Region-specific inhibition of prostatic epithelial bud formation in the urogenital sinus of C57BL/6 mice exposed in utero to 2,3,7,8-tetrachlorodibenzo-p-dioxin

In utero 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure causes abnormal ventral, dorsolateral, and anterior prostate development in wild-type but not aryl hydrocarbon receptor (AhR) null mutant C57BL/6 mice. Experiments have now been conducted to test the hypothesis that TCDD causes an AhR-dependent inhibition of the earliest visible stage of prostate development, the formation of prostatic buds by urogenital sinus (UGS) epithelium. A novel method for viewing budding was developed that uses scanning electron microscopy of isolated UGS epithelium instead of three-dimensional reconstruction of serial histological sections of intact UGS. In the initial experiment, the time course for prostatic epithelial bud formation in vehicle- and TCDD-exposed wild-type C57BL/6J mice was determined. A single maternal dose of TCDD (5 mug/kg) on gestation day 13 delayed the appearance of dorsal, lateral, and anterior buds by about one day, reduced dorsolateral bud number, and prevented ventral buds from forming. No such effects were seen in TCDD-exposed AhR null mutant fetuses, while AhR null mutation, alone, had no detectable effect on budding. Treatment of wild-type dams with sufficient 5alpha-dihydrotestosterone (DHT) to masculinize female fetuses failed to protect against the inhibition of budding caused by TCDD. These results demonstrate that in utero TCDD exposure causes an AhR-dependent inhibition of prostatic epithelial bud formation commensurate with its inhibitory effects on ventral and dorsolateral prostate development, and that the inhibition of budding is not due to insufficient DHT. Inhibited bud formation appears to be the primary cause of abnormal prostate development in TCDD-exposed mice.

Beyond homeosis—HOX function in morphogenesis and organogenesis

Hox genes encode conserved transcription factors expressed along the antero-posterior axis of vertebrates and invertebrates. In both phyla, HOX proteins control the formation of specific structures in the segments where they are expressed. Because of the global effect they have on segment morphology, the Hox genes are said to control segment identity. Here we review the data available on how HOX proteins regulate their downstream targets and how they mediate the formation of segment-specific structures. Within the segment, the information provided by HOX proteins, tissue-specific transcription factors, and signaling pathway effectors becomes integrated at the enhancer of the target genes, resulting in their localized activation. In general, HOX proteins regulate the morphogenesis of specific organs indirectly by activating networks of transcription factors and signaling molecules, but they can also directly regulate the so-called realizator genes: genes that control the cell behaviors that induce morphogenesis. Here we review some of the Hox-activated networks, the most interesting realizator genes known to date, and summarize how organogenesis is affected in Hox mutants. These examples reveal that only a fraction of the transformations caused by Hox mutations are in fact homeotic (leading to the morphological transformation of a structure present in one segment into that present in another segment). In the cases where Hox gene mutants do not cause homeotic transformations, the wild-type function of the Hox gene is to activate specific cell behaviors (cell proliferation, survival, shape changes, and rearrangements) that lead to the morphogenesis of particular organs. This second non-homeotic function is common to vertebrates and invertebrates, and we argue that it may actually constitute the original HOX function.

FGF-10 plays an essential role in the growth of the fetal prostate

Induction and branching morphogenesis of the prostate are dependent on androgens, which act via the mesenchyme to induce prostatic epithelial development. One mechanism by which the mesenchyme may regulate the epithelium is through secreted growth factors such as FGF-10. We have examined the male reproductive tract of FGF-10(-/-) mice, and at birth, most of the male secondary sex organs were absent or atrophic, including the prostate, seminal vesicle, bulbourethral gland, and caudal ductus deferens. Rudimentary prostatic buds were occasionally observed in the prostatic anlagen, the urogenital sinus (UGS) of FGF-10(-/-) mice. FGF-10(-/-) testes produced sufficient androgens to induce prostatic development in control UGS organ cultures. Prostatic rudiments from FGF-10(-/-) mice transplanted into intact male hosts grew very little, but showed some signs of prostatic differentiation. In cultures of UGS, the FGF-10 null phenotype was partially reversed by the addition of FGF-10 and testosterone, resulting in the formation of prostatic buds. FGF-10 alone did not stimulate prostatic bud formation in control or FGF-10(-/-) UGS. Thus, FGF-10 appears to act as a growth factor which is required for development of the prostate and several other accessory sex organs.

Mouse urogenital development: a practical approach

A detailed knowledge of the developmental anatomy of the embryonic mouse urogenital tract is required to recognize mutant urogenital phenotypes in transgenic and knock-out mice. Accordingly, the purpose of this article is to review urogenital development in the mouse embryo and to give an illustrated methodological protocol for the dissection of urogenital organ rudiments at 12-13 days of gestation (E12-13) to isolate the urogenital ridge and at E16 to isolate the seminal vesicle, Müllerian duct, Wolffian duct, and prostatic rudiment, the urogenital sinus (UGS). The UGS can be cultured and, in the presence of testosterone, prostatic buds form in vitro. Because of the importance of mesenchymal-epithelial interactions in urogenital development, methods for the isolation of epithelium and mesenchyme from the embryonic urogenital sinus are also described. Urogenital sinus mesenchyme (UGM) and urogenital sinus epithelium (UGE) can be used to construct tissue recombinants that can either be grown in vitro or grafted in vivo for the study of epithelial-mesenchymal interactions in prostatic development.

