Nudel, a multifaceted cytoskeleton-associated protein involved in neuronal development

The cells in the cerebral cortex are organized into six layers characterized by the types of neurons that reside in them. This precise layering provides an efficient means of organizing the input-output relationships of the neocortical neurons. The cortical layers are established during development in an inside-out pattern. Failure of the neurons to migrate to their proper destination can result in a broad range of mental disorders. The analysis of mouse mutants or human disorders that disrupt normal neuronal migration has provided insight into molecular pathways guiding this process. Until recently, the signaling mechanisms that governed these pathways were largely thought to be working in parallel, with little cross regulation between them. However, recent evidence, including this work, indicates that there is a significant degree of convergence and coordination between the developmental pathways.; The primary focus of this dissertation is to try to understand the biological functions of Nudel, in particular as it relates to neuronal development. Through this body of work we now understand that Nudel is situated at a crossroad of molecular pathways that govern the development of the nervous system.; We identified Nudel in a yeast-two-hybrid screen looking for Lis1 interacting proteins. Nudel is highly enriched in the brain, where its expression is coincident with the onset of neurogenesis. In the cells, Nudel is highly associated with the centrosome and the microtubules network. Nudel is a member of a conserved family of proteins that are known for their function in nuclear distribution. Other members of this family are Lis1 and dynein. Like Lis1, Nudel is capable of interacting with dynein and serves as a positive regulator for dynein function. These proteins work in unison to regulate microtubule stability and centrosome-nucleus coupling during nucleokinesis in cortical radial migrating neurons. Thus, knock down of Nudel in radial migrating neurons results in positional defects along the developing cortex. Nudel is also a substrate of Cdk5 and phosphorylation seems to regulate the dynein transport-related function of Nudel. Therefore, Nudel serves as a link between the Cdk5 and the Lis1 migratory pathways.; As part of search to understand the functions of Nudel we performed a tandem affinity purification looking for Nudel interacting partners in the centrosome and in the cytosol. Results reveal that Nudel associates with centrosomal proteins in a dynein independent manner. Also, we found that Nudel is capable of interacting with members of all three cytoskeletal networks, and perhaps it might even play a role in Wnt signaling regulation.; We also describe the association between Nudel and non-muscle myosin II. These proteins are highly coexpressed in actively migrating neurons during cortical development and are found to associate at the centrosome independently of dynein or Lis1. Inhibition of myosin II in embryonic brains causes a reduction in neuronal migration and a dramatic redistribution of Nudel, resulting in the dissociation of the Nudel-myosin II interaction and promoting association of Nudel with Lis1. Thus, Nudel may serve as a switch between the myosin II and dynein motors to coordinate cytoskeletal dynamics during development.; In conclusion, we have found that Nudel is a perfect model protein to study the integration of molecular pathways responsible for neuronal migration.