p53 and Mdm2: not all cells are equal

The human TP53 gene is well known as a tumour suppressor. Less well appreciated are the potential roles of p53 in regulating postnatal development and the cell-type specific effects of p53. In this issue of the Journal of Pathology, Lozano and colleagues show that p53 has the ability to block progenitor cell expansion in haematopoiesis and spermatogenesis but not in specific epithelial tissues. These data challenge the view that p53 acts equally in all cell types and have important implications for the applicability of p53 therapeutics in the treatment of human cancers.