GSI reverses the Notch target gene expression and blocked myeloid differentiation induced by Notch ligand in OP9 culture. (A) Expression of Hes1 and Deltex1 was analyzed by quantitative RT-PCR from 4-day CMP culture on OP9-Dll1 cells relative to the levels detected in OP9-control (set at 1) in the absence (Dll1) or the presence of 10 μM GSI (Dll1, GSI). (B) Day 14 culture of bone marrow–derived CMP cells, cocultured with OP9-control cells (no ligand) or OP9 cells expressing Notch ligand, in the absence or presence of 10 μM GSI, was analyzed for Gr-1 expression. Data are mean values (± SD) of at least 4 determinations and expressed as percentage of Gr-1⁺ cells relative to that from WT cells grown on OP9-control (no GSI; set at 100%).