Instructive induction of prostate growth and differentiation by a defined urogenital sinus mesenchyme

Single-cell RNA sequencing of human prostate basal epithelial cells reveals zone-specific cellular populations and gene expression signatures

Despite evidence of genetic signatures in normal tissue correlating with disease risk, prospectively identifying genetic drivers and cell types that underlie subsequent pathologies has historically been challenging. The human prostate is an ideal model to investigate this phenomenon because it is anatomically segregated into three glandular zones (central, peripheral, and transition) that develop differential pathologies: prostate cancer in the peripheral zone (PZ) and benign prostatic hyperplasia (BPH) in the transition zone (TZ), with the central zone (CZ) rarely developing disease. More specifically, prostatic basal cells have been implicated in differentiation and proliferation during prostate development and regeneration; however, the contribution of zonal variation and the critical role of basal cells in prostatic disease etiology are not well understood. Using single-cell RNA sequencing of primary prostate epithelial cultures, we elucidated organ-specific, zone-specific, and cluster-specific gene expression differences in basal cells isolated from human prostate and seminal vesicle (SV). Aggregated analysis identified ten distinct basal clusters by Uniform Manifold Approximation and Projection. Organ specificity compared gene expression in SV with the prostate. As expected, SV cells were distinct from prostate cells by clustering, gene expression, and pathway analysis. For prostate zone specificity, we identified two CZ-specific clusters, while the TZ and PZ populations clustered together. Despite these similarities, differential gene expression was identified between PZ and TZ samples that correlated with gene expression profiles in prostate cancer and BPH, respectively. Zone-specific profiles and cell type-specific markers were validated using immunostaining and bioinformatic analyses of publicly available RNA-seq datasets. Understanding the baseline differences at the organ, zonal, and cellular level provides important insight into the potential drivers of prostatic disease and guides the investigation of novel preventive or curative treatments. Importantly, this study identifies multiple prostate basal cell populations and cell type-specific gene signatures within prostate basal epithelial cells that have potential critical roles in driving prostatic diseases. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Female Prostate Development: Morphological Analysis of the Budding Dynamic

The presence of the prostate in female mammals has long been known. However, pieces of information related to its development are still lacking. The aim of this study was to explore the budding dynamic during the initial prostate development in female gerbils. Pregnant females were timed, the fetuses were euthanized, and the urogenital sinus was dissected out between the embryonic days 20 and 24 (E20-E24 groups). Newborn pups (1-day-old; P1 group) underwent the same procedures. The female prostate development was based on epithelial buds which arose far from the paraurethral mesenchyme (PAM). The epithelial buds reached the PAM at prenatal day 24, crossing a small gap in the smooth muscle layer between the periurethral mesenchyme (PEM) and the PAM. Steroid nuclear receptors such as the androgen receptor and estrogen receptor alpha were localized in the PEM through the urethral wall, although some epithelial labeling was also present in the urogenital sinus epithelium (UGE). P63-positive cells were found only in the UGE, becoming restricted to the basal compartment after the 23rd prenatal day. The results showed that the gerbil female prostate exhibits a distinct budding pattern as compared to the male prostate development.

Stromal cell interplay in prostate development, physiology, and pathological conditions

Advances in prostatic stroma studies over the past few decades have demonstrated that the stroma not only supports and nourishes the gland's secretory epithelium but also participates in key aspects of morphogenesis, in the prostate's hormonal metabolism, and in the functionality of the secretory epithelium. Furthermore, the stroma is implicated in the onset and progression of prostate cancer through the formation of the so-called reactive stroma, which corresponds to a tumorigenesis-permissive microenvironment. Prostatic stromal cells are interconnected and exchange paracrine signals among themselves in a gland that is highly sensitive to endocrine hormones. There is a growing body of evidence that telocytes, recently detected interstitial cells that are also present in the prostate, are involved in stromal organization, so that their processes form a network of interconnections with both the epithelium and the other stromal cells. The present review provides an update on the different types of prostate stromal cells, their interrelationships and implications for prostate development, physiology and pathological conditions.

Correlation Between Testosterone Replacement Treatment and Lower Urinary Tract Symptoms

Lower urinary tract symptoms (LUTS) are a cluster of voiding symptoms, such as weak stream, hesitancy, intermittency, urinary frequency, urgency, and nocturia. LUTS are frequent in elderly men and it considered the ultimate clinical symptoms of benign prostatic hyperplasia. With aging, male hypogonadism is increased which is defined as decreased ability of the testes to produce sperm and sex steroids because of a pituitary/hypothalamic, or testicular deficiency. In academic andrology associations, the term "male hypogonadism" is commonly used to categorize testosterone deficiency. Testosterone deficiency syndrome (TDS) is defined as a decrease in serum testosterone accompanied by symptoms such as libido decrease, depressive disorder, erectile dysfunction, and fatigue. Although the mechanism about testosterone-replacement therapy (TRT) effects on men with hypogonadism is not yet identified, TRT has been shown to effectively relieve the symptoms of TDS as well as LUTS by several studies. Although the present review demonstrates the effectiveness and safety of TRT in men with TDS by prior studies, future large scale of clinical trials should be conducted to present more high-quality evidence to clinicians and patients.

Prenatal exposure to finasteride promotes sex-specific changes in gerbil prostate development

Finasteride is a drug that is widely used in the treatment of benign prostatic hyperplasia, hair loss and even as a chemotherapeutic agent in the treatment of prostatic adenocarcinoma. However, its use is known to cause several side effects in adults and it can also cause changes in the embryonic development of the male prostate, which is a cause for concern given the possibility of the accumulation of finasteride in the environment. Nevertheless, no studies have investigated the effects of finasteride on the development of the prostate in females, which occurs in several species of mammals. To evaluate the effects of intrauterine exposure to finasteride (500μgkg-1 day-1) on postnatal prostate development in the Mongolian gerbil in the present study, we used immunohistochemistry, immunofluorescence, serological analysis and three-dimensional reconstruction techniques. Differences were observed in the effects of finasteride on periductal smooth muscle and cell proliferation between the sexes, as well as intersex differences in the presence of the androgen receptor, which was elevated in males, and the oestrogen receptor ERα, which was increased in females. Together, the data indicate that the female prostate has its own hormone dynamics and that there are sex-specific differences in the way in which the female prostate reacts to prenatal exposure to finasteride.

Differences between male and female prostates in terms of physiology, sensitivity to chemicals and pathogenesis-A review in a rodent model

The prostate is a gland that is not exclusively present in males, being also found in females of several mammalian species, including humans. There is evidence that the prostate in both sexes is affected by the same pathologies such as prostatitis, benign alterations and even cancer. In view of the difficulties of manipulating the prostate gland, the Mongolian gerbil (Meriones unguiculatus), a rodent species with high incidence of functional prostates in females, is widely used in studies of the female prostate. However, despite knowing much about the similarities between the female and male prostate, little emphasis has been placed on the differences between them. This review investigates the intersex differences in prostate development, physiology and pathogenesis. The female prostate develops earlier than in males and studies indicate that it is more sensitive to oestrogens than the male prostate, as well as being more sensitive to exposure to xenoestrogens, such as Bisphenol A and methylparaben, with a higher susceptibility to benign lesions in the adult and senile prostate than in males. In addition, the female prostate is impacted by pregnancy and the oestrous cycle, and is also dependent on progesterone. The peculiarities of the female prostate raise concerns about the risk of it undergoing neglected changes as a result of environmental chemicals, since safe dosages are established exclusively for the male prostate.

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.

