Expression of Fzd9 mRNA in B-cell progenitor subsets. (Left) B-cell progenitors subsets were sorted by surface phenotype from WT adult C57/Bl6 and 129SvEv mice, and 1000 to 2000 cell equivalents were subjected to RT-PCR amplification of Fzd9 and beta-actin, as described in “Materials and methods.” Lanes are labeled for the Hardy B-cell subset tested, A to F, from bone marrow. The presence or absence of reverse transcriptase (RT) in the initial cDNA reactions is indicated by + or -, respectively. Mature B cells (CD19⁺ or B220⁺) from spleen and peritoneum were flow sorted for CD5 and surface IgD expression prior to RT-PCR (right panel). Splenic plasma cells (PCs) were isolated as CD138⁺B220^lo/negIgD^- cells. Data are representative of more than 4 experiments for each cell type.