Morphogen gradients are shaped by several dynamic processes, and on p. 307, Suzanne Eaton and colleagues determine the contribution of endocytosis to the maintenance of the Wingless (Wg) gradient, which is secreted at the dorsal-ventral boundary of the Drosophila melanogaster wing disc. Endocytosis requires the Rab GTPases, and specific endosomes are associated with specific Rab proteins. So the researchers used dominant-negative Rab proteins to disrupt particular branches of the endocytic pathway, and found that preventing Wg endocytosis increased its extracellular spread. Curiously, although overexpression of the glypican Dally-like (Dlp) - which is required for long-range Wg movement - caused the accumulation of extracellular Wg, it was not required for the spread of Wg when endocytosis was blocked. The authors report that Wg is only internalized from the apical and basal surfaces of the disc, and propose that Dlp promotes the spread of Wg by directing it to lateral membranes, where it is endocytosed less efficiently.
- © 2006.