POU5F1 and embryonal carcinoma: The half-life of c-MycT58A is shorter than that of Oct3/4 and Klf4 in some cell types (Klf4, 120 min in human esophageal cancer cells [67], [68]; Oct3/4, 90 min in mouse embryonic carcinoma cells [69]; and c-MycT58A, 51–63 min in NIH3T3 and REF52 fibroblasts [43], [45]), but the differences in stability do not appear great enough to explain the large differences in the number of supporting cells expressing detectable levels of Oct3/4 and Klf4 compared to c-MycT58A (Fig. 4).