Type I iodothyronine deiodinase in euthyroid and hypothyroid chicken cerebellum.

Immunocytochemistry using polyclonal anti-type I deiodinase (D1) led to the localization of D1 protein in the internal granule cells of the cerebellum in 1-day-old chicks, which was confirmed by the presence of in vitro D1 activity. Western blot analysis of hepatic and cerebellar extracts revealed a band of 27 kDa. In hypothyroid embryos D1 was expressed in both the internal and external granule cell layer and the signal diminished with more severe hypothyroidism, which is in agreement with the expected downregulation of D1 activity during hypothyroidism. In accordance with the protein data, hypothyroidism resulted in the downregulation of cerebellar D1 mRNA. Finally, histological stainings confirmed that the lack of staining in the external germinal layer of 1-day-old euthyroid chicks was due to the fact that migration of immature granule cells from the external towards the internal layer was completed at this stage while cell migration was retarded in hypothyroid animals.