Meeting Abstract

P1.6  Jan. 4  A Dramatic Influence of Thyroid Hormone on Larval Southern Flounder Otolith Development WANG, X; TAN, Y; SCHREIBER, AM*; Carnegie Institution, Embryology schreiber@ciwemb.edu

Fish inner ears include three pairs of otoliths that are implicated in hearing (saccula and lagenae) and postural orientation (utricles). Flatfish metamorphosis is accompanied by a 90 degree change in swim posture as the bilaterally symmetrical larva transforms into an asymmetric juvenile that swims on one side. This study profiles the morphological development of each otolith. Intriguingly, the utricles are asymmetric in adult flounder: in left-sided flounder the top (left) utricle is elongated and comma shaped, whereas the bottom (right) utricle is scalloped and oval shaped. In right-sided flounder the utricles are mirror-image reversals of their left-sided siblings�. In contrast, no obvious asymmetries are visible in the adult saccula or lagenae. During pre-metamorphosis (3~23 dph) only the saccula and utricles are present. The lagenae form during metamorphosis (24~30 dph) and the saccula and utricle sizes increase 2-4 fold. Interestingly, otolith size is entirely dependent on thyroid hormone (TH): pre-metamorphic larvae treated with methimazole (an inhibitor of endogenous TH production) for 7d displayed no otolith growth, whereas treatment with methimazole + TH caused utricle and saccula sizes to triple and the lagenae to form. We have identified otopetrin-1, a gene implicated in zebrafish embryonic otolith growth, as a new flounder TH direct-response gene. Our findings suggest that TH plays a critical role in otolith growth and development during flounder metamorphosis.