Fzd/Wnt expression can be monitored throughout leukemogenesis in Eμ-TCL1 transgenic mice. (A) Eμ-TCL1 transgenic mice show expansion of CD5⁺ B cells in blood at 6 months, but not at 6 weeks, of age. Gating on CD5⁺ and CD5⁻ B cells reveals the usual 2% to 7% Igλ-expressing cells in CD5⁻ B cells (population A), but a large clonal expansion of Igλ⁺ cells in the CD5⁺ compartment in this mouse (bottom right histogram, population C). (B) PCR of genomic DNA for Ig HC rearrangement confirms flow analysis, with the normal 4 bands in population A, oligoclonal (reduced) bands in population B, and a single intense band in population C. (C) Quantitative RT-PCR is performed on flow cytometrically sorted populations A, B, and C (> 95% purity) for Fzd6 expression, which is normalized within each sample to the β-actin RNA level. The data are representative of 3 separate analyses of λ⁺ clonal populations in different mice.