LAUSR

Genetically encoded probes are widely used to visualize cellular processes in vitro and in vivo. Although effective in cultured cells, fluorescent protein tags and reporters are suboptimal in vivo because of poor tissue penetration and high background signal. Luciferase reporters offer improved signal-to-noise ratios but require injections of luciferin that can lead to variable responses and that limit the number and timing of data points that can be gathered. Such issues in studying the critical transcription factor p53 have limited insight on its activity in vivo during development and tissue injury responses. Here, by linking the expression of the near-infrared fluorescent protein iRFP713 to a synthetic p53-responsive promoter, we generated a knock-in reporter mouse that enabled noninvasive, longitudinal analysis of p53 activity in vivo in response to various stimuli. In the developing embryo, this model revealed the timing and localization of p53 activation. In adult mice, the model monitored p53 activation in response to irradiation and paracetamol- or CCl4-induced liver regeneration. After irradiation, we observed potent and sustained activation of p53 in the liver, which limited the production of reactive oxygen species (ROS) and promoted DNA damage resolution. We propose that this new reporter may be used to further advance our understanding of various physiological and pathophysiological p53 responses. Description A reporter allows noninvasive, longitudinal imaging of p53 activation in mice. A live reporter for p53 The transcription factor p53 is best known for its role as a critical tumor suppressor. Much of our insight on p53 has been obtained from cell culture studies. Tools to explore p53 activity in live animals tend to be invasive or are limited by detection issues. Humpton et al. generated knock-in mice expressing a fluorescent, p53-responsive reporter that they developed to overcome both limitations. The reporter revealed the dynamics of p53 activity during embryonic development and after injury in adult liver. Its use may elucidate the roles of p53 in normal physiology and disease.