Predominant expression of Rap1b isoform in B cells and slight impairment of early B-cell development in Rap1b-deficient mice. (A) Expression of Rap1a and Rap1b in wild-type (+/+) and Rap1b-deficient (−/−) T and B cells. Based on the expression of B220 and Thy1.2, splenic T and B cells were sorted from wild-type and Rap1b-deficient mice. Total cell lysates were subjected to Western blot analysis with anti-Rap1b, anti-Rap1 or anti-Actin antibodies. (B) The numbers of total BM cells and total BM B cells in wild-type and Rap1b-deficient mice. Data shown are obtained from 12 mice of each genotype. (C) B-cell development in BM of wild-type and Rap1b-deficient mice. BM cells from wild-type and Rap1b-deficient mice were stained with anti-B220, anti-CD43, and anti-IgM antibodies. Percentages indicate cells in the gated lymphoid population. Data are representative of 12 mice per genotype. (D) Pro- and pre-B cells in BM of wild-type and Rap1b-deficient mice. Percentages indicate cells in the gated B220⁺IgM⁻ population. Data are representative of 12 mice per genotype. (E) The numbers of pro-/pre-, immature, and mature B cells in BM of wild-type and Rap1b-deficient mice. Data shown are obtained from 12 mice of each genotype.