Frog Deformities: Role of Endocrine Disruptors During DevelopmentEPA Grant Number: R827398
Title: Frog Deformities: Role of Endocrine Disruptors During Development
Investigators: Gardiner, David M.
Current Investigators: Gardiner, David M. , Blumberg, Bruce
Institution: University of California - Irvine
EPA Project Officer: Klieforth, Barbara I
Project Period: October 1, 1999 through September 30, 2002
Project Amount: $1,194,536
RFA: Endocrine Disruptors (1999) RFA Text | Recipients Lists
Research Category: Environmental Justice , Endocrine Disruptors , Human Health , Safer Chemicals
To assess the significance of endocrine disruptors that activate retinoid signaling pathways for their role in causing limb developmental deformities in frogs and to understand their mechanism of action in order to assess their implications for human health.
Objectives/Hypothesis: The goal of our studies is to assess the significance of endocrine disruptors that activate retinoid signaling pathways for the development of deformities in frogs, and to understand their mechanism of action so as to better assess the implications for human health. In preliminary studies we have discovered a frequent yet novel malformation which we call a bony triangle. Triangles have been seen before in several species of animals and in humans, but only as a result of exposure to retinoids. Hence our central hypothesis is that inappropriate activation of retinoid signaling pathways at sensitive stages causes deformities, and that triangles are diagnostic of exogenous retinoids. Mechanistically, we propose that triangles arise as a consequence of changes in pattern specification along the proximal-distal limb axis, mediated by retinoid-induced alterations in the expression of genes important for establishment of limb pattern. We further propose that the triangles in deformed frogs in the wild arise as a result of exposure to endocrine disruptors acting on retinoid signaling pathways.
We will test this hypothesis by achieving three objectives. The first (1) objective is to characterize the formation of bony triangles in response to retinoid exposure. We will treat metamorphosing Xenopus larvae with receptor-selective retinoids to establish the time, dose, stage and signaling pathway involved in triangle formation. Once the treatment is optimized for consistent triangle formation, we will examine the molecular mechanisms of triangle formation, establish the target genes, and study the role that altered growth might play. In the second (2) objective we will determine whether commonly used chemicals induce triangles. Because most deformed frogs come from agricultural areas it is plausible that a commonly used agrochemical is involved. Chemicals that test positive in our Xenopus assay will be retested using a native frog species (Rana pipiens) known to develop deformities in the wild. In the third (3) objective, we will screen and fractionate field samples collected from deformed frog sites to identify the agent(s) causing abnormalities in the wild. We will use a high-throughput bioassay-guided screen for fractions that can activate retinoid receptors in cultured cells. Positive fractions will be assayed for their ability to induce triangles.
This study will provide critical information about the links between deformed frogs and environmental retinoids. Accomplishment of the first objective will establish the connection between retinoid exposure, altered gene expression and altered pattern specification leading to abnormal morphogenesis and formation of triangles. Accomplishment of the second objective will establish the potential for currently-used agricultural/industrial chemicals to cause triangles in frogs. Accomplishment of the third objective will identify chemicals that can disrupt retinoid signaling and cause bony triangles in the environment where deformed frogs have been collected.
Improvements in Risk Assessment/Management: The results of this study are important for understanding what agents in the environment are causing frog abnormalities, not only to be able to assess the relevance of such agents for the health and survival of amphibian populations, but also to assess their possible significance for human health, both in terms of teratogenesis and carcinogenesis and other developmental diseases.