Spatiotemporal regulation of multipotency during prostate development

The prostate is formed by a branched glandular epithelium composed of basal cells (BCs) and luminal cells (LCs). Multipotent and unipotent stem cells (SCs) mediate the initial steps of prostate development whereas BCs and LCs are self-sustained in adult mice by unipotent lineage-restricted SCs. The spatiotemporal regulation of SC fate and the switch from multipotency to unipotency remain poorly characterised. Here, by combining lineage tracing, whole-tissue imaging, clonal analysis and proliferation kinetics, we uncover the cellular dynamics that orchestrate prostate postnatal development in mouse. We found that at an early stage of development multipotent basal SCs are located throughout the epithelium and are progressively restricted at the distal tip of the ducts, where, together with their progeny, they establish the different branches and the final structure of prostate. In contrast, pubertal development is mediated by unipotent lineage-restricted SCs. Our results uncover the spatiotemporal regulation of the switch from multipotency to unipotency during prostate development.

Highlighted Article: A combination of lineage tracing and whole-mount imaging uncovers how the multipotency of basal stem cells is regulated during postnatal prostate development in mouse.

Genome-wide analysis of androgen receptor binding and transcriptomic analysis in mesenchymal subsets during prostate development

Prostate development is controlled by androgens, the androgen receptor (AR) and mesenchymal–epithelial signalling. We used chromatin immunoprecipitation sequencing (ChIP-seq) to define AR genomic binding in the male and female mesenchyme. Tissue- and single-cell-based transcriptional profiling was used to define mesenchymal AR target genes. We observed significant AR genomic binding in females and a strong enrichment at proximal promoters in both sexes. In males, there was greater AR binding to introns and intergenic regions as well as to classical AR binding motifs. In females, there was increased proximal promoter binding and involvement of cofactors. Comparison of AR-bound genes with transcriptomic data enabled the identification of novel sexually dimorphic AR target genes. We validated the dimorphic expression of AR target genes using published datasets and confirmed regulation by androgens using ex vivo organ cultures. AR targets showed variable expression in patients with androgen insensitivity syndrome. We examined AR function at single-cell resolution using single-cell RNA sequencing (scRNA-seq) in male and female mesenchyme. Surprisingly, both AR and target genes were distributed throughout cell subsets, with few positive cells within each subset. AR binding was weakly correlated with target gene expression.

Summary: A study of how androgens lead to sexually dimorphic development of the prostate using transcription factor genome binding and transcriptome analysis in mesenchymal subsets.

Testosterone and Benign Prostatic Hyperplasia

INTRODUCTION

Benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS) are frequent in aging. Nonetheless, their pathogenesis is largely unknown. The androgen dependence of the first phases of prostate development have inspired the historical view that higher testosterone (T) may be involved in BPH occurrence; however, recent evidence suggests a different scenario.

AIM

To review the available knowledge on the pathogenesis of BPH particularly concerning the role of T and the possible connections with metabolic impairments.

METHODS

Relevant records were retrieved by an extensive search in Medline, including the following keywords ("testosterone"[MeSH Terms] OR "testosterone"[All Fields]) AND ("prostatic hyperplasia"[MeSH Terms] OR ("prostatic"[All Fields] AND "hyperplasia"[All Fields]) OR "prostatic hyperplasia"[All Fields] OR ("benign"[All Fields] AND "prostatic"[All Fields] AND "hyperplasia"[All Fields]) OR "benign prostatic hyperplasia"[All Fields]). There were no limitations in terms of publication date or study design.

MAIN OUTCOME MEASURES

Preclinical and clinical studies have been reported, with special emphasis on our contribution and interpretation.

RESULTS

Inflammation is a key aspect of BPH development. Along with infectious agents, prostate inflammation can be triggered by metabolic stimuli, such as dyslipidemia, an important component of metabolic syndrome (MetS). Low T and hyperestrogenism frequently occur in MetS. Mounting evidence shows that low, rather than high, T and hyperestrogenism may favor prostate inflammation. Considering these data as a whole, we postulate that BPH is the result of the action of multiple factors, which reinforce their mutual detrimental effects.

CONCLUSION

T is not detrimental for the prostate, and treating hypogonadism could even produce relief from LUTS and limit prostatic inflammation, which generates and maintains the process leading to BPH. Rastrelli G, Vignozzi L, Corona G, et al. Testosterone and Benign Prostatic Hyperplasia. Sex Med Rev 2019;7:259-271.

Development of the human prostate

This paper provides a detailed compilation of human prostatic development that includes human fetal prostatic gross anatomy, histology, and ontogeny of selected epithelial and mesenchymal differentiation markers and signaling molecules throughout the stages of human prostatic development: (a) pre-bud urogenital sinus (UGS), (b) emergence of solid prostatic epithelial buds from urogenital sinus epithelium (UGE), (c) bud elongation and branching, (d) canalization of the solid epithelial cords, (e) differentiation of luminal and basal epithelial cells, and (f) secretory cytodifferentiation. Additionally, we describe the use of xenografts to assess the actions of androgens and estrogens on human fetal prostatic development. In this regard, we report a new model of de novo DHT-induction of prostatic development from xenografts of human fetal female urethras, which emphasizes the utility of the xenograft approach for investigation of initiation of human prostatic development. These studies raise the possibility of molecular mechanistic studies on human prostatic development through the use of tissue recombinants composed of mutant mouse UGM combined with human fetal prostatic epithelium. Our compilation of human prostatic developmental processes is likely to advance our understanding of the pathogenesis of benign prostatic hyperplasia and prostate cancer as the neoformation of ductal-acinar architecture during normal development is shared during the pathogenesis of benign prostatic hyperplasia and prostate cancer.

Identification of genes expressed in a mesenchymal subset regulating prostate organogenesis using tissue and single cell transcriptomics

Prostate organogenesis involves epithelial growth controlled by inductive signalling from specialised mesenchymal subsets. To identify pathways active in mesenchyme we used tissue and single cell transcriptomics to define mesenchymal subsets and subset-specific transcript expression. We documented transcript expression using Tag-seq and RNA-seq in female rat Ventral Mesenchymal Pad (VMP) as well as adjacent urethra comprised of smooth muscle and peri-urethral mesenchyme. Transcripts enriched in female VMP were identified with Tag-seq of microdissected tissue, RNA-seq of cell populations, and single cells. We identified 400 transcripts as enriched in the VMP using bio-informatic comparisons of Tag-seq and RNA-seq data, and 44 were confirmed by single cell RNA-seq. Cell subset analysis showed that VMP and adjacent mesenchyme were composed of distinct cell types and that each tissue contained two subgroups. Markers for these subgroups were highly subset specific. Thirteen transcripts were validated by qPCR to confirm cell specific expression in microdissected tissues, as well as expression in neonatal prostate. Immunohistochemical staining demonstrated that Ebf3 and Meis2 showed a restricted expression pattern in female VMP and prostate mesenchyme. We conclude that prostate inductive mesenchyme shows limited cellular heterogeneity and that transcriptomic analysis identified new mesenchymal subset transcripts associated with prostate organogenesis.

Desquamation takes center stage at the origin of proliferative inflammatory atrophy, epithelial-mesenchymal transition, and stromal growth in benign prostate hyperplasia

In this commentary, we propose a relationship between desquamation, initially described as the collective detachment and deletion of epithelial cell in the prostate gland after castration, and proliferative inflammatory atrophy (PIA) and stromal growth in benign prostate hyperplasia (BPH). First, in response to diverse stimuli, including inflammatory mediators, epithelial cells desquamate and leave a large surface of the luminal side of the basement membrane (BM) exposed. Basal cells are activated into intermediate-type cells, which change morphology to cover and remodel the exposed BM (simple atrophy) to a new physiological demand (such as in the hypoandrogen environment, simulated by surgical and/or chemical castration) and/or to support re-epithelialization (under normal androgen levels). In the presence of inflammation (that might be the cause of desquamation), the intermediate-type cells proliferate and characterize PIA. Second, in other circumstances, desquamation is an early step of epithelial-to-mesenchymal transition (EMT), which contributes to stromal growth, as suggested by some experimental models of BPH. The proposed associations correlate unexplored cell behaviors and reveal the remarkable plasticity of the prostate epithelium that might be at the origin of prostate diseases.

