LAUSR

Significance P53 is an important tumor suppressor that is found throughout metazoans, including invertebrates that do not develop malignancies. The prevailing theory for why these invertebrates possess a tumor suppressor is that P53 originally evolved to protect the germline of early metazoans from genotoxic stress such as ultraviolet radiation. Here, we examine the function of two P53 homologs in the parasitic flatworm Schistosoma mansoni. The first is orthologous to canonical P53 and regulates flatworm stem cell maintenance and differentiation. The second P53 gene is a parasite-specific paralog that is required for the normal response to genotoxic stress. The existence of this parasite-specific paralog implies that the ability to respond to genotoxic stress in parasitic flatworms may have arisen from convergent evolution.