Autumn Marsden and Eric Monson to Present at Student Seminar 8/9/2016
Drosophila vs The World: The Nkd EF-Hand Domain Modulates Divergent Wnt Signaling Outputs
Autumn N. Marsden, Sarah W. Derry, Trudi A. Westfall, Diane C. Slusarski
The Wnt signaling network plays critical roles in development and is implicated in human disease. Wnts comprise a complex signaling network that, upon ligand binding, activates the phosphoprotein Dishevelled (Dvl), leading to distinct outputs including polarized cell movement (known as planar cell polarity, Wnt/PCP) and stabilization of the transcription factor β-catenin (Wnt/β-catenin). The mechanisms that determine a specific output are not completely understood, especially because they share receptors and cellular effectors, such as Naked-cuticle (Nkd), a Dvl-interacting protein. The Nkd protein contains a myristoylation domain and an EF-hand, a putative calcium binding domain. Genetic evidence in Drosophila demonstrates that Nkd acts as a Wnt/β-catenin antagonist, while in contrast, Nkd modulates both branches of Wnt signaling in vertebrates. We hypothesize that the specialized role of Nkd in Drosophila is due to a disrupted EF-hand that cannot not bind calcium. Indeed, this change is unique to Drosophila and is not present in closely related insects. To test the role of the Nkd EF-hand in Wnt signal integration, we created Nkd with a neutralized EF-hand, as well as a Drosophila-like EF-hand, and manipulate Nkd activity in the zebrafish. Using a combination of biochemical and functional assays, we identified a requirement for the Nkd EF-hand in Wnt/PCP but not in Wnt/β-catenin transcriptional outputs. We demonstrate that the Drosophila-like Nkd antagonizes Wnt/β-catenin more robustly than zebrafish Nkd. The EF-hand of Nkd is similar to the EF-hand of a known calcium binding protein, Recoverin, a myristoyl-swtich protein that shuttles between the membrane and the cytoplasm depending on its calcium bound state. Consistently, we observe that NkdWT shows localization changes in the calcium fluxing DFCs versus calcium quiescent cells but not the mutant forms. The Nkd EF-hand may serve to interpret the physiology of a cell receiving multiple cues and provides mechanistic insight into Wnt signal integration in vivo.
Assessment of Whole-Exome Sequence Data in Attempted Suicide within a Bipolar Disorder Cohort
Suicidal behavior, which includes both attempted and completed suicide, is the source of tremendous cost and loss of life. Within the United States alone, suicidal behavior accounts for approximately 836,000 emergency room visits and over 41,000 deaths, ranking as the 10th leading cause of death overall and the 2nd leading cause of death for ages 10-34 as reported by the CDC. Efforts to better understand the biological basis and risk factors for suicidal behavior have included a large number of genetic studies due to a significant genetic component to this phenotype. Existing genetic studies have focused primarily on specific candidate genes and/or common variation and have left a significant proportion of the expected heritability of suicidal behavior unexplained. Our current work is focused on the investigation of the contribution of rare functional variation to the risk for suicidal behavior through the use of next-generation sequencing techniques. Specifically, we have performed a comprehensive analysis of 1,018 whole-exome sequences, divided into 387 individuals with bipolar disorder and a history of suicide attempt and 631 individuals with bipolar disorder and no past suicidal behavior. We performed analyses within ~490,000 single variants, across all covered genes, and within 3,621 pathways. No result from any of these analyses survived conservative Bonferroni correction, though several suggestive and potentially important findings were identified within the gene and pathway-based results. In addition, this study generated a large and highly novel dataset that will be of substantial value to future genetic investigations within suicidal behavior. This effort marks the first large-scale effort to identify the contribution of rare functional variation to suicidal behavior and provides the basis for expanded efforts to explain the biological basis of this devastating phenotype.