Wnt proteins are secreted signaling factors that regulate cell fate specification and patterning decisions throughout the animal kingdom. In the Drosophila wing epithelium, Wingless (Wg, the homolog of Wnt1) is secreted from a narrow strip of cells at the dorsal-ventral boundary. However, the route of Wg secretion in polarized epithelial cells remains poorly understood and key proteins involved in this process are still unknown.
our results further indicate that apically secreted Wg activates target genes that require high signaling activity. In conclusion, our results demonstrate that the exocyst is required for an apical route of Wg secretion from polarized wing epithelial cells.
exocyst complex preferentially regulates apical secretion of Wg proteins. Taken together, this study identifies routes and regulators for secretion of signaling-active Wnt proteins from polarized epithelial cells.
While we have learned much about Wnt/Wg secretion in general, the mechanism of polarized Wg secretion has remained unclear. In particular, from which side of the polarized wing epithelial cells the active pool of Wg is secreted has been long debated, and both apical as well as basolateral routes have been suggested. In this study, we demonstrate that a highly active pool of Wg is secreted from the apical side of polarized wing epithelial cells, a process that requires the function of members of the exocyst complex.
different signaling abilities are bestowed on Wnt proteins by various carriers and that their different secretion routes in polarized cells can create an activity difference between apical and basolateral Wg.
Taken together, our study provides a mechanism for the secretion of endogenous Wg from polarized epithelial cells and identifies exocyst members required for apical secretion. It will be of further interest to analyze the role of the exocyst in secretion of Wnt proteins in other developmental and niche/stem cell contexts.
Common Design 