Molecular cloning, expression, and radiation hybrid mapping of the bovine deiodinase type II (DIO2) and deiodinase type III (DIO3) genes

Thyroid hormones play a critical role in mammalian development and metabolism. Their activity is regulated in a complex, tissue-specific manner by three isoforms of deiodinases. The goal of this study was to sequence the full-length bovine type II deiodinase (DIO2) and type III deiodinase (DIO3) cDNAs and characterize mRNA expression levels of each of the three deiodinase isoforms in several bovine tissues. Sequencing of bovine DIO2 and DIO3 cDNAs revealed a high degree of predicted amino acid sequence identity with their orthologs in other mammalian species and demonstrated the conservation of selenocysteine residues within the catalytic domains of both bovine proteins. Bovine DIO2 and DIO3 were positioned on chromosomes 10 and 21, respectively, by radiation hybrid mapping. Expression patterns of the three deiodinase isoforms were similar for deiodinase type I (DIO1) and DIO2 to those observed in other species. Expression level of DIO3 transcripts was greatest in mammary gland and kidney, although low-level expression was detected in most tissues sampled. Results of this work will aid in the study of deiodinase gene expression and thyroid hormone regulation in cattle.