Alterations in the Hypothalamus-Pituitary-Gonadal Axis in Amphibians Following Xenobiotic Exposure
In 1998, the EPA outlined a plan for the Endocrine Disruptor Screening Program (EDSP) that incorporated a two tier testing approach. This project entails development of an amphibian life cycle assay utilizing the Tropical Clawed frog (Xenopus tropicalis) that would be suitable as a second tier EDSP test. Endpoints are designed around three specific androgen- or estrogen-mediated processes: 1) differentiation of the gonads, 2) secondary sex characteristic development, and 3) reproductive maturation. Development of a method for genotyping sex in this species will increase the statistical power of these types of assays as well as reduce the number of animals used in toxicity testing. Gene expression methods for assessing intersexuality of gonads at metamorphosis are being developed that will provide less subjective and more quantitative results than those obtained by traditional histological techniques. Methods for evaluating secondary sex characteristic development (e.g., nuptial pad formation, androgen sensitive tissue and oviduct formation, estrogen sensitive tissue formation) are being developed. As a surrogate for measuring fecundity in this organism, oocyte and sperm counting methods are utilized in adult frogs. These methods are combined in a proposed full life cycle amphibian development, growth, and reproduction test that would be used as part of the battery of tests in the EDSP. Model endocrine disrupting chemicals will be assessed using this assay with the results used to improve and streamline the methods.
Olmstead, A.W., P.A. Kosian, R.D. Johnson, P. Blackshear, J. Haselman, C. Blanksma, J.J. Korte, G.W. Holcombe, E. Burgess, A. Lindberg-Livingston, B.A. Bennett, K.K. Woodis, and S.J. Degitz. Effects of trenbolone exposure during larval development of Xenopus tropicalis. Environmental Toxicology and Chemistry (submitted).
Olmstead, A.W., S. Ostazeski, B.A. Bennett, and S.J. Degitz. Genetic and dietary impacts on scoliosis development in larval Xenopus tropicalis. Journal of Herpetology, in press.
Olmstead, A.W., L.S. Blake, P.A. Kosian, J.T. Haselman, J.J. Korte, R.D. Johnson, C. Blanksma, K. Lillegard, S. Zavodnik, B. Heggestad, and S.J. Degitz. Assessment of the endocrine toxicity of the fungicide prochloraz using the Larval Amphibian Growth and Development Assay. SETAC, Boston, MA, November 13-17, 2011.
Miranda, R.A. , A.W. Olmstead, L.S. Blake, S.J. Degitz, D.R. Garcia, A.A. Owolabi, and C.R. Propper. Developmental trenbolone exposure affects adult breeding behavior, fecundity and morphology of Xenopus tropicalis. 7th International Symposium on Amphibian Endocrinology and Neurobiology (ISAREN), Ann Arbor, MI, July 11-13, 2011.
Olmstead, A.W. and S.J. Degitz. ZWY sex determination in Xenopus tropicalis. 1st North American Society for Comparative Endocrinology (NASCE), Ann Arbor, MI, July 13-16, 2011.
Olmstead, A.W., P.A. Kosian, R.D. Johnson, J.T. Haselman, and S.J. Degitz. Endocrine toxicity of trenbolone during larval development of Xenopus tropicalis. 7th International Symposium on Amphibian Endocrinology and Neurobiology (ISAREN), Ann Arbor, MI, July 11-13, 2011.
Porter, K.L., A.W. Olmstead, D.M. Kumsher, W.E. Dennis, R.L. Sprando, G.W. Holcombe, J.J. Korte, A. Lindberg-Livingston, and S.J. Degitz. 2011. Effects of 4-tert-octylphenol on Xenopus tropicalis in a long term exposure. Aquatic Toxicology103:159-169.
Korte, J.J., R.M. Sternberg, J.A. Serrano, K.R. Thoemke, S.M. Moen, K.E. Lillegard, M.W. Hornung, J.E. Tietge, and S.J. Degitz. 2011. Thyroid-stimulating hormone (TSH): Measurement of intracellular, secreted, and circulating hormone in Xenopus laevis and Xenopus tropicalis. General and Comparative Endocrinology 171:319-325.
Olmstead, A.W., P.A. Kosian, L.S. Blake, J.T. Haselman, J.J. Korte, G. Holcombe, and S.J. Degitz. Endocrine toxicity of trenbolone in the western clawed frog, Xenopus (Silurana) tropicalis. SETAC North America 31st Annual Meeting, Portland, OR, November 7-11, 2010.
- PCR method for assessing genotypic sex
- ELISA for measuring X. tropicalis vitellogenin (complete)
- Quantitative PCR method for biomarkers of intersexuality in newly metamorphed frog gonads (complete)
- Methodology for assessing nuptial pad and oviduct formation
- Oocyte and sperm counting methods (complete)
- Baseline data on the reproductive maturation of males and females of this species (complete)
- Effects of an estrogen, androgen, and anti-thyroid model chemical on the full life cycle of X. tropicalis
Research project update date
January 23, 2012