E18.5 (A, C, and E) control and (B, D, and F) mutant thyroids stained for (A and B) NKX2.1, (C and D) PTEN, and (E and F) p-AKT. Note that the Nkx2.1-positive cells are detected in the mutant. Pten expression is strongly decreased in the mutant epithelial cells. Conversely, p-AKT signal is increased in the mutant thyroid. Upper right panels are the corresponding high magnification pictures. (G) Relative expression level for Pten by qPCR proving Pten deletion in the mutant thyroids in both C57BL/6 and BALB/c genetic backgrounds. *p<0.05.