Deformed frogs and environmental retinoids
D. Gardiner, A. Ndayibagira, F. Gr�n, and B. Blumberg
Department of Developmental and Cell Biology, University
of California, Irvine, CA 92697-2300, USA
Abstract: Since the early 1990s, a substantial number of deformed
frogs have been observed in North America, particularly in the upper
Midwest and Canada. Attempts to understand the etiology of the deformed
frog problem have met with limited success to date with nearly as many
proposed explanations as research groups working on the problem. Models
for the mechanism underlying the development of deformed frogs include
parasite/predation, ultraviolet radiation, and chemical exposure. Each
model has its strengths and weaknesses. Despite contentious debate among
researchers, there is an overall consensus that the increasing prevalence
of deformed frogs is the result of a water-borne contaminant that has
recently appeared, or reached a critical concentration. Our detailed
analysis of malformed frogs collected in Minnesota ponds and lakes suggested
that limb patterning was being modified by the disruption of a retinoid-sensitive
developmental signaling pathway. Accordingly, we focused in the identification
and characterization of bioactive retinoids from lake water and showed
that retinoid treatment of frog embryos at sensitive times of development
could recapitulate the full spectrum of limb abnormalities observed
in field specimens in the laboratory. These data have led to the conclusion
that inappropriate modulation of retinoid signaling by environmental
contaminants is the mechanism underlying the increased incidence of
frog malformations.
*Report from a SCOPE/IUPAC project: Implication of
Endocrine Active Substances for Human and Wildlife (J. Miyamoto and
J.Burger, editors). Other reports are published in this issue,
pp. 1617-2615.
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