Differentiation of mesenchymal tissues during phallic morphogenesis with emphasis on the os penis: roles of androgens and other regulatory agents

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.

On the socio-sexual behaviour of the extinct Ursid Indarctos arctoides: an approach based on its baculum size and morphology

The fossil bacula, or os penis, constitutes a rare subject of study due to its scarcity in the fossil record. In the present paper we describe five bacula attributed to the bear Indarctos arctoides Depéret, 1895 from the Batallones-3 site (Madrid Basin, Spain). Both the length and morphology of this fossil bacula enabled us to make interpretative approaches to a series of ecological and ethological characters of this bear. Thus, we suggest that I. arctoides could have had prolonged periods of intromission and/or maintenance of intromission during the post-ejaculatory intervals, a multi-male mating system and large home range sizes and/or lower population density. Its size might also have helped females to choose from among the available males.

Clitoral sexual arousal: neuronal tracing study from the clitoris through the spinal tracts

PURPOSE

Although genital tactile stimulation is regarded as a precursor to sexual arousal and a recognized initiator of central nervous system arousal, specific afferent neural pathways transmit sensory stimuli of arousal, beginning at the epithelial level on the clitoris and following the course of arousal stimuli through the central nervous system. Limited knowledge exists of the pathway from the cutaneous receptors of nerves originating in the epithelial tissue of the clitoris and continuing to spinal cord afferents. Such information may contribute to an understanding of sexual arousal, particularly in female vertebrates. We further defined the neural pathways and mechanisms responsible for arousal originating in the epithelium of the clitoris as well as related neural pathways to the spinal cord in a murine model.

MATERIALS AND METHODS

We performed a comprehensive review of the published relevant clinical and histological material from human and nonhuman vertebrate studies. In 29 adult female C57B1/6 mice the distribution of pelvic nerves and vessels was mapped. Gross dissection of 4 female mice was facilitated by resin injection of the vascular system in 2. Neuronal tracing was performed in 25 mice that received clitoral injection of wheat germ agglutinin-horseradish peroxidase into the clitoris and were sacrificed after 72 to 96 hours. The spinal cord and periclitoral tissue were removed and fixed. Immunohistochemistry was performed.

RESULTS

Gross anatomy of the mouse clitoris showed that pudendal and hypogastric nerves have a major role in the innervation of the external genitalia. Neuronal tracing revealed that the greatest nerve density was noted in the L5/6 spinal cord. The distribution extended from S1 to L2 with no labeling seen in the L3 spinal cord. Wheat germ agglutinin-horseradish peroxidase labeling was seen caudal in levels S1 through L4 and rostral in L2.

CONCLUSIONS

Understanding the neuroanatomy of the clitoris using a murine model may provide a valuable tool for the study of sexual arousal disorders and the further understanding of sexual function related to neural pathologies and trauma.

Estrogen receptor alpha mediates estrogen-inducible abnormalities in the developing penis

Previously, we reported an association between estrogen receptor-alpha (ERalpha) upregulation and detrimental effects of neonatal diethylstilbestrol (DES) exposure in the rat penis. The objective of this study was to employ the ERalpha knockout (ERalphaKO) mouse model to test the hypothesis that ERalpha mediates DES effects in the developing penis. ERalphaKO and wild-type C57BL/6 mice received oil or DES at a dose of 0.2 microg/pup per day (0.1 mg/kg) on alternate days from postnatal days 2 to 12. Fertility was tested at 80-240 days of age and tissues were examined at 96-255 days of age. DES caused malformation of the os penis, significant reductions in penile length, diameter, and weight, accumulation of fat cells in the corpora cavernosa penis, and significant reductions in weight of the bulbospongiosus and levator ani muscles in wild-type mice. Conversely, ERalphaKO mice treated with DES developed none of the above abnormalities. While nine out of ten male mice sired pups in the wild-type/control group, none did in the wild-type/DES group. ERalphaKO mice, despite normal penile development, are inherently infertile. Both plasma and intratesticular testosterone levels were unaltered in the DES-treated wild-type or DES-treated ERalphaKO mice when compared with controls, although testosterone concentration was much higher in the ERalphaKO mice. Hence, the resistance of ERalphaKO mice to developing penile abnormalities provides unequivocal evidence of an obligatory role for ERalpha in mediating the harmful effects of neonatal DES exposure in the developing penis.

