Expansion of C3G-F⁺ DN cells is independent of pre-TCR. (A,B) Rag2^−/− (•) and Rag2^−/− SPA-1^−/− (○) HPCs were infected with empty or C3G-F–containing retrovirus followed by transplantation into irradiated B6 mice. Twelve weeks later, mice were killed, and the proportions and numbers of GFP⁺ thymocytes were determined. The thymocytes were 3-color analyzed by FACSCalibur, and CD4/CD8 expression profiles in GFP⁺ population are indicated.