Bisphenol a induces both transient and permanent histofunctional alterations of the hypothalamic-pituitary-gonadal axis in prenatally exposed male rats

Exposure to bisphenol A (BPA) in utero has been shown to induce alterations in the prostate of 30-d-old Wistar rats. Herein, we examine both the time course of BPA action on the rat prostate and the effects of BPA on the male hypothalamic-pituitary-gonadal axis. This was achieved by exposing rats to BPA in utero, followed by immunohistochemistry and morphometric analysis of prostatic tissue, evaluation of estrogen receptor-alpha (ERalpha) and ERbeta mRNA expression in both the preoptic area (POA) and medial basal hypothalamus, and determination of PRL, LH, and testosterone serum levels. On d 30 (peripubertal period), the prostatic periductal stroma of BPA-exposed rats demonstrated a significantly larger layer of fibroblasts than that of controls, whereas on d 120 (adulthood) no significant differences were observed. Moreover, BPA-exposed rats on d 15 exhibited an increase in stromal cellular proliferation compared with controls. Decreased expression of both androgen receptor in prostatic stromal cells and prostatic acid phosphatase in epithelial cells was observed only on d 30 in BPA-exposed males. BPA did not alter POA ERalpha mRNA expression, whereas a 4-fold increase in POA ERbeta mRNA expression was observed on both d 30 and 120. No alterations were observed in either ERalpha or ERbeta expression in the medial basal hypothalamus. BPA-exposed males exhibited increased PRL levels only on d 30, whereas a transient increase in serum testosterone levels was observed on d 15. These results support the hypothesis that prenatal exposure to environmental doses of BPA induces both transient and permanent age-dependent alterations in the male reproductive axis at different levels.

Laminin alpha-1, alpha-3, and alpha-5 chain expression in human prepubertal [correction of prepubetal] benign prostate glands and adult benign and malignant prostate glands

BACKGROUND

Laminins (Lns) are a family of extracellular matrix glycoproteins located in the basement membrane (BM) of epithelial cells. They exist as heterotrimers composed of an alpha, beta, and gamma chain. Presently, five alpha (alpha1-5), three beta (beta1-3), and three gamma (gamma1-3) chains have been identified with different combinations of these chains resulting in 14 laminin heterotrimers thus far identified (1, 3-5).

METHODS

In this study, using immunohistochemistry with chain-specific antibodies, we characterized the expression of the alpha1 (Lns-1/3), alpha3 (Lns 5,6,7), and alpha5 (Lns 10/11) chains in fetal, newborn, infant, prepubertal, and adult benign and malignant prostate glands.

RESULTS

In general, alpha1 expression was higher in normal fetal prostate glands and declined by full-term birth, whereas the alpha3 and alpha5 chains remained highly expressed in the adult normal glands. In carcinoma alpha1 (Lns 1/3) and alpha5 (Lns 5,6,7) are lost, whereas alpha5 (Lns 10/11) persists.

CONCLUSIONS

Alpha 1 (Lns 1/3) is prominent in BM, but is replaced by a laminin matrix rich in alpha3 (Lns 5,6,7) and alpha5 (Lns 10/11) in benign adult prostate glands. In carcinoma, both alpha1 (Lns-1/3) and alpha3 (Lns 5,6,7) are not expressed with persistence of a BM rich in alpha5 (Lns 10/11).

Spontaneous mutation in mice provides new insight into the genetic mechanisms that pattern the seminal vesicles and prostate gland

The seminal vesicles and prostate gland are anatomically adjacent male sex-accessory glands. Although they arise from different embryonic precursor structures and express distinct sets of secretory proteins, these organs share common features in their developmental biology. A key shared developmental feature is the elaboration of complex secretory epithelia with tremendous surface area from simple precursor structures with juxtaposed epithelial and mesenchymal cells. In this study, new insight into the nature of the biological processes that underlie glandular morphogenesis is achieved by analyzing the phenotypes present in mice that harbor a spontaneous mutation, seminal vesicle shape (svs), previously identified for causing altered seminal vesicle morphology in adults. An examination of seminal vesicle development in svs mice provides the first evidence that the concurrent processes of epithelial branching and epithelial infolding are distinct processes under separate genetic control. It also provides the first direct evidence that the thickness and topology of the smooth muscle layer in the seminal vesicles are determined by interaction with the glandular epithelium during the branching process. In addition, the seminal vesicle phenotype in svs mice is shown to phenocopy the morphologic form present in certain other mammals such as the guinea pig, raising the possibility that the svs mutation is the sort of variant that arises during evolution. By also including an investigation of the prostate gland, this study also identifies previously unrecognized phenotypes in svs prostates, including increased gland size and dramatically reduced levels of branching morphogenesis. Finally, this study advances the goal of identifying the svs gene by mapping the svs mutation relative to known molecular markers and testing Fgfr2 as a candidate gene. The finding that the svs mutation maps to a genomic region syntenic to a region frequently deleted in human prostate tumors, together with the prostatic phenotype present in svs mice, further raises the interesting possibility that the svs mutation will identify a candidate prostate tumor suppressor gene.

