Artwork: the molecular evolution of NRK (IMAGE) Tokyo Institute of Technology Caption Here, the function of NRK at each stage of evolution is depicted frame by frame of a movie film. The rightmost frame shows its involvement in the development of the mouse and human placenta. The frame of the film is a double helix structure of DNA, which gives an image of the major changes that occurred at the DNA level just before the mouse and human frames. Credit Conceptualization by the authors. Illustration by Felipe Serrano (http://www.illustrative-science.com/). Usage Restrictions State the credit License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.