@article {2677, title = {Molecular mechanisms of corticosteroid synergy with thyroid hormone during tadpole metamorphosis.}, journal = {General and Comparative Endocrinology}, volume = {168}, year = {2010}, month = {2010 Sep 1}, pages = {209-19}, abstract = {

Corticosteroids (CS) act synergistically with thyroid hormone (TH) to accelerate amphibian metamorphosis. Earlier studies showed that CS increase nuclear 3,5,3{\textquoteright}-triiodothyronine (T(3)) binding capacity in tadpole tail, and 5{\textquoteright} deiodinase activity in tadpole tissues, increasing the generation of T(3) from thyroxine (T(4)). In the present study we investigated CS synergy with TH by analyzing expression of key genes involved in TH and CS signaling using tadpole tail explant cultures, prometamorphic tadpoles, and frog tissue culture cells (XTC-2 and XLT-15). Treatment of tail explants with T(3) at 100 nM, but not at 10 nM caused tail regression. Corticosterone (CORT) at three doses (100, 500 and 3400 nM) had no effect or increased tail size. T(3) at 10 nM plus CORT caused tails to regress similar to 100 nM T(3). Thyroid hormone receptor beta (TRbeta) mRNA was synergistically upregulated by T(3) plus CORT in tail explants, tail and brain in vivo, and tissue culture cells. The activating 5{\textquoteright} deiodinase type 2 (D2) mRNA was induced by T(3) and CORT in tail explants and tail in vivo. Thyroid hormone increased expression of glucocorticoid (GR) and mineralocorticoid receptor (MR) mRNAs. Our findings support that the synergistic actions of TH and CS in metamorphosis occur at the level of expression of genes for TRbeta and D2, enhancing tissue sensitivity to TH. Concurrently, TH enhances tissue sensitivity to CS by upregulating GR and MR. Environmental stressors can modulate the timing of tadpole metamorphosis in part by CS enhancing the response of tadpole tissues to the actions of TH.

}, keywords = {Adrenal Cortex Hormones, Animals, Biological, Cell Line, Drug Synergism, Larva, Metamorphosis, Reverse Transcriptase Polymerase Chain Reaction, Triiodothyronine, Xenopus}, issn = {1095-6840}, doi = {10.1016/j.ygcen.2010.03.014}, author = {Bonett, Ronald M and Hoopfer, Eric D and Denver, Robert J} } @article {6498, title = {Comparative endocrinology in the 21st century.}, journal = {Integrative and Comparative Biology}, volume = {49}, year = {2009}, month = {2009 Oct}, pages = {339-48}, abstract = {

Hormones coordinate developmental, physiological, and behavioral processes within and between all living organisms. They orchestrate and shape organogenesis from early in development, regulate the acquisition, assimilation, and utilization of nutrients to support growth and metabolism, control gamete production and sexual behavior, mediate organismal responses to environmental change, and allow for communication of information between organisms. Genes that code for hormones; the enzymes that synthesize, metabolize, and transport hormones; and hormone receptors are important targets for natural selection, and variation in their expression and function is a major driving force for the evolution of morphology and life history. Hormones coordinate physiology and behavior of populations of organisms, and thus play key roles in determining the structure of populations, communities, and ecosystems. The field of endocrinology is concerned with the study of hormones and their actions. This field is rooted in the comparative study of hormones in diverse species, which has provided the foundation for the modern fields of evolutionary, environmental, and biomedical endocrinology. Comparative endocrinologists work at the cutting edge of the life sciences. They identify new hormones, hormone receptors and mechanisms of hormone action applicable to diverse species, including humans; study the impact of habitat destruction, pollution, and climatic change on populations of organisms; establish novel model systems for studying hormones and their functions; and develop new genetic strains and husbandry practices for efficient production of animal protein. While the model system approach has dominated biomedical research in recent years, and has provided extraordinary insight into many basic cellular and molecular processes, this approach is limited to investigating a small minority of organisms. Animals exhibit tremendous diversity in form and function, life-history strategies, and responses to the environment. A major challenge for life scientists in the 21st century is to understand how a changing environment impacts all life on earth. A full understanding of the capabilities of organisms to respond to environmental variation, and the resilience of organisms challenged by environmental changes and extremes, is necessary for understanding the impact of pollution and climatic change on the viability of populations. Comparative endocrinologists have a key role to play in these efforts.

}, issn = {1557-7023}, doi = {10.1093/icb/icp082}, author = {Denver, Robert J and Hopkins, Penny M and McCormick, Stephen D and Propper, Catherine R and Riddiford, Lynn and Sower, Stacia A and Wingfield, John C} } @article {2683, title = {Basic transcription element binding protein is a thyroid hormone-regulated transcription factor expressed during metamorphosis in Xenopus laevis.}, journal = {Development, Growth \& Differentiation}, volume = {44}, year = {2002}, month = {2002 Oct}, pages = {365-81}, abstract = {

Basic transcription element binding protein (BTEB) is a member of the Kr{\"u}ppel family of zinc finger transcription factors. It has been shown that BTEB plays a role in promoting neuronal process formation during postembryonic development. In the present study, the biochemical properties, transactivation function, and the developmental and hormone-regulated expression of BTEB in Xenopus laevis (xBTEB) are described. xBTEB binds the GC-rich basic transcription element (BTE) with high affinity and functions as a transcriptional activator on promoters containing multiple or single GC boxes. xBTEB mRNA levels increase in the tadpole brain, intestine and tail during metamorphosis, and are correlated with tissue-specific morphological and biochemical transformations. xBTEB mRNA expression can be induced precociously in premetamorphic tadpole tissues by treatment with thyroid hormone. In situ hybridization histochemistry showed that thyroid hormone upregulates xBTEB mRNA throughout the brain of premetamorphic tadpoles, with the highest expression found in the subventricular zones of the telencephalon, diencephalon, optic tectum, cerebellum and spinal cord. xBTEB protein parallels changes in its mRNA, and it was found that xBTEB is not expressed in mitotic cells in the developing brain, but is expressed just distal to the proliferative zone, supporting the hypothesis that this protein plays a role in neural cell differentiation.

}, keywords = {Animals, Biological, Blotting, Brain, Cell Division, DNA-Binding Proteins, Genetic, Kruppel-Like Transcription Factors, Metamorphosis, Northern, Promoter Regions, Rats, Receptors, Thyroid Hormone, Transcription Factors, Triiodothyronine, Up-Regulation, Xenopus laevis, Xenopus Proteins}, issn = {0012-1592}, author = {Hoopfer, Eric D and Huang, Liyue and Denver, Robert J} }