The EGFR ligand Spitz, which is crucial for several aspects of Drosophila development, is produced as an inactive membrane-bound precursor that is cleaved and activated in the Golgi or endosomal compartments. The essential transmembrane protein Star mediates the trafficking of the Spitz precursor, but what is the molecular basis of Star's activity? On page 2643, Thomas Hays and colleagues provide evidence that Star-directed transport of Spitz requires the activity of the microtubule-associated motor dynein and its activator dynactin. The authors show that Star disruption enhances the rough-eye phenotype in a fly strain that is mutant for Glued (a subunit of the dynactin complex), as well as in strains that have mutations in Dhc (which encodes the dynein heavy chain). Moreover, Star- and dynein-associated vesicles cofractionate in a partitioning assay. Importantly, overexpressing truncated Spitz (which mimics the activated protein) rescues the rough-eye phenotype of Glued-mutant flies. In S2 cells that express Star, Spitz-GFP colocalises with dynein and, when the dynein heavy chain is knocked down, vesicle motility is significantly impaired. Therefore, dynactin and dynein appear to mediate Star-directed trafficking of Spitz, a result that advances our understanding of how EGFR signalling is controlled in development.
Star and dynein make a move
Star and dynein make a move. J Cell Sci 15 August 2008; 121 (16): e1605. doi:
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