Fig 3.

E3′ and Ed are required for Igκ gene expression in splenic B cells of conditional E3′^F/F Ed^−/− mice harboring CD23-Cre. (A) FACS analysis was performed to measure the percentages of Igκ⁺ B cells in spleen (SP) or bone marrow (BM) of the indicated genetic lines of mice. Data are representative of independent FACS analyses from at least 4 mice of each genotype. In addition, we obtained essentially identical results with respect to Igκ gene expression in splenic B cells from E3′^F/F Ed^−/− mice that possessed or lacked the flanking Neo gene in the germ line or in samples from E3′^F/F Ed^−/− CD23-Cre mice that possessed or lacked the flanking Neo gene in the germ line. This rules out the possibility that the prior presence of the Neo gene in the targeted locus affects subsequent Igκ gene expression upon its deletion together with E3′. (B) Splenic cells (SP), bone morrow cells (BM), B220⁺ Igκ⁺ B cells (κ⁺B), or B220⁺ Igκ⁻ B (κ⁻B) cells were isolated from spleen or bone marrow of the indicated genetic lines of mice. Southern blotting was performed to assay for the loss of E3′. (C) Total splenic B cell numbers in the indicated genetic lines of mice. Data are presented as means plus SD (n = 5, WT or E3′^F/F Ed^−/− versus E3′^F/F Ed^−/− CD23-Cre, P < 0.05 by Student's t test [∗]). (D) Percentages of Igλ⁺ B cells in spleen (SP) and bone marrow (BM) of the indicated genetic lines of mice. Data are representative of independent FACS analyses from at least 5 mice of each genotype. (E) FACS analysis was performed to measure the percentages of immature B, pre-B, and pro-B found in bone marrow of the indicated genetic lines of mice. Data are representative of independent FACS analyses from at least 3 mice of each genotype.