Characterization of OP9 stromal cells expressing murine Jagged1. (A) Flow cytometric analysis of OP9-MigR1, OP9-Jagged1 (Jag1), and OP9-Delta1 for GFP expression (top row) or for cell surface expression of Jagged1 (bottom panels). Empty histograms show negative controls. For GFP, control is fluorescence in nontransduced OP9 cells (top panels). For anti-Jagged1 staining, control is OP9-MigR1 cells stained with anti-Jagged1 (bottom row). (B) Expression of Notch ligand mRNAs in OP9 stromal cells and normal thymic epithelial cells (TECs) by RT-PCR followed by Southern blot. cDNAs were normalized by TaqMan PCR for HPRT, and 5-fold serial dilutions of normalized cDNAs were subjected to PCR for different Notch ligands or G3PDH as a loading control. (C) OP9 cell lysates were immunoprecipitated with an antibody directed against the extracellular domain of Jagged1, and Western blots were probed with antisera directed against the intracellular domain of Jagged1.