Thyroxine-induced changes in ovarian protein and ecdysteroid levels in the silkworm, Bombyx mori L.: Effect on ovarian maturation and egg production

The evolutionary road to invertebrate thyroid hormone signaling: Perspectives for endocrine disruption processes

Thyroid hormones (THs) are the only iodine-containing hormones that play fundamental roles in chordates and non-chordates. The chemical nature, mode of action and the synthesis of THs are well established in mammals and other vertebrates. Although thyroid-like hormones have been detected in protostomes and non-chordate deuterostomes, TH signaling is poorly understood as compared to vertebrates, particularly in protostomes. Therefore, the central objective of this article is to review TH system components and TH-induced effects in non-vertebrate chordates, non-chordate deuterostomes and protostomes based on available genomes and functional information. To accomplish this task, we integrate here the available knowledge on the THs signaling across non-vertebrate chordates, non-chordate deuterostomes and protostomes by considering studies encompassing TH system components and physiological actions of THs. We also address the possible interactions of thyroid disrupting chemicals and their effects in protostomes and non-chordate deuterostomes. Finally, the perspectives on current and future challenges are discussed.

Iodotyrosine deiodinase: a unique flavoprotein present in organisms of diverse phyla

Iodide is required for thyroid hormone synthesis in mammals and other vertebrates. The role of both iodide and iodinated tyrosine derivatives is currently unknown in lower organisms, yet the presence of a key enzyme in iodide conservation, iodotyrosine deiodinase (IYD), is suggested by genomic data from a wide range of multicellular organisms as well as some bacteria. A representative set of these genes has now been expressed, and the resulting enzymes all catalyze reductive deiodination of diiodotyrosine with kcat/Km values within a single order of magnitude. This implies a physiological presence of iodotyrosines (or related halotyrosines) and a physiological role for their turnover. At least for Metazoa, IYD should provide a new marker for tracing the evolutionary development of iodinated amino acids as regulatory signals through the tree of life.

From insect ovaries to sheep red blood cells: a tale of two hormones

This printed version of the Wigglesworth Lecture reviews the evidence that juvenile hormone (JH) acts on the follicular epithelium of the ovary through a membrane receptor to control access of yolk proteins to the oocyte surface. The thyroid hormones mimic this action through the same receptor. Conversely, both JH III and 3,5,3' triiodothyronine (T3) increase the activity of Ca ATPase in isolated erythrocyte membrane preparations from sheep, apparently through the same membrane receptor. These effects are mimicked by exposure of the respective tissues to CO(2). These findings suggest that the hormones arose as biotic signals, originally using existing CO(2) receptors.

Do thyroid hormones function in insects?

Earlier work demonstrated that phenoxy-phenyl compounds such as fenoxycarb and thyroxine mimicked the effects of JH III in causing a reduction in volume of the follicle cells of Locusta migratoria. While these compounds were only moderately effective, a derivative of thyroxine, 3,3',5-triiodothyronine (T3) was as effective as JH III, and T3 has been shown to bind to the same membrane receptor and activate the same pathway as JH III. The current paper shows that other thyroxine derivatives vary in activity. 3,3', 5'-Triiodothyronine (reverse T3) is inactive. 3,5-Diiodothyronine (T2) is more active than JH III, while its relatives (iodines at 3', 5' or at 3,3') are inactive. When follicles are exposed in vitro to rhodamine conjugated T3, the fluorescent compound can be seen to enter the cells and accumulate there: this process is inhibited by cycloheximide or by a temperature of 0 degrees C. The accumulation is antagonised by JH III but not JH I (which does not bind to the JH III membrane receptor) and by an antiserum raised against the putative membrane receptor protein. The action of T3, but not T2, is inhibited by 6-n-propyl-2-thiouracil or by aurothioglucose, both known to inhibit deiodinases. The activity of T3, but not of T2, increases with time of exposure to the follicle cells. These facts suggest that T3 enters the cells by receptor mediated endocytosis and is converted to a more active compound. Immunoreactivity to T3, but not thyroxine, can be detected in the haemolymph of locusts, and the titre varies slightly with the gonotrophic cycle. The food shows immunoreactivity for both thyroxine and T3. These findings suggest that thyroid hormones are ingested by locusts and have the potential to be used as hormonal signals in the control of egg production.

Fenoxycarb and thyroid hormones have JH-like effects on the follicle cells of Locusta migratoria in vitro

Earlier work had shown that JH acts on the membrane of the follicle cell of Locusta migratoria, bringing about a rapid reduction in volume which can be detected in vitro by measuring the increase in optical path difference using quantitative interference microscopy. The juvenoid fenoxycarb, a phenoxyphenyl derivative, is unrelated in structure to the juvenile hormones (which are derivatives of farnesoic acid), but it also caused a reduction in volume of the cells in vitro as measured by an increase in the optical path difference. The vertebrate hormone thyroxine, and thyronine, the non-iodinated derivative of thyroxine, also phenoxy phenyl compounds, evoked a response like fenoxycarb. The effect of thyroxine was abolished by ouabain, which inhibits Na+/K+ ATPase, the effector molecule for JH, and inhibited by ethoxyzolamide which inhibits the binding of JH to a putative membrane receptor. Triiodothyronine, the effective vertebrate hormone, acted at a lower threshold and optimum concentration, and had a greater magnitude of effect than the other compounds tested. These facts suggest that these phenoxyphenyl compounds are JH agonists and that the membrane receptor for JH may resemble a possible membrane receptor for thyroxine.