Endodermal origin of bladder trigone inferred from mesenchymal-epithelial interaction

Abstract

Purpose: In the classic view of bladder development the trigone originates from the mesoderm derived wolffian ducts while the remainder of the bladder originates from the endoderm derived urogenital sinus. Recent molecular developmental studies have questioned the veracity of this received wisdom, suggesting an endodermal origin for the trigone. To shed further light on this issue we observed mesenchymal-epithelial interactions between trigone epithelium and fetal urogenital sinus mesenchyma to infer the trigonal germ layer of origin.

Materials and methods: Mouse trigone epithelium was recombined with fetal rat urogenital sinus mesenchyma in tissue recombinant grafts that were placed beneath the renal capsule of athymic mouse hosts. Grafts were harvested at 4 weeks. Control grafts with bladder dome and ureteral epithelium were also examined. Tissues were evaluated with hematoxylin and eosin, and Hoechst dye 33258 to confirm cell species origin. Immunohistochemistry was done with androgen receptor, broad spectrum uroplakin, dorsolateral prostate secretions and seminal vesicle secretions to differentiate prostatic and seminal vesicle differentiation.

Results: Grafts of mouse trigone epithelium with fetal rat urogenital sinus mesenchyma yielded epithelial tissue that stained for dorsolateral prostate secretions but not for seminal vesicle secretions. Control grafts of bladder dome epithelium yielded the expected endodermal prostate differentiation. Control grafts of ureteral epithelium yielded the expected mesodermal seminal vesicle differentiation.

Conclusions: The consistent finding of prostatic epithelium in tissue recombinants of trigone epithelium and fetal urogenital sinus mesenchyma reinforces the hypothesis that the trigone is derived from the endoderm and not from the mesoderm, as commonly accepted.

Figure 1. Expression of markers in mouse dorsolateral prostate (DLP)

Control mouse seminal vesicle immunohistochemistry for dorsal lateral prostate secretions (mDLP), seminal vesicle secretions (mSV), androgen receptor (AR) and uroplakin. As expected mouse DLP shows cytoplasmic brown staining in the luminal epithelial cells with antibodies raised against mDLP secretions (a) but not with those raised against mouse seminal vesicle secretions (b) or uroplakin (d). Nuclear brown staining is seen in both epithelial and some stromal cells when antibodies against AR were used (c)

Figure 2. Expression of markers in mouse seminal vesicle

Control mouse seminal vesicle immunohistochemistry for dorsal lateral prostate secretions (mDLP), seminal vesicle secretions (mSV), androgen receptor (AR) and uroplakin. As expected mouse seminal vesicle shows cytoplasmic brown staining in the luminal epithelial cells with antibodies raised against mSV secretions (b) but not with those raised against mDLP (a) or uroplakin (d). Nuclear brown staining is seen in both epithelial and some stromal cells when antibodies against AR were used (c)

Figure 3. Development of prostatic tissue

Recombinant graft of trigone epithelium and urogenital sinus mesenchyme demonstrating the development of prostatic structure from urothelium under the influence of urogenital sinus mesenchyme. Fragments of the grafted urothelium can be seen (arrows)continuing to express uroplakin (a). More characteristic prostatic glandular epithelium grows from these structures (arrowheads) under the influence of urogenital sinus mesenchyme (as previously described) these structures show positive staining using antibodies targeting dorsal lateral prostate secretions (mDLP) (b).

Figure 4. Tissue recombinant composed of mouse trigone epithelium and rat urogenital sinus mesenchyme

Recombinant graft of trigone epithelium and urogenital sinus mesenchyme stained with H&E (a), Hoechst 33258 (b), mDLP (c), mSV (d), AR (e), and uroplakin (f). Clear glandular epithelial differentiation with columnar secretory luminal cells is seen. Epithelial nuclei stained with Hoechst 33258 (b) demonstrates the speckled nuclear patterning characteristic of mouse chromatin packaging (white arrowheads) in epithelial cells while the stromal cells show the more diffuse staining characteristic of rat nuclei. Recombinant glandular structures show brown cytoplasmic staining in luminal epithelial cells for mDLP (c) not mSV (d) or uroplakin (f). Brown nuclear staining is seen using antibodies against AR (e).