Thyroid hormone-dependent differential regulation of multiple arginase genes during amphibian metamorphosis.

We have cloned three nonhepatic arginase genes in Xenopus laevis. The deduced amino acid sequences of the three arginases are almost identical and share about 60% identity with mammalian as well as Xenopus liver arginase. Both the liver and nonhepatic arginase genes are activated early during embryogenesis. The liver arginase gene is strongly expressed in tadpole liver, but weakly in other tissues. In contrast, the nonhepatic arginase genes have the strongest expression in the tadpole tail. During metamorphosis, the liver and nonhepatic arginase genes show distinct regulation patterns. In the intestine, both types of arginase genes are activated during the remodeling period. In the tail, the liver arginase gene is activated during tail resorption, whereas the nonhepatic ones are highly expressed throughout all stages examined. Finally, in the hindlimb, the liver arginase is up-regulated slightly during development, whereas the nonhepatic ones have low levels of expression until the end of metamorphosis. During 3,5,3'-L-triiodothyronine (T3)-induced metamorphosis, the nonhepatic arginase genes are activated very quickly, whereas the liver arginase gene is a late T3 response gene. These differential regulation patterns during normal and T3-induced metamorphosis suggest potential functions for the arginases during tissue remodeling.