UCSB stem cell researchers, working with Minerva Biotechnologies, recently reported that a cleaved form of MUC1, a transmembrane mucin protein aberrantly expressed in most solid human tumors, acts as a growth factor receptor on undifferentiated human embryonic stem cells. Lead author Sherry Hikita and coworkers show that activation of MUC1* stimulates growth of hESC and therefore may prove useful in culture and maintenence of hESC cell lines.