B-cell defects in the absence of Ptch1. (A) Southern blot analysis for Ptch1 deletion status. Bone marrow (BM), spleen (Sp), and thymus (Thy) from MxPtch1^+/fl and MxPtch1^fl/fl mice harvested 4 weeks after administration of poly(I:C). Wild-type Ptch1 allele (+) and loxP-flanked Ptch1 allele (fl) have the same size band. Deleted Ptch1^fl allele (Δ). (B) Dot plots of BM cells stained with B220 and CD25. The MxPtch1^Δ/Δ dot-plot is an example of a severely affected animal. (C) B-cell subsets in BM from Ptch1-wild-type (Ptch1^fl/fl), heterozygous (MxPtch1^+/Δ) and null (MxPtch1^Δ/Δ) mice: see supplemental Figure 1 for definitions of B-cell subsets. Mean plus SD calculated from 5 mice of each genotype. *P < .05 by one-way ANOVA. (D) Annexin V expression on pre-BII and recirculating B cells within the BM. The mean percentage of annexin V⁺ cells calculated from 3 mice for each genotype is shown.