Three types of iodothyronine deiodinase have been identified in vertebrate tissues. cDNAs for the types I and III have been cloned and shown to contain an inframe TGA that codes for selenocysteine at the active site of the enzyme. We now report the cloning of a cDNA for a type II deiodinase using a reverse transcription/polymerase chain reaction strategy and RNA obtained from Rana catesbeiana tissues. This cDNA (RC5'DII) manifests limited but significant homology with other deiodinase cDNAs and contains a conserved in-frame TGA codon. Injection of capped in vitro synthesized transcripts of the cDNA into Xenopus laevis oocytes results in the induction of deiodinase activity with characteristics typical of a type II deiodinase. The levels of RC5'DII transcripts in R. catesbeiana tadpole tail and liver mRNA at stages XII and XXIII correspond well with that of type II deiodinase activity but not that of the type III activity in these tissues. These findings indicate that the amphibian type II 5'-deiodinase is a structurally unique member of the family of selenocysteine-containing deiodinases.
"The cDNAs coding for the three deiodinases have been isolated from rat, human and other species (Berry et al. 1991, Croteau et al. 1995, 1996). All of them contain one in-frame TGA codon that is translated as selenocysteine due to the presence of a specific structure, the selenocysteine insertion sequence (SECIS), in the 3-untranslated region of their mRNAs (Berry et al. 1991, Davey et al. 1995). "
[Show abstract][Hide abstract] ABSTRACT: Type II 5' deiodinase (D2) activity produces triiodothyronine (T3) from thyroxine (T4) and is induced by cold and norepinephrine (NE) in brown adipose tissue. T3 is required for and amplifies the adrenergic stimulation of D2 activity and mRNA in cultured brown adipocytes. D2 is upregulated by insulin and decrease in fasting. We now study the regulation by insulin of the adrenergically induced D2 activity and mRNA in primary cultures of rat brown adipocytes. Insulin alone does not increase D2 activity or mRNA. Insulin-depleted cells show a reduction in the adrenergically induced D2 activity, which is proportional to the length of insulin depletion and is restored after insulin addition. IGFs mimic this effect at higher doses. ERK 1/2 MAPK activity (p44/p42), stimulated by insulin, serum and NE, is an absolute requirement for the adrenergic stimulation of D2 activity and mRNA. PI3K is stimulated by insulin and serum, and NE increases the effect of insulin. The action of insulin on D2 is not due to changes in D2 half-life or in the proteasome-mediated degradation of D2, but it seems to modulate the transcriptional induction mediated by NE. D2 mRNA expression, induced by NE plus T3, is reduced when insulin is withdrawn at early differentiation stages. Insulin or IGF-I promotes increases in D2 mRNA. Insulin is required for the induction of D2 mRNA by T3. In conclusion, MAPK signaling is required for the adrenergic stimulation of D2 activity and mRNA, and insulin stimulates D2 activity via MAPK and PI3K and enhances the adrenergic pathways.
"Deiodinases are selenoproteins, containing the rare amino acid selenocysteine in their active site (St Germain & Galton 1997). The cloning of the first deiodinase cDNA in the rat by Berry et al. (1991) led to a very rapid revelation of deiodinase sequences in other species such as the human (Mandel et al. 1992, Salvatore et al. 1995, 1996), the mouse (Maia et al. 1995), the dog (Toyoda et al. 1995), the chicken (Van der Geyten et al. 1997, Gereben et al. 1999), tilapia (Lee et al. 1993, Sanders et al. 1997, 1999), Rana catesbeiana (Becker et al. 1995, Davey et al. 1995) and Xenopus laevis (St Germain et al. 1994). "
[Show abstract][Hide abstract] ABSTRACT: Iodothyronine deiodinase in vitro activity studies in the chicken showed the presence of type I and type III iodothyronine deiodinase activity in both liver and kidney. Due to the lack of a specific antiserum the cellular localization of the deiodinase proteins could not be revealed until now. In the present study, specific antisera were used to study the renal and hepatic distribution of type I and type III iodothyronine deiodinase protein in the chicken. Immunocytochemical staining of liver tissue led to an immunopositive signal in the hepatocytes in general. Moreover, a zonal distribution could be detected for both enzymes. Maximum protein expression was shown in a thin layer of hepatocytes bordering the blood veins. Although pericentral localization of type I deiodinase protein has been previously reported in the rat, no data were given concerning type III deiodinase protein. In the present study, we report the co-localization of both enzymes in the chicken. Co-expression of the deiodinases was also found in the kidney. Expression of both proteins was associated with the tubular epithelial cells and with the transitional epithelium, and the inner longitudinal and outer circular muscle layers of the ureter. No staining could be detected in the lamina propria or in the fat tissue surrounding the ureter.
Journal of Endocrinology 05/2004; 181(1):85-90. · 3.72 Impact Factor
"The scale bar is 1 mm. mammalian brain in general but especially in the pituitary while hypothyroid mammals express high levels of D2 in their pituitaries (Croteau et al., 1998). The regulation of D2 levels in adult frogs has not been studied, but the situation is unique in the pituitary of a developing tadpole where TSH production by the pituitary is insensitive to high levels of TH until climax when D2 is up-regulated. "
[Show abstract][Hide abstract] ABSTRACT: The thyroid gland synthesizes thyroxine (T4), which passes through the larval tadpole's circulatory system. The enzyme type II iodothyronine deiodinase (D2) converts thyroxine (T4) to the active hormone 3,5,3'-triiodothyronine (T3) in peripheral tissues. An early response to thyroid hormone (TH) in the Xenopus laevis tadpole is the stimulation of cell division in cells that line the brain ventricles, the lumen of the spinal cord, and the limb buds. These cells express constitutively high levels of D2 mRNA. Exogenous T4 induces early DNA synthesis in brain, spinal cord, and limb buds as efficiently as T3. The deiodinase inhibitor iopanoic acid blocks T4- but not T3-induced cell division. At metamorphic climax, both TH-induced cell division and D2 expression decrease in the brain. Then D2 expression appears in late-responding tissues including the anterior pituitary, the intestine, and the tail where cell division is reduced or absent. Therefore, constitutive expression of D2 occurs in the earliest target tissues of TH that will grow and differentiate, while TH-induced expression of D2 takes place in late-responding tissues that will remodel or die. This pattern of constitutive and induced D2 expression contributes to the timing of metamorphic changes in these tissues.
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