Prostate organogenesis: tissue induction, hormonal regulation and cell type specification

Prostate organogenesis is a complex process that is primarily mediated by the presence of androgens and subsequent mesenchyme-epithelial interactions. The investigation of prostate development is partly driven by its potential relevance to prostate cancer, in particular the apparent re-awakening of key developmental programs that occur during tumorigenesis. However, our current knowledge of the mechanisms that drive prostate organogenesis is far from complete. Here, we provide a comprehensive overview of prostate development, focusing on recent findings regarding sexual dimorphism, bud induction, branching morphogenesis and cellular differentiation.

RET-mediated glial cell line-derived neurotrophic factor signaling inhibits mouse prostate development

In humans and rodents, the prostate gland develops from the embryonic urogenital sinus (UGS). The androgen receptor (AR) is thought to control the expression of morphogenetic genes in inductive UGS mesenchyme, which promotes proliferation and cytodifferentiation of the prostatic epithelium. However, the nature of the AR-regulated morphogenetic genes and the mechanisms whereby AR controls prostate development are not understood. Glial cell line-derived neurotrophic factor (GDNF) binds GDNF family receptor α1 (GFRα1) and signals through activation of RET tyrosine kinase. Gene disruption studies in mice have revealed essential roles for GDNF signaling in development; however, its role in prostate development is unexplored. Here, we establish novel roles of GDNF signaling in mouse prostate development. Using an organ culture system for prostate development and Ret mutant mice, we demonstrate that RET-mediated GDNF signaling in UGS increases proliferation of mesenchyme cells and suppresses androgen-induced proliferation and differentiation of prostate epithelial cells, inhibiting prostate development. We also identify Ar as a GDNF-repressed gene and Gdnf and Gfrα1 as androgen-repressed genes in UGS, thus establishing reciprocal regulatory crosstalk between AR and GDNF signaling in prostate development.

Postnatal development of Mongolian gerbil female prostate: An immunohistochemical and 3D modeling study

The development of the prostate in male rodents, which involves complex epithelial-mesenchymal interactions between the urogenital sinus epithelium (UGE) and the urogenital sinus mesenchyme (UGM), has been deeply studied. In females, however, this process is not very clear. In this study, the postnatal development of the prostate in female Mongolian gerbils employing three-dimensional (3D) reconstructions, histochemical, and immunohistochemical techniques was characterized. It was observed that prostatic branching and differentiation in females was induced by a single mesenchyme localized at a ventrolateral position, which was named as ventrolateral mesenchyme (VLM); furthermore, the canalization of solid buds began on the third postnatal day (P3) and the branching morphogenesis on P5. We observed secretions in the acini at the end of the first month, and, on P45, the acini were completely differentiated. The strong cell proliferation phase in the first week coincided with the mesenchymal expression of estrogen receptor 1 (ESR1). The expression of androgen receptor (AR) paralleled cell differentiation, and, on P30, immunolabelling with p63 was restricted to basal cells. This study serves as a baseline parameter for future research on disruptions that could affect the development of the female prostate.

Glial cell line-derived neurotrophic factor induces cell proliferation in the mouse urogenital sinus

Glial cell line-derived neurotrophic factor (GDNF) is a TGFβ family member, and GDNF signals through a glycosyl-phosphatidylinositol-linked cell surface receptor (GFRα1) and RET receptor tyrosine kinase. GDNF signaling plays crucial roles in urogenital processes, ranging from cell fate decisions in germline progenitors to ureteric bud outgrowth and renal branching morphogenesis. Gene ablation studies in mice have revealed essential roles for GDNF signaling in urogenital development, although its role in prostate development is unclear. We investigated the functional role of GDNF signaling in the urogenital sinus (UGS) and the developing prostate of mice. GDNF, GFRα1, and RET show time-specific and cell-specific expression during prostate development in vivo. In the UGS, GDNF and GFRα1 are expressed in the urethral mesenchyme (UrM) and epithelium (UrE), whereas RET is restricted to the UrM. In each lobe of the developing prostate, GDNF and GFRα1 expression declines in the epithelium and becomes restricted to the stroma. Using a well-established organ culture system, we determined that exogenous GDNF increases proliferation of UrM and UrE cells, altering UGS morphology. With regard to mechanism, GDNF signaling in the UrM increased RET expression and phosphorylation of ERK1/2. Furthermore, inhibition of RET kinase activity or ERK kinases suppressed GDNF-induced proliferation of UrM cells but not UrE cells. We therefore propose that GDNF signaling in the UGS increases proliferation of UrM and UrE cells by different mechanisms, which are distinguished by the role of RET receptor tyrosine kinase and ERK kinase signaling, thus implicating GDNF signaling in prostate development and growth.

Identification of multipotent luminal progenitor cells in human prostate organoid cultures

The prostate gland consists of basal and luminal cells arranged as pseudostratified epithelium. In tissue recombination models, only basal cells reconstitute a complete prostate gland, yet murine lineage-tracing experiments show that luminal cells generate basal cells. It has remained challenging to address the molecular details of these transitions and whether they apply to humans, due to the lack of culture conditions that recapitulate prostate gland architecture. Here, we describe a 3D culture system that supports long-term expansion of primary mouse and human prostate organoids, composed of fully differentiated CK5+ basal and CK8+ luminal cells. Organoids are genetically stable, reconstitute prostate glands in recombination assays, and can be experimentally manipulated. Single human luminal and basal cells give rise to organoids, yet luminal-cell-derived organoids more closely resemble prostate glands. These data support a luminal multilineage progenitor cell model for prostate tissue and establish a robust, scalable system for mechanistic studies.

Primary carcinoma of renal calyx

Renal calyx carcinoma (RCXC) may mimic collecting duct carcinoma (CDC) or urothelial carcinoma (UC) of the renal pelvis. RCXC is distinguished from CDC and UC of the renal pelvis as having the tumor epicenter in the renal calyx, with limited involvement of the surrounding renal pelvis surface urothelium. In this study, we summarize our experience with this entity. Ten cases of RCXC, including 9 cases with urothelial differentiation (RCXC-UC) and 1 case with salivary gland-type differentiation (RCXC-SC), were identified. Ten consecutive cases of UC were selected for comparison, with extensive renal pelvis involvement and with secondary renal parenchymal invasion. Two cases of collecting duct carcinoma (CDC) were also examined. Immunohistochemistry (IHC) was performed on representative tissue blocks for PAX8, PAX2, CK5, CK7, CK20, p63, GATA3, AMACR, RCC, CD10, vimentin, S100, and MSA. The 10 cases of RCXC (M:F=4:6, ages: 62-91 years, mean: 76) presented with renal masses of 3-6cm. Ureteroscopic studies and renal pelvic washings showed atypical/malignant cells in three cases. Seven patients were treated with nephrectomy followed by radiation±chemotherapy, and all cases developed metastases to lymph nodes or liver/lung/bone. In all 7 cases with nephrectomy, there was extensive renal parenchymal involvement with infiltrating borders and diffuse spread along collecting ducts. Six RCXC-UC contained focal squamous differentiation. The RCXC-SC displayed features of adenoid cystic and basaloid features. In situ UC, with or without papillary components, was identified in the calyces in all 7 nephrectomy cases with remaining renal pelvis harboring small tumor burden in 5 cases, and no tumor in another 2 cases. Of the three cases without nephrectomy, no tumor in the renal pelvis could be visualized with endoscopy, however one case was associated with UC of the urinary bladder. Of 10 control UC cases, tumor was limited to the tip of renal papilla in 7 cases, extensive in 3 cases, and with no extension into the collecting ducts. RCXC-UC were all positive for p63, CK5, CK7, and PAX2, with all negative for RCC. PAX8 (70% positive) and GATA3 (50% positive) reactivity was variable. The 10 UC cases shared IHC properties with RCXC-UC but frequent negativity for PAX8 and positivity for GATA3. RCXC is an aggressive neoplasm with high risk of metastases. Similar to CDC, it is located in the renal papilla and rarely with clinically visible renal pelvis tumor or ureteral urine positive for tumor cells. Unlike CDC and non-calyceal UC, RCXC shows predominantly urothelial and squamous differentiation and is associated with an in situ component of adjacent renal calyces. By IHC, RCXC exhibited features intermediate between UC and CDC with decreased or negative immunoreactivity for PAX8 and GATA.

