Thyroids from 1-month-old or E16.5 embryos of T/ebp(fl/fl) or T/ebp(fl/fl); TPO-Cre mice were subjected to T/ebp immunostaining, TUNEL assay, or hematoxylin and eosin (H&E). T/ebp immunostaining and TUNEL assay of 1-month-old thyroids were performed on serially prepared sections. A and B, In control T/ebp(fl/fl) mice, T/ebp is highly expressed in most follicular cells of 1-month-old mice (panel A: representative is shown by arrow). In T/ebp(fl/fl); TPO-Cre mouse thyroids, the expression of T/ebp is frequently lost (panel B: representatives are shown by arrowheads). C and D, T/ebp is highly expressed (representative is shown by arrow), weakly expressed (representative is shown by arrowhead), or not expressed (representative is shown by red arrow) in both T/ebp(fl/fl) and T/ebp(fl/fl); TPO-Cre E16.5 thyroids. E and F, TUNEL analysis shows no evidence of apoptotic degeneration in either 1-month-old T/ebp(fl/fl) or T/ebp(fl/fl); TPO-Cre mouse thyroids. G and H, Hematoxylin and eosin staining of 1-month-old adult thyroid glands revealed no gross histological differences between T/ebp(fl/fl) and T/ebp(fl/fl); TPO-Cre mouse thyroids. Magnification, ×200. mo, Month.