Molecular Evolution of Steroid Hormone Receptor Functions and Interactions Joseph W. Thornton University of Oregon
Virtually everything that living cells do is made possible by very specific interactions between molecules. For example, steroid hormones produced in the gonads or adrenal gland-such as estrogen, testosterone, and cortisol-regulate development, reproduction, behavior, and countless other processes. Each hormone produces a unique suite of effects by binding to a specific receptor protein in target cells; the hormone-bound receptor then enters the nucleus, binds to a specific set of DNA sequences, and activates the expression of nearby genes. Despite the great biological importance of specific interactions like this, there has been very little work to understand how tight molecular partnerships evolve. This career plan integrates research on the evolution of molecular interactions with education and outreach activities that strengthen understanding of evolution, endocrinology, and the deployment of scientific knowledge in public policy. In the project's research component, steroid hormones and their receptors will be used as a model system, with the goal of reconstructing the evolutionary mechanisms by which the specific interactions between hormones and receptors evolved. First, the investigators will isolate and characterize receptors from several target species that, because of their position in the tree of life, will provide crucial information about the diversification of the receptor gene family. Phylogenetic techniques will be used to infer the dynamics by which the family diversified in number, molecular sequence, structure, and the ability to be activated by new hormones. The investigators will then test hypotheses about how receptors evolved novel functions by "resurrecting" ancestral receptor genes and studying their functions in the laboratory. Finally, experiments will be performed to determine how changes at the DNA level caused receptors to evolve new functions by re-introducing historical mutations into resurrected ancestral genes and determining their effects on the receptors' interactions with various hormones. The education and outreach components of this proposal are focused on the interface of science with real-world policy issues. A new course will be developed, which prepares young scientists to participate in societal decision-making by teaching them to think critically about the ways that science is deployed in the policy process; environmental endocrine disrupters-pollutants that interfere with the body's steroid hormones - will be used as an extended case study. A large undergraduate course in Evolutionary Biology will be revised to better incorporate the applied implications of evolutionary knowledge. Finally, the principal investigator will serve as an occasional science advisor to two nongovernmental organizations that work directly with large constituencies on environmental endocrine disruption and human health.
This project combined leading-edge research to understand the mechanisms of molecular evolution in a biologically essential gene family with education/ outreach activities that strengthen critical thinking about evolution and the intersection of scientific knowledge and policy decisions. The research component of this project addressed the evolution of function in the steroid hormone receptors, a family of proteins that mediate the effects of hormones like estrogens, androgens, and cortisol on reproduction, development, and physiological processes. We developed a strategy called ancestral protein reconstruction to reveal the mechanisms by which members of this protein family evolved their unique specificities for different hormones and target genes. This strategy uses phylogenetic analysis of large databases of present-day proteins to infer the sequences of ancestral proteins; genes coding for these ancient proteins are then synthesized, expressed in the laboratory, and characterized using a diverse array of molecular and biochemical assays. This approach allowed us to reconstruct the history of functional diversification among SR proteins. Also, by introducing historical mutations into the ancestral proteins, we were able to identify the key genetic changes that took place hundreds of millions of years ago that caused the diversification of receptor function. Finally, by applying structural biology and other biophysical methods to these ancestral proteins, we were able to identify the specific physical mechanisms by which ancient mutations produced the biologically crucial functions of present-day receptors. The project served as an exemplar for how evolutionary, biochemical, and molecular approaches can be integrated into a new "Functional Synthesis" in order to answer important questions about evolution and biochemistry, and molecular biology. The education/ outreach activities focused on policy issues related to steroid hormones, their disruption by synthetic pollutants, and the evolution of complex systems. I linked teaching of evolution and molecular endocrinology to their real-world policy implications in order to 1) improve students mastery of fundamental concepts in these fields and 2) train students in the life sciences to think critically about he ways that science is deployed in the policy process concerning health and the environment. I developed and repeatedly taught a new course, "Biology and Politics," which used endocrine disrupting chemicals in the environment as a case study for developing a critical understanding of different models for making use of scientific information in the public policy proess. I also revamped and repeatedly taught a large course in Evolution to emphasize the importance of Evolution in current social issues, including medicine, public health, agriculture, race, and psychology. Outreach activities were in two major areas. 1) I provided technical expertise to non-governmental organizations working directly with large public constituencies on environmental endocrine disruption and human health. 2) I worked through media outreach and the delivery of public lectures to improve the general public’s understanding of evolution, particularly with respect to recent discoveries concerning how complex systems evolve; this has been a particularly important area in which to improve public understanding of evolution, because of the emphasis that creationists have placed on "irreducibly complex" systems in their arguments.