TCDD inhibition of canonical Wnt signaling disrupts prostatic bud formation in mouse urogenital sinus

In mice, in utero exposure to 2,3,7,8-tetrachlorodibenzo-p- dioxin (TCDD) reduces the number of dorsolateral prostatic buds resulting in a smaller dorsolateral prostate and prevents formation of ventral buds culminating in ventral prostate agenesis. The genes and signaling pathways affected by TCDD that are responsible for disrupting prostate development are largely unknown. Here we show that treatment of urogenital sinus (UGS) organ cultures with known inhibitors of canonical Wnt signaling also inhibits prostatic bud formation. In support of the hypothesis that TCDD decreases canonical Wnt signaling, we identify inhibitory effects of TCDD on multiple components of the canonical Wnt signaling pathway in the UGS that temporally coincide with the inhibitory effect of TCDD on prostatic bud formation: (1) expression of R-spondins (Rspo2 and Rspo3) that promote canonical Wnt signaling is reduced; (2) expression of Lef1, Tcf1, and Wif1, established canonical Wnt target genes, is decreased; (3) expression of Lgr5, a RSPO receptor that activates canonical Wnt signaling, is reduced; and (4) expression of Dickkopfs (Dkks), inhibitors of canonical Wnt signaling, is not increased by TCDD. Thus, the TCDD-induced reduction in canonical Wnt signaling is associated with a decrease in activators (Rspo2 and Rspo3) rather than an increase in inhibitors (Dkk1 and Dkk2) of the pathway. This study focuses on determining whether treatment of TCDD-exposed UGS organ cultures with RSPO2 and/or RSPO3 is capable of rescuing the inhibitory effects of TCDD on canonical Wnt signaling and prostatic bud formation. We discovered that each RSPO alone or in combination partially rescues TCDD inhibition of both canonical Wnt signaling and prostatic bud formation.

Dose-related estrogen effects on gene expression in fetal mouse prostate mesenchymal cells

Developmental exposure of mouse fetuses to estrogens results in dose-dependent permanent effects on prostate morphology and function. Fetal prostatic mesenchyme cells express estrogen receptor alpha (ERα) and androgen receptors and convert stimuli from circulating estrogens and androgens into paracrine signaling to regulate epithelial cell proliferation and differentiation. To obtain mechanistic insight into the role of different doses of estradiol (E2) in regulating mesenchymal cells, we examined E2-induced transcriptomal changes in primary cultures of fetal mouse prostate mesenchymal cells. Urogenital sinus mesenchyme cells were obtained from male mouse fetuses at gestation day 17 and exposed to 10 pM, 100 pM or 100 nM E2 in the presence of a physiological concentration of dihydrotestosterone (0.69 nM) for four days. Gene ontology studies suggested that low doses of E2 (10 pM and 100 pM) induce genes involved in morphological tissue development and sterol biosynthesis but suppress genes involved in growth factor signaling. Genes involved in cell adhesion were enriched among both up-regulated and down-regulated genes. Genes showing inverted-U-shape dose responses (enhanced by E2 at 10 pM E2 but suppressed at 100 pM) were enriched in the glycolytic pathway. At the highest dose (100 nM), E2 induced genes enriched for cell adhesion, steroid hormone signaling and metabolism, cytokines and their receptors, cell-to-cell communication, Wnt signaling, and TGF- β signaling. These results suggest that prostate mesenchymal cells may regulate epithelial cells through direct cell contacts when estrogen level is low whereas secreted growth factors and cytokines might play significant roles when estrogen level is high.

Estrogenic environmental chemicals and drugs: mechanisms for effects on the developing male urogenital system

Development and differentiation of the prostate from the fetal urogenital sinus (UGS) is dependent on androgen action via androgen receptors (AR) in the UGS mesenchyme. Estrogens are not required for prostate differentiation but do act to modulate androgen action. In mice exposure to exogenous estrogen during development results in permanent effects on adult prostate size and function, which is mediated through mesenchymal estrogen receptor (ER) alpha. For many years estrogens were thought to inhibit prostate growth because estrogenic drugs studied were administered at very high concentrations that interfered with normal prostate development. There is now extensive evidence that exposure to estrogen at very low concentrations during the early stages of prostate differentiation can stimulate fetal/neonatal prostate growth and lead to prostate disease in adulthood. Bisphenol A (BPA) is an environmental endocrine disrupting chemical that binds to both ER receptor subtypes as well as to AR. Interest in BPA has increased because of its prevalence in the environment and its detection in over 90% of people in the USA. In tissue culture of fetal mouse UGS mesenchymal cells, BPA and estradiol stimulated changes in the expression of several genes. We discuss here the potential involvement of estrogen in regulating signaling pathways affecting cellular functions relevant to steroid hormone signaling and metabolism and to inter- and intra-cellular communications that promote cell growth. The findings presented here provide additional evidence that BPA and the estrogenic drug ethinylestradiol disrupt prostate development in male mice at administered doses relevant to human exposures.

A high-resolution molecular atlas of the fetal mouse lower urogenital tract

Epithelial-stromal interactions in the lower urogenital tract (LUT) are integral to prostatic and seminal vesicle development in males, vaginal and uterine development in females, and urethral development in both sexes. Gene expression profiling of isolated LUT stroma and epithelium has unraveled mechanisms of LUT development, but such studies are confounded by heterogeneous and ill-defined cell sub-populations contained within each tissue compartment. We used in situ hybridization to synthesize a high-resolution molecular atlas of 17-day post-coitus fetal mouse LUT. We identified mRNAs that mark selective cell populations of the seminal vesicle, ejaculatory duct, prostate, urethra, and vagina, subdividing these tissues into 16 stromal and 8 epithelial sub-compartments. These results provide a powerful tool for mapping LUT gene expression patterns and also reveal previously uncharacterized sub-compartments that may play mechanistic roles in LUT development of which we were previously unaware.

