By sequencing the genes that are regulated by TH, the team identified the protein that each gene encodes. Knowing the identity of the gene and where and when it is expressed provided clues on the possible role of each gene in metamorphosis. This guarantees that all the cells of the embryo and the tadpole will contain the gene. Using this powerful method, the Brown group has tested many of their genes and developed functional assays for gene function in metamorphosis. The hormone prolactin, previously thought to be a juvenile hormone for anuran tadpoles, does not retard metamorphosis.
Growth hormone has the same effect on tadpoles and frogs as it does on mammals.
Both kinds of genes are introduced under the control of a specific promoter. The resulting transgenic animals are unable to complete specific sets of functions. These new methods are making possible a new approach to the age-old problem of amphibian metamorphosis. This is a picture of frogs with overexpressed prolactin. The result is inhibited tail reabsorption.