Auto-regulation of thyroid hormone receptors in the goldfish ovary and testis

Thyroid hormones, acting via their cognate thyroid receptors (TRs) act as mediators and modulators of several physiological processes and homeostasis. A clear role for the TRs in reproduction has not yet been established although several lines of recent evidence suggest that they are involved in the regulation of reproduction. To further study the role of TRs in control of reproduction, we investigated homologous regulation of TR subtypes in the gonads of goldfish, in vivo and in vitro. It was found that tri-iodothyronine (T3) down-regulates the traditional TRs (TRα-1 and TRβ) and up-regulates a dominant-negative form, TRα-t. This indicates a ‘feedback’ mechanism whereby an acute treatment with T3 down regulates further T3 mediated response. The results provide novel information on auto-regulation of TRs in the goldfish ovary and testis, and support the hypothesis that thyroid hormones are involved in the control of reproduction.

Research highlights
► Thyroid hormone (tri-iodothyronine, T3) regulates its own receptors (TRs) in the gonads of goldfish.
► T3 decreases the gonadal expression of full length receptors TRα and TRβ.
► T3 increases expression of dominant-negative form of receptor, TRα-truncated.
► ‘Feedback’ where acute treatment with T3 down regulates further T3 mediated response.