Figure S1.

Early DN3 cells (DN3a) express pre-TCR structural and signaling molecules. Primary T cell precursors from mouse fetal liver were cocultured for 9 d with OP9-DL1 stromal cells. DN3a cells were purified from the coculture and assessed for the levels of expression and phosphorylation of the pre-TCR structural and signaling molecules, as shown by the histograms. The black line indicates Alexa Fluor 647 staining without primary antibody, and the red lines are the pre-TCR–associated proteins. The results are representative of three independent experiments.