Presence of a human-like thyroid stimulating hormone (TSH) in Ciona intestinalis

Using a monoclonal antibody against human Thyroid Stimulating Hormone (TSH), we have found that the invertebrate Ciona intestinalis (phylum Chordata, subphylum Tunicata) contains a previously unreported protein which is immunoreactive for anti-human TSH. The amount of this hormone in the blood, endostyle and ovary of C. intestinalis was found to be 0.01+/-0.003, 1.05+/-0.2 and 3.61+/-1.25 microIU/g of tissue, respectively, using the RIA method, and a value of 0.013+/-0.0043, 1.16+/-0.30 and 3.85+/-1.32 microIU/g using an immuno-chemiluminescent method. In addition to possessing immunological properties, this protein is able to induce the synthesis of cAMP in rat thyroid cell culture (FRTL-5) and in Chinese Hamster Ovary cells (CHO) transfected with the cDNA for human TSH receptor. This indicates that the putative ciona TSH has the capability to react specifically with receptors for mammalian TSH. Maximum concentrations of ciona TSH-like factor occur during periods of sexual maturity (between May to July), whereas very low concentrations were assayed during the rest of the year suggesting that this hormone may be involved in hormonal function related to sexual maturity. From a phylogenetic point of view, the above data supports the hypothesis for a common origin of a thyroid hormonal system between Tunicata and vertebrates.