RT-PCR analysis of gene expression of β-actin, CYCLIN D1, and CYCLIN D2 in the pro–B-cell leukemia of an Eμ-ret mouse. Bone marrow was recovered from an Eμ-ret mouse (2-19) with adenopathy and splenomegaly and directly cultured for 4 days with or without IL-7 (100 U/mL). The cells survived without proliferation in media without IL-7 and proliferated fourfold in media supplemented with IL-7. The autoradiograms shown represent 30-minute exposures of 22 (β-actin) or 30 cycles (CYCLINS) of amplification.