BARON, M.P.; Univ. of New Hampshire: Retinoic Acid Stimulates Pigmentation Development In Summer Flounder: Insight Into Nuclear Receptor Dynamics

This study examined the effect of retinoic acid (RA) on pigmentation development in summer flounder (Paralichthys dentatus). Flounder larvae were immersed in 5 and 10 nM concentrations of RA for a period of 10 days, and then reared through metamorphosis. Both RA-treated and untreated fish developed normal ocular side pigmentation. However, over 60% of the fish in the RA-treated groups expressed partial or total pigmentation of the blind side. None of the untreated fish exhibited pigmentation on the blind side. These results are consistent with similar results in Japanese flounder (Paralichthys olivaceus) (Miwa and Yamano, 1999). The effects of RA on pigmentation development may be mediated through interaction with thyroid hormone (TH). In flounder, as in amphibians, TH is the �master control� of metamorphosis (Inui and Miwa, 1985). Receptors for both RA and TH dimerize with the retinoid X receptor (RXR), and normal function of both RA and TH depends on the availability of RXR (Yu et al., 1991). This co-dependency may result in competition for RXR. Evidence for competition exists both in the ability of excess RA to inhibit a function of TH (metamorphosis) (Miwa and Yamano, 1999), and in the ability of excess TH to inhibit a function of RA (pigment development) (Yoo et al., 2000). Supported by New Hampshire Sea Grant #111381 to J. Bolker.