Argosomes Help Wingless Take Flight

Abstract

Morphogens can spread by simple diffusion to create gradients that establish future zones of differentiation in developing organisms. The spread of some morphogens, like Wingless (Wg), is regulated by heparan sulfate proteoglycans. However, Wg is also strongly bound to plasma membranes. Greco et al. now find that Wg spreads by a process of exosomal transmission in vesicles termed argosomes [named after Jason's ship (Argos) in ancient Greek mythology]. After secretion from Wg-producing cells, Wg interacts with extracellular heparan sulfate and becomes endocytosed. These endosomal vesicles then translocate to multivesicular bodies. These vesicles are then transported to the plasma membrane where argosomes are released containing the Wg-heparan sulfate complexes. Adjacent cells can then endocytose the high-density Wg-containing Wg argosomes, whereupon Wg remains associated with the plasma membrane. As supporting evidence, heparinase treatment of imaginal discs in Drosophila embryos greatly reduced the ability of Wg to localize in argosomes and to spread throughout the embryo. Thus, argosomal translocation appears to be a new method of dispersing morphogens through developing embryos. V. Greco, M. Hannus, S. Eaton, Argosomes: A potential vehicle for the spread of morphogens through epithelia. Cell 106 , 633-645 (2001). [Online Journal]