How Blood Flow Dictates Gene Expression (IMAGE) University of Pennsylvania School of Medicine Caption Klf2 is expressed (red) on the flow side (arrows) of developing mitral and aortic valves in a 14-day-old mouse embryo. Credit John Lee, MD, PhD, Lan Chen, PhD, Mark Kahn, MD, University of Pennsylvania School of Medicine, Developmental Cell Usage Restrictions None License Licensed 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.