Molecular cloning and sequence analysis of chicken type I deiodinase cDNA: expression in normal and dwarf broiler chickens.

A cDNA encoding the chicken type I iodothyronine deiodinase (cDI-1) was isolated and sequenced from a cDNA library prepared from ConA-activated chicken splenic T-lymphocytes. The coding region of cDI-1 cDNA is composed of 738 basepairs (bp) which encodes a 246 amino acid protein. The predicted amino acid sequence of cDI-1 indicates only 60% identity to several mammalian type I deiodinases. The cDI-1 cDNA contains a codon for a highly conserved selenocysteine residue (Cys124). Northern blot analysis of total RNA prepared from different tissues of a 3-week-old broiler chicken shows a single transcript (2 kb) in liver and kidney. The abundance of hepatic cDI-1 transcripts in growth hormone receptor (GHR)-deficient dwarf chicken was similar to normal chickens despite lower levels of plasma T3 (37% lower) and elevated levels of T4 (21% higher) in dwarf chickens. This finding suggests that regulation of hepatic cDI-1 mRNA is GH-independent in the post-hatch chicken.