Loss of CD38 correlates with simultaneous up-regulation of human leukocyte antigen-DR in benign prostatic glands, but not in fetal or androgen-ablated glands, and is strongly related to gland atrophy

OBJECTIVE

To determine whether CD38 loss in benign and malignant prostatic disease is related to human leukocyte antigen (HLA)-DR up-regulation, by assessing the histopathology of the prostate and the effect of androgen deprivation.

MATERIALS AND METHODS

Serial sections of frozen fetal (eight), infant (six), normal adult (10), benign hyperplastic (BPH, 24), and primary (10) and hormone-treated (11) carcinomatous human prostatic tissues were analysed by immunohistology for anti-CD38 and HLA-DR antigens.

RESULTS

In BPH samples there was a significant correlation between CD38 loss (mean 21% of acini) and HLA-DR up-regulation (mean 20%; P < 0.001). Moreover, 76% of all CD38-negative acini in BPH had HLA-DR up-regulation in the same prostate epithelial cells, predominantly in atrophic and cystic glands, and in cells with retained secretions (74%). In contrast to the uniform expression in normal adult prostate, CD38 was negative or partly expressed in fetal acini (mean 19%) and almost completely negative in acini of the early infant period (mean 0.7%). In contrast to BPH, cancer cells did not selectively up-regulate HLA-DR when CD38 was lost. In patients with cancer treated by androgen deprivation, cancer cells were CD38-negative.

CONCLUSIONS

The absence of CD38 and presence of HLA-DR expression in prostatic epithelium is consistent in BPH and tissue surrounding tumour, and strongly related to gland atrophy. This is particularly interesting as HLA-DR triggering can induce apoptosis of cells, whereas CD38 prevents it. A permissive role for androgens to maintain full CD38 expression in epithelial cells is suggested.

Hormonal, cellular, and molecular control of prostatic development

The prostate is a male accessory sex gland found only in mammals that functions to produce a major fraction of seminal fluid. Interest in understanding the biology of the prostate is driven both by the fascinating nature of the developmental processes that give rise to the prostate and by the high incidence in humans of prostatic diseases, including prostatic adenocarcinoma and benign prostatic hyperplasia. This review summarizes the current state of knowledge of the cellular and molecular processes that control prostatic development. Insight into the mechanisms that control prostatic development has come from experimental embryological work as well as from the study of mice and humans harboring mutations that alter prostatic development. These studies have demonstrated a requirement for androgens throughout prostatic development and have revealed a series of reciprocal paracrine signals between the developing prostatic epithelium and prostatic mesenchyme. Finally, these studies have identified several specific gene products that are required for prostatic development. While research in recent years has greatly enhanced our understanding of the molecular control of prostatic development, known genes cannot yet explain in molecular terms the complex biological interactions that descriptive and experimental embryological studies have elucidated in the control of prostatic development.

Prostate Development and Carcinogenesis

The process involved in the development and carcinogenesis of the prostate gland is complex. During early prostate development, the androgenic hormone from embryonic testicles is required for ductal formation, growth, and branching morphogenesis of the prostate gland. From this early stage, interactions between the epithelium and mesenchyme become firmly established through paracrine influence (i.e., growth factors) from mesenchyme (stroma), in response to testosterone, acting on epithelium to stimulate its proliferation, morphogenetic differentiation, and function. In return, the epithelium also exerts its paracrine effects on mesenchyme by regulating the differentiation and specific organizational pattern of its stromal smooth muscle. In a normal adult prostate, the maintenance of normal glandular structure and function is dependent not only on the constant presence of testosterone, but also on a normal intact and stable stroma. This chapter will concentrate first on factors involved in the normal development of the prostate gland and then on the aberrant changes in the homeostatic balance arising either from within (i.e., mutations) or outside (i.e., changes in hormonal balance) that result in derangements of the prostate gland. Finally, environmental and genetic factors that lead to prostate carcinogenesis including activation of oncogenes and mutations of tumor suppressor genes are also discussed.

