Embryos of the African clawed frog, Xenopus laevis, represent a long-standing model of vertebrate development. They are also used in FETAX (Frog Embryos Teratogenesis Assay-Xenopus) and similar assays of the developmental toxicity of chemicals and environmental samples. 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) is a potent developmental toxicant in most vertebrates. However, frogs are generally insensitive to TCDD toxicity, especially at early life stages. Thus, FETAX and other frog embryo toxicity tests may be poorly suited for determining the developmental toxicity of samples containing dioxin-like compounds. This research seeks to delineate the molecular mechanisms underlying TCDD insensitivity in frogs, using X. laevis as a model system. During the previous grant period, we cloned cDNAs encoding two distinct X. laevis aryl hydrocarbon receptors, AHR1A and AHR1B both of which exhibit extraordinarily low affinity for TCDD in vitro and unusually late onset of detectable signaling activity during development. The proposed project will elucidate the functions of the two AHRs and the regulation of their activity in embryo and tadpole stages. Specifically, we will (1) Dissect the transcriptional properties of AHR1A and AHR1B in reporter gene assays using transiently transfected cells; (2) Determine the timing of onset of AHR protein expression and functional AHR signaling during development; (3) Determine the role of AHR Repressor protein in the attenuation of AHR signaling in early embryos, and (4) Compare TCDD-induced lethality and elimination rates in tadpoles and early embryos. Understanding the molecular mechanisms of TCDD insensitivity in different life stages is important for determining the human health relevance of frog embryo toxicity assays. Moreover, the unique features of frog AHR function and expression may provide a novel perspective on the relationship between AHR expression, AHR activity, mechanisms developmental TCDD toxicity, and the endogenous functions of AHRs during vertebrate development.

Agency
National Institute of Health (NIH)
Institute
National Institute of Environmental Health Sciences (NIEHS)
Type
Academic Research Enhancement Awards (AREA) (R15)
Project #
2R15ES011130-02
Application #
6806295
Study Section
Special Emphasis Panel (ZRG1-DIG-F (02))
Program Officer
Heindel, Jerrold
Project Start
2001-09-01
Project End
2007-08-31
Budget Start
2004-09-01
Budget End
2007-08-31
Support Year
2
Fiscal Year
2004
Total Cost
$183,735
Indirect Cost
Name
Kenyon College
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
063580369
City
Gambier
State
OH
Country
United States
Zip Code
43022
Taft, Justin D; Colonnetta, Megan M; Schafer, Rachel E et al. (2018) Dioxin Exposure Alters Molecular and Morphological Responses to Thyroid Hormone in Xenopus laevis Cultured Cells and Prometamorphic Tadpoles. Toxicol Sci 161:196-206
Freeburg, Scott H; Engelbrecht, Eric; Powell, Wade H (2017) Subfunctionalization of Paralogous Aryl Hydrocarbon Receptors from the Frog Xenopus Laevis: Distinct Target Genes and Differential Responses to Specific Agonists in a Single Cell Type. Toxicol Sci 155:337-347
Shoots, Jenny; Fraccalvieri, Domenico; Franks, Diana G et al. (2015) An Aryl Hydrocarbon Receptor from the Salamander Ambystoma mexicanum Exhibits Low Sensitivity to 2,3,7,8-Tetrachlorodibenzo-p-dioxin. Environ Sci Technol 49:6993-7001
Odio, Camila; Holzman, Sarah A; Denison, Michael S et al. (2013) Specific ligand binding domain residues confer low dioxin responsiveness to AHR1? of Xenopus laevis. Biochemistry 52:1746-54
Iwamoto, Daniel V; Kurylo, Chad M; Schorling, Kelly M et al. (2012) Induction of cytochrome P450 family 1 mRNAs and activities in a cell line from the frog Xenopus laevis. Aquat Toxicol 114-115:165-72
Laub, Leo B; Jones, Brian D; Powell, Wade H (2010) Responsiveness of a Xenopus laevis cell line to the aryl hydrocarbon receptor ligands 6-formylindolo[3,2-b]carbazole (FICZ) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Chem Biol Interact 183:202-11
Zimmermann, Anna L; King, Elizabeth A; Dengler, Emelyne et al. (2008) An aryl hydrocarbon receptor repressor from Xenopus laevis: function, expression, and role in dioxin responsiveness during frog development. Toxicol Sci 104:124-34
Philips, Blythe H; Susman, Thomas C; Powell, Wade H (2006) Developmental differences in elimination of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during Xenopus laevis development. Mar Environ Res 62 Suppl:S34-7
Lavine, Jeremy A; Rowatt, Ashley J; Klimova, Tatyana et al. (2005) Aryl hydrocarbon receptors in the frog Xenopus laevis: two AhR1 paralogs exhibit low affinity for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Toxicol Sci 88:60-72
Rowatt, Ashley J; DePowell, John J; Powell, Wade H (2003) ARNT gene multiplicity in amphibians: characterization of ARNT2 from the frog Xenopus laevis. J Exp Zool B Mol Dev Evol 300:48-57