In Drosophila embryos, the longitudinal muscle cells surrounding the gut – the caudal visceral mesoderm (CVM) – arise in the posterior mesoderm and migrate anteriorly to reach their destination where they differentiate. Although this represents the longest cell migration event of Drosophila embryogenesis, the signals directing it are poorly understood. On p. 699, Angelike Stathopoulos and colleagues identify the FGF ligands Pyramus and Thisbe as crucial guidance cues for the CVM, signalling via the Heartless receptor to promote proper migration. The researchers use detailed live imaging and cell tracking analyses to describe wild-type migration, and analyse the consequences of disrupting FGF signalling, revealing defects in migration speed, directionality and cell survival. Intriguingly, by manipulating both the levels and location of ligand expression, they provide evidence for synergistic effects of Pyramus and Thisbe, although the mechanistic basis of such synergism remains to be investigated. Together, these data establish a new system for studying collective cell migration, and suggest additional complexities in FGF ligand-receptor interactions and signalling.

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