Proposed Model of Stem Cell Self-renewal (IMAGE) University of Pennsylvania Caption This is a proposed model of human SSC self-renewal regulation by glial cell line-derived neurotrophic factor (GDNF), which has been demonstrated to have an essential role in regulating rodent SSC self-renewal. Credit Ralph L. Brinster and the University of Pennsylvania School of Veterinary Medicine. 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.