Role of stroma in carcinogenesis of the prostate

Prostatic development is induced by androgens acting via mesenchymal-epithelial interactions. Androgens elicit their morphogenetic effects by acting through androgen receptors (ARs) in urogenital sinus mesenchyme (UGM), which induces prostatic epithelial development. In adulthood reciprocal homeostatic stromal-epithelial interactions maintain functional differentiation and growth-quiescence. Testosterone plus estradiol (T+E2) have been shown to induce prostatic carcinogenesis in animal models. Thus, tissue recombinant studies were undertaken to explore the mechanisms of prostatic carcinogenesis in BPH-1 cells in which ARs and estrogen receptors (ERs) are undetectable. For this purpose, BPH-1 cells were combined with UGM, and the UGM+BPH-1 recombinants were grafted to adult male hosts. Solid branched epithelial cords and ductal structures formed in untreated UGM+BPH-1 recombinants. Growth was modest, and tumors did not develop. UGM+BPH-1 recombinants treated with T+E2 formed invasive carcinomas. BPH-1 cells lack ARs and ERs, whereas rat UGM expresses both of these receptors. These data show that immortalized nontumorigenic human prostatic epithelial cells can undergo hormonal carcinogenesis in response to T+E2 stimulation via paracrine mechanisms and demonstrate that the stromal environment plays an important role in mediating hormonal carcinogenesis. During prostatic carcinogenesis the stroma undergoes progressive loss of smooth muscle with the appearance of carcinoma-associated fibroblasts (CAF). This altered stroma was tested for its ability to promote carcinogenesis of nontumorigenic but immortalized human prostatic epithelial cells (BPH-1). CAF+BPH-1 tissue recombinants formed large carcinomas. In contrast, recombinants composed of normal prostatic stroma+BPH-1 cells exhibited minimal growth. This stroma-induced malignant transformation was associated with additional genetic alterations and changes in gene expression. Thus, alteration in the stromal microenvironment was sufficient to promote malignant transformation of human prostatic epithelial cells.

In utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin in the C57BL/6J mouse prostate: lobe-specific effects on branching morphogenesis

Branching morphogenesis is an essential component of prostate development. This study was conducted to test the hypothesis that in utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure differentially inhibits branching morphogenesis and ductal canalization in the ventral, dorsal, lateral, and anterior mouse prostate. Pregnant C57BL/6J mice were given TCDD (5 microg/kg, orally) or vehicle on gestation day (GD) 13 and their pups examined at 1, 7, 14, 21, 35, and 90 days of age. Prostate lobes were microdissected after incubation in 0.5% collagenase and the numbers of ductal tips, main ducts, and ductal tips per main duct were determined by examining photographs of microdissected, whole-mount specimens. Ductal canalization was determined using histological sections of the dorsolateral and anterior prostate lobes. TCDD inhibited branching morphogenesis in all prostate lobes. The ventral prostate (VP) was extremely small throughout development and never developed any ductal structure. TCDD reduced the numbers of ductal tips and main ducts in the dorsal (DP) and lateral prostate (LP), but reductions in ductal tip numbers appeared to result entirely from reductions in the number of main ducts. Dorsolateral prostate (DLP) weights were slightly reduced by TCDD, but there was no effect on ductal canalization in the dorsal, lateral, or anterior lobes. TCDD had no effect on main duct number in the anterior prostate, but weight, ductal tip number, and the number of ductal tips per main duct was substantially reduced. These results demonstrate that the severe inhibition in ventral prostate development caused by in utero and lactational TCDD exposure is accompanied by a complete absence of branching morphogenesis. The impairment in dorsal, lateral, and anterior prostate (AP) development is associated with a lobe-specific inhibition of the various processes involved in duct formation.

The human prostate expresses sonic hedgehog during fetal development

PURPOSE

The keynote event of prostate ductal development is the formation of epithelial buds that invade the urogenital sinus mesenchyma. Studies in mice have shown that budding requires the signaling peptide, which is expressed in the epithelium of the prostatic anlagen. We report our characterization of (SHH) expression in the human fetal prostate.

MATERIALS AND METHODS

Reverse transcriptase-polymerase chain reaction was performed in fetal prostate RNA isolated at 15.5 and 18 weeks of gestation, respectively. Immunostaining was performed on sections from 7 male fetuses at 9.5 to 34 and in 4 female fetuses at 9 to 18 weeks of gestation.

RESULTS

Weak staining for was seen in the prostatic urethra at 9.5 weeks. Intense staining was seen at 11.5 and 13 weeks in the prostatic urothelium and nascent prostatic buds. Staining was slightly diminished at 16.5, further diminished at 18 to 20 and absent at 34 weeks. expression at 15.5 and 18 weeks was confirmed by reverse transcriptase-polymerase chain reaction assay of freshly isolated prostate tissue. Comparative immunostaining in the female showed urothelial staining at 9 and 12 weeks with staining greatest above the entrance of the müllerian ducts. Staining diminished earlier in the female (14 weeks) than in the male and was almost absent at 18 weeks.

CONCLUSIONS

expression in the human fetal prostate is contemporaneous with the fetal testosterone surge and with ductal budding of the prostatic urothelium. expression is also present in the female urogenital sinus but in the absence of testosterone it is not associated with ductal budding.

Do different branching epithelia use a conserved developmental mechanism?