Role of estrogen in induction of penile dysmorphogenesis: a review

In this review, we report permanent dysmorphogenesis of the penis and loss of fertility in adult rats treated neonatally with estrogen. Specifically, we report replacement of smooth muscle cells and cavernous spaces by fat cells in the corpus cavernosum penis, but not in the adjoining corpus spongiosum. Induction of these novel, region-specific phenotypes is dose-dependent, requires a critical window of exposure and associated with decreased testosterone and up-regulation of estrogen receptor α (ERα). The resistance of ERα knockout mice to develop these abnormalities implies an unequivocal role for ERα in mediating maldevelopment of the penis. Additionally, the prevention of estrogen-inducible penile abnormalities by ER antagonist ICI 182 780 implies that a functional ER-mediated pathway is essential for inducing penile abnormalities. Likewise, the ability of testosterone or dihydrotestosterone to negate these abnormalities suggests a role for an androgen receptor (AR)-mediated pathway. Taken together, these observations led us to hypothesize that neonatal estrogen exposure, via an ER-mediated pathway (direct action) or an AR-mediated pathway (indirect action through decreased testosterone) or both pathways, up-regulates ERα expression in stromal cells of the penis, which are then reprogrammed such that their differentiation into smooth muscle cells is inhibited and their differentiation into adipocytes is stimulated.

Estrogen-induced abnormal accumulation of fat cells in the rat penis and associated loss of fertility depends upon estrogen exposure during critical period of penile development

We previously reported that diethylstilbestrol (DES) or estradiol valerate (EV) exposure at a dose of 0.10-0.12 mg/kg, or higher, per day, on alternate days, from postnatal days 2-12, resulted in abnormal penis development and infertility (H. O. Goyal et al., 2005, J. Androl. 26, 32-43). The objective of this study was to identify a critical developmental period(s) during which EV exposure results in the observed penile abnormalities. Male pups received EV at a dose of 0.10-0.12 mg/kg on postnatal day(s) 1, 1-3, 4-6, 1-6, 7-12, 13-18, 19-24, or 25-30. Fertility was tested at 102-115 days of age and tissues were examined at 117-137 days. Both penile morphology and fertility were unaltered in rats treated with EV after 12 days of age. Conversely, except in rats treated on postnatal day 1 only, none of the males treated prior to 12 days of age sired pups, and all had abnormal penises, including varying degrees of abnormal accumulation of fat cells and loss of cavernous spaces and smooth muscle cells in the corpora cavernosa penis, which were maximal in the 1-6-day group. Also, the preputial sheath was partially released or its release was delayed, and the weight of the bulbospongiosus muscle was significantly reduced. Plasma testosterone (T) in the 1-6- and 4-6-day groups and intratesticular T in the 4-6-day group were significantly lower. The testosterone surge, characteristic of controls in the first week of life, was suppressed in the 1-3-day group. Estrogen receptor alpha mRNA expression was enhanced in the body of the penis in the 1-3-day group, but not in the 13-18-day group. Hence, EV exposure prior to 12 days of age (as short as 1-3 days postnatal), but not after 12 days of age, results in long-term abnormal penile morphology, characterized by abnormal accumulation of fat cells in the corpora cavernosa penis and, consequently, loss of fertility.

Placebo-controlled study on efficacy and safety of daily apomorphine SL intake in premenopausal women affected by hypoactive sexual desire disorder and sexual arousal disorder

OBJECTIVES

To verify whether apomorphine SL is effective in premenopausal women affected by arousal disorder with hypoactive sexual desire disorder.

METHODS

Sixty-two volunteer women, aged 26 to 45 years, affected by arousal disorders and hypoactive sexual desire disorder participated in the study, which consisted of two parts. The first was 4 weeks of a taken-as-needed, open-label, dose-escalation regimen starting at 2 or 3 mg of apomorphine SL. The second part of the study was for the nonresponders, who were randomly allocated to treatment in one of six possible sequences of three 2-week double-blind, crossover study periods with apomorphine 2 mg or 3 mg, washout, and placebo. Efficacy was assessed with the Personal Experiences Questionnaire using the 5-point Likert scale. The Personal Experiences Questionnaire quantified subjective arousal, desire, orgasm, enjoyment, and frequency of sexual relationships.

