RT-PCR analysis of gene expression of β-actin, CASPASE-1, and CYCLIN D1 in the sorted late pro–B cells (Fr C) of 13-week-old well-appearing Eμ-ret (Tg⁺) and transgene-negative littermates (Tg⁻) mice. Ret 02/1 is a pro–B-cell leukemia line derived from an Eμ-ret mouse. The autoradiograms shown represent 30-minute to 1-hour exposures of 22 (β-actin) or 26 cycles (CASPASE-1 and CYCLIN D1) of amplification.