Identification of thyroid hormone receptors α and β genes and their expression profiles during metamorphosis in Rana chensinensis

Abstract

To explore the role of thyroid hormones in organ remodeling during the metamorphosis of amphibians, the cDNAs of twothyroid hormone receptors ( TRαandTRβ ) inRana chensinensiswere identified. The 1257 bp ofrcTRαcDNA encoding 418 amino acidsand the 1122 bp ofrcTRβcDNA encoding 373 amino acids were cloned. Their polypeptide sequences contain two highly conservedcysteine-rich zinc fingers in the DNA-binding domain, while rcTRβ is 42 amino acids shorter in its A/B domain when compared withrcTRα. Fifty-five amino acids differed between the TRα and TRβ domains. ThercTRαandrcTRβmRNA levels in the liver, brain, skin,and tail of tadpoles were analyzed via qRT-PCR during metamorphosis. The results showed that the changes ofrcTRαmRNA levelswere moderate while those ofrcTRβwere dramatic in all 4 tissues during metamorphosis. In addition, the levels ofrcTRβmRNA wererelatively low at premetamorphosis and reached a peak around the climax. Tissue-specific expression ofrcTRαandrcTRβsuggests thatthyroid hormones play various roles in different organs or tissues at different developmental stages of metamorphosis.