Question

Correct and appropriate signal transduction processes are generally under strong selective pressure and are determined by the properties of the molecules involved, the concentrations of signal and receptor molecules, and the binding affinities between signal and receptor. Therefore, a hormone action is very specific in a species at any one point in time. However, there are examples of very diverse functions of a specific hormone between groups of organisms. For example, thyroxine, which is produced in all vertebrates and many invertebrates, can trigger growth, differentiation, metamorphosis, maturation, reproduction, behavior, temperature tolerance, osmoregulation, or seasonal adaptation depending on the organism in which it is produced. What is the most logical explanation for such different responses triggered by thyroxine in organisms

Answer 1

Different responses triggered by thyroxine in different organisms is most likely due to different kinds of receptor and consequently different signal cascade and response.

The thyroid hormones (including thyroxine) bind to a specific types of nuclear receptors, termed the thyroid hormone receptors which together with corepressor molecules, bind DNA regions called thyroid hormone response elements.