Cloning and expression of two isoforms of deiodinase gene DIO3 in spotted sea bass (Lateolabrax maculatus)

Type 3 iodothyronine deiodinase (DIO3) is a key enzyme for thyroid hormones, which plays a role in the growth and development of animals. In this study, we identified and cloned two isoforms of DIO3 (LmDIO3a and LmDIO3b) from spotted sea bass (Lateolabrax maculatus). The nucleotide sequences of both LmDIO3a and LmDIO3b had a SECIS (SElenoCysteine Insertion Sequence) element and a T4 domain, and the deduced amino acid sequence similarity was 64.42 %. The mRNAs of both LmDIO3 isoforms were widely distributed in the brain, with high expression levels in the hypothalamus, pituitary, telencephalon and saccus vasculosus (SV). In the non-brain tissues, the expression of LmDIO3a was higher in the retina, heart and spleen, while LmDIO3b was highly expressed in the head kidney and skin. The expression levels of LmDIO3a and LmDIO3b in the hypothalamus and SV were lower in the early stage of gonadal development. However, the expression levels of both in the hypo-thalamus increased significantly in the stage IV of gonadal development, but in the SV were up-regulated significantly in the stage V. The photoperiod experiment showed that the expressions of them were promoted by short photoperiod (8L:16D) and inhibited by long photoperiod (16L:8D) in the hypothalamus. In the SV, their expression trends were consistent (They firstly decreased, and then increased). In the pituitary, the expression of LmDIO3a presented a trend of up and down, while the expression of LmDIO3b showed an opposite trend. In the gonad, long photoperiod promoted the expression of LmDIO3a, but inhibited the expression of LmDIO3b (P < 0.05). There was no significant change in the expression of LmDIO3a in the retina, but the expression of LmDIO3b was significantly inhibited by short photoperiod and promoted by long photoperiod (P < 0.05). That different tissues have different responses to photoperiod, indicating photoperiod induction may have tissue specificity. Altogether, this study provides a reference for further research on the photoperiod regulation mechanism of DIO3 gene in fish.