Identification of stromally expressed molecules in the prostate by tag-profiling of cancer-associated fibroblasts, normal fibroblasts and fetal prostate

The stromal microenvironment has key roles in prostate development and cancer, and cancer-associated fibroblasts (CAFs) stimulate tumourigenesis via several mechanisms including the expression of pro-tumourigenic factors. Mesenchyme (embryonic stroma) controls prostate organogenesis, and in some circumstances can re-differentiate prostate tumours. We have applied next-generation Tag profiling to fetal human prostate, normal human prostate fibroblasts (NPFs) and CAFs to identify molecules expressed in prostatic stroma. Comparison of gene expression profiles of a patient-matched pair of NPFs vs CAFs identified 671 transcripts that were enriched in CAFs and 356 transcripts whose levels were decreased, relative to NPFs. Gene ontology analysis revealed that CAF-enriched transcripts were associated with prostate morphogenesis and CAF-depleted transcripts were associated with cell cycle. We selected mRNAs to follow-up by comparison of our data sets with published prostate cancer fibroblast microarray profiles as well as by focusing on transcripts encoding secreted and peripheral membrane proteins, as well as mesenchymal transcripts identified in a previous study from our group. We confirmed differential transcript expression between CAFs and NPFs using QrtPCR, and defined protein localization using immunohistochemistry in fetal prostate, adult prostate and prostate cancer. We demonstrated that ASPN, CAV1, CFH, CTSK, DCN, FBLN1, FHL1, FN, NKTR, OGN, PARVA, S100A6, SPARC, STC1 and ZEB1 proteins showed specific and varied expression patterns in fetal human prostate and in prostate cancer. Colocalization studies suggested that some stromally expressed molecules were also expressed in subsets of tumour epithelia, indicating that they may be novel markers of EMT. Additionally, two molecules (ASPN and STC1) marked overlapping and distinct subregions of stroma associated with tumour epithelia and may represent new CAF markers.

Expression of pleiotrophin in the prostate is androgen regulated and it functions as an autocrine regulator of mesenchyme and cancer associated fibroblasts and as a paracrine regulator of epithelia

BACKGROUND

Androgens and paracrine signaling from mesenchyme/stroma regulate development and disease of the prostate, and gene profiling studies of inductive prostate mesenchyme have identified candidate molecules such as pleiotrophin (Ptn).

METHODS

Ptn transcripts and protein were localized by in situ and immunohistochemistry and Ptn mRNA was quantitated by Northern blot and qRT-PCR. Ptn function was examined by addition of hPTN protein to rat ventral prostate organ cultures, primary human fetal prostate fibroblasts, prostate cancer associated fibroblasts, and BPH1 epithelia.

RESULTS

During development, Ptn transcripts and protein were expressed in ventral mesenchymal pad (VMP) and prostatic mesenchyme. Ptn was localized to mesenchyme surrounding ductal epithelial tips undergoing branching morphogenesis, and was located on the surface of epithelia. hPTN protein stimulated branching morphogenesis and stromal and epithelial proliferation, when added to rat VP cultures, and also stimulated growth of fetal human prostate fibroblasts, prostate cancer associated fibroblasts, and BPH1 epithelia. PTN mRNA was enriched in patient-matched normal prostate fibroblasts versus prostate cancer associated fibroblasts. PTN also showed male enriched expression in fetal human male urethra versus female, and between wt male and ARKO male mice. Transcripts for PTN were upregulated by testosterone in fetal human prostate fibroblasts and organ cultures of female rat VMP. Ptn protein was increased by testosterone in organ cultures of female rat VMP and in rat male urethra compared to female.

CONCLUSIONS

Our data suggest that in the prostate Ptn functions as a regulator of both mesenchymal and epithelial proliferation, and that androgens regulate Ptn levels.

Identification of EphrinB1 expression in prostatic mesenchyme and a role for EphB-EphrinB signalling in prostate development

Paracrine signalling from mesenchyme to epithelium plays a key role in regulating prostate organogenesis and it is important to identify the mesenchymally expressed molecules that regulate organ growth, though currently few such molecules are known. Tyrosine kinase signalling via EphB receptors has been characterised in many developmental processes, and EphB3 mRNA expression was detected in prostate inductive mesenchyme in previous gene profiling studies. This led us to examine the expression and function of EphrinB signalling in prostate development, to determine if EphrinB ligands might function as mesenchymal paracrine regulators of prostate growth. Using PCR, wholemount in situ hybridisation, and immunohistochemistry we examined the expression of EphB receptors and EphrinB ligands in rat prostate during development to determine which showed mesenchymal expression. EphB3 and EphrinB1 transcripts and proteins were expressed in the mesenchyme of developing prostate and in female urogenital mesenchyme and smooth muscle. The function of EphrinB signalling was examined using in vitro organ culture assays of ventral prostate (VP), which were treated with EphB3-Fc and EphrinB1-Fc proteins to inhibit or augment Ephrin signalling. Addition of recombinant EphB3-Fc resulted in a significant decrease in VP organ size, while recombinant EphrinB1-Fc resulted in a significant increase in VP organ size and epithelial proliferation. Additionally, EphrinB1-Fc reduced the degree of epithelial branching in VP organs and increased ductal tip size, though without disrupting normal differentiation. We have identified expression of EphrinB1 in prostatic mesenchyme and suggest that the EphrinB signalling system acts as a regulator of prostate growth. EphrinB-EphB signalling may function as an autocrine regulator of mesenchyme and/or as a paracrine regulator of epithelia.

The developmental expression profile of PAX2 in the murine prostate

BACKGROUND

Nine transcription factors comprise the PAX gene family that regulate organogenesis. The urogenital system of PAX2 null male mice fails to develop properly. PAX2 is overexpressed in PC3 cells. Therefore, PAX2 is implicated in both prostate organogenesis and cancer. However, the expression pattern/profile of PAX2 in the prostate is unknown.

METHODS

PAX2/5/8 expression was surveyed in E16.5 male urogenital sinus (UGS) by RT-PCR. Prostate samples from 10 developmental stages in C3H male mice were used in quantitative reverse-transcript PCR (Q-PCR) and Western blotting (WB). RT-PCR and WB measured PAX2 expression in prostatic lobes or UGS layers, to identify local-regional expression patterns. Cytoplasmic versus nuclear expression was examined by WB. A castration series in adult C3H male mice and R1881 treatment in serum-free LNCaP cells examined androgen control of PAX2.

RESULTS

PAX2 mRNA levels are higher in early developmental stages as compared to postpubertal prostates. RT-PCR and/or WB indicated a dorsal epithelial-nuclear localization of PAX2. PAX2 mRNA and protein increase postcastration. R1881 decreases expression of PAX2 mRNA in LNCaP cells as compared to controls.

CONCLUSIONS

The expression profile of PAX2 indicates that it may regulate early, androgen-independent stages of murine prostate development, particularly for dorsally derived prostate glands. PAX2 expression appears to be associated with a dorsally localized epithelial cell population that is castration insensitive and retains proliferative and differentiative potential. Such a population of cells may represent a subset of stem-like cells having some characteristics in common with castrate-resistant prostate cancer cells.

2,3,7,8-Tetrachlorodibenzo-p-dioxin inhibits fibroblast growth factor 10-induced prostatic bud formation in mouse urogenital sinus

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) dorsalizes the pattern of prostatic buds developing from the urogenital sinus (UGS) of male fetal mice, causing some buds to form in inappropriate positions while blocking formation of others. This teratogenic TCDD action significantly reduces prostate main duct number and causes ventral prostate agenesis in exposed males. The purpose of this study was to determine whether inhibition of fibroblast growth factor 10 (FGF10) signaling is mechanistically linked to mouse prostatic budding impairment by TCDD. In utero TCDD exposure induced aryl hydrocarbon receptor-responsive cytochrome P450 1b1 messenger RNA (mRNA) in ventral UGS regions where Fgf10 and fibroblast growth factor receptor 2 (Fgfr2) mRNA were expressed and where budding was most severely inhibited by TCDD. However, TCDD exposure did not reduce Fgf10 or Fgfr2 mRNA abundance in the UGS or alter their distribution. Addition of FGF10 protein to UGS organ culture media increased the abundance of UGS basal epithelial cells immunopositive for phosphorylated extracellular signal-regulated kinase (ERK). FGF10 also increased the number of 5-bromo-2'-deoxyuridine (BrdU)-labeled UGS epithelial cells and increased the number of prostatic buds formed per UGS. Addition of TCDD to UGS organ culture media did not alter FGF10-induced ERK activation in UGS basal epithelium but prevented FGF10-induced BrdU incorporation and blocked FGF10-induced prostatic bud formation. These results identify basal urogenital sinus epithelium cells as the key site of FGF10 action during fetal prostate development and suggest that TCDD likely acts downstream of FGFR2 and ERK to restrict UGS epithelial cell proliferation and prevent prostatic bud formation.

