The role of Fgf10 signaling in branching morphogenesis and gene expression of the rat prostate gland: lobe-specific suppression by neonatal estrogens

Brief exposure of rats to high-dose estrogen during the neonatal period interrupts prostate development in a lobe-specific manner and predisposes the gland to dysplasia with aging, a phenomenon referred to as developmental estrogenization. Our previous studies have revealed that these effects are initiated through altered steroid receptor expression; however, the immediate downstream targets remain unclear. We have recently shown that developmental expression of Shh-ptc-gli is downregulated in the dorsolateral prostate following estrogenization, and this is responsible, in part, for branching deficits observed in that prostatic region specifically. In the present study, we examine the role of Fgf10 signaling during rat prostate development and as a mediator of the developmental estrogenized phenotype. Fgf10 and FgfR2iiib localize to the distal signaling center of elongating and branching ducts in separate prostate lobes where they regulate the expression of multiple morphoregulatory genes including Shh, ptc, Bmp7, Bmp4, Hoxb13, and Nkx3.1. Ventral and lateral lobe organ cultures and mesenchyme-free ductal cultures demonstrate a direct role for Fgf10/FgfR2iiib in ductal elongation, branching, epithelial proliferation, and differentiation. Based on these findings, a model is proposed depicting the localized expression and feedback loops between several morphoregulatory factors in the developing prostate that contribute to tightly regulated branching morphogenesis. Similar to Shh-ptc-gli, neonatal estrogen exposure downregulates Fgf10, FgfR2iiib, and Bmp7 expression in the dorsolateral prostate while ventral lobe expression of these genes is unaffected. Lateral prostate organ culture experiments demonstrate that growth and branching inhibition as well as Fgf10/FgfR2iiib suppression are mediated directly at the prostatic level. Furthermore, exogenous Fgf10 fully rescues the growth and branching deficits due to estrogen exposure. Together, these studies demonstrate that alterations in Fgf10 signaling are a proximate cause of Shh-ptc-gli and Bmp7 downregulation that together result in branching inhibition of the dorsolateral prostate following neonatal estrogen exposure.     

The role of Wnt5a in prostate gland development

The Wnt genes encode a large family of secreted glycoproteins that play important roles in controlling tissue patterning, cell fate and proliferation during development. Currently, little is known regarding the role(s) of Wnt genes during prostate gland development. The present study examines the role of the noncanonical Wnt5a during prostate gland development in rat and murine models. In the rat prostate, Wnt5a mRNA is expressed by distal mesenchyme during the budding stage and localizes to periductal mesenchymal cells with an increasing proximal-to-distal gradient during branching morphogenesis. Wnt5a protein is secreted and localizes to periductal stroma, extracellular matrix and epithelial cells in the distal ducts. While Wnt5a expression is high during active morphogenesis in all prostate lobes, ventral prostate (VP) expression declines rapidly following morphogenesis while dorsal (DP) and lateral lobe (LP) expression remains high into adulthood. Steroids modulate prostatic Wnt5a expression during early development with testosterone suppressing Wnt5a and neonatal estrogen increasing expression. In vivo and ex vivo analyses of developing mouse and rat prostates were used to assess the functional roles of Wnt5a. Wnt5a^−/− murine prostates rescued by organ culture exhibit disturbances in bud position and directed outgrowth leading to large bulbous sacs in place of elongating ducts. In contrast, epithelial cell proliferation, ductal elongation and branchpoint formation are suppressed in newborn rat prostates cultured with exogenous Wnt5a protein. While renal grafts of Wnt5a^−/− murine prostates revealed that Wnt5a is not essential for cyto- and functional differentiation, a role in luminal cell polarity and lumenization of the ducts was indicated. Wnt5a suppresses prostatic Shh expression while Shh stimulates Wnt5a expression in a lobe-specific manner during early development indicating that Wnt5a participates in cross-talk with other members of the gene regulatory network that control prostate development. Although Wnt5a does not influence prostatic expression of other Wnt morphogens, it suppresses Wif-1 expression and can thus indirectly modulate Wnt signaling. In summary, the present finds demonstrate that Wnt5a is essential for normal prostate development where it regulates bud outgrowth, ductal elongation, branching, cell polarity and lumenization. These findings contribute to the growing body of knowledge on regulatory mechanisms involved in prostate gland development which are key to understanding abnormal growth processes associated with aging.     

