Ecdysteroid receptors in the neuroendocrine-endocrine axis of a moth

With a combination of thaw-mount autoradiography using a tritiated 20-hydroxyecdysone agonist, ponasterone A, and immunocytochemistry with a monoclonal antibody to 29 K-prothoracicotropic hormone, high affinity binding sites for ecdysteroids were identified in the tissues of the neuroendocrine-endocrine axis inManduca sexta larvae. At specific times during larval-pupal development in fifth stadium larvae, nuclear ecdysteroid binding sites were present in the cerebral prothoracicotropes, the corpora allata and prothoracic glands, the main axis for the regulation and production of ecdysteroids. A stage-specific appearance of ecdysteroid receptors also occurred in cells of fat body, midgut and Malpighian tubules, tissues which convert ecdysone into 20-hydroxyecdysone. Our data identify new target tissues for ecdysteroids and suggest that ecdysteroids could affect their own production at the genomic level via long and short feedback loops.     

Evidence for an unusual multifunctional protoreceptor in hormone action

Summary Contrary to the techniques of mere association, column chromatography has revealed a protoreceptor that accepts aldosterone agonists and antagonists only in the physiological target, the kidney, and is absent in non-targets, liver and serum; it is furthermore different from the aldosterone specific receptor in renal cytosol.Supported in part by grants from the CNRS AI 03 1917 and UER Broussais Hôtel Dieu.     

Ecdysteroid titers during larval reproduction of the dipteran insectHeteropeza pygmae

Summary Ecdysteroid titers were measured in whole-body extracts of pedogenetically reproducing larvae of the dipteran insectHeteropeza pygmaea and in the dietary fungus. The titers are very low in the first 3 days of larval growth, but increase during the last 2 days. The level of 20-hydroxyecdysone is then significantly higher than that of ecdysone. Measurements of the titers in the fungus gave no conclusive results.Supported by the Swiss National Science Foundation, grants No. 3.218-0.77 to D.F.W. and 3.714-0.80 to B.L. We thank Xiang-Xiong Zhu for help with the RIA and Mrs G. Rhyner for technical assistance. Gifts of ecdysone antiserum from Dr J. D. O'Connor and of 23,24-[³H₂]-ecdysone from Dr J. Koolman are also gratefully acknowledged.     

Ecdysteroid receptors located in the central nervous system of an insect

Summary Using thaw-mount autoradiography for steroid hormones, we obtained direct evidence for a nuclear localization of ecdysteroid binding sites in target organs of blowfly (Calliphora vicina) larvae. The binding sites revealed properties of ecdysteroid receptors. Endocrine cells of the ring gland were found to be target tissues of ecydysteroids. This observation provides morphological evidence for a network of complex interendocrine regulation. In the central nervous system receptorcontaining neurons were identified which include many, if not all, neurosecretory cells of the brain. A map of ecdysteroid sensitive cells of the larval brain is presented.     

The deiodinase family: selenoenzymes regulating thyroid hormone availability and action

Thyroid hormones control growth, development, differentiation and metabolism in vertebrates. Most of the actions of the active thyroid hormone T3 (3,5,3'-triiodo-L-thyronine) are exerted via ligand-activated nuclear T3 receptors. Activation of the secretory product of the thyroid gland, L-thyroxine (3,3',5,5'-tetraiodo-L-thyronine), or T4, is catalyzed by two enzymes, iodothyronine-5'-deiodinases type I and type II. Inactivation of T4 and T3 occurs via type III iodothyronine-5-deiodinase and to some extent by type I 5'deiodinase. Complementary DNAs (cDNAs) encoding the substrate-binding selenocysteine-containing subunits of the deiodinases were cloned, though some controversy still exists on the type II 5'-deiodinase subunits. Characterization of tissue-specific expression patterns indicates that these selenium-dependent enzymes exert tight control on local and systemic availability of active T3. Thus, deiodinases are envisaged as guardians to the gate of thyroid hormone action mediated by T3 receptors.     

Number of glucocorticoid receptors in lymphocytes and their sensitivity to hormone action

The study demonstrated a decreased level of glucocorticoid receptors (GR) in peripheral blood lymphocytes from hypercholesterolemic subjects, and an elevated level in patients with acute myocardial infarction. In the lymphocytes with a high GR number, dexamethasone inhibited [3H]-thymidine and [3H]-acetate incorporation into DNA and cholesterol, respectively, in the same manner as in the control cells. On the other hand, a decreased GR number resulted in a less efficient dexamethasone inhibition of the incorporation of labeled compounds. These data showed that the sensitivity of lymphocytes to glucocorticoids changed only with a decrease of GR level.     

Activation and inactivation of thyroid hormone by deiodinases: Local action with general consequences

The thyroid hormone plays a fundamental role in the development, growth, and metabolic homeostasis in all vertebrates by affecting the expression of different sets of genes. A group of thioredoxin fold-containing selenoproteins known as deiodinases control thyroid hormone action by activating or inactivating the precursor molecule thyroxine that is secreted by the thyroid gland. These pathways ensure regulation of the availability of the biologically active molecule T3, which occurs in a time-and tissue-specific fashion. In addition, because cells and plasma are in equilibrium and deiodination affects central thyroid hormone regulation, these local deiodinase-mediated events can also affect systemic thyroid hormone economy, such as in the case of non-thyroidal illness. Heightened interest in the field has been generated following the discovery that the deiodinases can be a component in both the Sonic hedgehog signaling pathway and the TGR-5 signaling cascade, a G-protein-coupled receptor for bile acids. These new mechanisms involved in deiodinase regulation indicate that local thyroid hormone activation and inactivation play a much broader role than previously thought. Received 29 August 2007; received after revision 11 October 2007; accepted 16 October 2007     

Ecdysteroid titre and caste determination in the ant,Pheidole pallidula (Nyl.) (Hymenoptera: Formicidae)

Summary In the antPheidole pallidula, ecdysteroid level is higher in worker-biased eggs than queen-biased eggs. Moreover queens laying worker-biased eggs exhibit a higher ecdysteroid level than queens laying queen-biased eggs.     

Ecdysteroid conjugates in the ovaries of the silkworm,Bombyx mori: 3-phosphates of 2,22-dideoxy-20-hydroxyecdysone and of bombycosterol

Summary Two novel ecdysteroid conjugates, 2,22-dideoxy-20-hydroxyecdysone 3-phosphate (1) and bombycosterol 3-phosphate (2), as well as four known ecdysteroid 22-phosphate esters, have been isolated and characterized from the ovaries of the silkworm,Bombyx mori.     

Intracellular osmotic action

Water often acts as a critical reactant in cellular reactions. Its role can be detected by modulating water activity with osmotic agents. We describe the principles behind this 'osmotic stress' strategy, and survey the ubiquity of water effects on molecular structures that have aqueous, solute-excluding regions. These effects are seen with single-functioning molecules such as membrane channels and solution enzymes, as well as in the molecular assembly of actin, the organization of DNA and the specificity of protein/DNA interactions.