The roles of thyroid hormone receptor and T3 in meta-morphosis of Haliotis diversicolor

Thyroid hormone is a kind of important hormone which regulates metamorphosis. Its role is well described in amphibian metamorphosis. Thyroid hormones (T3 and T4) have also been demonstrated to play a role in metamorphosis of marine invertebrates. However, the mechanism of thyroid hormone in metamorphosis of marine invertebrates remains unknown. A homolog of vertebrate thyroid hormone receptor (TR) was cloned and identified in abalone Haliotis diversicolor and was named HdTR. The mRNA expressions of HdTR, thyroid peroxidase (TPO), thyroid peroxidase 1 (TPO1), idothyronine deiodinase III (IDIII ) and integrin alpha-V (ITGAV) had significant difference in metamorphosis of H. diversicolor. Metamorphosis rate and mortality rate were significantly different in HdTR RNAi experiment and T3 inducing experiment. In RNAi experiment, ITGAV and CCND1 (cyclin D1) expression of dsRNA HdTR exposing group were significantly lower than those of blank control and negative control. But CTNNB (catenin beta) expression of dsRNA HdTR exposing group was higher than that those of blank control and negative control. ERK (extracellular signal regulated kinases) and PI3K (phosphoinositide-3-kinase) had no significant difference in RNAi experiment. Moreover, ITGAV of 1 mu mol/L T3 group was significantly lower than that of 0 mu mol/L T3 group, PI3K expression of 10 mu mol/L T3 group was higher than that of 0 mu mol/L T3 group, and the other genes expression had no significant difference in T3 inducing experiment. The data of genes expression suggested that CCND1 might be an effector gene of TR genomic action, while CTNNB might be regulated by unliganded TR. CCND1 and CTNNB may be involved in cell proliferation of metamorphosis. T3 might regulate the expression level of PI3K via nongenomic way. These results shed light on the mechanism of thyroid hormone in abalone metamorphosis.