Identification of Genes Involved in the C. elegans VAB-1 Eph Receptor Tyrosine Kinase Signaling Pathway

The generation of a functional nervous system requires that neuronal cells and axons navigate precisely to their appropriate targets. The Eph Receptor Tyrosine Kinases (RTKs) and their ephrin ligands have emerged as one of the important guidance cues for neuronal and axon navigation. However, the molecular mechanisms of how Eph RTKs regulate these processes are still incomplete. The purpose of this work was to contribute to the understanding of how Eph receptors regulate axon guidance by identifying and characterizing components of the Caenorhabditis elegans Eph RTK (VAB-1) signaling pathway. To achieve this objective I utilized a hyper active form of the VAB-1 Eph RTK (MYR-VAB-1) that caused penetrant axon guidance defects in the PLM mechanosensory neurons, and screened for suppressors of the MYR-VAB-1 phenotype. Through a candidate gene approach, I identified the adaptor NCK-1 as a downstream effector of VAB-1. Molecular and genetic analysis revealed that the nck-1 gene encodes for two isoforms (NCK-1A and NCK-1B) that share similar expression patterns in parts of the nervous system, but also have independent expression patterns in other tissues. Genetic rescue experiments showed that both NCK-1 isoforms can function in axon guidance, but each isoform also has specific functions. In vitro binding assays showed that NCK-1 binds to VAB-1 in a kinase dependent manner. In addition to NCK-1, WSP-1/N-WASP was also identified as an effector of VAB-1 signaling. Phenotypic analysis showed that nck-1 and wsp-1 mutants had PLM axon over extension defects similar to vab-1 animals. Furthermore, VAB-1, NCK-1 and WSP-1 formed a complex in vitro. Intriguingly, protein binding assays showed that NCK-1 can also bind to the actin regulator UNC-34/Ena, but genetic experiments suggest that unc-34 is an inhibitor of nck-1 function. Through various genetic and biochemical experiments, I provide evidence that VAB-1 can disrupt the NCK-1/UNC-34 complex, and negatively regulate UNC-34. Taken together, my work provides a model of how VAB-1 RTK signaling can inhibit axon extension. I propose that activated VAB-1 can prevent axon extension by inhibiting growth cone filopodia formation. This is accomplished by inhibiting UNC-34/Ena activity, and simultaneously activating Arp2/3 through a VAB-1/NCK-1/WSP-1 complex.

Breaking New Ground: The First Generation of Women to Work as Professional Authors in English Canada (1880-1920)

In the later decades of the nineteenth century and the early decades of the twentieth, large numbers of Canadian women were stepping out of the shadows of private life and into the public world of work and political action. Among them, both a cause and an effect of these sweeping social changes, was the first generation of Canadian women to work as professional authors. Although these women were not unified by ideology, genre, or date of birth, they are studied here as a generation defined by their time and place in history, by their material circumstances, and by their collective accomplishment. Chapters which focus on E. Pauline Johnson (Tekahionwake), the Eaton sisters (Sui Sin Far and Onoto Watanna), Joanna E. Wood, and Sara Jeannette Duncan explore some of the many commonalities and interrelationships among the members of this generation as a whole. This project combines archival research with analytical bibliography in order to clarify and extend our knowledge of Johnson’s and Duncan’s professional lives and publishing histories, and to recover some of Wood’s “lost” stories. This research offers a preliminary sketch of the long tradition of the platform performance (both Native and non-Native) with which Johnson and others engaged. It explores the uniquely innovative ethnographic writings of Johnson, Duncan, and the Eaton sisters, among others, and it explores thematic concerns which relate directly to the experiences of working women. Whether or not I convince other scholars to treat these authors as a generation, with more in common than has previously been supposed, the strong parallels revealed in these pages will help to clarify and contextualize some of their most interesting work.