Notch pathway–induced myeloid development block is fucosylation dependent. Expression of Gr-1 from day 14 culture CMP cells derived from FX^−/− mice maintained on standard chow (FX^−/−, no fucose; B) or maintained on fucose-supplemented chow at least 4 weeks and with 1 mM fucose in the culture medium (C), was compared with WT CMP culture on OP9-control and OP9-Dll1 (A), in the absence or presence of 10 μM GSI. Data are mean values (± SD) of at least 4 determinations and expressed as percentages of Gr-1⁺ cells relative to that on OP9-control (no GSI; set at 100%). Cells from panels B and C cultured on OP9-control and OP9-Dll1 were examined by May-Grünwald-Giemsa staining and FACS analysis of CMP to GMP conversion (D,E). Numbers on plots are percentages of the indicated cell types. (F) Day 14 culture of marrow CMP cells derived from WT, FX^−/− mice maintained on standard chow (FX^−/−, no fucose), and mice with double deficiency for the 2 alpha1,3fucosyltransferases Fuc-TIV^−/−Fuc-TVII^−/− (Fuc-T^−/−), cocultured with OP9-control cells (no ligand) or OP9 cells expressing Notch ligands, 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 cells grown on OP9-control (set at 100%). Student t test was performed to compare the parameters obtained with GSI to those without GSI (A-C) or parameters obtained from Fuc-T^−/− and FX^−/− mice to those from WT mice (F).