In many organisms, primordial germ cells (PGCs) migrate to the gonad in response to directional cues from surrounding somatic tissues. In this example of directed cell migration, as in the others that occur during development, the migrating cell has to transduce extracellular cues intracellularly into directional migration. On p. 4787, Erez Raz and colleagues investigate the signalling pathways downstream of the cues provided by the ligand SDF-1a and its receptor CXCR4b during zebrafish PGC migration. By tracking GFP-tagged PGCs, the authors show that inhibition of G-protein-dependent signalling prevents PGCs reaching their normal target, which is what happens if CXCR4b is lost. Inhibition of phosphoinositide 3-kinase (PI3K) signalling, however, does not prevent PGCs reaching their target but slows down their migration and reduces the stability of filopodia. Furthermore, unlike in cell types in which PI3K activity controls directional cell migration (e.g. neutrophils), the PI3K products phosphatidylinositol (3,4,5)-trisphosphate and phosphatidylinositol (3,4)-bisphosphate are not polarized in zebrafish PGCs. Thus, although G-protein-dependent signalling is essential for directional migration of PGCs, PI3K signalling plays a permissive role, controlling overall motility rather than directing migration.