Effect of Salinity on the Alteration of Thyroid Hormone Receptor Alpha (TRα) Protein Expression in the Chinese edible Frog, Hoplobatrachus rugulosus, Tadpole

Abstract

Thyroid hormone (TH) promotes growth and remodels of the tadpole into complete adult frog. Since water salinity is a one factor effect on metamorphosis of anuran. Thus, the present study aims to study the effects of saline water on the levels of total body fluid of TH (T₄ ) and TRα protein expression in gill, skin, and tail fin of Hoplobatrachus rugulosus tadpoles at pro-metamorphic stage. Tadpoles (stage 27–30) were exposed to salinities (NaCl); 0, 2, 4 and 6 parts per thousand (ppt) for 21 days. The total body fluid of T₄ increased in 2 and 4 ppt groups, while in 6 ppt group was not change. Western blot analysis revealed that 34 kDa of TRα was detected in the larval gill, skin and tail fin. The expression of TRα protein increased in gill and kin in 2 and 4 ppt groups, but decreased in 6 ppt group. Decreased of TRα protein expression in tail fin was found in tadpoles exposed to 2 ppt, but not in 4 and 6 ppt groups. These suggest that at low water salinity (≤4 ppt) increased in T₄ and TRα protein could be involved in promoting growth and metamorphosis in H. rugulosus tadpoles.