Hematopoietic stem celldeletion of Cdc42 causes defective B-cell development in bone marrow. (A) Bone marrow cells from Mx-Cre;Cdc42^loxp/loxp donor mice were transplanted by intravenous injection into lethally irradiated BoyJ mice. Recipient mice were injected with polyI:C to delete Cdc42 in hematopoietic stem cells. (B) Bone marrow cells and splenocytes were isolated from WT and Cdc42^−/− (KO) mice, counted, stained with anti-B220 antibody, and then analyzed by flow cytometry. The number of B220⁺ cells was calculated by multiplying the total number of bone marrow cells and splenocytes by the percentage of B220⁺ cells (**P < .01; *P < .05). The data are means ± SD. (C) Bone marrow cells were stained for IL-7R, lineage (Lin) markers (ie, B220, CD3, CD4, CD8, Gr1, CD11b, and TER119), Sca-1, and c-Kit followed by flow cytometric analysis. Common lymphoid progenitor (CLP) cells (Sca1^medc-kit^med-high) were gated from Lin⁻IL-7R⁺ cell population. Data are representative of 4 mice. (D) Bone marrow cells were stained with antibodies against B220 and IgM and, using flow cytometry, analyzed for proB/preB cells ((B220^lowIgM⁻), immature B cells (B220^lowIgM⁺), and mature recirculating B cells (B220^highIgM⁺). Data are representative of 4 mice.