CRIPTO (image) Salk Institute Caption When scientists add CRIPTO to a population of breast stem cells, they retain their ability to produce more stem cells, keeping the population constant. But when CRIPTO's action is blocked with the molecule ALK4, the cells differentiate into mature cells and the population of stem cells shrinks. Credit Stem Cell Reports, Spike, Benjamin T. et al. / Salk Institute for Biological Studies Usage Restrictions None 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.