A fat ride

The Wingless (Wg) and Hedgehog (Hh) morphogens spread beween cells by catching a ride on lipoprotein particles, say Daniela Panáková, Hein Sprong, Christoph Thiele, Suzanne Eaton, and colleagues (Max Planck, Dresden, Germany).The group had earlier spotted unidentified intercellular signaling particles that they dubbed argosomes. Argosomes are now shown to be distinct from exosomes, a set of intercellular travelers derived from the exocytosis of multivesicular bodies. Instead, the argosome passengers Wg, Hh, and assorted glycophosphatidylinositol (GPI)-linked proteins colocalize with the fly protein lipophorin. This is the fly homologue of vertebrate lipoproteins, which scaffold low- and high-density lipoprotein (LDL and HDL) particles.

Getting rid of lipophorin with RNAi caused Wg and Hh to pile up near the cells that synthesize them in wing imaginal discs. The morphogens failed to spread as far as they normally do, although a...