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Histological development of the gonad in juvenile Xenopus laevis
Citation:
Blanksma, C., A. Olmstead, S. Degitz, J. Haselman, AND R. Johnson. Histological development of the gonad in juvenile Xenopus laevis. Presented at Society for Environmental Toxicology and Chemistry, March 20 - 21, 2012.
Impact/Purpose:
Not applicable
Description:
As directed by the Food Quality Protection Act, the US Environmental Protection Agency is developing a screening program for endocrine disrupting compounds. The Larval Amphibian Growth and Development Assay (LAGDA) is a tier II test intended to identify and characterize the adverse consequences of toxicants that interfere with normal growth and development of larval and juvenile frogs with particular emphasis on disruption of estrogen, androgen, and thyroid mediated processes. A particularly important aspect of this assay is the detection of alterations in gonad differentiation and development. Assessments of gonad malformations in anuran species have traditionally relied on gonad histology of tadpoles at the completion of metamorphosis (NF stage 66). Preliminary experiments using Xenopus exposed to three model endocrine disruptors possessing estrogenic, androgenic, or anti-aromatase activities indicated that the gonads were not sufficiently developed at this stage to detect mixed sex phenotypes. In addition, exposure to ethynylestradiol and fadrozole, which induces testicular oocytes in older frogs, did not in stage 66 samples. We propose that assessing the gonads at a later stage of development would allow for improved detection of aberrant gonad differentiation and development, yielding more informative results for risk assessment purposes. In order to identify the appropriate level of gonad development for use in the LAGDA, we characterized normal gonad development in the test species, Xenopus laevis, at two week intervals from completion of metamorphosis until 12 weeks post-metamorphosis.