UC Santa Barbara

The Wnt pathway is essential for the healthy construction and maintenance of the metazoan anatomy and initiates carcinogenesis when dysregulated. Though a rich body of work on tissue- and organ-level roles of key pathway components exists, relatively little is known about the intracellular mechanisms that transduce Wnt signals into changes in cell behavior and identity. This dissertation project was conceived with two guiding goals: 1) characterize the native structure and function of the canonical Wnt pathway in human cells, and 2) determine how Wnt signaling dynamics are relayed through the pathway into cell fate decisions.Using CRISPR-Cas9 gene editing, super-resolution microscopy, optogenetics and computational modeling, we find that the central regulator of Wnt signal transduction, the β-catenin (β-cat) Destruction Complex (DC), exists in liquid-like condensates nucleated by the centrosome. Our results suggest that centrosomal nucleation drives β-cat degradation by lowering the concentration threshold required for condensate formation, locally enriching DC components compared to the cytoplasmic dilute phase. This work is covered in depth in Chapter 2. In Chapter 3 I incorporate live reporters of cell cycle progression, high content single-cell tracking and dynamical inputs to construct a systems-level understanding of intracellular Wnt signal transduction and differentiation. This approach revealed that unsynchronized cell populations respond heterogeneously to Wnt stimulation, and that transcriptional response trajectory can be predicted by the cell cycle phase in which stimulus is withdrawn. We find evidence that Wnt “off-time sensing” tunes the pathway 7 to specific input frequencies, a capability that may protect against carcinogenic Wnt secretion states. This work provides novel insights into the architecture, functions and vulnerabilities of human Wnt signaling. Despite its clear connection to these processes, there are no FDA-approved therapeutics that leverage the Wnt pathway to regenerate damaged tissues or treat cancer. By adding to our understanding of Wnt signal transduction, I hope to assist in the development of working knowledge we may leverage for treating Wnt-driven pathologies