Imprinting by neonatal sex steroids on the structure and function of the mature mouse prostate.

Perinatal sex-steroid exposure may result in permanent modifications in the structure and function of the prostate gland. The mechanism of such long-range alterations in hormonal sensitivity is not known. This study aimed to define the molecular requirements for neonatal sex-steroid imprinting and to investigate whether combined administration of neonatal androgens and estrogens had synergistic effects upon the mature mouse prostate. Since the interaction between endogenous and exogenous sex steroids in normal mice makes it difficult to dissociate direct from indirect effects, we used the hypogonadal (hpg) mouse, characterized by congenital androgen deficiency yet still fully responsive to exogenous androgens. Newborn mice (Days 1-2) were administered a single s.c. injection of androgens alone or in combination with an estrogen followed by testosterone-induced maximal prostate growth at maturity. The final effects were determined in 7-wk-old mice through study of ductal architecture in microdissected ventral prostates (VP) and quantitation of volume densities and diameters of prostate tissue components. A single neonatal dose of androgens, but not of estrogen, increased branching morphogenesis and VP weights at adulthood. These effects did not differ significantly between various androgens; in addition, combined androgen and estrogen treatment failed to demonstrate any synergistic effects on the prostate. We conclude that neonatal androgens induce long-range effects upon the mature VP structure as well as its secretory function and that this imprinting occurs via the androgen receptor without requiring aromatization of androgens. However, these conclusions, based on a specific treatment protocol, are confined only to the distal segment of VP, and effects of neonatal sex-steroid exposure in other regions or lobes of VP may differ.     

Inhibition of epithelial ductal branching in the prostate by sonic hedgehog is indirectly mediated by stromal cells

Sonic hedgehog (Shh), a vertebrate homologue of the Drosophila segment-polarity gene hedgehog, has been reported to play an important role during normal development of various tissues. Abnormal activities of Shh signaling pathway have been implicated in tumorigenesis such as basal cell carcinomas and medulloblastomas. Here we show that Shh signaling negatively regulates prostatic epithelial ductal morphogenesis. In organotypic cultures of developing rat prostates, Shh inhibited cell proliferation and promoted differentiation of luminal epithelial cells. The expression pattern of Shh and its receptors suggests a paracrine mechanism of action. The Shh receptors Ptc1 (Patched1) and Ptc2 were found to be expressed in prostatic stromal cells adjacent to the epithelium, where Shh itself was produced. This paracrine model was confirmed by co-culturing the developing prostate in the presence of stromal cells transfected with a vector expressing a constitutively active form of Smoothened, the real effector of the Shh signaling pathway. Furthermore, expression of activin A and TGF-beta1 that were shown previously to inhibit prostatic epithelial branching was up-regulated following Shh treatment in the organotypic cultures. Taken together, these results suggest that Shh negatively regulates prostatic ductal branching indirectly by acting on the surrounding stromal cells, at least partly via up-regulating expression of activin A and TGF-beta1.     

