PURPOSE - Identifying developmental proteins could lead to markers of bladder progenitor cells, which could be used to investigate bladder diseases. We recently reported a novel embryonic stem cell model in which to study differential protein expression patterns during bladder development. Differential and temporal expressions of the endodermal proteins known as forkhead box (Foxa1 and Foxa2) were observed. In the current study we further delineated these protein expression patterns.
MATERIALS AND METHODS - Epithelium was removed from the underlying mesenchyma from embryonic day 18 rat bladders. Heterospecific recombinant xenografts were created by combining embryonic stem cells plus embryonic bladder mesenchyma and placed beneath the renal capsule of mouse hosts. Grafts were harvested at 16, 18, 21, 28, 35 and 42 days, and evaluated with hematoxylin and eosin, trichrome staining, and immunohistochemistry for uroplakin, smooth muscle alpha-actin, p63, Foxa1, Foxa2 and androgen receptor.
RESULTS - At 16 days uroplakin was detectable and it seemed to correlate with the loss of Foxa2, while Foxa1 remained at all time points. Androgen receptor was first noted in stroma at day 16. It localized to urothelial nuclei at day 21 and was undetectable at 42 days. Adjacent to the urothelium alpha-smooth muscle actin was seen on day 16 and it was localized in bundles to the periphery of the graft at later time points. Staining for basilar urothelium with p63 confirmed basilar orientation at all time points.
CONCLUSIONS - We report the temporal spatial expression of various genes in early bladder development. This suggests that some proteins may be potential markers of bladder progenitor cells. Characterizing these markers may potentially identify bladder progenitor cells that have been directed toward a lineage path destined to become urothelial cells. Ultimately these multipotential progenitor cells could be isolated and used to study and treat diseases that affect the bladder.