Isl1loxP/loxP;Tg(Tshb-cre) mice have impaired thyroid function. A, H&E stain of thyroid gland sections from 8-week-old Isl1loxP/loxP;Tg(Tshb-cre) mice and controls. Photos were taken at ×100. Scale bar, 100 μm. B, The average follicular area in Isl1loxP/loxP;Tg(Tshb-cre) was 221 ± 35 pixels (n = 4) vs control mice 325 ± 53 pixels (n = 3); **, P < .001 according to Mann-Whitney U test. C, ISL1 immunostaining (green) on thyroid gland sections from 8-week-old mice. Photos taken at ×630. Scale bar, 50 μm.