Prostate development requires Sonic hedgehog expressed by the urogenital sinus epithelium

The prostate gland develops from the urogenital sinus by a testosterone-dependent process of ductal morphogenesis. Sonic hedgehog (Shh) is expressed in the urogenital sinus epithelium and the time course of expression coincides with the formation of the main prostatic ducts. Expression is most abundant in the lumen of the urogenital sinus and in the contiguous proximal duct segments. The initial upregulation of Shh expression in the male urogenital sinus depends on the presence of testosterone. The function of Shh was examined in the male urogenital sinus which was transplanted under the renal capsule of an adult male host mouse. Blockade of Shh function by a neutralizing antibody interferes with Shh signaling and abrogates growth and ductal morphogenesis in the transplanted tissue. These observations show that testosterone-dependent Shh expression in the urogenital sinus is necessary for the initiation of prostate development.     

Neonatal low- and high-dose exposure to estradiol benzoate in the male rat: I. Effects on the prostate gland.

Brief exposure of rats to high doses of natural estrogens early in life results in permanent alterations of the prostate gland, which include differentiation defects, altered gene expression, and dysplasia with aging. Whether low-dose treatments can cause similar effects in the developing prostate remains controversial. The current project was designed to determine the dose-response relationship of the prostate gland to estradiol exposure during the developmentally critical neonatal period in the rat. Male Sprague-Dawley (SD) rats were treated on Days 1, 3, and 5 of life by s.c. injections of a 7-log range of doses (0.015 microg/kg to 15.0 mg/kg) of beta-estradiol-3-benzoate (EB) in 25 microl of peanut oil (Arachis) as vehicle. In a separate block, neonatal Fisher 344 (F344) rats received 0.15, 15.0, or 1500.0 microg EB/kg. Rats were killed on Postnatal Day (PND) 35 or 90, and the prostates were microdissected, weighed, and frozen for immunohistochemistry. Preputial separation and hepatic testosterone hydroxlase activities were monitored and measured to determine the onset of puberty. On PND 35, there was an increase in prostate weights of SD rats treated with low doses of EB and a decrease in prostate weights of SD rats treated with high doses. The low-dose effect was entirely abolished by PND 90, and only high-dose suppression of organ sizes was found. The transient nature of the effect in low-dose animals suggests an advancement of puberty as the cause for increased reproductive organ weights on PND 35. F344 rats were more sensitive than SD rats to the suppressive effects of high doses of neonatal EB on PND 90. Despite this heightened responsiveness in the F344 rats, a low-dose estrogenic effect on adult prostate weights was not observed. Thus, in the rat model a sustained effect at low doses of natural estrogens is not present in the prostate glands.     

Morphogenesis and ductal development of the prostatic complex of the guinea pig

The morphogenesis of glandular architecture of the three lobes of prostate gland of the guinea pig, lateral, dorsal, and coagulating gland was studied from 35 days gestation to 90 postnatal days. Epithelial ductal tubules of various lobes of the gland were microdissected after treatment by collagenase and displayed two dimensionally. The number of ductal tips was counted, and the volume of the ductal network was quantified using a graphic tablet. The results show that the growth and ductal morphogenesis fall into two phases: prenatal and postnatal. The first outgrowth of prostatic buds begins at 35 days gestation (gestational length is 65 days). Ductal growth and branching continues over the next 15–20 days and by 55 days gestation, approximately 60%, 79%, and 71% of the adult number of ductal tips of the lateral and dorsal lobes and coagulating gland respectively, are formed. The figures increase to 89%, 84%, and 106%, respectively, by birth. There is little increase in number of ductal tips thereafter. Postnatal growth is accomplished mainly by elongation of existing ductal network with a little additional branching but with an increase in size (volume) of the tubules. Canalization of ductal tubules occurs prenatally in all lobes but postnatal functional cytodifferentiation takes a slightly different pace among them. Ductal morphogenesis of the guinea pig prostate gland differs significantly in time-course from that of the mouse in which ductal development occurs mainly postnatally. © 1993 Wiley-Liss, Inc.     

fucosyltransferase1 and H-type complex carbohydrates modulate epithelial cell proliferation during prostatic branching morphogenesis

