Identifying the dynamic oligomerization of Wntless
Date
2016
Authors
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Publisher
University of Delaware
Abstract
Wnt proteins are a highly conserved family of secreted glycoproteins that act as ligands in receptor-mediated signaling pathways. These complex pathways are present, and tightly regulated, at various stages of development including early embryonic patterning, cell fate decisions, and proliferation of stem cells. The Wnt signal transduction pathway is one of the best characterized intercellular signaling networks. It is strictly regulated in signal-receiving cells by multiple cytoplasmic and nuclear factors, as well as receptor-ligand specificity. Regulation also occurs in the signal-producing cells at the level of Wnt production, transport, and secretion. Post-translational modifications are critical to proper intracellular trafficking and secretion of Wnt proteins. N-glycosylation and lipid modification mediated by the ER resident protein Porcupine is recognized by Wntless, the dedicated Wnt chaperone protein. Proper Wnt secretion and subsequent downstream activation is dependent upon Wntless (Wls) binding and its consequent escort of Wnts through the secretory pathway to the plasma membrane for release. Previous studies using co-immunoprecipiation assays revealed that Wls homo-oligomerization is required for interaction with Wingless (Wg), the prototypical Drosophila Wnt. In this study fluorescence correlation spectroscopy with photon counting histogram analysis was used to analyze the oligomeric state of Wls within Drosophila S2R+ cells. Results of these experiments indicate that Wls exists as a monomer within the plasma membrane in the absence of Wg; however, other intracellular compartments were not analyzed in this study.