Formation of branching epithelial trees from unbranched precursors is a common process in animal organogenesis. In humans, for example, this process gives rise to the airways of the lungs, the urine-collecting ducts of the kidneys and the excretory epithelia of the mammary, prostate and salivary glands. Branching in these different organs, and in different animal classes and phyla, is morphologically similar enough to suggest that they might use a conserved developmental programme, while being dissimilar enough not to make it obviously certain that they do. In this article, I review recent discoveries about the molecular regulation of branching morphogenesis in the best-studied systems, and present evidence for and against the idea of there being a highly conserved mechanism. Overall, I come to the tentative conclusion that key mechanisms are highly conserved, at least within vertebrates, but acknowledge that more work needs to be done before the case is proved beyond reasonable doubt.

Sonic hedgehog activates mesenchymal Gli1 expression during prostate ductal bud formation

Ductal budding in the developing prostate is a testosterone-dependent event that involves signaling between the urogenital sinus epithelium (UGE) and urogenital sinus mesenchyme (UGM). We show here that ductal bud formation is associated with focused expression of Sonic hedgehog (Shh) in the epithelium of nascent prostate buds and in the growing tips of elongating prostate ducts. This pattern of localized Shh expression occurs in response to testosterone stimulation. The gene for the Shh receptor, Ptc1, is expressed in the UGM, as are the members of the Gli gene family of transcriptional regulators (Gli1, Gli2, and Gli3). Expression of Ptc1, Gli1, and Gli2 is localized primarily to mesenchyme surrounding prostate buds, whereas Gli3 is expressed diffusely throughout the UGM. A strong dependence of Gli1 (and Ptc1) expression on Shh signaling is demonstrated by induction of expression in both the intact urogenital sinus and the isolated UGM by exogenous SHH peptide. A similar dependence of Gli2 and Gli3 expression on Shh is not observed. Nonetheless, the chemical inhibitor of Shh signaling, cyclopamine, produced a graded inhibition of Gli gene expression (Gli1>Gli2>Gli3) in urogenital sinus explants that was paralleled by a severe inhibition of ductal budding.

Critical windows of vulnerability for effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on prostate and seminal vesicle development in C57BL/6 mice

A single maternal dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on gestation day (GD) 13 can greatly impair ventral prostate, dorsolateral prostate, anterior prostate, and seminal vesicle development in wild-type C57BL/6 mice. The developmental stages at which these organs are most sensitive to TCDD exposure have now been investigated. Pregnant mice were dosed orally with 5 micro g TCDD/kg or vehicle on GD 13, and their pups were fostered at birth to dams of the same treatment or cross-fostered to dams of the opposite treatment. Additional males had in utero and lactational TCDD exposure following maternal dosing on GD 16. Organ weights and secretory protein, cytokeratin 8, and cyclophilin mRNA expression were determined at 35 days of age. Effects of TCDD on ventral prostate development were due primarily to in utero exposure; the critical window was between GD 13 and birth. Dorsolateral prostate development was inhibited about equally by in utero or lactational exposure, and vulnerability did not begin until GD 16. Anterior prostate development was also affected by both in utero and lactational TCDD exposure, particularly the former. Vulnerability began before GD 16 and continued into postnatal life. Seminal vesicle development was essentially unaffected by in utero or lactational exposure alone but was significantly inhibited by combined exposure, regardless of whether dams were dosed on GD 13 or 16. In summary, the time during which each organ was most vulnerable to TCDD exposure varied from one organ to another. These findings provide insights into the developmental processes that TCDD inhibits in each organ, and demonstrate that TCDD inhibits ventral prostate development before this organ first appears, presumably via effects on the urogenital sinus. The observation that in utero TCDD exposure (alone) inhibited development of each prostate lobe is significant because previous studies have shown that little TCDD is transmitted to mice before birth.

Effects of oestrogen treatment on testicular descent, inguinal closure and prostatic development in a male marsupial, Macropus eugenii

This study reports the effect of oestrogen treatment on the development of the genital ducts, prostate gland, testicular descent and inguinal canal closure in male tammar wallaby young treated with oestrogen over four time spans during the first 25 days of pouch life (days 0-10, 10-15, 15-25 and 0-25) and sampled at day 50. In control males, the Müllerian ducts had regressed and the Wolffian ducts had developed into the vas deferens and epididymis. The prostate gland had formed epithelial buds extending from the ventral, lateral and posterior walls of the urethra. The testes were in the neck of the scrotum and the gubernaculum and processus vaginalis were present at the base of the scrotum. In most males treated with oestradiol from day 0 to day 25, the testes had failed to descend by day 50. The gubernaculae were long and thin. The retained Müllerian ducts formed a lateral vaginal expansion like that of normal day 50 females. The Wolffian ducts of the males treated on days 0-25 were regressed, but were present in males in the other three treatment groups. The prostate glands were hyperplastic and epithelial budding was highly invasive. Some treated males from the day 10-25 and 0-25 groups had inguinal hernias. These results demonstrate that oestrogen treatment has profound effects on the development of the internal genitalia of a male marsupial, preventing inguinal closure and interfering with testicular descent. Therefore, the tammar wallaby may provide a useful experimental model animal in which to investigate the hormonal control of testicular migration and closure of the inguinal canal.

