BAKER, M.E.; Univ. of California, San Diego: Xenobiotics and the Evolution of Multicellular Animals

Multicellular animals, which evolved about 700 to 1000 myr ago, contain many of the genes found in yeast and other protists. Important and necessary for the evolution of multicellular animals was the evolution of new pathways for intercellular signaling that regulated more complex physiological responses. We focus on the contribution to this process of lipophilic molecules that interact with nuclear receptors and the aryl hydrocarbon receptor. Members of both gene families are found in invertebrates and vertebrates. We propose that environmental chemicals have been an important influence on the evolution of multicellular animals by providing a selective pressure for the evolution of proteins that signal the presence of these chemicals in the environment and enzymes that detoxify these chemicals. In some cases xenobiotics were recruited as signals that regulated differentiation and development. Indeed, this cooption of xenobiotic swords into adaptive plowshare signals contributed to the diverse physiology found in multicelluar animals.