Overexpression of Id2 blocks B-cell development. (A) Illustration of MSCV-IRES-GFP and MSCV-Id2-IRES-GFP retroviral vectors (left panel). Id2 expression levels in BMC-GFP and BMC-Id2-GFP were determined by Western blot analysis (right panel). (B) BMC-GFP and BMC-Id2-GFP were transplanted into lethally irradiated mice with supporting BMCs. A representative from 4 independent experiments is shown here. Eight mice were analyzed in each transplantation. Hematopoietic reconstitution in recipient BM was examined 4 weeks after transplantation by analyzing the percentage (left panel) and the total cellularity (right panel) of GFP-positive cells. (C) B-cell reconstitution in recipient BM was examined 4 weeks after transplantation by FACS analysis of GFP-positive BMCs using B220 and CD43 antibodies.