ERas is Expressed in Primate Embryonic Stem Cells but not Related to Tumorigenesis

The ERas gene promotes the proliferation of and formation of teratomas by mouse embryonic stem (ES) cells. However, its human orthologue is not expressed in human ES cells. This implies that the behavior of transplanted mouse ES cells would not accurately reflect the behavior of transplanted human ES cells and that the use of nonhuman primate models might be more appropriate to demonstrate the safety of human ES cell-based therapies. However, the expression of the ERas gene has not been examined in nonhuman primate ES cells. In this study, we cloned the cynomolgus homologue and showed that the ERas gene is expressed in cynomolgus ES cells. Notably, it is also expressed in cynomolgus ES cell-derived differentiated progeny as well as cynomolgus adult tissues. The ERas protein is detectable in various cynomolgus tissues as assessed by immunohistochemisty. Cynomolgus ES cell-derived teratoma cells, which also expressed the ERas gene at higher levels than the undifferentiated cynomolgus ES cells, did not devel...