Expression of estrogen receptor beta in the fetal, neonatal, and prepubertal human prostate

BACKGROUND

Although androgens have long been implicated in the development, regulation, and pathophysiology of the prostate, evidence suggests that estrogens may also affect these processes. Specifically, estrogens have been shown to influence the development of the fetal and neonatal rodent prostate and to induce a pathognomonic change, termed squamous metaplasia, in the developing and adult prostate. Studies have been inconclusive, however, as to whether estrogens enhance or restrain the growth of the gland. Although the fetal rodent prostate has been reported to contain both estrogen receptor alpha (ER-alpha) and beta (ER-beta), there have been no reports as to whether either of the ER subtypes is expressed in the developing human prostate.

METHODS

In the present study, we used a novel antibody, directed against a unique sequence in the F domain of ER-beta, and laser capture microdissection/reverse transcriptase-polymerase chain reaction to study the expression of the receptor in the fetal, neonatal, and prepubertal human prostate. Results were compared with the expression of ER-alpha, androgen receptor (AR), prostatic acid phosphatase (PAP), prostate specific antigen (PSA), high molecular weight cytokeratin (HMCK), and the proliferative marker Ki67.

RESULTS

For the first time, we report that ER-beta is the only estrogen receptor detected at the protein level in the morphologically normal developing human fetal prostate. By midgestation, strong immunostaining for ER-beta was detected in the nuclei of nearly 100% of epithelial and in the majority of stromal cells. This pattern of expression was evident in the fetal, neonatal, and early prepubertal prostate. However, by 11 years postnatal, staining for the receptor became restricted primarily to the basal epithelial and stromal compartments, a pattern analogous to that observed in the normal adult gland. ER-alpha mRNA was present in microdissected stroma of the fetal gland. Although ER-alpha was not immunodetected in any morphologically normal fetal epithelial or stromal cells, weak staining for the receptor, however, was found in some examples of squamous metaplasia, suggesting the role of alpha-subtype in this lesion. ER-alpha was clearly visualized immunohistochemically at 1 month of postnatal development where it was then localized exclusively in periacinar stromal nuclei, which suggests that it may exert paracrine influences on further prostatic glandular development. Interestingly, the expression of ER-beta early in prostatic development occurred coincident with both the increasing rate of epithelial cell proliferation, observed in the first half of gestation, and the reported high levels of estrogen in the gland from midgestation until term. Paradoxically, however, staining for the receptor remained intense, despite the dramatic decrease in Ki67 labeling observed in the second half of gestation.

CONCLUSION

Our results indicate that the effects of estrogens on the growth of the human fetal prostate are mediated primarily by ER-beta but that ER-alpha contributes to postnatal glandular development. Furthermore, these results suggest that ER-beta, possibly in concert with androgens, may mediate diverse effects on prostate epithelial proliferation by first promoting cell expansion early in gestation, and then acting to limit growth later in prostatic development.

The role of smooth muscle in regulating prostatic induction

We have examined the role that smooth muscle plays during prostatic organogenesis and propose that differentiation of a smooth muscle layer regulates prostatic induction by controlling mesenchymal/epithelial interactions. During development of the rat reproductive tract, an area of condensed mesenchyme involved in prostatic organogenesis is formed. This mesenchyme (the ventral mesenchymal pad, VMP) is found in both males and females, yet only males develop a prostate. We demonstrate that a layer of smooth muscle differentiates between the VMP and the urethral epithelium, and that there is a sexually dimorphic difference in the development of this layer. Serial section reconstruction showed that the layer formed at approximately embryonic day 20.5 in females, but did not form in males. In cultures of female reproductive tracts, testosterone was able to regulate the thickness of this layer resulting in a 2.4-fold reduction in thickness. We observed that prostatic buds were present in some female reproductive tracts, and determined that testosterone was able to stimulate prostatic organogenesis, depending upon the bud position relative to the smooth muscle layer. In vitro recombination experiments demonstrated that direct contact with the VMP led to the induction of very few epithelial buds, and that androgens dramatically increased bud development. Taken together, our data suggest that differentiation of a smooth muscle layer regulates signalling between mesenchyme and epithelium, and comprises part of the mechanism regulating prostatic induction.

