Figure 4.

Control of cell differentiation fates by type 3 deiodinase (DIO3). A, DIO3 critically limits the 3,5,3′-triiodothyronine (T3) signal to allow normal differentiation vs T3-induced cell death. Examples show differentiation of cone photoreceptors in the retina and myoblasts during muscle regeneration. B, For Sertoli cell precursors in the testis, DIO3 limits the T3 signal to allow an appropriate period of proliferation vs premature arrest of proliferation, thereby generating a full complement of Sertoli cells.