In both embryos and adults, cell fate specification is often directed by morphogeneticfields of signaling proteins, such as Wnt proteins. Cells in target tissues produce concentration dependentresponses, resulting in the generation of different cell fates. Thus, morphogenetic gradients prefigurepatterns of cell fate specification and differentiation. The movement of signaling protein away from the siteof synthesis is key to the formation of a gradient. One of the best-characterized vertebrate Wnt gradients isin the chick neural tube, where a dorsal to ventral gradient of Wnt-1/3a regulates the balance betweenproliferation and differentiation. The recent discovery that the post-translational modification of Wnt proteinswith palmitate regulates their activity and distribution has revealed a gap in the understanding of themechanistic underpinnings of this process. The objective of this proposal is to determine the mechanism bywhich palmitoylation regulates the distribution and activity of Wnt proteins. The PI hypothesizes thatPorcupine-mediated palmitoylation regulates the activity and distribution of Wnt-1 and Wnt-3a in the chickneural tube by facilitating their assembly into multimers as well as by reducing their stability and their rate ofdiffusion away from the site of synthesis. The rationale for the proposed studies is that an understanding ofthese processes is required for the development of therapeutic strategies to deliver lipid-modified signals toappropriate tissues or to inhibit the delivery of lipid-modified signals to their target tissues. For the firstspecific aim, the Burrus lab will first use biochemical approaches to identify and characterize the enzymethat is responsible for palmitoylating Wnt proteins. For the second specific aim, The Burrus lab will utilizebiochemical and in vivo approaches to determine the mechanism(s) by which palmitoylation regulates Wntactivity. Lastly, the Burrus lab will use a combination of conventional imaging, live imaging and functionalanalysis to define the mechanism(s) by which palmitoylation regulates the distribution of Wnt proteins.Relevance to Public Health: 'These data are significant because they will provide knowledge that is criticalfor the development of therapies that involve tissue engineering or delivery of Wnt ligands to particulartarget cells as well as therapies that involve the inhibition of aberrant Wnt signaling. Once such strategiesare developed, there is the promise of targeting Wnts to stem cells for the generation and expansion ofhealthy tissues, including muscle, cartilage, neurons, and hematopoietic cells. The identification of theupstream regulator of palmitoylation will also provide a potential therapeutic target for treating cancers thatrely on the deregulation of Wnt ligand expression for their progression, including sarcoma, malignantmesothelioma, colorectal cancer, and melanoma.
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