Embryonic stem cells (ES-5) were transfected with PSV 2-neo-EJ-Ras and the cell colonies were chosen in the selection medium containing Geneticin. Southern-blot analysis showed that all the transfected cells possessed the whole EJ-Ras DNA. Northern-blot analysis demonstrated that the selected clones express higher level of Ras mRNA than the control. When the transfected ES-5 cells were injected into the flanks of nude mice, they formed bigger tumors and more stem cell nests were found. The chimeric ability of the transfected ES-5 cells decreased when the cells were injected into the blastocysts which were then transferred back into the uterine of foster mother. We propose that the over-expression of EJ-Ras in ES-5 cells increase the proliferation ability but decreases the chimeric potential of cell.