RESULTS

Fifty women completed the 4-week "as required" drug regimen, and 6 of them benefited from this treatment regimen (P <0.05). The 44 women who reported no change with respect to baseline participated in the double-blind crossover part of the study. Six women stopped taking the drug because of a fear of problems (two each during the 2-mg apomorphine, 3-mg apomorphine, and placebo periods). Adverse events were mild or moderate, both occurred during the "as required" part (10 patients) and during daily usage (6 patients) and were mainly nausea, vomiting, dizziness, or headache. However, during the placebo period, 2 women had adverse events, mainly headache. The daily intake of the drug was effective with both the 2-mg and 3-mg dosages compared with placebo for arousal and desire (P <0.05). The effects of 3 mg of apomorphine were better than those obtained with 2 mg (P <0.05). The orgasm, enjoyment, and satisfied by frequency scores improved during treatment with daily apomorphine compared with baseline and placebo.

CONCLUSIONS

The results of our study suggest that daily apomorphine SL may improve the sexual life of women affected by sexual difficulties. Additional studies are needed to define the daily use of apomorphine SL in large subgroups of women on the basis of etiology and the severity of sexual dysfunction.

Dynamic expression of murine Cux2 in craniofacial, limb, urogenital and neuronal primordia

CDP/Cut homeodomain factors are a divergent group of transcriptional repressors that are conserved during metazoan evolution. The cut locus of Drosophila is required for external sensory organ development and dorso-ventral boundary formation in the wing. In vertebrates, two CDP/Cut genes have been identified, Cux1 and Cux2. While Cux1 is widely expressed in mouse embryos particularly in the nephrogenic and urogenital systems, in contrast the early embryonic expression of Cux2 has not been characterized. Here we describe the dynamic profile of Cux2 during mouse embryogenesis. Cux2 expression becomes elaborated in a number of tissues during organogenesis including the olfactory epithelium, branchial arch and limb bud progress zones, roof plate, motor neurons, dorsal root ganglia and urogenital tissues. The conservation of signaling pathways between the branchial arches and limb buds is well documented and surprisingly this can also be applied to the developing urogenital system. Cux2 expression coincides with many tissue regions undergoing proliferative growth or cell rearrangements, however some later expression domains also include sites of programmed cell death. Cux2 is hypothesized to function as a transcriptional regulator that inhibits terminal differentiation and cell cycle exit.

Sonic hedgehog signaling from the urethral epithelium controls external genital development

External genital development begins with formation of paired genital swellings, which develop into the genital tubercle. Proximodistal outgrowth and axial patterning of the genital tubercle are coordinated to give rise to the penis or clitoris. The genital tubercle consists of lateral plate mesoderm, surface ectoderm, and endodermal urethral epithelium derived from the urogenital sinus. We have investigated the molecular control of external genital development in the mouse embryo. Previous work has shown that the genital tubercle has polarizing activity, but the precise location of this activity within the tubercle is unknown. We reasoned that if the tubercle itself is patterned by a specialized signaling region, then polarizing activity may be restricted to a subset of cells. Transplantation of urethral epithelium, but not genital mesenchyme, to chick limbs results in mirror-image duplication of the digits. Moreover, when grafted to chick limbs, the urethral plate orchestrates morphogenetic movements normally associated with external genital development. Signaling activity is therefore restricted to urethral plate cells. Before and during normal genital tubercle outgrowth, urethral plate epithelium expresses Sonic hedgehog (Shh). In mice with a targeted deletion of Shh, external genitalia are absent. Genital swellings are initiated, but outgrowth is not maintained. In the absence of Shh signaling, Fgf8, Bmp2, Bmp4, Fgf10, and Wnt5a are downregulated, and apoptosis is enhanced in the genitalia. These results identify the urethral epithelium as a signaling center of the genital tubercle, and demonstrate that Shh from the urethral epithelium is required for outgrowth, patterning, and cell survival in the developing external genitalia.

