BAKER, M.E.; Univ. of California, San Diego: Role of the Environment on the Evolution of Signal Transduction Proteins and Metamorphosis

Signal transduction proteins regulate differentiation and development, which are central to metamorphosis. We focus on the role of environmental factors (e.g. climate, chemicals) in the evolution of nuclear receptors and Mitogen-Activated Protein Kinases (MAPK), two classes of signal transduction proteins, which regulate developmental transitions in animals. Heat shock protein 90 (HSP90) chaperones proper folding of nuclear receptors and MAPKs into active structures. HSP90 also promotes folding of mutant nuclear receptors and MAPKs, which would be otherwise destabilized. Stress diverts HSP90 from stabilizing mutant signal transduction proteins and towards its role as a chaperone to promote proper folding of stress-damaged proteins and to prevent the aggregation of denatured proteins. Reduced HSP90 levels allow expression of cryptic mutations in signal transduction proteins and new developmental patterns. By affecting HSP90 levels, environmental stress in the form of extreme climate can influence the evolution of metamorphosis. We discuss how extreme cooling called �snowball earth�, which occurred in two periods from ~760 to 700 myr ago and ~620 to 580 myr ago, diverted HSP90 from chaperoning signal transduction proteins that regulate development in animals. As a result, pre-existing mutant signal transduction proteins were expressed in animals. Some of these mutations were a source for selectively advantageous developmental pathways in animals during the Cambrian. Similarly, chemicals (e.g. the antibiotic geldanamycin) inhibit HSP90, providing a mechanism for chemicals to influence metamorphosis evolution and a method to study how alterations of HSP90 affect the evolution of metamorphosis.