Plant & Animal Genome IX Conference

Poster: Genes & Pathways
P07_15.html

CLONING OF A FUNCTIONALLY ACTIVE TYPE I 5'-DEIODINASE FROM BOVINE THYROID

¹ Growth Biology Laboratory, USDA-ARS, Beltsville, MD 20705, USA

² Equipe Croissance et Metabolismes du Muscle, INRA, Centre de Clermont-Ferrand/Theix, 63122 St. Genes-Champanelle, France

Thyroxine (T4) is produced by the thyroid gland and is converted to the metabolically active form triiodothyronine (T3) by the enzyme 5'-deiodinase. Conversion of T4 to T3 occurs primarily in the liver by type I 5'-deiodinase (5'-DI), although high levels of 5'-DI activity have been demonstrated in the thyroid gland of rats. There are conflicting reports on the presence of 5'-DI activity in the thyroid gland of ruminants. Our objective was to determine whether functional 5'-DI is expressed in the bovine thyroid gland. Liver and thyroid tissues were collected from four 16-month old steers and total RNA was extracted for RT-PCR. Sequence-specific primers were designed from conserved regions of rat, mouse, human, canine and turkey 5'-DI nucleotide sequences. The 5'-DI partial cDNA from bovine liver and thyroid gland were cloned and sequenced. The bovine sequences share 88, 87, 84 and 83% identity with canine, human, rat and mouse sequences, respectively. Activity of the 5'-DI enzyme in both liver and thyroid tissues was estimated by quantifying ¹²⁵I^- released from 3,3' ,5'-[¹²⁵I]-T3. Specific activity of 5'-DI was 3.5x10³ times greater in liver than in the thyroid gland. This study demonstrates both expression of 5'-DI mRNA and functional activity of the enzyme in bovine thyroid gland.