Premenopausal women affected by sexual arousal disorder treated with sildenafil: a double-blind, cross-over, placebo-controlled study

OBJECTIVE

To verify whether sildenafil is effective in young premenopausal women affected by arousal disorder.

DESIGN

A double-blind cross-over study.

SETTING

Centre for Sexological Research, Department of Microbiological and Gynaecological Science, University of Catania, Italy.

SAMPLE

Fifty-three volunteer women aged 22-28 years affected by arousal disorders.

METHODS

The study consisted of three 4-week periods: sildenafil, washout, placebo, by six possible sequences. sildenafil was used at 25 mg or 50 mg.

MAIN OUTCOME MEASURES

Efficacy was assessed at baseline and once monthly by the Personal Experiences Questionnaire based on the 5-point Likert scale. The questionnaire quantified subjective arousal (primary endpoint), and orgasm, enjoyment, sexual frequency, and the number of sexual fantasies.

RESULTS

Fifty-one women completed the study. Mean (SD) usage of sildenafil 25mg and 50mg was, respectively, 2.8 (0.8) and 2.7 (1.3) times weekly, while mean usage of placebo was 2.8 (1.6) times weekly. During both sildenafil dosages, arousal and orgasm improved with respect to placebo (P < 0.001). Therapeutically significant differences were not noted during the treatment with both 50 mg and 25 mg of sildenafil for arousal and orgasm. The frequency of sexual fantasies and of sexual intercourse, and enjoyment, improved in the women treated with sildenafil (P < 0.05).

CONCLUSIONS

Our study suggests that sildenafil may improve sexual performance of women affected by sexual difficulties such as arousal disorder, and may indirectly improve other aspects of sexual life. Moreover, further studies need to define the use of PDE type 5 inhibitors in this sexual pathophysiology.

Anatomy of the baculum-corpus cavernosum interface in the norway rat (Rattus norvegicus), and implications for force transfer during copulation

The baculum is a nonappendicular bone found in the glans tissue of members of five orders of mammals. Its function during copulation is unknown. Anatomical examination of the baculum and corpus cavernosum in the Norway rat (Rattus norvegicus) shows that the two structures are connected by a layer of fibrocartilage, and that the distal tip of the corpus cavernosum swells during erection to surround the proximal end of the baculum. Microradiographs of bacula from sexually experienced males show that regions of the bone may be remodeling; these data suggest that the baculum is load-bearing. On the basis of this anatomy, I propose that the baculum increases the overall flexural stiffness of the penis during copulation by transferring bending and compressive forces from the distal end of the glans to the tensile wall of the corpus cavernosum. Forces on the distal end of the penis during copulation press the baculum against the corpus cavernosum, reducing its internal volume and increasing intracavernosal pressure and corpus cavernosum wall strains. Because the wall of the erect corpus cavernosum is reinforced with inextensible collagen fibers, an increase in wall strain will also increase wall tissue stiffness, and thereby increase the flexural stiffness of the corpus cavernosum.

Microphallus: eventual phallic size is dependent on the timing of androgen administration

Micropenis secondary to hypogonadotropic hypogonadism in the Sprague-Dawley rat was induced by either injection of supraphysiological doses of dihydrotestosterone to the timed pregnant dam on gestational days 16 and 17 or by long acting microspheres of the gonadotropic agonist, leuprolide acetate. Following the induction of micropenis the animals were treated with dihydrotestosterone beginning at either day 7, 28, 56 or 84 of life. Within the study populations all animals treated with dihydrotestosterone had phallic enlargement greater than untreated controls (p < 0.01). However, animals beginning treatment on day 7 or 28 had persistent microphallus (p < 0.01). In contrast, if hormonal therapy was initiated on day 56 or 84 the phallus became normal in length. Immunohistological studies for androgen receptor expression revealed that early androgen exposure accelerated the loss of androgen receptor protein from the penis during growth. These data suggest that prepubertal exposure of the penis to androgens may significantly reduce the eventual penile size of the hypogonadotropic hypogonadal micropenis.