inflammation, epithelial desquamation, and congestion in vascular structures compared to the controls (p < 0.05). The urethral tissue in the stricture group showed an increased ratio of inflammation parameters, including Collagen 1A1, Collagen 3A1, elastin, Transforming growth factor β1, α Smooth muscle actin, Platelet-derived growth factor α, and Platelet-derived growth factor β. Transforming growth factor β1, Platelet-derived growth factor α, and Platelet-derived growth factor β each correlated highly with the other six parameters (r > 0.60, p < 0.05).

CONCLUSION

Developing electrocoagulation-induced urethral stricture in rats is a simple, reliable, inexpensive, and reproducible. Reporting histologic data with qualitative and semi-quantitative scoring will enhance data standardization, aiding reader understanding and analysis. Transforming growth factor β and Platelet-derived growth factor play key roles in fibrosis during stricture development. Incorporating these cytokines in urethral stricture animal model studies can demonstrate successful stenosis creation.

The Biology and Evolution of Fierce Females (Moles and Hyenas)

Talpid moles and spotted hyenas have become the paradigms of anatomical and behavioral female masculinization. Females of many mole species develop ovotestes that produce testosterone, show external genitalia that resemble that of males, and close their vaginal orifice after every estrus, and female spotted hyenas lack an external vaginal orifice and develop a pseudoscrotum and a large pseudopenis through which they urinate, mate, and give birth. We review current knowledge about several significant aspects of the biology and evolution of these females, including (a) their specific study methods; (b) their unique anatomical features, and how these peculiarities influence certain physiological functions; and (c) the role that steroid hormones as well as genetic and environmental factors may have in urogenital system development, aggressive behavior, and social dominance. Nevertheless, both mole and hyena females are exceptionally efficient mothers, so their peculiar genitalia should not call into question their femininity.

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.

Female Genital Variation Far Exceeds that of Male Genitalia: A Review of Comparative Anatomy of Clitoris and the Female Lower Reproductive Tract in Theria

A review of the literature on the anatomy of the lower female genital tract in therian mammals reveals, contrary to the general perception, a large amount of inter-specific variation. Variation in female external genitalia is anatomically more radical than that in the male genitalia. It includes the absence of whole anatomical units, like the cervix in many Xenarthra, or the absence of the urogenital sinus (UGS), as well as the complete spatial separation of the external clitoral parts from the genital canal (either vagina or UGS). A preliminary phylogenetic analysis shows two patterns. Some morphs are unique to early branching clades, like the absence of the cervix, while others arose multiple times independently, like the flattening out or loss of the UGS, or the extreme elongation of the clitoris. Based on available information, the ancestral eutherian configuration of the external female genitalia included a cervix, a single vaginal segment, a tubular UGS, and an unperforated clitoris close to the entrance of the genital canal. The evidence for either bilobed or unitary glandes clitorides is ambivalent. Despite the wealth of information available, many gaps in knowledge remain and will require a community-wide effort to come to a more robust model of female genital evolutionary patterns.

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.

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.

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.

Development of urogenital system in the Spix cavy: A model for studies on sexual differentiation

This study documented, for the first time, the morphological patterns of differentiation of male and female genital organs of Spix cavy (Galea spixii) using histological and ultrastructural analyses, with immuno-localization of steroidogenic enzymes, cytochromes P450 aromatase (P450arom) and 17α-hydroxylase/17, 20-lyase (P450c17), involved in the synthesis of estrogens and androgens respectively throughout fetal sexual development. Undifferentiated gonads of Spix cavy develop into ovaries in females after 25 days of gestation (DG), exhibiting P450arom immunoreactivity. After 25 DG, paramesonephric ducts develop and form oviducts, uterine horns and cranial portion of the vagina. The caudal portion of the vagina originates from the urogenital sinus, and a vaginal closure membrane is present at the end of gestation. Partial channeling of the urethra into the clitoris occurs after 40 DG, but complete channeling never occurs. A preputial meatus emerges near the tip of organ. In males, undifferentiated gonads develop into testes at 25 DG and develop immunoreactivity for P450c17, which is required for androgens synthesis and likely maintenance of mesonephric ducts. Mesonephric ducts develop subsequently, forming the epididymis and ductus deferens. The pelvic urethra develops after 25 DG with channeling into the penis occurring around 30 DG. This is the first morphological study describing the process of sexual differentiation during gestation in a hystricomorph rodent and one of the most comprehensive analyses conducted in any mammal. Male genital organ development follows the general pattern described in other domestic mammals, but does not include formation of the baculum as occurs in mice and rats. In females, clitoral development includes partial canalization by the urethra and development of a preputial meatus. Further studies are required to clarify the mechanisms involved in the differentiative processes described.

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.

Expression patterns of Fgf8 and Shh in the developing external genitalia of Suncus murinus

Reciprocal epithelial–mesenchymal interactions and several signalling pathways regulate the development of the genital tubercle (GT), an embryonic primordium of external genitalia. The morphology of the adult male external genitalia of the Asian house musk shrew Suncus murinus (hereafter, laboratory name: suncus) belonging to the order Eulipotyphla (the former order Insectivora or Soricomorpha) differs from those of mice and humans. However, the developmental process of the suncus GT and its regulatory genes are unknown. In the present study, we explored the morphological changes and gene expression patterns during the development of the suncus GT. Morphological observations suggested the presence of common (during the initial outgrowth) and species-specific (during the sexual differentiation of GT) developmental processes of the suncus GT. In gene expression analysis, fibroblast growth factor 8 (Fgf8) and sonic hedgehog (Shh), an indicator and regulator of GT development in mice respectively, were found to be expressed in the cloacal epithelium and the developing urethral epithelium of the suncus GT. This pattern of expression specifically in GT epithelium is similar to that observed in the developing mouse GT. Our results indicate that the mechanism of GT formation regulated by the FGF and SHH signalling pathways is widely conserved in mammals.

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.