NSF Award
1557414
Developing nerve cells must often migrate through the brain to form the circuits that control behavior, but how this process is controlled is not understood. One group of molecules that are important for nerve cell migration (called Ephrins) exist as multiple types in mammals, making their detailed functions difficult to study. Taking advantage of the fact that insects (including the tobacco hornworm Manduca used here) produce a single type of Ephrin protein, a molecule (RACK1) that Ephrin interacts with in a major way during nerve cell development has been identified. This project will determine how RACK1 works together with Ephrin to regulate nerve cell migration and circuit development. The new discoveries made during this project will provide valuable information about how Ephrins function during nervous system development in more complex animals, including the human brain. The project will also provide unique opportunities for undergraduate students to learn advanced methods for investigating how specific proteins regulate nerve cell growth. Students will conduct experiments in Manduca to test the role of Ephrin and RACK1 in this process, and to identify other proteins that are required for Ephrin function. The data and resources produced by this project will be presented at major scientific conferences, published in scientific journals, and be posted on web sites that are freely available to other scientists and to the public. In addition, discoveries from this project will be presented to more general audiences at the Oregon Health and Science University Brain Fair, an interactive educational opportunity that is held annually at the Oregon Museum of Science and Industry.<br/><br/>This project will investigate how type-A Ephrins (which are attached to cells by GPI lipid anchors) can regulate the activity of intracellular tyrosine kinases in the Src family, and how this signaling pathway controls the migratory behavior of developing neurons. Preliminary studies indicate that the adapter protein RACK1 (Receptor of Activated Protein Kinase C) functions as a molecular rheostat that restricts Src signaling until MsEphrin signaling is initiated. Studies will be carried out using a well-characterized assay of neuronal migration in cultured Manduca embryos. Targeted manipulations of gene expression will test whether RACK1 is essential for the activation of a specific Src kinase (Src42) by type-A Ephrins. Biochemical assays of Src activity and Src-RACK1 interactions will test whether RACK1 functions as both a regulator and substrate for Src42 in this process. Time-lapse imaging and quantitative assays of neuronal migration will be used to investigate how this signaling pathway affects specific aspects of neuronal behavior in the developing nervous system. Similar methods will test whether a toll family protein (Toll-7) functions as a novel co-receptor for type-A Ephrins in this pathway. These experiments will also permit the downstream effectors of type-A Ephrins to be identified in related projects that will be conducted by selected undergraduate participants.
