Androgenic regulation of ventral epithelial bud number and pattern in mouse urogenital sinus.

The ventral urogenital sinus (UGS) of control male mice has two rows of 3-4 prostatic buds at birth, but how androgens regulate ventral bud (VB) number and patterning is unclear. VBs in both sexes appeared to be a mixture of prostatic and urethral buds. UGSs from Tfm male and antiandrogen (flutamide)-exposed mice had small VBs, suggesting that initiation of some VBs is androgen independent. Tfm male mice are widely considered completely androgen insensitive yet their UGSs were 5alpha-dihydrotestosterone (DHT)- responsive. VBs (6-8) were generally distributed bimodally on the left-right axis at both minimal and normal male androgen signaling. Yet control females and DHT-exposed Tfm males had 13-14 VBs, whose left-right distribution was fairly uniform. These results suggest that VB number and distribution respond biphasically as androgen signaling increases from minimal, and that androgens regulate bud specification. Complete VB agenesis by the selective budding inhibitor 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) required high androgen signaling.

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.

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.

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.