Mesenchymal mechanisms in prostate organogenesis

The development of the prostate is dependent upon androgens and stromal-epithelial interactions. Understanding the molecules and mechanisms by which androgens control prostate organogenesis has been a considerable challenge over the past few decades. Similarly, identifying the molecular signals passing between stromal and epithelial cells has been difficult, and consequently understanding how androgens and stromal-epithelial signalling interact is poorly understood. There remains significant uncertainty regarding how androgens control the growth of the prostate, although several pathways have been identified that are required for prostate development or which alter prostate growth. This review will summarize past findings relating to the pathways that might mediate the effects of androgens as well as molecules that act as stromal to epithelial signals in the prostate. It will also examine the approaches used to identify pathways of importance and the historical concepts that have informed these studies. In particular, the question of which mechanisms might be involved in early prostate organogenesis as well as anatomic aspects of organ induction will be described. Finally, models of prostatic development will be proposed and discussed.

A role for notch signaling in stromal survival and differentiation during prostate development

Notch1 signaling is involved in epithelial growth and differentiation of prostate epithelia, and we have examined the role that notch signaling plays in the stroma of the developing prostate. We initially observed expression of delta-like 1 (Dlk1) and Notch2 in gene profiling studies of prostatic mesenchyme, and anticipated that they might be expressed in a key subset of inductive mesenchyme. Using quantitative RT-PCR, Northern blotting, and whole mount in situ hybridization, we confirmed that both Dlk1 and Notch2 mRNAs showed a restricted expression pattern within subsets of the stroma during prostate development. Localization of Dlk1 and Notch2 proteins mirrored the transcript expression, and showed both distinct and overlapping expression patterns within the stroma. Dlk1 and Notch2 were coexpressed in condensed inductive mesenchyme of the ventral mesenchymal pad (VMP), and were partially colocalized in the smooth muscle (SM) layer of the urethral stroma. In addition, Dlk1 was not expressed in SM adjacent to the VMP in female urethra. The function of notch signaling was examined using organ cultures of prostate rudiments and a small molecule inhibitor of notch receptor activity. Inhibition of notch signaling led to a loss of stromal tissue in both prostate and female VMP cultures, suggesting that this pathway was required for stromal survival. Inhibition of notch signaling also led to changes in both epithelial and stromal differentiation, which was evident in altered distributions of SM alpha-actin and p63 in prostates grown in vitro. The effects of notch signaling upon the stroma were only evident in the presence of testosterone, in contrast to effects upon epithelial differentiation.

Retinoic acid induces prostatic bud formation

Formation of prostatic buds from the urogenital sinus (UGS) to initiate prostate development requires localized action of several morphogenetic factors. This report reveals all-trans-retinoic acid (RA) to be a powerful inducer of mouse prostatic budding that is associated with reciprocal changes in expression of two regulators of budding: sonic hedgehog (Shh) and bone morphogenetic protein 4 (Bmp4). Localization of retinoid signaling and expression of RA synthesis, metabolism, and receptor genes in the UGS on embryonic days 14.5-17.5 implicate RA in the mechanism of bud initiation. In UGS organ culture, RA increased prostatic budding, increased Shh expression, and decreased Bmp4. Prostatic budding was stimulated in the absence of RA by recombinant SHH, by blocking BMP4 signaling with NOGGIN, or by combined treatment with SHH and NOGGIN in UGS organ culture media. These observations suggest that reciprocal changes in hedgehog and BMP signaling by RA may regulate bud initiation.

Region-specific growth effects in the developing rat prostate following fetal exposure to estrogenic ultraviolet filters

BACKGROUND AND OBJECTIVES

Exposure to environmental endocrine disruptors is a potential risk factor for humans. Many of these chemicals have been shown to exhibit disruption of normal cellular and developmental processes in animal models. Ultraviolet (UV) filters used as sunscreens in cosmetics have previously been shown to exhibit estrogenic activity in in vitro and in vivo assays. We examined the effects of two UV filters, 4-methylbenzylidene camphor (4-MBC) and 3-benzylidene camphor (3-BC), in the developing prostate of the fetal rat.

METHODS

Pregnant Long Evans rats were fed diets containing doses of 4-MBC and 3-BC that resulted in average daily intakes of these chemicals corresponding to the lowest observed adverse effects level (LOAEL) and the no observed adverse effects level (NOAEL) doses in prior developmental toxicity studies. Using digital photographs of serial sections from postnatal day 1 animals, we identified, contoured, and aligned the epithelial ducts from specific regions of the developing prostate, plus the accessory sex glands and calculated the total volume for each region from three-dimensional, surface-rendered models.

RESULTS

Fetal exposure to 4-MBC (7.0 mg/kg body weight/day) resulted in a significant increase (p < 0.05) in tissue volume in the prostate and accessory sex glands. Treated males exhibited a 62% increase in the number of ducts in the caudal dorsal prostate. Increased distal branching morphogenesis appears to be a consequence of exposure in the ventral region, resulting in a 106% increase in ductal volume.

CONCLUSIONS

4-MBC exposure during development of the male reproductive accessory sex glands exhibited classical growth effects associated with estrogenic endocrine disruptors. The different regional responses suggest that the two developmental processes of ductal outgrowth and branching morphogenesis are affected independently by exposure to the environmental chemicals.

The role of Sox9 in prostate development

The mammalian prostate arises from the urogenital sinus under the influence of testicular androgens. Few factors have been identified to be important in the early stages of prostate development. Here we review the role of the transcription factor Sox9 in prostate development. Sox9 is a member of the Sox gene family that plays an important role during embryogenesis in the cellular differentiation of various tissues, including testicular Sertoli cells, neural crest cells and chondrocytes. This gene is expressed in the epithelia of all mouse prostatic lobes from the initial stages of their development. Mice with a prostate specific deletion of Sox9 showed a lack of ventral prostate development and abnormal anterior prostate differentiation. In depth analysis of these mutant animals suggested that Sox9 is required for the early differentiation of the prostate bud epithelia, consistent with the function of this factor in other developmental processes. These studies also revealed different phases of prostate bud development. These phases were characterized by being dependent on different molecular pathways and having lobe specific properties. Future studies on the identification of pathways regulated by Sox9 will provide insight into the molecular networks required for prostate epithelia differentiation.

Mesenchymal-epithelial interactions: past, present, and future

This review summarizes the history of research on mesenchymal-epithelial interactions in prostatic development from the first studies in 1970 to the present. From this study we have learned that prostatic development requires a reciprocal interaction between epithelium and mesenchyme in which urogenital sinus mesenchyme induces and patterns epithelial development and differentiation, while developing prostatic epithelium induces and patterns mesenchymal differentiation into smooth muscle and other resident cell types in the stroma. Prostatic development requires androgen action mediated by the androgen receptor (AR). Through analysis of tissue recombinants composed of wild-type and AR-null epithelium and mesenchyme, we have learned that many "androgenic effects" on prostatic epithelium do not require epithelial AR, but instead are elicited by the paracrine action of AR-positive mesenchyme. Present and future studies reviewed in this issue deal with the molecular mechanisms in this developmental communication between epithelium and mesenchyme.