5alpha-reductase activity in the prostate

The prostate gland depends on androgen stimulation for its development and growth. However, testosterone is not the major androgen responsible for growth of the prostate. Testosterone is converted to dihydrotestosterone (DHT) by the enzyme Delta(4), 3 ketosteroid, 5alpha-reductase in prostatic stromal and basal cells. DHT is primarily responsible for prostate development and the pathogenesis of benign prostatic hyperplasia (BPH). Inhibitors of 5alpha-reductase reduce prostate size by 20% to 30%. This reduction in glandular tissue is achieved by the induction of apoptosis, which is histologically manifested by ductal atrophy. Inhibition also diminishes the number of blood vessels in the prostate because of a reduction in vascular-derived endothelial growth factor. 5alpha-Reductase occurs as 2 isozymes, type 1 and type 2, with the prostate expressing predominantly the type-2 isozyme, and the liver and skin expressing primarily the type-1 isozyme. Patients have been identified with deficiencies in the type-2 5alpha-reductase, but not type 1. Knockout mice with the type-2 5alpha-reductase demonstrate a phenotype similar to that seen in men with 5alpha-reductase deficiency. Type-1 5alpha-reductase knockout male mice are phenotypically normal. Enzymatic activity for 5alpha-reductase or immunohistochemical detection has been noted in other genitourinary tissues, such as the epididymis, testes, gubernaculum, and corporal cavernosal tissue. Preputial skin predominately expresses the type-1 5alpha-reductase, whereas stromal cells in the seminal vesicle also express type-2 isozyme. However, epithelial cells in the epididymis, but not surrounding stroma, express type-1 5alpha-reductase. In addition to influencing prostatic growth, 5alpha-reductase also influences the expression of neuronal nitric-oxide synthase in the corpus cavernosum. The contribution of DHT in the serum, which is partially derived from type-1 5alpha-reductase in the liver and the small amount of type-1 5alpha-reductase in the prostate, may play a role in maintaining prostatic enlargement. Thus, in an effort to increase efficacy of treatment for BPH, clinical trials are under way using new drugs, such as GI-198745 (Glaxo-Wellcome, Research Triangle Park, NC), PNU 157706 (Pharmacia & Upjohn, Peapack, NJ), FR146687 (Fujisawa, Osaka, Japan), and LY 320236 (Lilly, Indianapolis, IN), which inhibit both the type-1 and type-2 5alpha-reductase.

Cell differentiation lineage in the prostate

Prostatic epithelium consists mainly of luminal and basal cells, which are presumed to differentiate from common progenitor/stem cells. We hypothesize that progenitor/stem cells are highly concentrated in the embryonic urogenital sinus epithelium from which prostatic epithelial buds develop. We further hypothesize that these epithelial progenitor/stem cells are also present within the basal compartment of adult prostatic epithelium and that the spectrum of differentiation markers of embryonic and adult progenitor/stem cells will be similar. The present study demonstrates that the majority of cells in embryonic urogenital sinus epithelium and developing prostatic epithelium (rat, mouse, and human) co-expressed luminal cytokeratins 8 and 18 (CK8, CK18), the basal cell cytokeratins (CK14, CK5), p63, and the so-called transitional or intermediate cell markers, cytokeratin 19 (CK19) and glutathione-S-transferase-pi (GSTpi). The majority of luminal cells in adult rodent and human prostates only expressed luminal markers (CK8, CK18), while the basal epithelial cell compartment contained several distinct subpopulations. In the adult prostate, the predominant basal epithelial subpopulation expressed the classical basal cell markers (CK5, CK14, p63) as well as CK19 and GSTpi. However, a small fraction of adult prostatic basal epithelial cells co-expressed the full spectrum of basal and luminal epithelial cell markers (CK5, CK14, CK8, CK18, CK19, p63, GSTpi). This adult prostatic basal epithelial cell subpopulation, thus, exhibited a cell differentiation marker profile similar to that expressed in embryonic urogenital sinus epithelium. These rare adult prostatic basal epithelial cells are proposed to be the progenitor/stem cell population. Thus, we propose that at all stages (embryonic to adult) prostatic epithelial progenitor/stem cells maintain a differentiation marker profile similar to that of the original embryonic progenitor of the prostate, namely urogenital sinus epithelium. Adult progenitor/stem cells co-express both luminal cell, basal cell, and intermediate cell markers. These progenitor/stem cells differentiate into mature luminal cells by maintaining CK8 and CK18, and losing all other makers. Progenitor/stem cells also give rise to mature basal cells by maintaining CK5, CK14, p63, CK19, and GSTpi and losing K8 and K18. Thus, adult prostate basal and luminal cells are proposed to be derived from a common pleuripotent progenitor/stem cell in the basal compartment that maintains its embryonic profile of differentiation markers from embryonic to adult stages.

Activins as regulators of branching morphogenesis

Development of glandular organs such as the kidney, lung, and prostate involves the process of branching morphogenesis. The developing organ begins as an epithelial bud that invades the surrounding mesenchyme, projecting dividing epithelial cords or tubes away from the site of initiation. This is a tightly regulated process that requires complex epithelial-mesenchymal interactions, resulting in a three-dimensional treelike structure. We propose that activins are key growth and differentiation factors during this process. The purpose of this review is to examine the direct, indirect, and correlative lines of evidence to support this hypothesis. The expression of activins is reviewed together with the effect of activins and follistatins in the development of branched organs. We demonstrate that activin has both negative and positive effects on cell growth during branching morphogenesis, highlighting the complex nature of activin in the regulation of proliferation and differentiation. We propose potential mechanisms for the way in which activins modify branching and address the issue of whether activin is a regulator of branching morphogenesis.

