EFFECT OF THYROID-HORMONE ON DEVELOPMENTAL TRANSITION OF MYOSIN LIGHT-CHAINS DURING FLOUNDER METAMORPHOSIS

Thyroidal control of the transition of myosin isoforms during flounder metamorphosis was examined by the administration of either only thiou rea (TU), a potent inhibitor of thyroid hormone synthesis, or thyroxin e (T-4) together with TU into premetamorphic larvae. Immersion of prem etamorphic larvae in 400 mu M of TU inhibited the appearance of the ad ult-type DTNB (5,5'-dithio-bis-nitrobenzonic acid) light chain, LC(2), whereas administration of T-4 with TU induced a precocious appearance of LC(2) and decreased the relative amount of the larval-type DTNB li ght chain, LC(2). TU was administered into juveniles just after compl etion of metamorphosis. The treatment did not affect the composition o f the myosin light chains. These results suggest that thyroid hormone irreversibly turns on the switch for transition of the DTNB light chai ns from larval to adult type during metamorphosis of the flounder. (C) 1994 Academic Press, Inc.