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 hormon e 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 mu IU/g of tissue, respectiv ely, using the RIA method, and a value of 0.013+/-0.0043, 1.16+/-0.30 and 3.85+/-1.32 mu IU/g using an immuno-chemiluminescent method. In ad dition 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 hu man TSH receptor. This indicates that the putative ciona TSH has the c apability to react specifically with receptors for mammalian TSH. Maxi mum concentrations of ciona TSH-like factor occur during periods of se xual maturity (between May to July), whereas very low concentrations w ere assayed during the rest of the year suggesting that this hormone m ay be involved in hormonal function related to sexual maturity. From a phylogenetic point of view, the above data supports the hypothesis fo r a common origin of a thyroid hormonal system between Tunicata and ve rtebrates.