Prostate stromal and urogenital sinus mesenchymal cell lines for investigations of stromal-epithelial interactions

Bidirectional signaling between the urogenital sinus epithelium and mesenchyme is an essential element of prostate development that regulates ductal morphogenesis, growth, and differentiation. Comparable interactions between the epithelium and stroma in the adult prostate appear to regulate normal growth homeostasis. Alterations in the stromal-epithelial dialogue that recapitulate features of the mesenchymal-epithelial interactions of development may play a critical role in the development of benign prostatic hyperplasia and in the progression of prostate cancer. For this reason, the mesenchymal-epithelial interactions of development are of considerable interest. In this review, we provide an overview of the mesenchymal contribution to rodent prostate development with an emphasis on the stage just before ductal budding (embryonic day 16; E16) and describe the isolation, characterization and utility of a newly established E16 urogenital sinus mesenchymal cell line.

Prostate development: a historical perspective

The regional anatomy of the human prostate has been debated periodically over the last century with various levels of controversy and agreement, beginning with the concept of lobes and replaced by the current model of zones. During this period a variety of classifications have been proposed, based upon the studies of glandular morphogenesis, responses to hormones or histopathology. The current paradigm suggests that the regional differences seen in the prostate of both animal models and the human are a consequence of specific epithelial-mesenchymal interactions along the cranial-caudal axis of the urogenital sinus. The distinctive regional patterns seen in the rodent prostate and the histological heterogeneity of the human adult gland all point to the modification of the distal portion of the ducts, while the proximal segments retain their spatial relationship to the urethra that was formed during fetal development. This suggests that the early epithelial budding that occurs in utero represents a common, fairly symmetrical pattern of growth in many species, while the regional differences in branching morphogenesis and cytodifferentiation are controlled by the instructional influences of mesenchyme and temporal expression of growth factors. Perturbation of the normal processes involved during critical periods of fetal development during reproductive organ development may also play a role in the susceptibility of the prostate to disease in adulthood. Past descriptions of detailed anatomical studies, which span over a century, have provided much insight into the architecture and processes that form a complex tubulo-alveolar gland. New insights into the ductal detail and the advent of sophisticated analyses of cell-cell interactions and molecular mechanisms controlling pathways of cellular growth, differentiation, and apoptosis will likely lead to new approaches for prevention and therapy of prostatic diseases.

Transcriptional profiling of inductive mesenchyme to identify molecules involved in prostate development and disease

Comparison of SAGE libraries for prostatic inductive mesenchyme and the complete prostatic rudiment revealed 219 transcripts that were enriched in, or specific to, inductive mesenchyme. Further analysis suggested that Scube1 is a novel stromal molecule involved in prostate development and tumorigenesis.

Background

The mesenchymal compartment plays a key role in organogenesis, and cells within the mesenchyme/stroma are a source of potent molecules that control epithelia during development and tumorigenesis. We used serial analysis of gene expression (SAGE) to profile a key subset of prostatic mesenchyme that regulates prostate development and is enriched for growth-regulatory molecules.

Results

SAGE libraries were constructed from prostatic inductive mesenchyme and from the complete prostatic rudiment (including inductive mesenchyme, epithelium, and smooth muscle). By comparing these two SAGE libraries, we generated a list of 219 transcripts that were enriched or specific to inductive mesenchyme and that may act as mesenchymal regulators of organogenesis and tumorigenesis. We identified Scube1 as enriched in inductive mesenchyme from the list of 219 transcripts; also, quantitative RT-PCR and whole-mount in situ hybridization revealed Scube1 to exhibit a highly restricted expression pattern. The expression of Scube1 in a subset of mesenchymal cells suggests a role in prostatic induction and branching morphogenesis. Additionally, Scube1 transcripts were expressed in prostate cancer stromal cells, and were less abundant in cancer associated fibroblasts relative to matched normal prostate fibroblasts.

Conclusion

The use of a precisely defined subset of cells and a back-comparison approach allowed us to identify rare mRNAs that could be overlooked using other approaches. We propose that Scube1 encodes a novel stromal molecule that is involved in prostate development and tumorigenesis.

Sox9 is required for prostate development

The mammalian prostate arises from the urogenital sinus and few factors have been identified to be important in the early stages of prostate development. In this study we show that the transcription factor Sox9 is expressed in the epithelia of all mouse prostatic lobes from the initial stages of their development. We used a conditional approach with mice expressing Cre recombinase under the control of Nkx3.1 regulatory sequences to delete Sox9 from the developing prostate. Mice with a prostate specific deletion of Sox9 showed a lack of ventral prostate development and abnormal anterior prostate differentiation. Analysis of these mutant animals revealed an early loss of expression of genes specific to the prostate epithelia such as Nkx3.1 and Shh and a marked reduction in proliferation in the ventral prostate but not in other lobes. Fgf signalling, through the MAPK pathway, has been shown to be important in prostate development and a lobe specific phenotype was reported for a prostate specific Fgfr2 mutant mouse model. Here we show that the levels of Fgfr2 and Sprouty2, a downstream target of Fgf signalling, were severely reduced in the ventral prostate of Sox9 mutant animals but not in other lobes. Prostate organ culture studies with a Mek inhibitor, U0126, and a Fgf receptor inhibitor, SU5402, indicate that the timing of expression of Cre in the mutant animals could account for the lobe specific phenotype in the Sox9 and Fgfr2 mutants. These studies imply that Sox9 is required for the early differentiation of the prostate bud epithelia.

Androgen-dependent prostate epithelial cell selection by targeting ARR(2)PBneo to the LPB-Tag model of prostate cancer

Cell cultures representing different stages of prostatic carcinoma will be a useful tool allowing a more complete understanding of the role of individual genes in tumorigenesis. We used the androgen-regulated probasin promoter linked to the neomycin phosphotransferase (Neo) gene, to generate the ARR(2)PBneo transgenic mouse model. Development was normal and all six ARR(2)PBneo transgenic founder lines expressed the Neo gene in a prostate-specific manner. Line C, which expressed high levels of neo, was crossbred to LPB-Tag 12T-7f transgenic mice (in which the SV40 large T antigen (Tag) was targeted to the prostate by the large probasin (LPB) promoter). Three bigenic males (carrying both Neo and Tag transgenes) were identified. Prostatic lesions developed in these mice in a predictable and heritable manner, indicating that Neo did not alter Tag-induced prostate tumor development and progression. Three separate NeoTag epithelial cell strains were established from three bigenic mice. G418 selection was used to obtain immortalized epithelial cells in culture. Selected cells expressed the Neo and Tag transgenes, cytokeratins 8 and 18, and were androgen responsive for growth. To determine if these NeoTag cells maintained a similar in vivo phenotype to the 12T-7f transgenic line, tissue recombinations were made with rat urogenital sinus mesenchyme (rUGM) and grafted under the renal capsule of male nude mouse hosts. In recombinants, the three NeoTag strains developed PIN lesions and/or more extensive adenocarcinoma than seen in the 12T-7f mouse. Androgen ablation demonstrated that the grafts were androgen responsive. NeoTag cells grafted without rUGM developed undifferentiated adenocarcinoma demonstrating that prostatic stroma dictates the glandular architecture seen in the well-differentiated adenocarcinoma.

Regulation of urogenital smooth muscle patterning by testosterone and estrogen during prostatic induction

BACKGROUND

Smooth muscle (SM) has been proposed to play an important role in controlling prostate organogenesis by regulating signaling between inductive mesenchyme and developing epithelial prostatic buds.

METHODS

We have examined the effects of testosterone and estrogen upon SM patterning in the embryonic rat urogenital tract (UGT) using in vitro organ cultures, immunohistochemistry, and Western blotting.

