Early morphological and proliferative changes in young transgenic mice. A, Quantitative real-time PCR showing HPRT mRNA-normalized expression levels (mean ± sem) of endogenous (white bars) and mutant DREAM (black bars) in the thyroid of 2- to 3-month-old wild-type (wt) and LeuBTA7 and LeuBTA15 DREAM transgenic mice. B–E, Hematoxylin and eosin staining of paraffin sections from 2- to 3-month-old wild-type (B–D) and transgenic (C–E) mice. A representative example of the hyperproliferative phenotype observed in both transgenic lines is shown. Magnification, ×100 (B and C) and ×600 (D and E). F, Quantitative real-time PCR showing HPRT mRNA-normalized expression level (mean ± sem) of proliferating cell nuclear antigen in wild-type (n = 9), LeuBTA7 (n = 8), and LeuBTA15 (n = 11) mice. Significant differences from wild-type mice by unpaired Student’s t test are indicated: *, P = 0.0252; **, P = 0.0027.