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Endocrinology January 1, 2018; 159 (7): 2576-2595.
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RXR Ligands Modulate Thyroid Hormone Signaling Competence in Young Xenopus laevis Tadpoles.

Mengeling BJ , Goodson ML , Furlow JD .

Appropriate thyroid hormone (TH) signaling through thyroid hormone receptors (TRs) is essential for vertebrate development. Amphibian metamorphosis is initiated and sustained through the action of TH on TRs, which are conserved across vertebrates. TRs heterodimerize with retinoid X receptors (RXRs) on thyroid hormone response elements (TREs) in the genome; however, in most cell line and adult animal studies, RXR ligands do not affect expression of TR target genes. We used a quantitative, precocious metamorphosis assay to interrogate the effects of the RXR agonist bexarotene (Bex) and the RXR antagonist UVI 3003 (UVI) on T3-induced resorption phenotypes in Xenopus laevis tadpoles 1 week postfertilization. Bex potentiated gill and tail resorption, and UVI abrogated T3 action. These results held in transgenic tadpoles bearing a TRE-driven luciferase reporter. Therefore, we used poly-A-primed RNA sequencing transcriptomic analysis to determine their effects on T3-induced gene expression. We also assayed the environmental pollutant tributyltin (TBT), which is an RXR agonist. We found that the proteases that carry out resorption were potentiated by Bex and TBT but were not significantly inhibited by UVI. However, several transcription factors from multiple families (sox4, fosl2, mxd1, mafb, nfib) were all inhibited by UVI and potentiated by Bex and TBT. All required T3 for induction. Time course analysis of gene expression showed that although the agonists could potentiate within 12 hours, the antagonist response lagged. These data indicate that the agonists and antagonist are not necessarily functioning through the same mechanism and suggest that RXR liganding may modulate TH competence in metamorphic signaling.

PubMed ID: 29762675
PMC ID: PMC6692881
Article link: Endocrinology
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: adamts4 csnk1a1 dio3 fap fosl2 junb mafb mmp11 mmp13l mxd1 sox4 thibz thrb

References [+] :
Ayers, Genome-wide binding patterns of thyroid hormone receptor beta. 2015, Pubmed