Ornithine Decarboxylase Activity Is Required for Prostatic Budding in the Developing Mouse Prostate

<div><p>The prostate is a male accessory sex gland that produces secretions in seminal fluid to facilitate fertilization. Prostate secretory function is dependent on androgens, although the mechanism by which androgens exert their effects is still unclear. Polyamines are small cationic molecules that play pivotal roles in DNA transcription, translation and gene regulation. The rate-limiting enzyme in polyamine biosynthesis is ornithine decarboxylase, which is encoded by the gene <i>Odc1</i>. Ornithine decarboxylase mRNA decreases in the prostate upon castration and increases upon administration of androgens. Furthermore, testosterone administered to castrated male mice restores prostate secretory activity, whereas administering testosterone and the ornithine decarboxylase inhibitor D,L-α-difluromethylornithine (DFMO) to castrated males does not restore prostate secretory activity, suggesting that polyamines are required for androgens to exert their effects. To date, no one has examined polyamines in prostate development, which is also androgen dependent. In this study, we showed that ornithine decarboxylase protein was expressed in the epithelium of the ventral, dorsolateral and anterior lobes of the adult mouse prostate. Ornithine decarboxylase protein was also expressed in the urogenital sinus (UGS) epithelium of the male and female embryo prior to prostate development, and expression continued in prostatic epithelial buds as they emerged from the UGS. Inhibiting ornithine decarboxylase using DFMO in UGS organ culture blocked the induction of prostatic buds by androgens, and significantly decreased expression of key prostate transcription factor, <i>Nkx3</i>.<i>1</i>, by androgens. DFMO also significantly decreased the expression of developmental regulatory gene <i>Notch1</i>. Other genes implicated in prostatic development including <i>Sox9</i>, <i>Wif1</i> and <i>Srd5a2</i> were unaffected by DFMO. Together these results indicate that <i>Odc1</i> and polyamines are required for androgens to exert their effect in mediating prostatic bud induction, and are required for the expression of a subset of prostatic developmental regulatory genes including <i>Notch1</i> and <i>Nkx3</i>.<i>1</i>.</p></div

Allowing prostatic buds to grow before polyamine depletion did not rescue <i>Nkx3</i>.<i>1</i> expression.

<p>We determined the time course of prostatic bud formation over 2 days of culture in testosterone, by culturing the UGS in the presence of testosterone for the time indicated, fixed the cultures, and stained them with E-Cadherin to examine prostatic bud formation. After 24 hours or 1 day in culture, prostatic buds were still not apparent (A). After 1.5 days in testosterone, several prostatic buds were observed (B, white arrowheads). The buds were longer and more numerous after 2 days in testosterone (C, white arrowheads). Culturing the UGS in testosterone for two days to allow buds to grow, followed by polyamine depletion did not rescue <i>Nkx3</i>.<i>1</i> expression (D). *, p<0.05.</p

Ornithine decarboxylase protein was present in the urogenital epithelium in the developing urogenital sinus.

<p>In the male UGS before budding at E15 (A) and E16 (B), ornithine decarboxylase protein (green) was present in the epithelium. As the buds emerged from the epithelium at E17 (E) and E18 (G), ornithine decarboxylase protein was still expressed in the epithelium and buds. In the female UGS, ornithine decarboxylase was present in the epithelium at E15 (B) and E16 (D), the period before prostatic buds are initiated in the male UGS. At E17 (F) and E18 (H), ornithine decarboxylase protein continued to be expressed in the urogenital epithelium. Ornithine decarboxylase staining is in green, and vimentin staining is in red. There was some co-localization of ornithine decarboxylase and vimentin (yellow) in the mesenchyme. Arrowheads denote prostatic buds. Abbreviations: E epithelium, M mesenchyme.</p

<i>Odc1</i> mRNA levels in the developing urogenital sinus and in separated UGS tissue compartments.

<p><i>Odc1</i> transcripts were present in the male and female UGS throughout the period of prostatic bud induction from E15-E18, although they did not vary between males and females during this period (A). <i>Odc1</i> transcript abundance did not differ between the epithelium and mesenchyme at E16 (B), although there were significantly more <i>Odc1</i> transcripts in the mesenchyme compared to the epithelium at E18 (B). Abbreviations used: epi epithelium, mes mesenchyme. *, p<0.05.</p