The prostate undergoes branching morphogenesis dependent on paracrine interactions between the prostatic epithelium and the urogenital mesenchyme. To identify cell-surface molecules that function in this process, monoclonal antibodies raised against epithelial cell-surface antigens were screened for antigen expression in the developing prostate and for their ability to alter development of prostates grown in serum-free organ culture. One antibody defined a unique expression pattern in the developing prostate and inhibited growth and ductal branching of cultured prostates by inhibiting epithelial cell proliferation. Expression cloning showed that this antibody binds fucosyltransferase1, an alpha-(1,2)-fucosyltransferase that synthesizes H-type structures on the complex carbohydrate modifications of some proteins and lipids. The lectin UEA I that binds H-type 2 carbohydrates also inhibited development of cultured prostates. These data demonstrate a previously unrecognized role for fucosyltransferase1 and H-type carbohydrates in controlling the spatial distribution of epithelial cell proliferation during prostatic branching morphogenesis. We also show that fucosyltransferase1 is expressed by epithelial cells derived from benign prostatic hyperplasia or prostate cancer; thus, fucosyltransferase1 may also contribute to pathological prostatic growth. These data further suggest that rare individuals who lack fucosyltransferase1 (Bombay phenotype) should be investigated for altered reproductive function and/or altered susceptibility to benign prostatic hyperplasia and prostate cancer.     

The effect of androgen deprivation on branching morphogenesis in the mouse prostate

Androgen-induced prostatic development encompasses many individual processes such as ductal branching morphogenesis, cellular proliferation, and secretory cytodifferentiation. Previous studies of ductal morphogenesis (Y. Sugimura, G.R. Cunha, and A.A. Donjacour, 1986, Biol. Reprod. 34, 961-971) demonstrated that the majority (approximately 70%) of ductal tips and branchpoints in the mouse prostate is generated before 15 days of age. Since circulating androgen levels are low during this neonatal period, it is possible that ductal branching morphogenesis may not require the continuous presence of androgens. To test this hypothesis mice were castrated within 24 hr of birth, and prostates from these mice were microdissected at various ages from 5 to 120 days of age to assess the number of ductal tips and branchpoints; wet weight and DNA content were also determined. In intact males wet weight and DNA content increased rapidly between 15 and 60 days of age, after most of the prostatic ductal architecture had been laid down. Neonatal castration considerably reduced the number of tips and branchpoints in both the ventral and dorsolateral prostate, yet both lobes still underwent significant branching morphogenesis in the absence of testes. The administration of anti-androgens to neonatal castrates did not suppress ductal branching to any greater extent than did neonatal castration alone. Androgen replacement immediately following neonatal castration resulted in precocious attainment of the adult number of tips and branchpoints, but caused only modest increases in wet weight. In contrast, when androgen replacement was delayed until adulthood, prostatic wet weight increased to normal adult levels, but the number of ductal tips and branchpoints did not. These experiments show that neonatal prostatic ductal morphogenesis is sensitive to, but does not require, chronic androgen stimulation.     

Noggin is required for normal lobe patterning and ductal budding in the mouse prostate

Mesenchymal expression of the BMP antagonist NOGGIN during prostate development plays a critical role in pre-natal ventral prostate development and opposes BMP4-mediated inhibition of cell proliferation during postnatal ductal development. Morphologic examination of newborn Noggin^−/− male fetuses revealed genitourinary anomalies including cryptorchidism, incomplete separation of the hindgut from the urogenital sinus (UGS), absence of the ventral mesenchymal pad, and a complete loss of ventral prostate (VP) budding. Examination of lobe-specific marker expression in the E14 Noggin^−/− UGS rescued by transplantation under the renal capsule of a male nude mouse confirmed a complete loss of VP determination. More modest effects were observed in the other lobes, including decreased number of ductal buds in the dorsal and lateral prostates of newborn Noggin^−/− males. BMP4 and BMP7 have been shown to inhibit ductal budding and outgrowth by negatively regulating epithelial cell proliferation. We show here that NOGGIN can neutralize budding inhibition by BMP4 and rescues branching morphogenesis of BMP4-exposed UGS in organ culture and show that the effects of BMP4 and NOGGIN activities converge on P63⁺ epithelial cells located at nascent duct tips. Together, these studies show that the BMP-NOGGIN axis regulates patterning of the ventral prostate, regulates ductal budding, and controls proliferation of P63⁺ epithelial cells in the nascent ducts of developing mouse prostate.     

