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Alterations in the Hypothalamus-Pituitary-Gonadal Axis in Amphibians Following Xenobiotic Exposure
Project Summary
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.
Key products
Anticipated products:
- 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
Project personnel
| Name | Phone | |
| Allen Olmstead | olmstead.allen@epa.gov | 218-529-5112 |
| Sigmund Degitz | ||
| Jon Haselman | ||
| Pat Kosian |
Research project update date
February 29, 2008