Prerecombined antibody genes do not rescue Fnip1^−/− B cells. (A) Igκ staining in Fnip1^+/− and Fnip1^−/− BM B220⁺ B cells. (B) Histogram of intracellular Igμ expression in B220⁺CD43⁺ pro-B cells from Fnip1^+/− and Fnip1^−/− mice. (C) D-J and V-DJ recombination analysis in WT and KO fraction C/C′ B cells as determined by PCR-Southern blot. (D) B220/IgM expression profiles in Fnip1^−/− mice expressing B1-8 heavy chain (Igh^B18)²⁴  or the αHEL heavy and light chain transgene (MD4 HEL).²⁵  Right bar graph represents the mean ± SD of IgM⁺B220⁺ B cells from each strain; n values were as follows: 6 for Fnip1^+/− and Fnip1^−/−, and 3 for Fnip1^−/−Igh^B1-8 and Fnip1^−/−MD4 HEL. (E) Same analysis as in panel D but using CD19 and CD4 staining of splenocytes; n values: 5 mice for Fnip1^+/− and Fnip1^−/−, and 4 mice for Fnip1^−/−Igh^B1-8 and Fnip1^−/−MD4 HEL. Each FACS analysis is representative of at least 3 independent experiments.