MacCallum, D. E., Hall, P. A. and Wright, E. G. The Trp53 Pathway is Induced In Vivo by Low Doses of Gamma Radiation. Radiat. Res. 156, 324–327 (2001).

The induction of the Trp53 response after very low doses (0.01–1 Gy) of ionizing radiation was studied in the adult mouse using immunochemical and immunohistochemical methods. We found a detectable response at 0.01 Gy and an increased induction of Trp53 with increasing dose in both radiation-resistant and radiation-sensitive tissues. These results suggest that there is no lower threshold for induction. This response was heterogeneous, since cells that received the same dose had different staining intensities, suggesting that the induction of Trp53 is not based simply on dose-dependent responses to DNA damage. These data also demonstrate the exquisite sensitivity of the Trp53 pathway and show that this response is controlled by cell- and tissue-specific factors that have yet to be defined.