Both of the main epithelial cell types of the prostate – luminal and basal cells – develop from the urogenital sinus (UGS), but the cell lineage relationship between the two cell types is unclear. On p. 4955, Kurita et al. show that p63, a p53 tumour suppressor homologue, is essential for the differentiation of prostatic basal cells in mice, but that luminal cells develop independently of basal cells. The researchers transplanted UGSs from p63-/- mice, which die perinatally, into adult male nude mice, and show that the prostatic tissue formed by these grafts contains neuroendocrine and luminal cells but no basal cells. Some luminal cells transform into mucinous cells, indicating that basal cells are needed to maintain luminal cell differentiation. Finally, p63-/-grafts can regenerate after the host mice are castrated, suggesting that the mouse prostatic luminal epithelium contains self-renewing stem cells that could be the target of carcinogenesis.