BMP7 inhibits branching morphogenesis in the prostate gland and interferes with Notch signaling

The mouse prostate gland develops by branching morphogenesis from the urogenital epithelium and mesenchyme. Androgens and developmental factors, including FGF10 and SHH, promote prostate growth (Berman, D.M., Desai, N., Wang, X., Karhadkar, S.S., Reynon, M., Abate-Shen, C., Beachy, P.A., Shen, M.M., 2004. Roles for Hedgehog signaling in androgen production and prostate ductal morphogenesis. Dev. Biol. 267, 387-398; Donjacour, A.A., Thomson, A.A., Cunha, G.R., 2003. FGF-10 plays an essential role in the growth of the fetal prostate. Dev. Biol. 261, 39-54), while BMP4 signaling from the mesenchyme has been shown to suppresses prostate branching (Lamm, M.L., Podlasek, C.A., Barnett, D.H., Lee, J., Clemens, J.Q., Hebner, C.M., Bushman, W., 2001. Mesenchymal factor bone morphogenetic protein 4 restricts ductal budding and branching morphogenesis in the developing prostate. Dev. Biol. 232, 301-314). Here, we show that Bone Morphogenetic Protein 7 (BMP7) restricts branching of the prostate epithelium. BMP7 is expressed in the periurethral urogenital mesenchyme prior to formation of the prostate buds and, subsequently, in the prostate epithelium. We show that BMP7(lacZ/lacZ) null prostates show a two-fold increase in prostate branching, while recombinant BMP7 inhibits prostate morphogenesis in organ culture in a concentration-dependent manner. We further explore the mechanisms by which the developmental signals may be interpreted in the urogenital epithelium to regulate branching morphogenesis. We show that Notch1 activity is associated with the formation of the prostate buds, and that Notch1 signaling is derepressed in BMP7 null urogenital epithelium. Based on our studies, we propose a model that BMP7 inhibits branching morphogenesis in the prostate and limits the number of domains with high Notch1/Hes1 activity.     

Morphological and functional heterogeneity in the rat prostatic gland.

Ductal morphogenesis and adult ductal branching patterns were examined in the rat prostate by a microdissection method. The rat prostate consists of paired (right and left) subdivisions which correspond in large part to the classically defined lobes: ventral prostate, lateral prostate, dorsal prostate, and coagulating gland. Of particular interest was the finding that the lateral prostate consists of two different ductal zones: (1) lateral type 1 prostate with 5-7 long main ducts (resembling miniature palm trees) that extend cranially towards both the seminal vesicle and dorsal prostate to arborize near the bladder neck, and (2) lateral type 2 prostate with 5-6 short main ducts that arborize caudal to the bladder neck and give rise to compact bushy glands. Both lateral prostatic groups had a ductal-acinar organization. The adult structure of the other rat prostatic lobes was also examined, and closely resembled their mouse counterparts. The ventral prostate, which had 2-3 pairs of slender main ducts per side, and the coagulating gland, which had 1 main duct per side, was completely ductal in structure. In contrast, the dorsal prostate, which had 5-6 pairs of main ducts per side, had a ductal-acinar structure. Ductal branching morphogenesis occurred at different rates in different lobes and was essentially complete in the prostate at the 30 days. Immunocytochemical studies with an antibody to DP-1, a major secretory protein of the rat dorsal prostate, revealed that secretory function was initiated at approximately 30 days after birth in the coagulating gland, the dorsal prostate, and lateral type 1 prostate. A consistent feature of the lateral type 2 prostate was the absence of DP-1. On Western blots, DP-1 was detected in the secretion of the coagulating gland, lateral type 1 and dorsal prostate, but not in the ventral and lateral type 2 prostate. Polyacrylamide gel electrophoresis confirmed this result and demonstrated that the lateral type 2 prostate expressed several low-molecular weight secretory proteins not found in the other lobes of the prostate. On the whole, the rat prostate exhibited considerable heterogeneity both between and within lobes in developmental processes, ductal patterning, histology, and functional expression.     