Proliferative activity and branching morphogenesis in the human prostate: a closer look at pre- and postnatal prostate growth

BACKGROUND

To gain further insight into the molecular cell biologic features of prostate development, we investigated the proliferative activity of prostate epithelial and stromal cells and their topographic relationship with neuroendocrine (NE) cell distribution and regional heterogeneity.

METHODS

Consecutive sections from 43 prostates taken during autopsy representing fetuses (12-38 weeks of gestation), infants, prepubertal males and adults were double stained for chromogranin A and MIB-1. MIB-1 labeling index (LI) was calculated in the budding tips, forming acini, major collecting ducts, adjacent and non-adjacent stromal compartments. Furthermore, the topographic relationship between proliferating cells and NE cells was evaluated.

RESULTS

In the first half of gestation, cell proliferation as revealed by MIB-1 LI was significantly higher in epithelial structures and stroma than in older fetuses and other age groups. MIB-1 LI was higher in budding tips than in other epithelial regions. MIB-1 LI in stroma adjacent to budding tips was not higher than that adjacent to other epithelial branching segments. Co-expression of chromogranin A and MIB-1 staining was not observed. MIB-1 LI was lower in cells in the direct vicinity of chromogranin A positive NE cells than at a distance from NE cells.

CONCLUSIONS

Prostate development in the first half of gestation is explosive. Thereafter, the prostate basically is a slow-growing organ. Budding tips are the major growth foci during early prostate development, while stromal growth is evenly distributed throughout the prostate, probably indicating that stromal-epithelial interactions do not manifest in enhanced proliferation at their interface. NE cells may have an inhibitory effect on proliferation of exocrine epithelial cells and are probably only associated with differentiation of prostate exocrine cells in the prostate.

Regulation of prostate branching morphogenesis by activin A and follistatin

Ventral prostate development occurs by branching morphogenesis and is an androgen-dependent process modulated by growth factors. Many growth factors have been implicated in branching morphogenesis including activins (dimers of beta(A) and beta(B) subunits); activin A inhibited branching of lung and kidney in vitro. Our aim was to examine the role of activins on prostatic development in vitro and their localization in vivo. Organ culture of day 0 rat ventral prostates for 6 days with activin A (+/- testosterone) inhibited prostatic branching and growth without increasing apoptosis. The activin-binding protein follistatin increased branching in vitro in the absence (but not presence) of testosterone, suggesting endogenous activins may reduce prostatic branching morphogenesis. In vivo, inhibin alpha subunit was not expressed until puberty, therefore inhibins (dimers of alpha and beta subunits) are not involved in prostatic development. Activin beta(A) was immunolocalized to developing prostatic epithelium and mesenchymal aggregates at ductal tips. Activin beta(B) immunoreactivity was weak during development, but was upregulated in prostatic epithelium during puberty. Activin receptors were expressed throughout the prostatic epithelium. Follistatin mRNA and protein were expressed throughout the prostatic epithelium. The in vitro evidence that activin and follistatin have opposing effects on ductal branching suggests a role for activin as a negative regulator of prostatic ductal branching morphogenesis.

Novel expression patterns of the myc/max/mad transcription factor network in developing murine prostate gland

PURPOSE

Expression of myc proto-oncogenes and myc-antagonizing mad/mxi genes typically predominate in proliferating versus differentiating cells, respectively. C-myc expression in prostate cells is well established but to our knowledge that of several recently discovered mad/mxi genes is completely uncharacterized. Such characterization is particularly relevant because mxi1 is lost or mutated in some human prostate tumors and mouse mxi1-null mutants show prostatic hyperplasia.

MATERIALS AND METHODS

Developing murine prostatic lobes at select postnatal days 1 to 28 were analyzed by in situ immunohistochemical and in vitro RNA analysis. The expression patterns of the 3 myc genes c-, L- and N-myc, and the mad1, mxi1 and mad4 genes were studied in most detail with nonradioactive in situ and immunohistochemical analyses.

RESULTS

We describe what is to our knowledge previously unreported expression of N- and L-myc in the prostate with particularly the latter strongly expressed throughout development. High c-myc expression was lost at day 7 with re-elevation at day 14, followed by subsequent low expression, representing a unique in vivo confirmation of c-myc expression changes seen previously in several in vitro differentiation systems. The alternatively spliced weak and strong repressor mxi1 isoforms showed distinct, partially overlapping expression patterns. Of particular interest were continual mad1 and mad4 expression during the proliferative and differentiative phases. Similarly mad1 was evident in proliferating normal prostate cell cultures but not in tumor cell lines, suggesting that mad1 expression in prostate may be clinically relevant.

CONCLUSIONS

Myc network expression in developing mouse prostate is novel and does not completely fit previous simpler models of Myc versus Mad expression based on other cell types.