Asymmetric growth and development of the Xenopus laevis retina during metamorphosis is controlled by type III deiodinase

During the metamorphosis of the Xenopus laevis retina, thyroid hormone (TH) preferentially induces ventral ciliary marginal zone (CMZ) cells to both i ncrease their proliferation and give rise to ipsilaterally projecting gangl ion cells. Here we show that dorsal CMZ cells express type ill deiodinase ( D3), an enzyme that inactivates TH. The dorsal CMZ cells can be induced to proliferate if deiodinase activity is inhibited. D3 or dominant-negative th yroid hormone receptor transgenes inhibit both TH-induced proliferation of the ventral CMZ cells and the formation of the ipsilateral projection. Thus , the localized expression of D3 in the dorsal CMZ cells accounts for the a symmetric growth of the frog retina.