H and E staining of (A, C, and E) control and (B, D, and F) C57BL/6 homozygous mutant thyroids at different stages, demonstrating that in Pten mutants, the increase in size starts very early during thyroid organogenesis (compare B with A at E15.5). (C–G) At the adult stage, mutant thyroids are enlarged, with multilayered epithelial cells surrounding the colloid lumen. Some follicles are dysmorphic with abnormal material inside. (H) Statistical analysis of the weight of P=14 thyroids (n=10 for mutant and wild-type). p<0.05.