RESULTS

We observed that testosterone elicited a sexually dimorphic difference in SM structure of embryonic UGTs, in cultures grown with testosterone. The addition of estrogen led to an increase in the rate of SM closure, in both males and females. To quantify the effects of steroids upon SM we used Western blotting of SM actin, which showed that estrogen stimulated SM content, while testosterone reduced SM content. Finally, we examined the expression of ERalpha, ERbeta, PR, and SM actin under different hormonal treatments of UGTs grown in vitro. The expression patterns of ERalpha and ERbeta were largely unchanged by hormonal treatment, while PR showed a much broader expression pattern in response to estradiol.

CONCLUSIONS

Our results indicate that testosterone can directly regulate SM patterning and content in the UGT, and that SM is sensitive to both androgens and estrogens.

SAGE reveals expression of Wnt signalling pathway members during mouse prostate development

To identify genes and pathways not previously implicated in the mesenchymal-epithelial (M/E) interactions that are critical for normal mouse prostate development, we constructed six serial analysis of gene expression (SAGE) libraries. Bioinformatic analyses revealed expression of various members of numerous signalling pathways and the differential expression of several members of the wingless-related MMTV integration site (Wnt) signalling pathway. This pathway has not been previously implicated in prostate development thus expression of selected Wnt pathway members in the developing prostate was confirmed by RT-qPCR. Of particular interest, an antagonist of the Wnt pathway, secreted frizzled related protein 2 (Sfrp2), was highly expressed in the early prostate libraries and down regulated at later developmental stages. The expression levels of four Wnt ligands reported to interact with Sfrp2 were, therefore, examined by RT-qPCR. We found that only Wnt4 transcripts were detectable in the developing prostate. Expression of Sfrp2 was validated using RT-qPCR and localization of Sfrp2 transcripts and protein was carried out using in situ hybridization and immunofluorescence, respectively. These studies provide the first evidence that Wnt pathway members are expressed in the developing prostate. Functional analyses are now required to establish the biological significance of this observation.

Estrogenic chemicals in plastic and oral contraceptives disrupt development of the fetal mouse prostate and urethra

Exposure of human fetuses to man-made estrogenic chemicals can occur through several sources. For example, fetal exposure to ethinylestradiol occurs because each year approximately 3% of women taking oral contraceptives become pregnant. Exposure to the estrogenic chemical bisphenol A occurs through food and beverages because of significant leaching from polycarbonate plastic products and the lining of cans. We fed pregnant CD-1 mice ethinylestradiol (0.1 microg/kg per day) and bisphenol A (10 microg/kg per day), which are doses below the range of exposure by pregnant women. In male mouse fetuses, both ethinylestradiol and bisphenol A produced an increase in the number and size of dorsolateral prostate ducts and an overall increase in prostate duct volume. Histochemical staining of sections with antibodies to proliferating cell nuclear antigen and mouse keratin 5 indicated that these increases were due to a marked increase in proliferation of basal epithelial cells located in the primary ducts. The urethra was malformed in the colliculus region and was significantly constricted where it enters the bladder, which could contribute to urine flow disorders. These effects were identical to those caused by a similar dose (0.1 microg/kg per day) of the estrogenic drug diethylstilbestrol (DES), a known human developmental teratogen and carcinogen. In contrast, a 2,000-fold higher DES dose completely inhibited dorsolateral prostate duct formation, revealing opposite effects of high and low doses of estrogen. Acceleration in the rate of proliferation of prostate epithelium during fetal life by small amounts of estrogenic chemicals could permanently disrupt cellular control systems and predispose the prostate to disease in adulthood.

Prostate epithelial cell differentiation and its relevance to the understanding of prostate cancer therapies

Prostate cancer is the most common malignancy in males in the western world. However, little is known about its origin and development. This review highlights the biology of the normal prostate gland and the differentiation of basal epithelial cells to a secretory phenotype. Alterations in this differentiation process leading to cancer and androgen-independent disease are discussed, as well as a full characterization of prostate epithelial cells. A full understanding of the origin and characteristics of prostate cancer epithelial cells will be important if we are to develop therapeutic strategies to combat the heterogeneous nature of this disease.

Hormonal, cellular, and molecular regulation of normal and neoplastic prostatic development

This review on normal and neoplastic growth of the prostate emphasizes the importance of epithelial-mesenchymal/stromal interactions. Accordingly, during prostatic development urogenital sinus mesenchyme (a) specifies prostatic epithelial identity, (b) induces epithelial bud formation, (c) elicits prostatic bud growth and regulates ductal branching, (d) promotes differentiation of a secretory epithelium, and (e) specifies the types of secretory proteins expressed. In reciprocal fashion, prostatic epithelium induces smooth muscle differentiation in the mesenchyme. Epithelial-mesenchymal interactions during development continue postnatally into adulthood as stromal-epithelial interactions which play a homeostatic role and in so doing reciprocally maintain epithelial and stromal differentiation and growth-quiescence. Prostatic carcinogenesis involves perturbation of these reciprocal homeostatic cell-cell interactions. The central role of mesenchyme in prostatic epithelial development has been firmly established through analysis of tissue recombinants composed of androgen-receptor-positive wild-type mesenchyme and androgen-receptor-negative epithelium. These studies revealed that at the very least ductal morphogenesis, epithelial cytodifferentiation, epithelial apoptosis and epithelial proliferation are regulated by stromal and not epithelial androgen receptors. Likewise, progression from non-tumorigenesis to tumorigenesis elicited by testosterone plus estradiol proceeds via paracrine mechanisms. Thus, stromal-epithelial interactions play critical roles in the hormonal, cellular, and molecular regulation of normal and neoplastic prostatic development.

Aryl hydrocarbon receptors in urogenital sinus mesenchyme mediate the inhibition of prostatic epithelial bud formation by 2,3,7,8-tetrachlorodibenzo-p-dioxin

In utero exposure of male C57BL/6 mice to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) prevents prostatic epithelial buds from forming in the ventral region of the urogenital sinus (UGS) and reduces the number of buds that form in the dorsolateral region. This inhibition of budding is aryl hydrocarbon receptor (AHR) dependent and appears to be the primary cause of lobe-specific prostate abnormalities in TCDD-exposed mice. TCDD can inhibit prostatic epithelial bud formation by acting directly on the UGS in vitro, but whether it does so via AHR in UGS mesenchyme, epithelium, or both was unknown. To address this issue, UGS mesenchyme and epithelium from gestation day (GD) 15 wild-type C57BL/6J male mice were isolated, recombined, and cultured in vitro for 5 days with 10(-8) M 5alpha-dihydrotestosterone (DHT) and either 10(-9) M TCDD or vehicle. Prostatic epithelial buds were viewed by light microscopy after removal of mesenchyme. Effects depended greatly on which portions of the mesenchyme were used: TCDD had little if any effect when whole UGS epithelium (UGE) was recombined with ventral plus dorsolateral mesenchyme, tended to reduce bud numbers in recombinants made with UGE and dorsolateral mesenchyme, and severely reduced bud numbers in recombinants made with UGE and ventral mesenchyme (VM). [VM + UGE] recombinants prepared from wild-type and AHR knockout (Ahr(-/-)) mice were then cultured with DHT to determine the site of action of TCDD. AHR null mutation alone had no effect on budding. TCDD severely inhibited prostatic epithelial bud formation in recombinants that contained mesenchymal AHR, whereas bud formation was not inhibited by TCDD in recombinants lacking mesenchymal AHR, regardless of epithelial AHR status. These results demonstrate that UGS mesenchyme and not UGS epithelium is the site of action of TCDD. Therefore, the initial events responsible for abnormal UGS (and ultimately prostate) development occur within the UGS mesenchyme, and changes in gene expression in the UGS epithelium responsible for inhibited prostatic budding are secondary to the direct effects of TCDD on UGS mesenchyme.