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.

(Re)Imagining Relationality: Brad Isaacs and The Map of the Empire

The exhibition, The Map of the Empire (30 March – 6 May, 2016), featured photography, video, and installation works by Toronto-based artist, Brad Isaacs (Mohawk | mixed heritage). The majority of the artworks within the exhibition were produced from the Canadian Museum of Nature’s research and collections facility (Gatineau, Québec). The Canadian Museum of Nature (CMN), is the national natural history museum of (what is now called) Canada, with its galleries located in Ottawa, Ontario. The exhibition was the first to open at the Centre for Indigenous Research Creation at Queen’s University under the supervision of Dr. Dylan Robinson. Through the installment of The Map of the Empire, Isaacs effectively claimed space on campus grounds – within the geopolitical space of Katarokwi | Kingston – and pushed back against settler colonial imaginings of natural history. The Map of the Empire explored the capacity of Brad’s artistic practice in challenging the general belief under which natural history museums operate: that the experience of collecting/witnessing/interacting with a deceased and curated more-than-human animal will increase conservation awareness and facilitate human care towards nature. The exhibition also featured original poetry by Cecily Nicholson, author of Triage (2011) and From the Poplars (2014), as a response to Brad’s artwork. I locate the work of The Map of the Empire within the broader context of curatorship as a political practice engaging with conceptual and actualized forms of slow violence, both inside of and beyond the museum space. By unmapping the structures of slow, showcased and archived violence within the natural history museum, we can begin to radically transform and reimagine our connections with more-than-humans and encourage these relations to be reciprocal rather than hyper-curated or preserved.