Mesenchymal factor bone morphogenetic protein 4 restricts ductal budding and branching morphogenesis in the developing prostate

The budding of the urogenital sinus epithelium into the surrounding mesenchyme signals the onset of prostate morphogenesis. The epithelial and mesenchymal factors that regulate ductal budding and the ensuing process of ductal growth and branching are not fully known. We provide evidence that bone morphogenetic protein 4 (BMP4) is a mesenchymal factor that regulates ductal morphogenesis. The Bmp4 gene was most highly expressed in the male urogenital sinus from embryonic day 14 through birth, a period marked by formation of main prostatic ducts and initiation of ductal branching. From an initial wide distribution throughout the prostatic anlage of the urogenital sinus, Bmp4 expression became progressively restricted to the mesenchyme immediately surrounding the nascent prostatic ducts and branches. Exogenous BMP4 inhibited epithelial cell proliferation and exhibited a dose-dependent inhibition of ductal budding in urogenital sinus tissues cultured in vitro. Adult Bmp4 haploinsufficient mice exhibited an increased number of duct tips in both the ventral prostate and coagulating gland. Taken together, our data indicate that BMP4 is a urogenital sinus mesenchymal factor that restricts prostate ductal budding and branching morphogenesis.     

Expression of ptc and gli genes in talpid3 suggests bifurcation in Shh pathway

talpid3 is an embryonic-lethal chicken mutation in a molecularly un-characterised autosomal gene. The recessive, pleiotropic phenotype includes polydactylous limbs with morphologically similar digits. Previous analysis established that hox-D and bmp genes, that are normally expressed posteriorly in the limb bud in response to a localised, posterior source of Sonic Hedgehog (Shh) are expressed symmetrically across the entire anteroposterior axis in talpid3 limb buds. In contrast, Shh expression itself is unaffected. Here we examine expression of patched (ptc), which encodes a component of the Shh receptor, and is probably itself a direct target of Shh signalling, to establish whether talpid3 acts in the Shh pathway. We find that ptc expression is significantly reduced in talpid3 embryos. We also demonstrate that talpid3 function is not required for Shh signal production but is required for normal response to Shh signals, implicating talpid3 in transduction of Shh signals in responding cells. Our analysis of expression of putative components of the Shh pathway, gli1, gli3 and coupTFII shows that genes regulated by Shh are either ectopically expressed or no longer responsive to Shh signals in talpid3 limbs, suggesting possible bifurcation in the Shh pathway. We also describe genetic mapping of gli1, ptc, shh and smoothened in chickens and confirm by co-segregation analysis that none of these genes correspond to talpid3.     

Angiogenic factors stimulate tubular branching morphogenesis of sonic hedgehog-deficient lungs

