CASTELLANOS-KOTKOFF, M; CARPIZO-ITUARTE, E*; DE-LA-ROSA-V�LEZ, J; Fac. de Biolog�a. Univ. A. de Baja California; Inst. de Inv., Oceanol�gicas. Univ. A. de Baja California; Fac. de Ciencias Marinas. Univ. A. de Baja Califonrnia: Thyroxine effect in metamorphosis and presence of the nuclear receptor COUP-TF in the larvae of the sea urchin Lytechinus pictus
Several reports have documented the effect of thyroxine in the development of sea urchins and other echinoderms, including its effect on induction to metamorphosis of the sea urchin Evechinus chloroticus. The action of thyroxine as an inducer to metamorphosis has not been tested in species that inhabit the coast of Baja California. In the present study we induced to metamorphose competent larvae of three species of sea urchins Lytechinus pictus, Strongylocentrotus purpuratus, and S. fransicanus with different concentrations of thyroxine. We found a significant effect of thyroxine with concentrations between 10-4 M and 10-6 M , and L. Pictus, was the more responsive species. The effect was slightly lower for S. purpuratus, and the lowest for S. fransiscanus. Percentages of metamorphosis were always lower than the ones obtained with KCL as a positive control. As an additional approach we isolated from L. pictus, a fragment presumably belonging to the ligand-binding domain (LBD) of the orphan nuclear receptor COUP-TF, which belongs to the steroid/thyroid hormone receptor superfamily previously reported for S. purpuratus. With this fragment we constructed a probe to follow its expression in larvae of 6 and 8th arms of L. pictus. The alignment showed a homology of 98% between species. The expression of the COUP-TF isolated from L pictus has a pattern that is confined to the ciliary band and other ectodermal regions in larvae of 6 arms or younger. This initial pattern changes in larvae of the six and eight arms, when the juvenile rudiment is present.
