Amphibian metamorphosis

The amphibian metamorphosis test is based on the abiUty of thyroid hormones to induce precocious transformation of a tadpole into a frog or of the axolod into a salamander. It is rarely used because of solubiUty problems and the difficulty of applying the results to humans. 

Gutleb, A.C., Schriks, M., and Mossink, L. et al. (2007). A synchronized amphibian metamorphosis assay as an improved tool to detect thyroid hormone disturbance by endocrine disrupters and apolar sediment extracts. Chemosphere 70, 93-100. 

Benbassat J (1974) The transition from tadpole to frog haemoglobin during natural amphibian metamorphosis. I. Protein synthesis by peripheral blood cells in vitro. J Cell Sci 15 347-357... 

Tata JR (2006) Amphibian metamorphosis as a model for the developmental actions of thyroid hormone. Mol Cell Endocrinol 246 10-20... 

Gutleb, A.C, Mossink, L., van den Berg, H.J.H., Murk, A.J. (2007a). Amphibian metamorphosis assay using synchronized larvae of Xenopus laevis. Chemosphere 70 93-100. 

These hormones induce amphibian metamorphosis, the change of a tadpole into a frog—an obviously very complex series of biochemical and developmental reactions. Human fetuses will show skeletal abnormalities as well as neuromuscular and mental retardation if born with an inadequately functioning thyroid gland. 

ERa Transcriptional Activation AR Binding1 Steroidogenesis H295R Aromatase Recombinant In vivo Uterotrophic Hershberger Pubertal Male Pubertal Female Amphibian Metamorphosis Fish Short-term Reproduction (male female)... 

As in insects, a complex interaction of hormones in the amphibian larva precipitates metamorphosis. Ultimately, two major classes of hormones act together to control amphibian metamorphosis the thyroid hormones (made by the thyroid gland) and prolactin (made by the pituitary gland). Thyroid hormones function somewhat like the molting hormones of insects, in that an increase of their concentration relative to prolactin leads to metamorphosis of the larva into the adult. Prolactin functions somewhat like the juvenile hormones of insects, in that it tempers the action of the thyroid hormones. In most species, thyroid hormones increase dramatically in concentration during metamorphosis and this stimulates resorption of certain larval organs and differentiation of new adult organs. 

Iodine Essential in many organisms thyroxine imponant in metabolism and growth regulation, amphibian metamorphosis. Scarcely toxic as the iodide low iodide availability in certain areas increases the incidence of goiter, largely eliminated by the use of iodized salt. Elemental iodine is toxic like CU and Br Concentrated up to 2.5 ppt by some marine algae. 

Discrepancies have been seen between the results obtained with amphibian metamorphosis and those obtained with other assays. These discrepancies have been attributed to the ability of test animals, such as... 

Werner, E. E., 1996, Amphibian metamorphosis growth rate, predation risk and the optimal size at transformation. Am. W[Pg.348]

Volume 28. Morphogenesis, differentiation and development I. Fertilization by A. Monroy. II. Behaviour of nucleic acids during early development by J. Brachet. 111. Biochemical pathways in embryos by E. Scarano and G. Augusti-Tocco. IV. Factors of embryonic induction by T. Yamada. V. Biochemistry of amphibian metamorphosis by R. Weber. VI. Biochemical correlations in insect metamorphosis by L. I. Gilbert. Subject index. 

Cohen, P. P. (1970) Biochemical differentiation during amphibian metamorphosis Science, 168,533-543. 

Moss, B., and Ingram, V. M. (1965). The repression and induction by thyroxin of hemoglobin synthesis during amphibian metamorphosis. Proc. Natl. Acad. Sci. U.S. 54, 967-974. 

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