Sonic Hedgehog (Shh)-deficient mice have a severe lung branching defect. Recent studies have shown that hedgehog signaling is involved in vascular development and it is possible that the diminished airway branching in Shh-deficient mice is due to abnormal pulmonary vasculature formation. Therefore, we investigated the role of Shh in pulmonary vascular development using Shh/Tie2lacZ compound mice, which exhibit endothelial cell-specific LacZ expression, and Pecam-1 immunohistochemistry. In E11.5-13.5 Shh-deficient mice, the pulmonary vascular bed is decreased, but appropriate to the decrease in airway branching. However, when E12.5 Shh-deficient lungs were cultured for 4-6 days, the vascular network deteriorated compared to wild-type lungs. The expression of vascular endothelial growth factor (Vegf) or its receptor Vegfr2 (KDR/Flk-1) was not different between E12.5-13.5 Shh-deficient and wild-type lungs. In contrast, angiopoietin-1 (Ang1), but not Ang2 or the angiopoietin receptor Tie2, mRNA expression was downregulated in E12.5-E13.5 lungs of Shh null mutants. Recombinant Ang1 alone was unable to restore in vitro branching morphogenesis in Shh-deficient lungs. Conversely, the angiogenic factor fibroblast growth factor (Fgf)-2 alone or in combination with Ang1, increased vascularization and tubular growth and branching of Shh-deficient lungs in vitro. The angiogenic factors did not overcome the reduced smooth muscle cell differentiation in the Shh null lungs. These data indicate that early vascular development, mediated by Vegf/Vegfr2 signaling proceeds normally in Shh-deficient mice, while later vascular development and stabilization of the primitive network mediated by the Ang/Tie2 signaling pathway are defective, resulting in an abnormal vascular network. Stimulation of vascularization with angiogenic factors such as Fgf2 and Ang1 partially restored tubular growth and branching in Shh-deficient lungs, suggesting that vascularization is required for branching morphogenesis.     

Proprotein convertases modulate budding and branching morphogenesis of rat ventral prostate

The onset of prostate morphogenesis is involved in the interaction between mesenchyme and epithelium. Proprotein convertases (PCs) activate a variety of growth and differentiation factors including mesenchymal and epithelial factors, such as insulin-like growth factor (IGF) and transforming growth factor-beta (TGF-beta), which induce ductal budding and branching. In this study, we provide evidence that PCs play a critical role in prostatic budding from the urogenital sinus (UGS) and ductal branching morphogenesis of the neonatal rat ventral prostate. PCs were expressed only in the epithelial cells of neonatal rat prostate. PC activity in the ventral prostate was modulated by endogenous androgen. PC inhibition suppressed prostatic budding and branching. Taken together, our data indicates that androgen-induced PCs initiate the development of the prostate.     

Gene expression profiles of mouse submandibular gland development: FGFR1 regulates branching morphogenesis in vitro through BMP- and FGF-dependent mechanisms

Analyses of gene expression profiles at five different stages of mouse submandibular salivary gland development provide insight into gland organogenesis and identify genes that may be critical at different stages. Genes with similar expression profiles were clustered, and RT-PCR was used to confirm the developmental changes. We focused on fibroblast growth factor receptor 1 (FGFR1), as its expression is highest early in gland development. We extended our array results and analyzed the developmental expression patterns of other FGFR and FGF isoforms. The functional significance of FGFR1 was confirmed by submandibular gland organ culture. Antisense oligonucleotides decreased expression of FGFR1 and reduced branching morphogenesis of the glands. Inhibiting FGFR1 signaling with SU5402, a FGFR1 tyrosine kinase inhibitor, reduced branching morphogenesis. SU5402 treatment decreased cell proliferation but did not increase apoptosis. Fgfr, Fgf and Bmp gene expression was localized to either the mesenchyme or the epithelium by PCR, and then measured over time by real time PCR after SU5402 treatment. FGFR1 signaling regulates Fgfr1, Fgf1, Fgf3 and Bmp7 expression and indirectly regulates Fgf7, Fgf10 and Bmp4. Exogenous FGFs and BMPs added to glands in culture reveal distinct effects on gland morphology. Glands cultured with SU5402 were then rescued with exogenous BMP7, FGF7 or FGF10. Taken together, our results suggest specific FGFs and BMPs play reciprocal roles in regulating branching morphogenesis and FGFR1 signaling plays a central role by regulating both FGF and BMP expression.     

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.