p53 pathway is involved in cell competition during mouse embryogenesis.

The function of tumor suppressor p53 has been under intense investigation. Acute stresses such as DNA damage are able to trigger a high level of p53 activity, leading to cell cycle arrest or apoptosis. In contrast, the cellular response of mild p53 activity induced by low-level stress in vivo remains largely unexplored. Murine double minute (MDM)2 and MDM4 are two major negative regulators of p53. Here, we used the strategy of haploinsufficiency of Mdm2 and Mdm4 to induce mild p53 activation in vivo and found that Mdm2Mdm4 double-heterozygous mice exhibited normal embryogenesis. However, closer examination demonstrated that the Mdm2Mdm4 cells exhibited a growth disadvantage and were outcompeted during development in genetic mosaic embryos that contained wild-type cells. Further study indicated the out-competition phenotype was dependent on the levels of p53. These observations revealed that cells with mild p53 activation were less fit and exhibited altered fates in a heterotypic environment, resembling the cell competition phenomenon first uncovered in Drosophila By marking unfit cells for elimination, p53 may exert its physiological role to ensure organ and animal fitness.